Explanation​:
Choice A is correct because insulin is a peptide hormone, which is polar so cannot directly pass through the plasma membrane. Instead it binds to receptors in the plasma membrane which triggers intracellular signalling pathways.

Choices B, C and D are all incorrect, as they are all non-polar steroids so can diffuse through the plasma membrane and bind directly to receptors inside the cell, affecting gene expression.

Explanation:
For oxygen to diffuse into the blood, there must be a higher concentration of oxygen in the alveoli than in the blood (Choice D). This is because gases only diffuse down their concentration gradients.

Similarly, for carbon dioxide to diffuse into the alveoli, there should be a lower concentration of carbon dioxide in the alveoli (Choice C) and a higher concentration of carbon dioxide in the blood (Choice B).

Explanation​:
Amino acids (Choice B) can form polypeptides through the formation of peptide bonds as a result of condensation reactions. Fatty acids (Choice A) are involved in the formation of lipids and are not monomers. Proteins (Choice C) are composed of one or more polypeptides and are polymers. Nucleotides (Choice D) are the building blocks of DNA and RNA.

Explanation​:
A potometer is used to measure the rate of transpiration in a plant. When transpiration takes place, water loss occurs because water evaporates inside the leaves and then diffuses out of the leaves. The bubble in the capillary tube will move in the direction of the plant along with the water in the capillary tube which is being absorbed by the plant (Choice C).

Choice B is incorrect because the water and bubble are moving towards the plant, not away from it.

Choice A is incorrect because the water in the reservoir will stay at the same level. The reservoir contains a switch that is used to refill the capillary tube and push the bubble back to the start position. This is done at the end of the experiment to reset the apparatus for the next measurement.

Choice D is incorrect as the water level in the beaker will decrease as water enters the capillary tube and also because of evaporation from the beaker to the atmosphere.

Explanation:
Saprotrophs are decomposers that secrete digestive enzymes onto organic molecules and then absorb the digested nutrients. This is a form of extra-cellular nutrition. Fungi and certain bacteria are examples of saprotrophs. Woodlice or pill bugs are detritivores. Detritivores are decomposers, but they ingest the organic molecules before digesting them into smaller, soluble ones. Choice D is, therefore, correct. Mushrooms and yeast are fungi, and Bacillus subtilis is a bacterium. Therefore Choices A, B and C are all saprotrophs and therefore are incorrect.

Explanation​:
Choice D is correct because line transects can be used to show animal or plant distributions. Choices A, B and C are all factors that could be measured using different sensors that could provide meaning to plant or animal distributions.

Explanation​:
When two monosaccharides are joined together to form a disaccharide, water is produced, therefore it is a condensation reaction. Choice A is correct.

Choice B is incorrect as hydrolysis uses water to break bonds, in this case converting a disaccharide into a monosaccharides. Choice C is incorrect as catabolism breaks down large molecules into smaller molecules. Choice D is incorrect as oxidation means adding oxygen or losing electrons.

Explanation​:
Autotrophs are producers (Choice A) which synthesize their own organic compounds. Consumers gain their nutrition by feeding (Choice B) on other organisms. Detritivores consume dead organic matter (Choice C) by ingestion. Saprotrophs break down food outside their bodies (Choice D) by secreting enzymes and then ingesting the digested compounds.

Explanation​:
Sieve plates (Statement I) and plasmodesmata (Statement II) are features found in phloem. Sieve plates possess pores which allow continual flow of sap through the sieve tubes. Plasmodesmata are small channels which connect the sieve tube elements to the adjacent companion cells. A high lignin content (Statement III) is found in xylem vessels. It provides support to withstand hydrostatic pressure, and is also impermeable to water.

Explanation​:
Choice C – The statement is false. Phospholipids are a class of lipids which have a hydrophilic “head” and two hydrophobic “tails.” The heads contain a phosphate group and the two tails each contain one fatty acid.

Choice A, B, and D – These statements are all true.

Explanation​:
Veins carry deoxygenated blood from the body back to the heart. As muscles surrounding the veins contract, they push the blood towards the heart and venous valves open to allow the flow of blood. When the muscles relax, the valves close to prevent the blood from flowing backwards in response to gravity. So, venous valves help prevent the backflow of blood away from the heart (Choice B).

