Species, Communities, Ecosystems & Energy Flow (DP IB Biology: HL)

The diagram shows the flow of energy through a sheep. The figures are in kJ × 10⁶ year^–1.

Suggest what label F represents

Calculate the value of P. Give your answer in kJ × 10⁶ year^–1.

A sheep farmer wanted to increase the amount of energy used for the production of new tissue (P) in his livestock (his sheep). 

Suggest two methods that could be used by the farmer to achieve this.

When the sheep have grown to a specific body mass they can be consumed for food by humans. Assume that the sheep consume grass, and that humans gain 0.57 kJ x 10⁶ year^-1 from eating sheep meat. 

Draw a labelled pyramid of energy to represent this food chain.

Elodea canadensis (Canadian pondweed) is a species of aquatic plant from North America. A student grew Elodea canadensis, along with a pondweed species native to the UK, in water tanks both separately and together. The graphs below show their results.

State two abiotic factors the student should have controlled throughout the experiment. 

Calculate the difference in biomass between native pondweed grown separately and native pondweed grown in a tank together with E. canadensis after 15 days. 

Explain the results for native pondweed for when both species of pondweed are grown together.

Evaluate the benefit of mesocosm experiments, similar to the one in part (a), in understanding interactions between organisms in their natural environment.

Ecologists studied a rocky shore habitat which contained, among other organisms, several barnacle species, purple topshell snails (Gibbula umbilicalis), seaweeds, and lichens. 

State, with a reason, which of the organisms listed above make up a single population. 

The ecologists wanted to find out whether there was an association between the distributions of purple topshell snails and the common rock barnacle, Semibalanus balanoides. 

Outline the method ecologists would use to collect data to determine whether or not such an association existed.

A chi-squared test was carried out to determine whether or not there was a significant association between purple topshells and common rock barnacles on a rocky shore. When the calculated chi-squared value was compared to values in a critical values table it was found to be smaller than the critical value at a 0.05 probability level. 

Deduce what can be concluded from this analysis?

The diagram below shows a soil food web.

State the specific mode of nutrition used by the following organisms:

Draw a food chain that includes bacteria from the food web shown above

The longest food chain in the food web above contains 7 organisms. Explain why it is unusual to see food chains of this length.

Outline how the soil food web will be affected by a farmer harvesting crop plants from a field.

One mark is available for clarity of communication throughout this question.

Outline the processes by which energy flows through ecosystems.

Some plants are parasitic, gaining their carbon compounds by tapping into the roots of other plants, for example. 

Explain how this mode of plant nutrition is unusual.

Explain the concept of ecosystem sustainability.

The images show two organisms from the genus Canis.

Grey wolves, Canis lupus, are wild animals native to Eurasia and North America.

Domestic dogs, Canis familiaris, descended from wolves and became domesticated over many years.

A wolfdog is a hybrid produced when a domesticated dog (Canis familiaris) breeds with a wolf (Canis lupus). Genetically, dogs and wolves are very similar and the resulting offspring are fertile. Wolfdog hybrids are rare as natural habitats and territorial behaviours isolate wolves from domestic dogs.

Using the information provided, discuss the validity of the claim that wolves and dogs are the same species.

Suggest how isolation may result in the development of a new species.

A taxonomist suggested that the wolf and the domestic dog should be re-categorised as follows:

• Canis lupus familiaris
• Canis lupus lupus

Identify the genus name and the species name for the wolf and the domestic dog under this re-categorisation.

Outline how artificial selection has led to the domestication of wolves over many years to result in the domestic dogs of the modern day.

All ecosystems are powered by autotrophic organisms.

Discuss this statement.

Spirulina (Athrospira platensis) is a blue-green alga that is consumed for its nutritional benefits, which are considered to be good for oral health, eye health and maintaining healthy blood pressure, amongst other benefits.

The graph shows the results from an investigation into the optimum growing conditions for Spirulina. 

Spirulina was grown in a glucose medium and exposed to different intensities of light. The same method was carried out with an autotrophic species of alga.

Explain how the results show that Spirulina is a mixotrophic organism.

Compare the growth rate of Spirulina and the autotrophic algal species when light intensity was increased from 0 to 200 lx.

Suggest how Spirulina may be adapted to function as a mixotroph.

Another species of alga, Cephaleuros virescens, has been identified as a plant pathogen living on the leaves and fruit of guava plants in Hawaii. C. viscerens is non-photosynthetic and has been shown to cause a disease known as leaf and fruit spots.

Identify, with a reason, the mode of nutrition that is represented by C. viscerens.

Many large marine ecosystems across the world's oceans boast high productivity and biodiversity. As a result, they contribute substantially to the global economy through practices such as fishing.

The map below shows 66 large marine ecosystems, which are identified as being key areas of conservational interest, due to the risks associated with their proximity to developed coastlines and the impact this may have on the biodiversity of these ecosystems.

Suggest four abiotic factors that may impact communities living within large marine ecosystems.

A basic food web for a large marine ecosystem can be seen below.

Nutrient-rich sewage from coastal settlements results in rapid growth of algae (algal blooms), which leads to a reduction in light intensity on the ocean floor.

Suggest the general effects this may have on a community in a marine ecosystem.

Since 2013, numbers of starfish in the large marine ecosystems have been seen to dramatically reduce by up to 80% in some regions.

Starfish act as detritivores in the marine ecosystems, feeding on dead and decaying organic matter, as well as preying on organisms such as mussels and limpets.

Some scientists have suggested that a decline in starfish numbers may have a positive impact on the marine ecosystem.

Evaluate this statement.

Scientists investigated the production of high nutrient compost made from organic household waste.

The method they used was as follows:

1. Place waste in a large container for 125 days
2. Rotate the container each day
3. Record the temperature of the waste every 25 days
4. Remove samples of waste and test nutrient content

The temperature changes that they recorded were as follows:

Describe and explain what these data show about the processes occurring in the composter.

Explain the reason for step 2. in the method described in part a).

Nutrient content of the compost was measured at the start and the end of the process.

The results can be seen in the chart below.

Suggest reasons for the changes in carbon and nitrogen shown in the graph.

One mark is available for clarity of communication in this question.

Outline how scientists may simulate a naturally occurring ecosystem to establish how the sustainability of that ecosystem may be influenced by global warming.

Explain the use of the chi-squared test to analyse data collected from the simulated ecosystem.