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Describe the structure of chloroplasts in relation to their role in photosynthesis.
- Stroma: Site of light independent reactions. Contains enzymes, sugars.
- Grana: Site of light dependent reactions. Covered in photosystems, which absorb light. Provide large surface area.
- Thylakoid membranes: contain chlorophyll a, b, and carotene.
Describe the overall reaction of photosynthesis.
Describe the light dependent reaction.
- The light dependant reaction takes place on the thylakoid membrane in the grana.
- Photons from the sun raise the energy level of electrons in PS2 which contains chlorophyll and carotene.
- The electrons/chlorophyll become excited.
- The electrons are released from the photosystem.
- The electron that has left photosystem 2 is replaced by another which is obtained from photolysis of water.
- The electron then passes through an electron carrier chain by a series of redox reactions.
- As it does so its energy level decreases since it is used for chemiosmosis.
- Hydrogen ions are pumped through ATP synthase to photophosphorylate ADP into ATP
- The electron then enters PS1 and gets re-energised from photons.
- In cyclic photosynthesis the steps are repeated to produce more ATP.
- In non-cyclic photosynthesis the energised electrons are then used to reduce NADP to NADPH for the calvin cycle.
Describe how phosphorylation of ADP requires energy and how hydrolysis of ATP provides and immediate supply of energy for biological processes.
Describe the light independent reaction.
- is fixed by RuBP (5C) into 2 GP (3C). This step is catalysed by Rubisco.
- Reduced NADP is oxidised (therefore, GP is reduced) forming 2 x GALP (3C). ATP is also required.
- 5 out of 6 GALP are converted back to RuBP using ATP.
- 1 out of 6 GALP molecules are turned into Glucose (6C).Therefore, on average a glucose molecule is generated every 6 turns of the cycle.
- Glucose is used for respiration, to make A.A., nucleotides, cellulose.
How do you calculate NPP, and what is the relationship between GPP, NPP and respiration?
- NPP: The balance of glucose a plant has left over to use for growth. Proportional to biomass.
- GPP: The amount of glucose a plant generates through photosynthesis.
- R: The amount of glucose a plant uses in respiration.
How do you calculate % efficiency of energy transfers between trophic levels.
Describe how understanding the carbon cycle can lead to methods to reduce atmospheric levels of CO2.
- Reforestation schemes: More trees = more photosynthesis. Therefore,more CO2 fixed in the bodies of trees.
- Use biofuels instead of fossil fuels. Common biofuels are plantoils (e.g. palm oil) and ethanol from fermentation.
Explain that the numbers and distribution of organisms is a habitat are controlled by biotic and abiotic factors.
- Population size is affected by light, water, space, temperature and chemical composition of surroundings. (Abiotic)
- When abiotic conditions are ideal, growth is fast. E.g. More energy used for metabolic processes = more growth and reproduction.
- When abiotic factors aren't ideal, no growth. E.g. More energy used to maintain body temperature, less for growth.
- Population is also affected by inter and intra specific competition and predation (biotic).
- Inter = Different species compete for same resources, e.g. red and grey squirrels. This can also affect the distribution of species if one is out-competed.
- Intra = Same species compete for same resource e.g. rabbit population.
- Population size of predator and prey are interlinked, if one changes so does the other.
- Distribution varies because of abiotic factors, e.g. some trees cannot grow in polar regions because temp is too low.
Explain how the concept of niche accounts for distribution and abundance of organisms in a habitat.
- Niche: The role an organisms plays in a habitat.
- A niche can only be occupied by one species.
- Abundance of a species is affected if two species occupy the same niche, e.g. competition for food so less individuals of both species.
- Distribution can be explained by niche. Organisms can only exist in habitats where all conditions of their niche exist.
Ecology key terms.
- Habitat: The place where an organism lives
- Population: All the organisms of one species in a habitat.
- Population size: The number of individuals of one species in an area.
- Community: Populations of different species in a habitat.
- Abiotic: non-living factors
- Biotic: Living factors
- Abundance: The number of individuals of one species in a particular area.
- Distribution: Where a species is within an area.
- Edaphic: Factor of the soil
Describe the concept of succession to a climax community.
- Primary succesion: First stage, goes from abiotic land to ecosystem. Pioneer species change abiotic conditions and form basic soil. Grasses and shrubs begin to colonise and out compete lichens. Biodiversity and biomass increase over hundreds of years eventually reaching a climax community.
- Secondary succession: Soil layer already present. Seeds and root systems already established, so much faster growth. Over time species become better adapted and outcompete others. Dominant plants and animals will be present. Climax community will be reached.
Outline the causes of global warming.
- Greenhouse effect:
- 1.Incoming (short λ) solar light hits earth
- 3.Energy re-emitted as loger λ radiation
- 4.Longer λ absorbed by greenhouse gases in atmosphere
- 5.Reflected and re-emmitted back towards earth
- Cumulative effect: energy enters atmosphere and ultimately doesn’t leave, therefore, Earth is getting warmer =global warming.
- CO2: Comes from respiration & Combustion (particularly of fossil fuels).You could also argue deforestation led to an increase inPCO2 due to a decrease in global photosynthesis rates
- CH4: Comes from decomposition of bacteria and fungi and cows.
- Be aware that NOx, water vapour and CFCs are also greenhousegases. However, the vast global production of CO2makes the othersrelatively insignificant
Describe the effects of global warming
- Changing weather cycles:
- change in rainfall patterns
- impact on crops, housing and farming
- Shortage of drinking water
- Rising temperature:
- rise in sea levels
- melting ice caps
- loss of polar ecosystems
- polar migration of species
- famine, disease
- alterations in male:female ration in reptiles and fish
- alterations in insect life cycles
- impact on crops
- coastal flooding
Effects of increasing temperature on rate of enzyme activity.
- Increasing temperature provides more kinetic energy therefore more successful collisions between enzyme and substrate. Greater % of particles have E>Ea.
- If temp gets too high H bonds in enzymes break, changing the 3D shape of the active site and denaturing the enzyme. Substrate can no longer bind.
- Global warming = decrease in growth rate or increase it (polar organisms).
- Global warming will increase rate of growth of micro-organism→
- faster rate of decomposition
- increased probability of disease
Evidence for global warming
- Temperature records: In UK atmospheric temp. measures since 1889, showing 0.5-1.5 °C increase since then.
- CO2 levels: Ice cores trap bubbles of gas, allowing us to measure levels of CO2 every year for 50,000 years.
- Pollen in peat bogs: You can tell what species the pollen is from by its shape. Bogs are anoxic environments so pollen won't decay. Depth of a bog proportional to age, so we have a record of species that used to live near bogs at the time. If species that used to live near are further up north = warmer weather.
- Dendrochronology: Trees grow more when its hot. Thickness of ring of xylem is proportional to weather of particular year. Trees live for thousands of years, so we can see weather of particular year. Larger rings = warmer weather.