Topic 5: Energy Transfer In And Between Organisms Flashcards
3.5.1 Photosynthesis
What is photosynthesis?
- Photosynthesis is a reaction in which light energy is used to
produce glucose in plants. The process requires water and carbon
dioxide, with the products being glucose and oxygen.
What are the two key stages of photsynthesis?
- the light dependent reaction
- the light independent reaction
What factors affect the rate of photosynthesis?
- carbon dioxide concentration
- light intensity
- temperature
What are the four key stages in the light dependent reaction?
- Photolysis of water
- Photoionisation
- Chemiosmosis
- Production of ATP and reduced NADP
How are chloroplasts adapted for photosynthesis?
- contains stacks of thylakoid membrane called the grana, these are folded to provide a large surface area for the attachment of chlorophyll, electrons and enzymes
- the granal membrane has ATP synthase channels embedded allowing ATP to be synthesised and its selectively permeable which creates a proton gradient
- chloroplasts contain DNA and ribosomes allowing them to synthesise proteins needed in the light dependent reaction
What happens in photolysis?
- light energy is absorbed by the chloropyll
- this splits water into oxygen protons and electrons
- the protons are used to create reduced NADP and is used in the LIR
- the electrons are passed along a chain of electron carrier proteins
- the oxygen is either used for respiration or diffuses out of the leaf through the stomata
How many photons of light is required to split one molecule of water?
- 4 photons of light are required to split one molecule of water
How many molecules of oxygen protons and electrons does the photolysis of water produce?
- 1 molecule of oxygen
- 4 protons
- 4 electrons
What happens in photoionisation?
- The light energy absorbed by the chloropyll results in the electrons becoming excited
- the electrons raise up an energy level and leave the chloropyll
- chloropyll becomes positively charged and has now been ionised
What is some of the energy released from the electrons in photoionisation used for?
- is conserved in the production of ATP and
reduced NADP
What happens in chemiosmosis?
- the electrons move along a series of proteins embedded within the thylakoid membrane
- As the electrons move along the proteins they release energy and some of this energy is used to pump the protons across chloroplasts membranes
- An electrochemical gradient is created. The protons pass through the enzyme ATP synthase by facilitated diffusion which phosphorylates ATP from ADP + pi
- The protons combine with coenzyme NADP to become reduced NADPH
- Because the protons move from an area of high to low concentration gradient. This is known as chemiosmosis
- NADPH and ATP are now used in the LIR
Where does the light independent reaction take place?
- the stroma
- also known as the calvin cycle
What is the enzyme involved in the LIR?
- Rubisco which catalyses the reaction
- the stage is temperature reactive due to the fact it contains enzymes
What does the calvin cycle use to form a hexose sugar?
- CO2
- reduced NADP
- ATP
What is the role of ATP and NADPH in the calvin cycle?
- ATP is hydrolysed to provide energy for the reaction
- reduced NADP donates the hydrogen to reduces the molecule GP in the cycle
What are the main stages in the calvin cycle?
- carbon dioxide fixation
- reduction phase
- regeneration of RuBp
- organic molecule production
What happens in the first stage of the calvin cycle (carbon dioxide fixation)?
- CO2 reacts with ribulose bisphosphate (RuBP) in a process known as carboxylation
- to form 2 molecules of GP a three carbon compound
- this reaction is catalysed by the enzyme rubisco
What happens in the second stage of the calvin cycle (reduction phase)?
- GP is reduced by reduced NADP to form 2 molecules of TP and also energy is used by ATP
- All of the NADP from the LDR has been used
- Only some of the ATP has been used
What happens in the third stage of the calvin cycle (regeneration of RuBP)?
- Some of the carbon from TP leaves the cycle each turn to be converted into useful organic substances
- 5 molecules of triose phosphate are used in order to regenerate 3 molecules of RuBP
- The remaining amount of ATP from the light
stage is now used.
What happens in the last stage of the calvin cycle (organic molecule production)?
-
2 molecules of triose phosphate can combine to form
the intermediate hexose sugar - whilst glucose is the product this monosaccharide can join to form disaccharides such as sucrose and polysaccharides such as cellulose and starch
- glucose can also be converted to glycerol and therefore combine with fatty acids to make lipids for the plant
How many turns of the calvin cycle are needed to produce 1 molecule of glucose per molecule of CO2?
