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Flashcards in Photosynthesis Deck (51)
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Write out the overall chemical reactions for photosynthesis and respiration.

6CO2 + 6H20 ↔ C6H12O6 + 6O2
C6H12O6 + 6O2 ↔ 6CO2 + 6H20 (+ATP)


Describe the relationship between photosynthesis and respiration, and use this to explain the importance of photosynthesis for consumers as well as producers.

Photosynthesis produces glucose. Respiration uses the glucose to release energy. This energy/ glucose is passed to the consumers when they eat the producers.


Use the concept of “bond energy” to explain why photosynthesis requires energy from the sun and stores energy whereas respiration releases energy that can be used to make ATP.

In respiration, large organic molecules are broken down to small inorganic molecules. Small inorganic molecules have much stronger bonds than big organic molecules so they release a lot of energy when formed. As a result, the total energy required to break all the bonds in a complex organic molecule is less than the total energy released in the formation of all the bonds in the smaller inorganic products, so there is an excess of energy which is released. This is an exothermic reaction.

In photosynthesis, large organic molecules are made from small inorganic molecules. It requires more energy to break the bonds of the small inorganic molecules that is released in the formation of the large organic molecules. Therefore energy is required from the sun. This is an endothermic reaction.


Describe the structure of chloroplasts.

- Double membrane
- The interior fluid is called the stroma
- Thylakoids, internal network of membranes
- a granum is a stack of thylakoid membranes
- grana are joined together by inter-granal lamellae
- surface of thylakoid membranes has lots of chlororphyll.


Name the two main stages of photosynthesis and state where each occurs in a chloroplast.

1) LDR - happens in photosystems which are embedded in the thylakoid membranes.
2) LIR - Takes place in the stroma.


Define the term “photosynthetic pigment”.

- pigment molecules which can absorb light
- different pigments can absorb different wavelengths of light
- found in the chloroplasts
- used in the light dependent stage of photosynthesis


Define the term “light harvesting system/ antennae complex'

A group of protein and chlorophyll molecules found in the thylakoid membrane of the chloroplasts in a plant. The role of system is to absorb or harvest light energy of different wavelengths and transfer this energy quickly and efficiently to the reaction centre.


Define the term“reaction centre”.

The site in the chloroplast that receives the energy trapped by chlorophyll and accessory pigments and initiates the electron transfer process. Chlorophyll a is located in the reaction centre.
(the light harvesting system and reaction centre are collectively known as a photosystem)


Define the term “photosystem”.

Protein complexes involved in the absorption of light energy and electron transfers in photosynthesis.


Name the photosynthetic pigment in the reaction centre of a photosystem.

Chlorophyll a


Name 3 types of photosynthetic pigments found in the antennae complex/ light harvesting system.

chlorophyll b, carotenoides, xanthophylls,


Explain why it is useful for photosynthetic organisms to have many different photosynthetic pigments.

Because different photosynthetic pigments absorb different wavelengths. This means that they can adjust to different intensities of light.


Label and annotate an absorption spectrum graph to explain what it shows.

Graph: wavelength of light on x, absorbance at y.
Pattern: Peaks at red and dark blue, troughs at green and light blue.
This shows that the plant's photosynthetic are most suited to absorbing red/ dark blue light and cannot absorb green light.


Describe the purpose of chromatography.

To show the different photosynthetic pigments in a plant extract. The pigments are separated on the chromatography paper because the rate at which they diffuse up the paper is varied.
An RF values can be calculated for each pigment (RF values is distance moved by pigment/ over distance moved by solvent. This value will help you identify the different pigments: least soluble will have moved the least distance and so will have a smaller RF value.


Describe a step by step method for conducting thin layer chromatography to separate and identify photosynthetic pigments.

1) Draw pencil on chromatography paper.
2) Obtain leaf extract by grinding leaves with propanone until a dark green solution forms.
3) Transfer leaf extract with a capillary tube to the strip of chromatography paper, creating a small spot on the centre of the pencil line.
4) Put the strip in a chromatography tube with a solvent in the bottom. The solvent in the tube shouldn't reach the spot of plant extract.
5) Leave it and remove the strip once the solvent is about one centimeter from the top.
6) Mark the solvent line and each pigment line with pencil.
7) Calculate RF values to identify the different pigments.


Explain what determines how far a particular molecule travels in chromatography.

Depends on solubility of molecule and interactions (hydrogen bonds).


