Explanation:
Cells are the basic structural and functional units of life. They are the fundamental building blocks of all living organisms. Tissues are groups of specialised cells that work together to perform a specific function. Different types of tissues combine to form organs. Organs are composed of multiple tissues that work together to carry out complex functions. Organs have specific roles within the body. Organ systems are groups of organs that collaborate to perform broader functions necessary for the survival of the organism. Organism refers to the complete living individual made up of various organ systems working together. Therefore Choice B is correct.

Choices A, C and D are all in the incorrect order.

Explanation:
In glycolysis (Choice A), glucose is broken down into pyruvate and this happens in the cytoplasm. Glycolysis is incorrect because pyruvate is only produced at the end of glycolysis and is not converted to acetyl CoA.

Pyruvate produced during glycolysis enters the mitochondria where it is converted to acetyl CoA during the link reaction. (Choice B)

The Link reaction (Choice B) is the reaction that bridges glycolysis with the next stage which is the Krebs cycle (Choice C). Hence, the Krebs cycle is incorrect because acetyl CoA is the reactant and needs to be produced prior to entering the Krebs cycle.

The stage after the Krebs cycle is known as oxidative phosphorylation (Choice D) which involves the synthesis of ATP.

Explanation:
Both metabolic pathways are catalysed by a series of different enzymes. Pathway 1 proceeds in a linear manner, and the end product is D. Pathway 2 is a cycle where the various products, such as A, are constantly regenerated.
Pathway 1 is a chain reaction and Pathway 2 is a cyclical reaction, so Choices A and D are not correct.
The end product for Pathway 1 is D, and the products keep cycling in Pathway 2, so Choice C is not correct.

Explanation:
Choice C is correct because smallpox was the first human disease eradicated by vaccination. Choice A is incorrect because polio has not been fully eradicated. Choice B is incorrect because monkeypox has not been eradicated. Choice D is incorrect because there is no vaccine for bubonic plague.

Explanation:
A second infection by a pathogen triggers a much faster and more potent immune response, resulting in the production of greater levels of antibodies (Choice B), when compared to primary infection. Primary infection causes a smaller increase in antibody numbers; this is represented by Y (Choice A). Infection by a different pathogen (Choice C) would cause a raise in antibody numbers similar to levels in point Y. Antibiotics do not increase antibody numbers (Choice D).

Explanation:
The active site of an enzyme is specific to a particular substrate. All other statements are true (Choices A, C and D).

Explanation:
Photosynthesis (Choice B) is the process by which carbon dioxide in the air is converted to carbon compounds in green plants.

Respiration releases carbon dioxide (Choice A), and decomposition by decomposers (Choice C) also releases carbon dioxide. Transpiration is the process by which water is drawn up the stem of a plant to the leaves where it evaporates (Choice D) and is not involved directly in the carbon cycle.

Explanation:
Almost all enzymes are globular proteins and differ from fibrous proteins in that they are sensitive to pH and temperature and are mostly water soluble.

Fibrous proteins (Choice A), unlike globular proteins, are long and narrow, less sensitive to changes in pH and temperature and are generally insoluble in water. Enzymes are not lipids (Choices B, D). Enzymes tend to be hydrophilic, not hydrophobic since they are mostly soluble in water.

Explanation:
A respirometer is a device that is used to measure the rate of respiration. A basic feature of a respirometer is a sealed container containing the living organism and an alkaline substance such as soda-lime (Choice A) or potassium hydroxide to absorb the carbon dioxide gas, which is the product of respiration.

The rate of respiration is measured by a reduction in the volume of oxygen due to the oxygen consumed by the living organism. The reduction in the volume of oxygen inside the sealed container causes a reduction in pressure inside the container. This causes the syringe to move which is how oxygen consumption is measured (Choice B). The rate of respiration can then be calculated based on the amount of oxygen consumed over a period of time.

An oxygen gas sensor (Choice C) can also be used to measure the reduction in the amount of oxygen. However, the experimental setup for this question does not include a sealed bio chamber bottle that is designed to fit the gas sensor probe. Since this experimental setup used a bung to seal the container, removing it to place an oxygen gas sensor probe inside the flask will not provide an accurate measurement of the amount of oxygen consumed.

When using a respirometer, the temperature is a controlled variable and should be kept constant (Choice D) to avoid changes to the volume of oxygen gas. Temperature also affects the rate of respiration. There should not be more than one independent variable being tested in an experimental setup.

Explanation:
Neonicotinoids bind irreversibly to acetylcholine receptors at cholinergic synapses so that acetylcholine (a neurotransmitter) is unable to bind and an action potential cannot be generated.
Choices B, C and D are incorrect as they do not describe how neonicotinoids work.

Explanation:
Letter X indicates the cell body, which contains the cytoplasm and the nucleus. Choice A is correct.

An axon is a long, thin projection of a neuron that carries action potentials away from the cell body, Choice B is incorrect. Dendrites are multiple specialised extensions branching from a neuron’s cell body or dendron, responsible for receiving incoming signals from other neurons or sensory receptors, Choice C is incorrect. Nerve fibres are a general term for any long, slender projection from a cell body that is capable of transmitting electrical signals - it can be an axon or dendron, Choice D is incorrect.

Explanation:
Facilitated diffusion is a passive process that allows the movement of molecules across a cell membrane with the help of transport proteins. It does not require energy input (ATP) because molecules move down their concentration gradient. Therefore Choice B is correct.

