plant and animal responses

Question 1

what is abiotic stress

Answer 1

non living environmental aftor that could harm a plant
e.g mineral deficiency, drought, depleted oxygen supply, pollution

Question 2

response to abiotic stress

Answer 2

leaf loss: trees will loose there leaves in cold climate countries
day length sensitivity: when detect shorter dark periods leaves will bud and flower boom
abscission: when light levels decrease, ethene switches off genes for enzymes that digest and weaken the cell, leaving a water proof scab
preventing freezing: plants can contain chemicals that act as antifreeze
stomatal control: provides cooling effect

Question 3

how does mimosa pudica respond to being touched

Answer 3

touch sensitivity causes leaves to fold

Question 4

what is a plant tropism

Answer 4

directional growth response of plants
-phototropism- response to light
-geotropism- response to gravity
-hydrotropism- response to water
-thermotropism- response to temp
-thigmotropism- response to touching surface or object

Question 5

how is leaf loss (leaf abscission) in deciduous plants controlled

Answer 5

1 as leaf ages, cytokinin & auxin levels lower, ethene levels increases
2 triggers production of cellulase enzymes, which weaken leaves by breaking down call walls in abscission layer
3 leaves break from branch. below abscission layer, suberin layer forms to prevent entry of pathogens

Question 5

list the functions of gibberellins

Answer 5

-germination
-elongation at cell internodes
-fruit growth
-rapid growth/ flowering

Question 6

how is germination stimulated

Answer 6

1 seed absorbs water, activating embryo to secrete gibberellins
2gibberelins diffuse to aleurone layer, which produces amylose
3 amylase diffuses to endosperm layer to hydrolyse starch
4 hexose sugars act as respiratory substrate to produce atp as energy currency

Question 7

list the functions of auxins

Answer 7

-involved in trophic response
-control cell elongation
-supress lateral buds to maintain apical dominance
-promote root growth e.g in rooting powders

Question 8

explain why roots show positive gravitropism

Answer 8

1 gravity causes auxins to accumulate on lower side of the root
2 auxins inhibits elongation of root cells
3 cells on the upper side of root elongate faster, so the root tip bends downwards

Question 9

explain why shoots show positive phototropism

Answer 9

1 auxins diffuses to shaded side of shoot tip
2 as auxins diffuse down shaded side, it causes active transport of H+ ions into cell wll
3 disruption of H-bonds between cellulose molecules & action of expansins make cell more permeable to water
4cells on shaded side elongate faster due to higher turgor pressure
5bshoot bends towards light

Question 10

how do hormones stimulate stomata to close

Answer 10

1 abscisic acid binds to complementary receptors on guard cell membrane, causing CA2+ ion channels on tonoplast to open. CA2+ ions diffuse from vacuole into cytosol
2posotive feedback triggers other ion channels to open other ions e.g K+ diffuse out of guard cell
3 water potential of guard cell becomes more positive
water diffuses put via osmosis
4 guard cells become flaccid so stomata close

Question 11

explain why gibberellin is classed as a plant hormone

Answer 11

-is a chemical messenger
-is made in a part of the plant and has affect on another part
-long-lasting
-widespread effect