Exchange surfaces: small size and thin barriers matter
הוצג| English | משמעות |
|---|---|
| surface-area-to-volume ratio/ˈsɜːfɪs ˈeərɪə tə ˈvɒljuːm ˈreɪʃɪəʊ/ | יחס שטח הפנים לנפח |
| exchange surface/eksˈtʃeɪndʒ ˈsɜːfɪs/ | משטח החלפה |
What would explain this observation?
- A large animal cannot rely on diffusion through its outer surface to supply every cell quickly. Size changes the area available relative to the volume needing materials.
Build the model
- A single-celled organism has a relatively large surface-area-to-volume ratio 表面积体积比, allowing enough transport across its surface.
- Larger multicellular organisms need specialized exchange surfaces 交换表面 and transport systems.
- Large area, thin membranes, efficient blood supply and ventilation improve exchange when relevant to the organ.
- surface-area-to-volume ratio: Surface area compared with the volume of the same object.
- exchange surface: A surface adapted for transfer of substances.
Why does a thin alveolar wall support rapid gas exchange?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Diffusion rate falls steeply with distance, so a one-cell-thick alveolar wall gives the short path rapid exchange needs. The wall does not block molecules, and chromosome number is irrelevant.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Villi give the small intestine a large absorbing area.
- Lungs have many alveoli with thin surfaces, a blood supply and ventilation.
- Fish gills provide a large exchange surface supplied with blood.
- Root hairs increase plant absorbing area, while leaves provide a large gas-exchange surface and short paths through their tissues.
In the lab: Compare cubes or labelled organ models using the same units. For a cube of side L, area=6L² and volume=L³. Link each organ feature to how it increases transfer or maintains a concentration difference; do not simply list “large area” without naming the structure.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: a cube of side 1 cm has area 6 cm², volume 1 cm³ and ratio 6:1.
- At side 2 cm, area=24 cm² and volume=8 cm³, giving 3:1.
- Length doubles, but area grows fourfold and volume eightfold.
- Less surface per unit volume helps explain the need for internal exchange systems.
Your turn: A cube has side 3 cm. Calculate surface area divided by volume.
A cube has side 3 cm. Calculate surface area divided by volume.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 2 per cm. Known: cube side 3 cm. Surface area = 6 x 3^2 = 54 cm^2; volume = 3^3 = 27 cm^3. Ratio = 54/27 = 2 per cm. Larger cubes have smaller ratios, which is why large organisms need exchange systems.
Check the conclusion and its limits
- A bigger object has more total surface area but can have less surface per unit volume.
- Blood flow and ventilation maintain gradients rather than make molecules choose a direction.
- Plant roots and leaves do not use animal blood vessels.
Not true: Doubling a cube’s side doubles both its surface area and its volume. Area scales with the side squared and volume with the side cubed: doubling the side multiplies area by 4 and volume by 8. Equal scaling of both is impossible.
- A single-celled organism has a relatively large surface-area-to-volume ratio, allowing enough transport across its surface.
- Villi give the small intestine a large absorbing area.
- Watch for: A bigger object has more total surface area but can have less surface per unit volume.
Doubling a cube’s side doubles both its surface area and its volume.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Area scales with the side squared and volume with the side cubed: doubling the side multiplies area by 4 and volume by 8. Equal scaling of both is impossible.
Surface area compared with the volume of the same object: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
surface-area-to-volume ratio means Surface area compared with the volume of the same object.