Topic 6.7 To 6.14B Transport In Plants Flashcards
(32 cards)
Why do plants require water? (3)
Photosynthesis
Maintenance of structure (turgidity)
Cooling effect
Why do plants require mineral ions?
For growth eg 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 the 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 2 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 (eg mature green leaves) to non-photosynthetic tissues (eg developing seeds) via translocation
What are the 2 cell types that make up the phloem?
Sieve tube elements
Companion cells
Describe how the phloem is adapted to its function
Sieve tube elements:
These 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:
Adajacent to sieve tube elements - contain a dense cytoplasm, nucleus and mitochondria. They provide energy for processes in both cell types.
What is transpiration?
The loss of water Vapor 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 allows gas exchange
What are guard cells?
Specialised cells surrounding the stoma that change shape to control the size of the pore
How do guard cells control the size of stomata?
To open the stomata:
Water enters 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? (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 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
