Chapter 9: Respiration

Question 1

Aerobic respiration

Answer 1

• Cellular respiration is an exothermic reaction that occurs continuously in living cells

  o	Aerobic respiration is glucose + oxygen --> co2 + water (+ energy)

  o	The energy transferred supplies all the energy needed for living processes like:

Basic functions of cells
Making muscles contract (in animals)

Maintaining a constant inner body temp (mammals and birds)

Move mineral ions from the soil to the root cells (in plants)

Question 2

The response to exercise

Answer 2

• The energy that is transferred during respiration is used to enable muscles to contract
• During exercise the human body responds to the increased demand for energy
• Body responses to exercise include:

  o	An increase in heart rate, in the breathing rate and in the breath volume
  
  o	Glycogen stores in the muscles are converted to glucose for cellular respiration 
  
  o	The flow of oxygenated blood to the muscles increases

• These responses act to increase the rate of supply of glucose and oxygen to the muscles and the rate of removal of carbon dioxide from the muscles

Question 3

Anaerobic respiration

Answer 3

• If muscles work hard for a long time, they become fatigued and don’t contract efficiently. If they don’t get enough oxygen, they will respire anaerobically
• Anaerobic respiration is respiration without oxygen. When this takes place in animal cells glucose is incompletely broken down to form lactic acid
• The anaerobic breakdown of glucose transfers less energy than aerobic respiration
• After exercise, oxygen is still needed to break down the lactic acid that is built up. The amount of oxygen needed is known as the oxygen debt
• Anaerobic respiration in plant cells and some microorganisms, such as yeast, results in the production of ethanol and carbon dioxide
• Oxygen debt: the length of time you are panting after exercise depends on how fit you are. The waste lactic acid you produce you produce during anaerobic respiration is a problem. You cannot simply get rid of it by breathing it out like you can with co2. As a result, after exercise, lactic acid must be broken down into co2 and water. This needs oxygen. The amount of oxygen needed to break it down is the oxygen debt. After a race, your heart rate and breathing rate stay high to supply the extra oxygen needed to pay off the oxygen. The bigger the debt, the longer you will pant.

Question 4

Metabolism and the liver

Answer 4

• Metabolism is the sum of all the reactions in the body
• The energy transferred by respiration in cells is used by the organism for the continual enzyme-controlled process of metabolism that synthesise new molecules
• Metabolism includes the conversion of glucose to starch, glycogen and cellulose. Metabolism also includes the formation of lipid molecules, and the use of glucose and nitrate ions to synthesise proteins, and breakdown excess proteins to form urea
• Blood flowing through the muscles transports lactic acid to the liver where it is converted back to glucose
• The role of the liver:

  o	detoxifying poisonous substances such as ethanol from alcoholic drinks
  
  o	passing the breakdown products into the blood so they can be excreted in the urine via the kidneys
  
  o	breaking down old blood cells and storing the iron until it is needed to synthesise new blood cells