Which molecule forms the cell walls of bacteria but is not found in the cell walls of archaea?
Peptidoglycan
✓
Chitin
Cellulose
Glycogen
Correct Answer
Peptidoglycan
Bacterial cell walls are built from peptidoglycan, chains of sugars cross-linked by short peptides; archaeal walls use other materials, such as pseudopeptidoglycan or proteins. Chitin is the wall material of fungi. Cellulose forms the walls of plants and many algae. Glycogen is a storage carbohydrate, not a wall component.
Category: Prokaryote Structure
Question 2
Compared with Gram-positive bacteria, Gram-negative bacteria have which feature?
A thick wall made of many peptidoglycan layers
An outer membrane outside a thin peptidoglycan layer
✓
A cell wall made mostly of cellulose
A nucleus enclosed by a double membrane
Correct Answer
An outer membrane outside a thin peptidoglycan layer
Gram-negative bacteria have only a thin layer of peptidoglycan, covered by an additional outer membrane. A thick wall made of many peptidoglycan layers describes Gram-positive bacteria. A cell wall made mostly of cellulose is a plant feature. A nucleus enclosed by a double membrane is found only in eukaryotes.
Category: Prokaryote Structure
Question 3
A community of microbes attached to a surface and held together by a sticky matrix of polysaccharides, proteins, and nucleic acids is called a
Mycelium
Lichen
Biofilm
✓
Pellicle
Correct Answer
Biofilm
A biofilm is a surface-attached microbial community embedded in a gummy matrix, and it can clog pipes and contaminate food-processing equipment. A mycelium is the mass of hyphae forming a fungal body. A lichen is a partnership between a fungus and a photosynthetic partner. A pellicle is a protein covering on certain protists.
Category: Prokaryote Structure
Question 4
Which group of prokaryotes released oxygen through photosynthesis, gradually adding it to Earth's early atmosphere?
Methanogens
Spirochetes
Clostridia
Cyanobacteria
✓
Correct Answer
Cyanobacteria
Cyanobacteria split water during photosynthesis and release oxygen, which first saturated the oceans and then built up in the atmosphere. Methanogens are archaea that produce methane, not oxygen. Spirochetes are spiral-shaped heterotrophic bacteria. Clostridia are anaerobic bacteria that are harmed by oxygen.
Category: Early Earth and Endosymbiosis
Question 5
The bacterium Yersinia pestis, which caused the Black Death, is usually transmitted to humans by the bite of which animal?
Flea
✓
Mosquito
Tick
Tsetse fly
Correct Answer
Flea
Plague bacteria live in rodents such as black rats and are passed to people by the bites of infected fleas. Mosquitoes carry malaria parasites. Ticks carry diseases such as Lyme disease. Tsetse flies carry the trypanosomes that cause African sleeping sickness.
Category: Prokaryotes and Humans
Question 6
Clostridium botulinum can grow and produce its toxin inside improperly sterilized cans and jars because it is
Photosynthetic
Anaerobic
✓
Nitrogen-fixing
Halophilic
Correct Answer
Anaerobic
Clostridium botulinum is an anaerobic bacterium, so the oxygen-free interior of a sealed can lets it grow and release botulinum toxin. Photosynthetic bacteria need light, which a sealed can lacks. Nitrogen-fixing describes bacteria that convert atmospheric nitrogen, unrelated to canning. Halophilic describes salt-loving microbes, a trait unrelated to the oxygen-free conditions inside a sealed can.
Category: Prokaryotes and Humans
Question 7
Bacteria living in the human large intestine synthesize which vitamin that the body can then absorb?
Vitamin C
Vitamin D
Vitamin K
✓
Vitamin A
Correct Answer
Vitamin K
Intestinal bacteria synthesize vitamin K, which the body needs to make blood-clotting factors. Vitamin C must come from the diet because humans cannot make it. Vitamin D is made in the skin when it is exposed to sunlight. Vitamin A comes from foods containing it or its precursor beta-carotene.
