🧬 Classification, Bacteria & Viruses

📖

Scientists use a ranking system called taxonomy to organize all living things. This section explores the eight levels of classification and how organisms are grouped from broadest to most specific.

📖 Read

Have you ever noticed how a library organizes books? Fiction is separated from non-fiction, then books are sorted by genre, author, and title. Scientists use a similar system to organize the millions of species on Earth — it's called taxonomy.

Taxonomy is the science of naming, describing, and classifying organisms. Swedish scientist Carl Linnaeus invented our modern system in the 1700s. He created eight levels of classification, from the broadest group down to the most specific. Scientists use the memory trick Dear King Philip Came Over For Good Soup to remember the order: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Think of it like a set of nesting boxes. The Domain is the biggest box — it contains everything. Each level gets smaller and more specific, until you reach Species — the smallest box — which contains only organisms that can breed with each other and produce fertile offspring.

There are three Domains: Bacteria (single-celled, no nucleus), Archaea (single-celled, no nucleus, but biochemically different from bacteria), and Eukarya (organisms with a nucleus — including plants, animals, fungi, and protists).

The more classification levels two organisms share, the more closely related they are. A dog and a wolf share all eight levels except species. A dog and a cat share only the first five.

✏️ Respond

1. List the 8 levels of classification in order from broadest to most specific:

2. What memory trick helps you remember the order? Write it out:

3. What does it mean if two organisms share many levels of classification?

4. Name the three Domains and one key feature of each:

5. What is the definition of a species?

Quick Check

📖 Multiple Choice

Which of the following correctly lists the levels of classification from most specific to most broad?

A. Domain → Kingdom → Phylum → Species

B. Kingdom → Phylum → Family → Genus → Species

C. Species → Genus → Family → Order → Class → Phylum → Kingdom → Domain

D. Species → Family → Order → Domain → Kingdom → Phylum

📖 Multiple Choice

Humans belong to Domain Eukarya. Which other organism also belongs to Domain Eukarya?

A. E. coli bacteria

B. An oak tree

C. A heat-loving Archaea from a hot spring

D. A bacteriophage virus

Vocabulary

Taxonomy

Domain

Kingdom

Genus

Species

Eukarya

📖

Every organism on Earth has a unique two-part scientific name. This section explains the rules for writing and reading scientific names, and why this system matters in science.

📖 Read

Imagine if everyone in the world used different names for the same animal. In some countries, a "mountain lion" is called a "puma" or a "cougar." This causes confusion! That's why scientists use binomial nomenclature — a two-part naming system that gives every organism one unique scientific name recognized worldwide.

Linnaeus invented binomial nomenclature. Every scientific name has two parts: the genus name and the species epithet. Together they form the scientific name. For example, humans are Homo sapiens — Homo is our genus and sapiens is our species epithet.

There are strict rules for writing scientific names: (1) The genus name is always capitalized. (2) The species epithet is always lowercase. (3) The entire name is italicized when typed, or underlined when written by hand. For example: Canis lupus (gray wolf) or Canis familiaris (domestic dog).

Notice that both wolves and dogs share the genus Canis — that tells us they are very closely related and share a recent common ancestor. But their species epithets are different, meaning they are distinct species (though they can sometimes interbreed).

Scientific names are written in Latin or Greek because those were the languages of science when Linnaeus created the system, and because they are "dead" languages — they don't change over time, keeping the names stable.

✏️ Respond

1. What is binomial nomenclature and who created it?

2. What are the two parts of a scientific name?

3. Correctly format this scientific name: "homo sapiens"

4. A student writes "canis Lupus" on a test. List TWO errors they made:

5. Two organisms share the same genus name. What does this tell you about them?

Quick Check

📖 Multiple Choice

Which scientific name is written correctly?

A. Homo Sapiens

B. homo sapiens

C. HOMO SAPIENS

D. Homo sapiens

📖 Multiple Choice

A biologist discovers two species: Felis catus (domestic cat) and Felis silvestris (wild cat). What can you conclude?

A. They are the exact same species

B. They are closely related and in the same genus

C. They share only their Domain

D. They cannot interbreed because they have different genus names

Vocabulary

Binomial nomenclature

Genus name

Species epithet

Scientific name

📖

How do scientists decide which group an organism belongs to? They look at a variety of evidence — from body structure to DNA. This section covers the key criteria used in modern classification.

📖 Read

Early scientists classified organisms primarily by their appearance — how similar they looked. But looks can be deceiving! A dolphin looks like a fish, but it's actually a mammal. Modern scientists use multiple types of evidence to place organisms into the correct groups.

Morphology (body structure and form) is still important. Scientists compare physical features like bone structure, cell type, and body plan. Homologous structures — body parts with the same underlying structure but possibly different functions (like a human arm and a bat wing) — suggest a common ancestor.

Molecular evidence is one of the most powerful modern tools. Scientists compare DNA, RNA, and protein sequences. The more similar two organisms' DNA is, the more recently they shared a common ancestor. This can reveal relationships that physical appearance alone would miss.

Embryology — the study of early development — also provides clues. Many unrelated-looking organisms (fish, humans, chickens) have surprisingly similar embryos in their earliest stages, suggesting they evolved from a shared ancestor long ago.

Fossil evidence helps scientists trace the evolutionary history of organisms over millions of years. By comparing ancient fossils to modern species, scientists can reconstruct how life has changed over time.

A dichotomous key is a practical tool for identifying unknown organisms. It presents a series of paired (two-choice) statements that lead you step by step to the organism's identity.

✏️ Respond

1. Why can't scientists rely on appearance alone to classify organisms?

2. What are homologous structures? Give one example:

3. How does molecular (DNA) evidence help with classification?

4. What is a dichotomous key and how is it used?

5. List THREE types of evidence used to classify organisms:

Quick Check

📖 Multiple Choice

A scientist is comparing the wing bone of a bat to the arm bone of a human. Both have the same underlying bone structure. These are called:

A. Analogous structures

B. Homologous structures

C. Vestigial structures

D. Convergent structures

📖 Multiple Choice

Which type of evidence would be MOST useful for determining whether two species that look very different are actually closely related?

A. Comparing their habitat preferences

B. Comparing their diet

C. Comparing their DNA sequences

D. Comparing their body color

🛑

STOP HERE — Raise your hand so your teacher can check Sections 1–3 before you continue!

Vocabulary

Morphology

Homologous structures

Molecular evidence

Embryology

Dichotomous key

Fossil evidence

📖

Scientists use branching diagrams to show how species are related to each other. Learn how to read and interpret these diagrams to trace evolutionary history.

📖 Read

A cladogram is a branching diagram that shows evolutionary relationships among groups of organisms. Think of it like a family tree for species. The diagram shows which organisms share a common ancestor and which derived characteristics (new traits that evolved) different groups have developed.

Every branching point on a cladogram is called a node. A node represents a common ancestor — a species that gave rise to two or more different groups. Organisms that branch off from the same node share more recent ancestors than organisms at distant branches.

A phylogenetic tree is similar to a cladogram but may also include information about time — when different groups evolved. Both are used to show the evolutionary history, or phylogeny, of organisms.

A key rule: organisms that are on the same branch are more closely related than organisms on separate branches. If you trace backward from two species to the point where they share a node, you've found their most recent common ancestor.

Clade: A clade is a group consisting of an ancestor and ALL of its descendants. All members of a clade share a unique derived trait that they inherited from their common ancestor.

Scientists build cladograms using shared derived characteristics — traits that evolved in a common ancestor and were passed down to its descendants. The more shared traits two organisms have, the more closely related they are.

✏️ Respond

1. What is a cladogram and what does it show?

2. What does a node (branching point) on a cladogram represent?

3. How do you determine which two organisms are MOST closely related on a cladogram?

4. What is a "derived characteristic"? Give one example:

5. What is the difference between a cladogram and a phylogenetic tree?

Quick Check

📖 Multiple Choice

On a cladogram, Species A and Species B branch off from the same node. Species C branches off from a much earlier node. Which pair is most closely related?

A. Species A and Species B

B. Species A and Species C

C. Species B and Species C

D. All three are equally related

📖 Multiple Choice

Scientists use "shared derived characteristics" to build cladograms. What is a shared derived characteristic?

A. A trait found in all organisms on Earth

B. A trait that evolved separately in two unrelated species

C. A new trait that evolved in a common ancestor and was passed to its descendants

D. A trait that disappeared during evolution

Vocabulary

Cladogram

Node

Common ancestor

Phylogenetic tree

Clade

Derived characteristic

📖

How do scientists know which organisms are related? Multiple lines of evidence — from DNA to fossils to embryos — build the picture. This section ties classification back to evolution.

📖 Read

When we classify organisms, we're really asking: who is related to whom, and how closely? Scientists use multiple types of evidence to answer this question, and when multiple evidence types agree, scientists can be very confident in the relationship.

DNA Similarity: The closer two species' DNA sequences are, the more recently they shared a common ancestor. Humans and chimpanzees share about 98.7% of their DNA — meaning our ancestors split apart only about 6 million years ago. Humans and yeast share only about 31% — our common ancestor lived over a billion years ago.

Analogous vs. Homologous Structures: Homologous structures (same underlying structure, different function) indicate common ancestry. Analogous structures (same function, completely different structure) suggest convergent evolution — unrelated species evolved similar traits because they live in similar environments. A bird wing and a butterfly wing both enable flight but evolved completely independently.

Vestigial Structures: Vestigial structures are body parts that have lost their original function over evolutionary time but remain as evidence of ancestry. Humans have a tailbone (coccyx) — a remnant of our primate ancestors who had tails. Whales have tiny hip bones buried in their bodies — remnants of legs from when their ancestors lived on land.

Biogeography: Where species live also provides evidence. Islands that formed recently from the ocean floor tend to be colonized by species from the nearest mainland — and over time, those species evolve into new forms adapted to island life. This pattern supports evolution from common ancestors.

