Plant Adaptations To Water Availability

What do land plants exist in a state of?

Constant comprimise between getting the carbon dioxide they need for photosynthesis and losing the water they need for photosynthesis.

What must land plants have?

A large SA:V ratio for gaseous exchange and the capture of light for photosynthesis, but this greatly increases their risk of water loss by transpiration.

What do most plants have adaptations to conserve, and what do some of these include?

Water:

• Waxy cuticle - reduce transpiration from the leaf surfaces.

• Stomata found mainly on the underside of the leaf than can be closed - prevents the loss of water vapour.

In hot conditions, what happens in plants?

Water will evaporate from the leaf surfaces very rapidly.

What have plants in dry habitats evolved?

A wide range of adaptions that enable them to live and reproduce in places where water availability is very low.

What are xerophytes?

Plants in dry habitats where it is hot, dry and breezy.

What type of plants are those that live in very cold and icy conditions?

They are also xerophytes, - the water in the ground is frozen so it is not freely available to them

What are the different strategies xerophytes use for conserving water?

• Thick waxy cuticle.

• Sunken stomata.

• Reduced numbers of stomata.

• Reduced leaves.

• Hairy leaves.

• Curled leaves.

• Succulents.

• Leaf loss.

• Rot adaptations.

• Avoiding the problems.

How does a thick waxy cuticle conserve water in xerophytes?

In most plants, up to 10% of the water lost by transpiration is actually through the cuticle. The waxy cuticle is waterproof, minimising water loss.

How does sunken stomata conserve water in xerophytes?

Many xerophytes have their stomata located in pits, which reduce air movement, producing a microclimate of still, humid air that reduces the water vapour potential gradient and so reduces transpiration.

How does reduced numbers of stomata conserve water in xerophytes?

Reduced stomata conserve water by minimizing the number of openings on a plant leaf through which water vapor can escape, thus reducing the rate of transpiration (water loss) as there are fewer pathways for water to exit the plant; essentially, fewer stomata means less potential for water to be lost to the environment.

How does reduced leaves conserve water in xerophytes?

Reduced leaves conserve water by minimizing the surface area available for transpiration, meaning less water can evaporate from the plant through the stomata on the leaf surface, thus reducing overall water loss; this is a key adaptation seen in xerophytes (plants adapted to dry environments) where water is scarce. 

How do hairy leaves conserve water in xerophytes?

Hairy leaves conserve water by trapping a layer of humid air around the leaf surface, which reduces the water potential gradient between the leaf and the surrounding atmosphere, thus minimizing water loss through transpiration; essentially acting as a "microclimate" that slows down evaporation from the stomata.

How do curled leaves conserve water in xerophytes?

Curled or rolled leaves confine all the stomata within a microenvironment of still, humid air to reduce the diffusion of water vapour from the stomata.

How do succulents conserve water?

They store water in specialised parenchyma tissue in their stems and roots. Water is stored when it is in plentiful supply and then used in times of drought.

How does leaf loss conserve water in xerophytes?

Leaf loss conserves water in plants by significantly reducing the surface area of the plant, which minimizes the amount of water that can be lost through transpiration (evaporation from the leaves) during periods of drought or unfavorable conditions, essentially meaning less area for water to escape from the plant; this is a key adaptation for deciduous plants, especially in environments with seasonal changes in water availability.

How do root adaptations conserve water in xerophytes?

Long tap roots growing deep into the ground can penetrate several metres, so they can access water that is a long way below the surface. A mass of widespread, shallow roots with a large surface area able to absorb any available water before a rain shower evaporates is another adaptation.

How does avoiding the problem conserve water in xerophytes?

#some plants are adapted to cope with low water availability by avoiding the situation entirely. Plants may lose their leaves and become formant, or die completely, leaving seeds behind to germinate and grow rapidly when rain falls again. Others survive as storage organs such as bulbs, corms or tubers. A few plants can withstand complete dehydration and recover - they appear dead but when it rains and the cells recover, the plant becomes turgid and green again and begins to photosynthesise. The ability to survive in this way is linked to the disaccharide trehalose, which appears to enable the cells to survive unharmed.

What are hydrophytes?

Plants that live in water, either submerged, on the surface or at the edges of bodies of water.

What do hydrophytes need adaptations to cope with?

Growing in water or in permanently saturated soil.

Why is it important for plants on the surface of the water that the leaves float?

So they are near to the surface of water to get the light needed for photosynthesis.

Why is water-logging a major problem for hydrophytes?

The air spaces of the plant need to be full of air, not water for the plant to survive.

What are the adaptations of hydrophytes?

• Very thin or no waxy cuticle.

• Many always-open stomata on the upper surfaces.

• Reduced structure to the plant.

• Wide, flat leaves.

• Small roots.

• Large surface area.

• Air sacs.

• Aerenchyma.

How does a very thin or no waxy cuticle enable hydrophytes to survive?

A very thin or absent waxy cuticle allows hydrophytes to survive by enabling them to readily absorb water directly from their surroundings, as they live in aquatic environments where water conservation is not a concern; essentially, because they are constantly surrounded by water, they don't need a thick waxy layer to prevent water loss like land plants do.

How does many always-open stomata on the upper surfaces enable hydrophytes to survive?

It allows for maximum gas exchange with the atmosphere, which is essential for photosynthesis, without the concern of excessive water loss since they are already surrounded by water; this adaptation means they can readily take in carbon dioxide while releasing oxygen without worrying about dehydration like land plants would with open stomata.

How does a reduced structure to the plant enable hydrophytes to survive?

The water supports the leaves and flowers so there is no need for strong supporting structures.

How do wide, flat leaves enable hydrophytes to survive?

Wide, flat leaves on hydrophytes enable them to survive by providing a large surface area for maximum light absorption, which is crucial for photosynthesis, while also allowing them to float on the water's surface due to their buoyancy, ensuring access to optimal light conditions for growth.

How do air sacs enable hydrophytes to survive?

They enable the leaves and/or flowers to float to the surfce of the water.

How does aerenchyma enable hydrophytes so survive?

Specialised parenchyma tissue forms in the leaves, stems and roots of hydrophytes. It has many large air spaces, which:

• Make the leaves and stems more buoyant.

• Form a low-resistance internal pathway for the movement of substances such as oxygen to tissues below the water. This helps the plant to cope with anoxic (extreme low oxygen conditions) in the mud by transporting oxygen to the tissues.

Where is aerenchyma found?

In crop species that grow in water.

What happens in situations where there is plenty of water?

The roots can become waterlogged. It is air rather than water that is in short supply. Special aerial roots called pneumatophores grow upwards into the air. They have many lenticels, which allow the entry of air into the woody tissue.