Plant Osmoregulation

Question 1

In what ways can plants lose water?

Answer 1

Transpiration and transport.

Question 2

How may solute concentration impact the water balance of a plant?

Answer 2

For a land/freshwater plant, the solute concentration of the external environment is less than the solute concentration in the cytoplasm - water is attracted to the osmotic pressure of the plant.

Question 3

How are water/nutrients absorbed by plants?

Answer 3

• Absorbed by root hairs and transported through the xylem vessel.
• Xylem vessel flows from roots to leaves.
• From root hair; water travels along the cell walls to reach the xylem vessel of the stem.
  When it reaches the endodermis, water diffuses into the xylem vessel and travels to the leaf.

Question 4

What are the functions of water for a plant?

Answer 4

Water is used for metabollic purposes (photosynthesis) or evaporates via. the stomata - cooling the leaves; removing heat.

Question 5

Outline the function of the stomata.

Answer 5

Pores on leaf surfaces that open and take in CO2 for photosynthesis via a diffusion gradient into the mesphyll layer.
Water is lost via evaporation from the exposed wet cell walls surrounding the intercellular spaces.
The stomata closes from collapsing stomatal guard cells; if this watr isnt being replaced continuously.
Photosynthesis stops.

Question 6

Outline the function of the guard cells.

Answer 6

Two epidermal guard cells surround the stomata. They open and close the stomata relative to variations in water content of guard cells. Their cell walls are thicker next to the pore:
When filled with water - thin walls stretch more than the tick ones, opening the stomata.
When losing water - turgor pressure decreases, guard cells straighten - closing the pore.

Question 7

Display four examples of adaptations that plants use to conserve water.

Answer 7

1) Stomata lies in a pit to increase hummidity - decerease transpiration.
2) Leaf rolls - increase hummidity as hairs reduce air movement - decrease transpiration.
3) Fleshy stems to contain large sums of water.
4) Pointed leafs/spines - reducing transpiration.

Question 8

What is a Xerophyte?

Answer 8

Evolved plants enabled to survive in arid conditions - maintaining water levels in drought like conditions.
e.g. Spinifex, Prickly Pear, Pigface and Mulga.

Question 9

Outline Xerophyte adaptations to conserve water.

Answer 9

• Shallow root system - uptake of rainwater.
• Water storage tissues - fleshy stems (succulents).
• Deep roots - reach underground water.
• Leaves with low SA:V - reducing area for transpiration and aurface area exposed to the drying effect of sun/wind (spines for leaves).
• Stomata - fewer - less transpiration.
• Hairs on leaf surface - increase hummidity by reducing air flow.
• Rolling of leaves - increase hummidity.
• Stomata open at night - from decreased transpiration.
• Sunken stomat - increase hummidity and decrease transpiration.

Question 10

What is a Halophyte?

Answer 10

Plants able to grow in saline environments - coping with high salinity whilst also maintaining osmosis.
e.g. Salt bush.

Question 11

What adaptations do Halophytes exhibit?

Answer 11

• Higher osmotic pressure in the cytoplasm.
• Salt excluding leaves.
• Directing slat to the roots.
• Diluting salt levels by increasing growth.
• Shedding salt-laden leaves.
• Excreting salt from salt glands (on leaves).