Exchange surfaces: small size and thin barriers matter
| English | 中文 | Pinyin |
|---|---|---|
| surface-area-to-volume ratio/ˈsɜːfɪs ˈeərɪə tə ˈvɒljuːm ˈreɪʃɪəʊ/ | 表面积体积比 | biǎo miàn jī tǐ jī bǐ |
| exchange surface/eksˈtʃeɪndʒ ˈsɜːfɪs/ | 交换表面 | jiāo huàn biǎo miàn |
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.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
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?
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.
Match each technical term to its precise meaning.
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.
- 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?
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.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- 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.
A cube has side 3 cm. Calculate surface area divided by volume. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A cube has side 3 cm. Calculate surface area divided by volume.
The result is 2 per cm. 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.
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.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Doubling a cube’s side doubles both its surface area and its volume. This claim is false: 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.
Exchange surfaces: small size and thin barriers matter: 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.
Doubling a cube’s side doubles both its surface area and its volume.
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.
Surface area compared with the volume of the same object: write the technical term.
surface-area-to-volume ratio means Surface area compared with the volume of the same object.