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:
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 B is correct because insect-pollinated flowers have coloured petals (Statement II) to attract pollinators and a nectary (Statement I) to reward them, whereas all flowers have a stigma (Statement III). Choice A is incorrect because both statements I and II are correct. Choices C and D are incorrect because the stigma is not adapted for a mutualistic relationship with insects. Only the flower benefits from the presence of a stigma.

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 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 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:
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 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:
Reaction X represents the synthesis of a more complex compound from simpler molecules and therefore is a depiction of an anabolic reaction.

Reaction X cannot be catabolic (Choice A) since a more complex molecule is produced. Catabolism results in simpler products compared to the reactants. Reaction X cannot represent all metabolic reactions (Choice C) since metabolic reactions include both anabolic and catabolic reactions while reaction X represents only anabolic reactions. Reaction Y represents a catabolic reaction and not an anabolic reaction (Choice D).

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:
Calories (Choice A) and Kilocalories (Choice B) are measures for energy but do not include area and time which is how productivity is measured in an ecosystem. kJm−2−2 (Choice C) does include the area but not time. To see energy values over a specified time, usually a year, the units kJm−2−2y−1−1 are used.

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:
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:
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:
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 denatured enzyme has lost its tertiary structure. It is no longer able to function and cannot catalyze reactions.
The active site will not be able to bind to the substrate in most cases (Choice A).
Usually, the sequence of amino acids is not altered. A denatured enzyme has had its three-dimensional structure altered (Choice C).
High temperatures, specifically temperatures above the optimum temperature for a given enzyme cause denaturation and the enzyme can no longer catalyze reactions (Choice D).

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:
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:
The data collected for recording the presence and absence of two plants can be used in a chi-squared test to determine if the two plants are associated. This is a relevant statistical method.

The biodiversity found in an area (Choice A) is usually determined by using Simpson’s Diversity Index or other similar calculations. The chi-squared test cannot be used to find the range (Choice B) for heights of trees or predict the probability of finding certain plants (Choice C) in an area.

Explanation:
Neurotransmitters travel freely without energy from an area of high concentration at the presynaptic membrane to a low concentration at the postsynaptic membrane via simple diffusion, Choice C is correct.

Choice A is incorrect, as neurotransmitters do not use a channel to diffuse across the synapse. Choice B is incorrect, as neurotransmitters do not travel against the concentration gradient using energy across the synapse. Choice D is incorrect as although neurotransmitters are released from the presynaptic membrane via exocytosis, they do not travel across the synapse using this method.

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:
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:
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.