CB6c/d Absorbing water and mineral ions and transpiration and translocation Flashcards
Why do plants require water
- Photosynthesis
- Maintenance of structure
- Cooling effect
Why do plants require mineral ions
For growth e.g nitrates are required to produce proteins
Which structure in plants is adapted for the uptake of water and minerals
Root hairs
How is water transported into root hairs
Lower concentration of water in root hair cells than in soil
Water diffuses down its concentration gradient into root hair cells by osmosis
How are minerals transported into root hairs
Lower concentration of mineral ions in the soil than in the root
Root hair cells take up mineral ions by active transport
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 tissue
Xylem
Phloem
What is the function of xylem
Transports water and minerals up the plant, from the roots to the leaves via the transpiration system
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 provide 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 are the two cell types that make up the phloem
Sieve tube elements
Companion cells
Describe how the phloem is adapted to its function
Sieve tube elements are long, thin cells, laid end to end with perforated end plates to enable the flow of sugars. They contain no nucleus and little cytoplasm to allow sugars to flow easily
Companion cells contain a dense cytoplasm, nucleus and mitochondria. They provide energy for processes in both cell types
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 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 steam transport mineral ions
Mineral ions are dissolved in the water that is carried by the transpiration system
What are the 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 change shape to control the size of the pore
How do guard cells control the size of the stoma
To open the stomata:
Water enters the guard cells. They swell and become turgid. They bend and draw away from each other opening the stomata
To close the stomata:
Water leaves guard cells. They become flaccid, closing the stomata
What factors affect the rate of transpiration
- Light intensity
- Temperature
- Air movement
Describe how high light intensity affects the rate of transpiration
- High light intensity, greater number of stomata to 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 so 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 so 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 in water molecules out of the stomata
- Rate of transpiration increases
