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.

One of the fall leaf colours is in leaves all year but is hidden until the fall. Do an experiment to find out which fall colour is hidden in green leaves.

Cut a strip of filter paper about 1cm wide and about as tall as the tube (I make strips 12cm long for my 50ml "Falcon tube" pictured).
Cut a strip of spinach leaf, 1-2mm wide, and tape across the filter paper strip near one end (about 2cm in).
Use a coin to roll over the spinach leaf to transfer the colour from the leaf to the filter paper. (Leave the tape on when you are done, as it might rip the paper if you try and tear it off.)
Fold/roll the end of the filter paper over/around the toothpick, and hang it in the empty tube. Adjust the height so that the bottom of the filter paper hangs about 1cm above the bottom of the tube, and the green pigment is about 3cm from the bottom of the tube. Remove the filter paper and toothpick again.
Add rubbing alcohol to the tube to a height of about 2cm, then hang the filter paper back in the tube, making sure that the green pigment is not submerged, but the end of the filter paper strip is submerged. If it looks like the colour will dip into the liquid, fold/roll the filter paper a little higher. Also make sure that the filter paper is not touching the sides of the tube.

Allow the chromatogram to run. Almost immediately the colours will start to move up the filter paper, but the further up it moves, the more dramatic the separation of the colours will be. I suggest a minimum running time of 10 minutes; 20 minutes or more is ideal, as in the photo.
Note that in a class of students the results will be very variable, depending on how tidy their chromatogram assembly is; however almost all students should see some yellow separating from the green. (Using 70% isopropyl alcohol, the colours move more slowly and are not separated as well with 95% ethanol, so in this case a minimum would be 30 minutes. I have not tried 99% isopropyl alcohol but would guess that it is more like the 95% ethanol.)
To see the colours more clearly while the chromatogram dries, lay on a white paper towel or other white paper.

The leaf pigment molecules are soluble in alcohol and are carried along by it, but they also get caught up on the surface of the filter paper, before moving along again. Each molecule interacts with the filter paper and the alcohol a little differently (as the molecules have different shapes and charges), so they move at slightly different rates up the filter paper. The molecules become separated from each other more and more clearly as the chromatography proceeds.

In spinach leaves, a bright yellow colour separates out from the green.
The yellow is a pigment molecule (called xanthophyll) which moves ahead of the green chlorophyll molecules.
If you try other leaf colours, you will see their colours separate out too. Green leaves only have green and yellow pigment in them. Red leaves may also have yellow pigment in them. Yellow leaves only have yellow pigment in them. Therefore yellow pigment can be masked by the green or red pigments, so is only visible when neither are present.

Relate to fall leaf colours:
The yellow pigment molecules are always in leaves, and help with photosynthesis, but their colour is usually masked by the green chlorophyll. In the fall, the green chlorophyll molecules break down as the leaves die in preparation for winter. As the green molecules disappear, the yellow molecules become visible.
Red and brown pigments are not in leaves before the fall, but made as leaves break apart sugar molecules in preparation for winter. The red molecules appear around the same time that the green molecules disappear.

Lay the cheesecloth over one of the cups.
Secure with an elastic band near the rim of the cup.
Use the other cup to gently push down on the centre of the cheesecloth, while using the other hand to roll the elastic band down a little, to make a well in the cheesecloth.
Add 1 teaspoon vinegar to the other cup.
Heat the milk in the microwave until very warm (can be done in bulk and while students are preparing cups).
Add 1/4 cup warm milk to the vinegar in the cup.
Let sit for a minute for the solid "curds" to form.
The watery liquid that separates out from the curds is called "whey".

Protein molecules (specifically casein) in milk mix with the loose hydrogen atoms in the vinegar (an acid) and a chemical reaction happens, making solid "curds". Heating the milk helps the reaction.
(For older students: the casein molecules in the milk have a negative charge. The loose hydrogen atoms in the acid have a positive charge. Opposite charges attract, so the casein molecules and loose hydrogen atoms group together to make the curds.)

