Monday
Monday: A Cell Is a System
Rocket fills a clear plastic bag at the kitchen tap and seals it. He sets it on the Windowsill. "A cell," he announces.
Raven pokes it gently. "What do you notice? It holds its shape. Nothing gets in or out unless we let it."
"That is the membrane," Rocket says. "The bag. But a real cell has stuff inside. Lots of stuff."
Nova hovers over the bag, her light shining through the water. "A cell is a system," she says. "Every part has a job."
"Like a kitchen," Raven says. "Oven, fridge, sink, each with a job, all working together."
Rocket grabs a bead. "Then this is the nucleus." Nova hums. "Slow down. Learn the parts first. Then build."
Parts with jobs
Last week you learned that every living thing is made of cells. This week you look inside one.
The National Library of Medicine says cells have many parts, each with a different function. Some parts, called organelles, perform certain tasks.
A cell is a system. The parts work together, and the whole cell stays alive because each part does its job.
Cells take in nutrients from food, convert those nutrients into energy, carry out specialized functions and can make copies of themselves.
Four parts to know
The cell membrane, also called the plasma membrane, is the outer lining of the cell. It separates the cell from its environment and allows materials to enter and leave.
The cytoplasm is a jelly-like fluid inside the membrane. The other parts float in it. It is 70 to 80 percent water.
The nucleus houses DNA, the cell's hereditary material. It acts as the command center, sending directions to the cell to grow, mature and divide.
Mitochondria convert energy from food into a form the cell can use. Muscle cells have many of them because they need a lot of energy.
| Part | Job in the cell | In the bag model |
|---|---|---|
| Cell membrane | Boundary; controls what enters and leaves | the plastic bag |
| Cytoplasm | Jelly-like fluid that holds the parts | the water |
| Nucleus | Houses DNA; directs the cell | one large bead or button |
| Mitochondria | Convert energy from food | several small beads |
- Read the question.
- Tap your answer.
| Statement | True or false? |
|---|---|
| A cell is a system whose parts work together. | ? |
| The cytoplasm is mostly water. | ? |
| The nucleus is the outer lining of the cell. | ? |
| Materials can enter and leave a cell through the membrane. | ? |
- Tap a card.
- Then tap its spot.
Hold it up to the window. Can you see through it? Real cells are mostly transparent too.
Check the seed jar. Add water if needed and measure the longest root in millimeters.
Please help seal the bag and work over a tray or sink. Beads are small, so keep them away from younger children.
The facts this week come from the National Library of Medicine at medlineplus.gov and OpenStax at openstax.org. Others come from the National Human Genome Research Institute at genome.gov.
Good start. Tomorrow you look closely at how the membrane works and what the nucleus actually holds.