F214: Photosynthesis Flashcards
What are heterotrophs?
Organisms that ingest and digest complex organic molecules, releasing the chemical potential energy stored in them.
What are autotrophs?
Organisms that use light energy or chemical energy and CO2/H2O to synthesise complex organic molecules.
What are photo autotrophs?
Organisms that make food using energy from sunlight.
What is the equation for photosynthesis?
6CO2 + 6H2O + light —> C6H12O6 + 6O2
Where does photosynthesis take place?
Chloriplasts.
What are photosynthetic pigments?
Molecules that absorb light energy. Each pigment absorbs a range of wavelengths in the visible region and has it’s own distinct peak of absorption.
Other wavelengths are reflected.
Describe the structure of chloroplasts.
Disc shaped an between 2-10 nm long.
Surrounded by a double membrane (envelope).
Intermembrane space about 10-20 nm wide between the inner and outer membrane.
Outer membrane permeable to small ions.
Inner membrane is less permeable and has transport proteins embedded in it.
Inner folded into lamellae which are stacked.
Each stack is called a granum.
Between the grana are inter grana lamellae.
How long is a nanometre?
One millionth of a millimetre.
What are the regions inside the chloroplast?
Stroma: fluid filled matrix.
Light independent stage occurs here as it has the correct enzymes.
Grana: stacks of flattened thylakoids.
Sites of light absorption and ATP synthesis during the light dependent stage of photosynthesis.
How are chloroplasts adapted for their role?
Inner membrane has transport proteins that control the entry/exit of substances between the cytoplasm and the Stroma.
Grana provide a large surface area for the photosynthetic pigments, electron carriers and ATP synthase enzymes in the light dependent reaction.
Photosynthetic pigments are arranged into photo systems, which allow maximum absorption of light energy.
Proteins in the grana hold the photo systems in place.
Fluid filled Stroma contain the enzymes needed for the light independent stage.
Grana are surrounded by the Stroma so the products of the LDR can pass easily into the Stroma to be used in the LIR.
Describe the general structure of chlorophyll.
A long hydrocarbon chain and a porphyrin group.
Porphyrin is similar to haem, but has magnesium atom not iron.
Both appear yellow green and absorb red at slightly different wavelengths (absorption peak).
Both types are found at the centre of photo systems and are known as the primary pigment reaction centre.
Describe the two forms of chlorophyll.
a - P680 is found in photosystem II.
Peak of absorption at a wavelength of 680nm.
Absorbs blue light at 450nm.
b - P700 is found on photosystem I.
Peak of absorption at 700nm.
Absorbs light at wavelengths between 500-640nm and appears blue green.
What are accessory pigments?
Carotenoids reflect yellow and orange light and absorb blue light.
They do not contain a porphyrin group and are not directly involved in the LDR.
The main carotenoid pigments are:
Carotene - orange.
Xanthophyll - yellow.
What is photophosphorylation?
The making of ATP from ADP and an inorganic phosphate in the presence of light.
What are electron carriers?
Molecules that transfer electrons.
Proteins that contain iron atoms.
What are electron acceptors?
Chemicals that accept electrons from another compound.
They are reduced while acting as oxidising agents.
Where are the photosystems embedded?
PSI is embedded mainly on the intergranal lamellae.
PSII is almost exclusively on the granal lamellae.
They trap light energy to be converted to chemical energy in the form of ATP.
What is photolysis?
Splitting of water in photosystem II, requires light.
2H2O –> 4H+ + 4e- + O2
Some of this O2 is used for aerobic respiration but most diffuses through the stomata into the air.
