AP Biology: Cell Structure and Function — Practice Questions & Answers
How cell components, membrane structure, transport mechanisms, and water potential let cells maintain internal order, and how endosymbiosis explains mitochondria and chloroplasts.
745 practice questions available for this unit — here are 10 with full answers and explanations.
Which organelle is the primary site of ATP synthesis through aerobic cellular respiration?
Mitochondrion
Ribosome
Golgi apparatus
Lysosome
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WhyThe mitochondrion uses the electron transport chain across its inner membrane to generate the proton gradient that drives ATP synthase, making it the main producer of ATP in aerobic respiration.
2Multiple choice · Easy
Ribosomes attached to the rough endoplasmic reticulum are primarily responsible for synthesizing which class of molecules?
Lipids for the plasma membrane
Proteins for secretion or membrane insertion
Carbohydrate energy stores
Nucleic acids such as mRNA
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WhyRough ER ribosomes synthesize proteins destined for secretion, insertion into membranes, or delivery to certain organelles; free ribosomes generally make proteins used within the cytosol.
3Multiple choice · Easy
Which structure is found in plant cells but NOT in typical animal cells?
Plasma membrane
Mitochondrion
Cell wall
Nucleus
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WhyA rigid cell wall composed largely of cellulose surrounds plant cells and provides structural support; animal cells lack a cell wall.
4Multiple choice · Easy
As a cell increases in size while maintaining its shape, what happens to its surface area-to-volume ratio?
It increases
It decreases
It remains constant
It first decreases then increases
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WhyVolume increases with the cube of the linear dimension while surface area increases with the square, so the surface area-to-volume ratio decreases as a cell grows larger.
5Multiple choice · Easy
The fluid mosaic model describes the plasma membrane as primarily consisting of which two major components?
A phospholipid bilayer with embedded proteins
A cellulose matrix with starch granules
A double layer of nucleic acids
A rigid sheet of cholesterol crystals
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WhyThe fluid mosaic model describes a fluid phospholipid bilayer with embedded and associated proteins that can move laterally, hence fluid (lipids move) and mosaic (proteins scattered throughout).
6Multiple choice · Easy
Which process moves molecules across a membrane WITHOUT requiring an input of cellular energy?
Active transport
Endocytosis
Passive transport
Exocytosis
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WhyPassive transport, including simple and facilitated diffusion, moves substances down their concentration gradient and does not require ATP; active transport requires energy to move substances against a gradient.
7Multiple choice · Medium
Small, nonpolar molecules such as O2 and CO2 cross the plasma membrane most readily by which mechanism?
Simple diffusion through the lipid bilayer
Facilitated diffusion through channel proteins
Active transport by pumps
Receptor-mediated endocytosis
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WhySmall nonpolar molecules dissolve in the hydrophobic core of the phospholipid bilayer and pass through directly by simple diffusion, without needing transport proteins.
8Multiple choice · Medium
A red blood cell is placed in a solution and begins to swell and eventually lyse. The external solution is best described as which of the following relative to the cell?
Hypertonic
Isotonic
Hypotonic
Saturated
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WhyIn a hypotonic solution the surrounding fluid has a lower solute concentration than the cytoplasm, so water moves into the cell by osmosis, causing it to swell and potentially burst.
9Multiple choice · Medium
Which feature of facilitated diffusion distinguishes it from simple diffusion?
It requires ATP hydrolysis
It moves solutes against their concentration gradient
It requires specific membrane transport proteins
It only occurs across the nuclear envelope
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WhyFacilitated diffusion uses specific transport proteins (channels or carriers) to move polar or charged solutes down their gradient, whereas simple diffusion requires no proteins. Both are passive and require no ATP.
10Multiple choice · Medium
The sodium-potassium pump moves 3 Na+ out of and 2 K+ into the cell per cycle, both against their gradients. This is best classified as which type of transport?
Simple diffusion
Facilitated diffusion
Primary active transport
Osmosis
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WhyBecause solutes are moved against their concentration gradients using ATP directly, the Na+/K+ pump is an example of primary active transport.
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Cell: The smallest unit that can carry out all the activities of life, bounded by a membrane and capable of metabolism, growth, and reproduction.
Cell theory: The unifying principle stating that all living things are made of one or more cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.
Prokaryotic cell: A cell that lacks a true membrane-bound nucleus and membrane-enclosed organelles, with its DNA located in a region called the nucleoid; characteristic of bacteria and archaea.
Eukaryotic cell: A cell that contains a membrane-bound nucleus and specialized membrane-enclosed organelles, found in animals, plants, fungi, and protists.
Nucleoid: The irregularly shaped region in a prokaryotic cell where the cell's circular DNA is concentrated, not separated from the cytoplasm by a membrane.
Organelle: A specialized structure within a cell that performs a distinct function, often enclosed by its own membrane in eukaryotes.
Cytoplasm: The entire region of a cell between the plasma membrane and the nucleus, including the cytosol and all the organelles suspended in it.
Cytosol: The semifluid, jelly-like substance that fills the inside of a cell and surrounds the organelles, serving as the site of many metabolic reactions.