(Paper 1) 4.2 Bioenergetics: Respiration

Question 1

What is respiration?

Answer 1

An exothermic process that releases energy in cells.

Question 2

Is respiration the same as breathing?

Answer 2

No – breathing is ventilation, while respiration happens in cells.

Question 3

How is respiration different from photosynthesis?

Answer 3

Respiration releases energy (exothermic)

Photosynthesis requires energy (endothermic)

Question 4

What are five uses of energy released by respiration?

Answer 4

Driving chemical reactions (e.g. protein synthesis)

Muscle contraction and transport in plants

Active transport

Cell division

nerve transmission

Question 5

How do birds and mammals use the heat from respiration?

Answer 5

To maintain body temperature (homeostasis).

Question 6

What is the efficiency of respiration in terms of energy use?

Answer 6

About 40% efficient – the rest is released as heat.

Question 7

What is homeostasis and how is energy used for it?

Answer 7

Maintaining stable internal conditions; energy is needed to regulate temperature, water levels, etc.

Question 8

What is aerobic respiration?

Answer 8

Respiration with oxygen, where glucose is oxidised to release energy.

Question 9

What is the word equation for aerobic respiration?

Answer 9

Glucose + oxygen → carbon dioxide + water + energy released

Question 10

What is the symbol equation for aerobic respiration?

Answer 10

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP (energy released)

Question 11

Where does aerobic respiration mainly occur?

Answer 11

In the mitochondria (after initial stages in the cytoplasm).

Question 12

What is anaerobic respiration?

Answer 12

Respiration without oxygen, used when oxygen is in short supply.

Question 13

What is the word equation for anaerobic respiration in human muscles?

Answer 13

Glucose → lactic acid + energy released

Question 14

Why is anaerobic respiration used in muscles?

Answer 14

To release quick energy during exercise or emergencies when oxygen is limited.

Question 15

What is the word equation for anaerobic respiration in yeast?

Answer 15

Glucose → ethanol + carbon dioxide + energy released

Question 16

What is anaerobic respiration in yeast used for commercially?

Answer 16

In brewing (ethanol) and baking (CO₂) industries.

Question 17

Where does anaerobic respiration occur in cells?

Answer 17

Only in the cytoplasm.

Question 18

Which process releases more energy: aerobic or anaerobic respiration?

Answer 18

Aerobic respiration – much more efficient.

Question 19

Why does anaerobic respiration release less energy?

Answer 19

Because glucose is not fully broken down, so some energy remains in products.

Question 20

What are the products of anaerobic respiration in yeast and some plants?

Answer 20

Ethanol and carbon dioxide.

Question 21

What are the products of anaerobic respiration in yeast?

Answer 21

Ethanol, carbon dioxide, and energy.

Question 22

What is the word equation for anaerobic respiration in yeast?

Answer 22

Glucose → ethanol + carbon dioxide + energy released

Question 23

What is yeast used for in food and drink industries?

Answer 23

Brewing (alcohol production)

Baking (CO₂ makes bread rise)

Question 24

Why does bread rise when yeast is used?

Answer 24

Carbon dioxide bubbles from anaerobic respiration expand the dough.

Question 25

What happens to the ethanol produced during bread making?

Answer 25

It evaporates during baking.

Question 26

In what conditions might plant cells respire anaerobically?

Answer 26

In low-oxygen environments, such as marshy soils.

Question 27

Do plants produce the same products as yeast during anaerobic respiration?

Answer 27

Yes – they can produce ethanol and carbon dioxide.

Question 28

Why do muscles need energy during exercise?

Answer 28

To allow muscle contraction.

Question 29

What three body responses increase during exercise?

Answer 29

Breathing rate Breath volume Heart rate

Question 30

Why do breathing and heart rate increase during exercise?

Answer 30

To supply more oxygen and remove more carbon dioxide from muscles.

Question 31

What happens if oxygen supply to muscles is insufficient?

Answer 31

Muscles respire anaerobically, producing lactic acid.

Question 32

What are the products of anaerobic respiration in muscles?

Answer 32

Lactic acid and energy (no CO₂ or H₂O).

Question 33

How does anaerobic respiration affect muscle efficiency?

Answer 33

Muscles can continue contracting, but less efficiently.

Question 34

What is an oxygen debt?

Answer 34

The extra oxygen needed after exercise to remove lactic acid and repay the body.

Question 35

What happens to glycogen stores during long periods of exercise?

Answer 35

They become low, and extra glucose is sent from the liver.

Question 36

What is muscle fatigue?

Answer 36

When muscles become tired and stop contracting efficiently due to low glycogen and lactic acid build-up.

Question 37

What is an oxygen debt?

Answer 37

The amount of oxygen required after exercise to remove lactic acid and restore oxygen levels in the body.

Question 38

Why do heart and breathing rates stay high after exercise?

Answer 38

To supply oxygen needed to repay the oxygen debt.

Question 39

How long can it take to repay an oxygen debt?

Answer 39

From a few hours (normal activity) to several days (e.g. marathon).

Question 40

What happens to lactic acid after exercise?

Answer 40

It is carried in the blood to the liver.

Question 41

How does the liver deal with lactic acid?

Answer 41

It either: Oxidises it to carbon dioxide and water, or Converts it to glucose, then glycogen.

Question 42

What does the body restore after lactic acid is converted to glucose or oxidised?

Answer 42

Glycogen stores in the liver and muscles.

Question 43

Why does converting lactic acid require oxygen?

Answer 43

Because the processes are aerobic, needing oxygen to oxidise or convert the lactic acid.

Question 44

What is metabolism?

Answer 44

The sum of all chemical reactions in an organism’s body.

Question 45

What controls metabolic reactions?

Answer 45

Enzymes

Question 46

What are the two types of metabolic reactions?

Answer 46

Building up (synthesis) reactions Breaking down (catabolic) reactions

Question 47

What substances do plants build up using glucose from photosynthesis?

Answer 47

Starch (for storage) Cellulose (for cell walls) Amino acids (using nitrates) Lipids (for energy storage in seeds)

Question 48

What substances do plants break down during metabolism?

Answer 48

Stored starch to glucose Proteins to amino acids (when needed)

Question 49

What do animals build up from digestion products?

Answer 49

Glycogen (from glucose) Lipids (from fatty acids + glycerol) Proteins (from amino acids)

Question 50

What substances do animals break down for energy?

Answer 50

Glycogen (short-term energy) Lipids (longer-term energy) Proteins (during starvation)

Question 51

When are proteins broken down in animals?

Answer 51

During starvation, when no other energy source is available.