Which type of microscope reveals the surface features of a cell by sweeping a beam of electrons across a specimen that is usually coated with a thin layer of metal?
Scanning electron microscope
✓
Transmission electron microscope
Compound light microscope
Dissecting light microscope
Correct Answer
Scanning electron microscope
A scanning electron microscope moves its beam across the specimen's surface, producing detailed three-dimensional views of surface features. A transmission electron microscope sends its beam through a thin slice and reveals internal structures instead. A compound light microscope uses visible light, not electrons, and has much lower resolution. A dissecting light microscope also uses light and gives low-magnification views of whole objects.
Category: Microscopy and Cell Theory
Question 2
Who first used the word "cell" after observing tiny box-like compartments in a thin slice of cork in 1665?
Antony van Leeuwenhoek
Robert Hooke
✓
Matthias Schleiden
Theodor Schwann
Correct Answer
Robert Hooke
Robert Hooke described the box-like compartments he saw in cork in his book Micrographia and called them cells. Antony van Leeuwenhoek was a lens maker who later observed living protists, sperm and bacteria. Matthias Schleiden was a botanist who helped propose the cell theory in the late 1830s. Theodor Schwann was the zoologist who proposed the cell theory along with Schleiden.
Category: Microscopy and Cell Theory
Question 3
What term describes a microscope's ability to show two structures that are very close together as separate, distinct objects?
Magnification
Contrast
Resolving power
✓
Field of view
Correct Answer
Resolving power
Resolving power is the ability to distinguish two nearby points as separate, and higher resolving power gives a sharper, more detailed image. Magnification only describes how much larger the image appears, and enlarging a blurry image does not separate nearby points. Contrast is the difference in darkness between a structure and its background. Field of view is the size of the area visible through the lens.
Category: Microscopy and Cell Theory
Question 4
In a prokaryotic cell, where is the DNA located?
In the nucleolus
Inside a nuclear envelope
In the capsule
In the nucleoid
✓
Correct Answer
In the nucleoid
Prokaryotes have no nucleus, so their DNA sits in a darker central region of the cytoplasm called the nucleoid. The nucleolus is a region inside the nucleus of a eukaryotic cell, which prokaryotes lack. A nuclear envelope is the double membrane around a eukaryotic nucleus and is absent in prokaryotes. The capsule is a sticky outer polysaccharide layer outside the cell wall, not a place where DNA is stored.
Category: Prokaryotic Cells
Question 5
What substance, built from sugars and amino acids, makes up most of a bacterial cell wall?
Peptidoglycan
✓
Cellulose
Chitin
Collagen
Correct Answer
Peptidoglycan
Bacterial cell walls are made mainly of peptidoglycan, a polymer of sugars cross-linked by short chains of amino acids. Cellulose, a glucose polymer, forms plant cell walls. Chitin is the main component of fungal cell walls. Collagen is a protein of the extracellular matrix in animals and is not part of any cell wall.
Category: Prokaryotic Cells
Question 6
As a cell grows larger, which change limits how big it can get?
Its surface area increases faster than its volume
Its volume increases faster than its surface area
✓
Its DNA content becomes too large to copy
Its plasma membrane becomes too thick to cross
Correct Answer
Its volume increases faster than its surface area
When a cell grows, its volume rises faster than its surface area, so each unit of membrane must supply more cytoplasm with nutrients and remove more waste. Eventually the membrane cannot keep up, which is why most cells stay small. The reverse statement, that surface area outpaces volume, is backward. DNA content does not change with cell size. The plasma membrane stays about the same thickness as a cell grows.
Category: Prokaryotic Cells
Question 7
Which structure inside the nucleus is the site where ribosomal RNA and proteins are assembled into ribosomal subunits?
Chromatin
Nuclear pore
Nucleolus
✓
Centriole
Correct Answer
Nucleolus
The nucleolus is a dark-staining region of the nucleus where ribosomal RNA combines with proteins to form ribosomal subunits, which then leave through nuclear pores. Chromatin is the DNA-protein material that carries the genes. A nuclear pore is an opening in the nuclear envelope that controls traffic in and out of the nucleus. A centriole is a microtubule structure found in the centrosome outside the nucleus.
