2.2 Movement in and out Cells
1 Define diffusion
Diffusion is the net movement of molecules from a region of higher concentration to a region of lower concentration down a concentration gradient, as a result of their random movement 2 Describe the importance of diffusion of gases and solutes and of water as a solvent. Gases
Necessary for gas exchange in all living organisms
Necessary for obtaining Carbon Dioxide and releasing oxygen during photosynthesis. Solutes (liquids)
Dissolved salts dissolve through root hair cell.
Absorption of dissolved food material in many organisms, like amoeba, bacteria and fungi is carried out through diffusion. Some digested food material is absorbed by diffusion
Water as a solvent
Plants cannot obtain minerals unless they are dissolved in water Enzymes and hormones cannot be secreted unless they are dissolved in water Excretory products cannot be excreted unless they are dissolved in water. 3 Define osmosis (Supp. only)
Osmosis the diffusion of water molecules from a region of their higher concentration (dilute solution) to a region of their lower concentration (concentrated solution), through a partially permeable membrane. 4 Describe the importance of osmosis in the uptake of water by plants, and its effects on plant and animal tissues.
The importance of osmosis
Plants gain water through osmosis in their roots from the soil. Without a water potential gradient,water will be loss from the roots . Plant cells contain vacuoles, which, if not full with water, will cause the cell to become flaccid. If all the cells in a leaf become flaccid, the whole leaf will become flaccid, hence causing the plant to wilt. Plant cells therefore need water to remain turgid and keep firm.If an animal cell surrounded with a high water potential, osmosis will take place, and if the water is not expelled some way or another, the cell will burst. This is because an animal cell doesn’t have a cell wall to keep it strong. If an animal cell is surrounded with low water potential, the water in the cytoplasm will diffuse outwards, causing the cell to shrink. 5 Describe and explain the importance of a water potential gradient in the uptake of water by plants. The water potential determines whether the plant cell would be turgid or plasmolysed.
Since title says “uptake”, it means the plant cell taking in water. If the surroundings has a higher water potential than the plant cell, water molecules moves into the plant cell via osmosis. When the plant cell has sufficient water, it becomes turgid. The cell wall prevents the cell from bursting. Turgor pressure is exerted when the plant cell is swollen. This keeps the plant upright. 5.1 Transport in Plants
1 State the functions of xylem and phloem.
Xylem vessels transport water and dissolved minerals from the root up to all the other parts of the plant Phloem Vessels: The function of Phloem Vessels is to transport food nutrients such as glucose from the leave to other parts of the plant.
2 Identify the positions of xylem and phloem tissues as seen in transverse sections of unthickened, herbaceous, dicotyledonous roots, stems and leaves. Xylem Tissue and Phloem Tissue
In the diagram directly below, Xylem is shown as 8 (red circles), whilst Phloem is shown as 9 (blue circles)
3 Identify root hair cells, as seen under the light microscope, and state their functions.
The root hair cell basically helps absorb water and inorganic ions from the soil via osmosis, which we touched upon in Unit 2, Movement in and out of cells.
4 Relate the structure and functions of root hairs to their surface area and to water and ion uptake. Refer to the diagram above.
The elongated section of the root hair, which you can clearly see on the diagram (the extended bit which looks like something…yes, you know what i’m talking about now), basically provides a large surface area for the absorption of water and inorganic ions. Additionally, the membrane of the root hair...
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