The Biosphere, Grade 7

Plants do not need soil.

You will read that they do, twice, in the list of things living organisms must have. But a plant needs water, nutrients and something to hold it upright, and soil is only the most common way of getting all three at once. Hydroponic lettuce, an orchid on a branch and every plant in the sea manage without it.

The same topic quietly changes its own mind later and starts saying nutrients instead. This page uses the version that is right.

Where this fits in the curriculum

Subject Natural Sciences
Grade 7
Term 1
Strand Life and Living
Topic The biosphere
Status Class activities. Nothing here is formally assessed
Marks The topic revision is 40. Our worksheet is 35

The four spheres, and where life actually sits

Sphere What it is Example of life in it
Lithosphere The rocky outer layer of Earth, including soil Earthworms, mole-rats, plant roots
Hydrosphere All the water: oceans, rivers, ice, groundwater Fish, kelp, plankton
Atmosphere The layer of gases around Earth Birds, insects, drifting spores
Biosphere Not a fifth place. It is the thin overlap of the other three where life exists Everything that is alive

That last row is the whole idea and it is the one learners miss. The biosphere is not somewhere else. It is the parts of the rock, the water and the air that life has got into, plus every living thing in them.

The seven life processes

Something is alive if it does all seven. A car moves and uses fuel, but it does not grow, reproduce or respond, so it fails.

Process What it means
Nutrition Taking in or making food
Respiration Releasing energy from food. Not the same as breathing
Excretion Getting rid of waste made by the body
Growth Getting bigger and more complex
Reproduction Making more of its own kind
Sensitivity Responding to what happens around it
Movement Moving all or part of itself

Respiration and breathing get confused every single year. Breathing moves air in and out. Respiration happens inside cells and releases the energy. A plant respires and does not breathe. So does a worm, through its skin.

What living things actually need

Requirement Why
Energy Plants take it from sunlight; everything else takes it from food
Gases Most living things need oxygen to respire. Plants also need carbon dioxide
Water Every chemical reaction in a living cell happens in water
Nutrients Not soil. Soil is the usual delivery system, not the requirement
A survivable temperature Too hot or too cold and the chemistry stops

The seedling experiment, fixed

The version in circulation cannot be answered, and it is worth knowing why before you run it.

It sets up four containers: light and water, light only, water only, and neither. Then it asks learners to name the independent variable and to explain how they kept the test fair.

Two things are being changed at once, so there is no single independent variable and the test is not fair by its own definition. It then asks whether seedlings need water or light, which the design cannot separate.

Run one variable at a time and it works perfectly.

To test Keep the same Change only
Light Water both, same amount, same place, same temperature One in the light, one in a dark cupboard
Water Both in the light, same place, same temperature Water one, leave the other dry

And do not measure height for the light test

This is the part that catches everybody, including teachers.

Seedlings grown in the dark etiolate: they shoot up tall, pale and spindly, racing to find light they cannot reach. The seedlings in the cupboard are often TALLER than the ones on the windowsill.

So a class that measures only height concludes that darkness is better for growth. The measurement is right and the conclusion is wrong.

Measure colour, leaf size and sturdiness instead, or measure height and then explain it. The pale, floppy, leggy seedling is the result, and it is a far better lesson than a number.

Two South African names worth getting right

You will see It should be
"Erioloba acacia" for the camelthorn Vachellia erioloba. Genus first, and Africa's acacias were moved out of Acacia in 2011 into Vachellia and Senegalia
"Social weavers" Sociable weaver, Philetairus socius

There is a nice piece of symmetry in that first one. Port Jackson, the Australian invader, is correctly called Acacia saligna, because the Australian species kept the name when the African ones were moved out of it. So the alien gets named correctly and the indigenous tree does not.

Adaptations, with the vocabulary a marker wants

Organism Adaptation What it solves
Camelthorn Roots reaching tens of metres down, tiny leaves, thorns Finds deep water, loses little, and is not eaten
Sociable weaver A huge communal nest used year round Cool inside by day, warm at night, in a place with neither
Gemsbok Blood cooled in the nose before it reaches the brain Survives body temperatures that would kill most mammals
Kelp Holdfast, stipe and blade Grips rock in surf, bends without snapping, catches light

Kelp does not have roots, stems or leaves, and the words matter here.

It is an alga, not a plant. The holdfast grips but does not absorb water, which is exactly what makes it different from a root. The stipe is flexible where a stem is rigid, and the blade absorbs light and nutrients straight from the sea.

Using the right three words is the difference between describing kelp and describing a tree that happens to be underwater.

If it does not work

Problem Cause Fix
The dark seedlings are taller and the class is confused Etiolation. This is the expected result Use it. Compare colour and leaf size, and explain why they stretched
Nothing germinated at all Cotton wool or soil dried out Damp, not wet, and check daily. Radish is quickest at three to five days
The dry containers grew nothing Correct. Seeds need water to germinate That empty row is the result for the water test
A learner cannot name the independent variable Two things were changed at once Split it into two experiments. One variable each
Everything went mouldy Too wet, too warm, too long Less water, more air, and stop at two weeks

How the 35 marks are made up

Part Marks
The four spheres and the biosphere 8
The seven life processes 7
What living things need 6
The seedling investigation and fair testing 10
Adaptations 4

Nothing in this topic is formally assessed. The topic revision is 40 marks. Our worksheet is 35 and the split above is ours.

Free worksheet and marking memo

Both free, no sign up, straight to the PDF.

Related practicals

What you need to run it

A packet of radish seeds, cotton wool and something to put them in. That is the whole practical.

Item Price What it is for
Petri dish, sterile R48,88 One per group. Better than a saucer because you can see the roots from below
Safety goggles R30 Not needed here, but they live in the same drawer
Ecosystems wall chart R85 The spheres at a glance

Radish seeds, not beans, if you are short of time. Radish germinates in three to five days where beans take a week, and the whole investigation fits inside two weeks of lessons.

We do not sell seeds and we are not going to start. A supermarket packet costs a few rand and lasts for years.

Petri dishes are in laboratory plasticware, and the charts are in wall charts.