B9

Question 1

What is the word and symbol equation for aerobic respiration ?

Answer 1

oxygen + glucose -> carbon dioxide + water

6O(2) + C(6)H(12)O(6) -> 6CO(2) + 6H(2)O

Question 2

Is respiration an endothermic or exothermic reaction, and why is this useful to the organism ?

Answer 2

• exothermic reaction
• release of energy = energy for biological processes like chemical reactions, synthesis, movement and contraction of muscles etc.
  [] active transport in plants especially
• release of heat = a good way for organisms to control their body temperature
  [] useful in temperate climates where temperatures differ drastically across the year, as well as useful for consistent enzyme function

Question 3

Where does aerobic respiration take place in the cell and what adaptations make this place efficient ?

Answer 3

• mitochondria
• have large surface area via folded inner membrane, speeding up the reaction

Question 4

Describe the body’s main responses to exercise and why these responses occur

Answer 4

• breathing rate and depth increases
  [] ensures greater supply of oxygen to muscles
  [] waste carbon dioxide from increased respiratory levels during exercise can be removed more quickly, preventing damage to tissues caused by its toxicity
  [] continue breathing hard after exercise to pay off any “oxygen debts” caused by anaerobic respiration in the muscles, which occurs to fill in any gaps in energy that aerobic respiration cannot fill
• heart rate increases, and blood vessels dilate
  [] increases flow of oxygenated blood to muscles
  [] increases rate of supply of oxygen and glucose to muscles for respiration and continued contractions
  [] increases the rate at which carbon dioxide is removed from muscles
• glycogen stores in muscles are converted back into glucose for use in respiration

Question 5

What is the word equation and symbol equation for anaerobic respiration in animals ?

Answer 5

glucose -> lactic acid

C(6)H(12)O(6) -> 2C(3)H(6)O(3)

Question 6

Why don’t animals respire anaerobically ?

Answer 6

• anaerobic respiration produces lactic acid as an end product
  [] breakdown of glucose is incomplete, and so less energy is transferred (less efficient than aerobic respiration)
  [] lactic acid is poisonous to body cells, and must be removed quickly in the presence of oxygen to prevent damage being done to the muscles

Question 7

Why is build-up of lactic acid in muscles when exercising quicker for unfit people than fit people ?

Answer 7

unfit people’s hearts and lungs are less used to the exercise and thus less fit and less efficient at sufficiently supplying the muscles with oxygen and glucose quickly, so anaerobic respiration has to occur to provide energy for muscle contractions instead

Question 8

What is oxygen debt and how is it “paid off” ?

Answer 8

• lactic acid builds up in the muscles after a period of exercise, causing muscle fatigue
• lactic acid has to be converted back into glucose and then broken down into carbon dioxide and water in the liver, and this process requires oxygen
• the amount of oxygen needed to convert the lactic acid built up is the “oxygen debt”, and the animal breathes hard even after exercise to supply oxygen-rich blood to the liver, where oxygen diffuses into liver cells and the conversion can thus take place

lactic acid + oxygen -> water + carbon dioxide

Question 9

What is anaerobic respiration in plants and yeast called, where is it used and what is the word equation ?

Answer 9

• fermentation
• used in making leavened bread, alcoholic drinks etc.

glucose -> ethanol + carbon dioxide

Question 10

List the key metabolic reactions

Answer 10

• conversion of glucose to starch, cellulose and glycogen
• formation of lipid molecules
• protein synthesis
• amino acid synthesis
• respiration
• photosynthesis
• deamination of excess amino acids (broken down proteins)

Question 11

Give 3 of the main metabolic processes carried out by the liver

Answer 11

• detoxifying poisonous substances such as ethanol from alcoholic drinks, lactic acid and amino acids from extra protein
• passing breakdown products of toxic substances into blood to be excreted in urine via the kidneys
• breaking down old red blood cells and storing the iron in them for the synthesis of new red blood cells

Question 12

Describe how the liver detoxifies and breaks down lactic acid into non-toxic/less toxic molecules like water and carbon dioxide (or just glucose if the body needs more of it)

Answer 12

• blood flows through the muscles and picks up lactic acid via diffusion into the bloodstream
• transports the lactic acid back to the liver
  [] converted back into glucose, and then either broken down into carbon dioxide and water or stored as glycogen in the liver

Question 13

In the liver, describe the roles of the hepatic vein, the hepatic portal vein and the hepatic artery

Answer 13

• artery
  [] supplies liver with oxygenated blood and nutrients so it can respire and carry out metabolic reactions
• portal vein
  [] carries blood from small intestine and other organs with nutrients or toxic substances into the liver to be processed
• vein
  [] carries blood out of the liver with substances detoxified and removed from the blood, and levels of food adjusted

Question 14

What is metabolism ?

Answer 14

The sum of all chemical reactions taking place in an organism