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Life on Earth


An ecosystem can be defined as the interactions which take place between living and non-living organisms in a particular area.

Ecosystems are made up of a number of different components such as habitats, populations and communities.

Habitats – a place where an organism lives.

Population – a group of organisms made of one species.

Community – all of the living things found in one ecosystem.

species can be  defined as a group of organisms which can interbreed to produce fertile offspring.

Having been introduced to the wide variety of ecosystems, each group carried out some research into the organisms found in that habitat and how they behave.   They also learned about human behaviour which has positive or negative affects on that ecosystem.

If you have missed class this week, you will find the notes that you need below;


There are some excellent videos about ecosystems on from Twig on Glow.  Just follow the link.


Sampling techniques

Once we understood what an ecosystem was we then moved on to investigating ecosystems ourselves.  We discovered that both biotic and abiotic factors can be investigated.

Biotic factors are factors which relate to living things in the ecosystem.  Such as disease, competition, predation and grazing.

Abiotic factors are non-living factors which affect the ecosystem.  These include light intensity, moisture levels and pH.

Quadrats can be used to sample plants and slow moving insects.  It can be used to count the abundance or the number of organisms in a certain area.  When counting the abundance, the squares in which a buttercup is found should be counted.  When counting the number of buttercups, the total number of buttercups in the quadrat should be counted.

Pitfall traps can also be used to sample ground living invertebrates such as woodlice, beetles and centipedes.

light meter can be used to measure the light intensity in an ecosystem. Errors include, standing in the way of the light.  This can be overcome by ensuring that the observer stands to one side, out of the light.

Addition and Removal of Organisms

Ecosystems can also be greatly effected by the addition or removal of organisms.  However, before we can understand why this addition and removal has such a great effect we must learn about food chains and food webs.

An example of a food chain can be seen below;

The arrows in this food chain demonstrate the flow of energy from one organism to another.  A number of words can be used to describe the organisms found in a food chain.

Producer – an organism which produces it’s own energy through the process of photosynthesis.

Consumer – an organism which obtains energy by eating other organisms.

Herbivore – an organism which only consumes producers.

Carnivore – an organism which eats consumers.

Omnivore – eats consumers and producers.

When a number of different food chains are put together a food web is formed.  An example of  a food web can be seen below;

Food web

1. Pick out a food chain containing 3 organisms from the food web.

2.  How might the other organisms be affected is the barnacles are removed?

A fabulous video which can be used to investigate the effects of adding or removing organisms can be seen below;

This video in conjunction with the Upd8 websites lesson plan is thoroughly enjoyable for the pupils and really helps them to understand.

To finish off this section we did a little research into the re-introduction of beavers to Scotland.  The pupils have completed this research individually and wrote a short paragraph outlining the effects of this re-introduction on biodiversity.  This piece of writing was the classes first attempt at passing Outcome 2.3 in National 4 Biology.

Beaver Reintroduction

Finally, the class carried out an investigation into competition between cress seeds to practice there practical write-up for National 4 Biology.  Well done to those of you who completed this successfully!

If you have missed any notes through absences, this powerpoint might help;

Energy in Ecosystems N4

Human Impact on Biodiversity

Having learned about ecosystems and how to sample from them, we moved on to learn a little about how humans can have an impact on ecosystems.

Humans are primarily affecting ecosystems because the world’s population is ever-increasing.  This means that the demands which are being placed upon the Earth by humans are also increasing.

The only way in which this demand can be measured is by measuring our ecological footprint.

•An ecological footprint is a measure of human demand on the Earth’s ecosystems.
One example of an ecological footprint is our carbon footprint.  We used an excellent website called;


It was interesting to see the huge impact which travelling to and from school has on our carbon footprint.

Human Impact Research

The class then moved on to investigate particular examples of the ways in which humans impact biodiversity.  They could choose from subjects such as; deforestation,  oil spills and over-fishing.

We have learned now that all 3 of these have a negative impact on biodiversity.  This was a useful opportunity for the class to attempt a short scientific report for Outcome 2.3 which they did very successfully.

Having carried out more general research we learned in particular about the pollution of water as a result of sewage.  A summary note can be found below;

Water Pollution

Natural Hazards

To learn about natural hazards, the class watched a video about Natural Hazards from Dorling Kindersley.  They then filled in a table of the examples of natural hazard and the effect which they had on biodiversity.  Try to complete the table below;

Natural Hazards table


To finish off our work on the way humans can impact biodiversity, we looked at the positive impact which humans can have with regard to conservation.

The pupils watched a video clip about whether or not we should save the Panda.

They then read an article about a variety of opinions with regard to conservation.  At the end of the lesson, the majority of the class were still backing the Panda!!

If you have any notes to catch up on or you still need to practice your problem solving skills;  please use the powerpoint below.

Human Impact

Fertilisers and the Nitrogen Cycle

There are two main types of fertiliser available; natural or artificial.  Natural methods of adding nutrients to the soil include spreading manure or planting clover to fix nitrogen into the soil.  Artificial fertilisers involve the use of chemicals which contain nitrogen, phosphorus and potassium, N, P and K.


Natural fertilisers can cost less since they do not need to be bought in to the farm.  However, others would argue that the production of sufficient manure costs more since the cattle need to be fed.

When chemical fertilisers leach into the water they cause an algal bloom to develop.  Nitrogen from the fertilisers seeps into the fresh water causing an increase algal growth, blocking out the light. This causes death of organisms, which are decomposed by bacteria.  The bacteria use up the oxygen. The decrease of oxygen and means less life can be supported.

The Nitrogen Cycle

Nitrogen which is added to the soil in fertilisers is cycled through an ecosystem since their is a limited supply of it.  The image and sequence below summarise the main steps;

Nitrogen Cycle

  1. Nitrogen is fixed from the atmosphere by bacteria in root nodules to form nitrates.
  2. Plants take nitrates from the soil and form proteins.
  3. Animals eat the plants and use the nitrates to form proteins.
  4. Plants and animals die.  Protein is decomposed by bacteria into ammonium compounds in the soil.
  5. Nitrifying bacteria convert ammonium into nitrites.
  6. Other nitrifying bacteria convert nitrites into nitrates in the soil.
  7. Denitrifying bacteria convert nitrates in the soil back into nitrogen in the atmosphere.

Remember;   Am orite mate to help in remembering Ammonium, nitrite, nitrate.

Try watching the nice wee video on Twig Glow for help;  http://www.twigonglow.com/films/the-nitrogen-cycle-1224/

Again, if you have missed any work in class time, you should find the notes below;



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