Flashcards · 7402 · A Level Topic 5

Energy transfers in and between organisms (A Level) flashcards

15 cards on A Level Topic 5, subtopics 3.5.1 to 3.5.4. Pick a subtopic or study them all.

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Light-dependent reaction: site, inputs and products: Thylakoid membranes. Uses light, water, ADP, Pi and NADP; produces ATP, reduced NADP and oxygen.
Photoionisation: Light energy makes chlorophyll lose electrons, so the chlorophyll becomes ionised.
Photolysis of water: equation and use of the products: H₂O → 2H⁺ + 2e⁻ + ½O₂. Electrons replace those lost from chlorophyll; protons help reduce NADP; oxygen is released.
Light-independent reaction (Calvin cycle) in three steps: 1 CO₂ + RuBP, catalysed by rubisco, gives two GP. 2 GP is reduced to TP using ATP and reduced NADP. 3 Most TP regenerates RuBP (using ATP); some makes glucose and other organic substances.

Glycolysis: site and net products per glucose: Cytoplasm. Glucose is phosphorylated, split into two triose phosphate and oxidised to 2 pyruvate. Net: 2 ATP (4 made, 2 used) and 2 reduced NAD.
Link reaction: products per pyruvate: In the mitochondrial matrix, pyruvate (3C) is oxidised to acetate, which combines with coenzyme A: 1 acetyl CoA, 1 CO₂ and 1 reduced NAD per pyruvate.
Krebs cycle: products per turn: 1 ATP (substrate-level phosphorylation), 3 reduced NAD, 1 reduced FAD and 2 CO₂. Two turns per glucose.
Oxidative phosphorylation: Electrons from reduced NAD and FAD pass along the electron transfer chain, releasing energy that pumps protons into the intermembrane space. Protons flow back through ATP synthase, making ATP. Oxygen is the final electron acceptor, forming water.
Lactate and ethanol pathways: why do they happen?: To regenerate NAD from reduced NAD so glycolysis can continue. Lactate: pyruvate + reduced NAD → lactate + NAD (no CO₂). Ethanol: pyruvate → ethanal + CO₂; ethanal + reduced NAD → ethanol + NAD.

Net primary production: NPP = GPP − R, where R is respiratory loss. NPP is the chemical energy store in plant biomass after respiratory losses.
Net production of consumers: N = I − (F + R). I: chemical energy in ingested food; F: energy lost in faeces and urine; R: respiratory losses.
Gross primary production (GPP), and how biomass is measured: GPP: the chemical energy store in plant biomass in a given area or volume. Biomass is measured as mass of carbon or dry mass of tissue per unit area; its chemical energy store can be found by calorimetry.

Ammonification, nitrification and denitrification: Ammonification: saprobionts turn organic nitrogen compounds into ammonium ions. Nitrification: ammonium → nitrite → nitrate (aerobic). Denitrification: nitrate → nitrogen gas (anaerobic).
Role of mycorrhizae: Associations between fungi and plant roots. The fungal hyphae increase the surface area for absorbing water and mineral ions, such as phosphate; the fungus receives carbohydrates from the plant.
Leaching and eutrophication: Leaching: water-soluble nutrients such as nitrates are washed out of soil into rivers. Eutrophication: algae grow rapidly and block light, plants below die, saprobionts decompose them using oxygen, and fish die from lack of oxygen.