✏️ Respond

1. What does it mean if two species share 98% of their DNA?

2. Explain the difference between homologous and analogous structures:

3. What is a vestigial structure? Give one human example:

4. What is convergent evolution? Give an example from the reading:

5. Why is it important that MULTIPLE lines of evidence agree before classifying organisms?

Quick Check

📖 Multiple Choice

A dolphin fin and a shark fin look nearly identical and both are used for swimming. However, their internal bone structures are completely different. These fins are best described as:

A. Homologous structures indicating common ancestry

B. Analogous structures resulting from convergent evolution

C. Vestigial structures with no current function

D. Derived characteristics shared by a common clade

📖 Multiple Choice

Whales have small, hidden hip bones inside their bodies even though they have no legs. These bones are an example of:

A. Analogous structures from convergent evolution

B. Homologous structures that serve a new function

C. Vestigial structures that are remnants of their land-dwelling ancestors

D. Derived characteristics unique to the whale clade

🛑

STOP HERE — Great work on Classification! Check in with your teacher before moving to Bacteria & Viruses.

Vocabulary

Analogous structures

Homologous structures

Vestigial structures

Convergent evolution

Biogeography

📖

Bacteria and viruses both make us sick — but they are very different things. One is alive, one isn't (sort of). Learn the key structural differences and similarities between these two microscopic agents.

📖 Read

Bacteria are single-celled living organisms classified in Domain Bacteria. They are prokaryotes — their cells do NOT have a membrane-bound nucleus. Their DNA floats freely in the cell in a region called the nucleoid region.

A typical bacterial cell has: a cell membrane (controls what enters/exits), a cell wall (provides structure and protection — made of peptidoglycan), ribosomes (make proteins), flagella (tail-like structures for movement), pili (hair-like structures for attachment), and sometimes a plasmid (a small, extra circle of DNA).

Viruses are NOT cells and are NOT considered living organisms by most scientists. They are essentially genetic information (DNA or RNA) wrapped in a protein coat called a capsid. Some viruses also have an outer envelope made of lipids (stolen from host cell membranes).

Key comparison: Bacteria have all the parts needed to carry out life processes on their own. Viruses cannot carry out any life processes — they cannot eat, grow, or reproduce without a host cell to "hijack." This is the most fundamental difference.

Similarities: Both bacteria and viruses contain genetic material (DNA or RNA), both can cause disease, both can evolve (mutate), and both can be studied under a microscope (though viruses require electron microscopes — they are far smaller than bacteria).

✏️ Respond

1. What does "prokaryote" mean, and how does it apply to bacteria?

2. List THREE structures found in bacteria and their functions:

3. What two things make up a basic virus? (Hint: genetic material + ___ )

4. Why are viruses NOT considered living organisms?

5. Name ONE similarity between bacteria and viruses:

Quick Check

📖 Multiple Choice

Which structure is found in bacteria but NOT in viruses?

A. DNA

B. Protein coat

C. Genetic material

D. Cell wall made of peptidoglycan

📖 Multiple Choice

The main reason viruses are NOT classified as living organisms is because they:

A. Cannot carry out any life processes without hijacking a host cell

B. Do not contain any genetic material

C. Are too small to be seen under any microscope

D. Cannot cause disease in organisms

Vocabulary

Prokaryote

Nucleoid region

Cell wall

Plasmid

Capsid

Host cell

📖

Bacteria reproduce on their own. Viruses need a host to copy themselves. This section compares the two very different strategies these microscopic agents use to multiply.

📖 Read

Bacteria reproduce through binary fission — a simple process where one cell splits into two identical daughter cells. Here's how it works: (1) The bacterium copies its circular DNA. (2) The cell elongates and the two DNA copies move to opposite ends. (3) The cell pinches in half, creating two identical cells. Under ideal conditions, bacteria can double their population every 20 minutes!

Viruses reproduce differently — they cannot reproduce on their own. Instead, they inject their genetic material into a host cell and "hijack" the cell's own machinery. There are two main cycles:

In the lytic cycle, the virus injects its DNA into the host cell. The host's ribosomes are forced to make viral proteins and copy viral DNA. New viruses are assembled inside the cell. The cell then lyses (bursts open), releasing hundreds of new viruses that go on to infect more cells. This cycle kills the host cell.

In the lysogenic cycle, the viral DNA inserts itself into the host cell's own DNA and becomes dormant. This dormant viral DNA is called a prophage. Every time the host cell divides, the viral DNA is copied along with the cell's DNA. The virus can remain dormant for a long time before switching to the lytic cycle and destroying the cell.

Key difference: Bacteria reproduce independently; viruses always need a living host cell to replicate.

✏️ Respond

1. Describe the three steps of binary fission in bacteria:

2. Why can't viruses reproduce on their own?

3. In the lytic cycle, what happens to the host cell at the end?

4. What is a prophage and in which cycle does it form?

5. Which cycle is more immediately dangerous to the host — lytic or lysogenic? Explain why:

Quick Check

📖 Multiple Choice

A bacterium divides every 20 minutes. After 1 hour, how many bacteria will there be if you start with 1?

A. 2

B. 4

C. 8

D. 16

📖 Multiple Choice

Which correctly describes the lysogenic cycle?

A. The virus immediately destroys the host cell after injecting DNA

B. Viral DNA integrates into the host genome and is copied with each cell division

C. The virus reproduces by binary fission inside the host cell

D. Viral RNA replaces the host cell's entire genome immediately

Vocabulary

Binary fission

Lytic cycle

Lyse

Lysogenic cycle

Prophage

📖

For most of human history, people believed diseases were caused by bad air or evil spirits. The discovery of germ theory changed everything. Learn about the landmark experiments that proved microorganisms cause disease.

📖 Read

The germ theory of disease states that specific microorganisms (germs) cause specific diseases. This seems obvious today, but before the 1860s, most people — including doctors — believed diseases arose from "bad air" (miasma) or appeared spontaneously. The spontaneous generation theory held that life could arise from non-living matter on its own.

Pasteur's Experiment (Swan-Neck Flask Experiment): French chemist Louis Pasteur designed an elegant experiment to disprove spontaneous generation. He boiled broth in two flasks — one with a straight neck (open to air) and one with a long, curved swan neck (also open to air, but trapping microbes in the curve). The straight-neck flask grew microbes; the swan-neck flask stayed sterile — unless the neck was broken. This proved that microbes came from the air, not spontaneous generation. Pasteur also showed that microbes could be killed by heat (pasteurization).

Koch's Postulates: German physician Robert Koch developed a set of four steps (postulates) to prove that a specific microorganism causes a specific disease:

1. The suspected pathogen must be found in every individual with the disease. 2. The pathogen must be isolated from the sick individual and grown in pure culture. 3. When the cultured pathogen is introduced to a healthy individual, it must cause the same disease. 4. The pathogen must be re-isolated from the newly sick individual and shown to be the same original pathogen.

Koch used these postulates to prove that specific bacteria cause tuberculosis and anthrax — two major killers of his era. His postulates are still used today (with some modifications for viruses).

✏️ Respond

1. What is the germ theory of disease?

2. What did Pasteur's swan-neck flask experiment prove? How did the curved neck work?

3. Why was disproving spontaneous generation important for medicine?

4. List Koch's 4 Postulates in order:

5. Why are Koch's Postulates important even today?

Quick Check

📖 Multiple Choice

In Pasteur's experiment, the broth in the swan-neck flask did NOT develop microbes because:

A. No air could enter the flask at all

B. Microbes from the air were trapped in the curved neck before reaching the broth

C. The broth was too hot for any microbes to survive

D. Microbes could only grow in straight-neck flasks

📖 Multiple Choice

According to Koch's Postulates, after isolating a pathogen from a sick patient, the NEXT step is to:

A. Re-isolate it from the patient again

B. Immediately administer antibiotics to the patient

C. Grow it in pure culture and introduce it to a healthy individual

D. Compare its DNA to other known pathogens

Vocabulary

Germ theory

Spontaneous generation

Louis Pasteur

Robert Koch

Koch's Postulates

Pathogen

📖

How do we fight bacterial and viral infections? This section covers vaccines, antibiotics, antibiotic resistance, and why we need different treatments for bacteria vs. viruses.

📖 Read

Not all bacteria are harmful — in fact, most are helpful or neutral. But pathogenic (disease-causing) bacteria and viruses are responsible for enormous human suffering. Understanding how they work allows us to fight back.

Antibiotics: Antibiotics are medicines that kill or slow the growth of bacteria. They work by targeting specific bacterial structures — like the cell wall or ribosomes — that viruses don't have. This is crucial: antibiotics only work on bacteria, NOT on viruses. Taking antibiotics for a cold or flu (caused by viruses) is not just useless — it's dangerous.

Antibiotic Resistance: This is one of the most serious health threats of our time. When patients don't finish their full antibiotic prescription, the weakest bacteria die but the slightly-resistant ones survive and reproduce. Over generations, this results in populations of bacteria that are completely resistant to antibiotics. Bacteria like MRSA (methicillin-resistant Staphylococcus aureus) are now resistant to many common antibiotics.

Vaccines: Vaccines work by exposing the immune system to a weakened, killed, or partial version of a pathogen. The immune system learns to recognize it and builds "memory cells." If the real pathogen invades later, the immune system can respond quickly and destroy it before illness develops. Vaccines work for both bacterial and viral diseases. Pasteur created early vaccines for chicken cholera and rabies.

Viral treatments: Because viruses use the host's own cellular machinery, it's hard to kill them without also damaging the host. Antiviral drugs can slow viral replication but rarely completely eliminate a virus. The best defense against viruses is prevention through vaccination and good hygiene.