Category: Nucleus and Endomembrane System
Question 8
Which organelle makes steroid hormones, detoxifies drugs and stores calcium ions?
Rough endoplasmic reticulum
Golgi apparatus
Lysosome
Smooth endoplasmic reticulum
✓
Correct Answer
Smooth endoplasmic reticulum
The smooth endoplasmic reticulum has few or no ribosomes and synthesizes lipids and steroid hormones, breaks down drugs and poisons, and stores calcium ions. The rough endoplasmic reticulum is covered with ribosomes and mainly modifies new proteins. The Golgi apparatus sorts, tags and packages proteins and lipids. A lysosome digests macromolecules and worn-out organelles with its enzymes.
Category: Nucleus and Endomembrane System
Question 9
Which organelle consists of flattened membrane sacs with a receiving face near the endoplasmic reticulum and sorts, tags and ships proteins and lipids in vesicles?
Golgi apparatus
✓
Peroxisome
Nuclear envelope
Central vacuole
Correct Answer
Golgi apparatus
The Golgi apparatus receives vesicles from the endoplasmic reticulum on one face, modifies their contents, often by adding sugar chains, and sends them out from the opposite face. A peroxisome is a small organelle that carries out oxidation reactions. The nuclear envelope is the double membrane surrounding the nucleus. The central vacuole is a large plant storage organelle that helps regulate water.
Category: Nucleus and Endomembrane System
Question 10
Which small, single-membrane organelle breaks down fatty acids and amino acids by oxidation, producing hydrogen peroxide that it then converts to water and oxygen?
Lysosome
Peroxisome
✓
Ribosome
Centrosome
Correct Answer
Peroxisome
Peroxisomes carry out oxidation reactions that break down fatty acids and amino acids and detoxify poisons such as alcohol in the liver. The hydrogen peroxide these reactions form is broken down inside the peroxisome to water and oxygen. A lysosome digests materials using enzymes that work best at low pH. A ribosome builds proteins and has no membrane. A centrosome organizes microtubules in animal cells.
Category: Organelles for Energy and Breakdown
Question 11
According to the endosymbiotic theory, mitochondria are descended from which kind of organism?
Cyanobacteria
Single-celled fungi
Aerobic bacteria
✓
Free-living viruses
Correct Answer
Aerobic bacteria
Endosymbiotic theory, championed by Lynn Margulis, holds that mitochondria arose from aerobic bacteria taken in by an ancestral host cell, which explains why mitochondria have their own DNA and ribosomes. Cyanobacteria are photosynthetic bacteria thought to be the ancestors of chloroplasts. Single-celled fungi are eukaryotes and are not proposed ancestors of any organelle. Viruses are not cells and do not carry out respiration.
Category: Organelles for Energy and Breakdown
Question 12
Inside a chloroplast, what name is given to the stacks of thylakoids?
Stroma
Cristae
Matrix
Grana
✓
Correct Answer
Grana
Thylakoids are flattened membrane sacs, and a stack of them is called a granum, plural grana. The stroma is the fluid that surrounds the grana inside the chloroplast. Cristae are the folds of the inner mitochondrial membrane. The matrix is the fluid-filled space enclosed by the inner mitochondrial membrane.
Category: Organelles for Energy and Breakdown
Question 13
Which cytoskeletal fibers are the widest, are hollow tubes and pull chromosomes apart during cell division?
Microtubules
✓
Microfilaments
Intermediate filaments
Collagen fibers
Correct Answer
Microtubules
Microtubules are the thickest cytoskeletal fibers, built as hollow tubes of protein, and they form the spindle that separates chromosomes as well as the core of cilia and flagella. Microfilaments are the thinnest fibers, made of actin, and they function in muscle contraction and cell movement. Intermediate filaments have an in-between diameter and mainly bear tension and anchor organelles. Collagen fibers are part of the extracellular matrix, not the cytoskeleton.
Category: Cytoskeleton and Cell Connections
Question 14
Which arrangement of protein fibers forms the core of both cilia and flagella in eukaryotic cells?
