All Free Biology MCQs with Answers

• A. Phagocytosis
• B. Pinocytosis
• C. Endocytosis
• D. Exocytosis

Explanation: The correct answer is Pinocytosis. This process is specifically designed for the intake of extracellular fluid and dissolved solutes into the cell, forming small vesicles. Unlike Phagocytosis, which targets solid particles, pinocytosis focuses on liquids. Endocytosis is a general term for internalizing substances but does not specify the type of material, making it less precise in this context. Exocytosis involves expelling materials out of the cell, which is the opposite of what the question asks about.

• A. ER
• B. SER
• C. RER
• D. RAZ

Explanation: Steroid hormones are synthesized in the smooth endoplasmic reticulum (SER), which is involved in lipid metabolism and detoxification processes. The rough endoplasmic reticulum (RER) is associated with protein synthesis due to the presence of ribosomes on its surface. The option 'RAZ' does not represent any known cellular organelle. Thus, the correct answer is the SER.

• A. Nucleus
• B. Cell wall
• C. Cell membrane
• D. All of these

Explanation: The correct answer is the cell wall, which is a non-living component of the plant cell. It is primarily made of cellulose and provides structural support and protection. In contrast, the nucleus and cell membrane are living components. The nucleus contains the cell's genetic material and is crucial for cellular functions, while the cell membrane is involved in controlling the movement of substances in and out of the cell.

• A. Cellulose
• B. Chitin
• C. Peptidoglycan
• D. Glycogen

Explanation: The cell wall of fungi is primarily composed of chitin, a strong and flexible polysaccharide that provides structural integrity. Chitin is unique to fungi and some invertebrates, distinguishing it from cellulose, which is found in plant cell walls, and peptidoglycan, found in bacterial cell walls. Glycogen, on the other hand, serves as an energy storage molecule in fungi and is not part of the cell wall structure.

• A. Cellulose, hemicellulose, pectin
• B. Cellulose, hemicellulose, lignin
• C. Cellulose only
• D. Magnesium and calcium salts and pectin

Explanation: The secondary cell wall is a structure found in many plant cells, providing additional strength and rigidity beyond the primary cell wall. It is mainly composed of cellulose, hemicellulose, and lignin. Lignin is a key difference from the primary cell wall, as it adds significant rigidity and resistance to degradation. Option B correctly identifies these components. Option A includes pectin, which is primarily found in the primary cell wall. Option C lists only cellulose, omitting other crucial components. Option D includes pectin and mineral salts, which are not characteristic of the secondary cell wall composition.

• A. Tonoplast
• B. Protoplast
• C. Symplast
• D. Epiblast

Explanation: A plant cell devoid of cell wall is called a protoplast. Protoplasts are employed in tissue culture protocols as explants.

• A. Cell wall
• B. Cell membrane
• C. Vacuole
• D. Cytoskeleton

Explanation: The correct answer is Cell wall. The cell wall is a rigid structure that surrounds the cell membrane in plant cells, providing them with shape and support. This rigidity is what gives plant cells their characteristic rectangular shape. In contrast, the cell membrane is flexible and does not enforce a specific shape on the cell. The vacuole, while important for maintaining turgor pressure, does not define the overall shape of the cell. Lastly, the cytoskeleton offers internal structure but is not responsible for the cell's external shape.

• A. Lignin
• B. Cellulose
• C. All of them
• D. None of these

Explanation: Cellulose is the primary structural component of plant cell walls and is known for its hydrophilic properties, as it can form hydrogen bonds with water, resulting in a high affinity for water. Lignin, on the other hand, is a hydrophobic polymer that provides rigidity and water resistance, lacking the ability to interact with water. Therefore, 'Cellulose' is the correct choice. The option 'All of them' is incorrect because lignin does not have a high affinity for water, and 'None of these' is incorrect because cellulose clearly does have a high affinity for water.

• A. Lysosome
• B. Nucleosome
• C. Polysome
• D. Polysomic

Explanation: Sometimes, during protein synthesis, several ribosomes are attached to one mRNA molecule. Such a chain of many ribosomes is called polysome or polyribosomes.

• A. 1
• B. 2
• C. 3
• D. No similar protein

Explanation: Polysomes, or polyribosomes, are several ribosomes attached to a single mRNA molecule, each translating the mRNA into identical copies of a protein. In this scenario, three ribosomes attached to the mRNA will produce three identical proteins. Option A is incorrect because it suggests only one protein is made, which is not the case when multiple ribosomes are involved. Option B is incorrect as it implies one ribosome is inactive. Option D is incorrect because it suggests no protein is produced, contrary to the function of ribosomes in protein synthesis.