Y13 3.4 Plants and Animals

Part 1: The environment

The environment is the sum total of abiotic and biotic factors of an area that influence the lives of the organisms present.

Abiotic factorsPhysical factors that can act as stimuli (most have a latin prefix they are known by)

• Light (photo)• Gravity (geo)• Temperature (thermo)• Water (hydro)• Current (rheo)• Chemicals (chemo)• Touch (thigmo)

• Sound• Pressure• Wind• Substrate• fire

• Tolerance: most organisms try to keep within a narrow range of physical factors in order to stay in their ‘optimum range’ of tolerance.

Biotic factors

• All relationships between members of the same species (intraspecific) and members of different species (interspecific). Relationships can be harmful, beneficial or neutral.

Response of organisms to the environment

• The response of organisms to the above environmental factors (abiotic and biotic) is behaviour. If the behaviour is genetic (e.g. born with it) then it is called innate. Otherwise it is learned. Some behaviour can be a mix of both.

• Behaviour consists of:– Stimulus: a change in the environment that

causes a response in an organism.– Receptor: any cell or group of cells that can

detect this change.– Effector: a cell or group of cells that respond

to the change.

Behaviour operates on a feedback system – hence why you can learn it!

Some more definitions you need:

• Ecosystem: all living things and physical things in an area.

• Habitat: the place or environment in which a specific organism lives.

• Limiting factor: any factor of the environment that limits the activity of an organism or population.

• Anthropomorphism: ascribing human emotions to animals (DON’T DO IT).

• Ecological niche: an organisms way of life, describes the opportunities provided by the habitat and adaptations of the organism to make the most of the opportunities.

• Adaptations: are inherited and can be structural, behavioural, physiological or life history.

• Gause’s principle: this states that no two species with identical ecological niches can co-exist for long in the same place.

Biological Timing Responses

• Can be annual, daily or lunar and are governed by internal clocks.

• Biological clock: internal timing system that continues without external clues and can control the organisms response.

• Period of the rhythm: time it takes to complete one cycle of activity.

• Phase shift: when the start of the activity period is changed.

• Free running period; when the biological clock is running without any environmental clues.

• Entrainment: the resetting of the biological clock on a regular basis, done by a zeitgeber.

• Zeitgeber: environmental agent that resets the biological clock e.g. change in light etc.

• Circa: about, circadian = about a day.• Photoperiod: response of organism to length of

day or night.• Exogenous rhythm: one controlled by external

environmental stimuli detected by organism.• Endogenous rhythm; one controlled by internal

clock. E.g.

Biological orientation responses

• Tropism: growth towards or away from stimulus coming from a set direction

• Taxes: movement of whole organism toward or away from stimulus.

• Kinesis: non-directional response to stimulus• Nastic movement: response to stimulus but

independent of stimulus direction.• Homing: ability to find and return to a home site.• Migration: annual mass movement of animals

between breeding and non-breeding areas.

Responses to Biotic factors

• Intraspecific– Competition– Reproduction– Aggressive interactions– Cooperative interactions

• Interspecific– Competition– Predator/prey– Plant/animal– Succession– Stratification– zonation– Animal/animal and plant/plant