2: Photosynthesis

Question 1

Define ‘photosynthesis’.

Answer 1

the production of carbon compounds in cells using light energy

Question 2

State the substrates for photosynthesis.

Answer 2

simple inorganic substances:

• carbon dioxide
• water

Question 3

Give synthesis of glucose through photosynthesis equation.

Answer 3

CO2 + H2O + light energy –> glucose + oxygen

Question 4

Name some organisms who produce their carbon compounds by photosynthesis.

Answer 4

plants, algae, some bacteria

Question 5

State the stages of photosynthesis.

Answer 5

1. carbon dioxide converted into carbohydrates and other carbon compounds. high energy electrons needed for this.
2. electrons obtained by photolysis, which is splitting of water molecules. oxygen is a waste product from the photolysis of water. energy is needed for this.
3. energy obtained in form of light. light is absorbed by photosynthetic pigments.

Question 6

Name a waste product of photosynthesis.

Answer 6

oxygen

Question 7

How is oxygen produced in photosynthesis?

Answer 7

oxygen produced as waste product when water is split by photolysis

Question 8

What were the first organisms to release oxygen into the atmosphere? When?

Answer 8

bacteria, about 3.5 billion years ago

Question 9

What happened to atmospheric oxygen levels 2.4-2.2 billion years ago? What caused this event? What was the effect of this?

Answer 9

• rose from very low concentration to 2%
• due to photosynthesis in bacteria
• rise caused dissolved iron in oceans to precipitate as iron oxide, where it sank to the ocean bed, forming deposits of rock called banded iron formations

Question 10

What happened to atmospheric oxygen levels 750 million years ago? What caused this event?

Answer 10

• oxygen levels rose from 2% to 30%, before dropping back down to todays level of 20%
• probably due to evolution of multicellular algae and land plants, which raised global photosynthesis rates

Question 11

What is a spectrum?

Answer 11

the range of wavelengths of electromagnetic radiation

Question 12

What is the spectrum of visible light?

Answer 12

range of wavelengths from 400nm to 700nm that are used in human vision

Question 13

What is colour has the shortest wavelength? What has the longest?

Answer 13

• shortest = violet

- longest = red

Question 14

What spectrum - range of wavelengths of electromagnetic radiation - are is used in photosynthesis? Why?

Answer 14

• same as visible light (400nm-700nm)

- because photosynthetic pigments do not absorb other wavelengths

Question 15

What does the ‘absorption spectrum’ graph show?

Answer 15

the range of wavelengths absorbed by a pigment

Question 16

Draw the absorption spectrum. (p34)

Answer 16

it’s a gaph:

• chlorophyll a
• chlorophyll b

Question 17

What is the main photosynthetic pigment?

Answer 17

chlorphyll

Question 18

What does the absorption spectrum show?

Answer 18

• that chlorophyll absorbs red and blue light most effectively
• small amounts of green light are absorbed but most is reflected, making structures containing chlorophyll appear green to us

Question 19

Comment on the efficiency of photosynthesis for different wavelengths of light.

Answer 19

• efficiency here = percentage of light of a wavelength that is used in photosynthesis
• not the same in all wavelengths
• maximum photosynthesis rates are in blue light, and (slightly less efficient) in red light. green light is used less efficiently

Question 20

Name the graph showing the efficiency of photosynthesis for different wavelengths of light.

Answer 20

action spectrum of photosynthesis

Question 21

Draw the action spectrum of photosynthesis. (p.34)

Answer 21

2 peaks:

• first at 450
• second at 670

Question 22

Why does the action spectrum show some use of green light in photosynthesis, even though chlorophyll absorbs little of it?

Answer 22

accessory photosynthetic pigments are present, which absorb some green light that can be used in photosynthesis