Explanation:
Choice C is correct because ribosomes are organelles found on the surface of the rough endoplasmic reticulum and are needed to synthesise polypeptide chains.

The nucleus (Choice A) contains DNA, some of which codes for the polypeptides made by the ribosomes. The role of vesicles (Choice B) is to store substances and to transport substances, including proteins, between cellular compartments. The mitochondria (Choice D) are the organelles responsible for aerobic respiration.

Explanation:
Protein pumps are membrane proteins that pump molecules up their concentration gradient using energy in the form of ATP.

Protein channels (Choice A) carry out passive transport while receptors (Choice D) and peripheral proteins (Choice C) do not transport proteins.

Explanation:
Choice C is correct because the habitat is a place a community, population, species, or organism lives. Choice A refers to an organism's niche, Choice B refers to the ecosystem, and Choice D refers to a community.

Explanation:
Statements I and III are correct. Statement II is incorrect because only some joints (knee and elbow) allow movement in one direction; there are other synovial joints that allow movement in additional directions (hip and shoulder).

Explanation:
The enzyme lactase breaks down the substrate lactose into glucose and galactose.

Glucose and galactose are products of the reaction (Choices A and B).

Fructose is not a substrate for the enzyme lactase (Choice D).

Explanation:
The contraction and relaxation of muscles (Choice C) cause bones to move. Cartilage (Choice A) is the smooth tissue covering the end of bones in joints to reduce friction. Ligaments (Choice B) join bone to bone and help keep joints together. Tendons (Choice D) connect muscle to bone, but aren’t responsible for movement.

Explanation:
A community is a group of populations living and interacting in a shared habitat (biotic factors). The abiotic factors for this community have not been described but could be the depth of the water, light intensity and the nutrients available for phytoplankton.

A population (Choice A) is a group of organisms of the same species living in the same area at the same time which can interbreed. A habitat (Choice C) refers to the environment in which a species normally lives. An ecosystem (Choice D) is a group of populations living and interacting in a common habitat and includes both biotic and abiotic factors.

Explanation:
Choice A is correct because microvilli are present, increasing the cell's surface area for absorption. Cells of the proximal convoluted tubule in the nephron require a large surface area for selected reabsorption of substances in the filtrate. Choice B is incorrect because cells lining capillaries are flat (squamous epithelial tissue). Choice C is incorrect because cells of the immune system do not have microvilli. Choice D is incorrect because the function of microvilli is not insulation, and adipose cells do not have microvilli.

Explanation:
Choice A is incorrect as it describes how neurotransmitters are released from the presynaptic cleft. Choice C is incorrect as neurotransmitters do not require energy to move across the synaptic cleft. Choice D is incorrect as channels are not present in the synaptic cleft. They are only present in the membranes of neurons.

Explanation:
Veins carry deoxygenated blood from the body back to the heart. As muscles surrounding the veins contract, they push the blood towards the heart and venous valves open to allow the flow of blood. When the muscles relax, the valves close to prevent the blood from flowing backwards in response to gravity. So, venous valves help prevent the backflow of blood away from the heart (Choice B).

The relaxation of skeletal muscles decreases blood pressure in veins and does not play a role in preventing the backflow of blood in veins (Choice A). When the heart relaxes, this decreases blood pressure in arteries, it does not affect blood pressure in veins and plays no role in preventing the backflow of blood in veins (Choice C). Thin vessel walls are most exemplified in capillaries whose walls are one cell thick and allow exchange of substances. Thin walls play no role in preventing the backflow of blood (Choice D).

Explanation:
The quaternary structure of a protein can relate to the number of amino acid chains which make up the protein. These chains are held together by R-group interactions (Choice C). Choices A and B relate to the secondary structure of a protein. Choice D refers to the primary structure of a protein.

Explanation:
Choice C correctly describes the cell type adapted for gas exchange in the lungs. Choice A is incorrect because although it is a correct description of type II pneumocytes, these cells are not adapted for gas exchange. Choice B is incorrect because type I pneumocytes do not contain many secretory vesicles. Choice D is incorrect because type II pneumocytes are not extremely thin.

Explanation:
The protein filament that is thicker and has heads is made of myosin (arrow I). The thinner protein filaments are made of actin, troponin and tropomyosin. Arrow II is pointing to the actin component of the thin filament (Choice D). Tropomyosin is a protein in the thin filament that masks myosin-binding sites (shown as thin black lines). Troponin is also a protein found in thin filaments. It has binding sites for calcium ions (shown as small double circles attached to tropomyosin lines).

Explanation:
Centrifugation is a technique that primarily separates substances based on their density. When a mixture is centrifuged, particles or components with higher density sediment to the bottom of the tube. Choice A is, therefore, correct.

