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Biology Revision B4 It’s a Green World 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 Xylem Phloem Transpiration Translocation Movement of water & minerals Movement of dissolved sugar From roots to leaves From 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 Mineral Purpose Deficiency Nitrates Amino acids/proteins for growth Poor growth, yellow leaves Phosphates DNA & cell membranes, respiration & growth Poor root growth & discoloured leaves Potassium Enzymes for respiration & photosynthesis Poor flower & fruit growth, discoloured leaves Magnesium Chlorophyll Yellow leaves 4e Energy flow Food chain – shows transfer of energy Producer – green plant Consumer – organism that eats another organim Pyramid of numbers – the numbers of organisms at each trophic level 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 Method Reduction of energy transfer Problems Pesticides: herbicide, insecticide, fungicide To competing plants & pests Pesticides bioaccumulate in food chains or harm non target organisms Fertilisers Battery farming/fish farming Eutrophication 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 Advantages Disadvantages Minerals added can be carefully controlled Expensive addition of fertilisers Reduced risk of disease Lack of support/anchorage Organic Farming – high quality produce whilst maintaining welfare of animals & minimising environmental impact Advantages Disadvantages Food uncontaminated Less efficient – crops lost Limited soil erosion Manure takes time to rot & doesn’t provide specific balance of minerals Biodiversity promoted Biological 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 Method Explanation Canning Sealed to remove oxygen & prevent entry of microbes Cooling Low temperatures slow growth Drying Reduces moisture needed for growth Preserving (salt/sugar) Conditions are too concentrated for survival Pickling in vinegar Low pH denatures enzymes in microbes 4h Recycling Decay recycles chemicals e.g. carbon & nitrogen Carbon cycle 0.04% CO2 in air 4h Recycling Nitrogen Cycle 78% N2 in air N2 gas is too unreactive to use directly