Pour the curds and whey mixture into the cheesecloth on the cup, so that the curds are trapped in the cheesecloth and the whey drains into the cup below.
Pour 1/4 cup of drinking water over the curds to rinse the extra acid off.
Press the curds with the spoon, to drain any last liquid, then scoop out onto a plate.
Add a sprinkle of salt and mix in, before eating on a cracker. It is a great snack food.

Compare taste and ingredients with a commercially-produced cottage cheese.
The cottage cheese ingredients will include some kind of milk, as well as a bacterial culture (e.g. Lactobacillus) which does the same job as the vinegar (see notes below), and likely ingredients that make it more goopy (e.g. guar gum, carrageenen), and possibly some kind of preservative (e.g. potassium sorbate).

Notes on commercial cheesemaking:
Queso blanco (common cheese in Central and South America) is made in the same way as this activity, by adding an acid such as vinegar to warm milk.
Another methods for making a simple cheese use a bacteria (e.g. lactobacillus) instead of adding acid directly. As the bacteria grows it slowly releases an acid (lactic acid), which forms the curds. (Lactobacillus, naturally present in milk, can be used, and/or more lactic acid bacteria can be added.) Cottage cheese is made in this way. (Ricotta cheese is made from whey.)
Rennet is also used to help curd formation by many cheese-makers. It cleaves a piece from casein molecules, which, like the hydrogen ions, cause them to clump together.
Mature cheeses (which take longer to make than simple/quick cheeses) have other bacteria and mould cultures added to give the cheese more flavour and to change the texture. e.g. swiss cheese uses lactobacillus to form the curds, then other bacteria to remove the lactic acid to add other flavours and to make the holes.
https://www.uoguelph.ca/foodscience/book-page/cheese-making-technology-…

Notes on spoiled milk:
When milk is pasteurized most bacteria is killed, including harmful pathogens E.coli and Salmonella. However some spores and some kinds of bacteria survive e.g. lactobacilli. Milk "spoiling" i.e. forming curds when it gets old, is due to the lactobacillus bacteria growing and producing acid. Although lactobacillus is harmless, spoiled milk may also contain harmful bacteria which have grown from spores, so should not be drunk.

See the attached cheese booklet, for an inedible version of this activity run as a stand alone in a science museum (the curds are separated in a centrifuge for speed).

Bees can talk to each other with smelly molecules, called pheromones.

Students squeeze and sniff each of the bottles. Ask them what the smell makes them think of. (Likely lemon, banana, cheese and nothing.)

When a bee smells these same molecules it thinks of something quite different. Students match the molecule labels on each bottle with the molecules on the sheet to find out what each of these molecules means to a bee:
This might smell like bananas to you (banana smell), but to a bee it means war. This molecule signals bees to attack an intruder.
This molecule says it's moving day to a bee (lemon smell). Bees smelling this molecule swarm and move to a new hive
Feel alarmed when you smell this? A bee would (cheesy smell). Guard bees release this molecule to call for help when there is an intruder.
Although we humans can't smell this molecule (oxodecanoic acid, so use empty bottle), it is a perfume for bees. Queen bees release this molecule to attract males.

It may seem strange that other animals communicate with smell molecules. We mostly use our other senses to communicate.
Many creatures communicate with smell molecules.Dogs use smell molecules to mark territories. Ants leave pheromone molecules for each other to show the way to food.

Put 10 drops of fake stomach juice into each of two cups. Stomach juice contains loose hydrogen atoms.
Add a drop of dye to both cups of fake stomach juice. The color of the dye shows you the number of loose hydrogen atoms in the stomach juice.
How many hydrogen atoms are there in stomach juice?

