Chapter 8 Flashcards
Transport in Plants
What are the vascular bundles?
These contain specialised cells that conduct water, food and dissolved salts up or down the stem.
- The 2 main tissues are Xylem and Phloem.
* Xylem is on the inside, Phloem is on the outside.
What is the function of Xylem?
Xylem transports water and mineral ions from Roots -> Stem and leaves.
- It also provides structural support to the plant.
What is the structure and features of Xylem vessels?
The vessels are made up of long cells joined end to end to form a continuous tube.
- The vessels are dead cells.
- They have no cell contents.
- They have thick walls by Lignin, which strengthen and supports it, preventing inward collapsing.
- The cell walls become strong and impermeable.
What is the structure and features of Sieve tubes?
Sieve tubes are formed by conducting cells in Phloem.
- Perforations appear in end walls, allowing substances to pass from cell to cell. These are called Sieve Plates.
- Cell walls are NOT lignified
- They are living cells with contents
- Only Nuclei are lost
- Phloem have supporting cells + Sieve tubes.
What is the function of Phloem?
The Phloem transport food, (sucrose and amino acids) made by the plants leaves -> stem/ roots.
- They are transported from photosynthesising leaves to non-photosynthesising regions.
What are root hair cells?
They are specialised cells found in the roots of plants.
They penetrate between water and soil particles, absorbing them from soil.
- They have ROOT HAIRS, which are extensions of the cell.
- The root hairs INCREASE surface area from 200 m2 -> 400 m2 and increase uptake of water;
This increases absorption of:
>Water by Osmosis
>Mineral ions by Active Transport
What is the Cortex?
The tissue between vascular bundles and epidermis is called Cortex.
These cells store starch.
- OUTER CORTEX cells contain chloroplasts for photosynthesis.
What is the Pith?
The Pith is the central tissue of the stem.
What is the function of Cortex and Pith?
These two act as packing tissues and support the stem.
What is the Pathway taken by Water?
- Water is taken up by root hair cells by Osmosis, since water potential is lower in hairs.
- This increases the turgor pressure of root hair cells, forcing water out and into the next cell wall to the root cortex cells.
- Water travels up xylem by “Transpiration pull” and then goes to the Mesophyll cells.
- Finally it is removed and diffused through stomata of leaves.
What is Transpiration?
Transpiration is loss of water vapour from surface of mesophyll cells of leaves.
- The water evaporates into air spaces and then diffuses out of the stomata as water vapour.
What is the Transpiration pull?
It is the way water moves up the Xylem vessels.
- Water molecules are held together by forces of attraction between them called Cohesion.
- The Transpiration pull draws up a column of water molecules up the vessels.
- AS WATER EVAPORATES and diffuses out stomata, this causes low pressure, causing more water to be drawn up the plant.
How does water travel through vessels?
It travels by Diffusion.
- its not Osmosis since that involves movement across cell membranes.
- Xylem cells have no living contents.
What are the factors that affect Transpiration rate?
- Temperature increases rate (more kinetic energy so molecules diffuse faster).
- Wind speed increases rate (it removes water vapour around the leaf faster).
- Humidity decreases rate (if more water vapour around the leaf, the concentration gradient is less, and diffusion slows down)
What is wilting?
Wilting is when a plant loses more water than it uptakes.
- The plant loses turgor pressure and cells become Flaccid.
What is Translocation?
It is the movement of sucrose and amino acids in the Phloem from sources to sink.
- It is transported in Phloem tubes.
- Sources release sucrose/amino acids.
- Sinks use/store them.
What are Stomata?
Stomata are small pores mostly on the underside of leaves, that are involved in gas exchange and water regulation.
- Each Stomata is surrounded by 2 guard cells which control opening/closing.
What are the functions of Stomata?
- Gas exchange: let Co2 in, O2 out after photosynthesis.
- Transpiration: Allow water vapour to escape + They pull water up in transpiration stream.
- Water control: Stomata close in dry conditions to prevent water loss.
They open when water is sufficient
What is the role of stomata opening and closing?
The stomata is triggered by light intensity, Co2 concentration and Humidity.
- Stomata reacts to WATER STRESS.
When a plant loses water by transpiration faster than uptake, the Stomata CLOSE, to delay wilting.
