All Free Biology MCQs with Answers

971. Best description of the process of crossing over during meiosis:

• A. Duplication of chromosome
• B. Exchange of genes between non-sister chromatids
• C. Movement of chromosome to opposite poles
• D. Separation of sister chromatids

Explanation: During prophase I the homologues pair as bivalents and non sister chromatids exchange equal segments at chiasmata, producing chromosomes carrying combinations neither parent had. The exchange must be between non sister chromatids, since sister chromatids are identical and swapping between them would change nothing. Separation of sister chromatids happens later, in anaphase II.

972. Total number of linkage groups in a normal human is:

• A. 02
• B. 23
• C. 46
• D. 92

Explanation: All the genes on one chromosome form a single linkage group, and the number of linkage groups equals the haploid chromosome number, which for humans is 23. The figure 46 is the diploid number, counting both members of each homologous pair, but the two homologues carry the same set of loci and so form one group, not two. Ninety two would be the count of chromatids after replication.

973. Nissl granule is a specialized structure in neuron formed by modification of:

• A. Golgi bodies & Smooth ER
• B. Peroxisome & Mitochondria
• C. Lysosome & Vacuole
• D. Ribosome & Rough ER

Explanation: Nissl granules are dense stacks of rough endoplasmic reticulum studded with ribosomes, which is why they stain so darkly and why they are concentrated in the cell body where protein synthesis for the whole neurone takes place. Smooth ER carries no ribosomes and handles lipid synthesis instead. Their disappearance after injury, called chromatolysis, is a standard sign of nerve cell damage.

974. What is the function of a centromere?

• A. To protect the ends of chromosomes
• B. To hold sister chromatids together
• C. To carry genetic information
• D. To initiate DNA replication

Explanation: The centromere joins the two sister chromatids and carries the kinetochore, the protein plate that the spindle microtubules attach to during division. Protecting the chromosome ends is the job of the telomeres, which is the closest distractor here. Genetic information is carried along the whole length of the DNA rather than at one point, and replication begins at origins distributed across the chromosome.

975. All are the functions of lysosome EXCEPT:

• A. Intra cellular digestion
• B. Removal of the waste
• C. Autophagy
• D. Lipid synthesis

Explanation: Lysosomes contain hydrolytic enzymes and therefore break molecules down, digesting food vacuoles, clearing waste and destroying worn out organelles by autophagy. Building lipids is a synthetic process carried out by the smooth endoplasmic reticulum, which is the opposite kind of activity. Recognising that every genuine lysosomal role is destructive answers the question without recalling a list.

976. The first consequence of lymphatic blockage in tissues is:

• A. Deficiency of oxygen
• B. Loss of nerve signals
• C. Drop in blood pressure
• D. Excess fluid accumulation in tissue

Explanation: The lymphatic system is the only route by which surplus tissue fluid returns to the blood, so blocking it lets fluid collect between the cells and the limb swells, which is the oedema of filariasis. Blood flow through the arteries and capillaries continues normally, so oxygen delivery and blood pressure are not affected first. The swelling is soft and painless in the early stages for exactly this reason.

977. Which of the following is the auditory relay Centre and Centre that controls reflex movement of eyes?

• A. Forebrain
• B. Cerebellum
• C. Midbrain
• D. Cerebellum

Explanation: The midbrain carries four swellings, the corpora quadrigemina, of which the upper pair handle visual reflexes such as turning the eyes and head towards a movement and the lower pair relay auditory information. The cerebellum coordinates balance and fine movement but relays neither sound nor visual reflexes. Note that options (b) and (d) were printed identically in the original paper, which is a misprint in the paper itself and does not affect the correct answer.

978. Which of the following is the correct pathway of nerve impulse?

• A. Receptors to CNS to Effectors
• B. Effectors to Receptors to CNS
• C. CNS to Effectors to Receptors
• D. Effectors to CNS to Receptors

Explanation: A receptor detects the stimulus, a sensory neurone carries the impulse into the central nervous system, and a motor neurone carries the instruction out to the effector that responds. The direction is fixed by the one way nature of the synapse, since transmitter is released on one side only and receptors sit on the other. Any pathway beginning at the effector reverses the whole logic of the reflex.

979. The neurotransmitters are secreted by the neuron from:

• A. Axon ends
• B. Dendrite end
• C. Nissl's granules
• D. Cell body

Explanation: Vesicles of transmitter are stored in the swollen endings of the axon and released into the synaptic cleft when the impulse arrives. Dendrites carry the receptors that detect the transmitter on the other side of the synapse, which is why they are the tempting answer. This arrangement, with release on one side and reception on the other, is exactly what makes transmission one way.

980. Hippocampus plays an important role in the:

• A. Formation of short-term memory
• B. Formation of image on retina
• C. Formation of long-term memory
• D. Formation of emotions

Explanation: The hippocampus consolidates experiences into long term memory, which is why damage to it leaves a patient able to hold a conversation yet unable to form any lasting new memory. Short term working memory depends mainly on the prefrontal cortex, and emotion is handled largely by the amygdala nearby. Image formation on the retina is optical and involves no part of the brain at all.