Category: Prokaryotes and Humans
Question 8
According to endosymbiotic theory, mitochondria descend from which kind of ancestor?
A cyanobacterium
A green alga
A fungal cell
An aerobic bacterium
✓
Correct Answer
An aerobic bacterium
Mitochondria are thought to come from a free-living aerobic bacterium that was engulfed and kept alive by an ancestral host cell, giving the host the ability to use oxygen to release energy. A cyanobacterium is the proposed ancestor of chloroplasts, not mitochondria. A green alga is itself a eukaryote that already contains mitochondria. A fungal cell is also a eukaryote with its own mitochondria.
Category: Early Earth and Endosymbiosis
Question 9
Which feature of mitochondria supports the idea that they were once free-living prokaryotes?
A circular DNA chromosome
✓
A cell wall made of chitin
A single surrounding membrane
Linear chromosomes in a nucleus
Correct Answer
A circular DNA chromosome
Mitochondria carry their own circular DNA with genes resembling bacterial genes, just as prokaryotes have a circular chromosome. A cell wall made of chitin is a fungal trait that mitochondria do not have. A single surrounding membrane is incorrect because mitochondria have two membranes. Linear chromosomes in a nucleus are a eukaryotic trait, not a prokaryotic one.
Category: Early Earth and Endosymbiosis
Question 10
Why do biologists think mitochondria were acquired earlier in eukaryotic evolution than plastids?
Plastids are larger and were harder for early cells to engulf
All eukaryotes have mitochondria or related organelles, but only some have plastids
✓
Plastids lack DNA and could not have been free-living
Mitochondria divide more quickly than plastids do
Correct Answer
All eukaryotes have mitochondria or related organelles, but only some have plastids
Because every eukaryotic lineage has mitochondria or mitochondria-like organelles while plastids occur only in groups such as plants and algae, the mitochondrial event most likely came first. That plastids are larger and were harder to engulf is not the reasoning biologists use. Plastids lack DNA is false, since plastids have their own circular genomes. That mitochondria divide more quickly says nothing about the order of the two events.
Category: Early Earth and Endosymbiosis
Question 11
An amoeba takes in food by surrounding it with its plasma membrane and enclosing it in a food vacuole. This process is called
Exocytosis
Osmosis
Phagocytosis
✓
Binary fission
Correct Answer
Phagocytosis
In phagocytosis the cell membrane engulfs a particle, forming a food vacuole that later fuses with a lysosome for digestion. Exocytosis is the reverse, releasing materials such as wastes out of the cell. Osmosis is the diffusion of water across a membrane. Binary fission is a form of asexual cell division.
Category: Protist Diversity
Question 12
Land plants, red algae, and green algae are all placed in which eukaryotic supergroup?
Opisthokonta
Amoebozoa
Excavata
Archaeplastida
✓
Correct Answer
Archaeplastida
Archaeplastida includes red algae, green algae, and land plants, all descended from the ancestor that acquired a cyanobacterial chloroplast. Opisthokonta contains animals, fungi, and their close relatives such as choanoflagellates. Amoebozoa includes slime molds and many amoebas. Excavata includes groups such as euglenozoans and parabasalids.
Category: Protist Diversity
Question 13
In a person with malaria, Plasmodium parasites first develop in liver cells and then infect and burst which cells?
Red blood cells
✓
White blood cells
Nerve cells
Skin cells
Correct Answer
Red blood cells
After developing in the liver, Plasmodium invades red blood cells, multiplies inside them, and bursts them, which causes the fever and anemia of malaria. White blood cells are part of the immune response rather than the parasite's main target. Nerve cells are the tissue damaged by African sleeping sickness, not the cells Plasmodium cycles through. Skin cells are only the site of the mosquito bite.
