All Free Biology MCQs with Answers

• A. Proteins
• B. Carbohydrates
• C. Phospholipids
• D. All of the above.

Explanation: The structure of plasma membrane is mainly held together by proteins according to the sandwich model of cell membrane.

• A. Hydrophobic interactions between fatty acid tails
• B. Hydrophobic interactions between phosphate heads
• C. Hydrophilic interactions between fatty acid tails
• D. Hydrogen bonding between fatty acid tails

Explanation: Being cylindrical, phospholipid molecules spontaneously form bilayers in aqueous environments. In this energetically most-favorable arrangement, the hydrophilic heads face the water at each surface of the bilayer, and the hydrophobic tails are shielded from the water in the interior.

• A. Oxidative phosphorylation
• B. Liver cells
• C. To maintain calcium ions
• D. All of these
• E. Hormone release

Explanation: Mitochondria help in all of the given functions and are, therefore, very important organelles. It is found in almost every cell in the body, including liver cells. It helps play a role in most metabolic processes by producing ATP. The ATP can then be utilized in oxidative phosphorylation, hormone release, and the maintenance of intracellular and extracellular calcium ion concentration.

• A. Permeable
• B. Semi-permeable
• C. Impermeable
• D. None of these

Explanation: The lipid bilayer cell membrane of a cell is always semi-permeable because it is selectively permeable i.e. it lets only a select few molecules (mainly nonpolar molecules) pass through it.

• A. Carbohydrate
• B. Lipid
• C. Glucose
• D. Protein

Explanation: The cell membrane is composed of lipids and proteins. 60-80% are proteins and 20-40% are lipids, in addition to this there is a small quantity of carbohydrates as well. So, proteins are present in the largest quantity.

• A. Flexibility
• B. Chemical climate
• C. Transfer of molecules
• D. All of these

Explanation: In the plasma membrane, the lipids help in the transport of molecules, because the lipid-soluble non-polar substances can easily diffuse through them. Since many non-polar substances are chemicals, the lipid bilayer also helps maintain a specific chemical climate. Additionally, cholesterol is a lipid that alters the flexibility of the cell membrane. Hence, "All of these" would be the best option.

• A. Both transfer of molecules and chemical climate
• B. Chemical climate
• C. Flexibility
• D. Transfer of molecules

Explanation: In the plasma membrane, proteins help in the transfer of molecules by acting as carrier proteins that transport larger molecules/polar that cannot simply diffuse in or out. Other than helping in the transfer of molecules, they also maintain the chemical climate of the plasma membrane by maintaining the ideal intracellular chemical concentrations.

• A. Integral Proteins
• B. Peripheral proteins
• C. Cell wall
• D. Plasmodesmata

Explanation: Peripheral proteins, or peripheral membrane proteins, are a group of biologically active molecules formed from amino acids which interact with the surface of the lipid bilayer of cell membranes. Unlike integral membrane proteins, peripheral proteins do not enter into the hydrophobic space within the cell membrane. Instead, peripheral proteins have specific sequences of amino acids which allow them to attract to the phosphate heads of the lipid molecules or to integral proteins.

• A. Nucleus
• B. Cell membrane
• C. Tonoplast
• D. Chloroplast

Explanation: The plant cell if it receives the signal to die, it commits suicide in a programmed way. This happens by the release of enzymes internally. All enzymes in plant cells are in a vacuole which is covered by a membrane called tonoplast. Rupturing of that membrane leads to the enzymes within vacuoles spilling out in the protoplasm.

• A. Exocytosis
• B. Osmosis
• C. Diffusion
• D. Phagocytosis.

Explanation: The diagram shows phagocytosis, which is the process by which a cell uses its plasma membrane to engulf a large particle, giving rise to an internal compartment called the phagosome. It is one type of endocytosis.