AQA Additional Science B2 Part 2

  1. Photosynthesis
  2. Limiting Factors
  3. How Plants use Glucose
  4. Making the most out of Glucose
  5. Organisms in their Environment
  6. Measuring Distribution of Organisms
  7. How Valid is the Data
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  • Only Carried out by green plants and algae
  • Chlorophyll in the chloroplasts absorbs Light Energy
  • Photosynthesis equation:

 carbon dioxide + water (+ light energy)    →    glucose + oxygen

Process for photosynthesis is; 1) CO2 is taken in by leaves, water is aborbed by the roots;  2) The chlorophyll traps light energy needed for photosynthesis; 3) Energy used to convert CO2+H2O into Glucose (C6 H12 O6).

  • oxegen is a by-product of process
  • Some glucose converted into insoluble starch for storage
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Limiting Factors

  • Lack of light would slow down rate of photosynthesis as light provides energy for process, even on sunny days light can be limited to plants that are shaded by trees.
  • If it is cold, enzymes don't work efficiently and therefore slow down rate of photosynthesis.
  • If there is too little carbon dioxide, then rate will slow down. CO2 could be limited in a enclosed space e.g. a greenhouse.
  • Anything that puts a cap on rate of photosynthesis is a limiting factor
  • Independant Variable is one being tested
  • Dependant Variable is the one you measure
  • The Controlled variables in this context include light, temperature and the type of plant being used.
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How Plants use Glucose

Uses of Soluble Glucose

The Glucose produced by photsynthesis may be:

        • Converted into insoluble starch for storage
        • used for respiration
        • converted into fats and oils for storage
        • used to produce cellulose which strengthens cell walls
        • used to produce proteins

Plants and algal cells also need a supply of mineral ions such as nitrate ions in order to produce protein. Plants absorb nitrate ions from the soil. Algae absorb nitrate ions from the water they live in. 

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Making the most out of photosynthesis

  • Plant growers give plants best conditions for growth by conolling the enviroment
  • They evaluate benefits of increasing growth, with increased cost of heating & lighting or from providing carbon dioxide
  • Greenhouses & polytunnels constructed to grow plant in enclosed space if greenhouse has heaters & lamps the rate of photosynthesis will increase but may stop if temperature or light intesity is too high. By adding CO2 into the air in the greenhouse the rate of photosynthesis will increase, Nitrate ions are added to the soil to ensure plants can make proteins for healthy growth
  • Can be expensive to provide suitable temperature, light and carbon dioxide. The grower has to compare the biomass of plants grown indoors & outdoors without extra factors
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Organisms in their Enviroment

Physical factors that affect the distribution of organisms are;

  • Temperature - e.g. arctic plants are small which limits number of herbivores which can survive in the area
  • Availability of nutrients - most plants struggle to grow in areas where mineral ions are short supply
  • Amount of light - few plants live on a forest floor because light is blocked out by the trees, shaded plants usually have broader leaves or more chlorophyll
  • Availability of Water - water important to all organisms so few will live in the desert. If it rains in the desert, the plants grow, flower, and seed very quickly, meaning food for animals
  • Availability of Oxygen - water animals can be affected by lack of oxygen. Some invertebrates can live at very low oxygen levels, but most fish require high levels of oxygen dissolved in water
  • Availability of Carbon Dioxide - lack of carbon dioxide affects plant growth and consequently the food available for animals
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Measuring the Distribution of Organisms

Quantative Data can be used to describe how physical factors might affect the distribution of organisms in a partcular habitat

Quatative data obtained by; 

  • Random quantative sampling using a quadrat
  • sampling along a transect

A quadrat is square frame made from metal or wood which can be subdivided into a grid

Sample size is important. in alarge field enough random quadrats must be placed to be sure the sample is respresentative of the whole field

An estimate of e.g. daisies is usually given as a mean per square metre

A transect is not random. a line is marked between 2 points, and then a quadrat can be placed every 5 metres down the line for example. 

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Validity of the data

  • Investigations about the distribution of organising in their environment can be very difficult. That is because they are often done over along period of time and not all variables can be controlled.
  • if a transect is made at a beach during the morning, a comparative investigation must be good at the same time of day even if it's two months later. The time of day is a control variable. In a valid investigation all possible variables must be controlled.
  • A measurement is repeatable if the original experimenter repeats investigation using the same method and equipment and obtains the same results. However, sometimes experimenter maybe making the same mistake every time and get repeatable results. So it may also be necessary to check the results to ensure they are reproducible.
  • A measurement is reproducible if the investigation repeated by another person or by using different equipment or techniques, and the same results are obtained.
  • Sample size is an important factor in order to get valid, repeatable and reproducible results. If the sample is too small it may not be representative. So the larger the sample size, the more trust we can have in the data generated in an environmental investigation.
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