Bioenergetics (4.4) - AQA GCSE Biology Higher

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in food chains • photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplasts by light o the leaves of the plant are where most photosynthesis takes place - in specialised mesophyll cells which are packed with chloroplasts containing chlorophyll to absorb as much light energy as possible • the sugars produced by photosynthesis are used to make all the substances a plant needs, as well as being used in respiration to release energy Bioenergetics (4.4) WATER + CARBON DIOXIDE (+LIGHT) 6H₂0 600₂ GLUCOSE C6H12O6 + OXYGEN ÇO₁₂² 0₂ • carbon dioxide - diffuses into the leaf through the stomata • water - taken up by the roots and transported through the xylem to the leaves 2 glucose - used to make substances needed by the plant - used in repiration to release energy • oxygen - diffuses out of the leaf through the stomata - used in respiration ▼ RATE OF PHOTOSYNTHESIS - (4.4.1.2) • factors that affect photosynthesis o temperature - the lower the temp, the less kinetic energy particles have, resulting in fewer successful collisions occuring over a period of time - at too high temperatures, the enzymes that control the process of photosynthesis can be denatured - this reduces the overall rate. o light - the intensity of the light available to the plant will depend on the amount of energy it has to carry out photosynthesis - the more light a plant receives, the faster the rate of photosynthesis Bioenergetics (4.4) ■ the inverse square law shows the relationship between light intensity and distance ▪ as distance increases, light intensity decreases - this means they are inversely proportional ▪ light intensity = 1/distance(^2) o carbon dioxide conc. - the more carbon dioxide present, the faster the reaction can occur o chlorophyll - the number of chloroplasts will affect the rate of photosynthesis - the more chloroplasts a plant has, the faster the rate of photosynthesis - the amount can be affected by ▪ diseases ▪ lack of nutrients ■loss of leaves commercial horticulturalists grow their plants in a greenhouse • this means they can control as many of the limiting factors of photosynthesis as possible 3 SHADES REMOVED FROM CEILING TO ALLOW MAXIMUM LIGHT ARTIFICIAL LIGHT FOR WINTER/ DARKER HOURS GREENHOUSE TRAPS THE SUNS HEAT SO THAT TEMPERATURE DOESN'T LIMIT PHOTOSYNTHESIS Bioenergetics (4.4) ▼ RESPIRATION - (4.1.2) VENTILATION HELPS PREVENT PLANTS GETTING TOO HOT KEEPING PLANTS IN GREENHOUSE MAKES IT EASIER TO KEEP FROM PESTS AND DISEASES AND ADD FERTILISER Copyright © Save My Exams. All Rights Reserved HEATER BURNS PARAFFIN AND PRODUCES CO₂ USES OF GLUCOSE FROM PHOTOSYNTHESIS - (4.4.1.3) • the glucose produced in photosynthesis may be o used for respiration (both aerobic and anaerobic) o converted to insoluble starch for storage in the stems, leaves and roots WATERING SYSTEM TO MAKE SURE PLANTS STAY WELL WATERED o used to produce fat and oil for storage o used to produce cellulose which strengthens cell wall o combined with nitrate ions from the soil to produce amino acids for protein synthesis 4 ▼ AEROBIC AND ANAEROBIC RESPIRATION - (4.4.2.1) • exothermic reaction continuously occurring in living cells • the energy transferred supplies all the energy needed for living processes o chemical reactions to build larger molecules (protein synthesis) o movement (muscle contraction) o keeping warm (maintenance of a constant body temp) o passage of nerve impulses o active transport • respiration in cells can take place aerobically (with oxygen) or anaerobically (without oxygen) to transfer energy aerobic respiration GLUCOSE + OXYGEN CARBON DIOXIDE + WATER C6H12O6 + 602 + 6H2O → Bioenergetics (4.4) anaerobic respiration (in animals) GLUCOSE → LACTIC ACID 6CO2 aerobic respiration uses oxygen and most of the reaction takes place in the mitochondria • this occurs when the body can't supply enough oxygen for aerobic respiration - such as during exercise as the oxidation of glucose is incomplete in anaerobic respiration much less energy is transferred than in aerobic respiration 5 anaerobic respiration (in plants and yeast) GLUCOSE ETHANOL + CARBON DIOXIDE • plants and yeast produce ethanol and carbon dioxide • anaerobic respiration in yeast is called fermentation COM ARIS fermentation is economically important in the manufacture of bread (CO2 makes dough rise) and alcoholic drinks (as ethanol is a type of alcohol) OXYGEN GLUCOSE BREAKDOWN PRODUCTS - ENERGY RELEASED AEROBIC needed Bioenergetics (4.4) complete carbon dioxide and water a lot ANAEROBIC not needed incomplete animal cells: lactic acid yeast: carbon dioxide and ethanol a little ▼ RESPONSE TO EXCERCISE - (4.4.2.2) • the human body reacts to the increased demand for oxygen in a number of ways o the breathing rate and breath volume increase during exercise to increase the amount of oxygen absorbed into the bloodstream (by diffusion) o the heart rate increases • if the body cannot supply efficient oxygen, energy supplied to the muscle comes from anaerobic respiration (incomplete breakdown of glucose without oxygen) • this releases much less energy and results in the formation of lactic acid as glucose is incompletely oxidised • an oxygen debt is created after exercising this way 6 o the body can deal with lactic acid by oxidation to form carbon dioxide and water o blood flowing through the muscles transports the lactic acid to the liver where it is converted back to glucose • this is why people still breathe heavily with an increased heart rate • during long periods of exercise, the muscles become fatigued and stop contracting effectively due to the increased levels of lactic acid Bioenergetics (4.4) ▾ METABOLISM - (4.4.2.3) • metabolism is the sum of all the reactions in a cell or the body • metabolic substrates - o food eaten o digestion and absorption from the small intestine o glucose → in liver and muscle cells → converted into glycogen for storage o glucose - in all cells → used in respiration to release energy o fatty acids and glycerol → in liver cells → converted into triglycerides o fatty acids and glycerol → in all cells → used to build cell membranes and used in respiration to release energy o amino acids → in liver cells → excess amino acids broken down into carboxyl group and amino group converted into urea → urea excreted by the ▪ amino group → kidneys ■ carboxyl group → used in respiration to release energy o amino acids in all cells used to build proteins - (e.g. enzymes) use of metabolites o metabolism includes ■ conversion of glucose to cellulose in plants to strengthen cell walls 7 ■ conversion of glucose to glycogen in animals and starch in plants for storage ■ formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids - forms triglycerides - (insulation and energy storage) ▪ (plants) - the use of glucose and nitrate ions to form amino acids (synthesise proteins) Bioenergetics (4.4) ■ glucose is broken down in the process of respiration to release energy in cells ■ (animals) - the breakdown of excess proteins to form urea for excretion ▼ EXAM QUESTIONS / 6 MARK QUESTIONS Describe how the products of photosynthesis are used by a plant [6 marks] • glucose is the product of photosynthesis • some glucose is used for respiration by the plants cells • starch is built up and stored in the plant's cells including those of storage organs • starch can be broken down and the glucose used when it is needed - e.g. in respiration during the germination of seeds some glucose is converted into amino acids with the help of nitrate ions absorbed in the soil • amino acids built into proteins glucose converted into lipids 8