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Investigating cells
Aerobic Respiration
Mr G Davidson
18 April 2023 G Davidson 2
Energy
Energy cannot be created.Energy cannot be destroyed.Energy exists in a number of different forms, e.g. heat, light, sound, electrical, etc…
18 April 2023 G Davidson 3
Chemical Energy
This is stored energy.When one chemical substance is changed into another during a chemical reaction, this stored energy is often released.It may be released as heat, light, sound, etc..
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Chemical Energy
The sun is the primary source of energy for this planet.It is possible to trace the path of this energy from the sun to the cells in organisms.
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Chemical Energy
Not all the energy released by the sun arrives in the cells.Each time an energy conversion takes place some energy is “lost”.This lost energy is not destroyed – it simply passes out of the pathway in another form and is therefore, wasted energy.
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Energy Changes in Organisms
Energy is always associated with changes.Energy is continually being converted from one form to another.Animal and plant tissues contain chemical energy in the form of carbohydrates and fats.
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Energy Changes in Organisms
This energy can be converted into a variety of forms.Organisms consist of vast numbers of different kinds of cells.All cells need energy.Each cell or group of cells has a particular function to carry out.Individual cells are capable of carrying out several different energy conversions.
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Energy from Foods
All cells need a supply of food.Food contains chemical energy.The foods eaten by animals contain carbohydrates, proteins and fats.
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Energy from Foods
Foods can be analysed to find out the proportions of carbohydrate, protein and fat.These proportions are often given as percentages.It is also possible to find out how much energy a particular food contains.This is measured in kilojoules per gram. (kJg -1)
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Energy from FoodsFood
% Carbohydrate
% Fat % ProteinEnergy
Content (kJ/g)
Olive oil 0 100 0 39
Gelatin (dried) 0 0 100 19
Almonds 5 54 17 27
Sugar 100 0 0 19
Sausages 13 25 11 15
Pastry 8 33 55 25
If the numbers of the percentages don’t total 100, If the numbers of the percentages don’t total 100, then the food also contains water.then the food also contains water.
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The energy content of food is measured using a food calorimeterfood calorimeter.
Energy from Foods
ThermometerThermometer
Known volume of waterKnown volume of water
Known mass of foodKnown mass of foodThe food is set alight and the rise The food is set alight and the rise in temperature of the water is in temperature of the water is calculated.calculated.
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Food Calorimeter
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Respiration
Carbohydrate in the form of glucose is transported to each cell in an organism.The process by which cells release the energy stored in glucose molecules is called CELLULAR RESPIRATION.CELLULAR RESPIRATION.There are 2 types:
Aerobic respirationAerobic respiration – this occurs when there is a plentiful supply of oxygen to the cell.Anaerobic respirationAnaerobic respiration – this occurs when there is no oxygen available to the cell.
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Oxygen UptakeIt is possible to measure changes in oxygen content using a RESPIROMETER.Each type of respirometer contains a chemical to absorb and therefore remove carbon dioxide given out by the organism.The respirometer measures both the volume of oxygen taken up by a respiring organism, and the volume of CO2 released.They are equal.
GLUCOSE + OXYGENGLUCOSE + OXYGEN ENERGY + CO ENERGY + CO22 + WATER + WATER
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18 April 2023 G Davidson 16
Carbon dioxide Release
Before a gas can be identified, it must be collected or located.Once this is done an identification test can be carried out.
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Carbon dioxide ReleaseBicarbonate indicator solution changes colour from red to yellow when carbon dioxide is present.In order to prove that any CO2 detected around a respiring organism, has come from that organism, we have firstly to remove the CO2 from the organism’s air supply.
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Burning SugarIf glucose is burned it releases carbon dioxide. It also releases
water.
Glucose
Bicarbonate indicator
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Burning SugarThe carbon dioxide causes the
bicarbonate indicator to turn yellow.
Glucose
Bicarbonate indicator
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Burning SugarYeast is a fungus which can respire aerobically or anaerobically.If it has a goes supply of glucose and oxygen then CO2 is also released.This would seem to indicate that respiration and burning are quite similar in that the waste products are the same.
18 April 2023 G Davidson 21
Energy Release
Warm blooded animals maintain their body temperature above that of their surroundings.This means the animal is losing its heat to its surroundings.This heat energy must be coming from energy locked up in food.The heat energy is released as part of respiration.Plants also give off heat because they are respiring also.
18 April 2023 G Davidson 22
Why Cells Need Energy
Energy in cells is continually being converted from chemical energy to other forms according to the needs of the cell.All living cells respire.When a cell or entire organism ceases to respire it dies.Metabolism is a word used to describe what happens inside cells or whole organisms.