Cell structure and function MCQs
MDCAT · Biology · 10 questions
Untimed, with instant feedback. Answers are saved on this phone.
Revision summary
PMDC MDCAT syllabus: Cell structure
Every cell is either prokaryotic (no nucleus, no membrane-bound organelles, 70S ribosomes) or eukaryotic (a nucleus inside a double nuclear envelope, membrane-bound organelles, 80S ribosomes in the cytoplasm). The cell membrane follows the fluid mosaic model of Singer and Nicolson: a phospholipid bilayer with proteins floating in it. Learn each organelle by its job. Mitochondria run the Krebs cycle and electron transport, making most ATP. Rough ER, studded with ribosomes, makes proteins for export; smooth ER makes lipids. The Golgi apparatus modifies, sorts and packs proteins into vesicles. Lysosomes hold hydrolytic enzymes. Centrioles organise the spindle in animal cells. Plant cells add a cellulose wall, chloroplasts and a large vacuole. MDCAT questions usually test one fact per organelle, so the common traps are membrane counts (nucleus, mitochondria and chloroplasts have two; lysosomes and vacuoles one; ribosomes none) and ribosome sizes.
Questions with answers
Written by Parcha from the syllabus. Samples until a subject reviewer checks them; report anything wrong from the practice screen.
Q1 · Parcha original · Sample
Which organelle is the main site of aerobic respiration in a eukaryotic cell?
- A. Ribosome
- B. Mitochondrion
- C. Golgi apparatus
- D. Lysosome
Show answer
Answer: B. Mitochondrion
The Krebs cycle runs in the mitochondrial matrix and the electron transport chain sits on the inner mitochondrial membrane, so most ATP from aerobic respiration is made in mitochondria. Ribosomes make proteins, the Golgi apparatus packages them and lysosomes digest material.
Open this question on its own pageQ2 · Parcha original · Sample
Ribosomes of prokaryotic cells are of which type?
- A. 80S
- B. 60S
- C. 70S
- D. 90S
Show answer
Answer: C. 70S
Prokaryotic ribosomes are 70S, made of a 50S and a 30S subunit. Eukaryotic cytoplasmic ribosomes are 80S (60S + 40S). S (Svedberg) units measure sedimentation rate, so they do not add up simply.
Q3 · Parcha original · Sample
Which structure is present in a typical plant cell but absent in an animal cell?
- A. Cell membrane
- B. Ribosome
- C. Mitochondrion
- D. Cell wall
Show answer
Answer: D. Cell wall
Plant cells have a cellulose cell wall outside the cell membrane (and usually chloroplasts and a large central vacuole). Animal cells have a cell membrane, ribosomes and mitochondria too, but no cell wall.
Q4 · Parcha original · Sample
The fluid mosaic model of the cell membrane was proposed by:
- A. Singer and Nicolson
- B. Watson and Crick
- C. Schleiden and Schwann
- D. Robert Brown
Show answer
Answer: A. Singer and Nicolson
S. J. Singer and G. L. Nicolson proposed the fluid mosaic model in 1972: a phospholipid bilayer in which proteins float like tiles of a mosaic. Watson and Crick described the DNA double helix; Schleiden and Schwann proposed the cell theory; Robert Brown described the nucleus.
Q5 · Parcha original · Sample
Lysosomes are best described as sacs that contain:
- A. Chlorophyll
- B. Hydrolytic enzymes
- C. Starch grains
- D. Ribosomal RNA only
Show answer
Answer: B. Hydrolytic enzymes
Lysosomes are single-membrane sacs of hydrolytic (digestive) enzymes that work at acidic pH. They digest worn-out organelles (autophagy) and material taken in by the cell.
Q6 · Parcha original · Sample
Rough endoplasmic reticulum appears rough because of:
- A. Attached ribosomes
- B. Stored lipids
- C. Glycogen granules
- D. Folded DNA
Show answer
Answer: A. Attached ribosomes
Ribosomes attached to its outer surface give rough ER its grainy look; it makes proteins for secretion and membranes. Smooth ER has no ribosomes and makes lipids and detoxifies.
Q7 · Parcha original · Sample
Which organelle modifies, sorts and packages proteins for secretion?
- A. Nucleolus
- B. Centriole
- C. Golgi apparatus
- D. Peroxisome
Show answer
Answer: C. Golgi apparatus
Proteins made on rough ER travel in vesicles to the Golgi apparatus, which modifies them (for example by adding sugars), sorts them and packs them into secretory vesicles. The nucleolus makes ribosomal subunits; centrioles organise spindle fibres; peroxisomes break down hydrogen peroxide.
Q8 · Parcha original · Sample
In animal cells, centrioles help to:
- A. Synthesise proteins
- B. Form spindle fibres during cell division
- C. Store calcium ions
- D. Carry out photosynthesis
Show answer
Answer: B. Form spindle fibres during cell division
A pair of centrioles forms the centrosome, which organises the spindle fibres that pull chromosomes apart in mitosis and meiosis. Centrioles also form the basal bodies of cilia and flagella.
Q9 · Parcha original · Sample
Which of these is bounded by a double membrane?
- A. Lysosome
- B. Ribosome
- C. Vacuole
- D. Nucleus
Show answer
Answer: D. Nucleus
The nucleus is enclosed by a nuclear envelope of two membranes with pores (mitochondria and chloroplasts are also double-membraned). Lysosomes and vacuoles have a single membrane, and ribosomes have none.
Q10 · Parcha original · Sample
A prokaryotic cell does NOT have:
- A. Ribosomes
- B. A cell membrane
- C. A nuclear envelope
- D. DNA
Show answer
Answer: C. A nuclear envelope
Prokaryotes (bacteria) keep their DNA in a nucleoid region with no nuclear envelope and have no membrane-bound organelles. They do have DNA, ribosomes (70S) and a cell membrane.