The relaxation of skeletal muscles decreases blood pressure in veins and does not play a role in preventing the backflow of blood in veins (Choice A). When the heart relaxes, this decreases blood pressure in arteries, it does not affect blood pressure in veins and plays no role in preventing the backflow of blood in veins (Choice C). Thin vessel walls are most exemplified in capillaries whose walls are one cell thick and allow exchange of substances. Thin walls play no role in preventing the backflow of blood (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​:
Choice D is correct because starch is made of chains of alpha glucose, proteins are made of chains of amino acids and triglycerides are made of fatty acids and glycerol. Choice A is incorrect because starch is not composed of beta glucose and peptides are not the simplest units of proteins. Choice B is incorrect because starch is not composed of beta glucose and triglycerides do not contain glycogen. Choice C is incorrect because peptides are not the smallest unit of proteins and triglycerides do not contain glycogen.

Explanation:
Water is transported passively via protein channels known as aquaporins.

Cholesterol (Choice A) and glycoproteins (Choice B) are not components responsible for transport while protein pumps (Choice C) carry out active transport which is not utilized in the transport of water.

Explanation:
The disaccharide sucrose is made up of the monosaccharides glucose and fructose. Sucrose forms when glucose and fructose combine in a condensation reaction (a reaction that releases water).

Maltose (Choice A) is a disaccharide made up of two glucose molecules. Lactose (Choice B) is a disaccharide made up of glucose and galactose. Galactose (Choice D) is a monosaccharide, not a disaccharide.

Explanation:
Centrifugation is a technique that primarily separates substances based on their density. When a mixture is centrifuged, particles or components with higher density sediment to the bottom of the tube. Choice A is, therefore, correct.

Centrifugation does not separate substances based on their charge. Electrophoresis is a technique that separates particles or molecules based on their charge. Choice B is, therefore, incorrect. Centrifugation does not directly separate substances based on their chemical composition. Other techniques like chromatography may be more suitable for separating substances by chemical composition. Choice C is, therefore, incorrect. Centrifugation does not separate substances based on their colour. Colour differences might be observed during centrifugation, but they are not the basis for separation. Choice D is, therefore, incorrect.

Explanation:
The diagram shows glycerol and 3 fatty acids. When these are joined in a condensation reaction, a triglyceride is formed. Choice D is correct.

Choices A, B and C are incorrect.

Explanation​:
Choice B is correct because incisors are used for biting chunks of food. Choice A is incorrect because tearing is the role of canines. Choices C and D are incorrect because crushing or slicing is the role of the premolars, and grinding is the role of molars.

Explanation:
Choice A is correct because there is no compartmentalisation in prokaryotes, hence transcription and translation both take place in the cytoplasm.

Choice B is incorrect because mRNA splicing does not occur in prokaryotes, but does occur in the nucleus of eukaryotic cells. Choice C and D are incorrect because the regulation of transcription and translation of mRNA into a polypeptide chain occurs in both prokaryotes and eukaryotes.

Explanation:
Choice C is correct because the habitat is a place a community, population, species, or organism lives. Choice A refers to an organism's niche, Choice B refers to the ecosystem, and Choice D refers to a community.

Explanation:
Choice A is correct because a lysosome usually fuses with phagocytic vacuoles containing pathogens or cellular debris, or other vacuoles in the cytoplasm. The enzymes are then released from the lysosome into the vacuole to digest the contents.

Choice B is incorrect because lysosomes contain digestive enzymes that break down cellular components, which involve catabolic reactions, not anabolic reactions. Choice C is incorrect because lysosomes form from vesicles budding off of the Golgi apparatus. Choice D is incorrect because lysosomes are membrane-bound organelles.

Explanation​:
Choice A - There are still stem cells that can be found in the adult body. For example, stem cells are present in the bone marrow, skin, and liver.

Choice B - The foetal stage of development happens from the ninth week after conception until birth. In this stage, the organs have begun to form, and these developing organs come from differentiated stem cells.

Choice C - Stem cells are characterised by their capacity to divide and differentiate. These cells are similar to a blank canvas with the possibility of becoming any type of cell.

Choice D - Stem cells are yet to undergo specialisation through the process of differentiation.

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​:
Statement II is incorrect as both starch and glycogen are made up of $\alpha -$ glucose molecules (Choices B and D). Choice A is incorrect as it only includes one correct statement (statement I).

Explanation:
In arid environments, water availability is often a primary limiting factor. However, soil compaction (Choice C) can exacerbate this limitation by reducing water infiltration and root penetration. High humidity (Choice A), excessive rainfall (Choice B), and low light intensity (Choice D) are less likely to be limiting factors in arid environments.