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

ENTERS CELL, TRAVEL INTO NUCLEUS
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 top heavy, decreases down
Cytokinins bottom heavy, decreases up

Question 14

Which seed half has amylase activity?

Answer 14

Half with embryo
Shows clear zone on agar
As it contains gibberellin

Question 15

Suggest and explain how to investigate 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, 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 [Pfr spells longer so longer day - vice versa]

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

Question 32

Explain how red and far red light affects the germination of lettuce seeds. (Given lettuce seeds germinate when red is the last or only wavelength received) (4 marks)

Answer 32

- red light **stimulates conversion from Pr -> PFr** - far red **inhibits** conversion Pr -> PFr - PFr is the **active** phytochrome - **switches on gene** for germination, activating enzymes involved - last wavelength determines form of phytochrome present as conversion is **reversible**

Question 33

Suggest benefits to plants being only able to respond to changes in day length. (3 marks)

Answer 33

- so will flower at the right time - when insects are also available - a regular stimulus, day length is a set pattern in seasons

Question 34

Explain how auxin affects the **synthesis** of enzymes. (3 marks)

Answer 34

- auxin binds with receptors in cell (nucleus) - transcription factor (TF) activated - TF binds to DNA - switches on transcription

Question 35

**How** does Gibberellin affect growth on plant cells? (3 marks)

Answer 35

- Gibberelin enters nucleus - act as / activates transcription factor - cause cell elongation

Question 36

what takes up majority of a grain cell?

Answer 36

endosperm

Question 37

Explain how charged and uncharged auxin travels through cell surface membrane? (2 marks)

Answer 37

- uncharged auxins travel through uncharged fatty acid tails - charged auxins move through carrier proteins / protein channels

Question 38

Describe the mechanism (of auxin and expansin) that causes cells to elongate. (3 marks)

Answer 38

- at lower pH, elongation increases - as expansin is activated by lower pH - weakeining bonds between cellulose - water enters and expands cell

Question 39

Explain how seed banks can help to conserve the genetic diversity of plant species. (2 marks)

Answer 39

- large number of seeds collected and stored from many different plants - ensures large gene pool in seed collected

Question 40

Compare the central nervous system and the peripheral nervous system. (3 marks)

Answer 40

Both have - neurones - contain synapses CNS/PNS - no branches / somatic and autonomic - no / has sensory and motor input - processes info / no

Question 41

How does IAA stimulate cells to synthesise proteins? (4 marks)

Answer 41

- IAA enters cell - travels through cytoplasm to **nucleus** - joins **promotor region** - switches on gene - activity at promoter region - forms mRNA - translation produces protein

Question 42

How does acetylcholine lower HR? (3 marks)

Answer 42

- from the parasympathetic system - slows down heart rate - binds to receptors on SAN - lower frequency of depolarisation

Question 43

Given that lettuce are short day plants, explain how red and far red light affects the germination of lettuce seeds. (4 marks)

Answer 43

- red light stimulates Pr to Pfr - far red light stimulates Pfr to Pr - Pfr is the active phytochrome - **genes involved in germination are switched on** - enzymes involved in germination are synthesised

Question 44

Why do chemicals affecting translation have a bigger effect in pollen tube growth than chemicals affecting transcription?

Answer 44

mRNA already present To synthesise proteins and enzymes needed for growth of pollen tube

Question 45

Explain why plants grown from germinating seeds may not flower at the same time of year as they would have done in their county of origin. (2 marks)

Answer 45

Flowering is affected by day length Phytochromes respond to light exposed

Question 46

Explain how the seed viability test would be different for some seeds from other parts of the world, stored at the same seed bank. (3 marks)

Answer 46

- different conditions - such as temperature, humidity - **if correct conditions not used, viable seeds may still not germinate**