AQA A - LEVEL BIOLOGY PAPER 3 TOPIC 1 - 8 EXAM GUIDE QNS & ANS JUNE 2024.
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AQA BIOLOGY
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AQA BIOLOGY
AQA A - LEVEL BIOLOGY PAPER 3 TOPIC 1 - 8 EXAM GUIDE QNS & ANS JUNE 2024.AQA A - LEVEL BIOLOGY PAPER 3 TOPIC 1 - 8 EXAM GUIDE QNS & ANS JUNE 2024.AQA A - LEVEL BIOLOGY PAPER 3 TOPIC 1 - 8 EXAM GUIDE QNS & ANS JUNE 2024.
TOPIC 1 – 8 EXAM GUIDE
QNS & ANS
1. Describe the structure of a water molecule and explain how
its properties are conducive to its role in biological organisms.
Answer: A water molecule has a bent shape with one oxygen
atom covalently bonded to two hydrogen atoms. The oxygen
atom is more electronegative, creating a polar molecule with a
partial negative charge near the oxygen and a partial positive
charge near the hydrogens. This polarity allows water to form
hydrogen bonds, making it an excellent solvent for ionic and
other polar molecules. It also contributes to water's high specific
heat, surface tension, and cohesion, all of which are essential
for life.
2. Explain the fluid mosaic model of cell membranes and its
significance in the transport of substances.
Answer: The fluid mosaic model describes the cell membrane
as a fluid, dynamic structure with various proteins embedded in
or attached to a bilayer of phospholipids. The phospholipids
have hydrophilic heads and hydrophobic tails, creating a semi-
permeable barrier. Proteins serve functions such as transport,
signal transduction, and cell recognition, allowing cells to
exchange substances with their environment selectively.
3. Discuss how the structure of DNA relates to its function of
storing genetic information.
Answer: DNA's structure is a double helix with two strands
running in opposite directions, composed of nucleotides
, containing a phosphate group, a sugar (deoxyribose), and a
nitrogenous base. The sequence of bases (adenine, thymine,
cytosine, and guanine) encodes genetic information. Base
pairing (A with T, C with G) through hydrogen bonds allows for
replication and transcription, ensuring genetic information is
accurately passed on.
4. Compare and contrast aerobic and anaerobic respiration in
terms of energy transfer within cells.
Answer: Aerobic respiration occurs in the presence of oxygen
and involves glycolysis, the Krebs cycle, and the electron
transport chain, resulting in the production of up to 36 ATP
molecules per glucose molecule. Anaerobic respiration, in the
absence of oxygen, results in less efficient energy transfer,
producing only 2 ATP molecules per glucose molecule through
glycolysis, followed by fermentation to regenerate NAD+.
5. Analyze the impact of gene mutations on protein synthesis
and resulting phenotypic effects.
Answer: Gene mutations can alter the sequence of nucleotides
in DNA, potentially leading to changes in the amino acid
sequence of proteins. This can affect protein structure and
function, resulting in various phenotypic effects. For example, a
missense mutation may result in a non-functional enzyme, while
a nonsense mutation can lead to a truncated protein, both of
which can have significant impacts on an organism's traits.
6. Evaluate the role of homeostasis in maintaining optimal
internal conditions for enzyme activity.
Answer: Homeostasis involves regulatory mechanisms that
maintain a stable internal environment, crucial for optimal
enzyme activity. Enzymes have specific temperature and pH
ranges where they function best. Homeostatic processes, such
as thermoregulation and pH balance, ensure that these
conditions are met, allowing enzymes to catalyze reactions
efficiently and maintain metabolic processes.
7. Discuss the significance of meiosis in generating genetic
diversity through independent assortment and crossing over.
Answer: Meiosis is a type of cell division that reduces the
chromosome number by half, resulting in genetically unique
gametes. Independent assortment and crossing over during
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