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Why is water important in plants? (5)
Used in photosynthesis. Enables chemical reactions to take place within cells. Transport medium for minerals, sugars, etc. Provides support (turgidity). Has a cooling effect.
Which structure in plants is adapted for the uptake of water and minerals?
Root hairs.
How is water taken up by root hairs?
Lower concentration of water in root hair cell sap than in the soil. Water diffuses down its concentration gradient into the root hair cell by osmosis.
Describe how water moves between cells across the root.
Water entering the root hair cell dilutes its cell sap. Higher concentration of water in the root hair cell sap than in the adjacent cell. Water diffuses down its concentration gradient into the adjacent cell by osmosis.
How are minerals transported into root hairs? (higher)
Lower concentration of mineral ions in the soil than in the root. Root hair cells take up mineral ions by active transport (uses energy).
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 energy for the 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 the structure of the xylem.
Composed of dead cells laid end-to-end to form a long, hollow, continuous column.
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 layer 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 factors affect the rate of transpiration? (3)
Temperature. Air movement. Humidity.
Describe how temperature affects the rate of transpiration.
As temperature increases, water molecules have more kinetic energy, so the rate of diffusion increases. More water vapour diffuses out of the stomata, so the rate of transpiration increases.
Describe how air movement affects the rate of transpiration.
Air movement increases, maintaining a high water concentration gradient between the air spaces in the leaf and the atmosphere. Increased rate of diffusion of water molecules out of the stomata. Rate of transpiration increases.
Describe how humidity affects the rate of transpiration.
As humidity increases, the water concentration gradient between the air spaces in the leaf and the atmosphere decreases. Decreased rate of diffusion of water molecules out of the stomata. Rate of transpiration decreases.
What apparatus is used to measure the rate of transpiration?
Potometer.
What is assumed when measuring the rate of transpiration using a potometer?
Rate of water uptake ≈ rate of transpiration.
What is the function of the phloem?
Transports sugars up and down the plant from photosynthetic tissues (e.g., mature green leaves) to non-photosynthetic tissues (e.g., developing seeds).
Describe the structure of the phloem.
Composed of living cells arranged in columns with perforated end plates to enable the flow of sugars.
What happens to sugars at non-photosynthetic areas of a plant?
Used immediately in respiration to release energy. Converted to starch and stored.
In the veins of a plant, where are the xylem and phloem located in comparison to one another?
Xylem is located towards the centre, with the phloem on the outsid
