Respiration

= the process by which chemical energy is released from a foodstuff by oxidation.

Oxygen + glucose water + carbon dioxide + energy

C6H12O6 + 6O2 -----> 6CO2 + 6H20 + energy (heat and ATP)

Chemistry of Respiration

We can split the process of respiration into 3 distinct stages, each occurring in a specific part of the cell.

Glycolysis - cytoplasm of cell

Kreb’s cycle - central matrix of mitochondrion

Cytochrome system - cristae of mitochondrion

Glycolysis

Glycolysis = ‘glucose splitting’

• 2 molecules of ATP are required to trigger glycolysis.

• 4 molecules of ATP are formed during the process, giving a net gain of 2 ATP.

• During glycolysis released hydrogen becomes temporarily bound to a hydrogen carrier (NAD NADH2).

• Oxygen is not required for glycolysis.

Kreb’s cycle

Kreb’s cycle (= Citric acid or Tricarboxylic acid cycle)

• During this aerobic stage of respiration, citric acid is broken down to 5 and 4 carbon intermediates.

• At each step hydrogen is released and binds to NAD.

• At the first two steps carbon is released to form CO2.

• The enzymes controlling carbon release are termed decarboxylases.

• Enzymes controlling the release of hydrogen are called dehydrogenases.

Cytochrome system / Hydrogen Transfer system

Cytochrome System

• During glycolysis and the Kreb’s cycle, there are 6 points where hydrogen is released to bind with NAD.

• The cytochrome system is a chain of hydrogen carriers that releases energy when hydrogen passes along it.

• Each hydrogen passing along the chain releases sufficient energy for the formation of 3 ATP.

• The complete oxidation of one glucose molecule generates 38 ATP.

Multiple choice test

Cell variety in relation to function Absorption and secretion of materials,

ATP and energy release.

1. Which of the following statements about a cell wall is true?

A It is living.B It is composed mainly of cellulose.C It is composed mainly of protein.D It is selectively permeable.

2. Which of the following processes requires infolding of the cell membrane?

A DiffusionB PhagocytosisC Active transportD Osmosis

3. Human red blood cells contain potassium ions at a concentration about 30 times greater than the concentration of potassium ions in the blood plasma. If red blood cells are cooled, potassium ions are lost to the surrounding plasma.If the cells are warmed again to body temperature, they regain their original concentration of potassium ions.These movements of potassium ions are explained by

Outward movement Inward movement

A Diffusion Active transport

B Diffusion Osmosis

C Active transport Diffusion

D Osmosis Active transport

4. The table below shows the concentration of three ions found in sea water and in the sap of cells of a seaweed.

Which of the following statements is supported by the data in the table?

A Potassium and sodium ions are taken into the cells by active transport.

B Potassium and chloride ions are removed from the cell by diffusion.C Sodium ions are removed from the cell by active transport.D Chloride and sodium ions are removed from the cell by diffusion.

Potassium Sodium Chloride

Sea water 0.01 0.55 0.61

Cell sap 0.57 0.04 0.60

Ion concentrations (mg l )-1

5. A piece of muscle was cut into three strips, X, Y and Z, and treated as described in the table.Their final lengths were then measured.

Muscle strip

Solution added to muscle

Muscle length at start (mm)

Muscle length after 10 minutes (mm)

X 1% glucose 50 50

Y 1% ATP 50 45

Z 1% ATP boiled & cooled

50 46

From the data it may be deduced that

A ATP is not an enzymeB muscles contain many mitochondriaC muscles synthesise ATP in the absence of glucoseD muscles do not use glucose as a source of energy

6. When a red blood cell is immersed in a hypertonic solution it will

A shrinkB become flaccidC burstD become turgid

7. Which of the following is a structural carbohydrate?

A GlucoseB StarchC GlycogenD Cellulose

8. Which two substances are found to occur in cell membranes?

A Cellulose and proteinB Protein and phospholipidC Phospholipid and carbohydrateD Protein and carbohydrate

9. Which of the following statements is false?

A Phagocytosis and pinocytosis are examples of exocytosisB Endocytosis involves the cell membrane folding inwards to form

a pouchC A cell may aquire hormones by pinocytosis D Molecules of carbon dioxide move out of a respiring cell by

diffusion

10. What compound is represented by the letters ATP?

A Adenine triphosphateB Adenine trinucleotide phosphateC Adenosine tricarboxylic phosphateD Adenosine triphosphate

Chemistry of Respiration

Anaerobic respiration

• In the absence of oxygen the Kreb’s cycle and the cytochrome system are unable to occur.

• In this process, little energy is released from the partial breakdown of sugar.

• An alternative metabolic pathway takes place in the cell’s cytoplasm. This pathway varies depending on the type of organism involved.