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Flashcards in 2: Photosynthesis Deck (22):

Define 'photosynthesis'.

the production of carbon compounds in cells using light energy


State the substrates for photosynthesis.

simple inorganic substances:
- carbon dioxide
- water


Give synthesis of glucose through photosynthesis equation.

CO2 + H2O + light energy --> glucose + oxygen


Name some organisms who produce their carbon compounds by photosynthesis.

plants, algae, some bacteria


State the stages of photosynthesis.

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.


Name a waste product of photosynthesis.



How is oxygen produced in photosynthesis?

oxygen produced as waste product when water is split by photolysis


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

bacteria, about 3.5 billion years ago


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

- 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


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

- 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


What is a spectrum?

the range of wavelengths of electromagnetic radiation


What is the spectrum of visible light?

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


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

- shortest = violet
- longest = red


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

- same as visible light (400nm-700nm)
- because photosynthetic pigments do not absorb other wavelengths


What does the 'absorption spectrum' graph show?

the range of wavelengths absorbed by a pigment


Draw the absorption spectrum. (p34)

it's a gaph:
- chlorophyll a
- chlorophyll b


What is the main photosynthetic pigment?



What does the absorption spectrum show?

- 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


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

- 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


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

action spectrum of photosynthesis


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

2 peaks:
- first at 450
- second at 670


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

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

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