The Hidden World of Cells

You need: a school microscope or digital microscope · slides · a hair, a wool thread, a scrap of newspaper, a grain of salt · sticky tape · drawing frame sheet

1. Carry the microscope with one hand under the base and one on the arm.
2. Tape a hair and a wool thread across a slide. Put it on the stage with the lowest-power lens in place.
3. Look from the side and move the lens close to the slide. Then look through the eyepiece and focus by moving it away.
4. Draw what you see inside a circle. Add a title and the magnification (eyepiece times lens, for example 10 × 4 = 40 times).
5. Try the newspaper and salt. Change to the next lens only when the view is sharp.

How you'll know: Your drawings are sharp, have a title and magnification, and you never crunched a slide.

Safety: Never point a microscope mirror at the sun; it can damage your eyes.

Go further: Work out how many times bigger the image is on each lens and explain why you see less of the slide on high power.

You need: an onion · moss from a damp wall or path · tweezers · slides and plastic coverslips · dilute iodine solution in a dropper bottle · paper towels · goggles

1. Peel the thin see-through skin from inside an onion layer with tweezers.
2. Lay it flat on a slide, add one drop of iodine and lower a coverslip at an angle.
3. Find the cells on low power, then medium. Draw four cells and label the wall, nucleus and cytoplasm.
4. Put one tiny moss leaf in a drop of water on a new slide. Look for the green chloroplasts.
5. Compare: why does the moss leaf have chloroplasts and the onion skin not?

How you'll know: Your drawing shows brick-like cells with walls and a nucleus, and you can explain that onion bulbs grow underground where there is no light.

Safety: Goggles on for iodine. It stains skin and clothes; wipe spills straight away.

Go further: Look at a thin slice of red capsicum skin or a spinach leaf peel and compare the cells.

You need: zip-lock bags · clear hair gel or cornflour gel (cytoplasm) · a small ball or grape (nucleus) · green beads or peas (chloroplasts) · a small water balloon (vacuole) · rice grains (mitochondria) · a small plastic box (cell wall) · labels

1. Fill a bag with gel. This is the cytoplasm and the bag is the membrane.
2. Add the nucleus and the mitochondria. You have a model animal cell.
3. Make a second bag and add chloroplasts and a big vacuole, then put it inside a box for the wall. That is a plant cell.
4. Label each part with its job in your own words.
5. Squeeze each model. Which keeps its shape? Why do plants need walls?

How you'll know: You can point to every part and say its job, and explain two differences between plant and animal cells.

Safety: Check for food allergies before using any food items, and do not eat the models.

Go further: Make a model of a specialised cell, such as a root hair cell or a guard cell, and explain how its shape suits its job.

You need: a microscope · a clear plastic ruler with millimetre marks · your onion slide · a calculator

1. Put the clear ruler on the stage and focus on the lowest power. Count how many millimetres fit across the circle.
2. Swap in the onion slide on the same lens. Count how many cells fit across the circle end to end.
3. Divide the circle width by the number of cells to get one cell's length in millimetres.
4. Multiply by 1000 to change millimetres into micrometres (µm).
5. Compare with other groups. Why might results differ?

How you'll know: You have a cell length with units, and it is in the right range for onion cells (roughly 0.1 to 0.4 mm).

Go further: On higher power the field of view shrinks. Work out the new width from the magnification and measure a smaller cell.

You need: a screw-top jar of pond, wetland or slow stream water with some weed or mud · droppers · cavity slides or slides and coverslips · a microscope · gloves · pond ID sheet

1. Collect water from a safe edge with an adult. Include a little floating weed or bottom sludge; that is where most life is.
2. Leave the jar near a window for a day with the lid loose.
3. Put one drop on a slide and search slowly on low power. When something moves, follow it.
4. Draw each organism. Is it green (can make food) or not green (must eat)? Is it one cell or many?
5. Return the water to where it came from or pour it on the garden.

How you'll know: You have drawn at least three different organisms and said which ones are producers and which are consumers.

