All Free Biology MCQs with Answers

2401. The given diagram shows the structure of the cell membrane.Which of the labelled components, if removed from the cell membrane, will limit the movement of large and charged particles across the cell membrane?

• A. W
• B. X
• C. Y
• D. Z

Explanation: The correct answer is Option D: ZProteins embedded in the cell membrane, such as channel and carrier proteins, are crucial for transporting large and charged particles across the membrane. These proteins facilitate the movement of substances that cannot easily pass through the lipid bilayer due to their size or charge. Options A, B, and C refer to components that do not primarily regulate this specific type of transport.

2402. An example that demonstrates apoptosis is

• A. A severe burn causes skin cells to die
• B. The self-destruction of an immune cell
• C. The irreversible loss of the liver cells in liver cancer
• D. An over stretched muscle fibre due to heavy exercise

Explanation: The correct answer is Option B:the self-destruction of an immune cell.Apoptosis is a programmed process of cell death that occurs in multicellular organisms, helping to remove cells that are no longer needed or are a threat to the organism, like immune cells after they've served their purpose. Option A describes necrosis, which is uncontrolled cell death due to injury. Option C relates to the pathological cell changes in cancer. Option D describes muscle fiber damage, not cell death through apoptosis.

2403. Protein layers which are NOT continuous on the surface make _ percent of total in plasma membrane.

• A. 50 - 60
• B. 60 - 70
• C. 60 - 80
• D. 70 - 80
• E. 70 - 90

Explanation: The plasma membrane is composed of lipids, proteins, and carbohydrates. Proteins play an important role in the structure and function of the membrane, including transport of molecules, cell recognition, and communication between cells. The protein layers on the surface of the plasma membrane are not continuous, and they make up approximately 60-80% of the total proteins in the membrane. Option C, 60-80%, is the correct answer.

2404. The power of a microscope by which we can distinguish two closely located points is termed as:

• A. Magnification
• B. Resolution
• C. Fixation
• D. Electrophoresis

Explanation: Magnification refers to the increase in the apparent size of an object, while resolution refers to the ability to distinguish two different points as distinct from each other. In other words, the resolution is the power of a microscope to reveal fine detail and distinguish between two closely spaced objects as separate.Fixation, electrophoresis, and are techniques used in cell biology for various purposes, but they are not related to the power of a microscope.

2405. The plasma membrane consists mainly of:

• A. Phospholipids embedded in a protein bilayer
• B. Proteins embedded in a phospholipid bilayer
• C. Proteins embedded in a polymer of glucose molecules
• D. Proteins embedded in a carbohydrate bilayer

Explanation: The plasma membrane consists mainly of lipids (20-40%) and proteins (60-80%). The lipid molecules form a bilayer structure, with proteins embedded within it.

2406. Out of the given options, choose the one which shows the structures found only in plants.

• A. Large central vacuole, Chloroplast, Ribosomes
• B. Chloroplast, Microtubules, Peroxisomes
• C. Chloroplast, Cell Wall, Large central Vacuole
• D. Chloroplast, Cell Wall, Mitochondria

Explanation: Option C is correct because the structures listed - chloroplast, cell wall, and large central vacuole - are found only in plant cells. These structures are not present in animal cells. The other options include structures such as ribosomes, microtubules, peroxisomes, and mitochondria, which are common to both plant and animal cells, making them incorrect choices.

2407. Holding neighboring cells together is function of:

• A. Primary cell wall
• B. Secondary cell wall
• C. Middle lamella
• D. None of these

Explanation: Middle lamella is composed of sticky, gel-like magnesium and calcium salts (pectates) and pectin. The middle lamella holds neighboring cell walls together.

2408. Which function cannot be attributed to plasma membrane lipids?

• A. Recognition of cells having non-self surface marker
• B. Maintaining cell membrane flexibility
• C. Control of metabolic reaction across cell membrane
• D. Binding ligands for intracellular response

Explanation: The correct answer is Option D: Binding ligands for intracellular response. This function cannot be attributed to plasma membrane lipids as they do not participate in binding ligands; instead, this role is fulfilled by membrane proteins that recognize and respond to signaling molecules.Option A is incorrect because the recognition of non-self cells is primarily a function of glycoproteins and glycolipids. Option B is also incorrect since maintaining cell membrane flexibility is indeed a role of lipids, particularly phospholipids. Option C is incorrect because controlling metabolic reactions across the cell membrane typically involves membrane proteins that facilitate reactions and transport, not lipids.

2409. Plasma membrane is differentially permeable due to the presence of:

• A. Carbohydrates
• B. Lipids
• C. Proteins
• D. Vitamins

Explanation: The correct answer is Lipids (Option B). The plasma membrane is primarily composed of a bilayer of phospholipids, which creates a hydrophobic environment that selectively allows certain substances to pass while blocking others. This selective permeability is crucial for maintaining the internal environment of the cell.Carbohydrates (Option A) are important for cell recognition and communication, but do not directly contribute to the structural integrity of the plasma membrane. Proteins (Option C) are involved in various functions such as transport and signaling, but do not form the membrane structure that determines permeability. Vitamins (Option D) are not involved in the architecture of the plasma membrane and do not play a role in its differential permeability.

2410. In plants the neighboring cells are connected with one another by:

• A. Plasmodesmata
• B. Cell walls
• C. Vacuoles
• D. Casparian strips

Explanation: In plants, neighboring cells are connected with one another by specialized channels called plasmodesmata. Plasmodesmata are microscopic channels that pass through the cell walls and connect the cytoplasm of adjacent plant cells, allowing for communication, transport of water, nutrients, and other molecules between cells.