✏️ Respond

1. Why don't antibiotics work on viruses?

2. Explain how antibiotic resistance develops:

3. How do vaccines protect against disease? (Explain the immune system response)

4. Why is it so hard to create drugs that kill viruses?

5. Why should you always finish your full antibiotic prescription even if you feel better?

Quick Check

📖 Multiple Choice

A patient has the flu (caused by a virus). Their doctor prescribes antibiotics. Which statement is correct?

A. The antibiotics will cure the flu by killing the virus

B. Antibiotics will speed up the immune response to the flu

C. The antibiotics will not treat the flu and may contribute to antibiotic resistance

D. Antibiotics will prevent the virus from entering new cells

📖 Multiple Choice

How does a vaccine protect a person from future illness?

A. It kills all copies of the virus in the body permanently

B. It trains the immune system to recognize and quickly destroy the pathogen in the future

C. It introduces a full-strength pathogen to make the person temporarily sick

D. It works only for bacterial diseases, not viral ones

🛑

STOP HERE — Check in with your teacher before moving to the Vocab Arcade and Practice Tests!

Vocabulary

Antibiotic

Antibiotic resistance

Vaccine

Antiviral drug

Pathogenic

Immune system

🕹️

Three ways to master your vocabulary: Flashcards to learn definitions, Matching to connect terms with meanings, and Fill-in-the-Blank to use them in context. Pick a mode and practice!

Click the card to reveal the definition!

Taxonomy

Click to see definition →

The science of naming, describing, and classifying organisms into groups based on shared characteristics.

1 / 30

Click a term on the left, then click its matching definition on the right. Match all 8 pairs!

Matched: 0 / 8

Terms

Definitions

Fill in each blank with the correct vocabulary word. Type carefully!

The two-part naming system for organisms is called .

The level of classification just above species is called .

Bacteria are , meaning they have no membrane-bound nucleus.

When a virus bursts out of a host cell, the cell (breaks open). This happens in the cycle.

The protein coat surrounding a virus's genetic material is called a .

Louis Pasteur proved that life does NOT arise from non-living matter, disproving the theory of .

Robert Koch developed four steps called to prove a specific microorganism causes a specific disease.

Bacteria reproduce by splitting in two through a process called .

A branching diagram showing evolutionary relationships among organisms is called a .

Medicines that kill or inhibit bacteria are called , but they have NO effect on .

A body part that has lost its original function over time is called a structure.

When two unrelated species develop similar traits because they live in similar environments, this is called .

🧬 Practice Test 1

20 questions • Read each scenario carefully • Select the best answer • Submit when finished

Question 1

Scientists use a system of eight classification levels to organize all known living things, from the broadest group down to the most specific.

Which of the following correctly lists the levels of classification from most broad to most specific?

a. Species, Genus, Family, Order, Class, Phylum, Kingdom, Domain

b. Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

c. Kingdom, Phylum, Domain, Class, Order, Family, Genus, Species

d. Domain, Phylum, Kingdom, Order, Class, Genus, Family, Species

Question 2

A biology student is writing a lab report and must use the scientific name of the gray wolf. She writes it as "canis Lupus" in her report.

Which statement correctly identifies the errors in how she wrote the scientific name?

a. The name is correct — no errors were made.

b. The genus should be lowercase and the species epithet should be capitalized.

c. The genus should be capitalized and the species epithet should be lowercase, and the name should be italicized.

d. Both parts of the name should be fully capitalized when typed.

Question 3

A biologist discovers two organisms that look nearly identical. However, when she compares their DNA sequences, she finds they share only 34% of their genetic code — about the same similarity as a human and a mushroom.

Which statement best explains what this DNA evidence tells us about these organisms?

a. The organisms are closely related because they look the same.

b. Appearance is always a reliable indicator of evolutionary relationship.

c. Despite their similar appearance, the organisms are very distantly related and likely evolved similar traits independently.

d. The organisms must belong to the same genus since they look alike.

Question 4

A cladogram shows three species: Species X, Species Y, and Species Z. Species X and Y branch off from the same node near the top of the diagram. Species Z branches off from a node much lower on the diagram, closer to the base.

Which conclusion is most accurate based on this cladogram?

a. Species X and Z are most closely related because they are both on the left side of the diagram.

b. All three species are equally related to each other.

c. Species X and Y are most closely related because they share a more recent common ancestor.

d. Species Z is the most recently evolved of the three species.

Question 5

Two species are given the following scientific names: Panthera leo (lion) and Panthera tigris (tiger). A third animal, the domestic cat, is named Felis catus.

Based on the scientific names alone, which statement is most accurate?

a. The lion and domestic cat are more closely related than the lion and tiger.

b. The lion and tiger are more closely related to each other than either is to the domestic cat.

c. All three animals are equally related to each other.

d. The domestic cat is more closely related to the tiger than to the lion.

Question 6

Scientists examining the fossil record discovered that a group of ancient four-legged land mammals gradually moved into the ocean over millions of years. Today, their descendants — dolphins and whales — have front flippers that contain the same internal bone structure as a human arm.

These flipper bones are best described as homologous structures because they

a. perform the same function of swimming in all mammals

b. have the same underlying bone structure, indicating a common land-dwelling ancestor

c. evolved independently in different species due to similar environments

d. are remnants of body parts that no longer serve any purpose

Question 7

A student is trying to identify an unknown plant species in the schoolyard. She uses a tool that presents a series of paired statements — for example, 'Does the plant have leaves with smooth edges? (Yes/No)' — that lead step-by-step to the plant's identity.

What is the name of this identification tool?

a. A cladogram

b. A phylogenetic tree

c. A taxonomic chart

d. A dichotomous key

Question 8

Sharks and dolphins both have streamlined bodies, dorsal fins, and similar shapes that make them excellent swimmers. However, a shark's skeleton is made of cartilage while a dolphin's skeleton is made of bone, and their internal fin structures are completely different.

These fins are most accurately described as analogous structures because they

a. share the same internal bone structure, indicating common ancestry

b. evolved from the same ancestral fin in an ancient common ancestor

c. look similar and perform the same function but evolved independently in unrelated species

d. are vestigial structures that have lost their original function over time

For questions 9 and 10, use the information in the table below.

Scientists studying a population of Canis lupus (gray wolves) and Canis latrans (coyotes) collected the following data about the two species:

Characteristic	Gray Wolf (Canis lupus)	Coyote (Canis latrans)
Domain	Eukarya	Eukarya
Kingdom	Animalia	Animalia
Phylum	Chordata	Chordata
Order	Carnivora	Carnivora
Family	Canidae	Canidae
Genus	Canis	Canis
Species	lupus	latrans
DNA Similarity to Domestic Dog	99.8%	96.1%

Question 9

Based on the data table, which conclusion is most accurate about the gray wolf and coyote?

a. They are the same species because they share the same genus name.

b. They are closely related and share a recent common ancestor, as shown by their shared classification levels through genus.

c. They are not related to each other at all because they have different species names.

d. The gray wolf is more closely related to the domestic dog than the coyote is, because wolves and dogs share more DNA.

Question 10

According to the table, which level of classification first distinguishes the gray wolf from the coyote?

a. Kingdom

b. Order

c. Family

d. Species

Question 11

The human appendix is a small, finger-shaped pouch attached to the large intestine. In humans, it has no known digestive function. However, in some herbivorous animals, a similar structure plays an important role in digesting plant material.

The human appendix is best described as a vestigial structure because it

a. performs an important function in the human immune system today

b. evolved independently in humans and other animals to serve the same function

c. is a remnant of a structure that served a function in our distant ancestors but has lost that function over time

d. indicates that humans are more closely related to herbivores than to other primates

Question 12

A node on a cladogram represents an important evolutionary event. Scientists use these branching points to understand the history of life on Earth.

A node on a cladogram represents

a. the most recently evolved organism in the group

b. a common ancestor from which two or more lineages diverged

c. a species that went extinct before the present day

d. the geographic location where a new species first appeared

Question 13

A group of biologists is building a cladogram for several species. They observe that Species A, B, and C all have a backbone. Species B and C also have hair. Only Species C has a placenta.

Based on these shared derived characteristics, which pair of species shares the most recent common ancestor?

a. Species A and B, because both have a backbone

b. Species A and C, because both are on the same clade

c. Species B and C, because both have hair — placing them closer on the cladogram

d. All three species are equally related because they all have a backbone

Question 14

A researcher compares the embryos of fish, frogs, birds, and humans. In the earliest stages of development, all four embryos look remarkably similar — each has gill slits, a tail, and a similar body plan. As development continues, they begin to look more distinct.

This similarity in embryological development is best explained by

a. the fact that all four species live near water at some point in their lives

b. convergent evolution — all four species developed the same traits independently

c. a common ancestor shared by fish, frogs, birds, and humans long ago

d. the fact that embryos are too simple to show differences between species

Question 15

Scientists classified whales under Domain Eukarya, Kingdom Animalia, Class Mammalia — alongside elephants, bats, and humans. Whales were once classified with fish because of their aquatic lifestyle and streamlined shape.

Which type of evidence most likely led scientists to reclassify whales as mammals rather than fish?

a. Comparing the color and texture of whale skin to fish scales

b. Observing that whales and fish both live in the same ocean habitat

c. Comparing DNA sequences and discovering hidden hip bones inside whale bodies (vestigial structures)

d. Finding that whales and fish eat the same prey in the ocean

Question 16

Organisms are grouped into three domains: Bacteria, Archaea, and Eukarya. Bacteria and Archaea are both prokaryotes, but they have significant biochemical differences. Eukarya includes all organisms with a true membrane-bound nucleus.

A scientist discovers a new single-celled organism with no nucleus. Its biochemistry is similar to organisms found in volcanic hot springs. The organism most likely belongs to

a. Domain Eukarya, Kingdom Protista

b. Domain Bacteria, because it has no nucleus

c. Domain Archaea, because it lacks a nucleus and has the biochemistry of extremophiles

d. Domain Eukarya, Kingdom Fungi

Question 17

Two populations of the same bird species have been geographically separated on two different islands for 50,000 years. Scientists observe that the two populations now have slightly different beak shapes, different coloration, and different calls, but can still interbreed and produce fertile offspring when brought together.

