Biology unit 2- organisms in the environment

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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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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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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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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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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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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