Tropisms and plant hormones Flashcards
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
What is a biotic factor
Living factor that affects a community therefore distribution of organisms e.g. Availability of food New predators New pathogens Competition
What do field studies enable us to do
Look at the distribution of organisms and the effects of environmental factors on this
Examples of field studies
Daisies may be more common in open field than under trees
some types of mayfly more common in colder parts of stream as can’t tolerate colder temps
How does the level of mineral ions available affect the distribution of venus fly traps
They thrive in areas where nitrate ion levels are very low as there are nitrate ions in the flys protein
What is random sampling
Using quadrats in areas in which distribution is quite uniform
What is systematic sampling
Using transects to observe changes in distribution across areas of the habitat
What is quantitative sampling
Take a number of random readings then find the mean number of organisms per m^2
How can you study distribution
Measure how common an organism is in 2 or more sample areas using quadrats and compare
study how distribution changes across an area placing quadrats along a transect
Why is random sampling a good idea when counting the number of daisies in a field
Too difficult to count them all so must estimate in logical way, avoiding bias and still getting accurate, representative reading
What else can you measure using a transect
abitoic factors such as light levels, soil pH that might affect the growth of plants along transect
What do plants compete for
Light
Space
Minerals from soil
What do animals compete for
Food
Mates
Territory
Structural adaptation
Features of an organism’s body structure e.g. fur colour, blubber
Behavioural adaptation
The way they behave e.g. huddling, migration, display, avoiding the sun
Functional adaptation
Process within organism e.g. hibernating lowers metabolism which conserves energy or conserving water my producing very little sweat
What are extremophiles
Mostly microorganisms that have adapted to live in extreme conditions
Conditions include extreme:
Temperatures Salinity pH Pressure Nutrients Oxygen levels etc.
Thermophiles
produce some of the bright colours in hot springs e.g. Yellow stone national park. They have thermostable enzymes that don’t denature at high temps
Ice fish found in Antarctica
Have no haemoglobin but enlarged hearts and very large blood vessels
Water bear
Many species of tardigrades live in water but on land you find them almost everywhere there’s moss or lichen. can survive long periods of desication and have survived being taken to space
How do rooting powders increase the chances of a plant growing
Contains auxin so when cutting dipped in powder, chances of success greatly increased as stimulates growth
How is auxin used as weed killer
If sprayed on weed, excessive auxin sends plant to uncontrolled growth, killing them.
Most weeds are broad leaved so large SA meaning more successful at killing but narrow leaved plants are unaffected as small SA
How is Auxin used in modern plant tissue cultures as part of plant cloning
They stimulate growth and cell division in the tissue culture, helping to produce many identical plants to help farmers
How are Gibberellins used
brewing industry to end seed dormancy, speeding up germination of barley seeds to make malt
promote flowering throughput year e.g chrysanthums
increase size of fruit e.g. seedless grapes would be small as seed contain gibberellins to make fruit grow
How is ethene used
growers harvest unripe fruit, transported and chilled so won’t get damaged and not over-ripe if any delays
stored until needed
warmers temps then ethene added to atmosphere meaning fruit can be rapidly ripened and sold when needed
