5.1 Ecosystems & Energy Transfer

The diagram below shows the net production of different trophic levels in a food chain.

State the equation for the net primary production of the grass.

The deer in the diagram above ingest 17 874 kJ m^-2 yr^-1 of food. The net productivity of consumers, such as deer, can be calculated using the following equation:

N = I - (F + R)

Where:

• I = the chemical energy stored in ingested food
• F = the chemical energy lost to the environment in faeces and urine
• R = the respiratory losses to the environment

Use the equation and information given in part (a) to calculate the total energy loss of the deer.

In the diagram, given in part (a), the net production of the deer is less than the net primary productivity of the grass.

Explain why.

The food chain shown in part (a) has three trophic levels. 

Explain why it is rare to find a natural food web or chain with more than five trophic levels. 

Communities are important parts of an ecosystem.

What is meant by an ecological community? 

Mountains are harsh environments.  A group of ecologists investigated a range of factors in a forest on the south-facing slope of a mountain. The higher up the mountain, the lower the temperature becomes. The upper boundary of the forest is called the tree line. Trees do not grow above the tree line.

The table below shows the data collected by the ecologists using 1m² frame quadrats. 

State which of the factors measured are abiotic.

(1)

Other than those in the table, suggest one abiotic factor that is likely to affect the position of the tree line on the mountain.

(1)

Name two biotic factors the ecologists could have measured.

(1)

Describe how the ecologists could obtain the value for vegetation cover in each quadrat.

The ecologists noticed that the density of some plant species on the mountain side appeared to differ depending on how far the plants were from the tree line.

The mean density of plants of species A, B and C was measured at different distances from the tree line. 

The results of this investigation are shown below. 

Comment on the relationships between different plant species' density and the distance from the tree line.

A gardener noticed earthworms in their garden occupied different areas and habitats. Samples were collected from their garden from within the soil underground and from debris and leaf litter above the ground. Earthworms of two different species were found. 

The results are shown in the table below. 

State which species of earthworm showed the greatest variation within the sample. Give evidence from the table for your answer.

Describe evidence from the table which suggests that the two species of earthworm occupy different ecological niches.

Explain the advantage of the two species of earthworm occupying different ecological niches.

The gardener further investigated the populations of Allolobophora chlorotica and the following data was collected.

The gardener concluded that the deeper the soil the greater the number of Allolobophora chlorotica.

Evaluate the gardener's conclusion.

Ecosystems are considered to be sustainable.

Which of the descriptions below explains this? 

A student wanted to investigate the distribution of Taraxacum officinale, the dandelion, growing along a roadside. They hypothesize that the nearer to the roadside the less dandelions would be found.

Identify the null hypothesis for this investigation.

(1)

Devise an investigation to measure the distribution of dandelion along a roadside. 

(6)

The dandelions along the road side had a combined dry mass of 18 kg. The dandelions were eaten by rabbits that had a collective dry mass of 1500 g.

Calculate the percentage efficiency of biomass transfer in this step of the food chain. Give your answer to two significant figures.