Trace all five steps of natural selection
Link inherited variation, many offspring, resource competition, reproductive chance and allele transmission.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Use the stated case, sample and assumptions. Diagrams and numerical records in this pathway are original teaching models; written answers are self-checked.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which order best explains natural selection?
What you will learn
- Explain the complete natural-selection sequence
- Use a new case without leaving out inheritance or reproduction
Original selection schematic. Population counts and scenarios are supplied teaching models; they are not field observations.
| Stage or record | Meaning |
|---|---|
| 1 · Variation | Inherited short and long beaks |
| 2 · Struggle | Many chicks; limited food |
| 3 · Reproduction | A greater chance in the stated food context |
| 4 · Next generation | Associated alleles can be passed to offspring |
Explain the complete natural-selection sequence
Use all five links in order. First, individuals within a population show inherited variation. Second, many offspring are produced. Third, individuals struggle to survive, including competition for limited resources. Fourth, those better adapted to the stated environment have a greater chance of reproducing. Fifth, they pass their alleles to the next generation.
In an original island bird case, the population contains short- and long-beaked birds, and the problem states beak length is inherited. After a shift in available food, many chicks hatch; only some reach breeding age while food is limited. The case reports that long-beaked birds leave more offspring when the remaining seeds are deep inside fruit.
Use a new case without leaving out inheritance or reproduction
The explanation is not “birds needed longer beaks, so their beaks grew.” It is that variation was already present, conditions affected reproductive success, and parents passed alleles to offspring. A single generation is a start, not proof of a long-term trend. Repeated population records would show whether the pattern continues.
Use the qualifier “greater chance”: some short-beaked birds may reproduce, and some long-beaked birds may not. Other environmental factors may matter. Unless genotypes are supplied, describe inherited features and allele transmission without inventing exact allele frequencies. The sequence should explain a population pattern, not assign intention to an individual.
Sources for this lesson
Pause and explain
Why does the complete explanation mention offspring alleles?
Worked example
In the island-bird case above, state the five natural-selection links in order and identify one conclusion the case does not establish.
Show the worked solution
- Start with the inherited beak variation, then account for many chicks and limited food.
- Link food access to a greater chance of breeding; finish with parents passing alleles to offspring.
Answer The population has inherited beak variation; many chicks are produced; food is limited and competition occurs; long-beaked birds have a greater chance of reproducing in the stated food context; they can pass associated alleles to offspring. The case does not show every long-beaked bird reproduces or guarantee the pattern in another habitat.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A population has inherited striping variation. A new substrate changes predator detection; the case records that more striped adults produce chicks. Give a complete five-link account.
Give me a hint
Use the five links and keep the advantage conditional.
Compare my reasoning
- Name inherited variation and many offspring.
- Add limited resources/struggle, compare reproductive chance and state allele transmission.
Inherited striping variation exists; many young are produced; individuals face survival pressures including the stated conditions; striped adults have a greater chance of producing offspring in this setting; they can pass associated alleles to descendants.
Look for these in your work
- All five links included
- Context and chance retained
An answer says, “The largest fish survive, so the species becomes stronger.” Identify two missing or unsupported parts.
Give me a hint
Check for a limited resource, offspring contribution and inherited transmission.
Compare my reasoning
- “Largest” is not linked to the stated environment or a measured resource.
- Survival alone omits reproduction; the answer also needs inherited variation and allele transmission.
The answer lacks evidence for inherited variation, resource competition, greater reproductive chance and allele transmission; “stronger” is vague and may imply a universal ranking.
Look for these in your work
- Missing selection links named
- Unsupported wording corrected
A dry-region plant population has inherited shallow and deep roots. In one season, deep-rooted plants produce more seeds; the next season rainfall shifts and seed counts are equal. Evaluate a claim that deep roots will inevitably take over.
Give me a hint
Compare both seasons and avoid extrapolating from one conditional record.
Compare my reasoning
- The first season supports a context-specific difference in seed output.
- The later equal counts do not show a continuing advantage; longer comparable records are needed.
The claim is not established. The advantage was conditional and not repeated in the second record; explain the full chain only where variation, competition, reproduction and inheritance are supported.
Look for these in your work
- Contrasting seasons used
- No inevitable trend
Common mistakes
- Omitting allele transmission
- Replacing reproductive chance with guaranteed survival
- Claiming individuals change beaks because they need to
What can you explain now?
Why does the complete explanation mention offspring alleles?
Compare with the explanation
They connect reproductive differences to the next generation
Allele transmission explains how an inherited population pattern continues.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Without your notes, explain the complete natural-selection sequence and use a new case without leaving out inheritance or reproduction. Explain the mechanism, use the given population or breeding records and state what the evidence does not establish.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.