Plant Adaptations- BIOLOGY

Plants living on land must be adapted to:

1.     Reduce loss of water

2.     Replace the water that is lost

Structural and behavioural adaptations done by terrestrial plants.

3.     A waxy cuticle-reduces water loss by evaporation

4.     Most stomata are closed at night

5.     Stomata often found on the under-surface of leaves, reduces the evaporation due to direct heating from the sun

6.     Deciduous plants lose their leaves in the winter when the ground is frozen due to less water available and too low temperatures for photosynthesis

Xerophytes: A plant adapted to living in dry conditions

Marram Grass:

Live on sand dunes

Harsh conditions- water in sand drains away quickly, sand is salty and the leaves are exposed to very windy conditions.

Adaptations include:

Ø  leaves rolled longitudinally so air is trapped inside- air is more humid- so less water loss

Ø  Thick waxy cuticle

Ø  Stomata are on the inner side of the rolled leaf so they are protected by enclosed space

Ø  Stomata are in pits in the lower epidermis, which is also folded and covered in hairs. Reduces air movement and therefore loss of water vapour.

Ø  The spongy mesophyll layer is very dense, few air spaces so less surface are for evaporation of water.

Cacti:

Ø  Succulents- store water in their stems which become fleshy and swollen

Ø  Often ribbed or fluted so that it can expand if water is available

Ø  Leaves are reduced to spines- lower surface area

Ø  Stem is green for photosynthesis

Ø  Widespread roots

Other features include:

Ø  closing of stomata when water availability is low

Ø  Low water potential inside their leaves so maintain a high salt concentration in their cells. - reduces the evaporation of water from the cell surfaces as the water potential gradient between the cells and leaf air spaces is reduced.

Ø  Long tap root

Hydrophytes:

Ø  Plants adapted to living in water or wet conditions

Ø  Issues are about getting oxygen to their submerged tissues and keeping afloat- they need to keep their leaves in the sunlight for photosynthesis

Adaptations of a water lily:

Ø  Many large air spaces in the leaf. Keeps the leaves afloat so that they are in the air and absorb sunlight

Ø  Stomata on the upper epidermis

Ø  Many large air spaces in the leaf stem so helps with buoyancy but also allows oxygen to diffuse quickly to the roots for aerobic respiration.

How do they transpire:

Ø  Water doesn’t transpire into water or into air that has a very high humidity.

Ø  If water cannot leave the plant, then the transpiration stream stops and the plant cannot transport mineral ions up to the leaves.

Ø  Many plants contain specialised structures at the tops or margins of their leaves called hydathodes- these structures can release water droplets which may then evaporate from the leaf surface.