4 - Bioenergetics

• Cellular respiration is an exothermic reaction which is continuously occurring in living cells.
• Inverse proportion is a relationship between two values where as one value increases, the other value decreases at the same rate.
• Limiting factor is a factor that limits the rate of a reaction when there is not enough of it.
• Metabolism is the sum of all the reactions in a cell or the body.
• Oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.
• Photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplasts by light.
• Urea forming from the breakdown of proteins for excretion
• Photosynthesis is the process by which plants make glucose from sunlight, it is an endothermic reaction in which energy is transferred from the environment to the chloroplasts by light.
• The equation for photosynthesis is: light carbon dioxide + water → glucose + oxygen.
• Each compound in photosynthesis has its own chemical symbol: Carbon dioxide: CO 2 Water: H 2 O Oxygen: O 2 Glucose: C 6 H 12 O 6.
• The rate of photosynthesis is affected by temperature, light intensity, carbon dioxide concentration, and the amount of chlorophyll.
• With an increase in temperature, the rate of photosynthesis increases until the enzymes begin to denature and the rate of reaction decreases.
• For most plants, the higher the light intensity, the faster the rate of the reaction.
• Carbon dioxide is also needed to make glucose, as seen in the equation for photosynthesis, and as the concentration of carbon dioxide increases, the rate of reaction increases.
• Chlorophyll is a pigment in the leaf that converts light energy to food for the plant, and is therefore essential.
• If chlorophyll levels are reduced through a magnesium deficiency, then the rate of photosynthesis would decrease.
• The rate of photosynthesis can be measured by carrying out an experiment measuring the oxygen production of a plant, such as pondweed placed in a test tube with water, a lamp, and a capillary tube attached to a syringe.
• Many variables can be changed to observe their effect on photosynthesis: the temperature (using a water bath), time the pondweed is left, the light intensity (varied by the distance the lamp is from the plant).
• It is important to control all factors that may affect photosynthesis except your independent variable (the one you want to observe), so it is a valid experiment.
• A graph involves one limiting factor if it has one line which levels off, with the factor on the horizontal axis and rate of photosynthesis on the vertical axis.
• A graph with two lines represents two limiting factors in two experiments, where the investigation involves increasing the factor on the horizontal axis, and is carried out at two different other environmental conditions, such as two different temperatures.
• Light intensity is measured in lux and in this graph we can see that the limiting factor is light intensity.
• Farmers can use the knowledge of limiting factors to enhance the conditions in the greenhouse for a greater rate of photosynthesis, which increases growth and leads to increased profits.
• Respiration occurs in every cell in the body, is exothermic as energy is transferred to the environment, can take place aerobically (with oxygen) or anaerobically (without oxygen), and is the process of transferring energy from glucose so living processes can occur.
• If a lamp is 2 metres away from a plant, then the light intensity of the lamp is a ¼ of its original value.
• The oxidation of glucose is complete in animals, with glucose converting to lactic acid, and in plant and yeast cells it is called fermentation, with glucose converting to ethanol and carbon dioxide.
• Metabolism is the sum of all the reactions in a cell or the body, with the energy transferred in the cells by respiration used in the processes of metabolism to make new molecules.
• A graph involving three limiting factors includes temperature, light intensity, and carbon dioxide, with the limiting factor being temperature.
• Examples of metabolic reactions include glucose molecules being converted to starch, glycogen and cellulose by being joined together, a glycerol molecule and three molecules of fatty acids forming a lipid molecule, glucose and nitrate ions forming amino acids, which are used to form proteins, and the reactions in respiration.
• Glucose from photosynthesis is used for respiration, converted into insoluble starch for storage in roots, stems and leaves, used to produce fat or oil for storage in seeds, used to produce cellulose to strengthen cell walls, combined with nitrates (absorbed from the soil) to form amino acids which produce proteins, and is used in the process of metabolism.
• Inverse proportion describes a relationship between two factors which involves one increasing whilst one decreasing, for example, as the distance between the light source and the plant increases, the light intensity decreases.
• Aerobic respiration uses oxygen, yields the most energy, and most of the reactions that make up aerobic respiration occur in the mitochondria.
• Anaerobic respiration does not use oxygen, yields less energy, and is only used as a last resort, for example during a sprint where it is difficult to breathe in enough oxygen.
• During exercise, more energy is needed for the muscles to contract, meaning respiration has to occur faster, and more oxygen needs to be supplied to cells (and more CO2 removed).
• If there is not enough oxygen being supplied, anaerobic respiration takes place instead, with lactic acid as a byproduct, and blood flowing through the muscles transports the lactic acid to the liver where it is converted back to glucose.
• The light intensity is inversely proportional to the square of the distance, known as the inverse square law.