Biology unit 2- organisms in the environment

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Photosynthesis & How Plants Use Glucose

  • Photosynthesis can only be carried out by green plants and algae.
  • Chlorophyll in the chloroplasts absorb light energy
  • CO2 is taken in by leaves, and water by roots
  • Chlorophyll traps the light energyneeded for photosynthesis.
  • The energy is used to conver CO2 and water into glucose.
  • Oxygen is released during this process
  • Some glucose is converted onto insoluble starch for storage.
  • Testing leaves with iodine shows the starch in a leaf. Green patches turn blue-black.
  • The glucose produced can be:
  • converted into insoluble starch for storage
  • Used for respiration
  • Converted into fats and oils.
  • Used to produce cellulose to strengthen cell walls
  • Used to produce proteins
  • Plant and algal cells also need mineral ions e.g. nitrate ions to produce protein.
  • They are absorbed from the soil
  • Algae absorb nitrate from the water they live in.
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Limiting Factors

  • Lack of light slows down photosynthesis as light provides energy for the process.
  • Plants shaded by trees may be limited too, even on a sunny day
  • If cold enzymes don't work effectively and slow down the rate of photosynthesis
  • Too little CO2 will slow down photosynthesis e.g. in a green house on a sunny day, plenty of light but not enough CO2
  • Limiting factor is anything that slows down the rate of photosynthesis
  • When doing photosynthesis experiments you must be aware of other limiting factors when testing one as the others need to be controlled.
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Advantages of Photosynthesis

  • Plant growers control the environments for their plants to get the best results.
  • They have to evaluate the benefits of increasing growth with the increased cost.
  • Greenhouses and polytunnels can be constructed to grow plants in an enclosed space.
  • The greenhouse heaters and lamps increases PhotoSyn but may stop if temp or light temperature is too high.
  • Adding CO2 will also increase photosynthesis
  • Nitrate ions can be added to soil to ensure that plants get the proteins they need.
  • It can be expensive to provide a suitable temperature, light and CO2
  • The grower has to compare the biomass of plants grown inddors and outdoors without these extra factors.
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Organisms In Their Environment

  • Living organisms form communities. The relation between the communities is important to understand.
  • The relationships may be influenced by external factors.
  • Physical factors that may affect the distribution of organisms are:
  • Temperature, e.g. arctic plants are small that limits number of plant eaters in that area.
  • Availability of nutrients, no mineral ions means no plants grow ergo no animals can feed on the plants.
  • Amount of light, few plants on forest floor as light is blocked by trees.
  • Shaded plants often have broader leaves or more chlorophyll.
  • Availablilty of water, no water = no growth = no plants for animals
  • Availability of oxygen, most fish need high levels of oxygen dissolved in water to survive
  • Availability of CO2, no CO2 = no plant growth ergo no food for animals.
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Measuring the Distribution of Organisms

  • Quantative data can be used to describe how physical factors might be affecting the distribution of organisms in a particular habitat
  • Quantative data can be obtained by:
  • Random quantative sampling using a quadrat
  • Sampling along a transect.
  • A quadrat is a square frame made of metal or wood that can be subdivided into a grid.
  • If several quadrats are placed randomly in a field the investigstor can count the numer of plants or animals in each quadrat.
  • This can be used to estimate e.g. daisies in a whole field
  • Sample size is important. ina large field enough random quadrats must be placed to be sure the sample represents the whole field.
  • The estimate amount is usually given as a mean per square metre.
  • Transects are not random. A line is marked between two points.
  • A quadrat can be placed every 5 metres along the line and the organisms counted.
  • Physical factors could also be measured at each quadrat point.
  • This method supplies a lot of info about the habitat and organisms in it.
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How Valid is the Data?

  • Investigations about the distribution of organisms in their environment can be very difficult
  • they are done over a long period of time and not all variables can be controlled.
  • Sample size is an importnat factor in order to get valid, repeatable and reproducible results.
  • If the sample is too small it may not be representative.
  • The larger the sample size, the more we trust we can have in the data generated in an environmental investigation.
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