Look inside the OCR A-Level Biology A guide (H420)

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OCR · A-Level · H420
Biology A
Active Recall Guide
1,833 questions
Biology AContents
Contents
26 sections, 151 subtopics
  1. Cell Structure68
  2. Biological Molecules113
  3. Nucleotides and Nucleic Acids58
  4. Enzymes43
  5. Biological Membranes60
  6. Cell Division, Cell Diversity and Cellular Organisation80
  7. Exchange Surfaces64
  8. Transport in Animals103
  9. Transport in Plants56
  10. Communicable Diseases, Disease Prevention and the Immune System88
  11. Biodiversity70
  12. Classification and Evolution52
  13. and 14 more
ii
Biological MoleculesQuestions
Biological Molecules
The properties of water
  1. Why is water described as a polar molecule?
  2. What charge does the oxygen atom carry in a water molecule?
  3. What charge do the hydrogen atoms carry in a water molecule?
  4. How do hydrogen bonds form between water molecules?
  5. Explain how water acts as a solvent for ionic compounds.
  6. What is a hydration shell?
  7. Give two examples of how water functions as a transport medium in organisms.
  8. Why does water have a high specific heat capacity?
  9. How does water's high specific heat capacity help organisms?
12
Biological MoleculesAnswers
Answers
The properties of water
  1. Water is polar because the oxygen atom has a slight negative charge and the hydrogen atoms have slight positive charges, creating an uneven distribution of charge across the molecule.
  2. A slight negative charge.
  3. Slight positive charges.
  4. Electrostatic attraction occurs between the slightly positive hydrogen atoms of one water molecule and the slightly negative oxygen atom of another water molecule, forming hydrogen bonds.
  5. Water's polarity allows it to surround ions with hydration shells, separating and dissolving ionic compounds and other polar molecules.
  6. A layer of water molecules that surrounds an ion due to the attraction between the polar water molecules and the charged ion.
  7. Water carries dissolved glucose in blood plasma of mammals and dissolved mineral ions in the xylem of plants.
  8. Large amounts of energy are needed to raise its temperature because energy is required to break the hydrogen bonds between water molecules.
  9. It buffers temperature changes, preventing rapid fluctuations in body temperature and maintaining stable conditions for metabolic reactions.
13
BiodiversityQuestions
Biodiversity
Sampling methods and equipment
  1. Why is sampling used to measure biodiversity rather than counting every organism?
  2. What requirement must sampling meet to give an accurate representation of biodiversity?
  3. What is random sampling and how is bias avoided?
  4. What is opportunistic sampling?
  5. Describe stratified sampling as a non-random method.
  6. What is systematic sampling?
  7. Why might a researcher choose stratified sampling over random sampling when studying a heterogeneous habitat?
  8. Give an example of when systematic sampling would be appropriate.
  9. What is a limitation of opportunistic sampling?
34
BiodiversityAnswers
Answers
Sampling methods and equipment
  1. It is impractical to count every organism in a habitat
  2. Sampling must cover the range of organisms present in a habitat
  3. Selecting sample sites using random number generators to avoid bias in site selection
  4. A non-random sampling method where organisms are sampled based on convenience or chance encounters, rather than following a systematic approach.
  5. The habitat is divided into distinct sub-groups (strata) based on a particular characteristic, and samples are taken from each stratum in proportion to its size or importance.
  6. A non-random sampling method where samples are taken at fixed, regular intervals, such as along a transect or using a grid pattern.
  7. Stratified sampling ensures that all distinct areas or sub-groups within the habitat are represented in the sample, preventing over- or under-representation of particular zones.
  8. When investigating changes in species distribution across an environmental gradient, such as along a transect from a shoreline inland.
  9. It introduces bias because samples are not representative of the whole population or area, making results difficult to generalise.
35
Cellular ControlQuestions
Cellular Control
Gene mutations and their effects
  1. What is a substitution mutation?
  2. Define an insertion mutation.
  3. What is a deletion mutation?
  4. Why might a single nucleotide substitution have no effect on the protein produced?
  5. What is a missense mutation and how does it arise?
  6. How does a nonsense mutation affect translation?
  7. Why do insertions or deletions of nucleotides not in multiples of three have such severe effects?
  8. Under what circumstances could a gene mutation be considered beneficial?
  9. When would a gene mutation be described as neutral?
56
Cellular ControlAnswers
Answers
Gene mutations and their effects
  1. The replacement of one or more nucleotides with different nucleotides in a DNA sequence.
  2. The addition of one or more nucleotides into a DNA sequence.
  3. The removal of one or more nucleotides from a DNA sequence.
  4. It may result in a silent mutation if the new codon still codes for the same amino acid due to the degeneracy of the genetic code.
  5. A missense mutation occurs when a substitution causes a different amino acid to be incorporated into the polypeptide, potentially altering protein structure and function.
  6. A substitution creates a premature stop codon, causing early termination of translation and producing a truncated, usually non-functional protein.
  7. They cause a frameshift mutation, altering all subsequent codons and typically producing a non-functional protein.
  8. When the altered protein confers a selective advantage to the organism.
  9. When the change does not significantly affect protein function or organism fitness.
57
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