Cells, Transport & Cellular Energy — Extension · Life Science & Scientific Inquiry, Grade 7
Five focused units, a three-session investigation, chapter review, and chapter quiz.
Read cell images and selective boundaries
Investigate
What can image scales and a transport model establish about cells?
Materials
- Supplied image measurements and membrane records
- Ruler and notebook; no microscope required
Before you begin
Use the provided records. Do not collect bodily samples or grow unknown microorganisms. Optional microscope extensions use suitable prepared materials under equipment instructions.
Plan a fair test
This is image calibration and model analysis, not a live-cell experiment. Compare measurements within each image’s own scale and keep permeability assumptions explicit. Supplied transport model: two equal-volume compartments begin at equal pressure. A has 5 solute units and B has 10; water crosses their shared membrane, but this solute cannot. Predict the initial net water movement and explain why the conditions matter.
Method
- Identify image and scale-bar units.
- Calculate each cell’s size using its own image ratio.
- Draw a cell boundary and label which modeled particles can cross.
- Explain why enlargement alone does not show every organelle or actual size.
- Revise one overstatement and suggest a useful additional observation.
Illustrative course data — use for analysis without equipment
Illustrative records: these are invented teaching data, not published measurements or the learner’s own observations. Actual measurements may differ; record them separately if you perform an optional suitable activity.
| Image | Cell length on image (cm) | Bar length (cm) | Bar real length (μm) |
|---|---|---|---|
| A | 1.2 | 4 | 200 |
| B | 1 | 2 | 100 |
Analyze and explain
- What are the estimated cell lengths?
- Can different image widths alone establish different real sizes?
- What must be known to predict net transport?
What a strong explanation includes
- Explain the relevant biological process accurately.
- Use the supplied evidence and show calculation steps with units where needed.
- Connect a labeled model or mechanism with the claim.
- State an assumption, evidence limitation, or useful next observation.
Parent / teacher guide: discuss after the investigation
A is 1.2/4×200=60 μm; B is 1/2×100=50 μm. Image length alone is insufficient because scales differ. Transport prediction requires permeability, concentration, and relevant conditions. In the supplied equal-pressure initial model with nonpenetrating solute, net water movement tends from A toward B, the side with more solute per equal starting volume. This predicts an initial net tendency, not that molecules stop moving or that all membrane situations behave identically. The record supplies selected model relationships, not observed organelle activity or a complete cell identification. A correctly scaled diagram and clear membrane assumptions support the explanation.
Compare this model with the learner’s actual evidence. Different measurements can support a different conclusion; check the reasoning and limitations, not matching wording.
Extend the chapter investigation by evaluating its evidence and proposing a better test.
Problem 1
Answer and explanation
A is 1.2/4×200=60 μm; B is 1/2×100=50 μm. Image length alone is insufficient because scales differ. Transport prediction requires permeability, concentration, and relevant conditions. In the supplied equal-pressure initial model with nonpenetrating solute, net water movement tends from A toward B, the side with more solute per equal starting volume. This predicts an initial net tendency, not that molecules stop moving or that all membrane situations behave identically. The record supplies selected model relationships, not observed organelle activity or a complete cell identification. A correctly scaled diagram and clear membrane assumptions support the explanation.
Problem 2
Answer and explanation
A is 1.2/4×200=60 μm; B is 1/2×100=50 μm. Image length alone is insufficient because scales differ. Transport prediction requires permeability, concentration, and relevant conditions. In the supplied equal-pressure initial model with nonpenetrating solute, net water movement tends from A toward B, the side with more solute per equal starting volume. This predicts an initial net tendency, not that molecules stop moving or that all membrane situations behave identically. The record supplies selected model relationships, not observed organelle activity or a complete cell identification. A correctly scaled diagram and clear membrane assumptions support the explanation.
Problem 3
Answer and explanation
A is 1.2/4×200=60 μm; B is 1/2×100=50 μm. Image length alone is insufficient because scales differ. Transport prediction requires permeability, concentration, and relevant conditions. In the supplied equal-pressure initial model with nonpenetrating solute, net water movement tends from A toward B, the side with more solute per equal starting volume. This predicts an initial net tendency, not that molecules stop moving or that all membrane situations behave identically. The record supplies selected model relationships, not observed organelle activity or a complete cell identification. A correctly scaled diagram and clear membrane assumptions support the explanation.