Centrifugation does not separate substances based on their charge. Electrophoresis is a technique that separates particles or molecules based on their charge. Choice B is, therefore, incorrect. Centrifugation does not directly separate substances based on their chemical composition. Other techniques like chromatography may be more suitable for separating substances by chemical composition. Choice C is, therefore, incorrect. Centrifugation does not separate substances based on their colour. Colour differences might be observed during centrifugation, but they are not the basis for separation. Choice D is, therefore, incorrect.

Explanation:
Cholesterol is a steroid, not a transport channel.

Reducing membrane fluidity (Choice A), increasing membrane flexibility (Choice B), and reducing permeability to hydrophilic substances (Choice D) are all roles of cholesterol in cell membranes.

Explanation:
When two monosaccharides are joined together to form a disaccharide, water is produced, therefore it is a condensation reaction. Choice A is correct.

Choice B is incorrect as hydrolysis uses water to break bonds, in this case converting a disaccharide into a monosaccharides. Choice C is incorrect as catabolism breaks down large molecules into smaller molecules. Choice D is incorrect as oxidation means adding oxygen or losing electrons.

Explanation:
Choice A - The surface area of a cell affects the rate of diffusion of materials in and out of the cell.

Choice B - A small cell will have a bigger surface area to volume ratio which means that diffusion will be easier and other cell processes will become faster.

Choice C - The volume of the cell affects the rate at which materials are produced.

Choice D - A larger spherical cell will have a low surface area to volume ratio. Therefore, the comparatively large volume of cytoplasm may produce waste products at a rate too high to rely on diffusion through the comparatively small surface area of the cell membrane.

Explanation:
Choice C is correct because immediately after prophase is prometaphase, during which the nuclear membrane breaks down into small vesicles.

Choice A is incorrect because, during prophase, the nuclear membrane already has existing pores. Choice B is incorrect because the nuclear membrane only reassembles during telophase, which is the last stage of mitosis, and not immediately after prophase. Choice D is incorrect because the mitotic spindle forms between the poles of the cell immediately after prophase.

Explanation:
Choice C – The statement is false. Phospholipids are a class of lipids which have a hydrophilic “head” and two hydrophobic “tails.” The heads contain a phosphate group and the two tails each contain one fatty acid.

Choice A, B, and D – These statements are all true.

Explanation:
A cell membrane is formed of two layers of phospholipids whereby hydrophilic phosphate heads face the cytoplasm of the cell (cell interior) and the cell's environment (exterior) while the hydrophobic lipid tails face each other and form the interior of the membrane.

Having lipid tails pointing away (Choice A) is not a valid choice since lipid tails are hydrophobic and cannot face the cell's aqueous interior and exterior. Proteins are embedded in the membrane and do not line the outer layer (Choice C). The cell membrane is a bilayer and not just a monolayer (Choice D).

Explanation:
Choice A is correct because dense bones would make the duck heavier, therefore making it harder for it to move.

Choice B is incorrect, as wings enable the duck to fly. Choice C is incorrect, as webbed feet aid the duck in swimming more efficiently. Choice D is incorrect as the oily coating on feathers helps to waterproof the duck and keep it light so it does not become waterlogged. This helps the duck to swim and fly more easily.

Explanation:
The Golgi apparatus is a membrane-bound organelle that processes, modifies and packages proteins and lipids for secretion or delivery to various cellular compartments. Choice C is, therefore, correct.

The cell wall (Choice A) does provide structural support and protection to plant cells, but it is not an organelle, it is an extracellular structure external to the plasma membrane. The cytoplasm (Choice B) is not an organelle, but its role is to provide a medium for metabolic reactions to occur in. Although anaerobic respiration occurs in the cytoplasm, the cytoplasm does not produce ATP itself.. Lysosomes (Choice D) digest worn-out organelles, pathogens, macromolecules and debris, however, they are membrane-bound organelles.

Explanation:
The diagram shows glycerol and 3 fatty acids. When these are joined in a condensation reaction, a triglyceride is formed. Choice D is correct.

Choices A, B and C are incorrect.

Explanation:
Choice D is correct because larger cells do not generally have fewer transport proteins. Choice D is also correct because as cell size increases, cytoplasmic volume increases, increasing the cell's metabolic demands which increases the cell’s need to exchange substances. Because cytoplasmic volume increases more rapidly than the surface area of the cell membrane, the surface area to volume ratio decreases. This means that as cell size increases, the cell membrane's surface area is soon unable to excrete waste and intake nutrients rapidly enough.

Choice A and C are incorrect as they include the statement that fewer transport proteins are present in the cell membranes of larger cells. Choice B is incorrect as it does not include the statement that increases in cytoplasmic volume increase metabolic demands

Explanation:
Antagonistic muscles in the upper leg of crickets allow a high power output to be generated (Choice D). Strong tendons (Choice A) and a strong exoskeleton (Choice B) are necessary for movement, but do not contribute directly when generating the power that allows significant height to be gained during jumping. Crickets do not have synovial joints (Choice C).