9.5- plants adaptations to water availability

What are xerophyte?

Plants adapted to survive in dry conditions with limited water availability.

Why do some plants have a thick waxy cuticle?

To help minimise water loss and help survive both hot dry summers and cold winters in when water is hard to absorb

What are examples of adaptions to help xerophytes to survive?

Thick waxy cuticle, sunken stomata, reduced number of stomata, reduced leaves, hairy leaves, curled leaves; succulents, leaf loss.

Why do exerophytes have a sunken stomata?

It reduces air movement producing a microclimate of still humid air that refuses the water potential gradient and so reduces transpiration

Why do some plants have reduced number of stomata?

It reduces water loss by transpiration and reduce their exchange capabilities

Why may some plants have conifers leafs?

These narrow leaves are almost circular in cross section which greatly reduces their SA:V ratio, minimising the amount of water lost in transpiration

Why do some plants have hairy leaves?

It creates a microclimate of still humid air which reduces the water potential gradient which reduces the loss of water by transpiration from the surface of the leaf

What are succulents plants?

Plants that store water in specialised parenchyma tissues in their stem and roots, water is stored when it’s in plentiful supplies and used in times of drought

What root adaptation do xerophytes have?

They have long tap roots growing deep into the ground that can penetrate several metres, allowing them to access water that is long way below the surface. Shallow Lateral roots with large surface area are able to absorb any available water before a rain shower evaporates

What happens to plants that die when water availability is low, but high when it rains again?

They loose their leaves and become dormant or die completely, leaving seeds behind to germinate and grow rapidly when rain falls again

What are hydrophytes?

Plants adapted to live in water or very wet environments

Why do hydrophytes have very little or no waxy cuticle?

Because they do not need to conserve water as there is always plenty available

Why do hydrophytes have many open stomata on the upper surfaces?

Maximising the number of stomata also maximises gaseous exchange, they are on the upper surface so they are in contact with the air

Why do hydrophytes have reduced structure?

Because the water supports the leaf so there is no need for strong supporting structures

Why do hydrophytes have wide and flat leaves?

Wide flat leaves means it spreads across the surface of the water to capture as much light as possible

Why do hydrophytes have small roots?

Water can diffuse directly into stem and leaf tissues so there is less need for uptake roots

Why do hydrophytes have large surface areas of stem and roots under water?

To maximise the area for photosynthesis and for oxygen to diffuse into submerged plants

Why do some hydrophytes have air sacs?

To enable for leaves and flower to float to the surface of the water

Why do hydrophytes have aeranchynma (specialised parenchyma)?

It makes the leaves and stems more buoyant, and it forms a low resistance internal pathway for the movement of substances such as oxygen to tissues below the water to help with anoxic conditions in the mud by transporting oxygen to the tissues

What is anoxic?

A condition where oxygen is absent or extremely low.