Real stomach juice, like the fake stomach juice in your experiment, has lots of loose hydrogen atoms in it. Your stomach uses the loose hydrogen atoms to digest food. But sometimes stomach juice spills into the tube above the stomach. Hydrogen atoms are not meant to be in the tube above the stomach, and cause a burning feeling. This pain is called heartburn. When we get heartburn, we take an antacid.

Take a small piece of antacid and grind into a powder with the mortar and pestle. Dip a wooden stick into one of your cups of stomach juice to make it wet. Pick up some of the antacid powder with the wet stick. You only need a small amount.

Mix the antacid powder into one of your cups of stomach juice and dye. Leave the other cup alone. Keep mixing until the stomach juice changes color. Be patient — it may take a minute. Compare your two cups. What did the antacid do to the number of hydrogen atoms in the stomach juice? (Look at what colour the dye turned and infer what has happened to the number of hydrogen atoms).

How did the antacid take away the hydrogen atoms?
The antacid contains carbonate molecules. Find carbonate in the active ingredients on the antacid bottle. The carbonate molecules capture the loose hydrogen atoms to make a different molecule. (Students can build the molecules to see the reaction: CO3 + 2H -> CO(OH)2

How do antacids get rid of heartburn?
Just like in your experiment, the carbonate molecules in the antacid capture the loose hydrogen atoms in your stomach tube and the burning pain of heartburn goes away.
antacid = "anti-acid": Antacids get their name because they remove (or neutralize) acid, which is the same as removing hydrogen atoms.

Hand out a bone to each student and ask them to walk around and find others with similar bones.
Bones to hand out (or subset):
shoulder blades (2) humerus (2) fused ulna/radius (with elastic holding them together) (2)
fused front toe (metatarsal) bones (2)
pelvis (1) femur (2) tibia (the tiny fibula is absent) (1)
fused back toe (metatarsal) bones (1)
back (lumbar) vertebrae (4) and tail bone (fused sacral vertebrae) (1)
chest (thoracic) vertebrae (4 or more) and associated ribs (4 or more)
neck (vertical) vertebrae (6)

Students circle around a sheet to assemble the deer skeleton together, students adding their bones when asked. Older students can direct the assembly themselves, optionally using an image.
Students do not step on the sheet unless told to.

Start with the skull, then cervical vertebrae to continue down spine. Then add shoulder blades, front legs. Last add pelvis, back leg (part of one bag leg missing).

Discuss who might have taken the leg away (bobcat, coyote, fox, bald eagle) and imagine the scenario of a scavenger finding this big meal!
Find the gnaw marks on a bone where likely a rodent chewed. Likely shrew, mouse, vole or rat.
Find the missing tooth, and the ones that have overgrown on the other side without being worn away.
Discuss what happened to the skeleton once most of the meat had been eaten by other animals after it died - the decomposers and bacteria that cleaned the bones.
Draw up a food web linked to the deer as each species is mentioned.
Note all the life cycles that are linked to the life cycle of the deer.

If the students are getting wiggly sitting so long, take the skeleton apart bone by bone, asking students to find the equivalent bone in their bodies. They can stand up for much of this, wiggling each part of their bodies in turn.

The skeleton is probably a white tailed deer, the most common deer in Virginia.
A few white tailed deer facts, from this link: http://www.fcps.edu/islandcreekes/ecology/white-tailed_deer.htm
White tailed deer is a herbivore, eating green plants in the Summer; acorns, fruits and nuts in the Fall; and twigs in the Winter. They also eat fungi when they can find it.
They have few predators. Most commonly humans, sometimes fox and bald eagle.
They can run up to 60 km per hour. They are good swimmers. Their leap can be 2.5m high and 9m long.

The skeleton can be used for a comparative anatomy study, as in the skeletal system lesson plan.
Image comparing horse (similar to deer) and human skeletons, showing the same bones in each: https://i.pinimg.com/originals/64/b8/f4/64b8f401376e3cf8eb012c9de816b3c…

White tailed deer bone photos at https://russellboneatlas.wordpress.com/home/white-tail-deer-bone-atlas/