ingridscience

Please note that in a class of students it is likely that one of them is at least partially colourblind (1 in 12 males are colourblind). As this is an activity distinguishing colours, these students will not be able to tell some colours apart and perceive some colours differently, although the activity will be no less interesting for them. The common red/green colour blindness means reds and greens (or colours containing reds and greens such as browns) look similar. More information at colourblindawareness.org and colorblindguide.com/post/the-advantage-of-being-colorblind.

Chop/cut the red cabbage leaf into small pieces, and put in the heatproof container. Pour boiling water over the red cabbage pieces. Let the cabbage pieces soak in the hot water for 5 mins or more, while stirring with the spoon. (The longer it soaks, the darker the dye will become. Overnight will give the darkest dye. The dye can be stored in the fridge for a week.) There is a physical change as the dye moves out of the red cabbage pieces into the hot water.
Pour off the red cabbage dye into squeeze bottles.

Red cabbage dye as an acid-base or pH indicator
Aliquot the dye into squeeze bottles for adding to separate wells of a white tray (or use a spoon).
The dye turns pink when an acid is added to it, and blue if a base is added to it. Something that is neither acidic or basic (e.g. water) will leave the dye purple.
Try adding household materials to the dye, to find out if they are an acid or a base. Best are those that are colourless or a light colour, so they don't mask any colour change in the dye.
To more accurately determine the pH of household materials, use the colour spectrum on the pH testing worksheet (attached below). The lower the pH, the more acidic. The higher the pH, the more basic (or alkaline). Students test individual liquids, record on a worksheet, then add to a class graph. Look at the graph together and discuss which materials are more acidic and which more basic, as well as other patterns that come out of the graph (e.g. outliers).
Foods that are sour are acidic, so you can find out if something is sour without even tasting it! If it turns the dye pink it will be sour. Interesting that lemon juice and lemonade have similar pH values although they taste quite different: lemonade is lemon juice with a lot of sugar added so that the taste is more appealing than straight lemon juice, though it has the same acidity. See sour foods activity for more detail on testing sour foods with red cabbage dye.

Students can follow with mixing the household liquids and testing for pH. Note that pH is a logrithmic scale, so the mixture will likely have an unexpected pH.
pH in our world:
Chemists, biologists use the pH scale to test chemicals and water for how acidic or basic they are.
The pH affects the chemistry of many solutions in different systems, as it affects what chemical reactions happen and what molecules are made.
pH is important in water and soil, changing how plants get nutrients and grow, and what minerals are dissolved and precipitated.
Important in our own bodies to make sure we digest food and make new cells for growth and to heal injuries. In humans blood pH must be 7.35 - 7.45. pH drop of 0.2-0.3 causes seizures, comas even death.

Optional for older students - explain the pink/purple/blue colour changes in terms of molecule structure:
Show students the structure of two dye colour molecules (see red blue pigment molecules file attached) - one is the colour molecule when cabbage dye is pink or red, the other the colour molecule when the dye is blue . Challenge them to spot the difference between them (one of them has an extra white hydrogen atom top left). This tiny difference between the two molecules makes them different colours - in acids there are extra hydrogen atoms around and the dye molecules gain a hydrogen, so turning the dye pink or red. In a base, the dye molecules lose a hydrogen atom and so turn blue. When the dye is purple (at neutral pH, between an acid and a base) there is a mixture of red and blue dye molecules, so making the dye purple.

The reason the red cabbage dye turns green at high pH values is due to another pigment molecule, an anthoxanthin, which is colourless until high pHs, when it turns yellow. The mixture of the yellow anthoxanthin and the blue anthocyanin at high pH values gives the green colour.

Red cabbage as a paint or fabric dye
Painting - paint the juice onto paper and let dry, then paint on it with acid/base with Q-tips.
Dyeing yarn - use acid/base to vary the colour of larger batches of red cabbage dye and add yarn to it (mordanting the wool before hand should make the dye stick better). Put individual yarn pieces in little pots to dry. Do not rinse with water as the dye will come out. Make contrasting colours then twine to make a bracelet, hairpiece or backpack/water bottle accessory.
Dyeing cloth - add to batches of dye or drip acid/base onto a piece of fabric dyed with the purple red cabbage dye. Lay cloth out on cardboard to dry.

Plant dye extraction activity: extraction of dyes from plants including native plants.

Using a cut flower:
Cut the stem of a white carnation (or other white flower).
Stand the flower in a tube of food colouring for an hour or more (test to check).
Watch for the petals turning the colour of the food dye.
Cut the stem after colouring (to remove mess).

Using one petal:
(See attached booklet used at the NY Hall of Science museum.)
Cut the pointed end off a white petal. Stick the petal on a piece of tape, with the cut side hanging over the edge. Make sure the petal is lying flat on the tape.
Fold the paper lengthwise and bridge across two thin books, so there is a small gap underneath the strip of paper. Arrange so that the fold of paper is the low point.
Stick the petal to the white paper, so that it hangs off the bottom of the fold of the paper, with its cut side just touching the table.
Put a piece of wax paper on the table, in front of the petal, then drip a drop of food color onto the wax paper.
Slide the wax paper under the petal, so that its cut tip dips into the food color.
Watch for several minutes to see the food color creeping up into the petal. It traces out the vessels in the petal, which carry food molecules to all parts of the petal. The vessels extend down the stem of a flower, allowing transport of water and nutrients throughout the plant.
Unfold the paper and put another piece of tape over the rest of the petal, to stop the food color from making a mess.

