Week 7 — Photosynthesis

Why this matters

A nursing student asking where the oxygen in every breath came from and a gardener picking a sunny spot for a houseplant both meet the process in every green leaf.

In plain language

Every green leaf you walk past is building sugar out of air, water, and light, and this week you learn how. You will meet photosynthesis (the way a plant uses light energy to build sugar from carbon dioxide and water, giving off oxygen). You will see that it runs in two stages, in two places inside a small green structure in the leaf. You will also learn to track the atoms (follow one kind of atom from what goes in to what comes out), which settles two old puzzles: where the oxygen you breathe comes from, and where a tree gets its mass. Last week you followed sugar being taken apart; this week you watch it being built.

• Already covered: Week 1 taught the controlled experiment, and Weeks 2 and 3 covered water, bonds, and glucose. Week 4 named the chloroplast, Week 5 introduced ATP and enzymes, and Week 6 traced cellular respiration from glucose to ATP.
• This week: photosynthesis, the equation, the chloroplast, its two stages in order with their locations, atom tracking, and how photosynthesis and respiration fit together.
• How they connect: photosynthesis builds the glucose that Week 6 took apart, it runs on the ATP and enzymes of Week 5 inside the chloroplast of Week 4, and its lab uses the control group from Week 1.
• Where we're going next: Week 8 reviews the first seven weeks for the midterm and adds one habit for any process: name each stage in order and the place it runs.

Focus

How does a leaf turn light, air, and water into sugar?

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

• [ ] name the inputs and outputs of photosynthesis
• [ ] name the two stages in order and where each runs
• [ ] trace the oxygen to water and the carbon to the air
• [ ] read the leaf disk test, its averages, and its control

To-do

Plan your week

1. Read Chapter 7 (about 40 minutes), then the lecture and slides.
2. Work the lecture tutorial (60–90 minutes) and the practice set (20 minutes).
3. Run the Biology Lab & Inquiry (2 hours), then the discussion and assignment.
4. Take the quiz.

This week's checkpoint: explain where the oxygen a leaf gives off comes from, and where the carbon in its sugar comes from.

You've got this

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

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