Free Cytoplasmic Organelles 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 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. In a chloroplast, the light dependent reactions take place in the

• A. stroma
• B. thylakoid membranes of the grana
• C. outer membrane
• D. intermembrane space

Explanation: Chlorophyll and the electron carriers are embedded in the thylakoid membranes, which are stacked into grana to give the largest possible area for absorbing light. The stroma is the surrounding fluid, and it is where the light independent reactions fix carbon dioxide using the ATP and reduced NADP made in the membranes. Dividing the organelle this way keeps the two stages physically separate.

8. Proteins made on the rough endoplasmic reticulum are modified, sorted and packaged for export by the

• A. lysosome
• B. nucleolus
• C. peroxisome
• D. Golgi apparatus

Explanation: Vesicles carry newly made protein from the endoplasmic reticulum to the Golgi, where sugars are added, the product is sorted and it is packed into vesicles for secretion or for use inside the cell. Cells that secrete heavily, such as those of the pancreas, have a large and active Golgi. Lysosomes are one of the products of the Golgi rather than an alternative to it.

9. The nucleolus is the site of

• A. DNA replication
• B. synthesis of ribosomal RNA and assembly of ribosomal subunits
• C. protein synthesis for export
• D. storage of the cell's lipid reserve

Explanation: The nucleolus is a dense region of the nucleus with no membrane around it, and it transcribes ribosomal RNA and combines it with proteins to form the subunits that are then exported through the nuclear pores. Cells making large quantities of protein have prominent nucleoli, which is a useful clue under the microscope. Protein synthesis itself takes place on the ribosomes in the cytoplasm.

10. The nuclear envelope differs from the plasma membrane in that it

• A. is made of protein only
• B. has no pores of any kind
• C. consists of two membranes perforated by pores
• D. is freely permeable to all molecules

Explanation: Two membranes enclose the nucleus, and the pores that pierce them at intervals let mRNA and ribosomal subunits out and let nucleotides, enzymes and regulatory proteins in, while keeping the chromosomes separate from the cytoplasm. The outer membrane is continuous with the rough endoplasmic reticulum. Free permeability would defeat the whole purpose of enclosing the genetic material.