Free Cytoplasmic Organelles MCQs with Answers

11. Peroxisomes protect the cell because they contain the enzyme catalase, which

• A. digests worn out organelles
• B. synthesises hydrogen peroxide for defence
• C. adds sugar groups to newly made proteins
• D. breaks down toxic hydrogen peroxide into water and oxygen

Explanation: Hydrogen peroxide is a damaging by product of several oxidation reactions, and catalase destroys it almost as fast as it forms, making it one of the fastest enzymes known. Peroxisomes are also active in the oxidation of fatty acids and, in liver cells, in detoxifying alcohol. Digestion of worn out organelles is the work of lysosomes, which is the usual confusion.

12. Which organelle is responsible for the synthesis of proteins destined for secretion?

• A. Smooth ER
• B. Golgi apparatus
• C. Rough ER
• D. Lysosomes

Explanation: Rough ER has ribosomes on its surface and synthesizes proteins that are either secreted or inserted into membranes.

13. Which cell junction allows direct cytoplasmic communication between adjacent cells?

• A. Tight junctions
• B. Desmosomes
• C. Gap junctions
• D. Adherens junctions

Explanation: Gap junctions (or plasmodesmata in plants) form channels that allow direct exchange of ions and small molecules between cells.

14. All are the functions of lysosome EXCEPT:

• A. Intra cellular digestion
• B. Removal of the waste
• C. Autophagy
• D. Lipid synthesis

Explanation: Lysosomes contain hydrolytic enzymes and therefore break molecules down, digesting food vacuoles, clearing waste and destroying worn out organelles by autophagy. Building lipids is a synthetic process carried out by the smooth endoplasmic reticulum, which is the opposite kind of activity. Recognising that every genuine lysosomal role is destructive answers the question without recalling a list.

15. The function of nucleolus is to make:

• A. rDNA
• B. Lysosomes
• C. Ribosomes
• D. Chromosomes

Explanation: The nucleolus transcribes ribosomal RNA and assembles it with proteins into the ribosomal subunits, which are then exported through the nuclear pores. Cells that make a great deal of protein have correspondingly prominent nucleoli. Lysosomes are budded off by the Golgi apparatus, and rDNA is the template the nucleolus reads rather than something it makes.