Explanation:
Oxidative decarboxylation involves oxidation and decarboxylation. During the link reaction, the oxidative decarboxylation of pyruvate produces a two-carbon acetyl group.

The phosphorylation of glucose (Choice B) occurs during glycolysis before the oxidative decarboxylation of pyruvate and not after. Phosphorylation is a reaction where a phosphate group is added which makes the molecule less stable.

In the electron transport chain, both NADH and FADH22 release their hydrogens (protons) and electrons which leads to the transport of electrons and movement of these protons (Choice C). Electron transport and proton movement are some of the stages of oxidative decarboxylation of pyruvate, hence it does not happen right after.

Hydrogen ions are then used to power ATP synthase, producing ATP which is the final stage of cellular respiration (Choice D). Hence it does not happen right after the oxidative decarboxylation of pyruvate.

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:
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:
In glycolysis (Choice A), glucose is broken down into pyruvate and this happens in the cytoplasm. Glycolysis is incorrect because pyruvate is only produced at the end of glycolysis and is not converted to acetyl CoA.

Pyruvate produced during glycolysis enters the mitochondria where it is converted to acetyl CoA during the link reaction. (Choice B)

The Link reaction (Choice B) is the reaction that bridges glycolysis with the next stage which is the Krebs cycle (Choice C). Hence, the Krebs cycle is incorrect because acetyl CoA is the reactant and needs to be produced prior to entering the Krebs cycle.

The stage after the Krebs cycle is known as oxidative phosphorylation (Choice D) which involves the synthesis of ATP.

Explanation:
The all-or-none law states that an action potential will only be transmitted if a threshold potential is reached, and the size of the action potential does not vary. Choice A is correct. Choice B is incorrect as if the threshold potential isn’t reached, then no action potential is triggered. Choice C is incorrect because if the threshold potential is not reached, then an action potential is not triggered and so neurotransmitters are not released at the synaptic cleft. Choice D is incorrect as an action potential only moves in one direction.

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:
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:
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:
Choice D is correct because cAMP binds to inactive PKA after being formed to activate PKA.

Choice A is incorrect because the enzyme adenyl cyclase (AC) acts on ATP to form cAMP. This has to take place first to form cAMP. Choices B and C are incorrect because these two reactions take place before cAMP is formed. A ligand such as epinephrine binds to the G protein-coupled receptor, resulting in guanosine triphosphate (GTP) binding to the G protein to activate it.

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:
Choice B is correct because Rubisco is the name of the enzyme which is responsible for the fixation of carbon during photosynthesis. Choice A is incorrect as rhodopsin is a pigment found in the retina which is responsible for detecting light . Choices C and D are incorrect as neither are enzymes, with collagen being a structural component of tissues such as skin and insulin being a hormone responsible for regulating blood glucose levels.

Explanation:
Saltatory conduction is when electrical impulses jump between nodes of Ranvier (the gaps between sections of the myelin sheath that surrounds axons).
Choice B is incorrect because it is a description of synaptic transmission.
Choice C is incorrect because it is a description of how the resting potential is maintained.
Choice D is incorrect as it describes how an action potential travels down an unmyelinated neuron.

Explanation:
The active site of an enzyme is specific to a particular substrate. All other statements are true (Choices A, C and D).

Explanation:
Both, the brewing of beer and baking of bread, involve anaerobic yeast fermentation. In the brewing of beer, yeast feeds on glucose and respires anaerobically to produce ethanol, carbon dioxide and energy. The ethanol produced is the alcohol found in beer. Similarly, with the baking of bread, yeast respires anaerobically to produce ethanol, carbon dioxide and energy. However, the ethanol that is produced evaporates during baking.

Carbon dioxide (Choice A) is a product present in both the brewing of beer and the baking of bread. Carbon dioxide is soluble in beer and is found in small amounts. It is responsible for the rising of the bread.

Likewise, water (Choice D) is also a substance present in both the brewing of beer and the baking of bread. In the brewing of beer and in the baking of bread, water is added to the mixture.

In addition to yeast fermentation, anaerobic respiration can also occur in humans and other animals. This is known as lactic acid fermentation. Glucose is not broken down completely and forms lactic acid (Choice B) in the absence of oxygen.

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:
The mass of enzyme added remains the same throughout because the enzyme acts as a catalyst and does not get used up during the reaction. All other choices (Choices A, B and C) are used in obtaining the rate of an enzyme-catalysed reaction since they involve measuring the substrate used or product formed over a specified amount of time.

Explanation:
In the light-dependent reaction, NADP is the final electron acceptor in Photosystem I and this is reduced to form NADPH.

CO22 is fixed by the enzyme Rubisco and is not an electron acceptor (Choice A).

ATP is synthesized by ATP synthase using the proton gradient in the thylakoids and is not an electron acceptor (Choice C).

Oxygen (Choice B) is the terminal electron acceptor in aerobic cell respiration, but not in photosynthesis.

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:
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:
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:
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 D is correct because a tropism is any growth response of a plant towards or away from a stimulus. Choice A is incorrect because this is the definition for only one type of tropism, geotropism. Choice B is incorrect because day length does not cause a plant to grow in one direction. Choice C is incorrect because this is a specific definition for phototropism whereas tropism in general is a growth response towards or away from a stimulus, and not only light.

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:
Choice B is correct because a protein called testis determining factor (TDF) stimulates the development of embryonic gonads as testes. Testosterone causes the development of the testes (Choice A), stimulates sperm production (Choice C) and stimulates the development of secondary male characteristics (Choice D).

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.