B4 It’s a Green World Biology Revision

4a Who Planted that there? Plants carry out photosynthesis in leaves: Leaves are adapted by: Broad – large s.a. Thin – short diffusion distance Chlorophyll – absorb light Veins – support & transport Stomata – gas exchange Transparent epidermis Palisade contain most chloroplasts Air spaces in spongy mesophyll Large internal s.a.

4b Water, water everywhere? Osmosis – the net movement of water across a partially permeable membrane from an area of high water concentration to low as a consequence of random movement of particles Effect of osmosis on animal cells: Lysis Crenation

4b Water, water everywhere? Effect of osmosis on plant cells: Inelastic cell wall provides support & prevents cell bursting

4b Water, water everywhere? Plants use water to: Keep cool Transport minerals Photosynthesise Keep cells firm & supported Water is: Absorbed through root hair cells (large s.a.) Transported through stem Lost by evaporation/transpiration from leaves Water loss reduced by: Waxy cuticle; small number of stomata on upper surface; guard cells

4c Transport in Plants Transpiration – diffusion & evaporation of water from a leaf Rate is effected by: Light – more light increases p/s & transpiration Temperature – hotter increases p/s & transpiration Air movement – air removes water vapour from around leaves, maintaining diffusion gradient Humidity – high water vapour in air reduces diffusion gradient Potometer measures rate

4c Transport in Plants Vascular bundles – arrangement of xylem & phloem XylemPhloem TranspirationTranslocation Movement of water & minerals Movement of dissolved sugar From roots to leavesFrom leaves to rest of plant Vessels – thick cellulose strengthened cell wall, dead cells so hollow lumen Vessels – column of living cells

4d Plants need minerals too Minerals are absorbed by root hairs by active transport – using energy from respiration to move substances against concentration gradient MineralPurposeDeficiency NitratesAmino acids/proteins for growth Poor growth, yellow leaves PhosphatesDNA & cell membranes, respiration & growth Poor root growth & discoloured leaves PotassiumEnzymes for respiration & photosynthesis Poor flower & fruit growth, discoloured leaves MagnesiumChlorophyllYellow leaves

4e Energy flow Food chain – shows transfer of energy Pyramid of numbers – the numbers of organisms at each trophic level Producer – green plant Consumer – organism that eats another organim

4e Energy Flow Pyramid of biomass – the mass of living material at each trophic level Always pyramid shaped because of efficiency of energy transfer i.e. Energy is lost as less useful forms at each trophic level e.g. by heat from respiration, egestion of undigested food, not all organism being eaten Energy efficiency = energy converted to biomass X 100 total energy taken in

4e Energy Flow Biomass/Biofuels Fuels – wood, biogas from manure, alcohol from corn or sugar cane, bioethanol Energy can be transferred by: Eating it Burning it Feeding to livestock Growing seeds to produce more biomass Advantages of biofuels Renewable, reduces air pollution, energy self-reliance

4f Farming Intensive Farming – to produce as much food as possible from the land, plants & animals available Improves energy transfer efficiency Farming MethodReduction of energy transfer Problems Pesticides: herbicide, insecticide, fungicide To competing plants & pestsPesticides bioaccumulate in food chains or harm non target organisms FertilisersEutrophication Battery farming/fish farming Limited movement Temperature control Moral/ethical – poor quality of life Spread of disease

4f Farming Alternatives to intensive farming Hydroponics – growing plants in solution without soil Organic Farming – high quality produce whilst maintaining welfare of animals & minimising environmental impact AdvantagesDisadvantages Minerals added can be carefully controlled Expensive addition of fertilisers Reduced risk of diseaseLack of support/anchorage AdvantagesDisadvantages Food uncontaminatedLess efficient – crops lost Limited soil erosionManure takes time to rot & doesn’t provide specific balance of minerals Biodiversity promotedBiological control of pests difficult to control & expensive Animal welfare

4g Decay Breakdown of complex substances into simpler ones Detritivores – feed on dead organisms or waste (detritus), form larger surface area – e.g. worms, woodlice, maggots Decomposers – feed on waste left by detritivores Saprophytes – secrete enzymes on to material then absorb digested products

4g Decay Rate effected by: 1. Temperature – microorganisms work best at 40°C, but enzymes denatured above this 2. Oxygen – needed for respiration 3. Water – grow best in moist conditions Food Preservation MethodExplanation CanningSealed to remove oxygen & prevent entry of microbes CoolingLow temperatures slow growth DryingReduces moisture needed for growth Preserving (salt/sugar)Conditions are too concentrated for survival Pickling in vinegarLow pH denatures enzymes in microbes

4h Recycling Decay recycles chemicals e.g. carbon & nitrogen Carbon cycle 0.04% CO 2 in air

4h Recycling Nitrogen Cycle 78% N 2 in air N 2 gas is too unreactive to use directly