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.
• The required practical involves investigating the effect of light intensity on 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.
• 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.
• The first use of the glucose produced in photosynthesis is to release energy in respiration, which takes place in the mitochondria.
• 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.
• If the light intensity is increased, the rate of photosynthesis increases, as the plant has more light energy to carry out the photosynthesis reaction.
• 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.
• 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.
• If the light intensity is limiting, it means that photosynthesis is not as fast as it could be because there isn't enough light.
• Starch can be converted back to glucose by the plant when it's needed, for example at night.
• 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.
• Carbon dioxide is the limiting factor when the light intensity is high, as the rate of photosynthesis increases with increased carbon dioxide levels.
• In many plants, the glucose produced in photosynthesis is converted to fats and oils such as olive oil, which are used by the plant as a storage form of energy.
• The experiment is repeated at different distances: 20 centimeters, 30 centimeters, and 40 centimeters.
• 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 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 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.
• The rate of photosynthesis can be affected by temperature, as enzymes involved in photosynthesis work faster at higher temperatures, leading to an increase in the rate of 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.
• 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.
• To make amino acids from glucose, plants need to absorb nitrate ions from the soil.
• 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.
• Aerobic respiration releases a great deal of energy because the glucose molecule has been fully oxidized.
• 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.
• The chemical symbols for the molecules in the equation for aerobic respiration are: C6H12O6 for glucose, OH- for oxygen, CO2 for carbon dioxide, and H2O for water.
• In the exam, you could be asked for the chemical symbols for the molecules in the equation for aerobic respiration.