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 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:
All the statements above are true. In most ecosystems, light energy from the Sun is captured by producers via photosynthesis and transferred to consumers through feeding. As organisms respire, they lose energy in the form of heat which cannot be reused by organisms. There is a constant input of energy from the Sun.

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:
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​:
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:
The length of food chains tends to be shorter than 6 organisms, even including parasites and detritivores. When energy is passed from one organism to the next, most of the energy is generally lost as heat which means that less and less energy is available to higher trophic levels.

All other statements are true.

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​:
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​:
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​:
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:
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​:
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​:
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:
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​:
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​:
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​:
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:
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​:
Statements I and III are correct and describe how enzymes interact with their specific substrates. Statement II is incorrect because, in many catabolic reactions, the substrate is larger than the enzyme.

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​:
Aquatic ecosystems take in inorganic carbon when carbon dioxide dissolves in water. Dissolved carbon dioxide can combine with water to form carbonic acid (H22​CO33​) 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​:
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.