Based on this information, which conclusion is most accurate?

a. The two populations have become entirely separate species.

b. The two populations are still the same species, because they can still interbreed and produce fertile offspring.

c. The geographic separation proves that the populations will never evolve further.

d. Coloration and beak shape are the only traits used to define a species.

Question 18

Carl Linnaeus created the modern system of taxonomy and binomial nomenclature in the 1700s. He used Latin for all scientific names because Latin was the common language of science at the time.

One major advantage of using Latin (a 'dead' language) for scientific names is that

a. Latin names are easier to pronounce than names in other languages

b. Latin names change regularly to reflect new scientific discoveries

c. Latin names remain stable over time and are universally understood by scientists worldwide, regardless of their native language

d. Latin names automatically reveal an organism's ecological role in its habitat

Question 19

Bacteria are prokaryotic cells. Scientists examining a bacterium under a microscope observe several structures: a cell wall, ribosomes, a flagellum, pili, and circular DNA floating in the cytoplasm.

Which of the following structures is most directly responsible for allowing the bacterium to move through liquid?

a. The ribosomes, which generate energy for movement

b. The pili, which pull the bacterium forward

c. The flagellum, which propels the bacterium through liquid like a tail

d. The cell wall, which pushes against the surrounding liquid

Question 20

A scientist cultures bacteria from a sick patient and introduces the pure culture to a healthy mouse. The mouse develops the same disease as the original patient. The scientist then re-isolates bacteria from the sick mouse and finds they are identical to the original culture.

Which of the following best describes what the scientist has demonstrated?

a. That the mouse was already sick before the experiment began

b. That the disease can spread from humans to mice through the air

c. That the cultured bacteria cause the disease, satisfying the requirements of Koch's Postulates

d. That antibiotics would be effective against this particular disease

Test 1 Complete!

--/ 20

🧬 Practice Test 2

20 questions • Read each scenario carefully • Select the best answer • Submit when finished

Question 1

A microbiologist studying an unknown microscopic agent discovers that it consists only of a strand of RNA surrounded by a protein coat. It has no ribosomes, no cell membrane, and cannot generate its own energy. It can only reproduce after entering a living cell.

Based on these characteristics, this agent is best classified as

a. a prokaryotic bacterium from Domain Bacteria

b. a eukaryotic organism from Domain Eukarya

c. a virus, because it lacks cell structures and requires a host to reproduce

d. an archaeon, because it lacks a membrane-bound nucleus

Question 2

During an infection, a bacteriophage (a virus that infects bacteria) injects its DNA into a bacterial host cell. The host cell's ribosomes begin producing viral proteins, and new viral DNA copies are made. Within 30 minutes, the bacterial cell bursts open, releasing 200 new virus particles.

The events described above represent

a. the lysogenic cycle, in which viral DNA integrates into the host chromosome

b. the lytic cycle, in which the virus replicates and lyses the host cell

c. binary fission, in which the viral DNA causes the bacteria to split in two

d. the immune response, in which the host cell destroys the virus from within

Question 3

A bacterium reproduces by copying its circular chromosome and then pinching in half, producing two identical daughter cells. Under ideal conditions, one bacterium can do this every 20 minutes.

Which statement best explains why bacteria can cause infections so rapidly?

a. Because bacteria evolve new DNA during each division, becoming stronger each time

b. Because bacteria use the lytic cycle to take over nearby cells

c. Because bacteria dividing every 20 minutes means populations can double repeatedly in a very short time

d. Because bacteria can switch to viral reproduction when conditions are favorable

For questions 4 and 5, use the information below.

In the 1860s, French chemist Louis Pasteur designed an experiment using two types of flasks. Both flasks contained nutrient broth and were boiled to kill any existing microbes. Flask 1 had a straight, open neck. Flask 2 had a long, curved 'swan neck' that was open to the air but trapped any particles drifting in. After several weeks, Pasteur examined both flasks.

Question 4

Which result did Pasteur most likely observe, and what did it prove?

a. Both flasks remained sterile, proving that microbes do not exist in the air.

b. Flask 1 grew microbes but Flask 2 stayed sterile, proving that microbes come from the air — not from the broth itself — disproving spontaneous generation.

c. Flask 2 grew microbes but Flask 1 stayed sterile, proving that curved necks cause microbial growth.

d. Both flasks grew microbes equally, proving that boiling does not kill microorganisms.

Question 5

Pasteur also discovered that heating liquids to a specific temperature could kill microorganisms without altering the liquid significantly. This process, named after him, is used today to make milk safe to drink. Which statement best explains the importance of Pasteur's work for medicine?

a. His work proved that all bacteria cause disease and should be eliminated.

b. His work demonstrated that microbes arise from non-living matter under the right conditions.

c. His work established that microorganisms exist in the environment and can contaminate liquids, providing the foundation for germ theory and sterilization practices in medicine.

d. His work showed that viruses — not bacteria — cause most infectious diseases.

Question 6

A virus particle is composed of two major components: its genetic material and its protein coat. Some viruses also have an additional outer layer.

The protein coat surrounding a virus's genetic material is called the

a. envelope

b. capsid

c. plasmid

d. nucleoid

Question 7

A virology student is comparing a bacterial cell to a virus. She lists characteristics of each: the bacterial cell has a cell wall, ribosomes, a cell membrane, circular DNA, and can reproduce independently. The virus has only a protein capsid and a strand of DNA.

Which characteristic best explains why viruses are not considered living organisms?

a. Viruses are too small to be seen under a standard light microscope.

b. Viruses do not contain any genetic material of their own.

c. Viruses cannot carry out any life processes on their own and must hijack a host cell to replicate.

d. Viruses lack a cell wall, which is required for all living organisms.

Question 8

During a lysogenic infection, a bacteriophage injects its DNA into a bacterial host cell. Instead of immediately replicating, the viral DNA inserts itself into the bacterium's chromosome and becomes dormant. Each time the host bacterium divides by binary fission, the viral DNA is copied along with the host's DNA.

The dormant viral DNA integrated into the host cell's chromosome is called a

a. lytic particle

b. capsid

c. prophage

d. plasmid

Question 9

A patient visits the doctor with a bad cold caused by a rhinovirus. The doctor explains that there is no antibiotic treatment that will help, and recommends rest and fluids.

Which statement best explains why antibiotics are not effective against this viral infection?

a. Antibiotics kill all pathogens, but rhinoviruses are immune to all known antibiotics.

b. Antibiotics work by targeting bacterial-specific structures like cell walls and ribosomes, which viruses do not have.

c. Antibiotics are too large to enter the cells where viruses are hiding.

d. Antibiotics only work at temperatures below normal body temperature.

Question 10

Robert Koch was a German physician who, in the 1870s, developed a set of four logical steps to prove that a specific microorganism is the cause of a specific disease. He used these steps to prove that specific bacteria cause tuberculosis and anthrax.

According to Koch's Postulates, after isolating a suspected pathogen from a sick individual and growing it in pure culture, what must a scientist do next?

a. Re-isolate the pathogen from the original patient a second time.

b. Immediately develop a vaccine to prevent the disease from spreading.

c. Introduce the cultured pathogen to a healthy organism and observe whether the same disease develops.

d. Compare the pathogen's DNA to that of all known bacteria to find its closest relative.

For questions 11 and 12, use the data table below.

A researcher treated a bacterial population with an antibiotic and tracked the number of surviving bacteria over four days:

Day	Total Bacteria	Antibiotic-Sensitive	Antibiotic-Resistant
Day 1 (before treatment)	10,000	9,950	50
Day 2 (treatment begins)	5,200	5,170	30
Day 3	800	600	200
Day 4	1,400	400	1,000

Question 11

Based on the data table, which statement best explains the increase in antibiotic-resistant bacteria from Day 1 to Day 4?

a. The antibiotic caused mutations in sensitive bacteria, turning them into resistant bacteria.

b. The antibiotic selected for naturally resistant bacteria — sensitive bacteria died, while resistant ones survived and reproduced.

c. The resistant bacteria infected the sensitive bacteria and passed on resistance through viral particles.

d. The bacteria developed resistance by producing enzymes that were learned from exposure to the antibiotic.

Question 12

A patient is diagnosed with this bacterial infection and begins a course of antibiotics. After Day 3, the patient feels much better and stops taking the antibiotic. Which outcome is most likely?

a. The patient is fully cured because the antibiotic killed most of the bacteria.

b. The remaining resistant bacteria will multiply and cause a more difficult-to-treat infection to return.

c. The immune system will immediately destroy the remaining 800 bacteria without any problem.

d. The bacteria will switch to the lysogenic cycle and become dormant permanently.

Question 13

A vaccination program is introduced to prevent a new viral disease. The vaccine contains inactivated (killed) virus particles that cannot cause disease. Millions of people receive the vaccine over the following year.

Which statement best explains how the vaccine protects vaccinated individuals from future infection?

a. The inactivated virus kills all copies of the real virus that may enter the body.

b. The vaccine introduces antibiotics that prevent the virus from attaching to cells.

c. The immune system learns to recognize the inactivated virus particles and builds memory cells, allowing a rapid response if the real virus is encountered later.

d. The vaccine causes a mild version of the disease, making the person temporarily sick but immune afterward.

Question 14

A biology teacher describes two types of bacteria: Streptococcus pneumoniae, which causes pneumonia, and Lactobacillus acidophilus, which is found in yogurt and benefits gut health.

Which statement about bacteria is most accurate based on this information?

a. All bacteria are pathogens that cause disease in humans.

b. Bacteria that are beneficial to humans belong to a different domain than harmful bacteria.

c. Not all bacteria are harmful — some are pathogenic while others are beneficial or neutral.

d. Only bacteria with Latin species names can cause disease in humans.

