Photosynthesis Flashcards
What are autotrophic organisms
They make complex organic compounds from the simple compound in their environment
What is photosynthesis
The process by which living organisms, particularly plants, capture the energy of the sun using chlorophyll and use it to convert carbon dioxide and water into simple sugars
What is glucose used for in the plant?
Energy source by the cell of the plant, and as the building blocks of other important molecules such as proteins.
What are heterotrophic organisms
Obtain complex molecules by feeding on other living organisms or their dead remains
What is the ultimate energy source for almost all organisms
The sun
What is the equation for photosynthesis
Carbon dioxide + water —> glucose + oxygen
6CO2 + 6H20 —> C6H12O6 + 6O2
What is the light energy used for in photosynthesis
What is the waste product for photosynthesis
It is used to split the strong H-O bond in the water molecules
Oxygen
What are the main 2 steps in photosynthesis
light dependent reaction and light independent reactions
What is chlorophyll
Relatively large organelles found in the cells of the green part of plants
What is chloroplast surrounded by
An outer and an inner membrane with a space between two, known as the chloroplast envelope
What is inside the chloroplast
There is a system of membranes that are arranged in stacks called grana
What is a single granum made from
They are made up of stacks of membrane disks known as thylakoids
What is chlorophyll
A green pigment found in the chloroplast
Where is the chlorophyll found
In the thylakoid
What is the grana membrane covered in and how do we know
In particles that are involved in ATP synthesis
seen in electron micrographs
How are the grana joined together
by lamellae
What do the lamellae act as in plants
As a skeleton within the chloroplast so they get maximum light and function properly
What is a stroma and what does it contain
Surrounds membrane stacks by a matrix
It contains all the enzymes needed to complete photosynthesis
What are the 4 main chlorophyll pigments
chlorophyll a (blue-green) chlorophyll b (yellow-green) carotenoids (orange carotene and yellow xanthophyll) Phaeophytin (grey pigment)
which chlorophyll pigment is the most abundant
chlorophyll a
Where is chlorophyll a always found
In all photosynthesizing plants
What does the absorption spectrum describe
The range of the amount of light of different wavelengths that a photosynthetic pigment absorbs
represented as a graph
How is the absorption spectra of different photosynthetic pigments absorbed
Measuring their absorption of light of different wavelengths
What is an action spectrum
A way of demonstrating the rate of photosynthesis against the wavelength of light
What do modern action spectra use
They use electronic data logging instead of bacterial movements
How can you show there are several different pigments in plants
Paper chromatography
What does chromatography help us work out?
The Rf value
compare it to the original Rf value
How can you calculate the Rf value
Distance traveled by the solvent
What are the photosystem 1 and photosystem 2
Photosynthetic pigments that carry out the absorption of light in two distinct chlorophyll complexes
Where are the following found:
PSI
PSII
Lamellae
grana
Which of the two stages of photosynthesis only takes place at night
Light-independent reactions
Where does the light-dependent stage take place
On the thylakoid membrane of the chloroplast
What are the two main functions of light-dependent reactions
To split water in a photochemical reaction, providing H+ ions to reduce carbon dioxide and produce carbohydrates
The other is to produce ATP
What is light
What is the smallest unit of light
A form of electromagnetic radiation
The smallest unit of light is a photon
Explain what happens during the light-dependent reaction
A photon of light hits a chlorophyll molecule
The energy is transferred to the electrons of the molecule
The electrons are excited and are raised to a higher energy level
It will leave the chlorophyll molecule completely
The electron can be accepted by an electron acceptor and results in the synthesis of ATP.
How do light-dependent reactions lead to the formation of ATP
Either by cyclic or non-cyclic phosphorylation
In non-cyclic phosphorylation what else along with ATP is formed
NADPH
What does cyclic phosphorylation involve
Only photosystem I and drives the production of ATP
Explain the process of cyclic phosphorylation
Light hits a chlorophyll molecule in PSI
A light excited electron leaves the molecule
It’s taken up by an electron acceptor and passed directly along an electron transport chain to produce
ATP
When an electron returns to the chlorophyll molecule in PSI, it can be excited in the same way
What happens during the Non-cyclic phosphorylation
Water molecules are split, providing hydrogen ions to reduce NADP.
Explain the process of Non-cyclic phosphorylation
Under light conditions, photons are constantly hitting chlorophyll molecules in both PSI and PSII
Excited electrons move to a higher energy level for them to be lost and picked up by an electron acceptor.
An excited electron from PSII is picked up by electron acceptor and passed along an electron transport chain to PSI
PSI receives an electron to replace one that was lost to the light-dependent reactions
The chlorophyll of PSII is unstable and lacking an electron
The electron comes from photolysis (splitting of water)
Once PSII has the electron it is restored to the original state, ready for the light to hit it and excite the electron
What is the electron acceptor in Non-cyclic phosphorylation
NADP
What is the NADP and ATP produced during no cyclic photophosphorylation used for
As a source of reducing power and energy respectively in the light-independent reactions of photosynthesis to make glucose
How do chlorophyll molecules reform oxygen
4OH- - 4e- (lost to chlorophyll) ——> O2 +2H20
How are carbohydrates formed
The light-dependent stage of photosynthesis uses the reducing power and ATP produced
What is the Calvin cycle
A series of small steps result in the reduction of carbon dioxide from the air to bring about the synthesis of carbohydrates
Explain what happens in the Calvin cycle
Carbon dioxide from the air combines with 5-carbon compound RuBP in the chloroplast
Carbon dioxide is said to be fixed (carbon fixation)
Carbon dioxide + RuBP = 6C
The 6C is immediately broken down into two glycerate-3-phosphate
glycerate 3 phosphate is then reduced to form glyceraldehyde 3-phosphate (GALP)
The hydrogen for this reduction comes from the NADP
The GALP replaces the RuBP in the first reaction however some of it forms glucose
When does the Calvin cycle take place
In both the light and dark
When does the Calvin cycle stop
In the dark when the products of the light reaction run out, leaving no reduced NADP or ATP available in the chloroplast
What is GALP
The primary end-product of the process of photosynthesis and it is the key molecule for the synthesis of everything else needed in the plant
What is the GALP produced in the Calvin cycle used for
To produce glucose in the process called gluconeogenesis
What are some of the GALP taken into the glycolysis pathway converted into
What can it be used for
Acetyl CoA
Which in turn can be used to synthesize fatty acids needed for the production of phospholipids for membranes, and lipids needed for storage and other functions within the plants
What are the 3 limiting factors of photosynthesis
Light
Carbon dioxide
Temperature
How does light affect photosynthesis
The amount of light available affects the amount of chlorophyll which is excited therefore the amount
How does carbon dioxide affect photosynthesis
If there is not enough carbon dioxide available, the reactions cannot proceed at the maximum rate
What is the biggest limiting factor in photosynthesis
Carbon dioxide
How does temperature affect photosynthesis
If there is not enough temperature available, the reactions cannot proceed at the maximum rate
