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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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.

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:
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:
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:
The endocrine system (Statement II) is involved in the fight or flight response through the release of hormones from endocrine glands, such as adrenaline (epinephrine), from the adrenal glands. Adrenaline (epinephrine) is released into the bloodstream and travels throughout the body to target organs and tissues, preparing the body for immediate action. When adrenaline (epinephrine) reaches its target tissues it binds to specific transmembrane receptors on the surface of cells (Statement I). This binding triggers a cascade of intracellular events that ultimately lead to physiological changes associated with the fight or flight response, such as increased heart rate and dilated airways. The autonomic nervous system (Statement III) plays a central role in the fight or flight response. In a frightening situation, the nervous system is activated, leading to the release of adrenaline (epinephrine), increased heart rate, increased blood flow to muscles, and other physiological changes that prepare the body for a rapid response. Choice D is therefore correct.

Choices A, B and C are all incorrect as they do not include all three statements.

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:
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:
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:
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.