The diagram shows a sealed glass ball which is a model habitat that can last for years. Inside the sealed glass ball are plants and animals living within the same habitat. It is a self-sustaining system and the ecosystem within is balanced.
Question: Explain why this sealed glass ball requires sunlight in order to ensure the survival of the green algae and other organisms within it. (2 marks)
Student’s answer: if there is no sunlight, the green algae will not be able to make food and survive, and if it dies there will be no food for the other organisms and they too will die (only 1/2 mark)
Seems reasonable and detailed. Why only half a mark? See comment for model answer and explanation via Facebook Pages http://ift.tt/2cv2DY1