Biology, Paper 1- Bioenergetics



Respiration is a exothermic reaction- giving out energy. This is because it releases energy from glucose molecules (digested food) for use by the body. This is needed for:

- Chemical reactions to build larger molecules.

- For movement, enabling muscles to contract.

- To keep warm.

Aerobic respiration: (in the presence of oxygen)

Glucose C6H12O6 (from the digestive system) + Oxygen O2 (from the respiratory system) --> Chemical Energy --> Carbon dioxide CO2 (waste product exhaled) + water H2(waste product exhaled) + ENERGY. 

The glucose and oxygen are transported through the body through the blood stream, oxygen by the red blood cells, and glucose dissolved in blood plasma. 

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Anaerobic Respiration

In anaerobic respiration the glucose is not fully broken down. This means it transferes much less energy that aerobic respiration. 

In animals: Glucose --> (energy 5%) --> latic acid 

In plants and yeast: Glucose --> Ethanol + carbon dioxide. This is called fermentation when it happens in yeast cells. This is used to produce alcohol and bread. 

In exersise the body needs more energy so the rate of respiration increases. This means the heart rate and breathing increases to supply the body with the oxygen and glucose it needs for aerobic respiration. However if the muscles are not supplied with enough oxygen anaerobic respiration starts to take place. This causes a build up of latic acid and forms an oxygen dept. The acid causes pain to the muscles and they don't work effeciently because latic acid is a posion. 

After exersize the blood transports the latic acid to the liver where it is broken down. The oxygen dept which needs to be repayed is the amount of oxygen the body now needs to react with the latic acid and remove it from the cells.

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Metabolism is the sum of all the chemical reactions in a cell or the body, they are controled by enzymes and many need a transfer of energy. This energy is transfered by respiration to form new molecules. 


- the conversion of glucose to starch, glycogen and cellulose

- the use of glycose and nitrate ions to form amino acids 

- the breakdown of exess protiens into urea for exretion

- the formation of lipid molecules 

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 Image result for word and symbol equation for photosynthesis (

CO2- from the atmosphere via the stomata. 

Water-  From the roots via osmosis in root hair cells 

Oxygen- released back into the atmosphere via the stomata, or used in respiration 

This reaction is endothermic, so energy is taken in as sunlight and stored in the chemical chlorophyl in chloroplasts. 

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Uses of Glucose

- Plus Nitrogen, to form protiens for growth and repair. the nitrogen is absorbed from the soil. 

- Sucrose, stored in fruit 

- Cellulose to form cell walls 

- Fats and oils food store and growth. 

- Stored in the stem and leaves as starch untill needed

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Factors Affecting Photosynthesis

Many factors affect the rate of photosynthesis. At any moment the factor which stops the reaction going any faster is called the limiting factor. 

Both Light intensity (more energy for photosynthesis) and Carbon dioxide (needed for photosynthesis) concentration have the same type of graph. This is where the more of the factor will increase the rate of photosynthesis, until a certian point when it has no more effect as it is no longer the limiting factor. 

As tempurature increases so does the rate of photosynthesis, because more energy is provided for the reaction. However when it reaches 45 degrees C photosynthesis drops to zero because the enzymes controlling photosynthesis have been denatured and no longer fit the active site for the reaction. 

Chlorphyll concentration can also effect plants long term as plants need to be grown in soil with enough minerals to form chlorophyl. 

Farmers can regulate this to optimum conditions using greenhouses where it is easy to control each factor. 

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