Stimulous + Response Flashcards
Stimulus
A detectable change in the internal or external environment of an organism that produces a response in the organism
Role of receptor
Detect stimulus
Role of coordinator
Formulates a suitable response to stimulus
Role of effector
produces a response
The importance of responding to stimuli (5 things)
- Increased chance of survival
- Detect + move away from harmful stimuli
- Detect + move towards a food source
- Organisms that respond and survive have a greater chance of passing on alleles to offpsing
- Selection preassure favours organism that are more able to repsond
How do receptors communicate with effectors?
- Plant growth factors - slow
- Nerves - Rapid
- Hormones - Slow/fast
Taxis + Kinesis
Simple response that can maintain a mobile organism in a favourable environment
Taxis
Simple response where direction of response is determined by direction of stimulus
Kinesis
A random response where movement is nt related ot the direction of stimulus
- Favourable conditions - organisms move around and chage directions less to remain in conditions longer
- Unfavourable conditions - the more unfavourable the more it moves around and changes directions to reduce time spent in conditions
Tropism
A growth response in plants where direction of response is determined by direction of stimulus (only part of plant moves - immobile)
The acid made in tropism
Indoleacetic acid (IAA)
Phototropism in shoots
- Shoot tips produces IAA
- In presence of light diffues away to the shady side
- Stimulates more elongation in shoot cels on the shady side whilist celss on the other side remain unstimulated
- Shots bend towards light to increase photosynthesis
Gravitropism in roots
- Roots grow in the direction of gravity to absorb mineral ions from soil
- IAA diffuses to the cells at the bottom of the root tip
- They inhibit elongation so upper cells elongate normally and root tips bends downwards
