B4 Bioenergetics Photosynthesis Plant use glucose for: The following equations summarise what happens in photosynthesis: Photosynthesis is the process by which plants make carbohydrates from raw materials, using energy from light. During photosynthesis: light energy is absorbed by chlorophyll - a green substance found in chloroplasts in green plant cells and algae absorbed light energy is used to convert carbon dioxide (from the air) and water (from the soil) into a sugar called glucose oxygen is released as a by-product Plant use glucose for: Making amino acids Glucose is combined with nitrate ions ( from the soil) to make amino acids, they are used to make up proteins Making cellulose Cellulose is present in cell walls, it strengthens cell walls Respiration Energy from respiration is use to convert rest of the glucose in to useful substances , build new cells and grow Storage of lipids and starch Plants can convert glucose in to lipids and store them in seeds Pants can convert glucose in to starch and store it in roots, stems, seeds and leaves B4 Bioenergetics temperature If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot. light intensity Without enough light, a plant cannot photosynthesize very quickly - even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the rate of photosynthesis. Enzymes increase rate of process, Their action depends from temperature rate increase with temperature To high (above 45 C) enzyme will be damaged carbon dioxide concentration The amount of CO2 will increase rate of process up to a point, after that point rate no longer increase As the light level is raised, rate of photosynthesis increase up to the point No increase after that point Factors affecting photosynthesis Three factors can limit the rate of photosynthesis: Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide

B4 Bioenergetics Metabolism Photosynthesis limiting factors: temperature, carbon dioxide, light HT: at any given time, any one of these factors may be limiting the rate of photosynthesis. This can be shown on graphs – see example. When it comes to light intensity, it varies with distance according to an inverse square law: In commercial growing of plants (e.g. tomatoes in a greenhouse), the conditions are optimised to maximise the rate of photosynthesis and obtain the highest profit. Chemical reactions are controlled by enzymes Metabolism Metabolic pathways can be described as a series of chemical reactions that start with a substrate and finish with an end product. The sum of ALL the chemical reactions happening in a cell or in the whole body. 1 Light intensity = --------------- distance (d) 2 Endothermic reactions – larger molecules are made up from smaller ones , reaction take in energy from environment Exotermic reactions: Larger molecules are broken down into smaller ones, energy is transferred in to the environment B4 Bioenergetics Making lipid (fat) molecules from one molecule of glycerol and three molecules of fatty acids Heat from the sun Conversion of glucose: to glycogen (in animals), to starch or cellulose (in plants). Breaking down excess proteins into amino acids, then into urea for excretion in the urine. Artificial light t after Sun CO2 concentration - Use of paraffin heater, Investigating photosynthesis rate In plants, glucose is combined with nitrate ions to make amino acids. These amino acids are then used to synthesise proteins. Glucose is broken down In Respiration, energy is used to power all reactions in the body Use a pondweed to investigate the effect of different light intensity on the rate of photosynthesis- the faster the rate of oxygen produced by pondweed, the faster the rate of reaction. cellulose Controlling variables: Independent variables – light intensity Dependent variable – amount of oxygen produced

Anaerobic respiration Aerobic respiration occurs when oxygen is used in the reaction. Anaerobic respiration happens inside the cell structures called mitochondria. Respiration. Respiration is a process of transferring energy from glucose, which goes on in every cell. All animals and plants respire, it’s how they release energy from their food. All reactions involved in respiration are catalysed by enzymes, respiration is exotermic – it transfers energy to the environment. There are two types of respiration aerobic and anaerobic. word equation: glucose + oxygen  carbon dioxide + water Symbol equation: C6H12 O6 + 6O6  6CO6 + 6H2O Living organism , use released energy for their life processes. • Chemical reactions to build larger molecules from smaller ones. E.g. making proteins such as enzymes from amino acids. • Keeping warm. This is an example of homeostasis: using energy from respiration to maintain body temperature at a set point (37 ֩C). • Movement. E.g. movements of our body are possible due to muscle contractions. This requires energy from respiration. Aerobic respiration Anaerobic respiration Is oxygen needed? yes no What products are made? CO2 and water Lactic acid (muscles), CO2, ethanol (plants, yeast) How much energy is transferred? Large amount Most efficient A small amount Plants and yeast: Word equation: glucose  ethanol + carbon dioxide Symbol equation: C6H12O6  2C2H5OH + 2CO2 Anaerobic respiration Anaerobic respiration occurs when there is insufficient oxygen available for complete breakdown of the glucose. The reaction that happens is different in animal cells compared to plant and yeast cells. Energy for exercise During exercise, more energy is required as muscle contract more frequently. This energy comes from increased respiration. Increased respiration in cells means that more oxygen is needed. Therefore physical activity: During exercise when body can’t supply oxygen to muscles, they start to respire anaerobically. Lactic acid builds up and exercise can cause muscle fatigue. Fermentation - we call the anaerobic respiration in yeast. This is a very useful process: for making bread; the CO2 makes it rise making alcoholic drinks, beer and wine; ethanol type of alcohol is produced. Increases heart rate to make blood flow in faster rate, delivering more oxygen and glucose to cells, and taking carbon dioxide away Animals Word equation in muscles: glucose  lactic acid Oxygen debt Is amount of extra oxygen the body need after exercise to react with build up lactic acid and remove it from the cells. Increases breathing rate and volume of each breath to meet demand for oxygen