bio - plant structures + functions (6)

• Plants and algae are the main producers of food – primary producers of biomass in food webs and food chains.
• Photosynthesis occurs in plants and algae and is an endothermic reaction, meaning that it takes in more energy than it releases.
• Light energy from the environment is transferred to chloroplasts in leaves.
• The equation for photosynthesis: carbon dioxide + water → glucose + oxygen.
• Each compound in photosynthesis has its own chemical symbol: Carbon dioxide: CO2 Water: H2O Oxygen: O2 Glucose: C6H12O6.
• Ethene is involved in controlling cell division and stimulates enzymes that result in fruit ripening.
• Ethene reduces wastage as more fruit is suitable to be sold and it does not ripen too early.
• The rate of the photosynthesis process is affected by several factors: Temperature, Light Intensity, Carbon dioxide concentration, and Limiting factors.
• With an increase in temperature, the rate of photosynthesis increases.
• Many plants are adapted to survive in extreme environments, needing specific adaptations which maximise their ability to take in sunlight and carbon dioxide, including leaf shape and size, and the presence of a waxy cuticle.
• Leaves are very thin, meaning that carbon dioxide only has a short distance to travel to enter the leaf and oxygen only has a short distance to diffuse out.
• The factors that affect the rate of water uptake are similar to those that affect the rate of evaporation, including an increase in temperature, relative humidity, and air movement.
• Having a large surface area allows a leaf to absorb more light, maximising the rate of photosynthesis.
• Translocation only occurs in the phloem.
• Translocation is the movement of food substances such as sucrose made in the leaves up or down the phloem, for use immediately or storage.
• Translocation of sucrose occurs from the sources to the sinks, which are the places where it is used or stored.
• Leaves have several adaptations to allow them to perform specific functions, including stomata that can close to minimise water loss and open to increase evaporation and transpiration.
• Measuring the uptake of water by the plant gives an indication to the rate of transpiration, because water is only taken up if water leaves the plant, observed by using a potometer, which involves placing a plant in a capillary tube in water, and measuring the distance travelled by a bubble.
• The location of the sources and sinks can vary depending on the season.
• Chlorophyll is green, which is the most efficient colour for absorbing light, maximising the rate of photosynthesis.
• As the reaction is controlled by enzymes, this trend continues until the enzymes begin to denature – rate of reaction decreases.
• For most plants, the higher the light intensity, the faster the rate of the reaction.
• As the concentration of CO2 increases, the rate of reaction increases.
• Any of the factors above may become a limiting factor.
• A limiting factor is an environmental condition which, in low levels, restricts any increase in the rate of photosynthesis.
• Despite increases in other factors, the rate of photosynthesis will not increase any more.
• This can be seen on a graph as the curve levelling off.
• By carrying out an experiment measuring the oxygen production of a plant, you can calculate the rate of photosynthesis.
• In the experiment, pondweed is placed in a test tube full with water, a capillary tube containing water leads into the test tube, and it is attached to a syringe.
• A lamp is placed at a measured distance from the test tube.
• Auxin is also used as rooting powders, promoting growth in tissue culture.
• Gibberellins allow seed germination to occur by breaking seed dormancy, they allow fruits to grow heavier and larger, increasing yields, and they encourage flowering plants to flower at a faster rate.
• Most shoots show negative gravitropism as they grow away from gravity.
• Most roots show positive gravitropism as they grow towards gravity.
• If a shoot is horizontal, auxin moves to the lower side, stimulating cells to grow more on the side with most auxin, causing the shoot to bend and grow away from the ground.
• Plants need hormones to coordinate and control growth, including for tropisms such as phototropism, the response to light, and gravitropism, the response to gravity.
• This is beneficial as light levels are likely to be higher further away from the ground.
• If a root is horizontal, auxin moves to the lower side, stimulating cells to grow more on the side with less auxin, causing the root to bend and grow downwards.
• This is beneficial as there are more likely to be increased levels of water and nutrients lower down, and it provides stability for the plant.
• Auxin is used as weed killers, as it causes the cells to grow too rapidly, resulting in the weed dying.