Section 3 Cells & Respiration

Food & Energy We know that the body needs energy from food in order to move, keep warm and grow The chemical process by which this energy is released from cells is called

Food & Energy The main energy source in a cell is GLUCOSE GLUCOSE Glucose is obtained by plants during photosynthesis and animals through feeding

Introduction Glucose has to be broken down to release its energy The chemical energy in glucose is released in a series of enzyme controlled steps Some energy is lost as heat energy The chemical energy is not used directly by the cell but is stored through the formation of a molecule called...

Energy Summary Chemical energy that we take in through food Glucose Chemical energy is released This process is controlled by enzymes of Breakdown Glucose Some of the chemical energy is lost as heat energy e.g. When the body moves Body Functions e.g. Muscle contraction

What is ATP? ATP or Adenosine triphosphate is a high-energy molecule that stores the energy we need to do just about everything ATP is the energy source for: –Muscle contraction –Cell division –Building up (synthesis) of proteins –Transmission of nerve impulses

The Role of ATP Energy released from the breakdown of glucose is not used immediately Instead energy is stored through the formation of ATP (think rechargeable batteries – lots of energy released slowly so your mobile phone lasts all day) ATP is stored in the body until it is needed The stored energy in ATP is released when ATP breaks down into ADP + Pi (e.g. for muscle contraction) (e.g. for muscle contraction)

Structure of ATP & ADP ADP molecule (low energy molecule) ATP molecule (high energy molecule) adenosine Pi 3 inorganic phosphate groups adenosine Pi 2 inorganic phosphate groups Pi+

Breakdown of ATP adenosine Pi Enzyme controlled reactions adenosine Pi + + energy for cell activities eg. muscle contraction ATP ADP

adenosine Pi + + energy Enzyme controlled reactions adenosine Pi from respiration of glucose Formation of ATP ADP ATP

Summary Notes Respiration is a chemical process in which energy is released from food molecules in cells The cell’s main energy source is glucose Energy is released from glucose using a series of enzymes to control each stage of the breakdown process Enzymes are needed so that our cells do not use all their energy at once or release it too slowly

ATP as a link Energy released from the breakdown of glucose is used to synthesise (build up) ADP + Pi into ATP The newly formed, energy rich ATP can then be broken down again to form ADP + Pi When ATP is broken down into ADP + Pi, energy is released for the body to use

ATP as a link energy ATP energy ADP + Pi cell respiration of glucose cell activities e.g. muscle contraction

Aerobic Respiration

Aerobic respiration is the process by which energy is released from food in cells using oxygen There are two stages involved in the breakdown of glucose The first stage is the splitting of glucose – this is known as glycolysis Glucose is broken down into another molecule called pyruvic acid

Glycolysis Glucose Energy taken in by eating “glucose splitting” is controlled by a series of enzymes Pyruvic Acid A smaller molecule called pyruvic acid is formed

ATP Production During each stage of aerobic respiration, ATP is built up from ADP + Pi In glycolysis, 2 molecules of ATP are built up from 2 ADP and 2 Pi 2 ADP + 2 Pi 2 ATP glycolysis

Glucose Pyruvic Acid 2 ADP + 2 Pi 2 ATP Remember the energy to make ATP from ADP and Pi comes from the breakdown of glucose Series of enzyme controlled reactions

Stage 2 of Aerobic Respiration In total, 38 molecules of ATP are produced from the breakdown of one molecule of glucose Glycolysis only produces 2 ATP so the remaining 36 ATP must be produced in the second stage Stage 2 is where pyruvic acid is broken down. This only happens when oxygen is present

Pyruvic Acid + Oxygen Carbon Dioxide + Water 36ADP + 36 Pi 36 ATP Remember stage 2 only occurs if oxygen is present! Series of enzyme controlled reactions

How many molecules of glucose are produced in aerobic respiration? Stage of aerobic respiration Number of resulting ATP molecules Stage 1: glycolysis Stage 2: breakdown of pyruvic acid Total overall process of aerobic respiration

Summary Aerobic respiration is the process of release of energy from food in cells using oxygen Glycolysis is the breakdown of glucose resulting in the formation of pyruvic acid (remember that pyruvic acid still has a lot of stored energy)

