Respiration (Biology)

Definition of respiration:

The breakdown of glucose through oxidation in living cells, with the release of energy

How does respiration contribute to body warmth?

Some energy is released as heat during respiration, which is then circulated around the body for warmth.

When does the rate of respiration exceed the rate of photosyntesis? (In plants)

When the plant is in the dark

There will be net removal of oxygen and net gain in amount of carbon dioxide produced in plants during the day (True/False)

False. This only takes place during the day, when only respiration occurs, and the rate of sugar breakdown during respiration is more than rate of sugar formed during photosynthesis

What is the compensation point for a plant?

The specific light intensity at which the rate of photosynthesis in a plant exactly matches the rate of respiration

What happens at the compensation point of a plant? (2)

• The rate of sugar breakdown due to respiration equals the rate of sugar formation due to photosynthesis

• the net uptake or loss of carbon dioxide or oxygen is zero

There is no net uptake or loss of carbon dioxide or oxygen at a plant’s compensation point (True/False)

True

Points to consider when involving the rate of photosynthesis and respiration in plants:

Rate of sugar breakdown or formation & net gain or loss of oxygen and carbon dioxide

What happens beyond a plant’s compensation point? (2)

• rate of sugar formation due to photosynthesis exceeds the rate of sugar breakdown due to respiration

• there will be a net removal of carbon dioxide and net gain in amount of oxygen produced

The two types of respiration:

Aerobic & Anaerobic

Equations for aerobic respiration (2):

Glucose + Oxygen ➔ Carbon dioxide + Water + Energy (ATP)

• C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP (Energy)

A large amount of (AT) energy is released (38 ATP/glucose molecule)

Equations of anaerobic respiration (4):

In animals (muscle contraction),

Glucose ➔ Lactic acid + Energy (ATP)

• C₆H₁₂O₆ ➔ 2C₃H₆O₃ + ATP (Energy)

In plants & yeast (fermentation),

Glucose ➔ Ethanol + Carbon dioxide +Energy (ATP

• C₆H₁₂O₆ ➔ 2C₂H₅OH + 2CO₂ + ATP (Energy)

A small amount of energy is released (2 ATP/glucose molecule)

Equations for photosynthesis (2):

Carbon Dioxide + Water + Light ➔ Glucose + Oxygen

• 6CO₂ + 6H₂O ➔ (Light energy) C₆H₁₂O₆ + 6O₂

Aerobic Respiration definition:

The breakdown of glucose in the presence of oxygen with release of a large amount of energy. Carbon dioxide and water are released as waste products

Anaerobic Respiration definition:

The breakdown of glucose in the absence of oxygen with release of a small amount of energy

Skeletal muscles can respire both aerobically and anaerobically (True/False)

True. All muscles do

When do muscle cells first respire aerobically?

During vigorous muscular contractions

What happens when muscle cells respire aerobically? (2)

Muscles start to vigorously contract, and the rate of breathing and heartbeats increases to take in and transport more oxygen around the body.

Why would muscles cells start to carry out anaerobic respiration?

When

• the demand for the need to release energy even after aerobic respiration surpasses the limit in the rate of breathing and heartbeats

Skeletal muscles can only respire either aerobically or anaerobically, at any given time (True/False)

False. all muscles generally use a combination of both processes simultaneously, including skeletal muscles

Oxygen debt definition:

The amount of oxygen needed to break down all the lactic acid accumulated in the muscles during anaerobic respiration

Why would muscles incur oxygen debts?

Sometimes, there is insufficient oxygen produced to meet the demands of muscular contractions

What is lactic acid?

A toxic waste product resulting from the incomplete breakdown of glucose during anaerobic respiration in animal cells

How does lactic acid cause fatigue?

It can build up slowly in high concentrations in muscles

How are oxygen debts repaid in the body?

• Rates of breathing are high enough

• to provide enough oxygen to the liver,

• where of the lactic acid removed from the muscles

• some are oxidised into water, carbon dioxide and energy

• the energy is used to convert the remaining lactic acid into glucose (which will be transported back to the muscle cells and stored as glycogen)

The oxygen debt is repaid when all of the lactic acid is used up or stored

Outline the experimental set-up that shows that carbon dioxide is released during aerobic respiration:

1. Connect four flasks A, B, C & D in order, with delivery tubes in bungs

2. Place equal volumes of potassium hydroxide, limewater, and limewater in flasks, A, B & D respectively

3. Place the organism for investigation in flask C

4. Attach a suction pump to the last delivery tube at flask D

Result: After some time, the limewater in flask D becomes cloudy, indicating that carbon dioxide has been released by the organism respiring in flask C

Purpose of the apparatus used:

Potassium hydroxide — to absorb carbon dioxide in the air

Limewater — to test for the presence of carbon dioxide by turning milky in its presence; it ensures that no carbon dioxide has entered the set-up at flask B, and shows that the organism in flask C produces carbon dioxide in respiration

Suction pump — to suck air out of the initial set-up, in order to draw air into flask A

If plants are used in place of animals, flask C has to be covered with aluminium foil or the set-up has to be placed in the dark. This is so that the plants would not be carrying out photosynthesis and using up the carbon dioxide produced at the same time

Outline the experimental set-up that shows that heat is released during respiration: