Biology - Unit 7: Transport in Flowering Plants

relate the structure of the root hair cells to their function of water and ion uptake

• root hair increases the surface area of the cells significantly which will increase the rate of absorption

• water enters root hair cells by osmosis

• mineral ions enter root hair cells by active transport

outline the pathway taken by water through the root, stem and leaf

• water enters roots via root hair cells, by the process of osmosis

• water then moves across the root, through the cells of the root cortex

• water travels from the roots to the leaves of plants in the xylem, where it moves into the cells of the leaf mesophyll

• the pathway of water through a plant can be summarised as follows:

root hair cell → root cortex cells → xylem → leaf mesophyll cells

what is transpiration?

loss of water vapour from leaves

how does transpiration occur?

• water travels from the roots to the leaves of plants in the xylem vessels

• when water reaches the leaves it enters leaf mesophyll cells

• water evaporates from the surface of leaf mesophyll cells into the air spaces in the leaf, from where it diffuses out of the leaf via the stomata in transpiration

what is the effect of temperature on transpiration rate?

• as temperature increases, transpiration rate increases as the kinetic energy of water molecules increases.

• thus, they evaporate and diffuse faster from the mesophyll cells.

what is the effect of wind speed on transpiration rate?

• as wind speed increases, transpiration increases

• the wind removes away the water vapour surrounding the leaf faster.

what is the effect of humidity on transpiration rate?

• as humidity increases, transpiration rate decreases.

• if the air surrounding the leaf has more water vapour, there’ll be a weak concentration gradient for diffusion.

what is the function of transpiration in plants?

• transporting mineral ions

• providing water to keep cells turgid in order to support the structure of the plant

• providing water to leaf cells for photosynthesis

• keeping the leaves cool

what is the effect of light intensity on transpiration rate?

• as light intensity increases, transpiration rate increases.

• increased light speeds up photosynthesis, causing the stomata to open for gas exchange.

• while open, water vapour escapes through the stomata.

how does wilting occur?

• if water loss from transpiration is faster than replacement, wilting occurs.

• plant cells lose water and turgidity, causing tissues to become floppy and stems to fall.

• prolonged wilting leads to leaf death, stopping photosynthesis and eventually killing the plan

what is the benefit of wilting?

wilted leaves may become folded, reducing the exposure of stomata to the outside air and slowing further water loss.

describe the transpiration stream?

• transpiration stream is upward movement of water through xylem vessels

• water moves from the roots to the leaves and is then lost from leaves by transpiration

• water loss by transpiration drives transpiration pull which draws water upwards in the transpiration stream

• each water molecule pulls on the molecule below it due to forces of attraction between water molecules

what is translocation?

the movement of sucrose and amino acids in the phloem from parts that produce or release them (sources) to parts of the plants that use or store them (sinks)

identify the positions of the xylem and phloem in this image of a transverse section of a stem.

identify the positions of the xylem and phloem in this image of a transverse section of the roots.

state the function of the xylem.

• transport of water and mineral ions

• support

relate the structure of xylem vessels to their function

• cells are joined end-to-end, thus forming a long continuous tube

• there are no cell contents which allows free passage of water

• outer walls are thickened with lignin which strengthens the tube

how can we investigate transpiration rate?

1. a single air bubble is introduced into the capillary tubing

2. the tap on the reservoir is opened to add water to push the air bubble back to zero on the scale

3. a timer is started and a set time is measured

4. the distance the air bubble travels along the scale is recorded

5. the experiment can be repeated with different environmental conditions

6. the faster the bubble moves, the greater the rate of water uptake — and so the greater the rate of transpiration

• to test how temperature affects transpiration rate: change the room temperature with a heater

• to test how wind speed affects transpiration rate: use a fan at different speeds

• to test how light intensity affects transpiration rate: place a lamp at different distances from the plant