Explanation​:
Peptide bonds form between amino acids as a result of condensation reactions. Statement II (Choice C) is correct because dipeptides are composed of two amino acids held together by a peptide bond and proteins (Statement III) are composed of one or more polypeptides, which are chains of amino acids held together by peptide bonds. Choice A, B and D are incorrect as individual amino acids (Statement I) do not possess peptide bonds.

Explanation​:
Sexual reproduction results in variation as it is the fusion of genetically distinct gametes from two genetically different individuals. Mutation results in variation as it produces new alleles. Meiosis results in variation as it produces new combinations of alleles. Choice C is correct.

Choices A, B and D are incorrect as they all include either mitosis, asexual reproduction or binary fission, which all produce genetically identical cells.

Explanation:
The bond formed between two glucose molecules to form maltose is an alpha 1-4 linkage. This is a covalent bond between two alpha glucose molecules, where the carbon #1 of one of the glucose molecules forms a bond with the carbon #4 of the other glucose molecule. Choice C is correct.

A hydrogen bond (Choice A) is a weak electrostatic attraction between a hydrogen atom that is covalently bonded to a highly electronegative atom and another electronegative atom in a different molecule or region of the same molecule. For example, between two water molecules. Peptide bonds (Choice B) are covenant bonds that hold amino acids together in polypeptide chains, and phosphodiester bonds (Choice D) are covalent bonds between the ribose sugars and phosphate groups, forming the backbone of DNA and RNA. Choices A, B and D are incorrect.

Explanation:
A greenhouse gas is a gas that contributes to the greenhouse effect. Greenhouse gases absorb the long wave infrared radiation (heat energy) emitted from Earth’s surface and can reradiate it back to Earth’s surface. So, one factor that determines whether a gas acts as a greenhouse gas is its ability to absorb long wave radiation: gases that are better able to absorb long wave radiation are more likely to act as greenhouse gases. A second factor that qualifies carbon dioxide as a greenhouse gas of concern is its relatively high concentration in the atmosphere: gases that are in higher concentration in the atmosphere have a larger effect on Earth’s temperature.

Active transport (Choice A) requires energy expenditure. Facilitated diffusion is a passive form of transport but active transport requires energy (Choice B). Facilitated diffusion (Choice D) does not require energy expenditure but this answer choice does not include osmosis.

Explanation:
Choice D is correct because transpiration is the loss of water from the stomata of a plant, it is not a stage of plant reproduction. Choices A, C and D are incorrect because pollination, fertilisation and seed dispersal are all stages of plant reproduction.

Explanation:
Choice A is correct because pollen is produced by the anther and the ovum (plural: ova) is produced by the ovule, found inside the ovary. Choice B is incorrect because the stigma is where pollen lands. Choice C is incorrect because the filament supports the anther and does not produce pollen. Choice D is incorrect because the filament supports the anther and the style is the part of the flower that the pollen passes through.

Explanation​:

During Prophase, chromosomes supercoil and become visible (Choice A). In Metaphase, chromosomes line up at the equator of the cell (Choices B and C). In Anaphase, sister chromatids are pulled apart (Choice D).

Explanation:
Choice A is correct because when there are fewer copies of a given strand of mRNA in the cytoplasm, ribosomes have fewer copies to bind to and thus the rate polypeptides are synthesised based on this strand will decrease, not increase (Choice B).

Choices C and D are incorrect because if the rate mRNA is degraded decreases, there will be more copies of this strand of mRNA resulting in an increase in the rate ribosomes bind to these strands and synthesise polypeptides.

Explanation​:
Choices A, B and D are all incorrect as they all cause changes to allele frequency.

Explanation:
Choices B, C and D are incorrect, as the gene pool consists of all the genes and alleles in an interbreeding population.

Explanation​:
Choices B, C and D are incorrect because as the trees get darker, the camouflage of the peppered moth will be less effective, meaning it is more visible to predators and therefore more likely to be eaten.

Explanation​:
Choice B is not true. Not all genes are expressed in each cell. Only the necessary genes are expressed based on the specialised function of the cell. All other statements are true.

