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:
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:
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:
Choice A is correct because the medulla is the inner region of the kidney.

Choice B is incorrect because the outer region of the kidney is the cortex.

Choice C is incorrect because it is the renal artery.

Choice D is incorrect because it is the ureter.

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

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:
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:
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:
Choice B is correct because a meristem is a part of a plant with undifferentiated cells that undergo cell division. Choice A is incorrect because meristems do not have differentiated cells that undergo cell division. Choice C is incorrect because a meristem is not defined as a region of a flower. Choice D is incorrect because cell division in a meristem is not influenced by day length.

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:
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 D is correct because there are four chromosomes, and each chromosome is composed of sister chromatids. Choice A and choice C are incorrect because, in metaphase, chromosomes are lined up on the equator. Choice B is incorrect because, during anaphase II, chromosomes are being pulled apart and towards opposite poles.

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:
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 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:
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).

Explanation:
Choice A is incorrect because urea is reabsorbed.

Choice B is correct because all glucose is reabsorbed by the proximal tubule, none is reabsorbed by the distal convoluted tubule.

Choice C is incorrect because water is reabsorbed by the distal convoluted tubule.

Choice D is incorrect because Na+ ions are reabsorbed by the distal convoluted tubule.

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 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:
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 A is correct because meiosis happens in the anther and ovule of flowers, it does not happen in the cells of the shoot apex. Choice B, Choice C and Choice D are incorrect because mitosis and cell elongation happen in the shoot apex to produce new cells and allow for primary growth (plant lengthening).

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 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:
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.