Energy Flow, Ecosystems and the Environment flashcards

Topic 5: Energy Flow, Ecosystems and the Environment

Overall equation for photosynthesis, and where the oxygen comes from

6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O. The oxygen released comes from water, split using light energy (photolysis).

Non-cyclic vs cyclic photophosphorylation

Non-cyclic: PSII and PSI; photolysis; makes ATP and reduced NADP and releases O₂. Cyclic: PSI only; no photolysis; makes ATP only, balancing the ATP supply with demand.

Light-independent reactions (Calvin cycle)

In the stroma: CO₂ + RuBP (5C) → 2 GP (3C), catalysed by RUBISCO. GP is reduced to GALP using ATP and reduced NADP. Most GALP regenerates RuBP (using ATP); some leaves the cycle to make carbohydrates and other molecules.

ATP and reduced NADP needed per CO₂ fixed

3 ATP and 2 reduced NADP per CO₂. One glucose needs 6 turns: 18 ATP and 12 reduced NADP.

GPP, R and NPP

GPP: total rate of energy capture by producers in organic molecules. R: energy released by plant respiration. NPP = GPP − R, the energy stored in new plant biomass (kJ m⁻² year⁻¹).

Why is energy transfer between trophic levels inefficient?

Not all of the organism is eaten; not all that is eaten is digested (egestion); respiration releases energy as heat; excretory products carry energy away. Only the remainder forms new tissue.

Herbivores receive 780 kJ m⁻² year⁻¹ from an NPP of 6240. What is the efficiency of transfer?

Efficiency = 780 ÷ 6240 × 100 = 12.5 %.

Population, community and ecosystem

Population: organisms of one species in one place at one time. Community: all the populations of all species sharing a place. Ecosystem: a community plus the abiotic factors it interacts with.

Primary succession from bare rock

Pioneers such as lichens and mosses; weathering and dead material form thin soil; grasses and small herbs; shrubs; trees as the climax community. Soil deepens and species diversity and biomass increase.

Evidence for climate change

Ice cores (CO₂ in trapped air), atmospheric CO₂ measurements, temperature records, pollen in peat bogs (past plant communities) and dendrochronology (tree ring widths).

How does the greenhouse effect work?

Short-wavelength sunlight reaches the surface, which emits longer-wavelength infrared. Greenhouse gases absorb the infrared and re-emit some back towards the surface, so more gas means more heat retained.

Q₁₀: definition, and Q₁₀ for rates of 3 at 20 °C and 12 at 40 °C

Q₁₀ = rate at (T + 10) ÷ rate at T. For any interval: (R₂ ÷ R₁)^(10 ÷ (T₂ − T₁)). Here (12 ÷ 3)^(10 ÷ 20) = 4^0.5 = 2.0.

Effects of climate change on organisms

Species shift towards the poles or to higher altitude; development speeds up (earlier hatching, flowering, migration); seasonal mismatch between predators and their food; drought or flooding reduces plant growth.

How does natural selection change allele frequency?

A random mutation produces a new allele. Overproduction and variation mean not all survive. A selection pressure favours individuals with the advantageous allele, which survive, reproduce and pass it on, so its frequency rises.

Allopatric vs sympatric speciation

Allopatric: a geographical barrier separates populations. Sympatric: in the same area, by behavioural, ecological or seasonal isolation, or polyploidy. In both, gene flow stops and allele frequencies diverge until the groups cannot produce fertile offspring.

Biofuels and reforestation: benefit and limitation

Biofuels: close to carbon neutral, but land competes with food and forest. Reforestation: habitat, carbon storage, less soil erosion, but slow, and plantations support less biodiversity.