plant growth and development

Question 1

what is an example of slow plant movement

Answer 1

bean wrapping round a pole.

Question 2

what is an example of rapid plant movement?

how does it work?

Answer 2

VENUS FLY TRAP

1. at the hinge, cells go turgid.
2. in response to stimuli these cells lose turgor.
3. this combined with mechanisation turns the hinge into a spring.

Question 3

how do Venus fly traps save energy?

Answer 3

shutting mouth is very energetically expensive so the following can be done to make sure jaw opens a minimal amount of times.

1. 3 sensitive hairs on inside of jaws to ensure only something right inside will set it off.
2. have to touch a hair twice for it to close.

Question 4

examples of directional stimuli

Answer 4

1. light
2. gravity
3. touch

Question 5

what is needed for gravitropism?

Answer 5

1. perception (statocytes)
2. signal transduction (auxin redistribution)
3. mechanical response (bending, differential cell expansion)

Question 6

which way do shoots and roots grow?

Answer 6

roots grow towards gravity.

shoots grow away from gravity.

Question 7

where does gravitropism perception occur?

Answer 7

root caps and shoot tip endodermis

Question 8

how are trees able to show gravitropism

Answer 8

when a woody stem is stimulated, tension wood pulls and contracts to pull the tree upwards.

Question 9

what happened when the root tip was surgically removed

Answer 9

the root still grew however it did not curl towards gravity as its perception cells were removed.

Question 10

statocytes

Answer 10

specialised cells in root cap.

they contain statoliths (starch filled bodies). these statoliths sediment with gravity. this directs growth of the root.

abolition of these statocytes - loss of gravitropism

Question 11

how does gravity inhibit growth in roots?

Answer 11

auxin is redistributed and this inhibits growth.

Question 12

how dos gravity promote growth in shoots?

Answer 12

on underside of curve, auxin accumulates to promote growth and push the root upwards.

Question 13

characteristics of auxin transport

Answer 13

1. long distance (shoot to root) in phloem sap
2. cell to cell - active transport NOT diffusion
3. highly polar - in shoots down not up.

Question 14

PIN proteins

Answer 14

pump auxin out of cells as it is a weak acid and can’t get through the polar membrane.

gradually pumps auxin from cell to cell down to the bottom of the root.

located on plasma membrane

Question 15

PIN 3

Answer 15

this protein re-localises in response to gravity - means that auxin accumulates on one side.

Question 16

lazy mutant

Answer 16

maize mutant that didn’t show gravitropism because lazy proteins moves with amyloplasts.

Question 17

short day plants

Answer 17

flower when day length is shorter than a defined period

(flower when days are short)

Question 18

long day plants

Answer 18

flower when day length is longer than a critical period.

(flower when days are long)

Question 19

phytochrome

Answer 19

pigment in plants which can detect light.

in sunlight it is in Pfr form.

in night it is in Pr form.

Question 20

external coincidence model

Answer 20

proposed that:

1. there is an internal rhythm with approx 24 hour period in the amount of a substance controlling flowering.
2. this substance is light sensitive at a particular phase in the rhythm.

Question 21

why do plants need a circadian rhythm?

Answer 21

allows plants to predict dawn and get ready for it (bring up its leaves and switch on photosynthesis)

Question 22

the photoperiod pathway

Answer 22

1. perception of light
2. things that perceive light (photoreceptors) keep the clock accurate
3. some genes are involved in flowering time (LHY, CCA1, TOC1 etc)
4. output - substance which is important for flowering or leaf movement.

Question 23

constans gene

Answer 23

output of photoperiod pathway

• inactivate this - affects the flowering time.
• promotes flowering in long days
• expression shows circadian rhythm
• lots of CO protein on a long day

Question 24

florigen

Answer 24

signal that moves from leaves to shoot apical meristem after induction by day length.

expressed in leaves in long day plants

Question 25

what properties should a gene for florin have?

Answer 25

1. mutants should not respond to day length 2. should be expressed in leaves in inductive conditions 3. should promote flowering across grafts 4. should make a product that can move from leaves to the shoot apical meristem where flowering occurs. 5. should be universal.

Question 26

spores are produced by...

Answer 26

diploid cells

Question 27

gametes are produced by...

Answer 27

haploid cells

Question 28

double fertilisation

Answer 28

egg cell is fertilised at the same time as a central cell. central cell is fertilized to make endosperm which provides nutrients to the embryo.

Question 28

alternation of generations

Answer 28

as well as having a multicellular diploid generation, plants also have a multicellular haploid generation.

Question 29

important steps in embryo development

Answer 29

1. Morphogenesis - establishing the basic pattern 2. Maturation - fuel storage and proteins that enable seed to survive desiccation 3. degreasing - chlorophyll broken down and embryo turns yellow. 4. desiccation - removal of moisture 5. dormancy

Question 30

seed dormancy

Answer 30

seeds are said to be dormant when fail to germinate even with the idea conditions.

Question 31

how is dormancy controlled?

Answer 31

1. ABA accumulates and promotes dormancy. 2. gibberellins promote germination

Question 32

what is the maize viviparous1 mutant?

Answer 32

germinates prematurely on the cob as it doesn't undergo dormancy. this mutant doesn't respond to ABA.

Question 33

abi3 mutant.

Answer 33

- ABA insensitive. - abi3 is thought to be involved in signalling - stops perception of ABA which stops dormancy. - plants with abi3 mutant don't survive storage.

Question 34

gibberellin

Answer 34

- promote germination. - involved in height growth - plants that can't make gibberellins tend to be dwarfed. - gibberellins inhibits effects of ABA.

Question 35

how does gibberellin work?

Answer 35

gibberellin signal is produced to promote aleurone to begin breakdown of endosperm after germination.

Question 36

what is a commercial application of GA?

Answer 36

to make malt whiskey.

Question 37

environmental controls on seed dormancy.

Answer 37

time - tough seed coat may gradually be broken down. light - flash of light when tree falls down and suddenly there is the chance to grow. nitrates - may indicate a nutrient rich soil. internal cellular controls - after ripening - GA and ABA.

Question 38

what effect does red light and far red light have on germination of seeds.

Answer 38

red light - promotes germination far red light - inhibits germination.

Question 39

how are light and GA levels connected?

Answer 39

1. red light converts phytochrome into its active form. 2. various signalling/transcription factors eventually connect phytochrome with an enzyme that is involved in gibberellin synthesis.

Question 40

what breaks seed dormancy?

Answer 40

1. fire - resistance to fire provides an advantage to the plant as it eliminates its competitors. 2. parasitic weeds

Question 41

karrikin

Answer 41

karrikin in smoke promotes germination in seeds

Question 42

parasitic weeds (Striga)

Answer 42

1. grows towards host root, attaches via adhesive hairs. 2. penetrates root via a haustorium which secretes enzymes that digest host cell walls. 3. transpires rapidly - pulling water and nutrients from the host.

Question 43

strigolactones

Answer 43

signals produced by plants that promote the germination of parasitic weeds (ONLY!!)

Question 44

pathway of how phosphorus concentration impacts plants.

Answer 44

1. in low phosphorous plant is starved and so makes more strigolactones. 2. this promotes less shoot branching but more root branching 3. more strigolactones also promotes more mycorrhizal colonisation 4. more strigolactones also advertises their presence to weeds however...