3.1.3 - Transport in plants Flashcards
Transpiration:
the evaporation of water from a plant’s surface.
Why does transpiration occur?
There’s a higher concentration of water inside the leaf than in the air outside, so water moves out of the leaf down the water potential gradient when the the stomata open.
List the four main factors that affect transpiration rate.
light, temperature, humidity and wind
Explain in detail how light has an effect on the transpiration rate.
the lighter it is the faster the transpiration rate.
- because the stomata open when it gets light, so CO2 can diffuse into the leaf for photosynthesis.
> when it is dark the stomata are usually closed, so there’s little transpiration
Explain in detail how temperature has an effect on the transpiration rate.
the higher the temperature the faster the transpiration rate.
- warmer water molecules have more energy so they evaporate from the cells inside the leaf FASTER.
∴ the water potential gradient increases between the inside and outside of leaf, making water diffuse out of leaf faster.
Explain in detail how humidity has an effect on the transpiration rate.
the lower the humidity, the faster the transpiration rate.
- if air around the plant is dry, the water potential gradient between the leaf and air is increased
∴ increased transpiration
Explain in detail how wind has an effect on the transpiration rate.
the windier it is, the faster the transpiration rate.
- lots of air movement blows away water molecules from around stomata.
∴ increases water potential gradient, which increases rate of transpiration.
Why is transpiration important?
- transports useful mineral ions up plant
- maintains cell turgidity
- supplies water for growth, cell elongation and photosynthesis
- supplies water that, as it evaporates, can keep the plant cool on a hot day.
What is a xerophyte?
a plant adapted to living in dry conditions
- their adaptations prevent them losing too much water by transpiration.
How has maram grass adapted to its environment?
- maram grass has stomata that are sunk in pits, so they’re sheltered from the wind
- this helps to slow transpiration down
- has a layer of ‘hairs’ on the epidermis
> traps moist air round the stomata, which reduces the water potential gradient between the leaf and the air
∴ slowing transpiration down
What does maram grass do in hot or windy conditions?
- rolls up its leaves
> this traps moist air, slowing down transpiration.
> also reduces the exposed surface area for losing water and protects the stomata from wind. - has a thick, waxy layer on the epidermis
> reduces water loss by evaporation because the layer is waterproof (water can’t move through it).
How are cacti adapted to their environment?
- cacti also have a thick, waxy layer on the epidermis
> reduces water loss by evaporation because the layer is waterproof (water can’t move through it). - have spines instead of leaves
> reduces the surface area for water loss - close their stomata at the hottest times of the day when transpiration rates are the highest.
What is a hydrophyte?
a plant adapted to living in water or where the ground is very wet.
How are hydrophytes different to xerophytes?
- hydrophytes live in aquatic habitats
- they grow in water/wet conditions
∴ they don’t need adaptations to reduce water loss like xerophytes.
BUT
- they do need adaptations to help them cope with a low oxygen level.
List several adaptions of hydrophytes.
- air spaces in the tissues
> help plants to float and can act as a store of oxygen for use in respiration.
e.g.water lilies have large air spaces in their leaves. Allows the leaves to float on the surface of the water, increasing the amount of light they receive.
Air spaces in the roots and stems allow oxygen to move from the floating leaves down to parts of the plant that are underwater. - stomata usually only present on the upper surface of the floating leaves
> helps maximise gas exchange. - hydrophytes often have flexible leaves & stems
> these plants are supported by the water around them, so they don’t need rigid stems for support.
Flexibility helps to prevent damage by water currents.
