Explanation:
The bond formed between two glucose molecules to form maltose is an alpha 1-4 linkage. This is a covalent bond between two alpha glucose molecules, where the carbon #1 of one of the glucose molecules forms a bond with the carbon #4 of the other glucose molecule. Choice C is correct.

A hydrogen bond (Choice A) is a weak electrostatic attraction between a hydrogen atom that is covalently bonded to a highly electronegative atom and another electronegative atom in a different molecule or region of the same molecule. For example, between two water molecules. Peptide bonds (Choice B) are covenant bonds that hold amino acids together in polypeptide chains, and phosphodiester bonds (Choice D) are covalent bonds between the ribose sugars and phosphate groups, forming the backbone of DNA and RNA. Choices A, B and D are incorrect.

Explanation:
Insulin is a hormone whose function is to maintain blood glucose levels (Choice A). Rhodopsin (Choice B) is a pigment responsible for the detection of light. Collagen (Choice C) is a structural protein and Rubisco (Choice D) is an enzyme.

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:
An ecosystem refers to an area where organisms interact with each other and with the physical environment.

A habitat (Choice A) refers to the environment in which a species normally lives. A population (Choice C) is a group of organisms of the same species living in the same area at the same time which can interbreed. A community (Choice D) is a group of populations living and interacting with each other in the same habitat.

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 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 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​:
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​:
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​:
Obligate anaerobes are single-celled organisms that will not survive if oxygen is present. Facultative anaerobes are organisms that can either respire aerobically or anaerobically. Obligate aerobes can only respire if oxygen is present and cannot survive in conditions low in oxygen. Therefore Choice A is correct.

Choices B and D are incorrect because obligate anaerobes cannot respire when oxygen is present. Choice C is incorrect as obligate anaerobes require anoxic conditions, and obligate aerobes cannot carry out anaerobic respiration.

Explanation​:
Amino acids (Choice B) can form polypeptides through the formation of peptide bonds as a result of condensation reactions. Fatty acids (Choice A) are involved in the formation of lipids and are not monomers. Proteins (Choice C) are composed of one or more polypeptides and are polymers. Nucleotides (Choice D) are the building blocks of DNA and RNA.

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:
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 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​:
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).

Explanation​:
Choice D is correct because zebras run away rather than towards predators. Choices A, B and C are incorrect because zebras move to find mates, escape grassland fires and find sources of food.

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:
Choice B is correct because disease is a living factor and is, therefore, a biotic factor, not an abiotic one. Sunlight (Choice A), precipitation (Choice C), and pH (Choice D) are all non-living factors and are therefore abiotic.

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​:
Autotrophs are producers (Choice A, B). They are self-feeding whereas heterotrophs are organisms that gain nutrition by feeding on another organisms (Choice C, D). Detritivores consume dead organic matter by ingestion (Choice C) whereas saprotrophs break down food outside their bodies by secreting enzymes into the environment.

Explanation​:
Choice A - There are still stem cells that can be found in the adult body. For example, stem cells are present in the bone marrow, skin, and liver.

Choice B - The foetal stage of development happens from the ninth week after conception until birth. In this stage, the organs have begun to form, and these developing organs come from differentiated stem cells.

Choice C - Stem cells are characterised by their capacity to divide and differentiate. These cells are similar to a blank canvas with the possibility of becoming any type of cell.

Choice D - Stem cells are yet to undergo specialisation through the process of differentiation.

Explanation:
Sieve plates (Statement I) and plasmodesmata (Statement II) are features found in phloem. Sieve plates possess pores which allow continual flow of sap through the sieve tubes. Plasmodesmata are small channels which connect the sieve tube elements to the adjacent companion cells. A high lignin content (Statement III) is found in xylem vessels. It provides support to withstand hydrostatic pressure, and is also impermeable to water.

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 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​:
Regular exercise prevents the buildup of fatty plaque in the coronary arteries thereby preventing heart disease (Choice D). Some of the factors that cause the buildup of fatty plaque and occlusion of the arteries causing chest pain are high blood pressure (Choice A), high blood sugar due to diabetes (Choice B) and some genetic factors (Choice C).