Adenine pairs with thymine and cytosine pairs with guanine
Explication
Chargaff’s rule states that adenine pairs with thymine and cytosine pairs with guanine in DNA. Uracil is found in RNA, not DNA.
It is made of deoxyribose sugar, a phosphate group, and a nitrogenous base
Explication
A DNA nucleotide consists of deoxyribose, phosphate, and one nitrogenous base. The other choices describe incorrect components or mix up DNA with RNA.
A DNA segment that carries instructions for making a particular polypeptide
Explication
A gene is a section of DNA that contains instructions for making a polypeptide. A locus is the location of a gene, while a chromosome is the DNA-containing structure.
An arranged set of stained chromosomes grouped into matching pairs by size and shape
Explication
A karyotype is a photographed and arranged set of chromosomes paired by size and shape. It is used to reveal chromosome abnormalities.
It produces haploid gametes by halving the chromosome number
Explication
Meiosis reduces the chromosome number from diploid to haploid so gametes can be formed for sexual reproduction. Mitosis, not meiosis, produces genetically identical body cells.
The fusion of haploid sperm and ovum to form a diploid zygote
Explication
Fertilisation is the joining of sperm and ovum, both haploid, to create a diploid zygote. The other options describe mitosis, crossing over, or meiosis.
It predicts the possible offspring genotypes from a genetic cross
Explication
A Punnett square is used to predict possible offspring genotypes by combining parental alleles. It does not show DNA sequences or chromosome counts.
1 EE : 2 Ee : 1 ee
Explication
Two heterozygous parents produce a 1:2:1 genotypic ratio of EE, Ee, and ee. The common 3:1 ratio refers to the phenotype, not the genotype.
A mutation that affects a single nucleotide in DNA
Explication
A point mutation affects one nucleotide in the DNA sequence. Chromosome-level changes and crossing over are different types of genetic change.
Because it changes how triplets are read during translation
Explication
Adding or removing a nucleotide shifts the reading frame, so every codon after the change can be read differently. This alters how the protein is built during translation.
All living things are made of cells, and new cells come from pre-existing cells
Explication
Cell theory states that all living things are made of cells and that cells arise only from pre-existing cells. The other options add incorrect claims about how cells originate or their structures.
It lacks a nucleus and has DNA mainly as a single circular loop
Explication
Prokaryotic cells do not have a nucleus or membrane-bound organelles, and their DNA is usually a single circular loop. The other choices describe eukaryotic cells or processes they do not use.
Mitochondrion
Explication
Mitochondria produce ATP during aerobic cellular respiration and generate most of the cell’s aerobic energy yield. Chloroplasts carry out photosynthesis, while lysosomes digest waste.
They contain circular DNA and replicate by binary fission
Explication
Endosymbiotic theory is supported by features such as circular DNA and independent replication by binary fission. The other options contradict the known characteristics of these organelles.
A smaller cell has a higher surface area to volume ratio, improving exchange
Explication
Small cells have a higher surface area to volume ratio, which makes transport of nutrients and wastes more efficient. Larger cells have more volume relative to surface area, so exchange becomes less efficient.
24 cm³
Explication
Volume of a cuboid is length × width × height, so 4 × 3 × 2 = 24 cm³. The other values come from using an incomplete or incorrect calculation.
Independent variable
Explication
The independent variable is the factor that is deliberately changed to test its effect. The dependent variable is measured, while controlled variables are kept the same.
To make the test fair and isolate the effect of the independent variable
Explication
Controlled variables are kept constant so that any change in the dependent variable is due to the independent variable. This makes the investigation fair and allows a valid comparison.
Non-maleficence
Explication
Non-maleficence means avoiding or preventing harm, which fits situations where immediate protection from injury is the priority. Consent, justice, and confidentiality are important ethical ideas but address different concerns.
Misuse that could lead to discrimination by insurers or employers
Explication
A major bioethical risk of genome data is that it could be misused to discriminate against people based on genetic predisposition. The other options do not reflect the ethical issue described.
Embryo splitting cloning
Explication
Embryo splitting cloning works by dividing an early embryo so each part can develop into an identical individual. Somatic cell nuclear transfer uses an adult cell nucleus instead of splitting an embryo.
The adult body cell donor
Explication
The clone receives its nuclear DNA from the donor body cell nucleus, so it matches the donor animal genetically. The egg donor and surrogate provide the cell environment and uterus, but not the donor's nuclear genome.
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DNA structure — base pairing?
A pairs with T; C pairs with G.
Genes — function?
Carry instructions for specific proteins.
Chromosomes — composition?
DNA tightly coiled with proteins.
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