Question 15

Bacteria have several external structures. The cell wall provides structure and protection. Pili are short hair-like projections used for attachment. Flagella are long whip-like structures. Some bacteria also have a capsule — a sticky outer coating.

A bacterium without a flagellum would most likely have difficulty

a. making proteins needed for reproduction

b. attaching to surfaces to form a biofilm

c. moving through liquid environments toward food sources

d. protecting itself from antibiotics that target the cell wall

Question 16

A virus infects a host cell and its genetic material enters the host's nucleus. The viral DNA integrates into the host chromosome and remains dormant for years. When the host experiences significant stress, the viral DNA becomes active.

When the viral DNA becomes active, which cycle most likely begins, and what is the immediate consequence?

a. The lysogenic cycle begins and the viral DNA continues to stay dormant indefinitely.

b. The lytic cycle begins — the virus replicates rapidly and lyses the host cell, releasing new virus particles.

c. Binary fission is triggered, causing the host cell to split and distribute the viral DNA.

d. The immune cycle begins — the host cell produces antibodies to neutralize the virus.

Question 17

Viruses are far smaller than bacteria. The average bacterium is about 1–10 micrometers in size, while most viruses are 0.02–0.3 micrometers — so small that they pass through filters that trap bacteria and can only be seen with an electron microscope.

Which of the following is a similarity shared by both bacteria and viruses?

a. Both have ribosomes that manufacture proteins inside the cell.

b. Both have a cell wall made of peptidoglycan for structural support.

c. Both contain genetic material (DNA or RNA) that carries the instructions for their traits.

d. Both can reproduce independently without needing a host cell.

Question 18

A bacterium has a small, circular loop of DNA that is separate from its main chromosome. This extra piece of DNA contains genes that give the bacterium resistance to a particular antibiotic.

This small, separate loop of DNA is called a

a. capsid

b. prophage

c. plasmid

d. nucleoid

Question 19

Prokaryotic cells differ from eukaryotic cells in a fundamental way. In prokaryotes, the genetic material floats freely in the cell in a region called the nucleoid. In eukaryotes, the DNA is enclosed within a membrane-bound nucleus.

Which domain contains organisms that are eukaryotic?

a. Domain Bacteria

b. Domain Archaea

c. Domain Bacteria and Domain Archaea

d. Domain Eukarya

Question 20

A group of scientists studying disease outbreaks follows the germ theory of disease. They identify a new pathogen causing illness in a local community and use Koch's Postulates to confirm it as the cause of the disease.

The germ theory of disease states that

a. diseases arise from bad air (miasma) in polluted environments

b. specific microorganisms cause specific diseases

c. all microscopic organisms are capable of causing disease in humans

d. diseases arise spontaneously from non-living matter under certain conditions

Test 2 Complete!

--/ 20

🧬 Practice Test 3

20 questions • Read each scenario carefully • Select the best answer • Submit when finished

For questions 1 and 2, use the information in the table below.

Scientists compared the classification of four different organisms. Use the data below to answer questions 1 and 2.

Classification Level	Organism A	Organism B	Organism C	Organism D
Domain	Eukarya	Eukarya	Eukarya	Bacteria
Kingdom	Animalia	Animalia	Animalia	—
Class	Mammalia	Mammalia	Reptilia	—
Order	Carnivora	Primates	Squamata	—
Family	Felidae	Hominidae	Colubridae	—
Genus	Felis	Homo	Lampropeltis	Escherichia
Species	catus	sapiens	triangulum	coli

Question 1

Based on the table, which two organisms are most closely related?

a. Organism A and Organism B, because both are mammals

b. Organism A and Organism C, because both are in Domain Eukarya

c. Organism B and Organism D, because Homo sapiens and E. coli are both well-studied

d. Organism A and Organism B are equally related to Organism C

Question 2

Organism D (Escherichia coli) belongs to Domain Bacteria. Which characteristic most clearly distinguishes Organism D from Organisms A, B, and C?

a. Organism D is microscopic while Organisms A, B, and C are visible to the naked eye.

b. Organism D is a prokaryote with no membrane-bound nucleus, while Organisms A, B, and C are eukaryotes with a true nucleus.

c. Organism D cannot cause disease while Organisms A, B, and C can.

d. Organism D reproduces sexually while Organisms A, B, and C reproduce asexually.

Question 3

A farmer notices that one of their cows is sick with an unknown disease. A veterinarian isolates a bacterium from the sick cow, grows it in a laboratory, and then introduces the cultured bacteria to two healthy cows. Both healthy cows develop the same disease. The veterinarian then re-isolates the bacteria from both sick cows and confirms they are identical to the original culture.

Which of the following best describes what the veterinarian has demonstrated?

a. That the disease is caused by a virus, not a bacterium

b. That the disease can only spread through direct contact between cows

c. That the isolated bacterium is the cause of the disease, satisfying all four of Koch's Postulates

d. That the vaccine for this disease will need to be developed immediately

Question 4

During a viral infection, scientists track what happens inside an infected cell over 48 hours. At hour 0, the virus injects DNA into the cell. At hour 12, the viral DNA has integrated into the host chromosome. At hour 30, nothing seems to happen — the cell continues dividing normally, with viral DNA being copied each time. At hour 48, something triggers the virus to become active.

The events from hour 0 to hour 30 are best described as the lysogenic cycle because

a. the host cell immediately bursts open to release new viruses

b. the viral DNA integrates into the host chromosome and lies dormant, being copied passively with each cell division

c. the virus is using the host cell's ribosomes to produce thousands of new viral proteins

d. binary fission is triggered, allowing the virus to reproduce independently

Question 5

A population of mice lives in a snowy mountain environment. Most mice have gray fur, but a small number have white fur. Over ten generations, scientists observe that the proportion of white-furred mice in the population increases significantly.

Which explanation best accounts for this change in the mouse population?

a. Gray mice chose to grow white fur to better survive in the snow.

b. White-furred mice were better camouflaged against the snow, were less likely to be spotted by predators, and therefore survived and reproduced more successfully.

c. The cold mountain environment caused mutations that turned gray fur into white fur in all mice equally.

d. White mice migrated into the population from a different mountain region.

Question 6

A group of researchers is studying bacterial structure. They want to understand what structure keeps the bacterium from collapsing and gives it its rigid shape. They also note that this structure is the target of penicillin, one of the most widely used antibiotics.

The structure described is the

a. cell membrane, which is made of a phospholipid bilayer

b. ribosome, which is involved in protein synthesis

c. cell wall, which is made of peptidoglycan and provides rigid structural support

d. nucleoid region, where the circular bacterial chromosome is located

Question 7

A botanist examining two flowering plant species notices they have very similar leaf shapes, flower structures, and root systems. She initially classifies them as close relatives. However, when she compares their DNA, she finds they share only 41% of their genetic code.

Which conclusion is most supported by all the evidence?

a. The similar physical appearance proves the two species are closely related, regardless of DNA.

b. The DNA data is more reliable — the similar physical features likely result from convergent evolution, not common ancestry.

c. The botanist should only use physical features to classify plants, because DNA testing is unreliable.

d. A 41% DNA similarity indicates the two plants are the most closely related species on Earth.

Question 8

A phylogenetic tree for four species of birds shows the following structure: Species W and X branch from the same node 5 million years ago. Species Y branches from a node shared with WX at 15 million years ago. Species Z branches from the base of the tree at 50 million years ago.

Based on the phylogenetic tree, which pair of species is most distantly related to each other?

a. Species W and X

b. Species W and Y

c. Species X and Y

d. Species W and Z

For questions 9 and 10, use the information below.

A school nurse recorded data about two different outbreaks at the school this winter. Outbreak 1 was caused by Streptococcus pyogenes (strep throat — a bacterial infection). Outbreak 2 was caused by Influenza A (the flu — a viral infection). The nurse notes that students with strep throat recovered quickly after taking a 10-day course of amoxicillin (an antibiotic). Students with the flu were told to rest, drink fluids, and take antiviral medication if symptoms were severe.

Question 9

Why did the amoxicillin help students with strep throat but not students with the flu?

a. Amoxicillin kills viruses but works even better against bacteria.

b. Amoxicillin targets bacterial cell walls, which bacteria have but viruses do not — making it effective against strep but useless against influenza.

c. The flu virus becomes resistant to amoxicillin too quickly for the drug to work.

d. Amoxicillin only works against throat infections, not lung infections.

Question 10

Several students with strep throat stopped taking their amoxicillin after five days because they felt better. Which outcome is most likely for those students?

a. They are fully recovered — once symptoms are gone, the bacteria are all dead.

b. The remaining bacteria, including any naturally resistant ones, may multiply and the infection could return, potentially with antibiotic-resistant strains.

c. Their immune systems will immediately destroy the remaining bacteria without any further help.

d. The amoxicillin they already took will continue working in their bodies for another 30 days.

Question 11

The human coccyx (tailbone) consists of fused vertebrae at the base of the spine. In most humans, it serves no known function. However, in primates such as chimpanzees, the coccyx is part of a tail structure used for balance and grip.

The human coccyx is best described as

a. a homologous structure indicating humans adapted to tree-dwelling environments

b. an analogous structure showing convergent evolution between humans and primates

c. a vestigial structure — a remnant of a functional tail from an ancestral primate species

d. a derived characteristic unique to the human clade that appeared recently in evolution

Question 12

Scientists classify living things into three domains. Domain Bacteria and Domain Archaea both contain prokaryotic organisms. Domain Eukarya contains all eukaryotic organisms. Archaea are often found in extreme environments such as hot springs, salt lakes, and deep-sea vents.

