Topic 9 Control Systems

Question 1

Why are embryos removed from seeds in CP14?

Answer 1

embryos are natural Gibberellin producers, so taking it away we can use known Gib. conc to conduct investigation
reducing validity

Question 2

why would contamination present a biohazard when growing the seed in agar?

Answer 2

Fungi and bacteria may also produce amylase, presenting a clear zone but reduces validity

Question 3

Why are there clear zones around seeds when growing in starch agar?

Answer 3

Gibberellin is a transcription factor, involved in synthesis of amylase
by aleurone layer around the endosperm
hydrolysing starch into maltose

Question 4

how do plants grow?

Answer 4

cell division and cell elongation

Question 5

what are 3 main plant growth chemicals?

Answer 5

auxins, cytokinins an gibberellins

Question 6

what do auxins do?

Answer 6

effects plant cell walls, promote cell elongation

Question 7

how do auxins increase the plasticity of the cell wall?

Answer 7

auxin binds to receptor sites, and pumps H+
reduced pH break bonds between adjacent cellulose microfibrils

Question 8

what is the acid growth hypothesis?

Answer 8

1. auxin molecules bind to receptor protein
2. ATP synthase pumps H+ into cell wall
3. loosen bond between cellulose microfibres
4. K+ travels into cytoplasm
5. water osmosise down, stretching cell

Question 9

What does auxin promote and inhibit, and how does the concentration distribute across the plant?

Answer 9

Conc decreases down
Promotes vertical growth and inhibits lateral growth

Question 10

What do cytokinins promote and how?

Answer 10

Lateral bud growth , cell division in roots and shoots
Acts by attaching to receptors, triggering transcription factors to switch on/form

Question 11

What is synergy in terms of plant pigments and give an example

Answer 11

Complimenting each other
Auxin and Gibberellin

Question 12

What is antagonistic in terms of plant pigments and give an example

Answer 12

Inhibit each other / work oppositely
Auxin and cytokinins

Question 13

How does cytokinins and auxin conc distribute in plants?

Answer 13

Auxin too heavy, decreases down
Cytokinins bottom heavy, decreases up

Question 14

Which seed half has amylase activity?

Answer 14

Half with embryo
Shows clear zone
As it contains gibberellin

Question 15

Suggest and explain how IAA in agar affects the growth of shoots. (5 marks)

Answer 15

• record height of shoot
• calc difference in height
• shoots w IAA are taller than control
• because IAA diffuses down
• so higher IAA conc causes more growth
• due to more cell elongation
• • deems of acid growth hypothesis

Question 16

What is photomorphogenesis

Answer 16

process where plant development is controlled by the levels and type of light

Question 17

What is photoperiodism in plants? And what are they controlled by?

Answer 17

Response of a plant to relative lengths of light and dark
Controlled by pigment called phytochrome

Question 18

What are phytochromes used for?

Answer 18

Initiating flowering, germination and shoot growth

Question 19

How do phytochromes work?

Answer 19

They are Conjugated proteins
With highly reactive photoreceptors
That absorbs light or particular wavelengths,
Causing conformational change

Question 20

What colour are phytochromes?

Answer 20

Blue green

Question 21

What are 2 forms of phytochromes?

Answer 21

Pr (inactive)
And
Pfr (active)

Question 22

How is Pr and Pfr interconverting?

Answer 22

Pr -> Pfr in natural light
Pfr -> Pr in the dark

Question 23

What are long day plants and their characteristics?

Answer 23

Bloom when days are longest
Nights are shortest

Question 24

What are short day plants and their characteristics?

Answer 24

Bloom in spring / summer, when days are shorter

Question 25

which phytochrome stimulates which plant to flower?

Answer 25

PFr stimulates long day plants
Pr stimulates short day (long night) plants

Question 26

What are benefits to plants being able to respond to changes in day length? (3 marks)

Answer 26

• flowering/development at the right time
  -so flowers when insects are available
• day length changes to set a pattern, e.g. always short days in winter, long in summer
• other stimuli are less regular eg temp

Question 27

How do auxins affect the synthesis of enzymes? (3 marks)

Answer 27

• auxin binds w receptor in cell
• transcription factor becomes active/activated
• transcription factor binds to DNA/promoter
• switches on transcription

Question 28

HOW does gibberellin affect growth of plants?

Answer 28

• gibberellin binds to cell surface receptors
• act as transcription factor
• activate protein synthesis
• causing cell elongation & division

Question 29

how do auxins and cytokinins control the growth of lateral buds? (3 marks)

Answer 29

• auxin is released from the terminal bud
• and diffuses down the stem to inhibit cytokinin action
• cytokinin stimulates lateral shoot growth
• is produced from base of shoot

Question 30

how does the structure of cell membrane affect the transport of auxin? (2 marks)

Answer 30

• uncharged auxin can diffuse through the hydrophobic/nonpolar fatty acid tails
• -ve charged auxin has to move through protein channels/carrier proteins

Question 31

what is the mechanism by auxin and expansin to cause cells to elongate? (3 marks)

Answer 31

• lower pH = elongation increases
• bcs expansin is activated by lower pH
• weaking intermolecular bonds between cellulose molecules
• cell takes in water -> expand