To investigate the microanatomy of a mammalian lung, a histologist stained a section of lung tissue containing capillaries and alveoli with two dyes. Dye A binds to DNA; Dye B binds to the fibrous protein that provides the alveolar walls with their elastic recoil property.
Explain why Dye A would not stain mature human red blood cells present in the capillaries, whereas it stains the squamous epithelial cells of the alveolar wall. Name the protein that Dye B binds to.
The histologist also compared the alveoli of a high-altitude mammal (llama) and a low-altitude mammal (pig) to study adaptations for gas exchange. They calculated the surface area to volume ratios of representative alveoli from both species. Some of the data are shown in the table below:
| Mammal | Surface area / μm2\mu\text{m}^2μm2 | Volume / μm3\mu\text{m}^3μm3 | Surface area:volume ratio |
|---|---|---|---|
| Llama | 1.8×1051.8 \times 10^51.8×105 | 5.2×1055.2 \times 10^55.2×105 | __________ |
| Pig | 4.4×1044.4 \times 10^44.4×104 | __________ | 0.065:10.065:10.065:1 |
Complete the table. State your calculated volume and surface area:volume ratio to 2 significant figures.
Pulmonary fibrosis is a lung disease where the delicate alveolar walls become scarred, thickened, and lose their elasticity. Other than a change in the surface area to volume ratio, describe one way this physical change affects the alveoli. Explain how this difference would affect gas exchange.