5.6 Photosynthesis Flashcards
What are the four processes that require energy?
- Movement
- growth and repair
- active transport
- protein synthesis.
Describe the process of active transport.
- Molecule binds to the outside receptors on the carrier protein.
- then ATP is hydrolyzed into ADP and 1 phosphate.
- The phosphate binds to the inside receptor, which changes the shape of the carrier protein.
- Molecule is released.
- Phosphate is released and binds with ADP to form ATP.
What is the compensation point?
When photosynthesis and respiration proceed at the same time. So there is no net gain or loss of carbohydrates.
What is photosynthesis?
A physiological process used to convert light energy from sunlight into chemical energy. This energy is then used to synphesise larger organic molecules from small inorganic molecules.
What is respiration?
The process were organic molecules are oxidised and broken down to produce inorganic molecules.
What 3 ways can ATP be synthesised?
- photophosphorylation
- oxidative phosphorylation
- substrate- level phosphorylation
What enzyme catalyses the hydrolysis of ATP?
ATP Hydrolase.
What enzyme catalyses for synthesis of ATP.
ATP Synphase.
What happens during photosynthesis?
Light energy provides the energy needed to form chemical bonds in ATP. These are then broken, which releases the energy needed to make the bonds for glucose to form
What happens during respiration?
Glucose is broken down, which releases energy. This energy is used to synthesise ATP, which is then used to supply energy to break the bonds in metabolic reactions of the cell.
What is a disadvantage of ATP?
A soluble so it can’t be stored, which means it must be used immediately.
What is the function of ATP?
To provide an immediate energy source.
How does ATP provide energy?
through the reforming of ADP and phosphate group one.
Why did ATP have a low activation energy?
As unstable bonds, which could break easily.
What is the equation for the hydrolysis of ATP?
ATP + H2O –> ADP + Pi + E
How much energy is released from the hydrolysis of ATP?
30.5 kilojoules.
What is chemiosmosis?
The diffusion of Protons from a region of high concentration to a region of low concentration through partialy permeable membrane. This releases energy to attach an inorganic phosphate to ADP, forming ATP.
What is the function of the electron transport chain?
to pump protons
(H+ ions) across a membrane.
what is the interrelationship between photosynthesis and respiration?
The sun provides light energy, which is used in photosynthesis to produce glucose and oxygen. This glucose and oxygen is then used in respiration, which produces carbon dioxide water. The carbon dioxide is then used as a reactant in the photosynthesis reaction.
what type of reaction occurs when ATP is converted into ADP?
hydrolysis
describe the electron transport chain
a high energy electron moves from one electron carrier to the next, it releases energy which is used to pump the proton across the membrane
describe ATP synthesis
protons move down their concentration gradient passing through the channel to ATP synthase. This provides energy to synthesis ATP from ADP and 1 inorganic phosphate
what colour light does chlorophyll absorb?
- red
- blue
what is chlorophyll?
5 closely related pigments
what colour light does chlorophyll reflect?
green
what chlorophyll pigment is most abundant?
chlorophyll A
what are the different chlorophyll pigments?
- chlorophyll A
- chlorophyll B
- carotenoids which are orange carotene and yellow xanthophyll
what are the components of a chloroplast?
- outer membrane
- intermembrane space
- inner membrane
- stroma
- starch grain
- ribosomes
- granum
- intergranal lamella
- circular DNA
- lipid droplet
what is a feature of the chloroplasts outer membrane?
it is permeable
what is are features of the chloroplasts inner membrane?
- selectively permeable
- transport proteins present
what is the function of a starch grain in a chloroplast?
to store starch, a polysaccharide made from glucose
what is stroma?
the fluid that fills chloroplasts
what does stroma contain?
enzymes for light independent (dark) reactions
what are granum?
- stacks of thykaloids
what part of the chloroplast is the site of light dependent reactions?
the granum
what does the circular DNA in chloroplasts code for?
enzymes such as rubisco
where does the light dependent stage of photosynthesis occur?
on the thylakoids of the grana
what are the 3 phases of the light dependent stage of photosynthesis?
- photolysis of water
- photophosphorylation
- formation of reduced NADP
where is the enzyme needed for the photolysis of water present?
in photosystem 2
what is formed from the photolysis of water?
