2h. Plant transport

1. 2h. Plant transport • Describe the role of phloem in transporting sucrose and amino acids between the leaves and other parts of the plant. • Describe the role of the xylem in transporting water and mineral salts from the roots to other parts of the plant. • Explain how water is absorbed by root hair cells • Recall that transpiration is the evaporation of water from the surface of a plant. • Explain how the rate of transpiration is affected by changes in humidity, wind speed, temperature and light intensity. • Describe experiments that investigate the role of environmental factors in determining the rate of transpiration from a leafy shoot.

2. Transport • Plants have 2 transport systems. • The xylem vessels carry water. • The phloem tubes carry food materials which the plant has made.

3. The phloem • Phloem tubes are made of phloem cells arranged end to end. • The ends of the cells have small holes in them and are called sieve plates (because they look like sieves). • The cells still contain cytoplasm but no organelles. • Each phloem tube has companion cells, which contain a nucleus and other organelles. Companion cells supply the phloem cells with the things they need (O2 and glucose).

4. Phloem and xylem

5. The phloem • Glucose is made by photosynthesis in the leaves and is converted to sucrose to be transported by the phloem. Amino acids are also carried in the phloem tubes. Sucrose and amino acids are taken to other parts of the plant which need them e.g. the roots.

6. The xylem • Xylem tubes are made of xylem cells stacked on top of each other. • The end of the cells disintegrate totally to leave a hollow tube. • The xylem cells are dead and lignified to strengthen them. • Xylem cells have lost all cytoplasm and organelles and so they die. • Xylem carries water and minerals and also provides support for a plant.

7. Root hair cell • Roots are covered in root hair cells to increase surface area to absorb more water. • Water enters roots by osmosis from a high water concentration in the soil to a lower water concentration in the root hair cells. • Once the water is in the roots it will be carried around the plant in the xylem.

8. Transpiration • Transpiration = evaporation of water from a plant through its leaves

9. Factors that affect transpiration • Humidity • This is the moisture content of the air. • Wind speed • Temperature • Light intensity • Water

10. Factors that affect transpiration