Free Cell Structure and Function MCQs with Answers

1. Which organelle is known as the powerhouse of the cell?

• A. Ribosome
• B. Mitochondrion
• C. Golgi apparatus
• D. Lysosome

Explanation: The mitochondrion generates most of the cell’s ATP through aerobic respiration, earning it the name powerhouse of the cell. Ribosomes synthesise proteins, the Golgi apparatus packages them, and lysosomes carry out intracellular digestion.

2. Which structure is present in a plant cell but absent from an animal cell?

• A. Mitochondrion
• B. Cellulose cell wall
• C. Ribosome
• D. Golgi apparatus

Explanation: A cellulose cell wall lies outside the plasma membrane of every plant cell and gives it a fixed shape and resistance to bursting when turgid. Mitochondria, ribosomes and the Golgi apparatus are found in both plant and animal cells. Note that fungi also have a wall, but it is chitin rather than cellulose.

3. The main difference between a prokaryotic and a eukaryotic cell is that a prokaryotic cell has

• A. no ribosomes
• B. no membrane bound nucleus or organelles
• C. no genetic material
• D. no plasma membrane

Explanation: Prokaryotes keep their DNA in a nucleoid region with no surrounding envelope and have no mitochondria, endoplasmic reticulum or Golgi apparatus. They do have ribosomes, though the 70S type rather than the 80S type of the eukaryotic cytoplasm, and that difference is exactly what several antibiotics exploit. Every cell has genetic material and a plasma membrane.

4. Ribosomes in the cytoplasm of a bacterium are of which type?

• A. 70S
• B. 80S
• C. 90S
• D. 60S

Explanation: Prokaryotic ribosomes are 70S, made of a 50S and a 30S subunit, while eukaryotic cytoplasmic ribosomes are 80S. Antibiotics such as streptomycin and tetracycline bind the 70S ribosome and leave the host's 80S ribosomes alone, which is why they kill bacteria without killing the patient. Mitochondria and chloroplasts also contain 70S ribosomes, evidence for the endosymbiotic theory.

5. Which organelle is the site of aerobic respiration and ATP synthesis?

• A. Lysosome
• B. Mitochondrion
• C. Golgi apparatus
• D. Smooth endoplasmic reticulum

Explanation: The Krebs cycle runs in the mitochondrial matrix and the electron transport chain sits in the inner membrane, where the proton gradient drives ATP synthase. The inner membrane is folded into cristae to increase that surface area, which is why heart muscle cells are packed with mitochondria. Lysosomes digest material, and the Golgi and smooth ER handle processing and lipid synthesis.

6. Lysosomes are formed by which organelle?

• A. Nucleolus
• B. Golgi apparatus
• C. Rough endoplasmic reticulum
• D. Centriole

Explanation: Hydrolytic enzymes are made on the rough endoplasmic reticulum but the Golgi apparatus packages and buds them off as lysosomes, after tagging them so they are sorted correctly. This is why the Golgi is described as the packaging and dispatch organelle. The nucleolus assembles ribosomal subunits and centrioles organise the spindle.

7. Rough endoplasmic reticulum is distinguished from smooth endoplasmic reticulum by the presence of

• A. cristae
• B. ribosomes on its surface
• C. thylakoids
• D. a double nuclear envelope

Explanation: Ribosomes bound to the outer face of the membrane give rough ER its appearance and its function, which is synthesising proteins destined for secretion or for membranes. Smooth ER has no ribosomes and handles lipid and steroid synthesis and detoxification, which is why liver cells are rich in it. Cristae belong to mitochondria and thylakoids to chloroplasts.

8. The organelle known as the suicidal bag of the cell is the

• A. ribosome
• B. lysosome
• C. peroxisome
• D. vacuole

Explanation: Lysosomes hold hydrolytic enzymes at an acidic pH, and if the membrane ruptures those enzymes digest the cell itself, a process called autolysis. This is deliberate during development, for example when the tail of a tadpole is removed. Peroxisomes also contain enzymes but they handle hydrogen peroxide and fatty acid oxidation rather than wholesale digestion.

9. Which of the following organelles is NOT bounded by a membrane?

• A. Ribosome
• B. Lysosome
• C. Mitochondrion
• D. Golgi apparatus

Explanation: A ribosome is a complex of ribosomal RNA and protein with no surrounding membrane at all, which is why it is found in prokaryotes as well as eukaryotes. Lysosomes and the Golgi apparatus each have a single membrane, and mitochondria have two. Nucleoli and centrioles are the other common non-membranous structures.

10. The fluid mosaic model describes the plasma membrane as

• A. a rigid protein sheet with lipids attached
• B. a phospholipid bilayer with proteins embedded in and moving through it
• C. a single layer of phospholipids
• D. a continuous layer of cholesterol

Explanation: Singer and Nicolson described a bilayer of phospholipids in which proteins float like icebergs, free to move laterally. Fluid refers to that lateral movement and mosaic to the scattered pattern of proteins. Cholesterol is present between the phospholipids and modulates fluidity, but it does not form a layer of its own.