Category: Protist Pathogens
Question 14
Trypanosoma brucei, which causes African sleeping sickness, escapes being cleared by the immune system by
Hiding inside the host's red blood cells
Repeatedly switching its surface glycoprotein coat
✓
Forming a thick wall of chitin
Destroying antibodies with secreted toxins
Correct Answer
Repeatedly switching its surface glycoprotein coat
Trypanosoma brucei keeps changing the glycoprotein coat on its surface, so each new wave of antibodies is soon useless and the infection persists. Hiding inside the host's red blood cells describes Plasmodium, not trypanosomes. Forming a thick wall of chitin is a fungal trait. Destroying antibodies with secreted toxins is not how this parasite evades immunity.
Category: Protist Pathogens
Question 15
The Irish potato famine of the 1800s was caused by Phytophthora infestans, a member of which group of protists?
Diatoms
Dinoflagellates
Oomycetes
✓
Ciliates
Correct Answer
Oomycetes
Phytophthora infestans is an oomycete, or water mold, that causes late blight and turns potato plants into black slime. Diatoms are photosynthetic algae with silica shells. Dinoflagellates are mostly marine plankton, some of which cause red tides. Ciliates such as Paramecium move with cilia and are not crop pathogens of this kind.
Category: Protist Pathogens
Question 16
Before absorbing their food, fungi first
Engulf it whole into food vacuoles
Convert sunlight into sugar in chloroplasts
Fix nitrogen gas from the air into it
Secrete enzymes that digest it outside their cells
✓
Correct Answer
Secrete enzymes that digest it outside their cells
Fungi release exoenzymes into their surroundings, digest food externally, and then absorb the small molecules across the large surface of the mycelium. Engulfing food whole into food vacuoles describes amoebas. Converting sunlight into sugar in chloroplasts is impossible for fungi, which have no chloroplasts. Fixing nitrogen gas from the air is something fungi cannot do; they get nitrogen from their food.
Category: Fungal Biology
Question 17
Bread molds have hyphae that lack cross walls, forming large cells with many nuclei. Such hyphae are described as
Coenocytic
✓
Dimorphic
Septate
Mycorrhizal
Correct Answer
Coenocytic
Coenocytic hyphae have no septa, so the cytoplasm and many nuclei form one continuous cell. Dimorphic describes fungi that can switch between yeast and filamentous forms. Septate hyphae are the opposite, divided by cross walls. Mycorrhizal describes a fungus partnered with plant roots.
Category: Fungal Biology
Question 18
Which fungal phylum is the only one whose gametes have flagella?
Basidiomycota
Chytridiomycota
✓
Ascomycota
Glomeromycota
Correct Answer
Chytridiomycota
Chytrids (Chytridiomycota) are the only fungi with flagellated gametes, which swim through water or moist soil. Basidiomycota are the club fungi, including most familiar mushrooms. Ascomycota are the sac fungi, such as morels and Penicillium. Glomeromycota are the fungi that form arbuscular mycorrhizae.
Category: Fungal Biology
Question 19
A lichen is a close partnership between a fungus and
The roots of a flowering plant
A colony of leaf-cutting ants
An alga or a cyanobacterium
✓
A soil-dwelling nematode worm
Correct Answer
An alga or a cyanobacterium
In a lichen, a fungus provides shelter and minerals while a photosynthetic alga or cyanobacterium supplies carbohydrates. The roots of a flowering plant partner with fungi to form mycorrhizae, not lichens. A colony of leaf-cutting ants farms fungi in a separate kind of mutualism. A soil-dwelling nematode worm is prey for trapping fungi such as Arthrobotrys.
Category: Fungal Biology
Question 20
Fungal infections are often harder to treat with drugs than bacterial infections because fungi
Have cell walls made of peptidoglycan
Reproduce only by binary fission
Lack ribosomes for drugs to target
Are eukaryotes with cells much like their human hosts
✓
Correct Answer
Are eukaryotes with cells much like their human hosts
Fungi are eukaryotes, so many targets in their cells also exist in human cells, and a drug that harms the fungus can harm the patient too. Having cell walls made of peptidoglycan describes bacteria, and fungal walls use chitin. Reproducing only by binary fission is false, since fungi produce spores sexually and asexually. Lacking ribosomes is false, because fungi have eukaryotic ribosomes.
Category: Fungal Biology