plant responses

Question 1

what are the limitations for plant responses

Answer 1

.the plants are rooted to the ground so they cannot move

.plants do not have a nervous system

Question 2

how do plants respond to their enviroment

Answer 2

via producing hormones which are transported throughout the plant

Question 3

what are gibberellins

Answer 3

plant growth regulators which stimulate seed germination

Question 4

how do gibberellins control plant height

Answer 4

they cause the elongation of plant stems during growth which increases the length of the internodes

Question 5

why can it be beneficial to have fewer gibberellins

Answer 5

.they have shorter stems which makes it less vulnerable to damage from weather or harvesting

Question 6

how does gibberellins start the germination process in seeds

Answer 6

.water enters the seed which causes the embryo to synthesise gibberellins

.as a response, amylase and maltose enzymes are synthesised

.amylase hydrolyses starch stored in the endosperm into maltose which can be further broken down into glucose

Question 7

what is evidence for the role of gibberellins in germination

Answer 7

.when gibberellins are added to seeds that cannot produce gibberellins germination occurs

Question 8

what are synergistic plant hormones

Answer 8

hormones that work together to give off a bigger response

Question 9

what are antagonistic plant hormones

Answer 9

hormones that have opposing effects
e.g. one causes growth and the other inhibits growth

Question 10

what do auxins regulate

Answer 10

.cell expansion and differentiation
.suppression of lateral bud growth(apical dominance)
.directional growth responses(tropisms)

Question 11

how do high levels of auxins effect plant tissues

Answer 11

.inhibit root growth and promote shoot growth

Question 12

how do low levels of auxins effect plant tissues

Answer 12

promote root growth and inhibit shoot growth

Question 13

process of elongation

Answer 13

auxins are synthesised by meristem in shoot tips

.auxins diffuse down shoot away from tip

.auxins bind to receptor sites on cell-surface membranes

.cell walls have low pH

.cells absorb water via osmosis forming vacuoles and increasing internal pressure

.this causes cell walls to expand which results in cell elongation = cell grows

Question 14

role of IAA (auxin) in apical dominance

Answer 14

.IAA is synthesised at shoot tips and stimulates growth of apical shoot and suppresses the growth of lateral shoots

.removal of apical bud where the IAA is synthesised means that lateral bud can growth leading to a bushier plant

Question 15

plant abiotic stresses

Answer 15

.day length changes
.excess cold or heat
.lack of water
.high winds
.change in salinity

Question 16

what is photoperiodism

Answer 16

the sensitivity of plants to levels of light

Question 17

what is the photoperiodism for deciduous trees

Answer 17

summer = daylight hours are at a maximum and trees are covered in leaf = maximising photo and growth

autumn = lengthening of dark period = leaf fall

winter = daylight hours are at a minimum = trees maintain a period of dormancy

spring = days lengthen and temp rises = trees come out of dormancy

Question 18

what are phytochromes

Answer 18

.pigment that sense the duration of light and darkness
.Pr and Pfr

Question 19

how do phytochromes effect plant responses

Answer 19

.breaking dormancy in buds
.initiating tuber formation
.timing the flower phase

Question 20

what is abscission

Answer 20

when plants loose leaves

Question 21

how is abscission triggered

Answer 21

.lengthening of dark period during autumn leads to lower photo rates
.energy demands for respiration outweighs glucose availability
.dormancy is needed to avoid winter damage

Question 22

process of leaf abscission

Answer 22

.decrease in light causes a decrease in auxin levels

.ethene is release by leaves

.ethene switches on genes in cells in the abscission zone at the base of the leaf stalk

.enzymes digest and weaken cell walls in the separation layer

.vascular tissues are sealed off blocking transport to the leaf

.fatty material is deposited in the cells in the inner protective layer of the abscission zone

.cells within the separation layer swell with water, straining weak walls

.environmental factors like winds separate the leaf from the plant

.protective layer that remains forms a scar to prevent the entry of pathogens

Question 23

what are some plant responses to freezing temperatures

Answer 23

.synthesising compounds e.g. sugars, amino acids and proteins acting as antifreeze
.modulating gene expression to bolster cold resistance
.adjusting sap solute concentration to lower freezing point

Question 24

the role of ABA in stomatal regulation

Answer 24

.when there is low water, ABA is produced
.the ABA moves from the roots to the leaves and binds on to guard cells
.ABA activates changes in the ionic conc of the guard cell reducing WP
.this makes the stomata close minimising water loss

Question 25

what are some of the physical defences against herbivores

Answer 25

.thorns, barbs and spikes .tough, fibrous tissue .stinging hairs .densely hairy leaves

Question 26

what are some of the chemical defences against herbivores

Answer 26

tannins alkaloids terpenoids

Question 27

what do alkaloids do

Answer 27

.alkaloids like cocaine and morphine to affect the metabolism of the animals alkaloids like caffeine and nicotine are toxic to animals

Question 28

what do VOCs do

Answer 28

the affect the social behaviour of the other members of the same species or a different species

Question 29

what is the purpose for having VOCs

Answer 29

.they attract predators .they repel herbivores .signalling neighbouring plants

Question 30

what are tropisms

Answer 30

.they are directional growth responses for plants

Question 31

what are phototropisms

Answer 31

they maximise the ability of the plant shoots and leaves to absorb light .positive = shoot grows towards light .negative = shoot grows away from light

Question 32

what is geotropism

Answer 32

.helps plants establish its roots and shoots in the optimal orientation .positive = root grows towards the gravitational pull .negative = root grows away from gravitational pull

Question 33

how are phototropism and geotropism regulated

Answer 33

IAA directs plant responses to the phototropism or geotropism

Question 34

positive phototropism in plant shoots

Answer 34

.IAA is produced in the tip of the shoot and is transported down the shoot .light stimulates IAA to move from light side of the shoot to the shaded side .IAA becomes concentrated and stimulates more cell elongation on the shaded side .shoot bends towards light

Question 35

negative phototropism/ positive geotropism in plant roots

Answer 35

.IAA is produced in the tip of the shoot and is transported along the root .any light stimulates IAA to move from the light side to the shaded side .gravity pulls IAA from the upper side to the lower side of the root .IAA becomes concentrated and inhibits cell elongation in the lower shaded side of the root .root bends away from light and downwards towards gravity

Question 36

what is etiolation

Answer 36

.the rapid upward growth that takes place in plants grown in the dark .thin and pale due to lack of chlorophyll

Question 37

gibberellins role in plants that are in the dark

Answer 37

.they cause extreme elongation of the internodes .this helps seedlings to grow out of soil

Question 38

what are some commercial uses for plant hormones

Answer 38

.ethene is used to control fruit ripening .auxins are used in rooting powders and micropropagation .auxins are also used for weedkillers