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Cells and Systems 6-8 / Week 03 / Friday
5/6
Week 03 · Inside a Cell

Friday

Systems everywhere
// A cell is a system of parts
⏱ about 20 min

Friday: Systems Everywhere

Rocket runs up the stairs two at a time and arrives at the Windowsill breathing hard.

"Mitochondria," he puffs. "My leg muscles have lots of them. They needed energy for that."

Raven laughs. "True. Muscle cells have a very high number of mitochondria. What do you notice about why?"

"Muscles need a lot of energy to contract," Rocket says. "So the cells that work hardest have the most power parts."

Nova hovers over the seed jar, where a pale stem is lifting the seed. "Every cell in that root is a system too," she says.

"Membrane, cytoplasm, nucleus, mitochondria, in every single one," Raven says. Nova hums. "Trillions of tiny systems. Review time."

Cells as systems, in daily life

Muscle cells have a very high number of mitochondria because they need a lot of energy to contract. Form follows function.

The same four parts you built are in nearly every cell of your body and your bean seedling.

In the seedling root, each cell has a membrane choosing what enters, a nucleus with instructions and mitochondria converting energy.

A system works because its parts work together. A nucleus without mitochondria has no energy. Mitochondria without a membrane have no food delivered.

Next week you will see what happens when many of these cell systems join into tissues and organs.

Everyday systemBoundaryInstructionsEnergyFluid or space
A cellcell membranenucleus with DNAmitochondriacytoplasm
A kitchenwalls and doorthe recipe bookoven and stovethe room
Your bag modelthe plastic bagthe large buttonthe small beadsthe water
SYSTEMS AND PARTS
  • Read the question.
  • Tap your answer.
Why do muscle cells have so many mitochondria?
A nucleus without mitochondria would have what problem?
In the kitchen comparison, what plays the part of the nucleus?
Week reviewTrue or false?
The cell membrane controls what enters and leaves the cell.?
The nucleus houses DNA.?
Mitochondria convert energy from food into a form the cell can use.?
The cytoplasm is a hard shell around the cell.?
A model must do everything the real cell does.?
WHY THIS EXERCISEThese five ideas describe the cell as a whole system with parts that each contribute.
OUR WEEK, IN ORDER
  • ?We built a bag-of-water cell model with beads and string.
  • ?We studied the membrane as a boundary and the nucleus as the command center.
  • ?We read the National Library of Medicine table of nine cell parts.
  • ?We learned that a cell is a system with four main parts.
  • ?We found cell systems in muscles, seedlings and kitchens.
WHY THIS EXERCISEThe week moved from one sealed bag to a model you can explain and judge.
Which cell part do hard-working muscle cells have a very high number of? Type one word.
WHY THIS EXERCISEThe number of a part matches the job of the cell. That is form following function.
Try it
Climb a flight of stairs at your usual pace, with shoes on. Notice your legs working. Which cell part was busy?
Check the seed jar. Measure the longest root and the stem, if one has appeared, in millimeters.
Try this
Look at the seedling's root with the hand lens. Every speck of it is cells with the four main parts.
Name one job each part is doing right now in that root.
Draw a muscle cell packed with many mitochondria beside a cell with only a few. Label which one works harder.

Strong week, biologist. Tomorrow is Nature Day: a garden look at living things made of cell systems.

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