Chapter 7

Question 1

What is the main substrate in energy production and how is it obtained?

Answer 1

glucose, obtained through digestion of carbohydrates form the food eaten

Question 2

What is cellular respiration?

Answer 2

• oxidation process of organic molecules through several stages to release energy

Question 3

What are the 2 types of respiration?

Answer 3

• aerobic respiration (occurs in presence of oxygen)
• anaerobic respiration (occurs in the absence if oxygen)
• fermentation: alternative pathway to obtain energy besides cellular respiration (breakdown of glucose is incomplete in conditions of limited/without oxygen)

Question 4

What is aerobic respiration? (2)

Answer 4

• breakdown of glucose involving oxygen to produce chemical energy
• oxygen is used to oxidise glucose to produce CO2, water & energy

Question 5

What is the first process in aerobic respiration? (3)

Answer 5

• begins with glycolysis process (breakdown of glucose by enzymes)
• occurs in the cytoplasm
• 1 glucose molecule break down into 2 pyruvate

Question 6

What is the following process of aerobic respiration after glycolysis? (3)

Answer 6

• occurs in mitochondrion
• pyruvate oxidised through a series of reaction to produce CO2, water & energy
• large amount of energy used to produce adenosine triphosphate (ATP) molecules

Question 7

word equation for glycolysis and oxidation of pyruvate?

Answer 7

Glycolysis Oxidation of Pyruvate
Glucose → pyruvate → CO2 + water + energy
(occurs in cytoplasm) (occurs in mitochondrion)

Question 8

How does aerobic respiration occur? ()

Answer 8

• ATP molecules produced when a group of non-organic phosphate is added to adenosine diphosphate (ADP)

                      ADP + phosphate (use energy) → ATP

• ATP molecules have weak phosphate links.
• When the phosphate links on ATP molecules are broken, the energy
  released is supplied to cells to help us carry out our daily activities.

                      ATP (release energy) → ADP + phosphate

Question 9

Word equation for complete process of glucose oxidation.

Answer 9

Glucose + oxygen → Carbon dioxide + water + energy (2898 kJ)

Question 10

What is fermentation? (3)

Answer 10

• incomplete breakdown of glucose in conditions of limited oxygen or
  without oxygen.
• different from aerobic respiration in its metabolic pathway after the glycolysis stage.
• After glycolysis, the pyruvate produced will undergo either
  alcohol fermentation or lactic acid fermentation.

Question 11

What is alcohol fermentation?

Answer 11

The incomplete breakdown of glucose to ethanol, carbon dioxide and energy.
Glucose → Ethanol + carbon dioxide + energy (210 kJ)

Question 12

What are the 2 examples of alcohol fermentation? (5)

Answer 12

Yeast:
• Ethanol is used in the making of beer and wine.
• The released carbon dioxide makes bread dough rise.

Plants:
• Paddy plants that grow in waterlogged areas with less oxygen are able to carry out alcohol fermentation.
• Ethanol produced in the tissues during the fermentation process is toxic to most plants but the cells of paddy plants have a higher tolerance for ethanol compared to other species.
• Paddy plants produce plenty of alcohol dehydrogenase enzymes that can break down ethanol molecules into non-toxic carbon dioxide.

Question 13

What is lactic acid fermentation?

Answer 13

The breakdown of glucose into lactic acid and energy.

Glucose → Lactic acid + energy

Question 14

What are 2 examples of lactic acid fermentation? (lactobacillus-3)

Answer 14

Lactobacillus
• The bacteria Lactobacillus carries out milk fermentation to produce yoghurt.
• Lactobacillus acts on the lactose (milk sugar) and turns it into lactic acid.
• The lactic acid will then coagulate casein (milk protein) to produce yoghurt.
• Lactic acid is the source of a sour taste in yoghurt.

Question 15

What are 2 examples of lactic acid fermentation? (human muscle cells-7)

Answer 15

• This process is carried out by the muscle cells during vigorous training.
• During vigorous training, the rate of oxygen used exceeds the oxygen supplied by the blood circulatory system.
• The muscle is in an oxygen-deficiency state and is said to undergo oxygen debt.
• During this process, glucose cannot break down completely. For each glucose molecule that is broken down, only two ATP molecules/150 kJ energy will be produced.
• The produced lactic acid accumulates until it reaches a level of concentration that can cause fatigue and muscle cramps.
• Once the vigorous activity stops, the intake of excess oxygen will oxidise the lactic acid into carbon dioxide, water and energy.
- When all the lactic acid has been expelled, the oxygen debt is repaid.

Question 16

What are the similarities between aerobic respiration and fermentation? (5)

Answer 16

• The breakdown process of glucose and its conversion to chemical energy
• Produces chemical energy in the form of ATP
• The process begins with glycolysis when glucose is converted to pyruvate
• Occurs in yeast, bacteria, animals and plants
• The process begins in the cytoplasm

Question 17

What are the differences between aerobic respiration and fermentation? (5)

Answer 17

Aerobic Respiration(AR) Fermentation (F) *not actual abbreviations

AR: The breakdown process of glucose is completed in the presence of oxygen.
F: The breakdown process of glucose is incomplete without oxygen or in limited oxygen conditions.

AR: Occurs in cytoplasm and mitochondrion.
F: Occurs in cytoplasm.

AR: Produces water.
F: Does not produce water.

AR: Glucose is oxidised completely into carbon
dioxide and water.
F:Glucose is not oxidised completely into ethanol
and carbon dioxide or lactic acid.

AR: One molecule of glucose generates 2898 kJ of energy
F: One molecule of glucose generates 210 kJ (alcoholic fermentation) or 150 kJ (lactic acidfermentation) of energy