Monday
Monday: A Living Thing You Cannot See
Rocket shakes a small packet over the Windowsill. Tan grains spill out beside the seed jar. "Yeast," he says. "For bread."
Raven leans in with the hand lens. "What do you notice? It looks like sand. Dry, still, nothing happening."
"Like the beans last week," Rocket says slowly. "Which turned out to be alive."
Nova hovers over the grains. "Those grains are full of yeast cells," she says. "One cell of this is a whole living thing."
Rocket stares. "A whole living thing in one cell? Then how many cells am I?"
"Trillions," Raven says. "Which is why you can see yourself and not a single yeast cell." Nova hums. "That difference is this week."
One cell or many
Every living thing is made of cells. Some organisms consist of one single cell. They are unicellular. Others are made of many cells. They are multicellular.
Many microbes, such as bacteria, consist of single cells. Plants and animals are made of numerous cells.
The National Library of Medicine says the human body is composed of trillions of cells. One estimate puts an adult body at 10 to 100 trillion cells.
In a multicellular organism, cells can be specialized. Different kinds of cells do different jobs, which a single cell cannot do.
Yeast is alive
Baking yeast is a fungus. Unicellular fungi are called yeasts, and the yeast used in baking is one example.
Each yeast cell has a true nucleus and other parts inside, like the cells in your own body.
Fungi cannot make food from light the way plants do. They take in complex food molecules, such as sugar, as their source of energy.
Yeast grows best with oxygen but can also work without it by fermentation. The carbon dioxide gas it releases is what makes bread rise.
Yeast is a lab material at the Windowsill, never a snack. Wash your hands after handling it.
| Organism | One cell or many? | Can you see one cell with your eyes? |
|---|---|---|
| Bacterium | one | no |
| Yeast | one | no |
| Bean plant | many | no |
| Snail | many | no |
| Human | trillions | no |
- Read the question.
- Tap your answer.
| Statement | True or false? |
|---|---|
| A yeast cell is a whole living organism. | ? |
| The human body is made of about one hundred cells. | ? |
| Yeast makes its food from sunlight like a plant. | ? |
| In a multicellular organism, different cells can do different jobs. | ? |
- Tap a card.
- Then tap its spot.
Look at a pinch of dry yeast with your hand lens. Describe the grains in your Windowsill Log.
Wash your hands afterward. Yeast is a lab material, not food.
Please handle the warm water yourself. Warm to the touch is right. Hot water is never used.
Yeast and sugar are lab materials in this course and are not eaten. Hands are washed after each lab.
The facts this week come from the OpenStax biology textbooks at openstax.org and the National Library of Medicine at medlineplus.gov.
Good start. Tomorrow you find out how small a cell really is, and why nobody saw one until 1665.