Year 7 Science · Unit 1 · Lesson 01

What Is Life?

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Learning Goals

Apply MRS GREN as a classification tool for unfamiliar objects.
Analyse a real-world organism against each of the seven characteristics.
Evaluate whether a single characteristic is enough to classify something as alive.

Warm Up

Order the steps

Number the steps from 1 to 6 to show the correct order for using MRS GREN to classify an unknown object. Step 1 = what you do first.

Order	Step
	Check whether the object excretes — does it remove waste chemicals produced inside itself?
	Count how many of the seven MRS GREN characteristics the object satisfies, and record your total.
	Observe the object — does any part of it move on its own, without being pushed?
	Test for reproduction — can the object make new copies of itself of the same type?
	Decide: if the object satisfies all seven characteristics, classify it as living. If any are missing, it is not living.
	Check for sensitivity — does the object detect and respond to changes in its environment, such as light or touch?

Your Turn

Real-world context

In April 2019, the Israeli spacecraft Beresheet crash-landed on the Moon, spilling thousands of tardigrades — microscopic animals sometimes called "water bears" — onto the lunar surface. Tardigrades are known for surviving extreme conditions: they can withstand radiation, the vacuum of space, temperatures from −272 °C to +150 °C, and decades without water by entering a suspended state called cryptobiosis. Scientists were left debating whether the tardigrades on the Moon could have survived the crash and, if so, what that means.

(a) In their normal, active state, tardigrades eat algae, drink water, grow, move using eight stubby legs, and reproduce by laying eggs. List at least four MRS GREN characteristics that a tardigrade clearly satisfies when it is active. For each one, identify the specific evidence from the passage or your lesson.

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(b) A tardigrade in cryptobiosis shows almost no signs of any MRS GREN characteristic. Does surviving extreme conditions in space make the tardigrade "more alive" than other animals? Use MRS GREN to explain your answer.

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Show What You Know

1. A student argues: "A car must be alive — it moves, it takes in fuel for energy, and it releases waste gases." Use MRS GREN to identify at least two characteristics the car is missing, and explain why each one disqualifies it.

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2. A eucalyptus tree does not walk, run, or swim. Explain, using two specific examples, how a eucalyptus tree still satisfies the characteristic of Movement in MRS GREN.

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Wrap Up

In one sentence, what was the main idea of this lesson?