Plant physiology

Question 1

What was the first multicellular eukaryote to have its genome sequenced?

Answer 1

Arabidopsis thaliana

Question 2

What is meant by etiolated?

Answer 2

• occurs when a seed germinates and doesn’t detect light
• extended hypocotyl
• cotyledons dont unfold

Question 3

Describe the features of a phytochrome

Answer 3

• N-terminal
• phytochromobilin
• photosensory domain
• regulatory domain
• C-terminal

Question 4

What are Pr and Pfr?

Answer 4

• two forms of phytochromobilin
• are cis-trans- isomers
• conversion mediated by red and far-red light

Question 5

Describe the conversion of Pr and Pfr

Answer 5

Pr - inactive form –> cytosolic
Pfr - active form –> moves to nucleus

Question 6

What does Pfr induce?

Answer 6

• change in gene expression
• germination induced

Question 7

List the processes involved in plant circadian rhythms

Answer 7

1. gene expression
2. cytosolic calcium levels
3. protein phosphorylation
4. chloroplast movement
5. stomatal opening
6. hypocotol length
7. cotyledon and leaf movement
8. petal opening
9. flowering

Question 8

List the three parameters of the circadian clock

Answer 8

period
amplitude
phase

Question 9

Describe the clock mechanism

Answer 9

night - gene Z active, producing Z protein

dawn - sufficient Z protein activates expression from gene X and gene Y

day - X and Y proteins inhibit expression of gene Z

Question 10

How can we see the rhythm of the clock?

Answer 10

luciferase –> from fireflies

Question 11

What is meant by entrainment?

Answer 11

in constant dark, the clock starts to get out of sync

Question 12

What is the role of phytochrome

Answer 12

• senses the start of the day
• induces expression from gene X and Y

Question 13

List the three parts of the circadian clock?

Answer 13

central oscillator - negative feedback loop

input for entrainment to local conditions

output to effect responses

Question 14

How do we calculate total water potential?

Answer 14

solute potential + pressure potential + gravitational potential

Question 15

What is the pressure potential of pure water at atmospheric pressure?

Answer 15

0

Question 16

What is the difference between turgid, flaccid and plasmolyzed?

Answer 16

turgid - water moving in
flaccid - no water movement
plasmolyzed - water moving out

Question 17

What does transpiration rate depend on?

Answer 17

• difference in water vapor concentration between leaf air spaces and atmosphere –> influenced by temp
• diffusional resistance of pathway from leaf air spaces to atmosphere –> leaf stomatal resistance, boundary layer resistance

Question 18

Describe the features of the boundary layer

Answer 18

• layer of unstirred air next to leaf surface
• water vapour must diffuse through
• thickness determines by wind speed and leaf size

Question 19

What is cavitation?

Answer 19

• occurs when negative pressure becomes too great
• water column snaps
• air cavity forms

Question 20

How can water bypass cavitation?

Answer 20

via pits connecting vessels and tracheids

Question 21

Describe the process of cavitation repair

Answer 21

• positive root pressure
• at night roots pump solutes from soil into xylem
• as solutes accumulate, water potential lowered so water moves from soil into root

Question 22

List the two specialised cell types key to C4 photosynthesis

Answer 22

• mesophyll
• bundle sheath

Question 23

Describe the C4 mechanism

Answer 23

1. CO2 fixed by PEPC into a 4 carbon acid in mesophyll cells
2. C4 acid is moved into the bundle sheath cells
3. C4 acid is decarboxylated to produce CO2
4. CO2 used by rubisco in calvin cycle
5. C3 acid is recycled back to mesophyll cell

Question 24

Where is rubisco present?

Answer 24

in bundle sheath cells

Question 25

What do BS cells have to minimise CO2 escape?

Answer 25

suberin

Question 26

List some examples of C4 plants

Answer 26

maize sugarcane miscanthus sorghum

Question 27

Where do C4 plants live?

Answer 27

- places with hot summers - tropical regions

Question 28

What is meant by crassulacean acid metabolism (CAM)?

Answer 28

temporal separation of initial carbon fixation by PEPC and refixation by rubisco

Question 29

List some examples of CAM plants

Answer 29

pineapple agave vanialla cacti

Question 30

Describe the mechanisms of CAM photosynthesis

Answer 30

1. stomata open at night 2. PEPC converts CO2 to a C4 acid (malic acid) 3. C4 acid stored in vacuole until dawn 4. During the day stomata close 5. C4 acid is decarboxylated, releasing CO2 and C3 acid 6. CO2 used by rubisco in calvin cycle 7. C3 acid is recycled back to the start

Question 31

List three macro nutrients

Answer 31

nitrogen phosphorus potassium

Question 32

List three secondary nutrients

Answer 32

sulphur calcium magnesium

Question 33

List some micronutrients

Answer 33

iron boron zinc copper manganese molybdenum

Question 34

How do different nutrient deficiencies display?

Answer 34

phosphate - reddish purple markings potash - firing along tips nitrogen - yellowing from tip that moves down magnesium - whitish strips and purplish underside

Question 35

What is the difference between the apoplastic and symplastic route

Answer 35

apoplastic - through cell walls symplasitc - through cytoplasm (plasmodesmata)

Question 36

What is the role of the casparian strip?

Answer 36

- band of suberin running through walls of endodermis - prevents water, ions and pathogens diffusing into vascular system through cell walls - also prevents nutrients diffusing back into soil via apoplast --> xylem contains higher nutrient conc than soil

Question 37

How do active transport and passive diffusion differ?

Answer 37

active transport - high-affinity, low capacity - H+/K+ symporter passive diffusion - low-affinity, high capacity - voltage depended channel

Question 38

List some carnivorous plants

Answer 38

pitcher plants venus flytrap sundews bladderwort