Biology Revision

1. Biology Revision B4 It’s a Green World

2. 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.

3. 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

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

5. 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

6. 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

7. 4c Transport in Plants • Vascular bundles – arrangement of xylem & phloem

8. 4d Plants need minerals too • Minerals are absorbed by root hairs by active transport – using energy from respiration to move substances against concentration gradient

9. 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

10. 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

11. 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

12. 4f Farming • Intensive Farming – to produce as much food as possible from the land, plants & animals available • Improves energy transfer efficiency

13. 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

14. 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

15. 4g Decay • Rate effected by: • Temperature – microorganisms work best at 40°C, but enzymes denatured above this • Oxygen – needed for respiration • Water – grow best in moist conditions • Food Preservation

16. 4h Recycling • Decay recycles chemicals e.g. carbon & nitrogen • Carbon cycle 0.04% CO2 in air

17. 4h Recycling • Nitrogen Cycle 78% N2 in air N2 gas is too unreactive to use directly