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- Subject: Biology
- AS: AS 91603
- Level: 3
- Credits: 5
- External
Biology 3.3 Demonstrate understanding of the responses of plants and animals to their external environment
Subject content
Responses are selected from those relating to:
- plant orientation in space
- tropisms – phototropism (response to light stimulus) and the role of auxin (hormone), geotropisms/gravitropism (response to gravity), thigmotropism (the response to touch), hydrotropism (response to water), and chemotropism (response to a chemical stimulus)
Tropisms may be positive or negative responses. - nastic responses eg Plants in Action
- animal orientation in space
- taxes types of taxes include: chemotaxis (chemicals), geotaxis (gravity), thermotaxis (heat), hydrotaxis(water), thigmotaxis (touch) Each type of taxis response is also to be described as negative (taxis is away from the stimulus) or positive (taxis towards the stimulus). For example, when an organism moves bodily towards a chemical stimulus, such as a pheromone, it is said to be positively chemotaxic. Read about animals that release or detect pheromones.
- kineses orthokinesis (the organism’s speed of movement), klinokinesis (the organism’s rate of turning)
- homing
- migration
Migration is an extraordinary behavioural adaptation that many species exhibit, and which contributes to the survival of a species. For example, to gain the benefits of staying in a perpetual summer, the New Zealand godwit or kuaka makes the longest non-stop bird migration known in the world from New Zealand to Alaska. Read about how they store enough fuel for this extraordinary flight. - orientation in time
- annual
- daily – diurnal, nocturnal, and crepuscular
- lunar
- tidal rhythms
- biological clocks – exogenous rhythms, endogenous rhythms, and understanding actograms
- interspecific relationships
- competition for resources
- mutualism
- exploitation including herbivory, predation, and parasitism Predator and prey are often tied together in many ways. The populations of predator and prey are related. If the predator population is low, the numbers of the prey species will increase. Most predator species will reproduce in larger numbers if food is abundant. As the numbers of the predator species increase, the prey population begins to decline. This process means the 'less fit' individuals are weeded out, helping the gene pool of both the predator and the prey to stay strong.
- intraspecific relationships
- competition for resources
- territoriality
- hierarchical behavior
- cooperative interactions – social behaviour, clumping
- reproductive behaviours – parental care, courtship, pair-bonding, monogamy, polygyny, polyandry, polygynandry, and polygamous
Both biotic and abiotic environmental factors need to be considered when explaining adaptive advantage for the organism in relation to its ecological niche.
Be familiar with the following terms:
| agonistic behaviour | auxin | biological clock | cooperative breeding |
| courtship | endogenous | entrainment | exogenous |
| free running period | home range | kin selection | photoperiodism |
| zeitgeber |
