A-LEVEL BIOLOGY
MODULE 5: Energy Transfer In And Between Organisms
TOPIC 1
Photosynthesis
•• Photosynthesis = plants convert sun energy into chemical
energy
○○ 6CO2 + 6H2O
C6H12O6 + 6O2
○○ Autotrophic nutrition
○○ In chloroplasts
○○ Sugar produced is glucose
•• Respiration = releasing energy (often as ATP) from
glucose
○○ C6H12O6 + 6O2
6CO2 + 6H2O
○○ Heterotrophic nutrition
○○ In mitochondria
•• Chloroplast structure
○○ Surrounded by ion-permeable envelope
○○ Inner membrane fold to form lamellae
○○ Granum = stacked thylakoids
–– Provide large SA
○○ Stroma filled with fluid matrix
•• Pigments in chloroplasts
○○ Photosynthetic
–– Absorb specific wavelengths
○○ Primary
–– Absorb energy from light or accessory
pigments
○○ Accessory
○○ Chlorophyll
•• Photosynthesis: light dependent stage
○○ Photophosphorylation
–– Sunlight energises electrons
–– Electrons move along electron carriers
–– Protons pumped across thylakoid membranes
–– Protons move down conc. grad. through ATP
channels
–– ATP is produced for use in light independent
stage
○○ Cyclic photophosphorylation
–– Only uses PS1
–– Small amounts of ATP made
–– Guard cells swell and stomata open
○○ Non-cyclic photophosphorylation
–– PS1 and PS2 involved
–– Sunlight energises 2 electrons which pass along
electron carriers
–– Energy released use to make ATP
–– Water is photolysed and protons released used
in chemiosmosis to make ATP
–– ATP stored in NADP for light independent stage
•• Photosynthesis: light independent stage
○○ In stroma
○○ Calvin cycle
–– Carbon dioxide diffuses into leaf
–– In stroma, CO2 binds 5C ribulose bisphosphate
(rubisco enzyme)
–– 2 x glycerate phosphate (GP) formed
–– GP reduced and phosphorylated to triose
phosphate (TP)
–– Pairs of TP make hexose sugar
–– Most TP recycled to ribulose bisphosphate
○○ Water in light dependent stage
–– Photolysis occurs in PS1
–– Water
electrons, protons, oxygen
–– Oxygen used in aerobic respiration
–– Protons (H+ ions) used in chemiosmosis
–– Protons accepted by coenzyme NADP
–– Reduces NADP to red.NADP used in light
independent stage
•• Carbon dioxide in light independent stage
○○ Source of carbon and oxygen for organic molecules
•• Factors affecting rate of photosynthesis
○○ Increased light intensity = greater rate
○○ Increased carbon dioxide availability = greater rate
until stress response begins
○○ Increased temperature = greater rate (up to
threshold)
TOPIC 2
•• ATP
○○ Consists of
–– Ribose sugar
–– Adenine
–– 3 phosphate groups
○○ High energy intermediate compound
○○ Stores energy which can be quickly released
•• Mitochondrion structure
○○ Link reaction and Krebs cycle in matrix
○○ Cristae folds = large SA
•• Glycolysis
–– In cytoplasm
–– 1. Phosphorylation
–– 2. Splitting hexosebisphosphate
–– 3. Oxidation of triose phosphate
–– 4. Conversion to pyruvate
•• Net products of glycolysis
○○ 2 x ATP
○○ 2 x NADH
○○ 2 x pyruvate
○○ These are transported to mitochondria
•• Link reaction
○○ In mitochondrial matrix
Respiration
•• Respiration
○○ Energy used to make ATP
○○ ATP = “universal energy currency”
○○ ATP needed to drive metabolic processes
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