Cellular Respiration

Syllabus Objectives

State that respiration takes place at the level of the cell

Describe the process of aerobic respiration

State the function of ATP (adeosine triphosphate) in energy transfer

Distinguish between aerobic and anaerobic respiration

Carry out and interpret results from simple controlled investigations to demonstrate the products of respiration

Introduction

DefinitionProcess living organisms undergo to release energy from food (substrate)

The energy released is used to carry out all metabolic activities in living organisms

Respiration involves several steps controlled by enzymes

There are TWO main types of respiration:AEROBIC

ANAEROBIC

AEROBIC Respiration

Glucose is oxidized in many small steps to form carbon dioxide, water and energy.

The important energy releasing steps take place in the mitochondria

The energy is stored temporarily in ATP molecules

The energy is readily available for use when required in this form

AEROBIC Respiration Equation

The overall equation can be summarized as follows:

C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy

glucose + oxygen carbon + water + ATP

dioxide

AEROBIC Respiration

Summary:Glucose (or fat) is used as a substrate to provide energy

Energy is released in slow, controlled process

The energy released is temporarily stored in ATP

Oxygen is used in the process

Carbon dioxide and water are released

ANAEROBIC RespirationThe food (sugar) is only partly oxidized producing a little energy

In animals that respire anaerobically the sugar is broken down to form LACTIC ACID and energy

No CO2 is given off

In plants and yeast (a fungus) the sugar is converted into ETHANOL (alcohol), carbon dioxide and energy.

There are microscopic organisms that are AnaerobesThey can live without oxygen

Larger organisms can survive for short periods without oxygen

ANAEROBIC Respiration

During strenuous exercise, mammalian muscle cells can respire anaerobically for a short time

Lactic acid accumulates in the cells causing fatigue

Lactic acid is toxic in large quantities and must be broken down before the cells can function normally again

ANAEROBIC Respiration

The temporary shortage of oxygen results in an OXYGEN DEBT

Extra oxygen is required to break down the lactic acid to carbon dioxide and water.

Heavy breathing which continues after vigorous exercise is necessary to pay back the oxygen debt

ANAEROBIC Respiration Equation

The overall equation can be summarized as follows:

Plants and yeasts

carbon dioxide + ethyl alcohol + energy (ATP)

glucose

lactic acid + energy (ATP)

Animals

ANAEROBIC Respiration

Summary:

The events taking place in anaerobic respiration are the same as the first steps in aerobic respiration. During anaerobic respiration:

No oxygen is used

Little energy is produced

Alcohol and carbon dioxide are produced by plants and yeast

Only lactic acid is produced by animals

ATP

The adenosine triphosphate (ATP) molecule has three phosphate groups.

The 3rd phosphate in adenosine triphosphate (ATP) is easily removed to form adenosine diphosphate (ADP).

Energy is released during that reaction

The ATP molecule stores energy temporarily and transfers it to the other reactions when necessary

Energy Transfer Equation

ATP ADP + P + Energy

The ADP formed by that reaction is used to make more ATP

ADP + P + energy from respirationATP

The table below shows the amounts of lactic acid in the blood of a man who exercised vigorously for ten minutes.

Lactic Acid Concentration in the Blood of an Exercising Man

Time/minutes Lactic acid conc./mg per 100 cm3

0 20

10 80

14 97

19 90

30 70

57 40

(a) Draw a graph to show how the lactic acid concentration changed. 7

(b) By how much did the lactic acid increase during the period of exercise? 1

(c) How do you account for the rise in lactic acid concentration during the first ten minutes after the start of the exercise? 3

(d) Suggest why it continued to rise for a short time after the exercise ended. 2

(e) State TWO factors that should be kept constant if this method is to be used to compare results from several different persons. 2

15 marks