Biology - B2.2 - Organisms In the Environment

B2.2.1 - Photosynthesis

  • Photosynthesis can only be carried out by green plants and algae
  • Chlorophyll in the chloroplasts absorbs the Sun's light energy
  • Carbon dioxide + water ->light energy-> glucose + oxygen
  • Process for photosynthesis - CO2 taken in by leaves and H2O taken in by roots -> chlorophyll traps light energy -> energy is used to convert the CO2 and H2O to glucose
  • Oxygen - by-product
  • Some glucose changed into insoluble starch for storage
  • Testing leaves with iodine solution - identify starch in leaf and show photosynthesis occured - variegated leaves have green (with chlorophyll) patches and white (without chlorophyll) patches - only green patches turn iodine blue/black - presence of starch
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B2.2.2 - Limiting Factors

  • Lack of light - slow down photosynthesis as light provides energy for process - sunny days, plants may be limited by shade
  • Cold - enzymes don't work effectively - slow down photosynthesis
  • Lack of CO2 - slow down photosynthesis - limited in a closed space eg. greenhouse - sunny day - plenty of light, not enough CO2
  • Anything stopping photosynthesis = limiting factor
  • When doing photosynthesis experiments - limiting factors must be controlled - variables to be controlled: light, temperature and type of plant
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B2.2.3 - How Plants Use Glucose

  • Uses of soluable glucose - glucose produced by photosynthesis may be:
    • converted to insluble starch for storage
    • used for respiration
    • converted to fats and oils for storage
    • used to produce cellulose - strengthens cell walls
    • used to produce proteins
  • Plant and algae cells - also need supply of mineral ions - eg. nitrate ions - to produce protein - absorb nitrate ions from soil or water they live in
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B2.2.4 - Making the Most of Photosynthesis

  • Plant growers ontrol environment - give plants best growing conditions - have to evaluate benefits of increading growth with increased cost of heating, lighting or producing CO2
  • Greenhouses and polytunnels - constructed to grow plants in enclosed space - may have heaters and lamps to increase photosynthesis, but may stop if too hot or too much bright
  • CO2 added to the air to increase photosynthesis
  • Nitrate ions added to soil so plants can make proteins needed for growth
  • Expensive to produce suitable temperature, light and CO2 - must compare biomass of plants grown inside and outside without extra factors
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B2.2.5 - Organisms In Their Environment

  • Living organisms form communities - relationships between and within communities - can be influenced by external factors
  • Physical factors affecting distribution of organims:
    • Temperature - small plants = limited number of plant eaters
    • Nutrients - short supply of mineral ions = less plants = less animals
    • Light - few plants live on forest floor - shade - shaded plants have broader leaves or more chlorophyll
    • Water - desert - when it rains, plants grow, flower and seed quickly - food for animals
    • Oxygen - water animals affected by low oxygen - some invertabrates can live at low oxygen levels but most fish need high levels
    • CO2 - low CO2 will affect plant growth = less animal food
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B2.2.6 - Measuring the Distribution of Organisms

  • Quantative data - used to describe affect of physical factors on distribution of organisms in a particular habitat - obtained by: random quantative sampling using a quadrat or sampling along a transect
  • Qudrat - square frame - may be subdivided into a grid - several quadrats placed randomly in a field, investigator counts number of a particular plant or animal - used to estimate no of (eg.) daisies in a field
  • Sample size - enough quadrats placed to be representative of entire area
  • An estimate is usually given by x mean/sq m
  • Transect - not random - line marked between two points -> quadrat placed at regular intervals down line -> organisms counted - physical factors could also be measured at each point - supplies lots of information about habitat and organisms in it
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B2.2.7 - How Valid Is the Data

  • Difficult to experiment on distribution of organisms - done over long period of time - uncontrollable variables
  • Transect made - comparative investigation must be done at same time of day - control variable
  • Valid investigation - all possible variables must be controlled
  • Repeatable - same experimenter does same thing with same equipment and gets same results - may make mistake both times
  • Reproducible - different person or different equipment and techniques are used and get same results
  • Sample size - needed for valid, repeatable and reproducible results - too small = not representative - larger sample size = more trusted data
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