Bioenergetics

• Plants use light for their source of energy, a reaction called photosynthesis.
• Photosynthesis takes an energy, making it an example of an endothermic reaction.
• The leaves of a plant contain the green chemical chlorophyll, which can absorb light energy.
• In the first stage of photosynthesis, light energy is absorbed by chlorophyll, then used to convert carbon dioxide and water into the sugar glucose, producing oxygen as a by-product.
• The chemical formulas for the molecules in the reaction are: CO2, H2O, C6H12O6, and O2.
• In order for photosynthesis to take place, we need carbon dioxide and light.
• If there's not enough carbon dioxide or light, the rate of photosynthesis decreases.
• If the light intensity is limiting, the rate of photosynthesis increases as the plant has more light energy to carry out the photosynthesis reaction.
• If the carbon dioxide level is limiting, the rate of photosynthesis increases as the plant has more carbon dioxide to carry out the photosynthesis reaction.
• The amount of chlorophyll in the leaf can affect the rate of photosynthesis, as leaves with less chlorophyll can trap less light energy and have a lower rate of photosynthesis.
• The temperature can affect the rate of photosynthesis, as enzymes involved in photosynthesis work faster at higher temperatures, leading to an increase in the rate of photosynthesis.
• However, if the temperature increases too high, the enzymes will denature, leading to a decrease in the rate of photosynthesis.
• In photosynthesis, carbon dioxide and water are chemically reacted using the energy from light, producing a sugar called glucose and the gas oxygen.
• The first use of the glucose produced in photosynthesis is to release energy in respiration, which takes place in the mitochondria.
• Plant cells respire all the time, including at night, so the second use of the glucose produced by photosynthesis is to produce the insoluble storage molecule starch.
• Starch can be converted back to glucose by the plant when it's needed, for example at night.
• In many plants, the glucose produced in photosynthesis is converted to fats and oils, which are used by the plant as a storage form of energy.
• The cell wall of a plant cell contains the molecule of cellulose, which gives it strength, and cellulose is made from the glucose produced by photosynthesis.
• The final use of the glucose produced in photosynthesis is to produce amino acids, which are used by the plant to synthesize proteins and foods such as peas, which are good protein sources.
• To make amino acids from glucose, plants need to absorb nitrate ions from the soil.
• The required practical involves investigating the effect of light intensity on the rate of photosynthesis.
• The experiment involves placing a 10 centimeters away from an LED light source, using a boiling tube, and filling it with sodium hydrogen carbonate solution, which releases carbon dioxide needed for photosynthesis.
• A piece of pond weed is placed in the boiling tube with the cut end, and the experiment is left for five minutes to acclimatize to the conditions in the boiling tube.
• The experiment involves counting the number of bubbles produced in one minute and repeating the process three times, then calculating the mean number of bubbles produced in one minute.
• The experiment is repeated at different distances: 20 centimeters, 30 centimeters, and 40 centimeters.
• The number of bubbles can be too fast to count accurately, and the bubbles are not always the same size, which can be solved by measuring the volume of oxygen produced instead of counting bubbles.
• If the distance from the lamp to the pondweed is doubled, the number of bubbles per minute falls by a factor of four, which is known as the inverse square law.
• The limiting factor in photosynthesis can be determined by interpreting graphs.
• Greenhouses are used to increase the rate of photosynthesis by farmers who want to increase the yield of crops.
• Farmers light and heat their greenhouses and add extra carbon dioxide to increase the rate of photosynthesis.
• The rate of photosynthesis increases as the light intensity increases, but at a certain point, the rate of photosynthesis stops increasing, indicating that light intensity is the limiting factor.
• The three other factors that limit photosynthesis are the carbon dioxide concentration, temperature, and the amount of chlorophyll in the leaves.
• The concentration of carbon dioxide can be increased to increase the rate of photosynthesis, as shown in a graph where the rate of photosynthesis increases as the concentration of carbon dioxide increases.
• If the concentration of carbon dioxide is increased further, the rate of photosynthesis doesn't change, indicating that carbon dioxide concentration is no longer the limiting factor.
• Temperature can also act as a limiting factor in photosynthesis, as shown in a graph where the rate of photosynthesis increases at a higher temperature but decreases at a higher temperature.
• The amount of chlorophyll in the leaves can also limit photosynthesis, as shown in a graph where the rate of photosynthesis doesn't change when the amount of chlorophyll in the leaves is increased.
• Greenhouses are used to increase the rate of photosynthesis by exploiting the idea of limiting factors.
• Farmers light and heat their greenhouses and add extra carbon dioxide to increase the rate of photosynthesis.
• The rate of photosynthesis increases as the light intensity increases, but at a certain point, the rate of photosynthesis stops increasing, indicating that light intensity is the limiting factor.
• The three other factors that limit photosynthesis are the carbon dioxide concentration, temperature, and the amount of chlorophyll in the leaves.