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Descripción
Fichas por megan.radcliffe16, actualizado hace más de 1 año
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Creado por megan.radcliffe16
hace casi 10 años
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| Pregunta | Respuesta |
| why are transport systems needed in multicellular plants? | The epithelial cells could gain all they need by simple diffusion, as they are close to the supply. But there are many cells inside the plant which are further from the supply, and would not receive enough water or nutrients to survive. |
| How is the xylem and phloem distributed in the roots? | The xylem is arranged in an X shape, with the phloem found between the arms of the xylem. |
| How is the xylem and phloem distributed in the stem? | The vascular bundles are found around the outside of the stem in a ring shape. The xylem is on the inside, with the phloem on the outside. They are separated by a layer of cambium. |
| What is the cambium? | a layer of meristem cells which can divide to produce new xylem and phloem. |
| How is the xylem and phloem distributed in the leaves? | They xylem is on top of the phloem in the ‘veins’ of a leaf |
| what is the structure of the xylem vessels? | Long, thick walls that have been impregnated by ligin. |
| What is the function of the ligin in the xylem vessles? | The ligin strengthens the walls and prevents the vessel from collapsing- the vessels stay open even when water is in short supply. The thickening of the ligin forms patters on the cell walls. This prevents the vessel from becoming too rigid and allows the stem or branch to be flexible. In some places the lignification is not complete. Pits or Bordered Pits, like pores in the walls, are left which allow water to leave the vessel to either join another vessel of pass into the living parts of the cell. |
| What is the structure of a sieve tube? | Form long tubes End walls are retained End walls contain many sieve plates Thin layer of cytoplasm Very few organelles No nucleus |
| Why are sieve tubes no true cells? | They have no nucleus and contain very little cytoplasm |
| What are companion cells? | They are support cells that provide all the metabolic functions for the sieve tube elements. |
| What is the structure of companion cells? | Connectedto sieve tube elements by many plasmodata Dense cytoplasm with many mitochindria Large nucleus |
| Define transpiration. | The loss of water vapour from the aerial parts of a plant due to evaporation |
| Why is transpiration a consequence of gas exchange? | For gas exchange to take place the stomata must be open, so water is lost through the stomata. |
| How is transpiration reduced? | 1. A waxy cuticle waterproofs the leaf preventing water loss through the epidermis 2. The stomata are on the underside of leaves, to reduce evaporation due to direct heating 3. Most stomata close at night. 4. Deciduous plants lose their leaves in winter. |
| What factors affect the rate of transpiration? | Number of leaves Number, size, position of stomata presence of a cuticle Light Temperature Relative humidity Air movement water avalibilty |
| How does the number of leaves affect the transpiration rate? | More leaves = large surface area which water can be lost from |
| How does the number,size and position of the stomata affect the transpiration rate? | If leaves have many, large stomata water vapour is lost more quickly If the stomata are on the lower surface, water loss is slower |
| How does the presence of a cuticle affect the transpiration rate? | A waxy cuticle prevents water loss from the leaf surface |
| How does light affect the transpiration rate? | In light, the stomata open to allow gaseous exchange for photosynthesis |
| How does temperature affect the transpiration rate? | 1. Higher temperature will increase the rate of water loss 2. Increase the rate of evaporation 3. Increase the rate of diffusion as the water molecules have more kinetic energy |
| How does relative humidity affect the transpiration rate? | Higher relative humidity in the air will decrease the rate of water loss. This is because there will be a smaller water potential gradient between the air spaces in the leaf and the air outside. |
| How does air movement affect the transpiration rate? | Air moving outside the leaf will carry water vapour away from the leaf. This will maintain a high water potential gradient |
| How does water availability affect the transpiration rate? | If there is little water available plants cannot replace water lost, so water loss has to be reduced by closing the stomata. |
