Explanation​:
Choice D is correct because homologous structures refer to structures inherited from a common ancestor which are similar but often used for different functions.

Choice A is incorrect, as ancestral structures refer to structures present in an ancestor species, not structures found in present day species. Choice B is incorrect as convergent structures are not a term used in biology. Convergent evolution, on the other hand, leads to analogous structures. Choice C is incorrect as analogous structures refer to structures used for the same function, which are significantly different when closely inspected. Analogous structures also have different evolutionary origins.

Explanation:
Choice B is correct because two reproductively isolated populations are a key component of the definition of a species.

Choice A is incorrect because allele frequencies often differ between different populations of the same species. Choice C is incorrect because varying DNA sequences in genes confirms the existence of different alleles, not the existence of two species. Choice D is incorrect because even when two populations are geographically isolated, they may still be the same species.

Explanation​:
Choice A is correct because Eukaryota are the only group with nuclei and membrane-bound organelles. Choice B and choice C are incorrect because organisms in these two domains (Archaea and Eubacteria) do not have membrane-enclosed organelles. Choice D is incorrect because prokaryotes are not the name of a domain.

Explanation:
Statement I is true because all cells have cytoplasm enclosed by the plasma membrane.

Statement II is also true because the invention of the microscope made viewing structures within the cell easier.

Statement III is false because all cells have genetic material. Eukaryotic cells have their genetic material inside of the nucleus, while prokaryotes have their genetic material in the nucleoid region.

Explanation:
Evolution is the change in the characteristics of a population over time; these characteristics can be passed from one generation to another (Choice A). Choice B is incorrect as it describes when organisms are reproductively isolated, which is a mechanism that may lead to evolution in a population. Choice C is incorrect because it refers to learned behaviours which are learned within an organism’s lifetime and are not genetically inherited. Choice D is incorrect as it refers to selective breeding.

Explanation​:
Eukaryotic cells contain mitochondria but prokaryotic cells do not. Choice A is correct.

Choices B and D are incorrect as the cell is not prokaryotic; it has a nucleus. Choice C is incorrect because the cell has a nucleus.

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​:
Gravity is responsible for holding water on Earth and is a fundamental factor in water retention within the planet's atmosphere and surface. Choice D is, therefore, correct.

Choice A is incorrect, as although rainfall is a part of the water cycle and is responsible for distributing water, it does not directly contribute to the retention of water on Earth.

Choice B is incorrect, as the moon's gravitational force regulates the tides of large bodies of water but does not directly contribute to water retention on Earth. Choice C is incorrect as water is lost from bodies of water on the surface of the Earth and evaporates into the atmosphere, which doesn't directly address water retention.

Explanation​:
The nucleotide strand CCUAGAGCUUACCG contains the bases cytosine (C), uracil (U), adenine (A), and guanine (G). While C, A, and G are found in both DNA and RNA, the base uracil is only found in RNA. So, the strand is an RNA strand.

RNA contains the pentose sugar ribose. Therefore, ribose is found in the nucleotides in the strand.

Choices A and C are incorrect because deoxyribose is only found in DNA, not RNA. The nucleotide strand cannot be DNA because it contains uracil in place of thymine (T).

Choice D is incorrect because the strand is RNA which contains ribose.

Explanation​:
Choice A - Excretion is the process wherein waste and excess water in the organism are removed. Paramecia expel waste products such as carbon dioxide through the process of diffusion.

Choice B - Homeostasis pertains to the ability of living things to maintain a stable internal environment. Paramecia maintain a stable internal condition by expelling excess water using the contractile vacuole.

Choice C - Reproduction is the biological process by which organisms produce offspring that are biologically similar to themselves. Paramecia can reproduce sexually through meiosis and asexually through mitosis.

Choice D - Metabolism refers to all the chemical reactions in organisms such as anabolic and catabolic reactions. Paramecia produce enzymes that catalyse different catabolic and anabolic reactions in the cell.

Explanation​:
Choice B is the correct definition for a clade, a group of organisms that share a common ancestor. Choice A and C are incorrect as they do not feature the idea of a common ancestor. Choice D is incorrect because organisms within a clade do share a common ancestor.

Explanation​:
Species that share a recent common ancestor, such as humans and chimpanzees, are more likely to have similar base sequences. Over time, as species diverge and evolve, mutations accumulate in their base sequences. The longer two species have been separated from their common ancestor, the more mutations will have accumulated in their genomes. Therefore, species that are closely related have fewer accumulated mutations and more similar base sequences (Choice B).