Explanation:
Choice C is correct, as the 9th nucleotide in the sequence (C) has been deleted from the original sequence.

Choice A is incorrect as it is the exact same sequence as the original sequence. Choice B is incorrect as it represents an insertion mutation, an adenine has been inserted in the 7th position. Choice D is incorrect as it represents a base substitution mutation, as G has replaced a T in the 14th position.

Explanation​:
Choice B is correct because, in a healthy kidney, white blood cells are too large to pass from the glomerulus into the Bowman’s capsule. Choices A, C and D are incorrect because amino acids, water and glucose are small enough to be filtered from the capillaries in the glomerulus into the Bowman’s capsule.

Explanation:
Choice A is correct because in both selective breeding and natural selection, favourable characteristics are “selected”, by either the environment (natural selection) or humans (selective breeding). Choice B is incorrect because natural selection doesn’t increase variation, it influences the proportion of existing variants. Choices C and D are incorrect because natural selection is not controlled by humans and does not contribute to the domestication of animals.

Explanation​:
Choice C is a correct definition of a gene. Chromosomes are made of DNA and protein (Choice A), while genes are only made of DNA. When DNA is at various levels of supercoiling, it is wrapped around histone proteins. However, the presence of histones is not part of the definition of a gene (Choice B). Genes control some characteristics, but some characteristics are also affected by the environment (Choice D).

Explanation​:
A base substitution is when one nucleotide randomly replaces another in a sequence causing a single nucleotide polymorphism. This can result in a shorter polypeptide being translated (Statement I) due to the base change causing a stop codon to appear earlier in the DNA/mRNA sequence. It can also cause an altered polypeptide chain to be translated (Statement II) if the base substitution causes a different amino acid to be translated. It can also have no effect on the polypeptide that is translated (Statement III), as the genetic code is degenerate, meaning many codons code for the same amino acid. Choice D is therefore correct.

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

Explanation​:
Protein pumps are membrane proteins that carry out active transport. They require the energy to pump molecules up their concentration gradient.

Protein channels (Choice A), protein carriers (Choice C), and aquaporins (Choice D) all conduct passive transport.

Explanation​:
Choice A, B, and D – These statements are true.

Choice C -This statement is false. In eukaryotic cells, translation takes place in the cytoplasm. Prokaryotic cells do not have a nucleus.

Explanation​:
Early in pregnancy, a human embryo secretes the hormone hCG, human chorionic gonadotrophin. This hormone maintains the corpus luteum in the ovary so that it secretes progesterone, which helps prepare the lining of the uterus for the implantation of the embryo.

LH (Choice A) and FSH (Choice D) are released by the pituitary gland, not the embryo. Oestradiol (Choice B) is released by the ovaries, not the embryo.

Explanation​:
Choice B is correct because pollination is the transfer of pollen from an anther to a stigma. Choice A is incorrect because the fusion of a male and female gamete is fertilization. Choice C is incorrect because the transfer of seeds away from the parent plant is dispersal. Choice D is incorrect because pollination can occur without a pollinator. Some plants are wind-pollinated.

Explanation:
Nitrogen makes up approximately 78% of dry air and is not a greenhouse gas.

All other gases when present in the air enhance the greenhouse effect to cause global warming. (Choices A, B and C)

Explanation:
If there are two alleles for a gene, but there are three possible phenotypes, this could suggest incomplete dominance (Choice C). This is when the dominant allele doesn’t completely suppress the effects of the recessive allele. Choice A is incorrect because if one allele was completely dominant over the other, then there would only be two possible phenotypes. Choice B is incorrect because if the alleles were codominant, then we would see both expressed in the phenotype. In this case, some petals would be white and others red, instead of the flower being pink. Choice D is incorrect because sex-linkage does not create an additional phenotype.

Explanation:
Haemoglobin is a globular protein which is responsible for transporting oxygen around the body (Choice A). Choice B is incorrect as collagen is a fibrous protein. Choice C is incorrect as haemoglobin is not a fibrous protein and does not provide structural support. Choice D is incorrect as collagen does not transport oxygen.