When you breathe air in your diaphragm tightens and moves downward. It also increases the space in your chest cavity causing your lungs to expand.The muscles in your ribs also help to enlarge your chest cavity. This causes your rib cage to pull upward and outward when you inhale. When you exhale the exact opposite happens.
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Answer:
1.Small cell: has larger surface-area to volume ratio
Bigger Cell: has little space to volume ratio
2. Surface area to volume ratio, in simple means the size of surface area to the volume of substance that can pass through it at a particular time.
Amoeba and some bacteria's are flat and have large surface area to volume ratio. So the diffusion rate is very high due to large surface area.
Where as humans have small surface area: volume so diffusion is very slow or does not take place at all.
3. Diffusion and Cell Size
The larger a cell is, the greater the surface area available for diffusion. ... Smaller cells have a much greater surface area to volume ratio allowing material to diffuse throughout the entire volume of the cell quickly and efficiently.