Nine triplets around an empty center
Nine doublets around two central tubules
✓
Two doublets around nine central tubules
Six doublets around three central tubules
Correct Answer
Nine doublets around two central tubules
Cilia and flagella share a 9 + 2 arrangement: nine pairs of microtubules form a ring around two single microtubules in the center. Nine triplets around an empty center describes a centriole, not a cilium. Two doublets around nine central tubules reverses the real pattern. Six doublets around three central tubules does not occur in these structures.
Category: Cytoskeleton and Cell Connections
Question 15
Which structures are channels through the cell walls that connect the cytoplasm of neighboring plant cells?
Gap junctions
Desmosomes
Plasmodesmata
✓
Tight junctions
Correct Answer
Plasmodesmata
Plasmodesmata pass through the walls between adjacent plant cells and join their cytoplasm, letting nutrients and signal molecules move from cell to cell. Gap junctions are channels between animal cells, which have no cell walls. Desmosomes are spot-weld connections that hold animal cells together in sheets. Tight junctions form watertight seals between animal epithelial cells.
Category: Cytoskeleton and Cell Connections
Question 16
In the phospholipid bilayer of a plasma membrane, what forms the interior of the membrane?
Hydrophilic phosphate heads
Carbohydrate chains
A layer of water
Hydrophobic fatty acid tails
✓
Correct Answer
Hydrophobic fatty acid tails
The fatty acid tails of phospholipids point toward each other in the middle of the bilayer, forming a water-repelling core. The hydrophilic phosphate heads face outward toward the watery fluid on both sides. Carbohydrate chains sit on the outer surface of the membrane, attached to proteins and lipids. A layer of water cannot sit in the membrane core because the tails repel it.
Category: Cell Membrane
Question 17
What role does cholesterol play in the plasma membrane of animal cells?
It helps regulate membrane fluidity
✓
It pumps ions across the membrane
It anchors ribosomes to the membrane
It forms channels for water to pass
Correct Answer
It helps regulate membrane fluidity
Cholesterol is tucked between phospholipids and keeps the membrane from becoming too fluid or too rigid as temperature changes, acting like an antifreeze. Pumping ions across the membrane is the job of transport proteins such as the sodium-potassium pump. Ribosomes attach to the endoplasmic reticulum, not to cholesterol in the plasma membrane. Channels for water and ions are formed by integral proteins, not by cholesterol.
Category: Cell Membrane
Question 18
What happens to a red blood cell placed in a hypotonic solution?
It shrivels as water leaves
It swells and may burst
✓
It keeps its normal shape
It pumps the extra water out using ATP
Correct Answer
It swells and may burst
A hypotonic solution has a lower solute concentration than the cell's cytoplasm, so water moves into the cell by osmosis, and an animal cell with no wall can swell until it lyses. Shriveling as water leaves happens in a hypertonic solution. A normal shape is kept in an isotonic solution, where there is no net water movement. Red blood cells have no mechanism for pumping water out with ATP.
Category: Passive Transport
Question 19
During each cycle of the sodium-potassium pump, which ions are moved and in which directions?
Two sodium out and three potassium in
Three potassium out and two sodium in
Three sodium out and two potassium in
✓
Two sodium in and two potassium out
Correct Answer
Three sodium out and two potassium in
Using the energy of one ATP per cycle, the sodium-potassium pump moves three sodium ions out of the cell and two potassium ions in, which also makes the inside of the cell more negative. Two sodium out and three potassium in reverses the numbers. Three potassium out and two sodium in reverses the directions. Two sodium in and two potassium out has both the numbers and directions wrong.
Category: Active Transport
Question 20
Familial hypercholesterolemia, in which LDL receptors on cells are missing or defective, is a failure of which process?
Phagocytosis
Pinocytosis
Exocytosis
Receptor-mediated endocytosis
✓
Correct Answer
Receptor-mediated endocytosis
In receptor-mediated endocytosis, a specific substance binds to receptors on the cell surface before the membrane folds inward to bring it in. Without working LDL receptors, cells cannot take up LDL particles, so cholesterol builds up in the blood. Phagocytosis takes in large particles such as whole bacteria, not individual molecules like LDL. Pinocytosis takes in extracellular fluid and its dissolved solutes nonspecifically. Exocytosis moves material out of the cell, not in.
Category: Active Transport