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​:
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​:
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 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​:
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​:
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:
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​:
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:
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​:
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​:
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 - 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​:
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:
Choice C is correct because P is pointing to a disulfide bond, which can only be formed between R groups of amino acids and is a feature of the tertiary structure. The primary structure (Choice A) is the sequence of amino acids in a polypeptide chain. The secondary structure (Choice B) is the formation of alpha-helices or beta-pleated sheets through hydrogen bonding between carboxyl and amino groups of different amino acids. The quaternary structure (Choice D) exists in proteins with more than one polypeptide chain.

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​:
Blood plasma (Choice D) is the liquid component of blood and is composed of water which contains proteins, ions, and dissolved nutrients.
Red blood cells (Choice A) transport oxygen.
Platelets (Choice C) are responsible for the process of blood clotting.
White blood cells (Choice B) are part of the immune system.

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​:
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:
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:
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:
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​:
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.