Tropisms and plant hormones Flashcards
(49 cards)
What is a tropism
Growth/ movement of part of a plant in response to directional stimulus
What’s a positive response
When the plant grows towards the stimulus
What’s a negative response
When a plant grows away from the stimulus
How do plants detect and respond to stimuli
Sense light and grow and grow towards it to maximise amount they receive
sense and respond to gravity, ensuring roots and shoots grow in right direction
What is the response for light and how does a plant show its response
Phototropism
positive in shoots grows towards light
negative in roots as they grow towards the ground
What is the response for gravity and how does a plant show its respnse
Geotropism
positive in roots to seek anchorage in soil
negative in shoots allowing it to grow in right direction without any light
What is the response to water and how does a plant show its response
Hydrotropism
positive in roots to seek water
negative in shoots
What is auxin
Plant hormone that controls growth near tips of roots and shoots in response to different stimuli
Which direction does auxin diffuse
Backwards to stimulate cell elongation which happens in cells just behind the tips
What happens if the tip of the shoot is removed
No auxin is available so the plant stops growing
What does auxin in the shoots do
Stimulates cell elongation
What does auxin in the roots do
It inhibits growth (in high concentrations)
What does unequal distribution of auxin cause
Unequal growth rates in plant shoots and roots
Auxin and gravity process
At start equal distribution of auxin in roots and shoots
auxin diffuses downwards behind tip of roots and shoots
cells in roots where no auxin is grow faster than other side where auxin is as it inhibits growth in roots and grows down
auxin on lower side in shoot stimulate elongation so shoot grows away from direction of gravity
Auxin and light process
If light from above: auxin diffuses behind shoot evenly so equal growth upwards
If light from side: auxin accumulates on shaded side so greater cell elongated on shaded side causing it to grow towards the light
What happens if tips of plant are capped
no stimulation from sun so no auxin production, no growth, auxin diffuses downwards so plant grows straight
Definition and example of population
All the organisms of one species living in a habitat e.g. cat tails
Definition and example of community
Populations of different species living in a habitat e.g. all organisms in a pond
Definition and example of ecostystem
The interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment e.g. rainforest, arctic, barier reef
Definition and example of habitat
Where an organism lives e.g. woodland, grassland, ice cap
What is interdependence
Organisms are dependent on their organisms within their community to survive and reproduce
What other organisms may organisms depend on
Food
Shelter
Pollination
Seed dispersal
What is a stable community
One where all the species and environmental factors are in balance so the population remains fairly constant
What is an abiotic factor
Non-living factors which can affect a community e.g. Light intensity Temperature Moisture levels Soil pH Soil mineral content Wind intensity and direction Carbon dioxide levels for plants Oxygen levels for aquatic animals
