All Free Biology MCQs with Answers

991. Self-fertilization in plants through successive generations can lead to the development of:

• A. Hybrid breeds of plants
• B. Variations in coming generation
• C. True breeding plants
• D. Adaptation with their environment

Explanation: Repeated self pollination steadily removes heterozygotes, since each generation halves their proportion, until the line is homozygous and breeds true for every character. This is exactly how Mendel obtained the pure lines his experiments depended on. Hybrids and new variation arise from cross fertilisation, which is the opposite process.

992. Which part of the neuron typically receives incoming signals from other neurons?

• A. Axon
• B. Dendrites
• C. Myelin sheath
• D. Synaptic knob

Explanation: Dendrites are the short branched processes that carry receptors for neurotransmitter and conduct the resulting signal towards the cell body. The axon carries impulses away, and its synaptic knobs are where transmitter is released rather than received. Myelin is an insulating sheath that speeds conduction and plays no part in reception.

993. Why thick filaments are unable to bind with thin filament in a relaxed muscle fiber?

• A. Actin blocks the myosin binding site
• B. Tropomyosin blocks the myosin binding site
• C. Troponin blocks the myosin binding site
• D. Tropomyosin blocks the troponin binding site

Explanation: In a relaxed fibre the long tropomyosin strand lies across the myosin binding sites on actin, so no cross bridge can form. Troponin is the tempting answer, but its job is to hold tropomyosin in that position and then pull it aside once calcium binds to it. Actin carries the binding sites rather than blocking them.

994. Which of the following best highlights the importance of proteins in immunity?

• A. They act as receptors of pathogens
• B. They are long term energy reserves
• C. They act as antibodies
• D. They act as mechanical barrier for pathogens

Explanation: Antibodies are immunoglobulins, that is proteins, and they are the specific weapon of the humoral response, binding one antigen each. Proteins do also serve as receptors, which makes the first option partly true, but antibodies are the direct and defining immune role the question asks for. Long term energy storage is the job of fat, not protein.

995. The secondary structure of proteins is stabilized by:

• A. Ionic bonds
• B. Hydrogen bonds
• C. Disulfide bridges
• D. Hydrophobic exclusion

Explanation: Regular hydrogen bonding between backbone carbonyl and amide groups coils the chain into an alpha helix or folds it into a beta pleated sheet. Ionic bonds, disulphide bridges and hydrophobic exclusion all act between side chains and belong to the tertiary level instead. Being weak, these hydrogen bonds are the first to break on heating, which is why helices unwind during denaturation.

996. The following is an example of a globular protein:

• A. Keratin
• B. Collagen
• C. Hemoglobin
• D. Histone

Explanation: Haemoglobin folds into a compact soluble ball with hydrophilic residues outside, which is what lets it dissolve in the cytoplasm of a red cell and carry oxygen. Keratin and collagen are fibrous structural proteins, long and insoluble. Histones are globular too, which makes the last option arguable, but haemoglobin is the standard textbook example the paper is looking for.

997. The process of osmoregulation refers to:

• A. The filtration of blood to remove metabolic waste
• B. The regulation of solute and water movement between an organism and its environment
• C. The creation of an osmotic gradient in the kidney medulla
• D. The secretion of hormones that control blood plasma

Explanation: Osmoregulation is the control of water and solute balance so that the water potential of body fluids stays steady, whatever the organism drinks or loses. Filtering waste out of the blood is excretion, a related but separate process, and it is the closest distractor. The medullary gradient is one mechanism the kidney uses to achieve osmoregulation, not the definition of it.

998. A baby girl is born with hemophilia, which is an X-linked recessive disorder. What are the most likely genotypes of her parents?

• A. The mother is a carrier and the father is normal
• B. The mother is hemophiliac and the father is normal
• C. The mother is carrier and the father is hemophiliac
• D. Both are normal

Explanation: A girl has two X chromosomes and needs the recessive allele on both, one from each parent, so the father must be haemophiliac himself and the mother must carry at least one copy. A carrier mother with a normal father could only produce affected sons, which is why the first option fails. This is why affected females are so rare.

999. Identify the most appropriate function of chromosomes

• A. Energy production and storage
• B. Protein synthesis and regulation
• C. Storage of genetic information
• D. Lipid metabolism and transport

Explanation: A chromosome is DNA packaged with histones, and its role is to hold the hereditary information and pass it on accurately when the cell divides. Protein synthesis is the tempting option, since genes direct it, but the synthesis itself happens on ribosomes and the chromosome only stores the instructions. Energy production belongs to mitochondria and lipid handling to the smooth endoplasmic reticulum.

1000. Enzymes belong to which class of biomolecules?

• A. Carbohydrates
• B. Lipids
• C. Proteins
• D. Nucleic acids

Explanation: Almost every enzyme is a globular protein whose precisely folded tertiary structure creates the active site, which is why heat and extreme pH destroy catalytic power. The one exception is the small group of catalytic RNA molecules called ribozymes, which is why nucleic acids are offered here. Carbohydrates and lipids never act as catalysts.