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Biology Revision B4 It’s a Green World Habitats Plants need different amounts of light, water and minerals. Factors such as soil pH, temperature, light intensity and the availability of water can be measured. Samples are taken to get a picture of what the habitat is like Measurements Quadrats (identification keys; percentage growth) Random (removes bias) Transect (how species change across landscapes) Light meters Mark, capture and recapture Trap animals and mark in a harmless way Release and then recapture Record animals with and without marks number in 1st sample x number in 2nd sample number in 2nd sample with marks Photosynthesis Capturing energy from sunlight, used to make molecules for growth – sugars, starch, enzymes and chlorophyll. These molecules feed others in the food chain Equation 6CO2 + 6H2O light C6H12O6 + 6O2 chlorophyll Glucose is made up of CHO so is a carbohydrate Photosynthesis takes place in chloroplasts. Contain chlorophyll which absorbs light and uses the energy to start photosynthesis Energy from light splits water molecules into H2 and O2 atoms. The H2 is combined with CO2 from the air to make glucose. O2 is released as a waste product Glucose and Starch Glucose can be converted into starch for storage or cellulose to make new cell walls. Both are polymers of glucose Glucose can also be built up into fats, proteins and chlorophyll Glucose molecules are broken down by respiration, releasing energy to power chemical reactions in cells Storage Glucose made by photosynthesis Glucose transported from leaves together cells where is stored until it is needed for respiration. Water would move to this area unless stored as starch Insoluble starch grains 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. Diffusion Molecules of liquids and gases move around randomly, collide with each other and spread out. They move from areas of high to low concentration Passive process To increase diffusion: Greater conc gradient Shorter distance Larger surface area Osmosis Special type of diffusion Move water molecules in and out of cells across a partially permeable membrane Water moves from area of high concentration to area of low concentration of water molecules Drives uptake of water Lack of water - wilting 4b Water, water everywhere? Effect of osmosis on plant cells: Inelastic cell wall provides support & prevents cell bursting 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 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 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 Need Nitrogen! Proteins are long chains of amino acids Nitrogen needs to be combined with carbon, hydrogen and oxygen from glucose made in photosynthesis Absorbed from soil as nitrate ions Absorbed by root hair cells What else do plants need? Magnesium to make chlorophyll Phosphates to make DNA Proteins are needed to build cells and make enzymes, so nitrates are needed in the highest quantities Fertilisers contain minerals such as phosphates and nitrates 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 Active Transport Nitrate ions are at a higher concentration inside the root cells, compared to the surrounding soil Diffusion should move ions out into soil. Plants use active transport to overcome this Cells use energy from respiration to transport molecules across the membrane Yields The amount of product a farmer has to sell Limiting factors of photosynthesis – temperature, light intensity, carbon dioxide, water and chlorophyll Stomata may close to conserve water, but stops carbon dioxide entering the leaf 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
