survival and response Flashcards
how do organisms increase their chance of survival?
organisms increase their chance of survival by responding to changes in their environment
what is a stimulus?
a stimulus is a detectable change in the external (or internal) environment that produces a response in an organism
what are two types of simple responses?
two types of simple responses that can maintain mobile organisms in a favourable environment are taxes and kineses
what is a taxis?
a taxis (singular) is a simple response in which direction of movement of the organism is determined by the direction of the stimulus
what do taxes involve?
taxes involve a movement of the whole organism towards (positive) or away (negative) from a directional stimulus
how are taxes classified?
taxes are classified according to the directional response and the nature of the stimulus
what is a positive or negative phototaxis?
positive phototaxis is the movement of simple photosynthesising organisms towards light. this increases their chance of survival as they need light to produce organic compounds during photosynthesis
earthworms move away from light, negative phototaxis, increasing their chance of survival as they move into the soil and are not exposed to predators e.g. birds and are also less likely to become dehydrated.
what is chemotaxis?
chemotaxis is the movement towards or away from a high concentration of a particular substance. this enables bacteria to move towards a food source or away from toxic compounds.
what is kinesis?
this is a form of response in which the organism does not move towards or away from a stimulus. instead the response is related to the intensity of the stimulus and involves a change in the rate of movement and/or change in the rate of turning of the organism.
what is an example of an organism that carries out kinesis?
for example, woodlice placed in a dry environment respond by moving more rapidly but also turning less often, thus increasing their chance of moving into a more favourable environment. however, in a more humid or damp area the rate of movement decreases but turning increases, so the animal remains in it. this is of survival value as woodlice live in damp places, usually under logs or stones, where they are protected from predators and dehydration.
how are kinetic responses of woodlice observed?
kinetic responses can be observed through the use of woodlice in a choice chamber
what are tropisms?
a tropism is a growth movement of part of a plant in response to a directional stimulus. tropic responses are described as positive or negative depending on whether growth is towards or away from the stimulus respectively. tropisms can maintain the shoots and roots of flowering plants in a favourable environment.
how do plant shoots and roots grow?
plant shoots grow towards light (positive phototropism) so that their leaves can absorb light for photosynthesis.
plant roots grow away from the light (negative phototropism) and towards gravity (positive geotropism). this increases the probability that roots will grow into the soil to absorb water and mineral ions. plant roots also grow towards water (positive hydrotropism).
what is IAA?
indoleacetic acid or IAA (also known as auxin) is a plant growth factor which stimulates plant growth. it is produced in the growing regions of a plant e.g. the shoot and root tips. it then diffuses from these growing regions to other tissues.
how does IAA effect phototropism?
cells in the shoot tip produce IAA which diffuses down the shoot and is normally distributed equally stimulating upward growth of the shoot.
however, if a shoot is exposed to a unidirectional (i.e. from one direction) light stimulus, the light causes the movement of IAA from the illuminated side to the shaded side of the shoot.
a greater concentration of IAA builds up on the shaded side of the shoot than on the illuminated side. the higher concentration of IAA on the shaded side stimulates greater elongation of the cells on the shaded side. the shaded side grows faster, causing the shoot to bend towards the light.
