Explanation​:
A mRNA strand contains four nitrogenous bases: adenine (A), cytosine (C), guanine (G) and uracil (U). It does not contain thymine (T) (Choice C and Choice D).

Most mRNA strands which code for polypeptides begin with the $\text{‘}$START$\text{’}$ codon AUG and end with a `STOP$\text{’}$ codon, UAG, UAA or UGA (Choice A). Choice B has a $\text{‘}$STOP$\text{’}$ codon at the beginning which would terminate translation before it begins.

Explanation​:
Choice C is correct because the biological mother passes on the X chromosome to a son and the biological father contributes only with Y. For the son to be colour-blind, he must have an allele for it on the X chromosome. Therefore the biological mother must have at least one recessive allele (n). Choices A and B are incorrect because individuals with X and Y are male. Choice D is incorrect because, in this case, no sons would have the condition.

Explanation​:
Photosynthesis (Choice B) is the process by which carbon dioxide in the air is converted to carbon compounds in green plants.

Respiration releases carbon dioxide (Choice A), and decomposition by decomposers (Choice C) also releases carbon dioxide. Transpiration is the process by which water is drawn up the stem of a plant to the leaves where it evaporates (Choice D) and is not involved directly in the carbon cycle.

Explanation:
Choice A is correct because during metaphase I homologous chromosomes align at the equator and are subject to random orientation. Choice B is incorrect as, during Prophase I, homologous chromosomes condense and crossing over occurs. Choice C is incorrect as, during Metaphase II, chromosomes align on the cell's equator, and there is random orientation of the sister chromatids and not homologous chromosomes. Choice D is incorrect as, during Prophase II, chromosomes align on the cell's equator.

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 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​:
Choice D is correct because low blood glucose concentration is detected by the alpha cells in the pancreas and they respond by releasing glucagon. Choice A is incorrect because high blood concentration does not cause the secretion of glucagon and it is not secreted by beta cells. Choice B is incorrect because high blood concentration does not cause the secretion of glucagon, it causes the release of insulin. Choice C is incorrect because glucagon is not secreted by beta cells.

Explanation​:
The question states that heterozygous individuals have the banded pattern on their hairs, which means that the agouti trait is dominant. Two heterozygous parents will produce offspring with the dominant and recessive characteristics in the ratio of 3:1 (Choice B). The offspring of a heterozygous individual and a homozygous agouti individual will all receive at least one dominant allele, so they would all be agouti (Choice A). The offspring of at least one parent that is homozygous for agouti will all have the agouti characteristic (Choices C and D).

Explanation:
At fertilisation, two gametes, which are haploid, fuse together to produce a diploid cell. Gametes of a fruit fly have a haploid number of 4, so fertilisation produces a cell with 8 chromosomes (choice A). Choice B is incorrect because 4 is the haploid number. Choice C is incorrect because fruit fly somatic cells have 8 chromosomes and fertilised egg cells have 8 chromosomes. Choice D is incorrect because 16 is twice the diploid number of fruit flies.

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​:
Mitosis forms two genetically identical daughter cells with the same number of diploid chromosomes as the parent cell.

18 (Choice B) is incorrect as it is the haploid number of chromosomes. 72 (Choice C) is incorrect as it is twice the diploid number of chromosomes. 9 (Choice D) is incorrect as it is a quarter of the diploid number and an odd number.

Explanation:
Choice C is correct because the transfer of seeds away from the parent plant is dispersal. Choice A is incorrect because the fusion of a male and female gamete is fertilization. Choice B is incorrect because the transfer of pollen from an anther to a stigma is pollination. Choice D is incorrect because pollen transfer involves the movement of pollen, not seeds.

Explanation​:
Choice B is correct because there are pairs of homologous chromosomes lined up on the equator, and each chromosome is attached to only one pole. Choice A is incorrect because in metaphase II, chromosomes are not in homologous pairs. Each chromosome, composed of sister chromatids, is attached to both poles. Choice C is incorrect because in anaphase I, homologous chromosomes are separated, and one chromosome from each pair is pulled to one pole. Choice D is incorrect because in telophase I, there are two sets of chromosomes that are already separated.

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:
The fossil record provides evidence of evolution, as the sequence in which fossils appear matches the sequence that they would be expected to evolve. Homologous structures provide evidence of evolution as they provide evidence that organisms shared a common ancestor. Speciation provides evidence of evolution as when populations become reproductively isolated, then natural selection can act differently on those populations, resulting in the formation of new species. Choice C is correct. Choices A and D are incorrect as the organisms becoming more complex does not necessarily correlate with evolution. Choice B is incorrect, as the increasing size of organisms does not necessarily correlate with evolution.

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​:
The nuclear envelope is the membrane that separates the nucleus from the cytoplasm. For mitosis to proceed it must be broken down in the first stage of mitosis which is prophase so that the spindle fibres are able to attach to the centromeres. Choice A is correct.

Metaphase (Choice B), Anaphase (Choice C) and Telophase (Choice D) all follow Prophase (Choice A) in the sequence of mitosis and do not involve the breakdown of the nuclear envelope.

Explanation:
Down syndrome is not caused by a trisomy of sex chromosomes (choice B). The other statements are correct. Down syndrome is caused by trisomy 21 (choice A). It is caused by a trisomy of autosomes (choice C) because chromosome 21 is an autosome. Down syndrome is caused by an incorrect number of chromosomes (choice D).

Explanation​:
Choice C is correct because meiosis halves the number of chromosomes, mitosis maintains the diploid number and fertilisation restores the diploid number.

Choice A is incorrect because meiosis separates pairs of alleles and produces nuclei with one allele for each gene.

Choice B is incorrect because mitosis produces genetically identical cells that have two alleles for each gene.

Choice D is incorrect because, in fertilisation, two gametes fuse, and each gamete has one allele for each gene.

Explanation​:
Telophase is the last phase of mitosis and does not cause mutations (Choice C). Single base substitutions cause a change in the base sequence of DNA, which is a mutation (Choice A). Carcinogens (Choice B) and high energy radiation (Choice D) are mutagens which means they can cause changes in the base sequence of DNA.

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 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:
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.

Explanation​:
Choice A is correct because if the heart were placed in a hypotonic solution (as opposed to isotonic) water would diffuse into the cardiac muscles.

Choice B is incorrect because there would be no net movement into the tissues of the heart in an isotonic solution, not a hypotonic or hypertonic solution. Choice C is incorrect because even if it is placed in a solution other than an isotonic solution, it cannot dry out as it is still bathed in a watery solution. Choice D is incorrect as the tonicity of the solution the heart is stored in has no effect on whether the recipient’s immune system identifies the heart as foreign which would lead to rejection of the heart by the immune system.

Explanation​:
Statement I (Choices A and D) is incorrect as learned behaviours are changes that occur during a lifetime, and so do not affect the genetic code and cannot be passed on. Statement III (Choices C and D) is incorrect as natural selection increases the frequency of characteristics that make individuals better adapted.