Which statement most accurately describes the difference between Domain Bacteria and Domain Archaea?

a. Bacteria are eukaryotic while Archaea are prokaryotic.

b. Both are prokaryotes, but Archaea have a fundamentally different biochemistry from Bacteria, including different cell membrane lipids.

c. Archaea contain a membrane-bound nucleus while Bacteria do not.

d. Bacteria only live in extreme environments while Archaea can live anywhere.

Question 13

A clade is a group that includes an ancestor and ALL of its descendants. Scientists sometimes debate whether a group of organisms forms a true clade.

Which of the following would NOT be considered a true clade?

a. A group that includes a common ancestor and all of its descendants

b. A group defined by a unique derived characteristic inherited from a common ancestor

c. A group that includes some, but not all, descendants of a common ancestor

d. A group that contains an ancestor and two lineages that branched from it

Question 14

When two unrelated species evolve similar traits because they live in similar environments and face similar survival pressures, biologists call this convergent evolution. The resulting similar structures are called analogous structures.

Which pair of structures is the best example of analogous structures resulting from convergent evolution?

a. The arm of a human and the wing of a bat — both have the same underlying bone structure

b. The eyes of an octopus and the eyes of a human — both evolved complex eyes independently

c. The spine of a human and the spine of a fish — both evolved from a shared vertebrate ancestor

d. The heart of a frog and the heart of a bird — both pump blood through a circulatory system from a common ancestor

Question 15

Scientists using a dichotomous key to identify an unknown organism follow a series of paired statements. At each step, they choose between two options that narrow down the possibilities until they arrive at the organism's identity.

A dichotomous key is most similar in structure to which of the following?

a. A cladogram, which shows branching evolutionary relationships

b. A phylogenetic tree, which shows time-based evolutionary history

c. A flowchart with yes/no decision points that narrow down possibilities at each step

d. A taxonomic chart that lists all organisms from Domain down to Species

Question 16

Vaccines have been one of the most effective tools in preventing infectious disease. When the MMR vaccine (measles, mumps, rubella) was introduced, rates of these diseases dropped by over 99% in countries with high vaccination rates.

The MMR vaccine prevents disease by

a. releasing antibiotics into the bloodstream when a pathogen is detected

b. eliminating all pathogens from the body permanently after a single dose

c. exposing the immune system to weakened or inactivated forms of the pathogens, triggering the production of memory cells that enable rapid response to future infection

d. directly attacking virus particles before they can attach to any body cells

Question 17

Binomial nomenclature gives every organism a unique two-part scientific name. This system was created by Carl Linnaeus in the 18th century and has been used by scientists worldwide ever since.

A student writes the scientific name for a domestic cat as follows: felis Catus. Which corrections are needed?

a. No corrections are needed — the name is written correctly.

b. The first letter of the genus (Felis) must be capitalized; the species epithet (catus) must be lowercase.

c. Both words should be fully capitalized: FELIS CATUS.

d. The species epithet should come first: catus felis.

Question 18

In binary fission, a bacterium first replicates its circular chromosome. The two copies of the chromosome then move to opposite ends of the cell. Finally, the cell membrane pinches inward and the cell divides into two daughter cells.

Which statement about the two daughter cells produced by binary fission is most accurate?

a. The daughter cells are genetically different from each other due to random mutation during division.

b. The daughter cells are genetically identical to each other and to the original parent cell.

c. Each daughter cell receives half the genetic material of the parent cell.

d. The daughter cells must grow to double the original size before they can divide again.

Question 19

Recent advances in DNA sequencing technology have allowed scientists to compare the genetic codes of organisms across all domains of life. Scientists discovered that the protein-coding DNA of Tyrannosaurus rex is most similar to that of modern birds.

How does DNA comparison evidence improve our ability to classify organisms?

a. It shows that organisms that look alike are always closely related.

b. It allows scientists to establish evolutionary relationships based on molecular data, which is more precise than relying solely on physical appearance.

c. It proves that extinct species are always more closely related to living species than to other extinct species.

d. It demonstrates that all species have the same rate of genetic mutation over time.

Question 20

The influenza virus has a lipid envelope surrounding its protein capsid. This envelope is made of lipids that the virus takes from the host cell's membrane when it exits. HIV also has a lipid envelope.

The lipid envelope on some viruses is thought to help the virus

a. reproduce independently without needing a host cell

b. survive antibiotic treatment by hiding from the drug

c. enter host cells more easily by fusing with the host cell's lipid membrane

d. produce energy for viral replication through photosynthesis

Test 3 Complete!

--/ 20

🧬 Practice Test 4

20 questions • Read each scenario carefully • Select the best answer • Submit when finished

Question 1

A scientist has discovered a new microorganism living in a deep-sea hydrothermal vent. The organism has no membrane-bound nucleus, its cell membrane contains unique ether-linked lipids not found in bacteria, and it thrives at temperatures above 100°C.

This organism most likely belongs to

a. Domain Bacteria, because it is prokaryotic and microscopic

b. Domain Eukarya, because it has a cell membrane

c. Domain Archaea, because it is a prokaryote with unique biochemistry adapted to extreme environments

d. Domain Eukarya, Kingdom Protista, because it lives in water

For questions 2, 3, and 4, use the cladogram information below.

A biologist constructed a cladogram for five vertebrate species using the following shared derived characteristics. Use this information to answer questions 2, 3, and 4.

Derived Characteristic	Lamprey	Salmon	Frog	Lizard	Mouse
Backbone	✓	✓	✓	✓	✓
Jaws	✗	✓	✓	✓	✓
Four limbs	✗	✗	✓	✓	✓
Amniotic egg	✗	✗	✗	✓	✓
Hair / Mammary glands	✗	✗	✗	✗	✓

Question 2

Based on the cladogram data, which two species share the most recent common ancestor?

a. Lamprey and Salmon, because both live in water

b. Frog and Lizard, because both have four limbs

c. Lizard and Mouse, because both have an amniotic egg and share four limbs

d. Salmon and Frog, because both are cold-blooded

Question 3

The lamprey is the only species in the table that lacks jaws. Based on the cladogram data, which conclusion is most accurate?

a. The lamprey is the most recently evolved species in the group.

b. The lamprey branched off from the common ancestor earliest, before jaws evolved — making it the most distantly related to the mouse.

c. The lamprey is most closely related to the mouse because both are vertebrates.

d. The lamprey evolved from the frog after losing its jaws over time.

Question 4

A biologist argues that the frog and mouse are more closely related to each other than either is to the salmon. Which piece of data from the table best supports this argument?

a. Both frog and mouse have a backbone, which the salmon also has.

b. The frog and mouse both share four limbs, which the salmon lacks — placing both in a clade that excludes the salmon.

c. The salmon lives in water while the frog and mouse live on land.

d. The mouse has hair while the frog does not, showing they cannot be closely related.

Question 5

A new infectious disease appears in a community. Epidemiologists observe that patients who are given a broad-spectrum antibiotic do not recover, while patients treated with antiviral medication show improvement.

Based on these observations, which conclusion is most supported?

a. The disease is caused by bacteria, because bacteria do not respond to antiviral drugs.

b. The disease is caused by a virus, because it does not respond to antibiotics but does respond to antiviral medication.

c. Both bacteria and viruses are causing the disease simultaneously.

d. The antibiotic was the wrong dose — a higher dose would have cured the bacterial infection.

Question 6

Louis Pasteur is known for two major contributions to science. First, he designed the swan-neck flask experiment that disproved spontaneous generation. Second, he developed vaccines for chicken cholera and rabies by using weakened forms of the pathogens.

Pasteur's swan-neck flask experiment was important because it proved

a. that vaccines are effective against bacterial diseases

b. that viruses — not bacteria — cause most infectious diseases

c. that living organisms do not arise spontaneously from non-living matter, establishing that microbes come from existing microbes

d. that antibiotics can be used to kill pathogens in liquid solutions

Question 7

Two species of finches live on separate islands in the Pacific Ocean. Island A finches have long, thin beaks suited for probing flowers for nectar. Island B finches have short, thick beaks suited for cracking hard seeds. Both populations descended from the same ancestral finch that arrived from the mainland 200,000 years ago.

The differences between the two finch populations are best explained by

a. The finches on Island A chose to evolve longer beaks because they preferred nectar.

b. Natural selection — finches with beak shapes better suited to available food on each island survived and reproduced more, leading to different beak shapes over generations.

c. Convergent evolution — both finch populations evolved from completely different ancestral species.

d. Spontaneous generation — new finch species appeared on each island independently from non-living matter.

Question 8

During a lytic viral infection, the following sequence of events occurs: (1) the virus attaches to a host cell, (2) viral genetic material is injected into the host cell, (3) the host cell produces viral proteins and copies viral DNA, (4) new viruses are assembled, (5) the host cell bursts open.

Step 5 — the bursting of the host cell — is called lysis. This step is significant because it

a. gives the host cell an opportunity to repair itself and produce antibodies

b. causes the virus to enter the lysogenic cycle and become dormant

c. releases hundreds of new viruses into the surrounding area, allowing them to infect more host cells

d. triggers the host's immune system to produce antibiotics against the virus

For questions 9 and 10, use the information below.

Researchers studying the spread of antibiotic resistance published the following findings: In 1950, nearly 100% of Staphylococcus aureus (staph) bacteria were killed by penicillin. By 1960, over 80% of staph bacteria tested in hospitals were resistant to penicillin. Today, a strain called MRSA (methicillin-resistant Staphylococcus aureus) is resistant to many common antibiotics and causes tens of thousands of deaths annually.

Question 9

The rapid increase in antibiotic-resistant staph bacteria from 1950 to today is best explained by which process?

a. Antibiotics caused mutations in bacteria, transforming them into resistant organisms.

b. Bacteria chose to become resistant to protect themselves from antibiotics.

c. Natural selection — bacteria with natural resistance genes survived antibiotic treatment, reproduced, and passed resistance to offspring over many generations.

d. Hospitals introduced new chemicals that caused bacteria to develop resistance as a side effect.

