BioAdditional Organisms in the Enviroment

What is Photosynthesis? Photosynthesis is the chemical change which happens in the leaves of green plants. It is the first step towards making food - not just for plants but ultimately every animal on the planet.  During photosynthesis:

• Light energy is absorbed bychlorophyll, a green substance found inchloroplastsin some plant cells and algae
• Absorbed light energy is used to convert carbon dioxide (from the air) and water (from the soil) into a sugar calledglucose
• Oxygen is released as a by-product

This equation summarises what happens in photosynthesis:

Some glucose is used for respiration, while some is converted into insolublestarch for storage. The stored starch can later be turned back into glucose and used in respiration.

Three factors can limit the speed of photosynthesis: light intensity, carbon dioxide concentration and temperature.

• Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis.
• Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide.
• If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot.

• If you plot the rate of photosynthesis against the levels of these three limiting factors, you get graphs like the ones above.

In practice, any one of these factors could limit the rate of photosynthesis.

Farmers can use their knowledge of factors limiting the rate of photosynthesis to increase crop yields. This is particularly true in greenhouses, where the conditions are more easily controlled than in the open air outside: 

The use of artificial light allows photosynthesis to continue beyond daylight hours. Bright lights also provide a higher-than-normal light intensity.

• The use of artificial heating allows photosynthesis to continue at an increased rate.
• The use ofadditional carbon dioxidereleased into the atmosphere inside the greenhouse also allows photosynthesis to continue at an increased rate

However, the additional cost of providing extra lighting, heat and carbon dioxide has to be weighed against the increased crop yield and the extra income it will provide. The cost of should not exceed the additional income it generates for the farmer. In practice, the farmer will need to find the optimum growing conditions for the crop, given the costs of providing extra lighting, heat and carbon dioxide. Paraffin lamps have traditionally been used in greenhouses. Their use increases the rate of photosynthesis because as well as the light generated from the lamps, the burning paraffin produces heat and carbon dioxide too.

The glucose produced in photosynthesis may be used in various ways by plants and algae.

Storage

Glucose is needed by cells for respiration. However, it is not produced at night when it is too dark for photosynthesis to happen. Plants and algae store glucose as insoluble products. These include:

• Starch
• Fats and oils

Use

Some glucose is used for respiration to release energy. Some is used to produce:

• Cellulose - which strengthens the cell wall
• Proteins - such as enzymes and chlorophyll

Plants also need nitrates to make proteins. These are absorbed from the soil as nitrate ions.

The distribution of living organisms in a particular habitat may be affected by physical factors such as temperature and amount of light. Transects and quadrats are used to help collect quantitative data about organisms in their habitats. The collected data can be analysed to find the mean, median and mode values of organisms in a particular area. The physical factors that may affect organisms include:

• Temperature
• Amount of light
• Availability of water
• Availability of nutrients
• Availability of oxygen and carbon dioxide.

For example: more grass plants are found in the full sunlight of a field rather than in a semi-shaded area or in shady woodland. This is because grasses need a lot of light energy to photosynthesise.

The distribution of living organisms in a particular habitat may be affected by physical factors such as temperature and amount of light. Transects and quadrats are used to help collect quantitative data about organisms in their habitats. The collected data can be analysed to find the mean, median and mode values of organisms in a particular area. The physical factors that may affect organisms include:

• Temperature
• Amount of light
• Availability of water
• Availability of nutrients
• Availability of oxygen and carbon dioxide.

For example: more grass plants are found in the full sunlight of a field rather than in a semi-shaded area or in shady woodland. This is because grasses need a lot of light energy to photosynthesise.

Key Terms - for Ecosystems

Enviroment = All the conditions that surround a living organism

Habitat = The place where an organism lives

Population = All the members of a single species that live in a habitat

Community = All the populations of different organisms that live together in a habitat

Ecosystem = A community and the habitat in which it lives

• Transects - A transect is a line across a habitat or part of a habitat. It can be as simple as a string or rope placed in a line on the ground. The number of organisms of each species can be observed and recorded at regular intervals along the transect.
• Quadrats - When using a quadrat:A quadrat is usually a square made of  wire. It may contain further wires to mark off smaller areas inside, such as 5 x 5 or 10 x 10 squares. The organisms underneath, usually plants, can be identified and counted.

• It should be placed randomly so that a representative sample is taken
• The validity and reproducibility of the results increases as the results from more quadrats are analysed

Quadrats may also be used for slow-moving animals such as slug and snails.

Mean

To calculate a mean value:

• Add the numbers together and divide the total by the amount of numbers

Median

The median is the middle number. To calculate a median:

• Put all the numbers in numerical order
• If there is an odd number of results, the median is the middle number
• If there is an even number of results, the median will be the mean of the two middle numbers

Mode

The mode is the number which occurs most often in a set of data.