Water movement through a plant

1. Water Movement through a Plant

2. To start with the Roots Most of the water absorption is carried out by the younger part of the roots. Just behind the growing tip of a young root,is a region made up of hundreds of projections of the epidermal tissue, the root hairs . Root hairs can be seen clearly in newly germinated seeds, such as the radish shown here in the photograph. The root hairs are short lived being constantly replaced as new growth takes its place. The narrow walled hairs greatly increase the surface area over which water absorption can take place faster. Water in the soil spaces is taken into the root hairs by the process of osmosis , there being a higher water concentration outside than within the root hair cells.

3. Further into the roots Once inside the root hair, the water needs to be transferred to the xylem, the vascular tissue , (also known as the vascular bundles ) involved in water transport through the plant. Vascular tissue is a complex conducting tissue, formed by more than one cell type. The primary components of vascular tissue are the  xylem  and  phloem . In the roots, the vascular tissue is found in the central column. There is a water concentration gradient across the root which means that water which has entered the root hair cell continues to move across the cortex to the endodermis by osmosis. The route taken by much of the water is through the cellulose cell walls, the rest of the water either passes through the cytoplasm of the cells or via the cell vacuoles.

4. Cross section of Root Root Hair Cortex Endodermis Phloem Xylem Dermal Tissue

5. Movement through the Stem The xylem vessels form continuous pipes from the roots to the leaves. Since the xylem vessels are dead, open tubes, no osmosis can occur within them. This causes low pressure in the leaves, so water is sucked up the stem to replace the lost water. The column of water in the xylem vessels is therefore under tension (a stretching force). The very strong lignin walls of the xylem vessels stops them collapsing under the suction pressure.

6. Cross section of Stem Xylem Phloem

7. Water transport through leaves I n broad leaved plants, the leaves are large, thin, flat structures. Large, in order to trap lots of light energy, and thin so that the carbon dioxide can diffuse into the leaf from the surrounding air. As transpiration takes place, water diffusing into the air spaces from the spongy mesophyll cells takes its place. This is turn sets up a concentration gradient across which water moves by osmosis out of the xylem cells and across the leaf. A similar concentration gradient occurs between the xylem and palisade layer so that water will also move by osmosis to the palisade cells in order that it can be used by these cells in the f ood manufacturing process of photosynthesis.

8. Credits to: Nawirah, Meldrick, Jieying & Jing Bo THANK YOU!!!!!!