MDCAT Biology chapter 4: Biology · Cell structure and function MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
52 exam-style questions on Biology · Cell structure and function, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Ten Biology · Cell structure and function questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Living cells can be watched under a light microscope but not under an electron microscope, mainly because
A
living cells move too fast to be seen at such a high magnification
B
the specimen must be in a vacuum, which living cells cannot survive
C
living cells are transparent to electrons and so give no image
D
the glass lenses would focus the heat of the beam onto the cells
Show answer
Answer: B. The electron beam can travel only through a vacuum, so specimens must be dried, fixed and therefore dead. Electron microscopes focus the beam with magnetic lenses, not glass ones.
2. An Amoeba living in pond water empties its contractile vacuole every minute or so. If it is moved to a solution that is still hypotonic to its cytoplasm but more concentrated than pond water, its contractile vacuole will empty
A
less often, because water now leaves the cell by osmosis
B
more often, because more water now enters by osmosis
C
less often, because less water now enters by osmosis
D
just as often, because the vacuole works at a fixed rate
Show answer
Answer: C. The cytoplasm of a freshwater protist is hypertonic to its surroundings, so water keeps entering by osmosis and the contractile vacuole expels it. In a less dilute medium the difference is smaller, less water enters, and the vacuole needs to empty less often; water would leave the cell only in a hypertonic solution.
3. Which of these structures is found in eukaryotic cells but never in prokaryotic cells?
A
mitochondria
B
ribosomes
C
a plasma membrane
D
DNA
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Answer: A. Mitochondria, like the nucleus and other membrane-bound organelles, occur only in eukaryotes. Ribosomes, a plasma membrane and DNA are present in all cells.
4. In a chloroplast, a granum is
A
the fluid matrix that surrounds the thylakoids
B
a stack of thylakoids, each enclosing a lumen
C
a single flattened sac that joins two stacks
D
a starch grain stored in the stroma
Show answer
Answer: B. Grana are stacks of disc-shaped thylakoids, and the space inside each thylakoid is its lumen (thylakoid space). The fluid matrix around the grana is the stroma, where the Calvin cycle runs, and single membrane sacs (lamellae) in the stroma link one granum to another.
5. The middle piece of a mammalian sperm is packed with mitochondria because they
A
digest the layers around the egg
B
supply the ATP that powers the beating tail
C
store food for the early embryo
D
carry the genes passed to the zygote
Show answer
Answer: B. The tail (flagellum) needs a steady supply of ATP to swim to the egg, and the mitochondria of the middle piece provide it. The enzymes that digest the egg coverings are in the acrosome.
6. In the fluid mosaic model, which job is done by the membrane proteins rather than by the phospholipids?
A
forming the continuous water-repelling layer of the membrane
B
acting as carriers, channels, receptors and enzymes
C
giving the membrane its two-layered structure
D
letting oxygen and carbon dioxide diffuse through
Show answer
Answer: B. Proteins scattered in the bilayer do specific jobs: transport (carriers and channels), signalling (receptors) and catalysis (enzymes). The phospholipid bilayer forms the basic two-layered, water-repelling barrier, through which small non-polar gases diffuse.
7. To study the three-dimensional surface of a pollen grain at high magnification, the most suitable instrument is
A
a transmission electron microscope
B
a compound light microscope
C
a scanning electron microscope
D
a hand lens
Show answer
Answer: C. The scanning electron microscope sweeps electrons over the surface and gives a three-dimensional image of it. The transmission electron microscope passes electrons through thin sections and shows internal detail.
8. Thyroid cells hold iodide ions at a much higher concentration than the blood, yet they keep taking in more iodide from the blood. The iodide must enter by
A
facilitated diffusion
B
simple diffusion
C
osmosis
D
active transport
Show answer
Answer: D. Moving ions into a cell against their concentration gradient needs carrier proteins and energy from ATP. Both kinds of diffusion carry substances only down a concentration gradient, and osmosis is the movement of water.
9. A plasmolysed onion epidermis cell is moved into distilled water. What happens?
A
water enters until the cell bursts, as a red blood cell does in water
B
water enters and the protoplast swells back until the cell is turgid
C
water leaves and the protoplast shrinks further from the wall
D
no water moves, because the wall now blocks osmosis
Show answer
Answer: B. Distilled water is more dilute than the cell sap, so water enters by osmosis and the protoplast swells back against the wall (deplasmolysis). The strong cellulose wall resists further stretching, so the cell becomes turgid but does not burst, unlike a red blood cell.
10. Prokaryotic cells divide by
A
mitosis, with a spindle made by centrioles
B
meiosis, producing four haploid cells
C
budding off from the nuclear envelope
D
binary fission, without forming a spindle
Show answer
Answer: D. A prokaryote copies its single circular chromosome and splits in two by binary fission; it has no nucleus, so there is no mitosis and no spindle.
Biology · Cell structure and function: questions students ask
How many Biology · Cell structure and function MCQs are there?
52, each with the answer and a short explanation, across 3 topics: Cell membrane and transport, Organelles, Prokaryotic and eukaryotic cells. Every chapter test draws ten of them, so you can take it many times.
Is the MDCAT Biology chapter 4 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
