Unit 5 Flashcards
Stages of photosynthesis
-Light-dependent reaction (LDR)- thylakoid membrane of chloroplast.
-Light-independent reaction (LIR)- stroma of chloroplast.
Photoionisation of LDR
-Chlorophyll absorbs light energy which excites its electrons.
-Electrons are released from chlorophyll so it becomes positively charged.
Chemiosmosis
-Electrons move along electron transfer chain, releasing energy.
-Energy is used to actively pump protons from stroma into thylakoid.
-Protons move by facilitated diffusion down electrochemical gradient into stroma via ATP synthase.
-Energy used to join ADP and Pi to form ATP (photophosphorylation).
-NADP accepts a proton and an electron to become NADPH.
Photolysis of water
-Water splits to produce protons, electrons and oxygen.
-H2O –> 1/2 O2 + 2e- + 2H+
-Electrons replace those lost from chlorophyll.
Calvin cycle
-CO2 reacts with ribulose bisphosphate (RuBP).
-Catalysed by enzyme rubisco.
-Forming 2 glycerate 3-phosphate (GP) molecules.
-GP gets reduced to triose phosphate (TP).
-Using products from light dependent reaction- NADPH and energy from ATP.
-Some TP is converted to useful organic substances (e.g. glucose).
-Some TP is used to regenerate RuBP in the Calvin cycle (using energy from ATP).
How does temperature affect rate of photosynthesis?
-As temp increases, rate increases.
-Enzymes gain kinetic energy.
-So more ES complexes form.
-Above the optimum temp, rate decreases.
-Enzymes denature as H bonds in tertiary structure break.
-Fewer ES complexes form.
How does light intensity affect rate of photosynthesis?
-As light intensity increase, rate increases.
-LDR increases so more ATP and NADPH produced.
-More GP reduced to TP and more TP regenerates RuBP.
-After a certain light intensity, rate stops increasing.
-Another factor is limiting (e.g. temperature/ CO2 conc).
How does CO2 conc affect rate of photosynthesis?
-As CO2 conc increases, rate increases.
-LIR increases as more CO2 combines with RuBP to form GP.
-More GP reduced to TP.
-More TP converted to organic substances and more RuBP regenerated.
-Above a certain CO2 concentration, rate stops increasing.
-Another factor is limiting (e.g. temp/ light intensity).
Why is respiration important?
-Respiration produces ATP.
-For active transport, protein synthesis, etc.
Stages of aerobic respiration
-Glycolysis (cytoplasm)
-Link reaction (mitochondrial matrix)
-Krebs cycle (mitochondrial matrix)
-Oxidative phosphorylation (inner mitochondrial membrane)
Stages of anaerobic
-Glycolysis (cytoplasm)
-NAD regeneration (cytoplasm)
Process of glycolysis
-Glucose is phosphorylated to glucose phosphate.
-Using inorganic phosphates for 2ATP.
-Hydrolysed to 2x triose phosphate.
-Oxidised to 2 pyruvate.
-2 NAD reduced
-4 ATP regenerated (net 2)
What happens after glycolysis if conditions are anaerobic?
-Pyruvate converted to lactate or ethanol.
-Oxidising reduced NAD- NAD regenerated.
-So glycolysis can continue allowing continued production of ATP.
Why anaerobic respiration produces less ATP?
-Only glycolysis is involved which produces little ATP.
-No oxidative phosphorylation which forms majority of ATP.
Process of link reaction
-Pyruvate oxidised (and decarboxylated) to acetate.
-CO2 is produced.
-Reduced NAD produced.
-Acetate combines with coenzyme A, forming Acetyl Coenzyme A.
Process of Krebs cycle
-Acetyl coenzyme A (2C) reacts with a 4C molecules (oxaloacetate).
-Releasing coenzyme A.
-Producing a 6C molecule (citrate) that enters the Krebs cycle.
-In a series of oxidation-reduction reactions, the 4C molecules is regenerated and:
-2x CO2 lost
-Coenzymes NAD and FAD reduced.
-Substrate level phosphorylation (direct transfer of Pi from intermediate compound to ADP–> produced)
Oxidative phosphorylation
-NADH and FADH2 are oxidised to release H atoms meaning it is split into protons and electrons.
-Electrons transferred down the electron transfer chain (chain of carriers at decreasing energy levels).
-By redox reactions.
-Energy released by electrons used in the production of ATP from ADP + Pi (chemiosmotic theory).
-Energy used by electron carriers to actively pump protons from matrix to the intermembrane space.
-Protons diffuse into matrix down an electrochemical gradient via ATP synthase (which is embedded in the membrane).
-Releasing energy to synthesise ATP from ADP + Pi.
-In matric at end of ETC, oxygen is final electron acceptor- electrons can’t pass along otherwise.
-So protons, electrons and oxygen combine to form water.
Examples of other respiratory substrates
-Fatty acids from hydrolysis of lipids- converted to Acetyl Coenzyme A.
-Amino acids from hydrolysis of proteins- converted to intermediates in Krebs cycle.
How does energy enter an ecosystem and how is it transferred?
-Energy enters by photosynthesis of the producers.
-Photosynthesis makes organic matter which makes up the biomass of an organism.
-It is transferred from prey to predator when the prey is eaten.
Producers
Photosynthetic organisms that manufacture organic substances using light energy, water, carbon dioxide and mineral ions.
Consumers
Organisms that obtain their energy by feeding on (consuming) other organisms rather than using the energy of sunlight directly.
Saprobionts
-Decomposers
-A group of organisms that break down the complex materials in dead organisms into simple ones.
-In doing so, they release valuable minerals and elements into a form that can be absorbed by plants and contribute to recycling.
-Fungi and bacteria.