Safety: Gloves on, cover any cuts, never collect from drains or stagnant sumps, never drink it, and wash hands after. Leave pest plants where they are.

Go further: Put a drop from near a fertilised lawn or farm drain beside a drop from a bush stream. Which has more green algae, and why might that be?

You need: clear cups · cold and warm tap water · food colouring · a stopwatch · a potato or firm jelly cut into cubes of 1 cm, 2 cm and 3 cm · a knife for the teacher · a ruler

1. Fill one cup with cold water and one with warm. Add one drop of colouring to each at the same moment.
2. Time how long until each cup looks evenly coloured.
3. Put the three cubes into a bowl of strongly coloured water for 15 minutes.
4. Take them out, have the teacher cut each in half, and measure how far the colour moved in.
5. Work out which cube is coloured all the way through. Explain what that means for a real cell.

How you'll know: Warm water mixes faster because particles move faster, and only the smallest cube coloured right through, so a small cell gets what it needs quickly.

Safety: Warm tap water only. The teacher does the cutting.

Go further: Calculate surface area divided by volume for each cube and show it on a bar graph.

You need: a tall clear plastic bottle with the top cut off, or a tall jar · mud from a pond edge or wetland · a spoon of shredded newspaper · half a boiled egg yolk · pond water · cling film and a rubber band · gloves

1. Wearing gloves, mix mud with shredded newspaper and egg yolk. Pack it into the bottom third of the bottle.
2. Fill with more plain mud to about two thirds, then top up with pond water, leaving a small air gap.
3. Seal the top tightly with cling film and a rubber band. It stays sealed from now on.
4. Stand it in a bright window (not full sun) and photograph it every few days for five weeks.
5. Record the colours and bands that appear. Each colour is a different community of bacteria or algae.

How you'll know: Your photo series shows colour bands forming over time, and you can say which layers probably have oxygen and light and which do not.

Safety: Never open the column once sealed; it can hold smelly gases and germs. The teacher disposes of it sealed.

Go further: Set up a second column in the dark and compare after five weeks. What does light change?

You need: fresh spinach or silverbeet leaves · a hole punch or a wide drinking straw · a 10 mL plastic syringe without a needle · water with a pinch of baking soda and one drop of dish soap · clear cups · a desk lamp · a ruler and stopwatch

1. Punch 30 leaf discs, avoiding the big veins.
2. Put 10 discs in the syringe with the baking soda water. Cover the tip with a finger and pull the plunger back to suck the air out of the leaves. Repeat until they sink.
3. Tip the sunken discs into a cup of the same solution. Do this for three cups.
4. Place the cups 10 cm, 25 cm and 50 cm from the lamp. Count the floating discs every minute for 20 minutes.
5. Graph discs floating against time for each distance.

How you'll know: The discs closest to the light float first, because photosynthesis makes oxygen that fills the air spaces in the leaf.

Safety: Lamps get hot. Keep water away from plugs and cords.

Go further: Wrap one cup in foil. Do those discs float? What does that prove about light?

You need: dried baker's yeast · sugar · warm tap water (about 35–40 °C) · 3 or 4 small plastic bottles · balloons · a funnel · string and a ruler · a thermometer

1. Put one teaspoon of yeast and 100 mL of warm water in each bottle.
2. Add sugar: none, one teaspoon, two teaspoons, three teaspoons. Swirl gently.
3. Stretch a balloon over each neck and stand the bottles side by side.
4. After 20 and 40 minutes, measure around each balloon at its widest point with string.
5. Explain: what did the yeast use, and what gas filled the balloon?

How you'll know: The bottle with no sugar barely changes, and the sugar bottles fill with carbon dioxide, showing yeast cells break down sugar to release energy.

Safety: Warm tap water only, not boiling. Do not drink or taste the mixture.

Go further: Keep the sugar the same and change the water temperature instead (cold, warm, hot tap). Explain the pattern using what you know about living cells.