Ecology

Rivers are sometimes polluted with untreated sewage. Figure 6 shows some changes that occurred when untreated sewage entered a river. Which type of organism had the most rapid increase in numbers when sewage entered the river?

Protozoa are single-celled organisms. Describe two ways Figure 6 shows that the protozoa in the river feed on bacteria.

When sewage enters a river, the concentration of dissolved oxygen decreases. The decrease in oxygen concentration is caused by organisms in the water. What process in living organisms uses oxygen?

As the numbers of green algae in the river increase, the concentration of dissolved oxygen increases. Explain why the concentration of dissolved oxygen increases.

Scientists counted the numbers of five different animals in the river at sites A and B. Table 2 shows the results. Complete Figure 7. You should use data from Table 2 for the sludge worm and the bloodworm.

The concentration of oxygen in the water at site A is much lower than at site B. - Sludge worms live in places which have a low concentration of oxygen. - Mayfly nymphs need a high concentration of oxygen. Give evidence from Table 2 for the difference in oxygen concentration at sites A and B. Refer to sludge worms and to mayfly nymphs in your answer.

The image shows a section through part of a peat bog. Layer B contains the dead remains of plants, has a low pH, and contains very little oxygen. Explain why most of the dead remains of plants in layer B do not decay.

The peat bog is a stable community. The moss produces biomass at a rate of 340 g/m²/year. What is the approximate biomass of the moss that becomes biomass in primary consumers?

The sundew plant has leaves with sticky hairs that trap and digest insects. Digestion of the insects releases phosphates and simple compounds of nitrogen that are used by the sundew plant. What substance can the sundew plant make using the phosphates?

What substance can the sundew plant make using the nitrogen?

Humans have destroyed large areas of peat bog to collect peat. The peat provides fuel and provides compost for gardeners. When peat is removed, it is often dried and the bog is drained. Explain how the destruction of peat bogs and the use of peat affects the temperature of the Earth's atmosphere.

Students investigated the number of tadpoles in a pond for 8 weeks using the following method: 1. Collect 10 dm³ of pond water in a bucket. 2. Count the number of tadpoles collected. 3. Put the tadpoles back into the pond. 4. Repeat steps 1 to 3 another three times in different parts of the pond. 5. Repeat steps 1 to 4 at intervals for 8 weeks. Suggest one improvement to the method.

After 4 weeks many of the tadpoles had died. Suggest two reasons why the tadpoles died.

A farmer has 1000 chickens. - The farmer feeds the chickens on seeds from maize plants. - 1 hectare of land produces 16.4 tonnes of maize seeds. - The maize seeds have an energy content of 16 MJ per kg. - Chickens can use 80% of the energy in maize seeds. - Each chicken needs 46 MJ of energy to grow to full size. Calculate the area of land needed to provide enough energy from maize seeds for 1000 chickens to grow to full size. Give your answer in m². Give your answer to 3 significant figures. 1 hectare = 10 000 m² 1 tonne = 1000 kg

Another farmer produced 4200 kg of maize seeds in a field. The farmer fed the maize to 1000 chickens. At full size, the mean mass of one chicken was 2.2 kg. Complete the pyramid of biomass for the food chain from the maize seeds to the 1000 chickens. You should: - label the x-axis - use a suitable scale - draw the two bars for the pyramid.

Calculate the ratio of chicken biomass to maize seed biomass. Use data from Question 07.2. Give your answer in its simplest form.

Chickens can use 80% of the biomass from the maize seeds they eat for respiration and growth. What happens to the remaining 20% of the biomass in the maize seeds?

The table compares the proportions of seven essential amino acids in normal maize and Quality Protein Maize (QPM). Which amino acids are found in significantly higher proportions in the QPM seeds?

Table 2 shows that 1 kg of QPM contains less leucine than 1 kg of normal maize. Suggest why a diet containing less leucine does not slow down the growth of chickens.