6.1- Survival and response

What is a stimuli?

A change in an organism’s internal or external environment that can be detected

What is a tropism? 

why do they rely on this?

how does the response take place?

A plant’s growth response to external, directional stimulus

They rely on this to maintain their roots and shoots in a favourable environment 

form of bending/turning in a certain direction

How is a response positive? 

how is a response negative?

If the growth is towards the stimulus 

if growth is away from the stimulus

Plant shoots grow towards light? (type of response + survival value)

Positive phototropism 

Absorb light for LDR in photosynthesis

Plant roots grow away from light (type of response + survival value)

Negative phototropism

Roots grow into soil- anchorage and increase chances of absorbing ions and water 

Young roots of seedlings grow towards gravity (type of response + survival value)

Positive gravitropism

Roots grow into soil- anchorage and increase chances of absorbing ions and water 

Young stems of seedlings grow away from gravity (type of response + survival value)

Negative gravitropism

Grow out of soil- leaves exposed to Sun 

Plant roots grow towards water (type of response + survival value)

Positive hydrotropism

Root systems grow and spread in soil- more water 

what possible conclusions can be made from the results?

stimulus detected by tip of shoot

shoot tip could somehow regulate bending response

What are plant growth factors?

why aren’t they called hormones? (3)

where are they produced and what do they do?

1) chemical messengers that allow plants to respond to external stimuli

2) Affect growth of the whole/part of a plant OR affect tissues that release them

Not secreted by glands and don’t travel in transport system 

3) Produced in growing regions of plant- either stimulate and inhibit growth 

What is IAA and what does it do?

One of the main ones auxins- controls directional growth seen in tropisms 

What is the role of IAA in shoots (in response to light)?

what kind of response is it?

IAA produced in tip of shoots 

Diffuses from light side to shaded side 

Higher concentration of IAA builds up on shaded side, causing more elongation of the cells than on the light side 

Causes shoot to bend and grow towards the light 

Positive phototropism

What is the role of IAA in roots (in response to light)? (4)

what kind of response it?

IAA moves away from the unilateral light source

Accumulates on the shaded side 

High IAA concentration on the shaded side inhibits growth 

The shaded side grows at a slower rate, causing roots to bend away from the light 

Negative phototropism 

if a seed is left horizontally to grow, how would the roots and shoots respond?

where does IAA move?

what are the responses called?

the root grows downwards and the shoot grows upwards 

IAA moves down to the lower side

Roots- positive gravitropism 

Shoots- negative gravistropism 

What are taxes and kinesis?

what do they allow mobile organisms to do?

Simple innate forms of behaviour that rely on simple reflex actions 

respond to environmental changes and maintain them in favourable conditions for survival

What are the charaacteristics of taxes and kinesis?

Genetically determined

Stereotyped pattern

What is taxis?

A simple, directional response to a stimulus and carried out by the whole organism 

Can be positive or negative 

Some bacteria move towards a high concentration of glucose (type of response + survival value)

Positive chemotaxis- more binary fission + respiration 

Male insects of some species fly towards chemicals secreted by mature females of the same species (type of response + survival value)

Positive chemotaxis- more likely to find mates 

Single-celled algae move towards light (type of response + survival value)

Positive phototaxis - more photosynthesis + increase survival chances 

earthworms move away from light (type of response + survival value)

Negative phototaxis- conserve water- avoiding dehydration 

What is kinesis?

what is the rate of movement related to?

Non directional response to a stimulus i.e random movement

Rate of movement/direction related to intensity of stimulus 

Woodlice move faster and change direction less often in drier conditions. how does this increases their chance of survival?

Move fast + turns less (moves in straight line) - in dry conditions

Move slow + turn in circles- if in damp conditions 

What is the nervous system split into?

Central nervous system: spinal cord + brain

Peripheral nervous system- sensory and motor neurons 

What do sensory neurons do?

What do motor neurons do?

Carry nerve impulses from the body to the CNS

Carry nerve impulses away from the CNS to the effectors

What is the summary of nervous control?

Receptor (on organ e.g skin) detects stimuli

Sensory neuron carries nerve impulse from body to CNS 

Relay neuron connects sensory and motor neuron 

Motor neuron carries nerve impulse from CNS to body 

Effector (muscle/gland) carries out response 

What is a reflex action?

A rapid, short lived, involuntary response to a specific stimulus