Plant Adaptations 9.5 Flashcards
Why do plants have to adapt?
They are in a constant compromise of getting the right amount of CO2 they need and also not losing too much water by transpiration.
Xerophytes
These are plants that live in conditions where water is very low and is not easily accessible. This can be either hot, dry and breezy like the desert, or it can be very cold and icy because the water isn’t readily available
Some examples of xerophyes
Conifers, Marram grass which is found on dunes in dry and salty conditions, plants in icy conditions and cactii in the desert
Adaptations of xerophytes
They are adapted to conserve water. These can include: thick waxy cuticle, sunken stomata, less stomata, reduced number of leaves, hairy leaves, curled leaves, succulents, leaf loss, root adaptations, avoiding the problems
Thick waxy cuticle
A lot of water lost by transpiration is actually lost through the cuticle so to stop this, they will have thick and waxy cuticles which will stop the water from diffusing out of the plant. An example of this adaptation is conifers.
Sunken Stomata
Having the stomata in pits will reduce air movement and have air on the exterior in those pits that is humid so will reduce the concentration gradient between the exterior and interior so the rate of transpiration will decrease. This is said to be a microclimate and some plants that do this include cactii, marram grass and conifers
Reduced number of stomata
This will decrease the rate of gas exchange but also means less water will be lost by transpiration as there aren’t as many stomata to go through.
Reduced leaf size
This reduces the surface area of the leaf so not as much water will be lost, as well as the SA:V ratio increasing so the diffusion rate will be lost as well. An example is conifers which have pine leaves which are very thin.
Leaves falling
Some plants like a desert tree called palo verde will lose it’s leaves when water is not available so that there is decreased water loss. It’s trunk will also turn green so photosynthesis still occurs.
Leaves curled
This is a good adaptation as it creates a microenvironment of moist humid air which will decrease the concentration gradient between water outside and inside the leaves so the rate of transpiration will decrease. An example of this is marram grass.
Leaves hairy
Having hairy leaves creates a microclimate again and will decrease the rate of transpiration. This is also used by marram grass which can have hairs in the sunken stomata.
Succellents
These plants will store water in parenchyma tissue when it’s in great supply and then use it up when there’s drought. They have a swollen fleshy appearance and some examples are aloe vera and desert cactii
Root adaptations
They are adapted to try and get water wherever they can find it. Some roots can sink for metres into the ground to get water from deep places. Other roots spread very wide so they can get the water from all areas around them. Cactii can show both of these adaptations and get water even in the driest environments. Marram grass roots are adapted to grow vertically down to penetrate very deeply in the sand as well as having horizontal rhizosomes which are modified stems for form an extensive network and allow sand to hold onto water
Avoiding the problem
Some plants become dormant and inactive when there is a water shortage and will grow rapidly when the rain falls. Others can survive by having storage organs like bulbs. A few can even survive even after being completely dehydrated and looking dead, they can take up water after it rains and be fully recovered which is because of a disaccharide called trehalose.
Hydrophytes
These are plants that live submerged or on the surface of water so need to adapt in order to overcome that.
Some examples of hydrophytes
Water lilies (lily pads), water cress which grows at the surface, duckweeds which are submerged. Also marginal plants like yellow iris that grows on the side.
Adaptations of hydrophytes
Water logging can be a major problem so need air spaces to survive, therefore some adaptations include: no waxy cuticle, many open stomata, great number of stomata, great number of leaves, many leaves, reduced structure of plants, wide flat leaves with big surface area, small roots, air sacs, aerenchyma
Thin cuticle or no waxy cuticle
The hydrophytes don’t need top conserve water so their cuticle can be thin to increase the rate of transpiration.
Big surface area
This is so that there is more light hitting the plant so it photosynthesizes more and therefore more gas exchange occurs and therefore more transpiration occurs
Many open stomata
These stomata will stay open all the time and the guard cells are inactive because water is always being taken up so will always be lost. It maximises gas exchange and there is no risk of the plant losing turgor because it’s got an abundance of water. Some plants like water lilies that are on the surface of the water will have their stomata on the surface
Reduced structure
This happens because the water supports the leaves and structure of the plant so it can have a reduced structure.
Air sacs
This enables some plants to float to the surface of the water and maximise photosynthesis.
Small roots
Water can move directly into the stem and leaves so they don’t need big roots to take up water.
Aerenchyma
Specialised parenchyma tissue that is adapted to have big air spaces and keeps the leaves and stems of the hydrocytes more buoyant so they float as well as forming a low resistance pathway so oxygen can be transported easier to cope with being in anoxic conditions which is where there’s low oxygen.
What problem can aerenchyma cause?
Because aerenchyma produce a low resistance pathway, it means methane produced can be transported and released easily. This causes a major problem on rice fields that are flooded and contributes to global warming
What happens when the plant becomes too waterclogged?
This happens when air is now in short supply instead of water. Special roots will grow in the air called pneumophores and these will allow air to enter the plant
