May 22, 2011

4.7 Energy Transfer

4.7 Explain why only about 10% of energy is transferred from one trophic level to the next

This Pyramid of Energy shows that of the 100% of energy from the producer only 10% makes it to the primary consumer and again only 1% of the original amount of energy makes it through to the Secondary consumer.

But Why?
If 100KJ of producer energy was eaten by the primary consumer, only 10% of this (10KJ) will become tissue of that animal. This is because the primary consumer has to travel to find it's food and respire, using up much of the 100kj of energy, What's more not all the energy can be digested by the animal, for example the cellulose and so the energy stored in here simply passes through the animal and is excreted as faeces.
Then the secondary consumer eats the 10KJ of primary consumer, but this animal still must respire and travel using up much of the energy and once again, not all the animal tissue can be digested so not all the energy is reclaimed, resulting in the secondary consumer only receiving 1KJ of the original 100KJ of energy

4.6 Energy and Substances in food chains

4.6 Understand the transfer of substances and of energy along a food chain.

 The producer turns Light Energy to Chemical Energy
  1. This Chemical Energy takes the form of Organic molecules (food)
    • Carbohydrates
    • Protein
    • Lipids
  2. These molecules contain bonds between Carbon, Hydrogen, Oxygen and Nitrogen
  3. These bonds contain Energy
  4. Carbon, Hydrogen, Oxygen and Nitrogen are the substances/matter that is transferred through each stage in the food chain
  5. Along with this, the energy in the bonds between the substances are also passed along to the next animal.

4.5b Food Webs

This Food Web show a much better representation of the full community in an ecosystem.
A food web  shows animals feeding at different trophic levels
meaning that an animal can have
  • Multiple predators
  • Multiple prey
  • Links with other food chains
In the web the producer (grass) is coloured Green, the Primary consumers are Red and the Secondary consumers are Blue.

But the Hawk and the Fox are both secondary and tertiary consumers:
Because, the hawk eats rabbit, a primary consumer, making the Hawk a Secondary consumer, but also feasts on small birds which are secondary consumers themselves, so the hawk is acting at the tertiary consumer level in this case.

4.5a Food Chains

This Food Chain links together the producer to the primary, secondary and tertiary consumer.
There is only ONE organism shown per trophic level.
  Because of this you cannot show an organism being an omnivore and you can't show an organism       feeding at more than two trophic levels
Food chains show the flow of Matter, and the flow of Energy

4.4 Trophic Levels

4.4 recall the names given to different trophic levels...

Trophic means 'of or relating to nutrition'
so a trophic level simply put is a feeding level.
  1. First we have the Producer, these are the plants, they take light energy and turn it into chemical energy
    • An example of this would be Grass.
  2. Secondly we have the Primary Consumers, these are the first animals that eat the plant themselves, commonly known as Herbivores.
    • For example a Grasshopper eats Grass.
  3. Next there are the Secondary Consumers; animals that eat the primary consumer and turn the chemical energy into another form of chemical energy to be used by this animal.
    • i.e. a Frog that eats Grasshoppers.
  4. Finally we have the Tertiary Consumer, they eat the secondary consumer and turn its chemical energy to chemical energy suitable for its own use.
    • Like a Bird of Prey or a Snake.
  5. After any of these organisms die their remains are broken down by a group of organisms called Decomposers.
    • Examples of these would be Fungi and Bacteria.
    • Their job is to recycle the molecules and break down some of the complex molecules of the animals into Nitrates and Phosphates.

4.3 Quadrat Sampling

4.3 Describe the use of the quadrats as a technique for sampling the distribution of organisms in their habitats.

Take the same Sand dune habitat as before, and say we wanted to sample the daisy population.

This sample must be unbiased and representative, meaning that it is of a random area of the region and as large as possible to be more reliable.

The easiest way to do this is to place a grid over the region and number it (like a graph) like below...

  • Then use a random number generator to calculate two integers (one for each co-ordinate) and select the appropriate quadrat.
  • Count the number of daisies in the randomly generated quadrat.
  • And repeat several times in other quadrats until roughly 10% of the total area is covered.
  • Finally find the average results by adding up the total number of daisies counted and dividing by the number of quadrats to give a result of 'so-many daisies per quadrat size'

4.2 Population Estimation

4.2 Recall the use of quadrats to estimate the population size of an organism in two different areas

Take an ecosystem, for example this Sand dune:

The sand dune is bisected into two parts by the fence through the middle, a Grazed area on the left, and an ungrazed region closer to the camera.

To study the population of a region like this a technique is used called quadrating.
A quadrat can be made of any material (inc. String, wood, metal, or plastic like below)
Usually a quadrat is between 0.25m2 and 1m2 in size.
The number of individuals in a quadrat is then counted and this is repeated several times.
And then the results from both regions can be compared.

May 10, 2011

4.1 Ecosystems

4.1 Understand the terms: population, community, habitat and ecosystem.


  • Habitat
    • Abiotic* factors (non-biological factors)
      • Light cycle
      • Temperature
      • Rainfall
      • Humidity
      • Slope
  • Community of Organisms.
    • Populations of different species interacting with one-another
      • Population: Number of individuals of a particular species
      • Species: Organisms that reproduce fertile offspring

*Abitotic: Physical rather than biological; not derived from living organisms

May 2, 2011

The Upcoming Test

Just as a reminder for anyone, we have a test on the 4th May
And the following syllabus statements will be included in it, most of which are explored on this blog or at

2.17-22 Plant Nutrition
2.39-43 Plant Gas exchange
2.51-56 Plant transport
2.67   Plant excretion
2.79-81 Plant sensitivity
3.3-8 Plant reproduction