Biology

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ECOLOGY IN THE LOCAL ENVIRONMENT

  • Ecosystem: made up of all plants and animals and their surroundings, an ecosystem is self supporting because gases are exchanged during respiration and photosynthesis so there is an overall balance of the gases, also a food chain is created
  • Habitat: where a plant or animal lives
  • Community: all animals and plants living in its habitat
  • Biodiversity: variety of different plants and animals

Natural ecosystem (lake, woodland etc) - good biodiversity

Artificial ecosystem (fish farms) - bad biodiversity - only have one species of animal

  • transect line: length of string laid across area to show zonation of species, show abiotic (not biological) factors such as trampling on a path
  • quadrat: placed at regular intervals along transect line

Capture re-capture: Population size = no. in 1st sample x no. in 2nd sample / no. in 2nd sample previously marked

Assumes: no deaths, reproduction, migration, immigration, identical sampling methods, markings dont affect survival of animal

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PHOTOSYNTHESIS

6CO2 + 6H2O ----> C6H12O6 + 6O2  (energy + cholorophyll also needed)

Water split by light releasing O2 and H+, CO2 combines with H+ to produce glucose and H2O

glucose can be:

  • used in respiration - releasing energy
  • converted into cellulose - cell walls
  • converted into proteins - growth + repair
  • converted into starch, fats + oils - for storage (insoluble, doesnt move from storage areas, doesnt affect water concentrations and cause osmosis)

Greeks believed plants took minerals from soil to grow and gain, Van Helmont concluded it must depend on something else, Priestley showed plants produce oxygen (jar experiment), Moderns can prove water is split by light not CO2, isotopes are different forms of the same element

  • photosynthesis increased by: more CO2, more light, higher temp (more enzyme action)
  • photosynthesis only takes place at daytime but plants respire all the time
  • respiration can only be recognised at night due to gas exchange in photosynthesis being more than that of respiration
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LEAVES AND PHOTOSYNTHESIS

  • outer epidermis - lacks chloroplasts and is transparent so no barriers for light
  • upper palisade layer - contains most chloroplasts as will receive most light
  • spongy mesophyll cells - loosely spaced for diffusion of gases between cells also large surface area/volume for gas diffusion, it's covered in a film of water in which gases can dissolve
  • waxy cuticle - prevents water loss which could cause wilting
  • stomata - where water can escape (water loss reduced by fewer, smaller and position)

Leaf adaptations: (book)

  • broad - large surface area for more light
  • thin - gases can diffuse and cells can get light easily
  • chlorophyll a and b and other pigments (carotene and xanthophylls) so can get light from a wide spectrum, each pigment absorbs light at different wavelengths
  • vascular bundles (veins) - support and transport oof chemicals such as water and glucose
  • guard cell - control open and closing of stomata regulating flow of CO2 and O2 and stopping water loss, contain chloroplasts so photosynthesis will produce sugars, due to different thicknesses the guard cells curve - opening the stomata
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DIFFUSION AND OSMOSIS

Diffusion: particles move from high concentration to low concentration, H2O, O2 and CO2 can enter and leave cells through cell membrane. If a plant uses CO2 there is lower conc' inside cell

Rate of diffusion increased by:

  • shorter distance for molecules to travel
  • steeper concentration gradient
  • greater surface area for molecules to diffuse from or into

Osmosis: relies on presence of partially permeable membrane that allows passing of water but not glucose - osmosis is movement of water from high conc' to low conc' (lots of molecules to few molecules) - osmosis is a consequence of random movement of water molecules

turgor pressure: supports cell from collapsing, if water leaves cell this pressure decreases

turgid = cell full of water, plasmolysed = loses water (flaccid)

Animal cells do not have a supporting cell wall so if too much water enters it will burst (lysis) and if too much leaves it will show crenation

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TRANSPORT IN PLANTS

(w)Xylem = water, phloem = food      - these form vascular bunded in broad leaved plants

  • Xylem are dead cells that are hollow lumen due to no cytoplasm, their cellulose walls have extra thickening of lignin = great strength and support
  • Ploem are living cells and arranged in columns

Transpiration: evaporation and diffusion of water from inside the leaves 

Root hairs: produce large surface area for water uptake by osmosis

Water needed for: cooling by evaporation, photosynthesis, support from cells' turgor pressure and for transport of minerals

Transpiration increased by:

  • light intensity - opens stomata
  • increased temp - causes increase in evaporation of water
  • increased air movement - blows away air containing evaporated water
  • decrease in humidity - allowing more water to evaporate
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PLANTS NEED MINERALS

Plants need minerals such as:

  • nitrates (nitrogen used) - to make  amino acids which form proteins for cell growth
  • phosphates (phosphorous used) - respiration and growth - make DNA which contains plants genetic code and cell membranes
  • potassium compounds (potassium used) - respiration and photosynthesis - enzyme action to speed up both
  • magnesium compounds (magnesium used) - photosynthesis - makes chlorophyll

Lack of:

  • nitrates = poor growth and yellow leaves
  • phosphate = root growth and discoloured leaves
  • potassium = poor flower and root growth and discoloured leaves
  • magnesium = yellow leaves

Active transport: enables minerals present in soil in low concentrations to eneter root hairs already containing higher amounts of minerals, this uptake that works against the concentration gradient requires energy from respiration

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DECAY

Detritivores: feed on dead and decaying material (detritus) increase rate of decay by breaking up detritus = increase surface area

Rate of Decay increased by:

  • temperature- Optimum = 37 c for bacteria and 25 c for fungi  
  • Amount of oxygen - for arobic respiration to grow and reproduce faster
  • Water - Allow material to be digested and absorbed to increase growth and reproduction of detritivores

Saprophyte: Eg fungus = organsims which feed on dead and decaying 

Extracellular digestion: fungi produce enzymes to digest food outside cell then reabsorb simple, soluable substances

Food preservation  

  • Canning: prevent entry of bacteria and oxygen
  • Cooling: slow down bacterial and fungal growth and reproduction
  • Freezing: Kill bacteria and fungi and slow down  ^
  • Drying: removes water so can't feed and grow 
  • Salt or sugar: Kill ^^ as removes water
  • Vinegar: produce acidic conditions killing most ^^^
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FARMING

disadvantages of pesticides, insecticides, fungicides and herbicides:

  • enter and accumulate in food chains
  • harm other organisms which are not pests
  • some take ages to break down

Organic farming: doesn't use artificial pesticides or fertilisers, instead uses manure and compost, crop rotation to avoid soil pests and varying seed planting times to get a longer crop time and avoid certain times of life cycle of insect pests - reduces disadvantages but produce pricey and small crops

Biological control: uses living organisms to control pests, once introduced dont often need replacing, problems such as species eating other useful species and showing rapid increase in their population and becoming pests (cane toads in Australia)

Intensive farming:  which makes use of artificial pesticides and fertilisers however methods raise concern about animal cruelty as animals kept in small area, but improves efficiency of energy tansfer, less energy goes into movement, more into growth

Hydroponics: type of intensive farming that doesnt use soil, water and nutrients flow over roots, used in places with barren soil and low rainfall - better control over mineral levels and disease

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