Week 4 — Cell Structure & Function

Why this matters

A nursing student learning why a cell swells or shrinks and a gardener reviving a wilted houseplant are watching the same thing: water crossing a cell's border.

In plain language

Every living thing is made of cells, and this week you look inside one. You will meet the two basic kinds of cell: prokaryotic cells (small cells with no nucleus, such as bacteria) and eukaryotic cells (larger cells with a nucleus and many inner compartments, such as yours). You will tour the organelles (the working parts inside a cell, each with one main job) and learn to read each one for the job it does. You will see how the plasma membrane (the thin border around every cell) decides what gets in and out, and why water moves the way it does. Finally, you will find out why cells stay so small, using nothing more than a few model cubes and some arithmetic.

• Already covered: Week 3's four classes of large molecules, including the phospholipid.
• This week: the two kinds of cell, the organelles, the membrane, transport, and cell size.
• How they connect: the membrane is Week 3's phospholipid put to work.
• Where we're going next: Week 5, Energy, Enzymes & Metabolism, follows the ATP the pump spends.

Focus

What is a cell built like, what crosses its border, and why must it stay small?

By the end of this module, you should be able to:

• [ ] sort a cell as prokaryotic or eukaryotic and match organelles to jobs
• [ ] predict water's direction in hypotonic and hypertonic settings
• [ ] tell passive from active transport
• [ ] compute a cube cell's surface-area-to-volume ratio

To-do

Plan your week

1. Read Chapter 4 (about 40 minutes), then the lecture and slides.
2. Work the lecture tutorial (60–90 minutes) and the practice set (about 20 minutes).
3. Run the Biology Lab & Inquiry (about 2 hours), then the discussion and the assignment.
4. Take the quiz.

This week's checkpoint: explain why salted lettuce goes limp, reading the salt from the cell's side.

You've got this

Take it in order, and ask your instructor if a step snags.

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