Yeast Experiment

Yeast is a fungus. They are one-celled organisms that eat sugar and then release carbon dioxide. Yeast is used for bread making to help the bread rise.

We did an experiment with dry yeast. The objective was to see what type of foods were good for the yeast. We put warm water in graduated cylinders and then put the yeast in the cylinders. Then we put different things in the cylinders. These were our results:

• honey - lots of small bubbles, smelled like bread


• molasses - big bubbles, smelled like molasses

• white sugar - lots and lots of bubbles, smelled like bread


• brown sugar - most bubbles, bubble explosions

The best food for yeast seems to be brown sugar because it is a mix of molasses and sugar.

The Nervous System

There are 3 kinds of nerves in the nervous system. Motor nerves are in charge of moving the body through voluntary and involuntary actions. Sensory nerves are in charge of picking up information from the senses. Connecting nerves connect the sensory and motor nerves to the brain and spinal cord.

For instance, you smell a flower, and the sensory nerves in your nose tell your brain, via the connecting nerves, that you smell the flower. However, sometimes the sensory signals do not go up to your brain. These are called reflexes. Say there is a bee coming by, flying right at your eye. Your eye blinks to protect the eye without you thinking about it. This is because if you did think about it, it would take too long. A reflex signal goes from sensory nerves, through connecting nerves to the spinal cord, then quickly back through connecting nerves to motor nerves that make you blink.

Sensory nerves are all over your body, but you have more in some places than in others. We did an experiment to show this. We opened a paperclip so that it had two points. Placing the points on the wrist, we recorded how many points were felt, either one or two. The feeling changed as the points were bent farther apart. Then we tried a fingertip and knee. Here are the results:

Body Part	Point Distance	# Felt
Wrist	0cm	1
	0.5cm	1
	1cm	1
	1.5cm	2
	2cm	2
Finger	0cm	1
	0.5cm	2
	1cm	2
	1.5cm	2
	2cm	2
Knee	0cm	1
	0.5cm	1
	1cm	1
	1.5cm	1
	2cm	2

We discovered some interesting things in this experiment. The finger has more sensory nerve cells close together than does the wrist or knee. This makes sense because we use fingers to feel things.

Muscle & Bone

Backbones
The backbone is made up of 32 little bones, and helps us bend and twist. Between each bone is cartilage that allows the bones to move around. As an example, we made a model backbone.

We tried bending a straw without letting it break, but we could hardly move it. A bone that can't bend is good for your arm or leg, but not your back.

We cut the straw into little pieces, and strung them onto a string. It was much easier to move this way. This is more like our backbones.















Muscle Fatigue

Muscle fatigue can happen when you do the same thing over and over without stopping, such as working in a factory. We found out about muscle fatigue with an experiment. I opened and closed a clothespin as many times as I could for 30 seconds, and recorded the results. We tried this four times, and the results are below:

1. 76 times
   


2. 73 times


3. 62 times


4. 61 times

This shows that if you do the same thing over and over again, you get worse at it because your muscles get tired. This is called muscle fatigue.