Summary Pyruvic acid is broken down into carbon dioxide and water – these are the end products of respiration Remember we do this too; breathe in oxygen, breathe out carbon dioxide and water

Production of ATP When glucose is broken down completely, during aerobic respiration, into CO 2 + H 2 0, a large quantity of energy is produced The first stage of the breakdown of glucose (glycolysis) only 2 molecules of ATP are produced From the second stage which involves the breakdown of pyruvic acid, 36 molecules of ATP are produced

Summary Flow Diagram Glucose Pyruvic acid + oxygen Carbon dioxide + water 2 ADP + Pi 2 ATP 36ADP + Pi 36 ATP The curved arrows indicate that these reactions use up energy

Anaerobic Respiration In Animals

Anaerobic Respiration During strenuous exercise, a lot of energy is used. This means that a lot of ATP is needed Aerobic respiration produces 38 ATP per glucose molecule so the ATP demand can be met But what happens when you run out of oxygen?

Anaerobic Respiration Imagine you are running a race. At the start you have lots of oxygen to breakdown glucose but as you continue, you cannot supply enough oxygen to your body As a result of this, you start to get aching, sore muscles This is called muscle fatigue Instead of breathing out carbon dioxide and water, you start to respire anaerobically (without oxygen) and lactic acid builds up in your muscles

Pyruvic Acid Lactic Acid The build up of lactic acid in muscles causes muscle fatigue during anaerobic respiration Series of enzyme controlled reactions

Anaerobic Respiration Anaerobic respiration is the breakdown of glucose in cells in the absence of oxygen

Anaerobic Respiration Anaerobic respiration starts with glycolysis (glucose splitting) but because there is not enough oxygen to continue breaking down glucose, a substance called lactic acid is formed Glucose Pyruvic acid Lactic acid 2 ADP + 2 Pi 2 ATP

Building Up An Oxygen Debt The build up of lactic acid causes an oxygen debt to be formed Lactic acid can be reversed back into pyruvic acid when this oxygen debt has been repaid When there is enough oxygen back in the cells, the normal aerobic pathway takes place and pyruvic acid is broken down to produce carbon dioxide and water as normal

Glucose Pyruvic acid Lactic acid 2 ADP + 2 Pi 2 ATP Not enough oxygen for aerobic respiration. Oxygen debt builds up NO ATP are produced here o Oxygen debt is repaid (i.e. Person stops exercising and breathes deeply) o Oxygen gets back into cells o Aerobic respiration can occur

Anaerobic Respiration In Plants & Yeast Anaerobic respiration in plants and yeast is different from animals because here pyruvic acid is broken down further into carbon dioxide and ethanol NO ATP are produced in the breakdown of pyruvic acid into carbon dioxide and ethanol

Anaerobic Respiration In Plants & Yeast Glucose Pyruvic acid Carbon Dioxide & Ethanol 2 ADP + 2 Pi 2 ATP

Anaerobic Respiration In Plants & Yeast Anaerobic respiration in plants and yeast is an irreversible process This means that the carbon dioxide and ethanol formed cannot be converted back into pyruvic acid as is the case for humans This is because carbon dioxide gas is given off into the atmosphere and lost Carbon dioxide and ethanol are useful products in industries such as bread making and alcohol

Summary of ATP Production in Aerobic & Anaerobic Respiration Aerobic Respiration Anaerobic Respiration AnimalsPlants GlycolysisYes ATP (No. Per molecule of glucose) 3822 Product(s) Carbon dioxide & Water Lactic Acid Carbon dioxide & Ethanol

Anaerobic Respiration And Beer Making Barley grains are essential for beer making because they are the energy source for yeast Barley grains contain starch. Starch is a large molecule that must be broken down to simple sugars for yeast feed on The process of breaking down starch into simple sugars is called germination

Anaerobic Respiration and Beer Making Yeast feed on sugar to produce carbon dioxide and ethanol The yeast population grows, but then starts to die off as the alcohol concentration increases Alcohol is a poison therefore it starts to kill off the yeast cells

Conclusion Yeast can respire aerobically or anaerobically When yeast respire anaerobically, they break down glucose into carbon dioxide and alcohol Carbon dioxide is used in bread making to make dough rise