Plant Biology

Question 1

Transpiration

Answer 1

inevitable consequence of gas exchange in a leaf. Exchange of two gases for photosynthesis

Question 2

Waxy cuticle

Answer 2

low permeability so stoma is used for gas exchange and guard cells used to minimize water loss (open and close)

Question 3

Xylem structures and Cohesive properties of water

Answer 3

Withstand low pressure and allows transport under tension.

Xylem - the long continuous tube which is thickened and has lignin for strength/rigidity to prevent collapse. Flow is passive and pressure inside the xylem is lower than ATP

Water - Can be pulled up through xylem in a cohesive stream due to cohesion and adhesion

Question 4

How is xylem formed

Answer 4

plasma membrane breaks down so mature xylem are not living.

Question 5

water properties

Answer 5

cohesion
adhesion

Question 6

Cohesion

Answer 6

water is polar so negative oxygen will attract positive hydrogen

Question 7

Adhesion

Answer 7

H2O is attracted to hydrophilic parts of the xylem

Question 8

Tension in cell leaf wall maintains the transpiration stream

Answer 8

water properties and evaporation will generate tension forces in the walls.

When water evaporates from leaf wall, adhesion will cause the closest source of water to replace the water lost. This nearest supply is in the xylem vessel

Question 9

Why is pressure low is xylem

Answer 9

adhesion between water and cell walls is strong enough to suck water out of the xylem. Further reducing pressure

generates pulling force to H2O from stem to root. This is called transpiration pull (H2O upwards).

Question 10

Cavitation

Answer 10

pressure is too low and it results in the breakage of the column of liquid which disrupts the transportation pull.

Question 11

Active transport of mineral ions

Answer 11

active uptake of mineral ions also will result in more absorption of water (osmosis).
Requires protein pumps in the membrane of the root cell. Or happen through mass flow as water carries ions.

Question 12

What do ions move through soil slowly how it relates to fungi

Answer 12

Ion binds to the surface of soil plants, so the relationship with fungi is important.

Fungus hyphae grow out of soil and absorb mineral ions on the surface. Allows plants to grow in nutrient deficient sol (mutualistic relationship)

Question 13

Replacing loss of transpiration

Answer 13

water travels into the leaf replacing the loss of water from transpiration.

Water in the xylem climbs the stem through transpiration pull with cohesion and adhesion. Once water is in the root travels through the xylem through the cell wall (apoplastic pathway) and through the cytoplasm (symplastic pathway)

Question 14

What is transpiration pull a result of

Answer 14

Low pressure generates fulling force from stem to root upwards

Question 15

diffusion space

Answer 15

small diffusion space leads to the fast rate of diffusion and H2o driven out by distance and gradient

Question 16

How does heat increase transpiration

Answer 16

heat turns water into gas leading to more evaporation and faster leaving of leaf

Question 17

xerophytes

Answer 17

adapted to dry habitats. Therefore increases H2o uptake and reduces H2o loss. short life cycle and go dormant

Question 18

cacti how its adapted

Answer 18

small leaves
water storage tissue (pleats swell after rainfall)
stoma spaced widely
thick waxy cuticle
open at night

Question 19

Marram how its adapted

Answer 19

rolled leaf creates a localized environment. Prevent H2o loss
Hair reduced air movement
Sunken stoma

Question 20

halophytes adaptations

Answer 20

reduced leaves
Leaves shed when h2o is scarce
sunken stoma
long root more water uptake
structure removes salt buildup

Question 21

Translocation

Answer 21

Occurs in the phloem from source to sink

Question 22

what are sieve tubes

Answer 22

phloem is composed of them. Columns of specialized cells are separated by perforated walls called sieve plated. Associated with companion cell.

• Reduced cytoplasm and no nucleus
• depends on membrane to maintain concentrations of organic molecules

Question 23

Phloem

Answer 23

transports organic material throughout the plant. Transport organic solute. Links to parts of plant that need amino acids, sugars etc…

Question 24

Phloem loading

Answer 24

How plants bring sugar into the phloem

• Active transport is used to load organic compounds into sieve tubes at source.

Question 25

Phloem loading of sucrose

Answer 25

Most prevalent solute in phloem sap
- Not easily metabolized therefore food for carbohydrate transport. Doesn’t change easily

• Travels through cell walls - from mesophyll cells to cell wall to companion cell and sometimes sieve tubes.
• Sucrose transports protein and then actively transports sugar through the apoplast route

Question 26

Companion cell and sucrose

Answer 26

Active transport develops a concentration gradient of sucrose.
- H+ ions transported out of companion cell using ATP
- Buildup of H+ ions flows down the concentration gradient through co-transport protein.
- Energy released is used to carry sucrose into companion cell-sieve tube complex

Question 27

Plasmodesmata

Answer 27

Symplastic route. When sucrose reaches companion cell convert to oligosaccaride to maintain sucrose concentration gradient

Question 28

How water potential impacts translocation

Answer 28

• Water cannot be compressed creating a hydrostatic pressure gradient. The buildup of carbohydrates draws water into companion cells by osmosis.
• Allows for high pressure so is able to flow from high-pressure areas to low
• Then solute is used therefore will be drawn back into the transpiration stream

Question 29

What is sucrose used for at the sink

Answer 29

used as an energy source for either growth or turned to starch to be stored.

Question 30

Companion cell

Answer 30

• has more mitochondria for active transport of sucrose
• unfolding to increase loading capacity through the apoplastic route

Question 31

Importance of perforated walls and reduced cytoplasm

Answer 31

less resistance to flow of phloem sap

Question 32

Photoperiods

Answer 32

switch to flowering is due to length of light and dark periods.

Question 33

Pigment in photoperiods

Answer 33

Phytochrome red - in light converted to Pfr conversion is fast
phytochrome far-red - In dark concerted to Pr is slow. Not as stable

used to determine the length of dark periods