User interface language: English | Español

Date November 2016 Marks available 1 Reference code 16N.1.SL.TZ0.4
Level Standard Level Paper Paper 1 Time zone Time zone 0
Command term Define Question number 4 Adapted from N/A

Question

Figure 4: The gross and net productivity at different trophic levels within the Silver Springs, Florida, ecosystem.

[Source: Kimball's Biology Pages © John W. Kimball, distributed under a Creative Commons Attribution 3.0 Unported (CC BY 3.0) license]

State the process represented in the box labelled X.

[1]
a.

Define net primary productivity.

[1]
b.

Describe how the second law of thermodynamics operates in relation to the transfer of energy within the Silver Springs ecosystem.

[2]
c.

Distinguish between a pyramid of numbers and a pyramid of productivity.

[2]
d.

Markscheme

respiration

[1 max]

a.

the gain by producers in energy or biomass per unit area per unit time remaining after allowing for respiratory losses (R).

[1 max]

b.

the 2nd law of thermodynamics has energy becoming dispersed, in the ecosystem /overtime there is an increase in entropy;

light energy is converted to chemical energy in plants, with some energy being dispersed in less useful forms /with an increase in entropy;

the chemical energy is passed down the food chain through eating/consumption;

the energy is used in respiration which releases some of the energy (in a less useful form) as heat which increases disorder of the system/increases entropy of the system;

90% of energy is lost as heat with each transfer;

the heat goes back to the atmosphere but is removed/lost from the ecosystem. 

Accept answers which correctly apply the concepts of entropy / energy/heat sources and sinks.

[2 max]

c.

pyramids of numbers display the number of organisms at each trophic level;
...whereas pyramids of productivity refer to the flow of energy through a trophic level (measured in gm/m2/yr or J/m2/yr);

pyramids of numbers can sometimes display different patterns / e.g. an inverted pyramid when individuals at lower trophic levels are relatively large (e.g. oak tree to aphids to blue tits to sparrow hawk);
...whereas a pyramid of productivity always shows a decrease along the food chain;

the data for pyramids of numbers are relatively easier to collect than for pyramids of productivity
...whereas pyramid of productivity requires rate of biomass production overtime which is more difficult to collect;

pyramid of productivity shows the flow of energy overtime. 

BOTH pyramid of numbers and pyramid of productivity must be addressed to achieve maximum 2 marks.

[2 max]

d.

Examiners report

Most candidate correctly responded to this question.

a.

Few students gave a comprehensive definition of net primary productivity. E.g. ‘per unit area per unit time’ was frequently omitted.

b.

Most candidates demonstrated limited understanding of the second law of thermodynamics and responses lacked sufficient detail e.g. marks were lost for not explaining how energy was lost through the trophic levels.

c.

In general this question was well answered by most candidates.

d.

Syllabus sections

Topic 2: Ecosystems and ecology » 2.3 Flows of energy and matter
Show 27 related questions
Topic 2: Ecosystems and ecology

View options