Question 10

A doctor recommends that a patient take a full 14-day course of antibiotics even though the patient typically feels better after day 5. Based on the information about antibiotic resistance, which statement best justifies this recommendation?

a. Antibiotics have no effect after the first five days, so the extra nine days don't matter.

b. Stopping early leaves partially resistant bacteria alive — completing the full course ensures all bacteria are eliminated, reducing the chance of resistance developing.

c. The immune system completely takes over on day 5 and the antibiotics become harmful after that.

d. Doctors always prescribe more antibiotics than needed as a precaution.

Question 11

Two species of moles — one from North America and one from Australia — both have large, flat front paws adapted for digging. However, their bone structures are completely different, and their most recent common ancestor did not have specialized digging paws.

The digging paws of North American and Australian moles are best described as

a. homologous structures, because they look similar and serve the same function

b. vestigial structures, because they evolved from a functional ancestor paw

c. analogous structures, because they evolved independently in unrelated species due to similar digging environments

d. derived characteristics shared by a common ancestor that lived underground

Question 12

A researcher writes the scientific name for a newly discovered beetle as Scarabaeus sacer. A colleague later refers to the same beetle in a published paper as Scarabaeus sacer.

This consistency in scientific naming is made possible because binomial nomenclature

a. requires all scientists to use the same common name for each species

b. uses Latin, a stable language that does not change over time, creating universally accepted names

c. is updated every ten years to reflect new discoveries and classification changes

d. allows individual scientists to create their own names for species they discover

Question 13

A physician treating a patient with a severe bacterial lung infection prescribes a 10-day course of antibiotics. The antibiotic works by binding to bacterial ribosomes and blocking protein synthesis. The drug has no effect on human ribosomes because they are structurally different from bacterial ribosomes.

This antibiotic is effective against the bacterial infection but safe for the human patient because

a. human cells do not have any ribosomes, so the antibiotic cannot cause any damage

b. the antibiotic specifically targets bacterial ribosomes, which differ structurally from human ribosomes, leaving human cells unharmed

c. the antibiotic destroys the bacterial cell wall rather than the ribosome

d. viruses also have bacterial-type ribosomes, making this antibiotic effective against all pathogens

Question 14

Germ theory transformed medicine in the 19th century. Before germ theory, surgeons operated without sterilizing their hands or instruments, and hospital mortality rates from infection were extremely high. After the acceptance of germ theory, antiseptic practices reduced surgical mortality dramatically.

Which statement best explains why the acceptance of germ theory led to improved surgical outcomes?

a. Germ theory proved that diseases are caused by chemical imbalances, leading to better medications.

b. Understanding that microorganisms cause disease led surgeons to sterilize instruments and disinfect wounds, preventing microbial contamination from causing post-surgical infections.

c. Germ theory eliminated all bacteria from hospital environments permanently.

d. Germ theory proved that viruses — not bacteria — cause surgical infections, allowing targeted viral treatments.

Question 15

A cell biologist examining cells under a microscope can distinguish eukaryotic cells from prokaryotic cells by looking for one key structural feature.

The structural feature that best distinguishes a eukaryotic cell from a prokaryotic cell is the presence of

a. a cell wall surrounding the cell membrane

b. ribosomes involved in protein synthesis

c. a membrane-bound nucleus enclosing the cell's DNA

d. a flagellum used for movement

Question 16

A species of tree frog lives in a tropical rainforest. Researchers observe the following four characteristics of this frog:
(1) Bright red coloration
(2) Produces a toxic skin secretion
(3) Lays eggs in water
(4) Can mate with a related frog species from a neighboring rainforest and produce fertile offspring

Which observation best supports the inference that this frog and the neighboring species belong to the same species?

a. Observation 1 — both species have similar bright coloration

b. Observation 2 — both species produce skin secretions

c. Observation 3 — both species lay eggs in water

d. Observation 4 — the two frogs can mate and produce fertile offspring

Question 17

A prophage is viral DNA that has been integrated into a host bacterial cell's chromosome. The host bacterium continues to divide normally, with the prophage being replicated along with the host's own DNA. Under certain stress conditions, such as UV radiation exposure, the prophage can become active.

When the prophage becomes active following UV radiation exposure, what is the most likely outcome?

a. The prophage permanently repairs the damage caused by UV radiation in the host cell.

b. The viral DNA exits the host chromosome, begins the lytic cycle, and ultimately causes the host cell to burst and release new viruses.

c. The host cell undergoes binary fission faster, producing more copies of the viral DNA peacefully.

d. The prophage becomes a new plasmid that gives the bacterium antibiotic resistance.

Question 18

Domain Eukarya is divided into four kingdoms: Animalia, Plantae, Fungi, and Protista. These kingdoms differ in how they obtain energy, their cell structure, and their body organization.

Which of the following organisms does NOT belong to Domain Eukarya?

a. A mushroom (Kingdom Fungi)

b. An amoeba (Kingdom Protista)

c. A pine tree (Kingdom Plantae)

d. A bacterium causing strep throat (Domain Bacteria)

Question 19

Comparative embryology reveals that the embryos of many different vertebrate species — including fish, reptiles, birds, and mammals — are nearly identical in their earliest stages of development. All have gill slits, a tail, and similar limb buds early in development.

This similarity in embryonic development is best explained by

a. the fact that all vertebrates need the same structures to survive outside the womb

b. convergent evolution — all vertebrates independently evolved to look similar as embryos

c. a shared common ancestor among all vertebrates — the retained embryonic similarity reflects their evolutionary relationship

d. spontaneous generation — all vertebrate embryos arise from the same non-living chemical mixture

Question 20

A science journalist reports: 'Scientists have discovered a 'living fossil' — an organism virtually unchanged from fossils that are 300 million years old. Comparisons of its DNA to that of its ancient relatives show remarkably few differences.'

The small number of DNA differences between the 'living fossil' and its ancient relatives is best explained by

a. The organism mutates at a much faster rate than other species.

b. The organism has remained in a stable environment with little selection pressure to change, resulting in very slow evolutionary change over time.

c. DNA does not change over time in any organism.

d. The organism reproduces by lytic viral cycles that keep its DNA constant.

Test 4 Complete!

--/ 20

🧬 Practice Test 5

20 questions • Read each scenario carefully • Select the best answer • Submit when finished

For questions 1, 2, and 3, use the information below.

A biology class conducted an investigation comparing bacteria and viruses. They used the following data table summarizing the characteristics of each:

Characteristic	Bacteria	Virus
Cell type	Prokaryotic cell	Not a cell
Genetic material	DNA (circular chromosome + plasmids)	DNA or RNA
Protein-making structures	Ribosomes present	No ribosomes
Outer structure	Cell wall (peptidoglycan) + cell membrane	Protein capsid (± lipid envelope)
Reproduction	Binary fission (independent)	Requires host cell
Size	1–10 micrometers	0.02–0.3 micrometers
Responds to antibiotics?	Yes (most species)	No

Question 1

Based on the data table, which characteristic is shared by both bacteria and viruses?

a. Both have ribosomes for making proteins.

b. Both contain genetic material (DNA or RNA).

c. Both can reproduce independently without a host.

d. Both respond to antibiotic treatment.

Question 2

A patient has a bacterial throat infection. Their friend has a viral throat infection. The doctor gives the first patient amoxicillin (an antibiotic) but tells the second patient antibiotics will not help. Based on the data table, which statement best explains this difference in treatment?

a. Amoxicillin kills all pathogens equally, but the viral patient is already recovering.

b. Antibiotics target bacterial structures like cell walls and ribosomes, which viruses lack — making antibiotics ineffective against viral infections.

c. The viral patient is too sick for antibiotics to work effectively.

d. Viruses respond only to penicillin, not amoxicillin.

Question 3

According to the data table, which statement about viral reproduction is most accurate?

a. Viruses reproduce by binary fission, producing two identical daughter virus particles.

b. Viruses use their own ribosomes to produce viral proteins needed for reproduction.

c. Viruses must enter a living host cell and use the host's cellular machinery to replicate.

d. Viruses reproduce inside the nucleoid region of bacterial cells only.

Question 4

A biologist studying taxonomy notes that the domestic dog (Canis familiaris), the gray wolf (Canis lupus), and the red fox (Vulpes vulpes) are all members of the family Canidae.

Based on the scientific names alone, which pair of species is most closely related?

a. The domestic dog and the red fox, because both are commonly found near humans.

b. The gray wolf and the red fox, because both are wild animals.

c. The domestic dog and the gray wolf, because both belong to the genus Canis.

d. All three are equally closely related, because they all belong to family Canidae.

Question 5

Robert Koch used his four postulates to prove that Mycobacterium tuberculosis (a bacterium) causes tuberculosis. Years later, virologists tried to apply Koch's Postulates to viruses but found they needed to modify the rules because viruses behave differently from bacteria.

Which aspect of viral biology would make Koch's original Postulates most difficult to apply directly to viruses?

a. Viruses are too small to be seen under any microscope.

b. Viruses cannot be grown in a pure culture independently — they require living host cells to replicate, which Koch's original method did not account for.

c. Viruses do not contain DNA, so they cannot be identified as specific pathogens.

d. Viruses cannot cause the same disease in different individuals.

Question 6

Scientists studying the evolutionary relationships of whales discovered that whales share more DNA similarity with hippopotamuses than with any other living land animal. They also found tiny hip and leg bones buried deep inside whale bodies.

The buried hip bones in whales are best described as vestigial structures because they

a. allow whales to move through the water more efficiently

b. are evidence that whale ancestors once lived on land and had functional legs, but the bones lost their function as whales evolved into fully aquatic animals

c. evolved independently in whales and hippos as a result of convergent evolution

d. represent a newly evolved feature that will become larger in future whale generations

For questions 7 and 8, use the information below.