Draw a diagram to summarise the light-dependent stage of photosynthesis and state where this occurs.

Non-cyclic photophosphorolation:
1) Light is absorbed by pigments in PSII. This absorbed light excites electrons at the reaction centre of the photosystem.
2) The excited are released from PSII and are passed on to the electron transport chain. ATP is produced by the process of chemiosmosis.
3) Electrons lost from PSII are replaced by the photolysis of water.
4) At PSI, the electrons receive another boost of energy and so become excited. They are then released from the reaction centre of PSI.
5) The electrons lost from PSI are replaced by electrons coming along the electron transport chain from PSII.
6) The electrons leaving the electron transport chain following PSI are accepted, along with hydrogen ions, by the coenzyme NADP, forming reduced NADP (uses enzyme NADP reductase).


Name the two useful products, the waste product, and the requirements, of the light-dependent stage of photosynthesis.

Two useful products:
- Reduced NADP

Waste product:
- Oxygen from the photolysis of water


Define the term “phosphorylation”.

The addition of a phosphate group to a molecule.


Define the term “photophosphorylation”.

The addition of a phosphate group to a molecule using light energy.


Define the term “cyclic photophosphorylation”.

Synthesis of ATP involving only PSI.


Define the term “non-cyclic photophosphorylation”.

The synthesis of ATP and reduced NADP involving PSII and PSI.


Define the term “photolysis”. Give the equation.

Water molecules are split into hydrogen ions, electrons and oxygen molecules using energy from the sun.

2H2O → 4e- + 2H+ + O2


Draw, label and annotate a diagram to show the process of cyclic phosphorylation (describe the process).

Process is the same up to PSI but then the electrons that leave PSI are returned to PSI instead of being used to form reduced NADP.
This means PSI can still lead to the production of ATP without any electrons supplied from PSII.


Describe the process of photolysis and what the products of photolysis are used for. (Cyclic photophosphorlyation)

1) There is an enzyme which is part of PSII which catalyses the breakdown (photolysis) of water. The products are electrons, hydrogen ions and oxygen.
2)The electrons are used to replace the lost electrons from the reaction centre of PSII.
3) The H+ ions build up in the lumen of the thylakoid. This causes the concentration of H+ ions to build up across the membrane = H+ ion concentration gradient.
4) This concentration gradient causes the H+ ions to move back through the thylakoid membrane down the concentration gradient, via the channel protein and enzyme, ATP synthase.
5) The H+ ions passing through the enzyme catalyses the production of ATP.
6) Once the H+ ions have returned to the stroma, they combine with NADP and an electron from PSI to form reduced NADP (catalysed by NADP reductase).


Draw a diagram to summarise the light-independent stage of photosynthesis and state where this occurs.

Calvin cycle - takes place in the stroma of chloroplasts
1) CO2 diffuses into stroma through the stomata and spongy mesophyll.
2) The CO2 combines with a five-carbon molecule called Ribulose Biphosphate (RuBP). The carbon in the carbon dioxide it therefore 'fixed' - it is incorporated into an organic molecule.
3) The enzyme ribulose bisphosphate carboxlyase (RuBisCo) catalyses this carbon fixation and an unstable 6-carbon molecule is formed. (RuBisCo is a very inefficient enzyme as it is competively inhibited by oxygen, so a lot of it is need for photosynthesis).
4) The unstable 6-carbon molecule immediately breaks down, forming two 3-carbon glycerate 3-phosphate (GP) molecules.
5) Each GP molecule is converted into another 3-carbon molecule, triose phosphate (TP), using a hydrogen atom from reduced NADP and the energy supplied by ATP.
6) Most of the TP is recycled to regenerate RuBP so that the calvin cycle can continue. The rest is used in the synthesis of glucose.


What is required for the Calvin Cycle to take place?

Name the useful product of, the three requirements of, and the molecules that are returned to the light-dependent stage from, the light-independent stage of photosynthesis.

- CO2, from the atmosphere
- RuBP, regenerated in Calvin Cycle
- ATP, from light-dependent stage
- reduced NADP, from light-dependent stage


What are the products of the Calvin?

- TP (triose phosphate)
- Regenerated RuBP
- Oxidised NADP


What is returned to the light-dependent reaction from the calvin cycle?

- Oxidised NADP


Define RuBisCo

A key enzyme involved in the carbon fixation stage of the calvin cycle.