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:
Okapi is a herbivore (II) because it only eats plants. Okapi is a species (III) since it can interbreed and produce fertile offspring.

They are not a hybrid of a giraffe and a zebra (I), even though they look like one.

Explanation:
Choice C is correct because antigens are chemicals that stimulate the production of antibodies. Choice A is incorrect because B lymphocytes produce antibodies, not antigens. Choice B is a description of antibodies, which binds to antigens so is incorrect. Choice D is incorrect because hybridoma cells produce antibodies, not antigens.

Explanation:
Depolarisation of the presynaptic membrane (Statement II) and the resulting influx of calcium ions into the presynaptic neuron (Statement III) cause the exocytosis (release) of neurotransmitters at the presynaptic membrane.

Statement I is false, as the postsynaptic membrane receives neurotransmitters that are released from the presynaptic membrane. Choices A, C and D are incorrect.

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:
As energy moves from producers to consumers, only about 10% is transferred to the next trophic level. So only about 0.1 % of the energy produced by the producers reaches the tertiary consumers. All other choices (Choice A, B, C) are not correct. Looking at the values in the diagram, producers start with 20 000 units of energy and tertiary consumers receive only 25 units. 25 divided by 20 000 is approximately 0.1%.

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:
Heat and pressure from the Earth’s crust decompose the remains of dead plants and animals over millions of years to form oil, natural gas or coal (fossil fuels).

Respiration (Choice B) takes place in a relatively short time as does photosynthesis which requires light to synthesize organic compounds (Choice C). Forest fires (Choice D) often occur naturally and release carbon dioxide into the atmosphere. Global warming has increased the number of wildfires.

Explanation:
Enclosed greenhouse experiments allow for wavelengths of light to be controlled by exposing the plants to different colours of light. By adjusting the spectrum of light, researchers can investigate the isolated effects of distinct wavelengths on plant responses to elevated carbon dioxide levels. Such control is typically unattainable in open-air experiments like the free-air carbon dioxide enrichment (FACE) system, where natural light conditions predominate. Choice A is correct.

Choice B is incorrect as an enclosed greenhouse space does not mimic a natural ecosystem as it is a man-made enclosed structure. Choice C is incorrect, as large trees cannot fit or grow freely in a greenhouse. Choice D is incorrect as in an enclosed greenhouse, water can be controlled, mimicking rainfall.

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:
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:
Diversity indices are used to measure the diversity of organisms in an area (Choice A). A t-test (Choice B) is used to see if there is a significant difference between the means of two groups. Chi-square analysis (Choice C) can be used to check for the association of two species after collecting data on the presence or absence of either or both in defined areas. More generally, Chi-square analysis is used to determine if there is a significant difference between observed and expected. Frequency found in quadrats (Choice D) records how frequently one or more species are found in quadrats and is not a statistical test.

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:
Thin-layer chromatography is a method that can be used to separate pigments extracted from a leaf. Paper chromatography uses paper with a line drawn approximately 1 cm from one end, which is called the baseline (Choice D). This is where a drop of leaf extract is placed. Then the paper is immersed in a solvent with the level of solvent being right below the baseline. This solvent will then move up the paper to separate the pigments found in the leaf extract.

The coloured spots show the distance moved by each pigment (Choice C). The solvent will then move further up and will eventually stop moving. The mark where the solvent stops is known as the solvent front and shows the distance moved by the solvent (Choice B).

In order to find the Rf value for a given pigment, the distance moved by the pigment is divided by the distance moved by the solvent (Choice A).

Explanation:
Choice A is correct because all statements are true. Plasma cells are clones of B lymphocytes, produce large numbers of antibodies and have extensive rough endoplasmic reticulum.

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.

Explanation:
Photosynthesis is the production of carbon compounds such as glucose using light energy. Oxygen is produced as a waste product which then diffuses out of the cell. Plants use smaller molecules such as carbon dioxide and water to build larger molecules like glucose. Hence, photosynthesis is an anabolic reaction. An anabolic reaction requires energy to build larger molecules. Photosynthesis takes in energy so is known as an endothermic reaction.

Cell respiration (Choices B and D) is the production of ATP, carbon dioxide and water using glucose and oxygen. Glucose is broken down to form smaller molecules so it is categorized as a catabolic reaction. A catabolic reaction releases energy when larger molecules are broken down to form smaller molecules. Reactions that release energy are known as exothermic reactions.

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:
Aquatic ecosystems take in inorganic carbon when carbon dioxide dissolves in water. Dissolved carbon dioxide can combine with water to form carbonic acid (H22CO33) which dissociates into hydrogen ions (H

) and hydrogen carbonate ions (HCO33

). So, inorganic carbon is present as both dissolved carbon dioxide and hydrogen carbonate ions in aquatic ecosystems.

Carbon dioxide, not carbon monoxide (Choice B) is the form of inorganic carbon that autotrophs can use. Methane (Choice C and D) is a form of organic carbon, not inorganic carbon.

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:
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:
Invasive species are introduced deliberately or accidentally to new areas outside of their native range, and so have no natural predators. An example would be the zebra mussel which originates from the lakes of Russia and Ukraine. It was accidentally introduced to the Great Lakes of the US through the discharge of a contaminated cargo ship's ballast water. Invasive species have been recognised as a major threat to biodiversity and ecosystems worldwide. They can disrupt native ecosystems, outcompete native species for resources, and lead to declines in native populations. Therefore Choice C is correct. While it is true that some invasive species have evolved and adapted to specific conditions (Choice A) in their native range, this characteristic is also true of native species. Invasive species often have a native region (Choice B), as do native species. Also, some invasive species have a broad native distribution, and when they are introduced to new areas, they can spread widely. Invasive species can be influenced by environmental changes (Choice D), but native species can also be affected by environmental changes, and vulnerability to these changes can vary widely among both invasive and native species.

Explanation:
Choice B is correct because vaccinations involve the deliberate introduction of antigens, which have been made harmless, to stimulate the production of antibodies and memory cells for long-term immunity. They do not contribute to antibiotic resistance.
Increased and incorrect use of antibiotics contributes to antibiotic resistance.
Choice A increases the use of antibiotics in raising livestock.
Choice C is an incorrect use of antibiotics because they are ineffective against viruses.
Choice D can lead to the development of antibiotic resistance because patients who fail to complete a course of antibiotics may not completely eliminate the infection and instead allow the survival of resistant bacteria.

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:
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.