Sodium-potassium pumps (Choice A) actively transport sodium ions out of cells and potassium ions into cells against their concentration gradients. This process requires energy in the form of ATP. Endocytosis (Choice C) is an active process by which cells engulf substances by invagination of the cell membrane to form a vesicle around them. This process requires energy in the form of ATP. Anabolic reactions (Choice D) involve the synthesis of complex molecules from more simple ones. These reactions typically require energy input in the form of ATP.

Explanation:
Choice B is correct because a protein called testis determining factor (TDF) stimulates the development of embryonic gonads as testes. Testosterone causes the development of the testes (Choice A), stimulates sperm production (Choice C) and stimulates the development of secondary male characteristics (Choice D).

Explanation:
Choice B is correct because in phototropism auxin efflux pumps move auxin to the shady side of the stem, which stimulates growth and results in the bending of the stem towards the light source. Choice A is incorrect because auxin moves downwards in stems. Choice C is incorrect because auxin efflux pumps move auxin to the shady side of a stem. Choice D is incorrect because auxin does not move into flowers.

Explanation:
Choice A – Catabolic reactions involve the breakdown of large molecules into smaller molecules.

Choice B – Fermentation refers to anaerobic respiration which occurs in the cytoplasm.

Choice C - Anabolic reactions build complex compounds from simpler molecules. In the case of photosynthesis, the reactants carbon dioxide and water are turned into glucose and oxygen gas.

Choice D – Hydrolysis is an example of a catabolic reaction which involves the splitting of water.

Explanation:
When organisms respire, they lose energy in the form of heat. This form of energy cannot be recovered and is finally lost from the system.

Initially, during photosynthesis, energy is captured from light (Choice A). Carbon dioxide is not a form of energy (Choice C), and chemical energy (Choice D) is held in the bonds of organic molecules made during photosynthesis.

Explanation:
Saltatory conduction is when electrical impulses jump between nodes of Ranvier (the gaps between sections of the myelin sheath that surrounds axons).
Choice B is incorrect because it is a description of synaptic transmission.
Choice C is incorrect because it is a description of how the resting potential is maintained.
Choice D is incorrect as it describes how an action potential travels down an unmyelinated neuron.

Explanation:
Choice A is correct because zoonotic diseases are diseases that can be transmitted from one species to another, such as from chickens to humans. Choice B is incorrect because zoonotic diseases do not only affect domesticated animals. Choice C is incorrect because zoonotic diseases are not only caused by viruses. Choice D is incorrect because zoonotic diseases do not only affect humans.

Explanation:
A positive feedback mechanism is a physiological process in which a response amplifies the initial stimulus, leading to an accelerated and often self-reinforcing outcome. The dilation of the cervix during childbirth stimulates the release of the hormone oxytocin. Oxytocin then brings about further uterine contractions, which brings about further cervix dilation. This is, therefore, an example of positive feedback, and Choice D is correct.

A negative feedback mechanism is a regulatory mechanism in which a response counteracts and reverses the initial stimulus, maintaining stability and homeostasis in the system. Choices A, B, and C are all examples of negative feedback mechanisms.

Explanation:
Choice C is correct, as ATP is short for adenosine triphosphate. As the name tells us, it has three phosphate groups, represented by the three circles attached to the central ribose sugar. The rectangle represents the adenine.

Choice A is a cholesterol molecule, Choice B is a glucose molecule, and Choice D is a molecule of ADP (adenosine diphosphate), which is the molecule that results when ATP loses its third phosphate molecule, releasing energy.

Explanation:
-50mV is the threshold potential that must be reached for voltage-gated sodium channels to open.
Choice A is incorrect, as -70 mV is the resting potential of a neuron. Choice C is incorrect as at +30 mV, voltage-gated potassium channels are triggered to open. Choice D is incorrect as at 0mV the voltage-gated sodium channels are already open.

Explanation:
Photolysis is the splitting of water molecules in the presence of light to produce electrons, hydrogen ions and oxygen. This is part of the light-dependent reaction of photosynthesis.

Chemiosmosis (Choice B) happens in both photosynthesis and cellular respiration. In both processes, ATP is formed from ADP and inorganic phosphate. Hence, the products are not electrons, hydrogen ions and oxygen molecules.

The Calvin cycle (Choice C) is part of the light-independent reaction of photosynthesis. It produces carbon compounds and does not require light.

The electron transport chain (Choice D) is a component of both photosynthesis and cellular respiration. In photosynthesis, it takes place after photolysis which is when water molecules are split, producing electrons, hydrogen ions and oxygen. Photolysis needs to take place first before these electrons can move down the electron transport chain.

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:
Choice A is correct because GTP, guanosine triphosphate, needs to bind with the G protein and replace the GDP to activate the G protein.

Choice C is incorrect because GDP is attached to an inactive G protein, which is then replaced by GTP to activate the G protein. Choices B and D are incorrect because cAMP is the secondary messenger that gets formed from ATP in reactions that take place after the G protein is activated.

Explanation:
Choice D is correct because the gland X is the pineal gland and it produces melatonin. Choice A is incorrect because leptin is produced by adipose tissue. Choice B is incorrect because thyroxine is produced by the thyroid gland. Choice C is incorrect because progesterone is produced by ovaries.