- oxygen
- 2 protons
- 2 electrons
what are the protons and electrons from photolysis used in?
photophosphorylation
outline the photolysis of water
H2O —> O + 2e- + 2H+
what is the oxygen atom produced in photolysis used in?
respiration
what is a photosystem?
a collection of photosynthetic pigments that absorb light energy and transfer it onto electrons
what pigment is found in photosystem 2?
p680
what pigment is found in photosystem 1?
p700
where does the photolysis of water take place?
photosystem 2
outline photophosphorylation
- high energy electron passes along electron transport chain, releasing energy so a proton passes along the membrane
- protons move down proton gradient by facilitated diffusion through ATP synthase enzymes (chemiosmosis)
- ATP is synthesized from ADP and an inorganic phosphate
describe cyclic phosphorylation
- involves photosystem 1 only
- produces smaller quantities of ATP
describe non-cyclic phosphorylation
- involves photosystems 1 and 2
- produces ATP, oxygen and NADPH
outline cyclic phosphorylation
- light is absorbed by p700 in photosystem 1
- electron is excited to a high energy level and emitted from a chlorophyll molecule
- electron is captured by an electron acceptor, then transported via a chain of electrons before being passed back to the chlorophyll molecule
outline non-cyclic phosphorylation
- light absorbed by photosystem 2 and passed to p680
- 2 electrons are excited and emitted from chlorophyll molecule
- excited electrons pass down an electron transport chain causing chemiosmosis
- excited electrons leave photosystem 2, replaced by electrons from photolysis
- excited electrons pass down an electron transport chain
- electrons combine with H+ ions and NADP to produce reduce NADP (NADPH)
what is photoionisation?
exciting electrons to a higher energy level, and then emitting them from a chlorophyll molecule
outline chemiosmosis
Protons move along the proton concentration gradient through a transmembrane ATP synthase. This provides energy for ATP to form from ADP and an inorganic phosphate.
What name is given to the light independent stage of photosynthesis?
The Calvin cycle.
Where does the Calvin cycle take place?
The stroma of the chloroplast.
What are the three parts of the Calvin cycle?
- fixation
- reduction
- regeneration
What happens during fixation?
Carbon dioxide enters the leaf via the stomata. The carbon dioxide then combines with RuBP to make an unstable six carbon compound, which then breaks down into 2 GP molecules. This is catalysed by the enzyme rubisco.
What happens during reduction?
GP is reduced to TP by adding protons from NADPH and using the energy generated from ATP.
How much ATP is needed for reduction?
12
How much ATP is needed for regeneration?
6
How much ATP is needed in total to complete one calvin cycle.
18
Where is the ATP and NADPH used in the Calvin cycle from?
The light dependent reaction.
What can TP be used for?
TP is used to synthesise complex biological molecules such as:
- glucose
- carbohydrates
- lipids
- proteins
What is the remaining 5 TP molecules used for?
The regeneration of RuBP.
What happens during photorespiration?
Oxygen can combine with RUBP in place of CO2. This would decrease the efficiency of photosynthesis. It could form toxic hydrogen peroxide and produce PGA and PPG.
What can photorespiration form?
- toxic hydrogen peroxide
- PGA
- PPG
what is a limiting factor?
a factor, that when in short supply affects the RATE of photosynthesis
what are examples of limiting factors?
- carbon dioxide concentration
- light intensity
- temperature
what is water not a limiting factor?
when water levels are too low, to limit photosynthesis, the stomata are already closed and photosynthesis stopped
what happens when temperature is too low?
- enzyme and substrate molecules lose kinetic energy so less GP, TP and RuBP are produced
what happens when temperature is too high?
- enzymes denature so less GP, TP and RuBP are produced
what happens when carbon dioxide levels are too low?
- less GP and TP produced
- TP forms RuBP but less is used to fix carbon dioxide, so CO2 levels increase
what happens when carbon dioxide levels are too high?
- increase in all products of the Calvin cycle as more CO2 is fixed
what happens when light intensity is too low?
- increase in GP
- decrease in TP as less ATP and NADPH are made in the LDR, so GP cant be reduced to TP
- less TP means less RuBP regenerates
what happens when light intensity is too high?
- increase in TP and RuBP
- decrease in GP due to abundance of ATP and NADPH from the LDR
