All Free Biology MCQs with Answers

• A. Lysosome
• B. Mitochondrion
• C. Golgi apparatus
• D. Smooth endoplasmic reticulum

Explanation: The Krebs cycle runs in the mitochondrial matrix and the electron transport chain sits in the inner membrane, where the proton gradient…

• A. Nucleolus
• B. Golgi apparatus
• C. Rough endoplasmic reticulum
• D. Centriole

Explanation: Hydrolytic enzymes are made on the rough endoplasmic reticulum but the Golgi apparatus packages and buds them off as lysosomes, after…

• A. cristae
• B. ribosomes on its surface
• C. thylakoids
• D. a double nuclear envelope

Explanation: Ribosomes bound to the outer face of the membrane give rough ER its appearance and its function, which is synthesising proteins destined…

• A. ribosome
• B. lysosome
• C. peroxisome
• D. vacuole

Explanation: Lysosomes hold hydrolytic enzymes at an acidic pH, and if the membrane ruptures those enzymes digest the cell itself, a process called…

• A. Ribosome
• B. Lysosome
• C. Mitochondrion
• D. Golgi apparatus

Explanation: A ribosome is a complex of ribosomal RNA and protein with no surrounding membrane at all, which is why it is found in prokaryotes as well…

• A. a rigid protein sheet with lipids attached
• B. a phospholipid bilayer with proteins embedded in and moving through it
• C. a single layer of phospholipids
• D. a continuous layer of cholesterol

Explanation: Singer and Nicolson described a bilayer of phospholipids in which proteins float like icebergs, free to move laterally.

• A. 23
• B. 44
• C. 46
• D. 92

Explanation: Human body cells are diploid with 46 chromosomes, which is 23 homologous pairs made up of 22 pairs of autosomes and one pair of sex…

• A. telomere
• B. centromere
• C. centriole
• D. chromomere

Explanation: The centromere holds sister chromatids together and carries the kinetochore, the protein structure the spindle microtubules attach to…

• A. histones
• B. collagens
• C. tubulins
• D. keratins

Explanation: Histones are small positively charged proteins that bind the negatively charged phosphate backbone of DNA, forming nucleosomes that…

• A. raising the temperature of the reaction mixture
• B. lowering the activation energy of the reaction
• C. changing the equilibrium position in favour of the products
• D. supplying the energy the reaction needs

Explanation: An enzyme provides an alternative route with a lower activation energy, so a much larger fraction of molecules has enough energy to react…

• A. is already an exact complement of the substrate before binding
• B. changes shape slightly as the substrate binds
• C. plays no part in catalysis
• D. binds any substrate regardless of shape

Explanation: Koshland's induced fit model replaced the rigid lock and key picture: the active site is flexible and moulds itself around the substrate…

• A. is used up by the reaction
• B. is denatured as its tertiary structure breaks down
• C. becomes a substrate itself
• D. loses its active site to the product

Explanation: Heat breaks the hydrogen bonds and other weak interactions holding the tertiary structure, so the active site loses its shape and can no…

• A. Salivary amylase
• B. Pepsin
• C. Trypsin
• D. Catalase

Explanation: Pepsin is secreted into the stomach where hydrochloric acid keeps the pH near 2, and its structure is stable and active in exactly those…

• A. the substrate begins to inhibit the enzyme
• B. all the active sites are occupied and the enzyme is saturated
• C. the enzyme is denatured by the excess substrate
• D. the products are used up

Explanation: Once every active site is engaged, adding more substrate cannot raise the rate, because the enzyme is already working as fast as it can…

• A. binding the active site because it resembles the substrate
• B. binding a site away from the active site and distorting it
• C. permanently destroying the enzyme
• D. lowering the pH of the surroundings

Explanation: A competitive inhibitor is structurally similar to the substrate and occupies the active site, so substrate and inhibitor compete for the…

• A. a competitive inhibitor
• B. a non-competitive inhibitor
• C. a low enzyme concentration
• D. a substrate below the saturation point

Explanation: A non-competitive inhibitor binds at a site other than the active site and changes the enzyme's shape, so the substrate cannot compete it…

• A. non-competitive inhibition
• B. competitive inhibition
• C. feedback inhibition
• D. denaturation

Explanation: Malonate is close enough in structure to succinate to occupy the same active site without being converted, which is the definition of…

• A. cofactor metal ion
• B. coenzyme
• C. prosthetic group of a haemoglobin type
• D. substrate

Explanation: Coenzymes are organic helper molecules, often derived from vitamins, that bind loosely and carry chemical groups or electrons between…

• A. They are consumed in the reactions they catalyse
• B. They remain chemically unchanged at the end of the reaction
• C. They can catalyse reactions that would otherwise be thermodynamically impossible
• D. They work equally well at every pH

Explanation: An enzyme releases the product and returns to its original state, ready to bind the next substrate molecule, which is why a small amount…

• A. are smaller than any known bacterium
• B. carry both DNA and RNA in the same particle
• C. have a cell wall made of peptidoglycan
• D. lack the ribosomes and enzymes needed to make their own proteins and ATP

Explanation: A virus particle has nucleic acid and protein but no ribosomes, no respiratory enzymes and no ATP generating system, so it can only…