Explanation:
Cell respiration is the controlled release of energy in the form of adenosine triphosphate (ATP) from organic compounds. Cell respiration occurs either in the presence of oxygen or in the absence of oxygen. In the presence of oxygen, the process is known as aerobic cell respiration. In the absence of oxygen, the process is known as anaerobic cell respiration (Choice A).

Anaerobic cell respiration produces a smaller yield of ATP from glucose which is 2 ATP molecules, compared to aerobic cell respiration’s larger yield of ATP, which is approximately 38 ATP molecules.

This is because aerobic cell respiration undergoes the complete metabolic pathway of cellular respiration which involves the reaction of organic compounds such as glucose, lipids or proteins (Choice C) in the presence of oxygen to produce carbon dioxide, water and a large yield of ATP.

On the other hand, anaerobic cell respiration only undergoes glycolysis, the first stage of the metabolic pathway of cell respiration. This involves the incomplete breakdown of glucose in the absence of oxygen to produce lactate, which is also known as lactic acid (Choice D).

Explanation:
Since the experiment is about testing the temperature; the temperature would be the independent variable, not the controlled variable. A water bath would be used in this experiment to set up different increments of the independent variable.

When investigating the effect of temperature on photosynthesis, the other limiting factors (concentration of carbon dioxide and light intensity) must be controlled. The light intensity can be controlled by placing the test tube containing the Elodea at a constant distance from the same light source for each trial (Choice C) to make sure that the light intensity is the same for all trials.

Using the same volume and concentration of sodium hydrogen carbonate solution (Choice B and Choice D)ensures that the source of carbon dioxide is controlled, and it is not a limiting factor.

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:
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:
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:
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:
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:
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 - 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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
Autotrophs are producers and form the base of food chains. They carry out photosynthesis and get their energy from the Sun.

The most abundant organisms (Choice A) are usually the producers but there are exceptions. Energy always enters the food chain via the autotrophs, not consumers (Choice C).

The flow of energy (Choice D) is from producers to primary to secondary to tertiary consumers.

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.

Individuals of the same species competing for resources (Choice B) is ‘intraspecific Competition.’ Choice A refers to predator-prey interactions and is not any type of competition. Individuals of different species cooperating for limited resources (Choice D) describes a mutualistic relationship, not a competitive one.

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.