Choice A is incorrect because genome size is not necessarily proportional to the size of the species. The genome size can vary significantly even among organisms of similar size, and organisms with similar-sized genomes, such as the horse and mouse vary greatly in size. Choice C is incorrect because it is possible to have a larger genome size with a comparable, or even smaller, number of genes, depending on the amount of non-coding DNA and repetitive sequences present in the genome. Humans have a larger genome but a similar number of genes to the chimpanzee, mouse and horse. Choice D is incorrect because although the nucleotide base sequence in the table for humans and chimpanzees is the same it does not mean that their whole genome is the same.

Explanation:
X is pointing to the nucleus and Y is pointing to a mitochondrion. Choice A is incorrect as neither organelle has a single membrane. Choice B is incorrect as only mitochondria contain cristae, the nucleus does not. Choice D is incorrect as neither the nucleus or mitochondria contain starch grains.

Explanation​:
Statement II is correct as prokaryotic cells do not have a Golgi apparatus and statement III is correct as prokaryotic cells do not have membrane bound organelles. Choices A, C and D are incorrect.

Explanation​:
Choice A is correct because the hierarchy of taxa is a domain, kingdom, phylum, class, order, family, genus, so class $\to$ order $\to$ family is in the correct order. Choice B is incorrect because the class is above order. Choice C is incorrect because the family is above genus. Choice D is incorrect because the phylum is above order.

Explanation:
Choice D is correct because water has a relatively high density compared to many substances which increases the buoyancy forces it exerts on objects submerged in it.

Choice B is incorrect because specific heat capacity refers to how much energy is required to raise the temperature of a unit of mass of a given substance by one degree Celsius. Choice C is incorrect because viscosity refers to the resistance of a fluid to an object moving through it or to flow of the fluid itself.

Explanation​:
The number of organisms found via the fossil record for any era is much lower compared to the number of organisms found on Earth now and those that continue to be found, so Choice B is correct. Choice A is incorrect as changing levels of atmospheric carbon dioxide provide evidence for humans' impact on carbon dioxide levels. Choices C and D are incorrect as evidence suggests that the rate of evolution and speciation are increasing, which provides evidence for increasing biodiversity.

Explanation​:
The endosymbiotic theory states that larger prokaryotes engulfed smaller prokaryotes, which were the ancestors of modern chloroplasts and mitochondria, eventually evolving into eukaryotes. Choice A is correct.

Statement I (Choices B and D) is incorrect as prokaryotes were not formed by the endosymbiotic theory. Statement III (Choice C) is incorrect as spontaneous generation is impossible.

Explanation:
Choice A is correct because Chargaff used paper chromatography to show that the proportions of adenine (A) and thymine (T) are the same, as are the proportions of guanine (G) and cytosine (C). There are not equal proportions of A, T, G and C.

Franklin (Choice B) and Watson (Choice D) are credited for their contributions to the overall structure of DNA structure. Hershey (Choice C), along with Chase, is famous for his research which provided evidence for the idea that DNA, rather than protein, carries the genetic code.

Explanation:
Hydrophilic (Choice C) substances dissolve in water through the formation of hydrogen bonds with water.
Non-polar (Choice D) substances are not attracted to water molecules and do not form bonds with them. These substances are hydrophobic (Choice B), making them insoluble (Choice A) in water.

Explanation:
The resolution is the ability to distinguish between two objects. Choice B is correct.

Choices A and D are incorrect because a photograph taken using an electron microscope would allow the ultrastructure of the cells (fine detail of cells, such as organelles) to be observed. Choice C is incorrect because these photographs are magnified at the same power.

Explanation​:
All 64 codons of the genetic code are present in all organisms, apart from minor variations indicating that all life evolved from the same original cells (Choice D).

Eukaryotic cells evolved from prokaryotic cells (Choice A) is incorrect as this is the endosymbiotic theory. Choice B is incorrect as mitochondria do not have a cell wall. Choice C is incorrect as bacteria do not have histones.

Explanation​:
Choices A, B and D are incorrect as they all have a single membrane.

Explanation​:
All three statements are correct. The first part of the binomial name is the genus, the second part is the species which is unique to platypus species. The binomial system and binomial names are agreed between biologists at international congresses.

Explanation​:
Isotopes with long half-lives (Choice C), such as uranium and potassium isotopes, are often used in absolute dating because they decay slowly and are suitable for dating older fossils.

Stable isotopes (Choice A) are not used for fossil dating because they do not undergo radioactive decay. Absolute dating relies on the measurement of the decay of radioactive isotopes into stable daughter isotopes to determine the age of a sample. Isotopes with short half-lives (Choice B) are typically used for dating more recent events, not older fossils. Isotopes with no half-lives (Choice D) cannot be used for fossil dating using the methods based on radioactive decay. Isotopes without half-lives do not undergo radioactive decay, so it is impossible to establish a chronology or estimate the age of a fossil using these isotopes.