AQA A Level Biology - Energy and Ecosystems 2024

AQA A Level Biology - Energy and Ecosystems 2024 Where do organic compounds come from in an ecosystem? in photosynthesis using atmospheric or aquatic CO2 Plants synthesise organic compounds What are most of the sugars produced in photosynthesis used for ? substrates) Respiration (as respiratory What are the two uses of organic compounds produced in photosynthesis ? Substrates Building other biological molecules e.g. cellulose What is biomass ? The mass of living material or the chemical energy stored (i.e. the biological molecules produced by photosynthesis that aren't respired) What are the two ways in which biomass can be measured? Respiratory Mass of carbon in a given area, per unit time Dry mass of tissue in a given area, per unit time How can the chemical energy store in dry biomass be measured ? Burn sample of dry mass (energy released heats water) Change in temperature of water used to determine chemical energy How can the dry mass (biomass) of a tissue be found ? temperature Weigh at regular intervals until constant mass Why is dry mass used instead of wet mass, as a measure of biomass ? t issue varies Why is biomass measured over a particular period of time ? when leaves are shed Calorimetry : Dry a sample in an oven at a low The water content of living Biomass changes over time e.g. trees The chemical energy stored in plant biomass, in a given What is gross primary production (GPP) ? area or volume, per unit time What is net primary production (NPP) ? (3 things) 1. The chemical energy stored in plant biomass once respiratory losses to the environment have been taken into account 2. The energy available to the plant for growth and reproduction 3. The energy available to organisms at the next trophic level What is the formula for NPP ? NPP = GPP - R What is the differene between net primary production and net production ? production is plants Net production is consumers Give ways why not all chemical energy is transferred to the next trophic level? is eaten (i.e. roots and bones) 2. Some is indigestible and egested as faeces 3. Some is lost by excretion or urine 4. Some is respired What is net production ? Net primary 1. Not all the food The energy in the consumer's biomass available to the next trophic level What is the formula for net production ? N = I -(F + R) What do the letters in N= I - (F +R) stand for ? (chemical energy): I= Ingested F= lost as faeces and urine R= lost as respiration What is primary/secondary productivity ? N= net production The rate of primary/secondary production How is primary/secondary productivity measured ? Biomass in a given area in a given time e.g. kJ/ha/year How is the efficiency of energy transfer calculated ? net production of previous tropic level ) x 100% (Net production of tropic level/ Why does the efficiency of energy transfer increase up a food chain? indigestible matter than plants What is a trophic level ? A stage in a food chain How do farmers try to increase efficiency of energy transfer? Consumers contain less 1. Simplifying food webs 2. Reducing energy lost through respiration of livestock How do farmers simplify food webs? 1. Insecticides 2. Herbicides Get rid of pests 3. Parasites/pathogenic bacteria or viruses How do farmers reduce respiratory losses? 2. Keep warm (keep indoors) 1. Reduce movement (keep in pens) What are the positives and negatives of increasing efficiency of food chains for farmers ? rate of primary/secondary productivity Lower cost Ethical issues (distress or cause animals pain)