13. Photosynthesis Flashcards
What is the reaction for photosynthesis?
Carbon dioxide + water ———> carbohydrate + oxygen
Describe the process of the light-dependent stage of photosynthesis.
Pigments including chlorophyll absorb energy from light and some of this energy is used to split water molecules into hydrogen and oxygen, this is called photolysis. The energy in the hydrogen is used to make ATP in a process called photophosphorylation. The hydrogen is picked up by a coenzyme called NADP to make reduced NADP
Describe the process of the light-independent stage of photosynthesis
The energy in the ATP and energy AND hydrogens in the reduced NADP are used to reduce carbon dioxide and produce carbohydrates- this stage is known as the Calvin cycle
What are the pigments that are found in a chloroplast?
Chlorophyll a and chlorophyll b
What is a photosystem?
Pigments in a thylakoid membrane are arranged in clusters called photosystems
What are the two types of photosystem and what are their wavelengths?
Photosystem I - wavelength of 700nm
Photosystem II- wavelength of 680nm
What is the difference between an absorption spectrum and an action spectrum?
An absorption spectrum is a graph showing the absorbance of different wavelengths of light by a photosynthetic pigment
An action spectrum is a graph showing the effect of different wavelengths of light on a process
What are the differences and similarities of cyclic photophosphorylation and non-cyclic photophosphorylation?
Cyclic- involves photosystem I whilst non-cyclic involves both photosystem I and II
Non-cyclic also produces reduced NADP
Cyclic and non-cyclic both produce ATP using energy from light
Describe the process of cyclic photophosphorylation
Light energy is absorbed by photosystem I and is passed to the reaction centre . This energy excites an electron in the chlorophyll a molecule to a higher energy level. The excited electrons are captured by an electron acceptor in a thylakoid membrane and passed along a chain of electron carriers. The carriers are alternatively reduced and oxidized. The electrons lose energy as they pass along the chain and this energy is used to actively move protons from the stroma across the thylakoid membrane into the thylakoid space and this sets up a gradient for protons which then move down their concentration gradient by facilitated diffusion through ATP synthase molecules.
Describe the process of non-cyclic photophosphorylation
Energy from light is absorbed by both photosystems. Energy from the electron emitted from photosystem II is used to form ATP but the energy from the electron emitted from photosystem I is passed to the coenzyme NADP. This produces reduced NADP.
What is the name of the water splitting enzyme found in photosystem II?
Oxygen-evolving complex / water-splitting complex
Explain what photolysis of water is.
It splits a water molecule into hydrogen ions, electrons and oxygen.
Explain what happens to the products of the photolysis of water process.
Oxygen is a waste product, diffuses out of the chloroplast
Hydrogen ions combine with electrons from photosystem I and the coenzyme NADP to give reduced NADP.
The ATP and reduced NADP that are synthesized in these light dependent reactions can now be used in the light independent reactions.
Describe the steps in the light-independent stage of photosynthesis.
Called the Calvin cycle.
- Carbon dioxide reacts with ribulose bisphosphate- a 5C compound catalyzed by the enzyme rubisco.
= produces two molecules of a 3C compound called glycerate-3-phosphate (GP) - Energy from ATP and hydrogen from reduced NADP are used to reduce the GP to a phosphorylated three carbon sugar - triose phosphate (TP)
Name the 5 different factors that plants need for photosynthesis to occur.
- the presence of photosynthetic pigments
- a supply of carbon dioxide
- a supply of water
- light energy
- a suitable temperature
