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Photosynthesis and transpiration in plants
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- 1During Photosynthesis, light energy is absorbed by chlorophyll in the chloroplasts of the green parts of the plants. It is used to convert carbon dioxide and water into sugar ( glucose). Oxygen is released as a by product.
- 2Adaptation of leaves- Most leaves are broad.Gives them large surface area, to absorb as much as light as possible.
- 3Contain chlorophyll in the chloroplasts to absorb the light energy
- 4The Stomataair spaces that allow carbon dioxide to get to the cells, and oxygen to leave them by diffusion
- 5They have veins which bring plenty of waters in the xylem to the cells of the leaves.The products of photosynthesis (sugars) are removed by the phloem
- 6Limiting factors- factor which limits the rate of reaction.Limiting factors for photosynthesis- Shortage of light, low temperature, shortage of carbon dioxide.
- 7People can artificially control the environment of their plants using greenhouses or polytunnels. Farmers benefit from this as the quicker a plant grow, the better the profit.In greenhouses, we can control the temperature, light and carbon dioxide levels to increase the rate of photosynthesis therefore increasing the yield of the crop
- 8Plants and algal cells use glucose they produce during photosynthesis.for respiration, to convert into insoluble starch for storage, to product fats or oils for storage and to produce fats, proteins or cellulose for use in the cell walls.
- 9Plants and algal cells also use glucose to make amino acids by combining with nitrate ions and mineral ions from the soil.Carnivorous plants produce proteins and minerals from the animals they digest. They are adapted to living in nutrient poor soil.
- 10Plants have stomata that allow the plant to obtain carbon dioxide from the atmosphere
- 11Carbon Dioxide enters the leaf by diffusion. Leaves have flat thin shape and internal air spaces to increase the surface area available for diffusion
- 12Plants mainly lose water through the stomata in the leaves.Most of the water and mineral ions needed by a plant are absorbed by the root hair cells, which increase the surface area.
- 13Transpiration is the evaporation of water at the surfaces of the spongy mesophyll cells in leaves, followed by loss of water vapour through the stomata.
- 14The transpiration stream has several functions. -transporting mineral ions -providing water to keep cells turgid in order to support the plant -providing water to leaf cells for photosynthesis -keeping the leaves cool by evaporationTranspiration produces a tension or ‘pull’ on the water in the xylem vessels by the leaves. Water molecules are cohesive so water is pulled up through the plant.
- 15Water moves through the xylem vessels in a continuous transpiration stream: root → stem → leafWater passes from the soil water to the root hair cell’s cytoplasm by osmosis. This happens because the soil water has a higher water potential than the root hair cell cytoplasm:
- 16If the rate of transpiration increases, the rate of absorption of water by the root increases too. Factors that affect the rate of transpiration also affect water uptake by the plant. If water is scarce, or the roots are damaged, a plant may wilt.The rate of transpiration is affected by several factors, including:
temperature
humidity
wind speed
light intensity - 17—Xylem transports water and mineral salts from the roots up to other parts of the plant, while phloem transports sucrose and amino acids between the leaves and other parts of the plant.
- 18Mature xylem vessels: -contain no cytoplasm -are impermeable to water -have tough walls containing a woody material called ligninPhloem transports sucrose and amino acids up and down the plant. This is called translocation
- 19—Auxin is a plant hormone responsible for controlling the direction of growth of root tips and stem tips in response to different stimuli including light and gravity. Auxin is made at the tips of stems and roots.
- 20the responses of roots and shoots to stimuli of light and gravity are the result of unequal distribution of auxin therefore un equal growthThe selective weedkiller contains growth hormone that causes the weeds to grow too quickly.
- 21Rooting powder makes stem cuttings quickly develop roots. Rooting powder contains growth hormones.Some hormones slow the ripening of fruits and others speed it up. These hormones and their inhibitors are useful for delaying ripening during transport or when fruit is displayed in shops.
- 22Dormancy stops seeds germinating until conditions are ideal for growth. Hormones can be used to remove the dormancy of a seed so it can germinate at all times of year.Plant growth hormones are used in agriculture and horticulture
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