Plant responses

Question 1

Abiotic environmental stimuli

Answer 1

Non-living components of the environment

Question 2

Biotic environmental stimuli

Answer 2

Living components of the environments

Question 3

Why do plants need to defend themselves?

Answer 3

Avoid predation- e.g plant toxins
Avoid abiotic stress- e.g carrots and antifreeze proteins
Survive- to ensure germination in suitable conditions, seed dispersal, cope with changing environmental conditions, maximise photosynthesis
Avoid herbivory

Question 4

Nastic response with e.g

Answer 4

A non-directional response to stimuli e.g thigmonasty- Mimosa pudica (rapid water uptake in cells at base and rapid loss from adjacent cells)

Question 5

Physical plant defences

Answer 5

Thorns, hairy leaves, leaf folding, bark and waxy cuticle

Question 6

Herbivory

Answer 6

The process by which herbivores eat plants

Question 7

Chemical plant defences

Answer 7

Tannins, alkaloids, pheromones

Question 8

Pheromones

Answer 8

-Chemicals released by one individual, which can affect the behaviour and physiology of another member of the same species
-Acting like hormones outside of the body of the secreting individual
-e.g alarm pheromones, food trail etc

Question 8

Alkaloids

Answer 8

-Nitrogenous compounds derived from amino acids
-Very bitter, noxious smells or poisonous characteristics that deter or kill herbivores
-Act as drug that affects metabolism of the animal
-Located in growing tips and flowers, peripheral cell layers of stems and roots

Question 9

Pheromones e.g

Answer 9

-maple trees release a pheromone in response to being attacked by insects
-absorbed by leaves on other branches
-these leaves make chemicals to help protect them
-leaves on nearby trees also prepare

Question 10

2 e.gs for responses to abiotic stress

Answer 10

Drought= shutting their stomata (reducing water loss through transpiration)
Freezing=producing antifreeze chemical in their cell (decreases the formation of ice crystals)

Question 11

Tropism definition

Answer 11

A directional growth response in which the direction of the response is determined by the direction of the external stimulus (positive-towards stimulus or negative-away from stimulus)

Question 12

Phototropism

Answer 12

Growth response to light
shoots- positive
roots-negative

Question 13

Thigmotropism

Answer 13

Growth response to touch
-shoots of climbing plants can wind around other plants and structures to gain support

Question 13

Geotropism

Answer 13

Growth response to gravity
roots-positive
shoots-negative

Question 14

Chemotropism

Answer 14

Growth response to chemicals
-occurs in flowers where pollen tubes are attracted by chemicals and grow down the style towards the ovary

Question 15

Hydrotropism

Answer 15

Growth response to water
-root tips grow towards damper areas of soil

Question 16

Groups of plant hormones

Answer 16

Auxins and gibberellins

Question 17

Abscission what, why and how triggered?

Answer 17

-deciduous plants lose their leaves in winter
-helps plants to conserve water during winter where difficult to absorb if soil is frozen and less light for photosynthesis
-triggered by shortening day length

Question 18

Abscission how controlled?

Answer 18

-controlled by auxins + ethene
-auxins inhibit leaf loss- produced by young leaves. As gets older, less auxin= leaf loss
-ethene stimulates leaf loss- produced by ageing leaves. As older, more ethene means layer of cells (abscission layer) develops at bottom of leaf stalk - separating from rest of leaf. More ethene stimulates abscission layer to expand, breaking cell walls and causing leaf to fall off

Question 18

Role of hormones in stomatal closure

Answer 18

Need to close stomata to reduce water loss through transpiration
-uses guard cells on either side of stomatal pore
-when full of water they are turgid and pore is open
-when lose water become flaccid and pore is closed
-ABA is able to trigger stomatal closure

Question 19

Role of ABA in stomatal closure

Answer 19

1.ABA binds to specific receptors on guard cell membranes
2.ABA causes calcium ions to move into cytoplasm of the guard cells
3.The increased conc of Ca^2+ causes other ion channels to open
4.Ions leave the guard cell increasing the water potential inside the guard cell
5.Water leaves the guard cells by osmosis
6.The guard cells become flaccid causing the stoma to close