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 *** KIT LIST ***
A variety of sea life and freshwater animals (volvox, rotifers, daphnia, paramecium, algae, hydra) - order these from Blades Biological
Microscope (ideally with a link to a tv)
Petri dishes
*** OVERVIEW ***
Look at miniature sea life and freshwater animals under a microscope. Key message is that there are organisms that are smaller than we can see just withour eye.
Possible Activities:
1) Look at different animals under the microscope – discuss their characteristics
2) Discuss microscopes and the concept of scale/size (i.e. with hairs under the scope, etc)
Other things to talk about:
TO DO
Tips for demonstrating:
1) What is written is a list of questions and explanations that assumes the child can't answer any of your questions. Modify the spiel depending on the feedback you get.
2) Focus less on the biology and more on scale for much smaller children; Also focus on the idea that every puddle is full of little animals so small they can't see them. Be sure to use simple language!!!
3) For older children and adults up the language (i.e. stomach becomes digestive system…you don't want to patronize anyone).
4) Also try and avoid using the kiddy voice. Not least because you get in the habit and can end up using it on teenagers.
*** BASIC PROCEDURE AND EXPLANATION ***
1) Fill a small petri dish with water from a sample jar and introduce a hair for scale. Ideally a fair hair, as the sample is illuminated from below.
2) Then start looking at the rotifers.
3) List of questions and explanations:
a. This is a microscope, which is a lot like a telescope. Do you know what a telescope does?
A telescope allows you to see large things a very long way away and a microscope allows you to see very small things very close by. So you see this dish of water here. This is what the microscope is looking into.
b. *Point to screen and image of the hair* What do you think this is here?
It's a hair, just like one of the ones on your head. *Pretending to pluck one of the hairs off their head keeps their attention!*
c. What are your hairs like: are they smooth or rough?
Smooth yes, but if you look under the microscope you can see it's rough.
Under a microscope things that look smooth can look very rough. *You can usually see scales on the hair.* For older kids you can bring in conditioner and how that keeps hair smooth and protects them from damage. Advertise science!
d. Find a rotifer - So how big do you think this is?
*Don't be surprised if small children still think it's much bigger than a
hair. Drive the point home.*
e. So this animal is very small, he's about as long as a hair is wide so that's less than a tenth of a millimetre.
f. What do you think this is?
His foot.
g. And what can you see on top of his head, can you see anything moving?
On top of his head there are two wheels covered in little hairs and these hairs are all waving together like a spinning wheel. (called the corona)
*Demonstrate with hands on top of head*
h. And what do you suppose that does to the water?
It makes it spin like water going down a plug-hole.
i. So what happens to any food that passes by his mouth?
It shoots straight into his head.
The name ‘rotifer’ actually means ‘wheel-bearer’.
j. Can you see what that is there. It looks like it's beating?
That's not his heart - he's too small to have a heart; it's his jaws, and he's chomping up his food.
k. What do you suppose that is there?
That's his stomach. So he's got a foot, stomach, mouth and head - But he doesn't have a heart, a brain, or eyes, and he doesn't breathe. *Try and remember how alien an idea this is*
j. Where do you suppose he lives?
He lives in your garden. In gutters and maybe a bird bath. Anywhere that's wet and then dries out.
*Remember to play to the adults
*He's got a great trick that biologists with their love of long words call anhydrobiosis.
*Ask the parents for any guesses as to what that means.*
It means life without water. Because when the puddle which he lives in
dries out he dries out with it. *Definitely playing to the adults here, young children aren't surprised!* and when he gets wet again within five minutes he's back to life and swimming about. When he dries out he replaces all of his water (he's over 90% water) with sugar. He's safe then…a little lump of sugar…for years until he becomes wet again and comes back to life. He's the most complicated animal that can do this trick; some bacteria and microscopic worms can do it but not many.
*I generally ask for questions and thank people at this stage and send them on their way.*
4) For really small children don't go all the way through that but divert to push the angle that these animals live in puddles. Every time they jump in a puddle they splash themselves with water full of these little animals.
5) You can also divert into the other animals if they are interested.
a. Rotifers are about 50-60 cells but paramecia are single cells (a big difference in size). The paramecia are covered in cillia which beat like a mexican wave to power them through the water and have a trench in their body in which they hold their food (bacteria, algae and yeasts).
b. Amoeba are also single cells, but they move by extending their membrane in some places (a ‘pseudopod’) and retracting it in others, unlike paramecia which use cilia. Often find them in decaying vegetation in fresh and salt water. They eat by endocytosis – they engulf food in their membrane.
c. Volvox – these are made of numerous cells each with 2 flagellae all interconnected and arranged in a sphere (filled with glycoproteins) – all the cells swim together in a coordinated way. Can see daughter colonies developing inside. Found in ponds, ditches and shallow puddles.
d. Daphnia – ‘water fleas’ (0.2-0.5 mm long). 5 or 6 pairs of legs. Can see heart beating (~180 bpm). Mainly eat single-celled algae.
e. Hydra. Freshwater animals. A few mm long. Tubular body, anchored at one end and with mouth and surrounding tentacles at other end. Some live in mutual relationship with algae – the algae photosynthesize to produce food for the hydra, and the hydra give the algae protection from predators. Can produce young by budding.
f. Algae. Simple plant-like creatures. Some unicellular, others multicellular. Can photosynthesize. Bottom of lots of food chains.
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