Photosynthesis Flashcards
Give the overall equation for photosynthesis
6CO2 + 6H20 —> C6H12O6 + 6O2
How is a carbohydrate formed?
CO2 is reduced as hydrogen and electrons from water are added to it
What kind of energy input is needed to break the bonds in photosynthesis?
Light energy
Why does carbohydrate act as a storage of energy?
Because more energy is needed to break the bonds of water than is given out in the by bond formation in the carbohydrate
This energy can then be released via oxidation at another time
Give examples of why plants need energy
- Photosynthesis
- Active transport
- DNA replication
- Cell division
- Protein synthesis
What is the immediate source of energy in a cell?
ATP
Where is the energy stored in ATP?
In the phosphate bond
What makes up ATP?
ADP + an inorganic phosphate
What enzyme catalyses the breakdown of ATP?
ATPase
What is ATP made up?
Adenine, ribose sugar and three phosphate groups
What enzyme catalyses the formation of ATP?
ATP synthase
Where does the energy come from to form ATP?
From glucose in respiration
What type of reaction is it going from ADP to ATP?
Phosphorylation
What type of reaction is it going from ATP to ADP?
Hydrolysis
Why is ATP a good source of energy?
The energy can be released very quickly via hydrolysis
What is a coenzyme?
How do they work?
Give an example
A molecule that aids the function of an enzyme
They transfer a chemical group from one molecule to another
NADP - Transfers hydrogen from one molecule to another in photosynthesis
Give examples of uses of glucose
- Energy source
- Converted into starch
- Cellulose
- Fats
- amino acids/proteins
- nucleic acids
Describe the structure of chloroplasts
- Small, flattened organelles found in plant cells
- Double membrane called the chloroplast envelope
- Contain thylakoids (fluid-filled sacs) which are stacked up into structures called grana (singular -granum)
- Grana are linked together by bits of thylakoid membrane called lamellae (singular - lamella)
- Chloroplasts contain photosynthetic pigments such as chlorophyll a
- These pigments are found in the thylakoid membranes attached to proteins
- Within the inner membrane of the chloroplast and surrounding the thylakoids is a gel-like substance called the stroma
- Stroma contains enzymes, sugars, organic acids and oil droplets which store non-carbohydrate organic material)
Two stages of photosynthesis
Light-dependent reaction
Light-independent reaction
Describe the light-dependent reaction
- Happens in the thylakoid membranes
- Starts in PSII chlorophyll
- Energy from light raises two electrons in each chlorophyll to a higher energy level
- The chlorophyll molecules are now in an excited state
- The electrons leave the chlorophyll molecule and pass along a series of electron carrier molecules which are embedded in the thylakoid membrane. This forms the electron transport chain
- The electrons from PSII pass along from one carrier to the next in a series of oxidation and reduction reactions, losing energy which is then used in the synthesis of ATP using photophosphorylation
- The electrons from the PSII chlorophyll replace those lost from the PSI chlorophyll when it’s electrons became excited and left
- The electrons from the PSII chlorophyll are replaced by the photolysis of water to produce oxygen, hydrogen and electrons
- The hydrogen ion concentration has increased
- The electrons from the PSI chlorophyll pass along the ETC and combine with the co-enzyme NADP and hydrogen ions from the water to form reduced NADP
Describe the light-independent reaction
- Takes place in the stroma of the chloroplasts
- Calvin cycle:
- Carbon dioxide combines with a 5-carbon compound called RuBP. This reaction is catalysed by the enzyme RuBISCO. The process is called carbon fixation
- The 6-carbon compound formed is unstable and immediately breaks down into two 3-carbon compounds, GP
- GP is reduced to form a 3-carbon sugar phosphate called GALP. Hydrogen used to reduce GP comes from the light-independent reaction as does the energy in the form of ATP
- 2 of the 12 GALPs formed are used to form hexose, a 6-carbon sugar, which can be converted into other organic compounds such as amino acids or lipids
- 10 out of every 12 GALPs are used to recreate RuBP
- This happens as the 10 GALP molecules form 6 lots of 5-carbon compounds which are then phosphorylated, using ATP, to RuBP
How is the structure of a chloroplast adapted for photosynthesis?
- Chloroplast envelope keeps reactants in photosynthesis close to their reaction sites
- Thylakoids have large surface area to allow as much light energy to be absorbed as possible
- Many ATP synthase molecules present in the thylakoid membrane to produce ATP
- Stroma contains enzymes, sugars and organic acids used in the light-independent reaction
