Explanation​:
Choice D is correct because a tropism is any growth response of a plant towards or away from a stimulus. Choice A is incorrect because this is the definition for only one type of tropism, geotropism. Choice B is incorrect because day length does not cause a plant to grow in one direction. Choice C is incorrect because this is a specific definition for phototropism whereas tropism in general is a growth response towards or away from a stimulus, and not only light.

Explanation​:
Inhibitors prevent enzymes from catalysing reactions and therefore decrease the rate of enzyme catalysed reactions.
Inhibitors do not activate enzymes, thereby increasing the rate of reaction (Choice A).
Inhibitors do not help the substrate bind to the active site (Choice B). In fact they usually prevent the substrate from binding to the active site.
Inhibitors decrease the rate of reaction, they do not speed it up (Choice C).

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​:
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​:
Cell respiration is the process where energy is released from organic compounds to form adenosine triphosphate (ATP). ATP consists of the nitrogenous base adenine, a ribose sugar and three phosphate groups. These three components contain the elements oxygen, hydrogen, phosphorus, carbon and nitrogen (Choice D). Even though ATP is made up of these five elements, they are not products of hydrolysis.

ATP is the immediately available source of energy in cells and fuels cell processes. This takes place when ATP undergoes hydrolysis and the energy which is stored in the phosphate bond of ATP is released. The phosphate bonds that are broken lead to the formation of adenosine diphosphate (ADP), inorganic phosphate and a release of energy.

Hydrolysis is a catabolic reaction of breaking down large molecules into small molecules. Water is required to split apart ATP, hence both water and ATP are the reactants in a hydrolysis reaction and not products (Choice C).

The main stages of cellular respiration are glycolysis, the Krebs cycle and the electron transport chain. In glycolysis, glucose is broken down to pyruvate (Choice A) which then moves on to the Krebs cycle and electron transport chain before generating a high yield of 38 ATP.

Explanation​:
ATP from cell respiration is an immediate source of energy for metabolic processes.

Neurons transmit information in the form of electrical impulses (Statement I). This transmission can only happen when there is a difference in concentrations of Na

and K

ions across the axonal membrane of a neuron. Energy in the form of ATP is required for the Na

/K

pump to restore the ionic balance after the voltage-gated response.

Osmosis (Statement II) does not require ATP. It is a passive transport process where water can move through a partially permeable membrane from an area of lower solute concentration to an area of higher solute concentration.

The condensation reaction of a polypeptide (Statement III) is the joining of amino acids together to form a polypeptide. It is an anabolic reaction where ATP is required to join amino acids together to form a peptide bond, and water is produced.

Explanation​:
Choice A - Cells of multicellular organisms have different functions. They interact with one another to perform more complex functions such as responding to the environment, movement and homeostasis.

Choice B - Cells of multicellular organisms communicate with each other. These cells communicate to coordinate the activities of organs, tissues and other cells.

Choice C - Cells interact with one another forming complex structures and functions that any one cell type alone could not perform

Choice D - Cells have different structures based on the cell’s specialised roles.

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:
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:
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​:
The digestion of starch is a catabolic reaction where starch molecules are broken down into maltose by hydrolysis.

Peptide formation from amino acids (Choice A), starch synthesis from glucose (Choice B), and DNA synthesis from nucleotides (Choice D) are all examples of anabolic reactions.

Explanation:
The statement for Choice B is incorrect, because longitudinal muscle does not stop the bolus from moving backwards, this is the role of the circular muscles. Choice A, Choice C and Choice D are correct statements because the longitudinal and circular muscles do work together, longitudinal muscle does move the bolus along the alimentary canal and the bolus is mixed with enzymes as a result of peristalsis.

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:
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​:
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​:
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 - Antibodies are globular proteins synthesized by plasma B cells. The genes associated with antibody synthesis are expressed in plasma B cells.

Choice B - Macrophages do not synthesize antibodies and therefore do not express these genes. Macrophages are large phagocytic cells and present antigens to helper T cells.

Choice C - Helper T cells do not synthesize antibodies. They stimulate B cells to divide by mitosis to produce plasma B cells and memory B cells.

Choice D - Red blood cells do not have a nucleus and therefore do not have the genes for antibody synthesis.

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

Explanation​:
In glycolysis, ATP is first needed to supply inorganic phosphate, which is attached to the glucose molecule to form a phosphorylated sugar molecule, fructose 6-phosphate. ATP is needed again to supply a second inorganic phosphate which is attached to this already phosphorylated sugar molecule to form fructose 1,6-bisphosphate.

Explanation​:
Glycolysis occurs in the cytoplasm of the cell. Then, in aerobic respiration, the product of glycolysis (pyruvate), then is transported into the mitochondrion, where it enters the link reaction. The link reaction takes place in the fluid part of the mitochondrion, the matrix. The product of the link reaction then enters the Krebs cycle, which also occurs in the matrix. The final stage, the electron transport chain, occurs in the membranes of the cristae. Choice B is, therefore, correct.

Choices A, C and D are incorrect as they give one or more incorrect locations.

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:
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:
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​:
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:
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.