Organisms in the Environment

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  • Some glucose produced is used immediately however some is converted into insoluble starch and stored.
  • You can use iodine solutiion to test for starch to show that photosynthesis has taken place in a plant (it will turn a dark blue)
  • most leaves are adapted for photosynthesis: broad (large SA), contain chlorophyll, have air spaces for O and CO2 to move in and out of cells and they have veins to provide plenty of water.

Limiting Factors: 

  • Light
  • Temperature - photosynthesis is controlled by enzymes that are denatured at around 40-50(degrees) so although the rate of photosynthesis will increase as temperature rises, if it gets too hot, it will fall dramatically
  • Carbon Dioxide - levels higher at night because plants still respire but don't photosynthesise (then in the morning CO2 gets used up
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How plants use glucose

Plants use glucose for respiration:


The energy made is used to build smaller molecules into larger ones, turn glucose into starch (or cellulose to strengthen cell walls).

They use some energy to make amino acids (combine sugars with nitrate ions and mineral ions) which are built up into proteins.

Plants and algae also use glucose from photosynthesis and energy from respiration to make fats and oils as an energy store - often in seeds for the new plant as it germinates (or to make walls stronger).

Glucose is made into starch so that it is not soluble in water and won't effect the water balance of the plant. The energy is stored in the leaves (or bulbs/tubules for winter - long periods of time) for at night or when light levels are low.

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Making the most of photosynthesis

Farmers use 'polytunnels' for growing crops as quickly as possible. In these tunnels, it is possible to completely control the environment. You can also grow fruits that you usually wouldn't be able to in the UK, such as lemons, peaches and oranges.

Hydroponics is a system scientists use for growing crops. This means they can even control and create a perfect balance of mineral ions.

It costs a lot of money but turnover is fast so profit is high, the crops are unspoiled and there is no ploughing or preparing land involved. Also, crops can be grown where the land is poor, without a lot of staff!

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Organisms in their environment

Temperature has an affect on photosynthesis and therefore the growth of plants. this mean it will limit the amount of herbivores that can live in that area (e.g. in the Arctic)

Nutrients has a big impact on the distribution of plants. Carnivorous plants thrive where nitrate levels are very low because they can digest animal prey - most other plants struggle to grow in these areas

The amount of light limits photosynthesis and so affects the distribution of organisms. Some plants are adapted to low light areas, with bigger leaves or more chlorophyll. The breeding cycle for some organisms are linked to day length so they will only live and breed in places where the day length and light intensity are right.

The availability of water affects the distribution as it will limit plant growth. After rain, plants will grow and flower and animals will move in to take advantage of this.

Availability of oxygen and carbon dioxide is also a factor. In water, some organisms can live with little oxygen however most need water in order to live. Carbon dioxide levels limit plant growth and also effect organism distribution, e.g. mosquitos are attracted  to animals whose blood is high in CO2.

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Measuring the distribution of organisms

A quadrat (square frame) can be used to sample an area often of 0.25m(squared) in order to measure numbers of plants or animals that move slowly/not at all.

You must choose your sample areas at random and do many of them to make it more valid. You can make them random using a number of techniques, such as a random number generator. You must find the mean and then use this qualititive data to compare distributions in different habitats or over time.

Sampling along a transect - the most common being a line transect - is not random. You stretch a tape measure between two points and, at regular intervals, measure the distribution of organisms using a quadrat. with this technique, you can measure physical factors, such as light levels, soil pH.

You can only use results as evidence if it is reproducible (another person can do the same and get similar/the same results) and valid (must answer the question you're asking).

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