- 6 turns of the Calvin Cycle are required in order to produce 1 molecule of glucose per
Describe the structure of a chloroplast
- usually disc shaped
- Double membrane
- Thylakoids-flattended discs stack to form grana
- Intergranal lamellae
- stroma-fluid filled matrix
How does the structure of the chloroplast maximise the rate of the LDR?
- ATP synthase channels within granal membrane
- Large surface area of thylakoid membrane for ETC
- photosystems position chlorophyll to enable maximum absorption of light
How does the structure of the chloroplast maximise the rate of the LIR?
- own DNA and ribosomes for synthesis of enzymes e.g. rubisco
- concentration of enzymes and substrates in stroma is high
What are the limiting factors of photosynthesis ?
- Light intensity (LDR)
- CO2 levels (LIR)
- Temperature (enzyme controlled steps)
- Mineral/magnesium levels (maintain normal functioning of chloropyll
- Chlorophyll concentration
Wnat are some techniques agricultural producers incorporate to remove limiting factors?
- growing plants with artificial lighting to maximise light intensity
- heating a greenhouse to increase temperature
- burning fuel to release more co2
Why do farmers try to overcome the effect of limiting factors?
- to increase yield
- additional cost must be balanced with yield to ensure maximum profit
3.5.2 Respiration
What are the two types of respiration?
- Aerobic and Anaerobic respiration
What is aerobic respiration?
- Aerobic respiration is the splitting of a respiratory
substrate, to release carbon dioxide as a waste product.
What is anaerobic respiration?
- Anaerobic
respiration occurs in the absence of oxygen.
What are the main stages of aerobic respiration?
- glycolysis (cytoplasm)
- the link reaction (mitochondrial matrix)
- the krebs cycle (mitochondrial matrix)
- oxidative phosphorylation (inner membrane cristae of mitochrondria)
What happens in glycolysis?
- this is the first process of both aerobic
and anaerobic respiration. - glucose is phosphorylated to glucose phosphate using ATP
- This produces 2 molecules of triose phosphate
- TP is oxidised to produce 2 molecules of pyruvate, with a net gain of 2× ATP and 2×NADH
What happens in the link reaction?
- the pyruvate from glycolysis is actively transported into the mitochondrial matrix
- pyruvate is oxidised to acetate producing reduced NAD in the process
- acetate combines with co-enzyme A in the link reacrion to produce acetylcoenzyme A
- Per glucose molecule 2 molecules of
acetyl coenzyme A are formed and 0 ATP
What happens in the krebs cycle?
-
acetylcoenzyme A reacts with a four-carbon molecule,
releasing coenzyme A and producing a six-carbon molecule
that enters the Krebs cycle - in a series of oxidation-reduction reactions, the Krebs cycle
generates reduced coenzymes and ATP by substrate-level
phosphorylation, and carbon dioxide is lost - The Krebs cycle turns
2 times per molecule of glucose -
per molecule of glucose 2 ATP molecules, 6
NADH molecules, 2 FADH molecules and 4 CO2 molecules are produced.
What happens in oxidative phosphorylation?
- the current model for this process is the chemiosmotic theory
-
synthesis of ATP by oxidative phosphorylation is associated
with the transfer of electrons down the electron transfer chain
and passage of protons across inner mitochondrial
membranes and is catalysed by ATP synthase embedded in
these membranes - Hydrogen atoms are donated by reduced NAD (NADH) and reduced FAD (FADH2) from the Krebs Cycle
- Hydrogen atoms split into protons (H+ ions) and electrons
- The high energy electrons enter the electron transport chain and release energy as they move through the electron transport chain
- The released energy is used to transport protons across the inner mitochondrial membrane from thematrix into the intermembrane space
- A concentration gradient of protons is established between the intermembrane space and the matrix
- The protons return to the matrix via facilitated diffusion through the channel protein ATP synthase
- The movement of protons down their concentration gradient provides energy for ATP synthesis
- Oxygen acts as the ‘final electron acceptor’ and combines with protons and electrons at the end of the electron transport chain to form water