Understanding Plant Biology: Leaf Structure to Energy Flow

1. Module B4 It’s a Green World

2. Transparent Structure of a Leaf Chloroplasts Diffusion Internal SA/volume ratio large Osmosis : flaccid, plasmolysed, turgid –H = crenation, lysis Transpiration: cooling, photosynthesis, support, movement of minerals, stomatal apertures – guard cell turgidity and number

3. Xylem –hollow lumen, dead cells - water Phloem – column of living cells- food substances Transpiration –evaporation and diffusion of water - from roots to shoots and leaves – light intensity, temp, air movement, humidity Translocation - to stems and storage tissues Vascular bundles

4. Minerals – active transport (low to high, uses energy) through root hairs Nitrogen/nitrates = amino acids – proteins for cell growth – Yellow leaves & poor growth Phosphorous/phosphates = synthesis of DNA, cell membranes for respiration & growth – poor roots, discoloured leaves Potassium - enzymes in photo. & respiration – poor flower and fruit growth, discoloured leaves Magnesium = make chlorophyll for photo. – yellow leaves

5. Energy Flow Pyramids of number and biomass Effect of removing one organism from a web or chain Energy is transferred at each trophic level – heat from respiration and egestion – calculate efficiency of energy transfer Biomass - burning trees, fermenting biomass – renewable, reduces pollution, energy self-reliance – uses: food for people/livestock, fuel, growing seeds

6. Farming Intensive - producing as much food as possible – improves energy efficiency by energy not going to : competing plants, pests, lost as heat or movement (pens) Pollution – pesticides in food chain (bioaccumulation), harming non-pests Hydroponics - uses glasshouse tomatoes, barren soil – adv. Control of disease, control of mineral levels – disadv. Lack of support, addition of fertilisers Organic Farming - uses manure & compost, crop rotation, legumes, weeding, varying seed planting times, biological control(adv, & disadv.)

7. Decay Rate of decay is affected by: temp, amount of oxygen, amount of water – these factors affect microbial respiration, growth and reproduction (producing sewage & compost) Detritivores (earthworms, maggots, woodlice) feed on detritus (dead/decaying material) – produce larger surface area- increase rate of decay Saprophyte – live on dead organic matter e.g bacteria & fungi Food preservation - canning, cooling, freezing, drying, salt/sugar, vinegar

8. Recycling Nutrients recycled through death and decay are Carbon and Nitrogen

9. Air is mainly composed of Nitrogen (78%), but is too unreactive to be used

10. Higher only Carbon is recycled in the sea – marine organisms make shells of carbonates – shells= limestone – carbon returns to CO2 through weathering and volcanic eruption. Nitrogen – decomposers convert protein & urea to ammonia, nitrifying bacteria convert ammonia to nitrates, denitrifying bacteria convert nitrates to N gas – nitrogen fixation occurs due to lightning or bacteria in root nodules