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​:
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:
Both oogenesis and spermatogenesis involve mitosis, increase in cell size (cell growth), two meiotic divisions and differentiation. Choice A is correct.

Choice B is incorrect as it includes both apoptosis (cell death) and decrease in size, which does not occur in either process. Choice C is incorrect as binary fission occurs in prokaryotic cells and the generation of a polar body only occurs in oogenesis. Choice D is incorrect as budding only occurs in fungi, and fertilization (when mature sperm and egg cells fuse) occurs after both oogenesis and spermatogenesis.

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 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 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​:
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​:
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​:
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.

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 A is incorrect as autosomes are chromosomes that are not the sex chromosomes and so do not determine biological sex. Choice B is incorrect as linked genes are genes that are found on the same chromosome. Choice C is incorrect as a gene locus is the position of a gene on a chromosome.

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​:
The four stages of mitosis are prophase, where chromosomes supercoil and become visible; Metaphase, where chromosomes line up at the equator of the cell; anaphase, where sister chromatids are pulled apart and telophase, where the nuclear envelope reforms and two new daughter nuclei are formed.

Statement I is incorrect as sister chromatids are not pulled apart during metaphase. They are pulled apart during anaphase.
Choice B is incorrect as both statements II and III are correct and should be included.

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​:

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​:
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 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​:
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:
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​:
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:
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 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 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:
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​:
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).