Systems and Models

Question 1

System (definition)

Answer 1

A set of inter-related parts working together to make a complex whole

Question 2

Open system (definition)

Answer 2

Exchanges matter + energy with its surroundings

Question 3

Both matter + energy move through ecosystems as…

Answer 3

Transfers

Transformations

Question 4

What are transfers and give 2 examples

Answer 4

Transfers occur when energy or matter change location but not state

e. g. water moving from river to sea
e. g. chemical energy moving from herbivore to carnivore

Question 5

What are transformations and give 3 examples

Answer 5

Transformations occur when energy or matter changes its state

e. g. matter to energy (burning fossil fuels)
e. g. liquid to gas (evaporation)
e. g. energy to matter (photosynthesis)

Question 6

What type of system are all ecosystems?

Answer 6

All ecosystems are open systems, exchanging matter and energy with their environment

Question 7

How are forest ecosystems open systems?

Answer 7

• Plants fix energy from light during photosynthesis
• Nitrogen from air fixed by soil bacteria
• Herbivores enrich soil with faeces
• Nutrients leached out of soil into groundwater, streams + rivers
• Water lost through evaporation + transpiration from plants

Question 8

What is a closed system?

Answer 8

Exchanges energy but not matter with its environment

Question 9

On a global scale, which cycles are closed systems?

Answer 9

On a global scale, the hydrological, carbon and nitrogen cycles are closed. They exchange only energy and no matter

Question 10

Can the planet itself be though of as a closed system?

Answer 10

The planet itself can be though of as an ‘almost’ closed system

Question 11

Give an example of a man-made closed system

Answer 11

Biosphere 2

Question 12

What was Biosphere 2?

Answer 12

• A human attempt to create a habitable closed system on Earth
• Arizona, 1980s
• Never managed to produce enough food to sustain participants
• Oxygen levels dropped from 21% to 14%

Question 13

What is an isolated system?

Answer 13

• Exchanges neither matter nor energy with its environment
• Do not exist naturally
• Universe?

Question 14

Why do we use models of systems?

Answer 14

We use models to help us understand how a system works and to predict what happens if something changes

Question 15

What are 4 strengths of models?

Answer 15

• Easier to work with than comprehend reality
• Can be used to predict the effect of a change of input
• Applied to other similar situations
• Used to visualise small things (atoms) and large things (solar system)

Question 16

What are 3 weaknesses of models?

Answer 16

• Accuracy is lost as simplified model
• If assumptions wrong, model is wrong
• Predictions may be inaccurate

Question 17

What was the Gaia Hypothesis?

Answer 17

• 1979, published by James Lovelock
• Earth is planet-sized organism
• Atmosphere is its organ that regulates it + connects all its parts
• Biosphere keeps composition of atmosphere within certain boundaries by negative feedback mechanisms