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Responses to the external environment · Part 2 of 5
12 exam-style questions with model answers, plus 16 quick multi-choice questions — every question on this part of the standard, grouped by the 4 pages of notes they come from.
Write a full answer before you reveal the model one. That comparison is where the learning happens.
Describe what is meant by a tropism, and describe the response of a shoot placed in one-sided light.
A young rimu seedling on the forest floor receives light only through a small gap in the canopy directly above and to one side. Explain how its phototropic response occurs and why it provides a selective advantage in relation to its ecological niche.
Compare the phototropic response of a shoot with the gravitropic response of a root, and discuss why a plant benefits from having both responses controlled by the same hormone.
Describe the difference between a tropism and a nastic response, and give one example of each.
The flowers of a coastal herb open during daylight and close at night and in heavy cloud. Explain how this response occurs and why it provides a selective advantage in relation to the plant's ecological niche.
A plant shows both a phototropic growth response and a photonastic flower response to the same stimulus — light. Discuss why natural selection has favoured two different mechanisms for responding to one stimulus.
Describe what is meant by a taxis and by a kinesis, and give one example of each.
Freshwater kōura shelter under rocks during the day and emerge to forage at night. In a laboratory tank with a light gradient, they consistently move to the darkest end by the most direct route. Explain how this response occurs and why it provides a selective advantage in relation to the kōura's ecological niche.
Two invertebrate species both end up concentrated in damp leaf litter, but one does so by chemotaxis towards humidity and the other by klinokinesis. Discuss the relative advantages of the two mechanisms, and evaluate under what conditions each would be favoured by natural selection.
Distinguish between homing and migration, and describe two cues an animal may use to orient over long distances.
Longfin eels (tuna) spend decades in New Zealand fresh water, then migrate thousands of kilometres to spawn in the tropical Pacific, breed once and die. Explain why this migration provides a selective advantage, despite its cost.
Migratory birds typically possess several navigation systems — magnetic, solar, stellar and olfactory — rather than one highly accurate system. Discuss why natural selection has favoured redundancy, and evaluate what this implies for migratory species facing environmental change.