Sometimes these branching patterns can be seen naturally in flowers. (see purple petunia photo)

Write your note in baking soda solution.
Allow to dry.
The note will be barely visible (though not invisible).

Paint grape juice over the note to make it visible.
(The grape juice turns a different colour when covering the basic baking soda solution).

Other idea for invisible ink:
lemon juice invisible until heated

On the blank paper, ask students to draw around their hand(s). They will add a fingerprint to each of their fingers.

Use the pencil to scribble a dark patch on the corner of the paper.
Rub a finger tip in the pencil patch, pressing it down and rolling it around to make sure the entire finger tip gets coated in graphite.
Stick a piece of tape on the darkened finger tip, then peel it off. Stick the tape on the card over the appropriate finger tip.

Use an identification sheet to first determine whether each of the fingers have loops, arches or whorls. You may also find more complex patterns such as double loops or other combinations. This pattern is caused by ridges of skin. They stay in this pattern throughout your life, and even if you damage your finger they will grow back in the same pattern. Everyone, even identical twins, has a unique collection of fingerprint patterns.

Then look for minutiae - the places where the ridges start and stop and fork and merge. Challenge students to find a bifurcation, lake or hook.
Ask them to work with the magnifier and a fine-tipped sharpie to circle the minutiae that they find, just as a forensic scientist does.

Try these websites for images of fingerprint patterns and minutiae (or google search for "fingerprint patterns" or "fingerprint minutiae"):
http://www.forensicsciencesimplified.org/prints/principles.html
https://www.ijser.org/paper/Fingerprint-Minutiae-Extraction-and-Orienta…
https://globalwrong.files.wordpress.com/2012/02/galton-characteristics1…

Find the horse foods on the table.
Notice that they each provide different nutrients: fibre, protein, fat and vitamins
We need the same nutrients.
Match each human food with the horse food that provides the same nutrition.

Sitting in a circle version (recommended):
Before the class, cut out and laminate the living things cards (attached below), then make a loop of wool from each (for hanging around the neck).
Count out enough cards, one for each student. Counting up with the numbered living things on the attached master sheet recommended, to more easily connect everyone into a food web. (Humans are optional.)

Sit at the carpet in a circle.
Hand each student a card with a living thing on it. Students hang it around their neck to display their living thing for everyone to see. Each student takes a turn to tell the class what living thing they are.
Tell students that energy comes into the living things from the sun. Place the sun card in the centre of the circle. Ask which living things use the energy of the sun to stay alive. [Any plant]
For the chosen plant, start the yarn at that student: tape the end of the yarn to the carpet with duct tape in front of them. Ask this student to take off their living things label and place it on the duct tape in front of them.
Using students' ideas, unwind the yarn ball to a student that has a living thing that would eat the plant. Make a line of wool stretching between them, then tape the yarn strand to the floor in front of the new living thing.
Continue, connecting more living things together with yarn (it will criss-cross). Each time a student is added to the line of yarn, ask them to take off their label and place it on the duct tape, so you can see who has not been included yet.
Once you get to the top of the food chain (top predator, like cougar), you can move back down the food chain to something that is eaten by the predator. Move up and down the food chain as needed to connect everyone. At any point, you can connect to decomposers (slug, wood bug, mushroom) as they eat or grow out of a living thing after it dies. The order does not matter, but just connect all the living things to something else by who eats who. (It helps to have two insect cards as they are well connected.)
A criss-crossing web of connections is made, forming a 'Food web'. (A food web is many connected food chains.)
Once the web is done, ask students to look at the web shape they have made with the yarn. This is why it is called a food web.

I also ask students that can sit a little longer to point to two other living things that they are connected to in addition to the ones they are linked to by yarn. (Read from the master sheet of what each living thing eats if necessary.) We have only made a part of the food web with the wool - there are many many other connections.

Discuss why biodiversity is important. If one living thing dies off (e.g. from a disease, or from extreme weather), living things connected to it can find other things to eat because there are so many connections. With less biodiversity, and fewer kinds of living things, there are less back-ups in the system, so it is not as resilient.

For clean up, ask students to hand in their labels, then they should peel up the duct tape without moving the yarn. The yarn can then be wound back up backwards along its path without getting tangled.

This activity is inspired by: https://betterlesson.com/lesson/640194/the-food-web (see the Explore/Explain section).

Tabletop version:
Give student groups a stack of index cards with a living thing named on each.
Students lay the cards on a table, then use lengths of wool to connect the living things that eat each other.
Students could add their own living things to their food web.
Compare the food webs that each group made.

As a class, discuss how complicated a food web is, and how living things depend on each other. If one living thing is removed, through habitat change or human interference, other living things are affected.

What is this? Look at it with your magnifiers. (don't tell students what it is until they have looked at it and identified grass/seeds etc in it first).
Animal dung! Here is one whole piece of dung. You each have part of one of these.

All animals make waste, once they have extracted as much nutrition from their food as they can.

Use magnifiers to see what is in in dung. Here is the food they eat. How does it compare?

The [horse] does not digest much of the plants they eat. Plants are hard to digest. There is a lot of nutrition left in [horse] dung. So much that it is food for another animal.
What animals might use the nutrition in [horse] dung?
Worms, wood bugs (they eat rotting plants), birds (they eat seeds).