Ecosystems (OCR A Level Biology)

The nitrogen cycle involves a range of reactions and microorganisms.

Which of the following processes, A to D, usually occurs under anaerobic conditions?

Which of the following bacteria, A to D, convert ammonium compounds to nitrites?

Ash trees are common throughout the UK. They often grow in dense woodland.

Which of the following, A to D, is an abiotic factor that is likely to affect the growth of young ash trees?

A teacher wrote:

“A garden pond is a dynamic environment that is home to a variety of organisms. The temperature of the pond varies depending on the weather and the time of year, and this affects the populations of the species that live there.”

Which of the following terms applies to the teacher’s description of the garden pond?

Which of the following statements about ecosystems is not true?

The first stage of primary succession is the pioneer community.

Which of the following statements about a pioneer community are correct?

The graphs below show the density of two different plant species as proximity to the coast changes.

Which of the following statements correctly describes one aspect of the technique used to collect these data?

Deep sea vents on the ocean floor are surrounded by unusual organisms such as chemosynthetic bacteria and eyeless shrimp.

Which of the following statement(s) about these ecosystems is/are true?

The energy transferred from the sun to the grass in this food chain is 65 000 kJ m^-2 year^-1.

Using your knowledge of the efficiency of energy transfer in food chains, approximately how much energy is passed from the shrew to the owl in kJ m^-2 year^-1?

Which option, A to D, would be the most appropriate unit for a measurement of the biomass of all the deciduous trees in a forest?

A group of ecologists surveyed a meadow over the course of a year. They calculated the average biomass of grass in the study area and the biomass of snails that fed on the grass. They found that the average grass biomass was 50kg m-2 yr-1  while the biomass of snails was 0.1kg m-2 yr-1. What could account for this difference between the biomass of the primary producer and the primary consumer?

The Net Primary Productivity of phytoplankton in an area of sea surface is 10,000 kJ m-2 yr-1. Of this, 3000 kJ m-2 yr-1 is ingested by zooplankton (primary consumers), of which 900 kJ m-2 yr-1 is lost through zooplankton respiration and 900 kJ m-2 yr-1 is lost through zooplankton faeces. What is the Net Productivity of the zooplankton and the efficiency of the energy transfer?

The surface of a pond receives 4,000,000 kJ m^-2 yr^-1, of which 1% is absorbed by the chlorophyll in the primary producers. The Net Productivity of Primary Consumers (NPPC) of the pond is 2000 kJm^-2 yr^-1. The Efficiency of Energy Transfer (EET) between the primary producers and primary consumers is 10%. What is the Net Primary Productivity (NPP) of the pond and what is the respiratory loss of the plants in a year?

Efficiency of Energy Transfer = (NPPC / NP of producers) X 100

Figure 1 shows the atmospheric carbon dioxide levels measured at Mauna Loa in Hawaii. The graph shows oscillations in atmospheric carbon levels over the course of each year. These are driven by processes occurring only in the Northern Hemisphere. What is the best explanation for this oscillation? 

A group of scientists wants to assess the population size of field mice in a meadow. What method should they use?