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Grade 8 · unit review

Review: Variation, Selection and Common Ancestry

Explain population change through inherited variation and evidence.

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Bring the unit skills together

Use these 4 new cases to check your reasoning. Choices are temporary and are not saved to an account, sent to staff or recorded as school grades. Download your current review choices before leaving or reloading.

Unit review questions
1. Which scientific label fits the specifically described step or feature? Supplied case: Variation exists before a habitat change.
Need a hint?
  • Look for the described feature: differences among individuals.
  • Compare the given mechanism with the other labels; do not infer unmentioned events.
2. Supplied case 5: trait count=36; population count=80, using the explicitly named quantities. Trait percentage equals 100 times trait count divided by total count. What result follows?
Need a hint?
  • Trait percentage equals 100 times trait count divided by total count.
  • Count the same trait definition across intervals.
3. Which scientific label fits the specifically described step or feature? Supplied case: DNA relationships support a branching model.
Need a hint?
  • Look for the described feature: sequence comparisons supporting relationships.
  • Compare the given mechanism with the other labels; do not infer unmentioned events.
4. Which scientific label fits the specifically described step or feature? Supplied case: Most recent shared branching point.
Need a hint?
  • Look for the described feature: branch point connecting lineages.
  • Compare the given mechanism with the other labels; do not infer unmentioned events.

The download contains your current choices and any checked feedback. Keep the separate transfer-task work in your own document; downloading its instructions does not mark it complete.

Use the skills in a new task

Create a four-panel explanation for “Variation, Selection and Common Ancestry” using one supplied case from each lesson. Include the observation, scientific mechanism or calculation, result and a limitation. You may draw and speak your explanation; all inputs are supplied.

Work on paper or in your own document. Explain the choices you made.

  • Use one supplied case from each of the four lessons.
  • Name the relevant structure, quantity or process in every panel.
  • Show calculations with units or a causal evidence chain.
  • Distinguish source facts from fictional classroom data.
  • State a model limit or a condition that would change the result.
Compare with a model response

Panel 1: A heritable beak-size variant exists before drought and leaves more offspring during drought. What sequence fits? Which inference or prediction is best supported? Result: Existing heritable variation can become more frequent through differential reproduction.. Reasoning: Variation precedes selection in this case; changing frequencies does not require intent. Model limitation: only the stated classroom boundary and supplied observations are established; unmeasured real-world performance remains unverified. Panel 2: Supplied case 1: trait count=15; population count=50, using the explicitly named quantities. Trait percentage equals 100 times trait count divided by total count. What result follows? Result: 30 %. Reasoning: Substitute the supplied values: 100*(15)/(50) = 30 %. Use total population as denominator. A frequency change alone does not prove its cause. Model limitation: only the stated classroom boundary and supplied observations are established; unmeasured real-world performance remains unverified. Panel 3: Two limbs share underlying bone organization but perform different tasks. What is supported? Which inference or prediction is best supported? Result: Different functions do not rule out homologous ancestry.. Reasoning: Homology concerns ancestry of structures; function can diverge and other evidence remains relevant. Model limitation: only the stated classroom boundary and supplied observations are established; unmeasured real-world performance remains unverified. Panel 4: A tree joins A and B at one recent node; C joins earlier but is printed beside A. Which inference follows? Which inference or prediction is best supported? Result: A and B share the more recent modeled common ancestry.. Reasoning: Branch connectivity and node order matter more than layout spacing. Model limitation: only the stated classroom boundary and supplied observations are established; unmeasured real-world performance remains unverified.

A different response can also meet the criteria. Compare the evidence and reasoning, rather than copying the wording.