Which of the following factors is not a source of variation in living organisms?

Step 1: Analyze the question We need the option that is NOT a source of variation among living organisms.

Step 2: Key concept Variation is the differences between individuals of the same species. It arises from:

• Environment: Differences in food, light, climate and soil cause differences in growth and appearance (e.g. plants of the same type grow taller in fertile soil).
• Inheritance (genetic factors): Offspring receive different combinations of genes from their parents.
• Meiosis: This is a major source of genetic variation because of crossing over and independent assortment of chromosomes, which produce genetically different gametes.
• Mutation and random fertilisation also contribute.

Step 3: Mitosis Mitosis produces two daughter cells that are genetically identical to the parent cell. It is used for growth, repair and asexual reproduction. Because it makes exact copies, it does not produce variation (barring rare mutations).

Step 4: Evaluate the options

• A. Environment: a source of variation.
• B. Inheritance: a source of variation.
• C. Mitosis: produces identical cells, so it is NOT a source of variation.
• D. Meiosis: a source of variation.

Answer: C. Mitosis

Exam tip: Remember "Mitosis = Make an Identical Twin cell" and "Meiosis = Mixes genes". If a question asks what does not cause variation, look for the process that makes exact copies.