← Back to course
Cells and Systems 6-8 / Week 02 / Friday
5/6
Week 02 · One Cell or Many

Friday

Cells all around you
// Living things, from one cell to trillions
⏱ about 20 min

Friday: Cells All Around You

Rocket holds up a slice of bread to the window. Light shines through dozens of little holes.

"Yeast did this," he says. "Every hole is a bubble of carbon dioxide from a living cell."

Raven points at the seed jar, where a root is now a centimeter long. "And that is millions of cells, working together."

"What do you notice?" she asks. "One thing is made by single cells. The other is made of many."

Nova hovers between the bread and the jar. "Both began as something small and still," she says.

Rocket nods. "A grain of yeast and a dried bean. Both alive. One cell, or many cells." Nova hums. "Review time."

One cell or many, in daily life

Bread rises because single yeast cells release carbon dioxide. The holes in a slice are the bubbles that gas made.

Bacteria are single cells too. They are present almost everywhere there is moisture, and they live on and inside other living things.

There are more of these single cells on and inside a human body than there are human cells in it. You cannot see a single one.

Your bean seedling, your houseplants, your pets and you are multicellular. Your body alone holds trillions of cells.

In a multicellular organism, cells are specialized. Some cells in a plant carry water. Other cells capture light. Each kind does its job.

The bread you eat is food. The yeast packet at the Windowsill is a lab material. Keep the two separate.

Living thingUnicellular or multicellular?Where you meet it
Baking yeastunicellularthe yeast packet in the pantry (lab material)
Bacteriaunicellularalmost every damp surface, and on and inside living things
Bean seedlingmulticellularthe seed jar on the sill
Houseplantmulticellulara sunny room
Youmulticellular, trillions of cellsat the Windowsill
CELLS IN DAILY LIFE
  • Read the question.
  • Tap your answer.
The holes in a slice of bread were made by which living things?
Which of these is a unicellular organism?
What advantage do multicellular organisms have, according to the biology text?
Week reviewTrue or false?
Some living things are made of a single cell.?
Yeast is a plant.?
Individual cells are usually too small to see with the naked eye.?
A micrometer is one millionth of a meter.?
The yeast balloon without sugar should inflate the most.?
WHY THIS EXERCISEThese five ideas are the evidence that living things are made of one cell or many.
OUR WEEK, IN ORDER
  • ?We inflated a balloon with yeast, sugar and warm water.
  • ?We met yeast and learned that one cell can be a whole living thing.
  • ?We learned how small cells are and how microscopes magnify.
  • ?We read a real table of cell sizes and magnifications.
  • ?We found one-celled and many-celled living things at home.
WHY THIS EXERCISEThe week moved from a packet of grains to evidence that fits the standard.
Baking yeast is a single-celled member of which group of living things? Type one word.
WHY THIS EXERCISEKnowing the group reminds you that yeast is neither a plant nor a chemical.
Try it
Hold a slice of bread up to a window. Count the holes you can see in one square the size of your thumbnail.
Check the seed jar. Measure the longest root in millimeters and compare it with Monday's number.
Try this
Ask a grown-up what in the kitchen was made with yeast. Bread, rolls and pizza dough all rise this way.
Name one thing in the room made of many cells and one place where single cells live unseen.
Draw a slice of bread with its holes. Beside it, draw one yeast cell with a bubble of gas leaving it.

Strong week, biologist. Tomorrow is Nature Day: a family look at where single cells and many cells live.

← Thursday