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Responses to the external environment · Part 3 of 5
9 exam-style questions with model answers, plus 12 quick multi-choice questions — every question on this part of the standard, grouped by the 3 pages of notes they come from.
Write a full answer before you reveal the model one. That comparison is where the learning happens.
Describe the difference between an endogenous and an exogenous rhythm, and describe how an experiment could distinguish between them.
Kiwi are nocturnal, emerging to forage shortly after dusk. Explain how this rhythm is controlled and why it provides a selective advantage in relation to the kiwi's ecological niche.
An internal clock is metabolically costly to build and run, and it must still be corrected daily by an environmental cue. Discuss why natural selection has favoured internal clocks rather than direct responses to the environment, and evaluate when a direct response might be favoured instead.
Describe what is meant by a tidal rhythm and a lunar rhythm, giving the approximate period of each, and describe one response controlled by each.
A bivalve living buried in a mudflat opens its shell to filter feed only when the tide covers it. Explain how this rhythm is controlled and why it provides a selective advantage in relation to the bivalve's ecological niche.
A single shore organism may show both a circadian and a tidal rhythm. Discuss why maintaining two separate clocks could be advantageous, and evaluate the difficulties this creates for the organism.
Describe what is meant by photoperiodism, and describe two annual responses it controls — one in a plant and one in an animal.
A deciduous tree sheds its leaves each autumn, triggered by shortening days rather than by falling temperature. Explain how this response occurs and why it provides a selective advantage in relation to the tree's ecological niche.
Climate change is causing spring temperatures in New Zealand to rise, but day length is unaffected. Discuss the implications for organisms whose annual rhythms are cued by photoperiod, and evaluate which species are most at risk.