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:
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 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 A is the correct response because arteries are not non-elastic, instead they do have a degree of elasticity. Choices B, C and D all correctly match the structure and function of each blood vessel.

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:
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​:
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 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​:
The sinoatrial node is a region of specialized cardiac muscle cells found in the wall of the right atrium. The sinoatrial node acts as a pacemaker and is involved in controlling heart rate (Choice A).
The opening of the atrioventricular valves occurs when there is an increase in pressure inside the atria. Blood flows to the ventricles when these valves are open. This action does not control the heart rate (Choice B).
Pulmonary circulation is when blood flows into the lungs from the right ventricle and is returned to the left atrium after it is oxygenated, and does not control the heart rate (Choice C).
The opening of the semilunar valves occurs when the pressure in the ventricles increases (Choice D). This does not control heart rate.

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​:
Structure X is a peripheral protein that is attached to one surface of the cell membrane.

Protein channels span the width of membranes (Choice B) as do transmembrane proteins (Choice A). Cholesterol molecules do not have a globular structure (Choice D).

Explanation​:
Choice C is correct because Y is the nucleus and is an organelle, whereas X is the cytosol and not an organelle.

Choice A is incorrect because only X, the cytosol, is primarily composed of water and solutes, Y, the nucleus, primarily contains the DNA. Choice B is incorrect because Y, the nucleus, has a specialised function. Choice D is incorrect because Y, the nucleus, is not found in prokaryotes, but both X, the cytosol, and Y, the nucleus, are found in eukaryotes.

Explanation​:
Choice A - Cholesterol is positioned between the phospholipids and maintains the fluidity of the cell membrane.

Choice B - Integral Membrane Proteins are responsible for the transport of materials in and out of the cell as well as other functions such as cell-cell communication.

Choice C - Glycolipids allow cells to recognize each other.

Choice D - Peripheral membrane proteins are involved in maintaining the extracellular matrix and cytoskeleton, in cell-cell communication, and sometimes function as enzymes.

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​:
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).

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​:
Sucrose is actively loaded into phloem at sites called sources, which are regions of the plant where photosynthesis occurs (such as the leaves) or where nutrients are stored (such as in storage organs). Sucrose is unloaded from phloem tubes in sinks, which are parts of the plant that can’t produce organic compounds themselves, such as the roots. The movement of sucrose in the phloem is bidirectional, meaning it can be transported upwards or downwards, depending on the location of the sink. This relates to Choice A.

Choice B refers to sugar being transported from sink to the source which is incorrect. Choices C and D refer to sugar transport being down only, which is 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​:
Saprotrophs are decomposers that secrete digestive enzymes onto organic molecules and then absorb the digested nutrients. This is a form of extra-cellular nutrition. Fungi and certain bacteria are examples of saprotrophs. Woodlice or pill bugs are detritivores. Detritivores are decomposers, but they ingest the organic molecules before digesting them into smaller, soluble ones. Choice D is, therefore, correct. Mushrooms and yeast are fungi, and Bacillus subtilis is a bacterium. Therefore Choices A, B and C are all saprotrophs and therefore are incorrect.

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:
The release of Calcium ions from the sarcoplasmic reticulum initiates the process of muscle contraction (Choice A). Potassium ions (Choice B) and sodium ions (Choice C) are involved in nerve transmission and raising the membrane potential of muscle fibres to bring about contraction, but they do not bind to the sarcomere. Hydrogen ions (Choice D) do not diffuse from the sarcoplasmic reticulum.

Explanation​:
Choice B is correct because Rubisco is the name of the enzyme which is responsible for the fixation of carbon during photosynthesis. Choice A is incorrect as rhodopsin is a pigment found in the retina which is responsible for detecting light . Choices C and D are incorrect as neither are enzymes, with collagen being a structural component of tissues such as skin and insulin being a hormone responsible for regulating blood glucose levels.

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:
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.