A greenhouse uses an embedded system to keep the plants healthy.
Explain how the embedded system controls the temperature in the greenhouse.
Mark scheme
Award up to two marks for a linked explanation such as:
- A temperature sensor measures/reads the temperature in the greenhouse (1) which the processor compares with the value stored in the system (1)
- The heater is switched on (1) when the temperature reading goes below the value stored in the system (1)
- A fan/vent/window is opened/a cooler is switched on (1) when the temperature reading goes above the value stored in the system (1)
- The temperature is checked/measured continuously (1) so the heater/fan is switched on or off as soon as the temperature changes (1)
For both marks, the expansion must follow/associate with the statement.
Allow one mark for a correct point on its own without a linked reason, e.g. 'a temperature sensor measures the temperature'.
Do not award 'the embedded system controls/keeps the temperature correct' as this repeats the question.
Do not accept naming a device without saying what it does, e.g. 'the greenhouse has a thermostat'.
Example answers and how they were marked
A temperature sensor measures the temperature in the greenhouse (1), which the processor compares with the value stored in the system (1).
Why: Point (1): the input and what it measures. Reason (1): the linked statement about what the processor does with the reading.
The embedded system uses a temperature sensor that measures the temperature in the greenhouse (1).
Why: A correct point on its own (1); no linked statement about what the system does with the reading, so the second mark is not awarded.
The embedded system controls the temperature so the plants do not get too cold (0).
Why: Rewords the question without saying how the temperature is measured or changed, so no mark is awarded.