Energy in ecosystems

This food web comes from an African ecosystem.

What is meant by the term ecosystem ?

Identify all the producers in this food web.

Give the trophic level of the lion in this food web.

Name an organism that occurs at two different trophic levels in this food web.

Give the food chain from this web that contains four different organisms including the baboon.

Explain why the number of organisms usually decreases along a food chain.

The diagram shows a food chain.

How many consumers are shown in this food chain?

What term describes the trophic level of the snake?

Light is an abiotic (non-living) factor that affects the growth of maize.

Explain the role of light in helping the growth of maize.

Scientists measured the average (mean) daily increase in mass of maize in a square metre of a field in two different regions of the world. They also measured the daily light energy available in a square centimetre of each of the two regions. The table shows their results.

The scientists expected that the same light energy would produce the same average daily increase in mass of maize in each region of the world. However, the results show that the average daily increase in mass of maize produced in the UK was less than they expected. Calculate the average daily increase in mass the scientists expected to be produced in the UK.

average increase in mass =_........

The scientists concluded that factors other than light must be limiting the growth of maize in the UK. Name two other abiotic factors that could limit the growth of maize.

Give three reasons why not all of the energy available in the maize is transferred to the snake.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow. Omega-3 Excess lipids (fats and oils) in the human diet can increase the risk of health problems such as obesity, heart disease and strokes. However, a balanced diet needs to contain fats and oils because they are needed in the human body for many important functions. Scientists have recently discovered that a type of fatty acid contained in oils can also benefit human health. The fatty acids that provide benefits to human health are called omega-3 fatty acids. A diet rich in these fatty acids is thought to lower blood pressure and reduce the risk of heart disease. Fish oils are known to contain high levels of omega-3 fatty acids. Fish farmers know that the fish they produce are of more value to the consumer if they contain oils rich in omega-3. As a result, about 80% of the fish oil produced globally from the oceans is used as food in fish farms. Small fish called anchovies live in our oceans. They eat microscopic plants called plankton that contain high levels of omega-3. As the anchovies grow, they also contain high levels of omega-3 in their oil. Fishing boats catch billions of these small fish, that are then ground up to be fed to bigger fish such as salmon, on fish farms. Fish farms consume vast quantities of anchovies. The increase in the number of fish farms is one reason why wild fish stocks of anchovies are declining. It takes about 5 kg of anchovies to produce 1 kg of farmed salmon. The high cost of this source of fish oil has encouraged fish farmers to use less, so the fish they produce contain lower levels of omega-3 in their oil, which is not good for human health. Recently, scientists have discovered another way to obtain high levels of omega-3 to feed to fish on fish farms. The scientists genetically modified a plant called Camelina to produce seeds containing omega-3 fatty acids. This discovery will enable these seeds to be fed to salmon in fish farms and could reduce overfishing of the oceans.

Suggest how excess lipids (fats and oils) increase the risk of heart disease (lines 1 and 2).

Fats and oils are large, insoluble molecules needed in a balanced diet (lines 2 and 3). Give the names of two small, soluble molecules needed in a balanced diet.

State a function of lipid in the human body.

Fatty acids are one component of a lipid molecule. Name another component.

Use the information in the passage to draw a food chain that includes anchovies (lines 13 to 17).

Suggest why wild fish stocks are declining.

Explain why 5 kg of anchovies only produce 1 kg of farmed salmon (line 20).

The genetic modification of Camelina plants involves the use of enzymes and a vector (lines 24 and 25).

Explain how enzymes are used in genetic modification.

Describe the role of a named vector in genetic modification.

Scientists want to compare the growth of the same species of plant in three different areas. The graph shows the biomass of the plants in each area in g per m² each year for a period of 20 years.

The table shows the increase in biomass in each area in g per m² per year for the 20-year period for areas A and B.

Calculate the increase in biomass in g per m² per year for area C Show your working.

Increase in biomass =_........ g per m² per year

After 20 years, the plants in area A had a greater biomass than those in area B.

Explain how abiotic (non-living) factors could cause this difference.

Explain how biotic (living) factors could cause this difference.

The scientists wanted to find out how efficient plants in area A were at converting light energy and using it to make biomass. The scientists knew the following information: the increase in biomass for the plant growth in area A is 115 g per m² per year one gram of the plants in area A contains 22 kJ of energy the amount of light energy available in area A is 3 200 000 kJ per m² per year The formula for calculating the percentage energy transfer efficiency is

Use this information to calculate the percentage energy transfer efficiency of the plants in area A. Show your working.

Energy transfer efficiency =_........

The diagram shows the energy transfer in a river ecosystem. The numbers on the diagram refer to the energy in the biomass at each trophic level in arbitrary units.

The formula shows how to calculate energy transfer efficiency as a percentage.

The total energy available to the producers from sunlight is 1 700 000 in arbitrary units. Use this information, and the formula, to calculate the percentage energy transfer efficiency from sunlight to plants. Show your working.

Suggest why the percentage energy transfer efficiency from sunlight to plants is low.

The table shows the calculated energy transfer efficiencies between the different trophic levels in the river ecosystem.

Suggest two reasons why the energy transfer from plants to primary consumers is not 100%.

The graph shows the units of energy in the plants and primary consumers in a food chain.

Not all the energy in the plants is transferred to the primary consumers.

Calculate the percentage of energy in plants that is transferred to the primary consumers. Show your working.

One reason why energy is not transferred is because certain molecules in plants cannot be digested. Give two other reasons why energy is not transferred.

Primary consumers can digest the starch from plants. Describe how starch is digested in humans.