5.6.1: The interrelationship between photosynthesis and respiration

Question 1

What is photosynthesis?

Answer 1

An important physiological process used in plants, algae and some types of bacteria to convert light energy from sunlight into chemical energy.

Question 2

How is photosynthesis an example of autotrophic nutrition?

Answer 2

chemical energy is used to synthesise large organic molecules (building blocks of living cells) from simple inorganic molecules such as H2O and CO2.

Question 3

What are organisms that photosynthesise called?

Answer 3

Photoautotrophs because they use light as the energy source for autotrophic nutrition.

Question 4

Why are organisms that photosynthesise described as ‘producers’?

Answer 4

Because they are the first trophic level of a food chain and provide energy and organic molecules to other, non-photosynthetic, organisms.

Question 5

What is the general equation for photosynthesis?

Answer 5

6CO2 + 6H2O → C6H12O6 + 6O2

Question 6

What is a photon?

Answer 6

a particle of light; each photon contains an amount (a quantum) of energy.

Question 7

What is the main product of photosynthesis?

Answer 7

A monosaccharide sugar which can be converted into disaccharides for transport and then starch for storage.

Question 8

photosynthesis is an example of carbon fixation, what is this?

Answer 8

• The process by which carbon dioxide is converted into sugars.
• The carbon for synthesising all types of organic molecules is provided by carbon fixation.

Question 9

What does carbon fixation need?

Answer 9

• Endothermic so needs energy.

- Electrons; the addition of electrons is reduction.

Question 10

What is the importance of carbon fixation?

Answer 10

Helps regulate CO2 concentration in atmosphere and

Question 11

What do plants do when they respire?

Answer 11

-Oxidise organic molecules previously synthesised by photosynthesis and stored releasing chemical energy.

Question 12

Why are non-photosynthetic organisms described as ‘heterotrophs’?

Answer 12

They obtain energy by digesting complex organic molecules of food to smaller molecules that they can use as respiratory substrates.
-They obtain energy from the products of digestion by respiration.

Question 13

The overall equation for respiration:

Answer 13

C6H12O6 + 6O2 → 6CO2 + 6H2O

Question 14

How is respiration exothermic?

Answer 14

-It releases chemical energy that can drive the organism’s metabolism.

Question 15

When do plants respire?

Answer 15

All the time

Question 16

When do plants photosynthesise?

Answer 16

During daylight

Question 17

Plants often compete for light, what does the light intensity have to be sufficient to allow?

Answer 17

A rate of photosynthesis that replenishes the carbohydrate stores used up by respiration.

Question 18

When is a plant at its compensation point?

Answer 18

When photosynthesis and respiration proceed at the same rate so there is no net gain or loss of carbohydrates.

Question 19

What is the time taken for a plant to reach its compensation point called?

Answer 19

-The compensation period.

Question 20

How are shade plants different to sun plants.

Answer 20

shade plants:
-Utilise light of lower intensity
-When exposed to light after bein in dark, they reach compensation point sooner.
-Shorter compensation periods.
Sun plants:
-Require higher light intensity to achieve their optimum rate of photosynthesis.