Plant Responses Flashcards
Tropism
A change in the growth of a plant in response to an external stimulus
Define stimulus
Anything that causes a reaction in an organism or in any parts of it
Positive tropism
When the growth is towards the stimulus
Negative tropism
When the growth is away from the stimulus
Phototropism
The change in the growth of a plant in response to light.
Increased photosynthesis when leaves are held up to more light
Geotropism
Change in growth of a plant in response to gravity
Roots grow down into soil for water and minerals
Thigmotropism
Change in growth of a plant in response to touch
Stem and tindrels of ivy wrap around objects to keep leaves upright
Hydrotropism
Change in growth of a plant in response to water
Roots grow towards water in the soil
Chemo tropism
Change in growth of a plant in response to chemicals
Roots grow towards minerals
What is a growth regulator
A chemical that controls the growth of a plant
Where are growth regulators made?
In the meristematic regions of a plant. I.e the shoot and root tips and the tips of side shoots
Where are growth regulators transported in?
The xylem and phloem
Similarity with growth regulators to hormones
Chemical in nature
Action is long lasting
Growth promotor example
Auxins , IAA
Growth inhibitor example
Ethene
Auxins
Transported in the…
Phloem
Where does auxin exactly promote growth?
Just behind the shoot and root tip, in the zone of elongation
Effects of auxins
Cause cell elongation and growth or bending in phototropism and geotropism
Describe auxins role in apical dominance
Auxin is produced in the apex of a plant and moves down the plant and inhibits growth in the lateral side shoots
This means the tip of the plant will grow but not the sides. ( think of a cyprus tree )
Gardeners prune the tips of plants to allow the side shoots to develop and grow a bushier full plant
Auxins role in fruit formation
IAA is made in developing seeds which stimulates the formation of fruit around the seeds ( help with protection, animal dispersal)
Auxin role in root growth
IAA at LOW concentrations causes roots to grow
Roots grow down LOW therefore LOW conc IAA
Auxins role in phototropism
Auxin loosens cell walls and allows them to expand which allows growth and tropisms
In a plant;
If the shoot is exposed to light from one side, auxin will diffuse down the shaded side
The higher concentration of auxin in the shaded side allows the cells to elongate more than unshaded cells on the bright side
As a result of the uneven elongation, the stem bends towards the light.
Growth inhibitors
Ethene - what is it and where is it made?
A gas
Made in stem nodes, ripe fruits and decaying leaves
Ethenes role
Plays a major role in ripening fruits, stimulating leaves to fall in autumn and ageing plants
Ethene is used commercially to ripen bananas
What is an adverse external environment ?
Surroundings that are harmful to an organism
Give 3 example of an anatomical protective feature of a plant
Cacti have sharp spines to protect against grazing animals
Nettle leaves have sharp hairs with a stinging poison
Plants are enclosed by a physical barrier consisting of epidermis , bark or a thick cuticle which prevents the entry of pathogens and reduces water loss.
3 examples of chemical protective features of plants
Oak trees produce tannins in their leaves to protect them against caterpillars
Rhubarb leaves contain oxalic acid which has a bitter taste
Plants contain heat-shock proteins which surround other proteins such as enzymes and help them maintain their shape
