aurvival and response

What is a stimulus

A change in the internal or external environment that is detected and leads to a response

The advantages to organisms of being able to respond to stimuli

• ability to respond rapidly increases chances of survival

• Organisms move away from harmful stimuli

• Organisms move towards food source

• Organisms are able to maintain a stable internal environment (homeostasis)

The simple reflex

1. Stimulus

2. Receptor- detects stimuli and are specific to type of stimuli

3. Coordinator- sensory neurone to relay neurone in CNS to motor neurone. Can be molecular or hormonal

4. Effector- produces the response from muscle or glands

5. Response

Why is reflex response to stimuli protective

It is immediate and automatic preventing harm and instinctive which increases chances of reproduction

What is taxes

Taxis is a movement towards or away from a stimulus

What is positive taxis

Towards a favourable stimulus

Negative taxis

Away from unfavourable stimulus

4 examples of taxis

Phtototaxis

Geotaxis

Chemotaxis

Rheotaxis- air/ water currents

Kinesis

A response where an organism changes the speed of movement and rate of change of direction of its random movement in response to an environmental stimulus to increase the chance of returning to a favourable environment

What are the 3 things you need to say in kinesis

• Speed of movement and degree of turning depends on strength of stimulus

• Stimulus isn’t localised

• Keeps organism in favourable conditions

What is a tropism

Growth of a plant in response to a directional stimulus

Tropism names for light, gravity and water

Light- phototropisn

Gravity- geotropism

Water- hydrotropism

Do plants have positive or negative hydrotropism

Positive hypotropism- move towards water

Tropism in plants shoots vs roots

Shoots- plant shoots grow towards light ( positive phototropism) and away from gravity (negative gravitropism) so leaves are in the most favourable position to capture more light for greater rate of photosynthesis.

Roots- plant roots grow away from light (negative phototropism) and towards gravity ( positive gravitropism) increasing the probability that roots will grow into the soil where they are better able to absorb more minerals and ions

What is IAA

Indoleacetic acid is a type of auxin which controls plant elongation

What does IAA do

Stimulates cell elongation in shoots

Inhibits cell elongation in roots

Phototropism in plant shoots using IAA

Gravitropism in plant roots using IAA