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​:
The solution used to bathe organs to be used in a transplant should have an osmolarity equal to that of the organ to be transplanted and so the solution is isotonic compared to the organ’s tissues.

A solution with an osmolarity higher than that of the organ to be transplanted (Choice A) would cause tissue cells to shrivel, while a solution with an osmolarity lower than that of the organ to be transplanted (Choice B) would cause organ cells to burst. There are no described protocols that indicate that the solution should be mixed with cells from the organ to be transplanted (Choice D).

Explanation​:
Sweat (Choice B) is a coolant and helps to cool the body.
Tears (Choice A), urine (Choice C) and saliva (Choice D) do not lower or raise the body temperature.

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​:

Taq polymerase was isolated from bacteria found in the hot springs at Yellowstone National Park, USA. This enzyme is able to withstand high temperatures used for PCR assays.
All other choices (Choice A, C and D) describe bacteria living in colder locations compared to hot springs which strongly suggests that enzymes present in these bacteria would not be adapted to higher temperatures.

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:
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 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​:
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​:
mRNA, also known as messenger RNA, carries the genetic information needed for protein synthesis (Choice B).

Ribosomal RNA is found in ribosomes. This RNA contributes to the structure of the ribosome and does not code for proteins (Choice A).

ATP (Choice C) is a molecule made out of a nucleotide (adenosine tri-phosphate), while nucleic acid is made out of many nucleotides.

tRNA (Choice D), also known as transfer RNA, brings amino acids to the ribosomes and does not code for proteins.

Explanation​:
Statement III is not true, as homologous chromosomes often have different alleles (forms of genes), so are generally not identical to each other.

Statements I and II are true, as homologous chromosomes are pairs of chromosomes that have their centromeres and genes at the same positions. Therefore, Choice C is correct.

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​:
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.

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​:
The largest area in the pie charts showing sources of methane and nitrogen oxides is agricultural production.

Land use and biomass burning (Choice A) are a source of both methane and nitrous oxide but the area in the pie charts is less than agricultural production.

Industrial use (Choice B) releases mainly nitrous oxide.

Residential sources (Choice C) also release both methane and nitrous oxide but in lesser amounts than agricultural production.

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​:
When the environmental temperature drops, your body responds by trying to conserve heat. Reducing sweat production means there is less sweat to evaporate from the skin's surface, so less heat is lost. Vasoconstriction of the blood vessels reduces the volume of blood reaching the surface of the heat, so less heat is lost by radiation. Contraction of the erector pili muscles makes the hairs of the skin stand up, trapping an insulating layer of air next to the skin, again reducing heat loss by radiation and also by convection. Choice B is, therefore, the correct answer.

Choices A, C and D are incorrect as they have one or more factors wrong.

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:
The graph shows an overall positive correlation, as maternal age increases, the incidence of non-disjunction increases (Choice A). Choice B is incorrect because there is a positive correlation not a negative correlation. Choice C is incorrect because there is a correlation. Choice D is incorrect because non-disjunction does occur below 35 years, but the incidence is lower when compared to above 35 years.

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:
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 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​:
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​:
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​:
PCR is used to amplify samples of DNA so they can be used for analysis.

PCR replicates DNA but does not show that replication is semi-conservative (Choice A).

PCR does not determine the base sequence of DNA. It produces copies of short sections of DNA that can then be further analyzed (Choice B).

Taq polymerase is an enzyme used in PCR but no Taq DNA is incorporated. (Choice D).