AQA GCSE Biology Biology Paper 2 (Foundation), June 2023: Question 9

✅ Correct Answers

09.1 (Genetically Different):

• Not all plants are susceptible to the same disease / pathogen.
• Produces variation in characteristics (e.g. flavours, colours) to meet different consumer preferences.
• Maintains / increases the gene pool.

09.2 (Genetically Identical):

• All plants share the same desirable trait (e.g. high yield, great taste).
• They grow at the same rate and are ready to harvest at the exact same time.

❌ Common Errors

• Vague statements: Saying "they are stronger" or "they taste better" without specifying consistency or variation.
• Confusing the two: Believing identical plants resist diseases better (the opposite is true: if one gets sick, all are vulnerable).

💡 Key Knowledge

Tissue culture: Growing a new organism using a small group of cells or tissue taken from a parent plant, placed on an agar medium with nutrients and hormones under sterile conditions.

Phenotype = Genotype + Environment: Clones have identical genotypes, but their final appearance (phenotype) is altered by differences in micro-environment.

✅ Accepted Answers

09.3 Definition:

(A group of) cells are grown (into a new plant/organism)

09.4 Reason for variation in height:

• Different exposure to light / shading.
• Different amounts of water (or rain).
• Different amounts of mineral ions (e.g. nitrates/magnesium).
• Different soil pH, spacing/plant density, or attack by pests/disease.

❌ Mark Scheme Traps

• 09.3: Writing simply "making clones" is ignored because it does not define the actual process.
• 09.4: Writing "nutrients" or "sun" without further qualification is often rejected. Always specify minerals/ions and light.

📐 Completed Punnett Square (09.5)

1 mark: Male gametes (X, Y) | 1 mark: Female gametes (X, X) | 1 mark: 4 correct offspring cells

🧠 Exam Technique (09.6)

Question: Why expect 3 male and 3 female puppies from a litter of 6?

• State the ratio or percentage shown by the grid: 50% / 1:1 probability.
• Mention that half of the offspring genotypes are XX (female) and half are XY (male).
• Alternatively: There is an equal probability of an X sperm or a Y sperm fertilising the egg.

💡 Control Variables (09.7)

To ensure a valid comparison between chicken varieties A and B, all other conditions must be controlled (choose any two):

• Type or amount of food / water
• Housing conditions (indoor vs outdoor temperature, space/stocking density)
• Light intensity or day length
• Age or starting mass of the chickens
• Health status / vaccination history

🧠 Why Sample 500 Chickens? (09.8)

Sample size questions appear frequently across GCSE papers. Memorise these exact phrases:

• Reduce the effect of anomalies / random variations
• To calculate a more representative / valid / accurate mean

❌ Common Misconceptions

• Never say "to prevent anomalies". A large sample does not stop anomalies happening; it reduces their effect on the mean.
• Avoid simply writing "to make it fair". "Fair test" is KS3 terminology—use valid or accurate.

✅ Model Answer (Full 4 Marks)

• Step 1: Cross / breed the best of variety A (high egg production) with the best of variety B (high growth rate / meat) [1 mark].
• Step 2: From the offspring, select those that produce the highest number of eggs and have the heaviest body mass [1 mark].
• Step 3: Breed these selected offspring together [1 mark].
• Step 4: Repeat this process over many generations [1 mark].

❌ What Loses the Final Mark?

Students often write: "Keep repeating by breeding the original parents again."

This gets 0 marks for step 4! You must state that you breed the offspring together and repeat over several / many generations.