A public health researcher published data comparing two methods of disease prevention: vaccines and antibiotics. The table below shows the outcomes for two different diseases over a 50-year period following the introduction of each treatment.

Disease (Cause)	Treatment introduced	Cases per 100,000 — Year 0	Cases per 100,000 — Year 50
Polio (Poliovirus)	Polio vaccine (1955)	38	0
Tuberculosis (Mycobacterium tuberculosis)	Antibiotic therapy	53	6

Question 7

Based on the data table, which statement best compares the effectiveness of vaccines and antibiotics in controlling disease?

a. Antibiotics were more effective than vaccines, because TB cases still exist while polio was fully eliminated.

b. The polio vaccine completely eliminated polio cases, while antibiotics reduced but did not eliminate tuberculosis cases — suggesting vaccines can be more effective for certain diseases.

c. Both treatments were equally effective at reducing disease cases over 50 years.

d. The polio vaccine only worked because polio is a bacterial disease, while TB persists because it is viral.

Question 8

The researcher notes that some strains of Mycobacterium tuberculosis have become resistant to multiple antibiotics. Based on your knowledge of natural selection and antibiotic resistance, which statement best explains how this resistance developed?

a. The antibiotics caused random mutations in TB bacteria, creating resistant strains intentionally.

b. TB bacteria with natural resistance genes survived antibiotic treatment, reproduced, and spread — while sensitive bacteria were killed, leaving a population dominated by resistant strains.

c. Resistant TB bacteria were created in a laboratory and accidentally released into the environment.

d. TB became resistant because doctors prescribed too many different antibiotics simultaneously.

Question 9

A researcher examining a cladogram notices that reptiles and birds share a node that is more recent than the node connecting both of them to amphibians. All three groups share an even earlier node with fish.

Based on the cladogram, which statement about evolutionary relationships is most accurate?

a. Fish and amphibians are more closely related than birds and reptiles.

b. Amphibians are more closely related to birds than birds are to reptiles.

c. Birds and reptiles share a more recent common ancestor than either shares with amphibians.

d. All four groups are equally related because they all share a vertebrate common ancestor.

Question 10

A physician encounters a patient with a strange new illness. She isolates a microscopic agent from the patient's blood and examines it under an electron microscope. She observes a protein capsid surrounding a strand of RNA. There are no ribosomes, cell membrane, or cell wall.

The physician concludes this agent is a virus. Which observation from her examination most strongly supports this conclusion?

a. The presence of RNA, because RNA is only found in viruses

b. The absence of ribosomes, cell membrane, and cell wall — combined with a protein capsid surrounding genetic material — is characteristic of a virus, not a living cell

c. The small size of the agent, because all viruses are smaller than bacteria

d. The presence of a protein capsid, which is also found in all bacteria

Question 11

When Pasteur's germ theory was first proposed, many physicians rejected it. Some believed that 'miasma' (bad air from rotting matter) caused disease. Others believed diseases arose spontaneously in the sick person's body. The acceptance of germ theory fundamentally changed medical practice.

Which of the following was a direct result of the acceptance of germ theory in medicine?

a. Doctors concluded that surgery was too dangerous and should be avoided.

b. Physicians began washing hands, sterilizing surgical instruments, and using antiseptics — dramatically reducing infection rates in hospitals.

c. Scientists stopped studying bacteria because germ theory proved viruses cause all diseases.

d. Hospitals were built with special 'clean air' ventilation systems to remove miasma.

Question 12

A species of bacterium (Streptomyces griseus) produces streptomycin — an antibiotic that kills other bacteria by disrupting their ribosomes. Streptomycin has no effect on human ribosomes.

The fact that streptomycin disrupts bacterial ribosomes but not human ribosomes is explained by the fact that

a. human cells do not contain ribosomes, so streptomycin has nothing to target

b. bacterial ribosomes and human ribosomes differ in their structure, allowing the drug to selectively target bacteria

c. streptomycin is too large to enter human cells but small enough to enter bacteria

d. bacteria and humans belong to different kingdoms and cannot be affected by the same chemicals

Question 13

The scientific classification system places all life into three domains. Scientists have recently debated whether viruses should be classified within this system, since they share some characteristics of life (genetic material, evolution) but lack others (cells, metabolism, independent reproduction).

Based on the criteria used to classify life, viruses are currently not classified in any of the three domains primarily because

a. viruses are too small to be analyzed by current classification methods

b. viruses do not cause disease in all organisms, so they are not considered biologically relevant

c. viruses are not made of cells and cannot carry out life processes independently — the fundamental criteria for living organisms in the three-domain classification system

d. viruses reproduce too rapidly to be placed into a stable taxonomic group

Question 14

A school nurse gives students a flu vaccine each fall. She explains that the flu vaccine is updated every year because the influenza virus mutates rapidly, changing the proteins on its surface.

The nurse's explanation for the annual vaccine update best illustrates which biological concept?

a. Lysogenic cycle — the flu virus inserts its DNA into human chromosomes each year

b. Antibiotic resistance — bacteria become resistant to the flu vaccine each year

c. Viral evolution — the influenza virus mutates and changes over time, requiring an updated vaccine to match current strains

d. Binary fission — the flu virus divides rapidly, requiring an annual vaccine to keep up

Question 15

A group of organisms called marsupials (kangaroos, opossums, wombats) live primarily in Australia. A separate group of placental mammals (deer, wolves, rabbits) live in North America. Scientists have found pairs of marsupial and placental species that look remarkably similar — for example, the marsupial wolf (now extinct) and the North American wolf had nearly identical skull shapes — but their DNA and reproductive methods are very different.

The similar skull shapes of the marsupial wolf and the North American wolf are best explained by

a. homologous structures from a shared wolf ancestor

b. vestigial structures from a common marsupial ancestor

c. convergent evolution — both species evolved similar skull shapes independently because they had similar predatory lifestyles

d. biogeography — species on different continents always evolve identical structures

Question 16

The table below shows four observations about two island frog populations:
(1) They have different skin colors
(2) They have slightly different calls
(3) They live in different microhabitats on the same island
(4) When placed together, they can interbreed and produce fertile offspring

Which observation most strongly supports the conclusion that these two frog populations belong to the same species?

a. Observation 1, because color differences are the most reliable indicator of species.

b. Observation 2, because different calls indicate they are the same species.

c. Observation 3, because sharing the same island means they must be the same species.

d. Observation 4, because the ability to interbreed and produce fertile offspring is the defining characteristic of a species.

Question 17

A virology student is studying two viruses. Virus A enters a host cell and immediately begins producing new viral particles. The host cell lyses within 24 hours. Virus B enters a host cell, integrates its DNA into the host chromosome, and remains dormant for 6 months before becoming active.

Which statements correctly match each virus to its reproductive strategy?

a. Virus A uses the lysogenic cycle; Virus B uses the lytic cycle.

b. Virus A uses the lytic cycle; Virus B uses the lysogenic cycle.

c. Both viruses use the lytic cycle, but Virus B delays lysis for 6 months.

d. Both viruses use the lysogenic cycle, but Virus A switches to the lytic cycle faster.

Question 18

Domain Eukarya includes four kingdoms: Animalia, Plantae, Fungi, and Protista. All eukaryotic organisms have membrane-bound nuclei, but they differ in how they obtain energy, their cell structure, and their degree of complexity.

Which pair of organisms would both be classified in Domain Eukarya?

a. A bacterium and a mushroom

b. An amoeba and a rose plant

c. An archaeon and an oak tree

d. Influenza virus and a human cell

Question 19

Scientists have compared the DNA sequences of humans and several other species. They found the following percent similarities: chimpanzee 98.7%, gorilla 97.7%, orangutan 96.3%, domestic cat 90%, and yeast 31%.

Based on the DNA evidence, which conclusion is most accurate?

a. Humans are most closely related to gorillas because gorillas look most similar to humans.

b. Humans are most closely related to chimpanzees, as shown by their highest DNA similarity — indicating the most recent common ancestor.

c. Humans are equally related to all primates because all primates share similar physical features.

d. The domestic cat and yeast are equally related to humans because both are non-primates.

Question 20

A microbiologist performs the following experiment: She takes broth from a sick chicken and passes it through a filter fine enough to trap all bacteria. The filtered liquid is then injected into a healthy chicken. The healthy chicken develops the same disease.

The most likely explanation for the result is that

a. Bacteria survived the filtration process and infected the healthy chicken.

b. The broth itself was toxic and caused disease regardless of any pathogen.

c. A virus caused the disease — viruses are much smaller than bacteria and pass through bacterial filters, remaining in the filtered liquid to infect the healthy chicken.

d. Spontaneous generation occurred inside the healthy chicken after injection.

Test 5 Complete!

--/ 20

🎉 All 5 Tests Complete!

Taxonomic Hierarchy

📖 Read

✏️ Respond

📖 Multiple Choice

📖 Multiple Choice

Binomial Nomenclature

📖 Read

✏️ Respond

📖 Multiple Choice

📖 Multiple Choice

Criteria for Classifying Organisms

📖 Read

✏️ Respond

📖 Multiple Choice

📖 Multiple Choice

Cladograms & Phylogenetic Trees

📖 Read

✏️ Respond

📖 Multiple Choice

📖 Multiple Choice

Evidence for Evolutionary Relationships

📖 Read

✏️ Respond

📖 Multiple Choice

📖 Multiple Choice

Structure: Bacteria vs. Viruses

📖 Read

✏️ Respond

📖 Multiple Choice

📖 Multiple Choice

Reproduction Processes

📖 Read

✏️ Respond

📖 Multiple Choice

📖 Multiple Choice

Germ Theory: Pasteur & Koch

📖 Read

✏️ Respond

📖 Multiple Choice

📖 Multiple Choice

Impacts on Human Health

📖 Read

✏️ Respond

📖 Multiple Choice

📖 Multiple Choice

Vocabulary Practice

Terms

Definitions