8.1.2.3 - Plants

Question 1

Homestasis in Plants

Answer 1

• Changes in temperature affect both their functioning and their growth (seen in variations of growth rings).
• Maintenance of a relatively stable internal environment is just as importantn for plants as for animals.
• Plants reponse to changes in light, water, availability and temperature which are all related to heat.
• Plants that liver where water is in limited supply must balance evaporative coolong, tansporation, gas exchange and hydration.
• They need to maintain water balance, remove metabolic waste and maintain internal concentrations of major nutrients (glucose etc.)

Question 2

Preventing water loss

Answer 2

Thick cuticle
* Slow down transpiration; reflecting surface reduce effect of sunlight
* Epidermal cells are waterproof, repventing evaporative water loss.
* E.g. eucalypts and banksia

Changing leaf orientation
* Prevent stomatas being exposed to direct light, keeping them closed.
* Vertically hanging leaves, reduce the surface area to sunlight and thus water loss by evaporation.
* E.g. eucalypts

Reduced leaf size
* Some leaves are reduced in size, and each leaf is divided into leaflets.
* Some plants have reduced their leaves to scales or needles.
* E.g. Grevillia, Casuarinas

Hairy leaf suface
* Reduce the surface area of the leaf, and therefore evaporative water loss.
* White hairs may reflect sunlight which reduces the surface temperature of the leaf.
E.g. bottlebrush

Question 3

Fruit structure

Answer 3

Plants with woody fruits will lose less water than fleshy fruits (water is lost in the flesh of the fruit)

Question 4

Responding to higher temperature change

Answer 4

**Evaporative cooling (transpiration): **water loss decreases the internal temperature of plants by evaporative cooling. Process of evaporation cools the internal temperature of the plant.

Wilting: Plants change the turgor pressure in their leaves, allowing them to droop and reduce the surface area exposed to the sun.

Leaf orientation: Hanging vertically in hot weather reduces surface area exposed to the sun.

Leaf fall: Some evergreen eucalyps shed leaves in the dry season in hot climates to reduce the surface area exposed to absorb heat and risk of excess transpiration.

Question 5

Responding to cold temperatures

Answer 5

Water can freeze within the plant in cold temperature

Organic anti-freeze:
Organic compounds acting as antifreeze to prevent water between cells freezing. The antifreeze reduces the temperature at which the cytoplasim or cell sap in the vacuole freezes.

Dormacy
Deciduous trees lose their leaves and undergo a period of dormancy which allows them to survive low temperatures, water shortages and reduced sunlight.

Question 6

Hydrophytes

Answer 6

Living in freshwater - large amount of available water.
* Internal environment has lower water concentration and a high solute concentration than their environment (ensures that diffusion and osmosis is effective)
* IF the plant cannot regulate water movement, their tissue floods and the plant cannot maintain its nutrient levels, cells swell and burst.
* Therefore, a large number of stomata throughout the plant and leaves with a large surface area.
* E.g. water lily

Question 7

Mesophytes

Answer 7

• Land plants with an adequate supply of water.
• Medium density of stomata on the undeside of the leaves. These remain open to ensure that maximum amount of photosynthesis can occur and water can evaporate from the plant.
• Not drought tolerant.

Question 8

Xerophytes

Answer 8

• Dry climates, focus on conservation of water.
• Small number of stomata, stomata hairs and depressions for the stomata to sit in.
• This builds a microclimate, in which air is trapped close to the stomata thus reducing air flow and the loss of water via transpiration. Also increases humidity, ensuring that gas exchange occurs and photosynthesis occurs at sufficient rates.

Other adaptions:
* Leaves with small surface area
* Thick waxy cuticles
* Hanging vertically
* Extensive root system to obtain water from a wider area
* Strap-like leaves that roll up
* Storing water in cacti and succulent plants

E.g. Cacti have no leaves - rather, photosynthesis occurs in the stem of the plants and spikes are a defense mechanism.