All Free Biology MCQs with Answers

• A. They are unable to cross the hydrophilic phosphate heads of the lipid bilayer
• B. They are unable to cross the hydrophobic tails of the lipid bilayer
• C. They are unable to cross both the phosphate heads and fatty acid chains of the lipid bilayer
• D. They are too big to cross the plasma membrane

Explanation: The plasma membrane is made up of a phospholipid bilayer, which is a double layer of phospholipids. Phospholipids have a hydrophilic head and a hydrophobic tail. The hydrophilic heads face the outside and inside of the cell, while the hydrophobic tails face each other. The hydrophobic tails of the lipid bilayer create a barrier that prevents ions from crossing the plasma membrane. Ions are charged particles, and they are attracted to water. The hydrophobic tails of the lipid bilayer are repelled by water, so ions cannot cross through them. Channel proteins are proteins that span the plasma membrane and create pores through which ions can pass. Channel proteins are selective, so they only allow certain types of ions to pass through.

• A. Endoplasmic Reticulum (ER)
• B. Cytoskeleton
• C. Golgi apparatus
• D. All of these

Explanation: The correct answer is the Endoplasmic Reticulum (ER), which is a network of interconnected membranes involved in protein synthesis and transport. The cytoskeleton provides structural support and does not participate directly in protein synthesis or transport. The Golgi apparatus is responsible for further processing and packaging proteins but does not synthesize them. Therefore, the only organelle described as a 'mesh of interconnected membranes' involved in both protein synthesis and transport is the ER.

• A. Magnification
• B. Resolving power or resolution
• C. Contrast
• D. Scanning power

Explanation: The correct answer is resolving power or resolution. Resolution refers to a microscope's ability to distinguish between two points that are close together. It is a key factor in visualizing fine details and is dependent on the microscope's optical properties, such as numerical aperture and the wavelength of light used. In contrast, magnification increases the size of the image without necessarily improving clarity. Contrast enhances visibility by differentiating the specimen from its background but does not affect resolution. Scanning power involves a lower magnification level for initial scanning and does not pertain to resolving power.

• A. Cytoplasm
• B. Nucleoplasm
• C. Protoplasm
• D. Protoplast

Explanation: Option B is correct because nucleoplasm is the soluble, gel-like substance within the nucleus, containing the chromatin and nucleolus. It is distinct from the cytoplasm, which surrounds the nucleus, and from protoplasm, which encompasses all living parts of the cell. The protoplast includes all cellular components except the cell wall, thus not specifically addressing the nucleus's contents.

• A. Grana
• B. Stroma
• C. Thylakoid
• D. Intergrana

Explanation: The ground mass of chloroplast is called stroma. It is the colourless proteinaceous substance which like mitochondrial matrix also contains a small circular DNA, all kinds of RNA, ribosomes (70S) and various enzymes.

• A. Glyoxysomes
• B. Lysosomes
• C. Ribosomes
• D. Peroxisomes

Explanation: The correct answer is Peroxisomes. Peroxisomes are organelles that contain enzymes, such as catalase, specifically involved in the metabolism of hydrogen peroxide. They help in detoxifying cells by converting hydrogen peroxide into water and oxygen. This function is crucial for maintaining cellular health and preventing damage from reactive oxygen species.Glyoxysomes, while a type of peroxisome found in plants, are primarily involved in lipid metabolism, not directly in hydrogen peroxide breakdown.Lysosomes are involved in digesting cellular waste and do not interact with hydrogen peroxide.Ribosomes are involved in protein synthesis and have no role in hydrogen peroxide metabolism.

• A. 21
• B. 9
• C. 27
• D. 36

Explanation: The most accurate and complete description of a centriole's structure is 27 microtubules arranged in 9 triplets, making Option C the correct answer.

• A. 2.0 μm
• B. 2.0 mm
• C. 1.0 μm
• D. 0.1 mm

Explanation: Resolution refers to the ability of an imaging system to separate or distinguish between two closely spaced objects. The resolution of the human eye is approximately 0.1 mm or 100 micrometers. This means that two objects need to be at least 0.1 mm apart to be perceived as distinct by the human eye.

• A. 10
• B. 23
• C. 24
• D. 48

Explanation: Somatic cells in humans are diploid, meaning they contain two sets of chromosomes, one from each parent, resulting in 23 pairs, totaling 46 chromosomes. Germ cells, such as sperm and egg cells, are haploid and contain 23 single chromosomes, one from each pair. Therefore, the correct answer is 23 pairs. Option A (10) is incorrect because it underestimates the number of pairs. Option C (24) is incorrect because it overestimates the number of pairs. Option D (48) is incorrect because it mistakenly represents the total number of chromosomes, not pairs.

• A. DNA polymerase
• B. Salivary amylase
• C. Pancreatic amylase
• D. Salivary lipase

Explanation: The correct answer is DNA polymerase. Free-floating ribosomes in the cytoplasm synthesize proteins that function within the cell, such as DNA polymerase, which is transported to the nucleus where it is needed. In contrast, salivary amylase, pancreatic amylase, and salivary lipase are synthesized by the rough endoplasmic reticulum (RER) because they are either secreted outside the cell or are destined for the digestive tract.