9.5 - Plant Adaptations to Water Avaliability Flashcards
What is a xerophyte?
A plant adapted to survive in dry or arid conditions by reducing water loss.
Why do xerophytes need special adaptations?
To balance water conservation with the need for photosynthesis and gas exchange. Without adaptations, they would lose too much water through transpiration and struggle to survive in dry conditions.
Name some examples of xerophytes.
Marram grass, cacti, conifers, and some cold-climate plants where water is frozen.
What are the key adaptations of xerophytes? (10)
- Thick waxy cuticle
- Sunken stomata
- Reduced number of stomata
- Reduced leaf area
- Hairy leaves
- Curled leaves
- Succulents
- Leaf Loss
- Root Adaptations
- Avoiding the problem
What is the purpose of a thick waxy cuticle in xerophytes?
It minimizes water loss by reducing transpiration from the leaf surface. This layer acts as a barrier against water evaporation, helping the plant conserve moisture.
How do sunken stomata help conserve water?
They create a humid microclimate, reducing the water potential gradient and limiting transpiration. By being located in pits, they slow down air movement, preventing excessive water loss.
How does reducing the number of stomata help xerophytes?
It decreases water loss by limiting gas exchange. However, this also means the plant has to carefully regulate carbon dioxide intake for photosynthesis.
How do xerophytes benefit from reduced leaves?
A smaller surface area reduces transpiration, as seen in conifers with needle-shaped leaves. Narrow or rolled leaves help minimize the surface area exposed to dry air, reducing water loss.
What role do hairy leaves play in xerophytes?
They trap moist air, reducing water loss by lowering the water potential gradient. The tiny hairs act as a barrier, creating a microenvironment that helps retain humidity around the leaf surface.
How do curled leaves help reduce transpiration?
They enclose stomata in a humid microenvironment, limiting water loss. This adaptation is especially effective in windy, dry environments where evaporation rates are high.
What are succulents, and how do they store water?
Succulents are plants that store water in swollen stems or roots, like cacti and aloe vera. These water reserves help the plant survive long periods of drought by providing a steady supply of moisture.
How do some xerophytes survive extreme drought?
Some shed leaves (e.g., Palo Verde trees) or store water in bulbs, corms, or tubers. Others enter a dormant state during dry seasons and resume growth when water becomes available again.
How do xerophytes’ roots help them survive?
They have deep taproots to access underground water and widespread shallow roots to absorb surface water quickly. This dual root system ensures they can take advantage of any available moisture.
What is an example of a xerophyte that can survive complete dehydration?
Some plants use trehalose sugar to protect cells and recover after rainfall. These “resurrection plants” appear dead but can revive rapidly when water becomes available.
What is a hydrophyte?
A plant adapted to live in or near water. These plants have special structures to cope with submerged or waterlogged conditions, ensuring they can still carry out gas exchange and photosynthesis.
Why don’t hydrophytes need water conservation adaptations?
They live in water, so they have constant access to moisture. Unlike xerophytes, their main challenge is often obtaining enough oxygen rather than conserving water.
Name some examples of hydrophytes.
Water lilies, duckweed, yellow iris, and water cress. These plants can be fully submerged, floating, or rooted in shallow water, each with unique adaptations to their environment.
What are the key adaptations of hydrophytes? (8)
- 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 areas of stems and roots on the water
- Air sacs
- Aerenchyma
Why do floating hydrophytes have stomata on the upper surface of leaves?
To ensure gas exchange since the lower surface is submerged. This allows them to take in carbon dioxide for photosynthesis without being blocked by water.
Why do hydrophytes have little or no waxy cuticle?
Because they don’t need to reduce water loss. A thick cuticle would only serve to hinder water absorption rather than help the plant in its aquatic habitat.
How does reduced structural support benefit hydrophytes?
Water provides natural buoyancy, so strong support tissues aren’t needed. This allows hydrophytes to allocate energy to other essential functions like photosynthesis and oxygen transport.
Why do hydrophytes have wide, flat leaves?
To maximize light capture for photosynthesis. This is especially important for plants floating on the water’s surface, where competition for sunlight can be high.
How do hydrophytes compensate for reduced roots?
They absorb water directly through stems and leaves. This reduces the need for extensive root systems, as water and nutrients are readily available from their surroundings.
Why do hydrophytes have large air spaces in stems and roots?
To help them float and transport oxygen to submerged tissues. These air pockets provide buoyancy and facilitate internal gas movement in low-oxygen environments.
What is aerenchyma, and why is it important?
A specialized tissue with large air spaces that helps with buoyancy and oxygen transport. It allows oxygen to diffuse efficiently through the plant, reaching areas that would otherwise be deprived of air.
How do hydrophytes deal with low oxygen in waterlogged conditions?
Aerenchyma forms low-resistance pathways for oxygen to reach submerged tissues. This adaptation is crucial for plants growing in stagnant water or muddy environments where oxygen levels are low.
