5A - Photosynthesis and Respiration Flashcards
What is the equation of photosynthesis?
- Carbon dioxide + water + energy -> glucose + oxygen
What is the equation for respiration?
- glucose + oxygen -> carbon dioxide + water + energy
What specific properties does ATP have that makes it a good energy source?
- stores and releases only small amounts of energy, no energy is wasted
- small, soluble molecule - easily transported
- easily broken down
- can be quickly re-made
- can make other molecules more reactive by transferring a phosphate group
- can’t pass out of a cell, cell always has immediate source of energy
What is the coenzyme used in photosynthesis?
- NADP
- transfers hydrogen from one molecule to another (reduction or oxidation)
What are coenzymes used in respiration?
- NAD, FAD and Coenzyme A
- NAD and FAD either reduce or oxidise a molecule
- Coenzyme A transfers acetate between molecules
Where does photosynthesis take place?
- chloroplasts
What are thylakoids?
- fluid-filled sacs stacked up into grana
What are grana linked together by?
- lamellae
What are photosynthetic pigments and what are the 3 types?
- coloured substances that absorb light energy
- chlorophyll a, chlorophyll b and carotene
What wavelength does Photosystem I absorb light best?
- 700nm
What wavelength does Photosystem II absorb light best?
- 680nm
What is the stroma?
- gel-like substance which contains enzymes, sugars and organic acids
What is the first stage of the light-dependent reaction?
- light energy is absorbed by chlorophyll in photosystems
- light energy excites electrons in chlorophyll, leading to eventual release (photoionisation)
What is the second stage of the light-dependent reaction?
- some of the energy from released electrons is used to add phosphate group to ADP to form ATP, and some is used to form reduced NADP
- H2O is oxidised to O2
The energy resulting from photoionisation in chlorophyll is used for what three things?
- photophosphorylation (ADP + Pi = ATP)
- making reduced NADP from NADP
- photolysis (splitting water into protons, electrons and oxygen)
What happens during the first stage of non-cyclic phosphorylation?
- light energy is absorbed by PSII
- light energy excites electrons in chlorophyll
- electrons move to higher energy level
- electrons are released from chlorophyll and move down electron transport chain to PSI
What happens during the second stage of non-cyclic phosphorylation?
- light energy splits water into protons, electrons and oxygen (photolysis)
- to replace the released electrons
What happens during the third stage of non-cyclic phosphorylation?
- excited electrons lose energy as they move down the electron transport chain
- energy is used to transport protons into thylakoid, so thylakoid has higher concentration of protons than the stroma
- proton gradient is formed across thylakoid membrane
- protons move down gradient into stroma via ATP synthase. Energy from this movement makes ATP.
What is the fourth stage of non-cyclic phosphorylation?
- light energy is absorbed by PSI, exciting electrons again to an even higher energy level
- electrons are transferred to NADP along with a proton to form reduced NADP
What is ‘cyclic phosphorylation’?
- electrons are passed back to PSI via electron carriers rather than being passed to NADP
- only produces small amounts of ATP
What is the first stage of the light-independent reaction?
- CO2 enters leaf through stomata and diffuses into stroma
- combines w/ ribulose biphosphate (RuBP), reaction is catalysed by rubisco
- gives unstable 6-carbon compound, which quickly breaks down into 2 glycerate 3-phosphate (GP)
What is the second stage of the light-independent reaction?
- hydrolysis of ATP from light-dependent reaction provides energy to turn GP into triose phosphate (TP)
- reaction also requires H ions, which come from reduced NADP. Reduced NADP is recycled to NADP.
- some TP is then converted into useful organic substances and some regenerates RuBP
What is the third stage of the light-independent reaction?
- 5/6 molecules of TP produced in the cycle is used to regenerate RuBP
- regenerating RuBP uses the rest of ATP produced by light-dependent reaction
What are the three limiting factors of photosynthesis?
- light intensity
- CO2 concentration
- temperature
What is the first stage of glycolysis?
- glucose is phosphorylated using a phosphate from ATP
- creates 1 glucose phosphate and 1 ADP
- ATP adds another phosphate, forming hexose bisphosphate
- hexose bisphosphate is then split into 2 triose phosphate
What is the second stage of glycolysis?
- triose phosphate is oxidised, forming two pyruvates
- NAD collects hydrogen ions, forming 2 reduced NAD
- 4 ATP are produced, but 2 were used up in the first stage, so net gain is 2 ATP
What happens to the pyruvate in anaerobic respiration?
- converted to ethanol or lactate
- regenerates oxidised NAD, means glycolysis can continue even when there isn’t much O2 around
What happens first in the link reaction?
- pyruvate is decarboxylated (one carbon atom is removed in the form of CO2
What happens second in the link reaction?
- pyruvate is oxidised to form acetate
- NAD is reduced to form reduced NAD
What happens third in link reaction?
- acetate is combined with coenzyme A to form acetyl coenzyme A
Is ATP produced in the link reaction?
- No
What happens in the first stage of the Krebs Cycle?
- acetyl CoA from link reaction combines with 4-carbon molecule to form 6-carbon molecule
- coenzyme A goes back to link reaction to be used again
What happens in the second stage of the Krebs Cycle?
- 6C citrate molecule converted to 5C molecule
- decarboxylation occurs, CO2 removed
- dehydrogenation also occurs, H removed
- hydrogen used to produce reduced NAD from NAD.
What happens in the third stage of the Krebs Cycle?
- 5C molecule converted to 4C molecule
- decarboxylation and dehydrogenation occur, producing 1 molecule of reduced FAD and 2 reduced NAD
- ATP is produced by direct transfer of phosphate group from an intermediate compound to ADP
- citrate is now converted into oxaloacetate
What happens first in oxidative phosphorylation?
- hydrogen atoms are released from reduced NAD and reduced FAD as they’re oxidised to NAD and FAD
- H atoms split into protons and electrons
What happens second in oxidative phosphorylation?
- electrons move down transport chain, losing energy at each carrier
- energy is used to pump protons from mitochondrial matrix into the intermembrane space
- concentration of protons is now higher in intermembrane space than the matrix - forms electrohemical gradient
What happens third in oxidative phosphorylation?
- protons move down electrochemical gradient via ATP synthase
- ATP is synthesised from ADP and P
What happens fourth in oxidative phosphorylation?
- in the mitochondrial matrix, protons, electrons and O2 combine to form water
- oxygen is the final electron acceptor
What is the process of ATP production being driven by the movement of H+ ions across a membrane called?
- chemiosmosis
