T6 - Transport In Plants Flashcards
Why do plants require water? (3)
Photosynthesis
Maintenance of structure (turgidity)
Cooling effect
Why do plants require mineral ions?
For growth e.g. nitrates are required to
produce proteins
Outline how plant roots are adapted for the absorption of water and minerals
Plant roots are composed of millions of root hair cells which have:
Long hairs that extend from the cell body, increasing the surface area for absorption
Many mitochondria which produce ATP for active transport of mineral ions
Name the two plant transport tissues
Xylem
Phloem
What is the function of the xylem?
Transports water and minerals up the
plant, from the roots to the leaves via the
transpiration stream
Describe how the xylem is adapted to its function
- Composed of dead cells laid end-to-end to form a long, hollow, continuous column
- No end walls which provides little resistance to the passage of water
- Thick cell wall strengthened with lignin to provide support
What is the function of the phloem?
Transports sugars up and down the stem from photosynthetic tissues (e.g. mature green leaves) to non-photosynthetic tissues (e.g. developing seeds) via translocation
What is transpiration?
The loss of water vapour from the parts of a plant exposed to the air due to evaporation and diffusion
Where does the majority of transpiration take place?
Leaves
Describe the process of transpiration
- Water evaporates from the mesophyll cell surfaces and diffuses out of the stomata
- Water molecules (which have cohesive properties) are drawn up the xylem vessels to replace the water that has been lost
- This causes more water molecules to be absorbed from the soil into root hair cells
How does the transpiration stream transport mineral ions?
Mineral ions are dissolved in the water that is carried by the transpiration stream
What are stomata?
They are pores found in the lower epidermis of a leaf which allow gas exchange
What are guard cells?
Specialised cells surrounding the stoma that change shape to control the size of the pore
What factors affect the rate of transpiration? (3)
Light intensity
Temperature
Air movement
Describe how high light intensity affects the rate of transpiration
- High light intensity, greater number of stomata open to allow gas exchange for photosynthesis
-Rate of photosynthesis increases so more water is taken up from the soil, pushing water up the xylem - More water vapour diffuses out of the stomata therefore rate of transpiration increases
Describe how low light intensity affects the rate of
transpiration
At a low light intensity, fewer stomata are open so the rate of transpiration decreases.
Describe how temperature affects the rate of transpiration
- Temperature increases, water molecules have more KE so rate of diffusion increases
- Photosynthesis also increases so more water is taken up from the soil, pushing water up the xylem
- More water vapour diffuses out of the stomata therefore the rate of transpiration increases
Describe how air movement affects the rate of transpiration
- Air movement increases, high water concentration gradient maintained between the air spaces in the leaf and atmosphere
- Increased rate of diffusion of water molecules out of the stomata
- Rate of transpiration increases
What is translocation?
The movement of sugars (sucrose, amino acids etc.) up and down a plant, from the source to the sink, via the phloem. Requires ATP
What is ATP
An energy-carrying molecule found in the cells of all living things
Describe how leaves are adapted for photosynthesis and gas exchange
- Broad - large SA for light absorption
- Thin - short diffusion distance for gases, allows light to reach all cells
- Vascular bundles (xylem and phloem) form a network to deliver water and remove glucose. Also provide support.
- Photosynthetic pigments (e.g. chlorophyll) absorb light
Describe how tissues of the leaves are adapted for photosynthesis and gas exchange
- Palisade mesophyll layer - receives most light so contains greatest concentration of chloroplasts
- Upper epidermis - transparent, allows light to reach palisade layer
- Spongy mesophyll layer - air spaces increase the rate of diffusion
- Lower epidermis - contains many stomata for gas exchange
Describe how plants are adapted to live in hot, dry conditions
- Small leaves/spines - reduce SA for water loss
- Thick waxy cuticle - reduces evaporation, conserving water
- Thick stem - provides a storage of water
- Shallow but widespread roots - large SA to absorb water
- Stomata sunken in pits and leaves curled - reduces air flow, lowering diffusion gradient and reducing water loss by evaporation
- Stomata close to reduce water loss
