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Cells and Systems 6-8 / Week 03 / Wednesday
3/6
Week 03 · Inside a Cell

Wednesday

Windowsill Lab: Build a cell model
// A cell is a system of parts
⏱ about 20 min

Wednesday: Windowsill Lab: Build a Cell Model

Rocket dumps a cup of beads and buttons onto the Windowsill. "Membrane, cytoplasm, nucleus, mitochondria. Build!"

Raven lines up the parts. "One big button for the nucleus. Small beads for mitochondria. String for the fibers that hold the shape."

"Fibers?" Rocket asks. Nova hovers over the pile. "The cytoskeleton," she says. "A network of fibers. It helps the cell keep its shape."

A grown-up holds the bag open. Rocket adds water, then the button, then the beads, then a loop of string.

"What do you notice?" Raven asks. "The parts move around in the water. The bag holds them all."

"A system in a bag," Rocket says. Nova's light glows. "A model. Now use it to explain the real thing."

Your mission

Today you build a model of a cell. A model is not the real thing. It helps you explain how the parts work together.

Each object in your bag stands for one cell part. Choose each object for a reason you can explain.

When it is built, use the model to describe what each part does, then record what the model gets right and wrong.

  • One clear plastic bag that seals, and a tray or bowl to work over
  • Tap water to fill the bag about two thirds
  • One large bead or button for the nucleus
  • Five to ten small beads or buttons for mitochondria
  • A piece of string about as long as your hand for the cytoskeleton fibers
  • A marker or tape for a label, and your Windowsill Log
Safety first
Beads and buttons are small. Keep them away from younger children and never put them in your mouth.
Work over a tray or a sink. A grown-up helps seal the bag so it does not leak.
The bag stays on the table or sill. Wipe up spills right away.
Wash your hands when you finish. Nothing from the lab is tasted.
  1. Open the bag and hold it upright in the bowl. A grown-up can hold it for you.
  2. Pour in tap water until the bag is about two thirds full. This is the cytoplasm.
  3. Drop in the large bead or button. This is the nucleus, holding the instructions.
  4. Add five to ten small beads. These are mitochondria, converting energy from food.
  5. Loop the string and slide it in. This is the cytoskeleton, the fibers that help the cell keep its shape.
  6. Press out the extra air and seal the bag. The bag itself is the cell membrane.
  7. Label the bag "cell model" and lay it flat on the tray. Gently press and watch the parts move.
  8. Fill in the data table: what each object is, which cell part it stands for, and how well it matches.
PREDICT BEFORE YOU BUILD
  • Read the question.
  • Tap your answer.
When you press the finished bag, what will the small beads do?
Which part of your model will be the hardest to make realistic?
Object in the bagCell part it stands forThe part's jobHow good is the match? (1 to 5)
Plastic bag
Water
Large button
Small beads
String

Reading the model

The National Human Genome Research Institute compares a cell to a water balloon. The cytoplasm is the water, and the organelles float in it.

Your model shows the boundary, the fluid and the parts. It shows that the parts are separate but held together as one system.

Your model does not show the jobs. A bead does not convert energy. A bag does not choose what to let in.

A good scientist says what a model gets right and what it gets wrong. Both go in your Windowsill Log.

What the model showsTrue or false?
The bag stands for the cell membrane.?
The small beads really convert energy from food.?
The water stands for the cytoplasm.?
A model must be exactly like the real thing to be useful.?
WHY THIS EXERCISEThe standard asks you to develop and use a model to describe how parts contribute to the whole.
How many large beads or buttons did your model need for the nucleus? Type a number.
WHY THIS EXERCISEThe nucleus is a single organelle that holds the instructions for the whole cell.
Sketch your finished bag from above. Label every object with the cell part it stands for.

A model built and judged. Tomorrow you read the National Library of Medicine's own table of cell parts.

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