| how is a potometer used to measure transpiration rates? | 1. Cut healthy shoot underwater to stop air entering xylem 2. Cut shoot at a slant to increase surface area 3. Ensure apparatus is full of water and that there is only the desired air bubble 4. Insert shoot into apparatus underwater 5. Remove potometer form water and ensure it is airtight around the shoot 6. Dry leaves 7. Keep conditions constant to allow shoot to acclimatise 8. Shut screw clip 9. Keep scale fixed and record position of air bubble 10. Start timing and measure distance moved per unit of time. |
| How does water movement occur between plant cells? | Water passes from the cell with the higher water potential to the cell with the lower water potential. |
| How does water movement occur between cells and the environment? | Water moves down the water potential gradient. If the water potential inside the cell is greater than the water potential outside the cell, water will move out of the cell by osmosis. |
| What pathways are used to transport water in the plant? | Apoplast pathway Symplast pathway Vacuolar pathway |
| What happens in the apoplast pathway? | Water is carried between cells through the cell walls. |
| What happens in the symplast pathway? | The water is taken from cell to cell through the cytoplasm of each cell. |
| What happens in the vacuolar pathway? | Water is carried through the cytoplasm and vacuole of each cell. |
| What does the Casparian strip stop? | It stops water returning to the cortex through the apoplast pathway |
| What is adhesion? | The attraction between the water molecules and the walls of the xylem vessel. |
| How does water move by adhesion? | Water molecules in the xylem form hydrogen bonds with the walls of the xylem vessel. Because the xylem vessels are narrow, the hydrogen bonds can pull the water up the sides of the vessel |
| What is cohesion? | The attraction between the water molecules |
| How is water moved by the cohesion tension theory? | These forces are strong enough to hold the molecules together in a long chain. As molecules are lost from the top, the whole column is pulled up as one chain. |
| What does the movement of water by the cohesion tension theory create? | Transpiration Stream |
| How are xerophytes adapted to reduce water loss in their leaves? | Smaller leaves- Densely packed spongy mesophyll Thicker waxy cuticle Closing the stomata when water availability is low Hairs on the surface of the leaf Stomata in pits Rolling the leaves |
| How does having smaller leaves reduce water loss? | reduces surface area, so less water is lost by transpiration |
| How does having Densely packed spongy mesophyll reduce water loss? | Reduces cell surface area is exposed to the air spaces. |
| How does having Hairs on the surface of the leaf reduce water loss? | Trap a layer of air close to the surface which can become saturated with moisture and so will reduce the diffusion of water out of the stomata as the water vapour potential is low. |
| How does rolling the leaves reduce water loss? | the lower epidermis is not exposed to the atmosphere |
| What is translocation? | The movement of assimilates around the plant. |
| Where does translocation occur? | In the Sieve tubes |
| What is a source? | part of the plant that has a supply of assimilates that are loaded into the phloem |
| What is a sink? | part of the plant that removes sucrose from the phloem and uses it or stores it. |
| What is the mechanism of phloem loading? | 1. H+ ions are pumped actively out of the companion cells which use ATP. 2. The H+ ions diffuse back into the companion cells through co-transporter proteins carrying sucrose molecules into the companion cells. 3. The sucrose builds up in the companion cells. 4. It diffuses into the sieve tube through the plasmodesmata. 5. The water potential is reduced in the sieve tube. 6. Water flows into the sieve tube by osmosis- this increases the pressure. |
| What evidence is there for active loading taking place? | We know that the phloem is used: Supply the plant with radioactively labelled Carbon Dioxide (for photosynthesis), and the labelled CO2 soon appears in the phloem We know that it needs ATP: Translocation can be stopped by using a metabolic poison that inhibits the formation of ATP We know that it uses this mechanism: The concentration of sucrose is higher in the source than in the sink |
| What evidence is there against active loading taking place? | 1. Not all solutes in the phloem sap move at the same rate 2. Sucrose moves to all parts of the plant at the same rate, rather than more quickly to areas with a low concentration 3. The role of sieve plates is unclear |
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