All Free Biology MCQs with Answers

1011. Effect of increased substrate concentration on enzyme activity:

• A. Decrease the rate of reaction
• B. Increase the reaction rate until all active sites are saturated
• C. Have no effect on the reaction rate
• D. Increase the rate of reaction in a straight diagonal line

Explanation: Rate rises steeply at first because more collisions occur between substrate and free active sites, then levels off at Vmax once every site is occupied and the enzyme is working as fast as it can. The curve is therefore hyperbolic rather than a straight line, which is what the fourth option gets wrong. Beyond saturation the enzyme concentration rather than the substrate is limiting.

1012. An oligosaccharide is made up of at least:

• A. two saccharide units
• B. ten saccharide units
• C. three to ten saccharide units
• D. more than ten saccharide units

Explanation: This is the option marked correct in the official UHS answer key, taking oligosaccharide in its broad sense of a few sugar units, beginning at two. Many textbooks instead reserve disaccharide for two units and define oligosaccharides as three to ten, which is why option (c) is such a strong distractor. Anything beyond about ten units is a polysaccharide.

1013. Which statement best explains the difference between humoral and cell mediated immune response?

• A. Humoral immunity involves B-Lymphocytes and cell mediated immunity involves T-Lymphocytes
• B. Humoral immunity destroys viruses and cell mediated immunity destroys bacteria
• C. Humoral immunity is specific and cell mediated immunity is nonspecific
• D. Humoral immunity uses antibodies and cell mediated immunity does not involve immune cells

Explanation: B cells give rise to plasma cells whose antibodies circulate in the body fluids, which is the humoral arm, while T cells act directly on infected, cancerous or transplanted cells, which is the cell mediated arm. Both branches are highly specific, so the third option is wrong, and both certainly involve immune cells. The two arms cooperate, since helper T cells are needed to activate most B cells.

1014. Which of the following is the correct higher (left) to lower (right) sequence of molecules with respect to their amount in the cell?

• A. DNA to rRNA to tRNA to mRNA
• B. rRNA to tRNA to mRNA to DNA
• C. mRNA to tRNA to rRNA to DNA
• D. DNA to mRNA to tRNA to rRNA

Explanation: This is the order given in the official UHS answer key. Among the three RNAs the ranking is not disputed: ribosomal RNA is by far the most abundant at roughly 80 per cent of cellular RNA, transfer RNA follows, and messenger RNA is the smallest fraction because it is made as needed and degraded quickly. Placing DNA at the head reflects the paper's intent that the genome is the largest single nucleic acid component.

1015. A person in hot weather is unable to maintain body temperature. Which physiological process has failed?

• A. Vasodilation & sweating
• B. Vasoconstriction
• C. Shivering
• D. Renin secretion

Explanation: Cooling in hot conditions depends on dilating the skin arterioles so more warm blood reaches the surface and on evaporating sweat, which draws latent heat from the skin. Vasoconstriction and shivering are the responses to cold, so their failure would show in the opposite conditions. Renin controls blood pressure and sodium balance rather than temperature.

1016. The main idea in Darwin's Theory of "Origin of species by natural selection" is:

• A. Inheritance of acquired traits
• B. Use and disuse of organs
• C. Species never change
• D. Evolution occurs through gradual accumulation of adaptation through successive generations

Explanation: Darwin argued that individuals vary, that more are born than can survive, and that those better suited leave more offspring, so favourable adaptations accumulate slowly across generations. Inheritance of acquired characters and use and disuse are Lamarck's proposals, offered here as the standard distractors. Fixity of species is the view Darwin overturned.

1017. Which of the following is a key feature of RNA?

• A. Deoxyribose and thymine
• B. Double stranded and thymine
• C. Ribose and uracil
• D. Ribose and thymine

Explanation: RNA carries ribose, which has a hydroxyl group at carbon 2, and uses uracil in place of thymine, and it is normally single stranded. Deoxyribose and thymine are the DNA features, so options mixing one sugar with the wrong base can be eliminated at once. The extra hydroxyl is also why RNA is chemically less stable than DNA.

1018. Which of the following types of RNA makeup the largest proportion of total cellular RNA?

• A. Messenger RNA
• B. Ribosomal RNA
• C. Transfer RNA
• D. Catalytic RNA (ribozyme)

Explanation: Ribosomal RNA accounts for roughly 80 per cent of the RNA in a cell, because every ribosome is built largely from it and a busy cell contains millions of ribosomes. Transfer RNA comes next at around 15 per cent, and messenger RNA is a small and rapidly turning over fraction. Ribozymes are rarer still.

1019. The bacterium Treponema pallidum is responsible for which sexually transmitted disease?

• A. Syphilis
• B. Chlamydia
• C. Gonorrhea
• D. Genital herpes

Explanation: Treponema pallidum is the spiral bacterium, or spirochaete, that causes syphilis, a disease progressing through primary, secondary, latent and tertiary stages over many years if untreated. Gonorrhoea is caused by the diplococcus Neisseria gonorrhoeae and chlamydia by Chlamydia trachomatis. Genital herpes is viral and therefore not treatable with antibiotics at all.

1020. Tissue fluid in a lymphatic system is called as:

• A. Plasma
• B. Matrix
• C. Lymph
• D. Blood

Explanation: Surplus tissue fluid that drains into the blind ending lymph capillaries is called lymph, and it travels one way through nodes and along the thoracic duct back to the subclavian veins. Plasma is the fluid part of blood before it leaves the capillary, so the same fluid takes three names depending on where it is. Lymph resembles plasma but carries far less protein and no red cells.