B9 Respiration

Aerobic respiration

• Called aerobic because it involes oxygen
• Glucose reacts with oxygen that transfers energy for body cell usage
• C02 and water are waste products
• Exothermic reaction - heats up surroundings 
• Takes place in the mitochondria
• Glucose + Oxygen ---> C02 + Water + Energy transferred to surroundings

Mitochondria = organelle in cell. Has large surface area for enzymes involved in aerobic respiration

Need for respiration

• Energy from respiration used in building large molecules and cell material
• Energy from respiration used in breaking down molecules e.g. in digestion
• Energy from respiration used in muscle contraction e.g. heartbeat, digestion, breathing
• Energy from respiration used for maintaining constant body temperature
• Plants = active transport of mineral ions from soil to root hair cells.

Muscles 

• Made of protein fibres that contract when energy is transferred from respiration
• Many mitochondria = carry out aerobic respiration to provide energy for contraction
• Muscles store glucose as glycogen which can be rapidly converted to glucose when energy is needed for exercise, when muscles have to contract

Glucose + Oxygen ---> C02 + Water + Energy transferred to the surroundings

Body's response to excercise 

During exercise:

• muscles contract harder and faster
• muscles need more glucose and oxygen to use in respiration for energy
• muscles produce increased amounts of C02 which needs to be removed fast

The changes taking place in the body during exercise 

• Increased heart rate
• Arteries carrying blood widen ---> increased flow of oxygenated blood to muscles ---> increased rate of oxygen and glucose for respiration ---> increased rate that C02 is removed

• Increased breathing rate and depth of breathing ---> breathe more often and more air breathed ---> increased rate of oxygen to muscles ---> more C02 breathed out

• Glycogen stored in muscles converted back to glucose for increased cellular respiration

Summary of body response to excercise 

• an increase in the heart rate, in the breathing rate and in the breath volume
• glycogen stores in muscles are converted to glucose for cellular respiration
• the flow of oxygenated blood to the muscles increases.

Anaerobic respiration

• Hardworking muscles for long duration = not enough oxygen ---> respire anaerobically (without oxygen)
• Not as effective - glucose molecules are not broken down completely ---> less energy transferred
• Equation - Glucose ---> Lactic acid + Energy transferred to the environment

Muscles can become fatigued and not contract efficiently because of the build-up of lactic acid, produced by cells in anaerobic respiration. Causes oxygen debt.

Oxygen Debt

• The build-up of lactic acid has to be broken down to produce C02 and water using oxygen
• Amount of oxygen needed to break down lactic acid = oxygen debt 

Heart rate and breathing rate stay high after exercise to supply body with extra oxygen needed to pay off oxygen debt. 

Equation = Lactic acid + Oxygen ---> C02 and Water 

Anaerobic respiration in plants 

Glucose ---> Ethanol + C02 + Energy transferred to the environment 

Yeast cells respire anaerobically to produce ethanol and C02 - known as fermentation - used in the manufacture of bread and alcoholic drinks

Metabolism = sum of all reactions taking place in a cell or body.

The energy that is transferred during respiration is used for enzyme-controlled reactions like the making of new molecules

Metabolic reactions

• Conversion of glucose to starch, glycogen and cellulose
• Formation of lipid molecules from glycerol and fatty acids
• Use of glucose and nitrate ions to form amino acids to make proteins
• Breakdown of excess proteins to form urea

The Liver

1. Lactic acid transported to liver. 

2. Liver converts lactic acid back to glucose 

3. Oxygen debt paid off = lactic acid converted to glucose + glucose broken down in aerobic respiration to form C02 and water

Oxygen debt not paid off = lactic acid converted to glycogen and stored

Summary : Blood flowing through the muscles transports lactic acid to the liver where it is converted back to glucose

Other uses of the liver 

• Detoxifying substances like ethanol from alcoholic drinks
• Passing breakdown products into the blood so they can be excreted in the urine via kidneys
• Breaking down old cells and storing the iron to make more cells