Bioenergetics Flashcards
Respiration
Cellular respiration is an exothermic reaction which is continuously occurring in living cells. The chemical process of respiration releases energy which is needed for living processes to occur within cells and organisms as a whole.
Uses of energy in the body
Cell division + growth
Maintenance of constant body temperature
Active transport
passage of nerve impulses
muscle contraction
Protein synthesis
Aerobic respiration
Respiration in cells can take place using oxygen to transfer energy; glucose is reacted with oxygen in this process.
Aerobic respiration takes place in the mitochondria of the cell.
Glucose + Oxygen —— Carbon dioxide + water
C6H12O6 + 6O2 —— 6CO2 + 6H2O
Anaerobic respiration in animals
Respiration in cells can take place without oxygen to transfer energy; it simply involves the incomplete breakdown of glucose into lactic acid. This occurs when the body can’t supply enough oxygen for aerobic respiration, such as doing vigorous exercise. As the oxidation of glucose is incomplete in aerobic respiration much less energy is transferred than in aerobic respiration (approximately 1/16).
Glucose —— Lactic acid
C6H12O6 —— 2C3H6O3
Anaerobic respiration in plants and yeast
Plants and yeast can respire without oxygen as well, breaking down glucose in the absence of oxygen to produce ethanol and carbon dioxide. Anaerobic respiration in yeast cells is called fermentation.
Glucose —— Carbon dioxide + Ethanol
C6H12O6 —— 2CO2 + 2C2H5OH
Effect of exercise
In order for an individual to be able to move their muscles need to contract which requires energy from respiration. when exercising the number of muscle contractions increases therefore there is a greater energy demand which means that the muscles need a greater supply of oxygen for aerobic respiration. This causes the human body to react by increasing the breathing rate and stroke volume so that more oxygen can be diffused into the bloodstream and the heart rate increases.
If exercising vigorously the body may no longer be able to supply sufficient oxygen to the muscles to meet the demand for energy so the body will resort to anaerobic respiration which releases far less energy. This causes lactic acid to form and lead to an oxygen debt. During long periods of vigorous exercise the muscles become fatigued and stop contracting efficiently as a result of increased levels of lactic acid build up.
Oxygen debt
It is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.
The body can deal with lactic acid in two ways.
It can be oxidised (react with oxygen) to form carbon dioxide and water - the same products formed in aerobic respiration.
Alternatively blood flowing through the muscles transport the lactic acid back to the liver where it is converted back to glucose.
Metabolism
Metabolism is the sum of all the reactions in the body.
They happen all the time in our body and are powered by energy transferred by respiration.
Enzyme controlled processes use this energy is metabolism to synthesise new molecules.
Metabolic substrates
Metabolic reactions include the synthesis and breakdown of carbohydrates, lipids and proteins.
Glucose is used in the synthesis of starch, glycogen or cellulose.
Fatty acids and glycerol are used in the synthesis of lipids.
Amino acids are used in the synthesis of proteins.
Examples of metabolic reactions
Conversion of glucose to cellulose in plants to build and strengthen cell walls
Conversion of glucose into glycogen in animals and starch in plants for storage
The formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids to form triglycerides which are used for energy storage and as insulation in animals
In plants: the use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins required by cells (such as enzymes)
Glucose is broken down in the process of respiration to release energy in all cells
In animals, the breakdown of excess proteins to form urea for excretion
Photosynthesis
Plants are autotrophs – this means that they can make their own food using light, water and carbon dioxide.
This is why they are called producers in food chains.
Photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplasts by light.
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.
Carbon dioxide + water —— oxygen + glucose
6CO2 + 6H2O —— 6O2 + C6H12O6
Factors affecting the rate of photosynthesis (temperature)
The temperature of the environment affects how much kinetic energy all particles have – so temperature affects the speed at which carbon dioxide and water move through a plant.
The lower the temperature, the less kinetic energy particles have, resulting in fewer successful collisions occurring over a period of time.
Increasing temperature increases the kinetic energy of particles, increasing the likelihood of collisions between reactants and enzymes which results in the formation of products.
At higher temperatures, however, enzymes that control the processes of photosynthesis can be denatured (where the active site changes shape and is no longer complementary to its substrate) – this reduces the overall rate.
Factors affecting rates of photosynthesis (light intensity)
The intensity of the light available to the plant will depend on the amount of energy that it has to carry out photosynthesis.
The more light a plant receives, the faster the rate of photosynthesis.
This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply.
Factors affecting rates of photosynthesis (CO2)
Carbon dioxide is one of the raw materials required for photosynthesis.
This means the more carbon dioxide that is present, the faster the reaction can occur.
This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply.
Factors affecting rates of photosynthesis (chlorophyll)
The number of chloroplasts (as they contain the pigment chlorophyll which absorbs light energy for photosynthesis) will affect the rate of photosynthesis.
The more chloroplasts a plant has, the faster the rate of photosynthesis.
The amount of chlorophyll can be affected by:
diseases (such as tobacco mosaic virus)
lack of nutrients (such as magnesium)
loss of leaves (fewer leaves means fewer chloroplasts)
