GCSE B2 Chapter 2

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Photosynthesis

  • Photosynthesis can only be carried out by green plants and algae because they contain the green pigment called chlorophyll which can photosynthesise
  • Carbon dioxide + water + light energy = glucose and oxygen
  • Carbon dioxide is taken in by the leaves
  • Water is taken up by the roots
  • Light energy is trapped by the chlorophyll
  • The light energy is used to convert CO2 and water into glucose
  • Oxygen is produced as a by-product
  • Some of the glucose is converted into insoluble starch for storage

Leaves can be tested for starch by using iodine solution

  • Iodine put on leaf
  • Iodine turns blue-black in presence of starch
  • Parts of leaves that turn blue-black have produced starch
  • They must have been photosynthesisng
  • Only green parts of leaf turn blue-black
  • Showing chlorophyll causes photosynthesis
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Limiting factors

  • Limiting factor: Anything that prevents photosynthesis from happenning any faster
  • Light intensity, CO2 concentration and temperature can all be limiting factors
  • As a limitng factor increases the rate of photosynthesis also increases until another factor becomes limiting
  • As temperature is increased reactions occur faster because particles have more energy. However only up to a certain point. Beyond this the enzymes denature and photosynthesis cannot take place
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How plants use glucose

  • Convert to insoluble starch for storage
  • Use for respiration
  • Produce cellulose in cell walls for support
  • Storage as fats and oils
  • Growth
  • Make proteins
  • Plants also need mineral and nitrate ions in the soil or water in which they grow in. Nitrates are used to produce amino acids which are the building blocks for proteins. 
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Making the most of photosynthesis

  • Plant growers try to give plants the best conditions for growth by controlling environment
  • They can control it by
    • Planting plants in indoor environments such as greenhouses and polytunnels
    • Increasing CO2 concentration
    • Adding parafin lamps which increase light intensity + CO2
    • Adding heaters
    • Adding nitrate and mineral ions to the soil
  • Plant growers must compare the biomass of plants grown with and without these extra factors to decide whether controlling the conditions is cost effective or not. They should evaluate the benefits of increased growth with the increased of costs of the extra factors
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Organisms in their environment

  • Living organisms form communities
  • It is important to understand the relationship within and between these communities
  • These relationships can be infuenced by external factors:
    • Temperature - arctic plants are smaller which means less animals can live there
    • Amount of light - Less light on forest floor, small plants have broader leaves and more  clorophyll
    • Availability of water - all organsims need water to survive, very few organisms can survive in the desert
    • Availability of nutrients - Plants need nutrients to grow, without nutrients few plants can    grow therefore few animals can live there
    • Availability of oxygen - water animals can be affected by lack of oxygen but some  invertabrates can live at low oxygen levels
    • Availability of carbon dioxide - plants need CO2 for photosynthesis, lack of CO2 will reduce amount of plants which survive and therefore the amount of animals in the area
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Measuring the distribution of organisms

  • Quantative data sampling can be used to measure the distribution of organisms and to describe how physical factors may be affecting distribution

Random quantative sampling

  • Quadrat (wooden or metal frame divided into grid) 1m2 
  • Place quadrat down at several points in habitat
  • Count the number of the specific organism in the quadrat
  • Calculate average number of organism in the quadrat
  • Multiply the average by the area of the whole habitat
  • Sample size is very important - sample must be representative of whole habitat

Sampling along a transect

  • Line is marked between two points of a change in habitat
  • Start at one point place quadrat down every 5m and count organisms in it
  • Very useful in finding out about the habitat and the organisms in it
  • Physical factors could also be measured at each quadrat point
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Validity of data

  • A valid investigation is one in which all control variables are kept the same so only the independent variable changes ensuring that the results are purely influenced by the independent variable
  • Repeatable - the same person can repeat the investigation in the same way and the same results are obtained
  • Reproducible - A different investigator repeats the experiment or it is repeated using different method or equipment and same results are obtained
  • Sample size - Larger the sample size the more likely it is to be representative so the more trustworthy the results generated
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