Correct Answer: D

Rationale: - Homozygous recessive genotype refers to an individual having two identical recessive alleles for a particular gene (e.g., rr for a trait where r represents the recessive allele).
- Homozygous dominant genotype refers to an individual having two identical dominant alleles for a particular gene (e.g., RR for a trait where R represents the dominant allele).
- The difference between the two genotypes lies in the specific alleles present in each case, with homozygous recessive having two recessive alleles and homozygous dominant having two dominant alleles.
- This genetic difference results in different phenotypes being expressed, as the dominant allele typically masks the expression of the recessive allele in heterozygous individuals.

Correct Answer: D

Rationale: The correct answer is D, Electromagnetic wave. Electromagnetic waves do not require a medium for propagation because they consist of oscillating electric and magnetic fields that can travel through a vacuum. In contrast, transverse and longitudinal waves are mechanical waves that require a medium (solid, liquid, or gas) for propagation.
Therefore, options A, B, and C are incorrect as they are all types of mechanical waves that necessitate a medium for transmission.

Correct Answer: D

Rationale: Half-life refers to the time it takes for half of the radioactive atoms in a sample to decay. This means that after one half-life, half of the initial quantity of the radioactive substance will have decayed.
Choice A is incorrect because radioactive intensity doesn't completely disappear during half-life.
Choice B is incorrect as half-life doesn't refer to the number of neutrons doubling.
Choice C is incorrect as half-life doesn't relate to the number of protons changing.

Correct Answer: C

Rationale: Valence electrons are the outermost electrons in an atom's electron cloud and are crucial in forming chemical bonds with other atoms. These electrons determine the reactivity and chemical properties of an element, making option C the correct statement. Option A is incorrect as valence electrons are found in the outer shell, not the innermost shell. Option B is incorrect because valence electrons have lower binding energy compared to inner electrons. Option D is incorrect since valence electrons play a significant role in an element's chemical behavior.

Correct Answer: D

Rationale: The correct answer is D: Synthesizing proteins. Ribosomes are cellular organelles responsible for protein synthesis. They read the messenger RNA (mRN
A) and utilize the information to assemble amino acids into proteins through a process known as translation.
Choice A, packaging and transporting proteins, is incorrect as this function is typically performed by the Golgi apparatus and vesicles.
Choice B, storing genetic material, is incorrect as genetic material is usually stored in the nucleus in the form of DNA.
Choice C, controlling cell division, is incorrect as this function is primarily regulated by the cell cycle checkpoints and specific proteins involved in cell cycle regulation.