RESPIRATION

7.1 THE RESPIRATORY PROCESS IN ENERGY PRODUCTION

CELL RESPIRATION

All organism require energy to carry out all living processes

Energy is required for various processes which occur in the cell such as: Cell division for growth Formation of gamete for reproduction Transmitting nerve impulses for response and

coordination Contraction of muscles for movement Synthesis of proteins, hormones, lipids and

enzymes

CELL RESPIRATION Respiration is the process in which nutrients

are converted into useful energy in a cell The main substrate for respiration is

glucose Glucose is obtained from:

Digestion of carbohydrates in humans and animals

The process of photosynthesis in plants Respiration at the cellular level is known as

cellular respiration The process occurs in the mitochondria and

cytoplasm of cells Respiration involves a series of reactions

controlled by enzymes

TYPE OF RESPIRATION

There are two types of respiration in the cell Aerobic respiration Anaerobic respiration

AEROBIC RESPIRATION

Aerobic respiration also known as 'oxidative metabolism‘

Aerobic respiration is the breaking down of glucose in the presence of oxygen to release chemical energy

Oxygen is required to oxidise the glucose to produce carbon dioxide, water and energy (ATP)

In aerobic respiration, the glucose is completely oxidised

AEROBIC RESPIRATION

Occurs in the mitochondria and cytoplasm of cells

The reactions occurs slowly and in stages controlled by enzymes

Some of the chemical energy released is changed to heat energy while the rest of the chemical energy is stored in the form of adenosine triphosphate (ATP), a carrier of chemical energy

ATP can be regenerated by combining inorganic phosphate (P) to adenosine diphosphate (ADP)

When body cells need energy, ATP molecules will be hydrolysed to yield energy, a molecule of ADP and an inorganic phosphate

During aerobic respiration, at least 38 molecules of ATP or 2898 kJ of energy is released

Aerobic respiration can be represented by the following equation:

The oxygen for aerobic respiration comes from inhaled air while the carbon dioxide released is removed during exhalation

ATP ADP + P + energy

Glucose + oxygen carbon dioxide + water + 38 ATP/ 2898 kJ

C6H12O6 + 6O2 6CO2 + 6H2O + 38 ATP/ 2898 kJ

ANAEROBIC RESPIRATION

Refers to the special type of respiration, which takes place without oxygen

Anaerobic respiration is the process of oxidation of molecules in the absence of oxygen

Anaerobic respiration is synonymous with fermentation

Glucose is not completely broken down. Not all the energy in glucose is released

Occurs in the cytoplasm of the cells

ANAEROBIC RESPIRATION IN HUMAN MUSCLES

Occurs in human muscles during vigorous activities

During vigorous activities, oxygen need to be transported fast enough to the muscles for rapid cell respiration

This will enable the release of sufficient energy for the vigorous muscle activity

The breathing rate and heart rate are increased to supply more oxygen quickly to the muscles for rapid muscular contraction

However, the supply of oxygen to the muscles is still insufficient and the muscles have to carry out anaerobic respiration to release energy

In the muscles cells, glucose is broken down in the absence of oxygen to form lactic acid and energy for muscle contraction

Lactic acid accumulates in the muscles causing muscular ache

An oxygen debt incurred because the maximum rate of oxygen used is less than the oxygen supplied

Oxygen is required to pay off the oxygen debt Rapid breathing continues after the vigorous

exercise obtain sufficient oxygen

Oxygen oxidises the lactic acid to carbon dioxide, water and energy When all lactic acid is oxidised, the oxygen debt is said to be paid

Oxidation of lactic acid mainly occurs in the liver Some of the lactic acid is oxidised to produce energy The remaining is converted to glucose and then glycogen which is then stored in the muscle cells

ANAEROBIC RESPIRATION IN YEAST Yeast carries out both aerobic respiration and

anaerobic respiration Anaerobic respiration in yeast cells is called

fermentation During fermentation, yeast secretes the enzyme

zymase which hydrolyses glucose in the absence of oxygen to form ethanol, carbon dioxide and 2 ATP

The enzyme zymase secreted by the yeast speed up the fermentation process

In the fermentation process, only a small amount of energy is released

A large amount of energy is still stored in the ethanol as chemical energy

This is because the glucose is not completely broken down

The products of fermentation such as carbon dioxide is used as raising agent in baking bread while ethanol is used to produce alcoholic drinks such as wine

COMPARISON BETWEEN AEROBIC AND ANAEROBIC RESPIRATION

Aerobic respiration Anaerobic respiration

Occurs in the _________ of oxygen

Occurs in the ____________ of oxygen

Releases _________ amount of energy (___ molecules of ATP or ______ kJ)

Releases ________ energy ( ____ molecules of ATP or ____ kJ (muscle cells) _____ kJ (yeast)

Produces ____________ and __________

Produces ____________ (human muscles) or ________________ (yeast)

Glucose is _______________ broken down

Glucose is ___________________ broken down

Occurs in the _________________ and _____________________

Occurs in the __________________ only