By eating plants and other animals, because they obtain their carbon from food.
The process of respiration system would not function well if the lungs was made up of only one big alveoli.
<u>Explanation:</u>
The main role of alveoli is to help the lungs to breath, for ventilation, diffusion and perfusion. The process of respiration system would not function well if the lungs was made up of only one big alveoli.
Alveoli are tiny to help the flow of oxygen and carbon dioxide, it helps the oxygen flow into the lungs and remove the carbon dioxide. If the alveoli is just one and big, then it would be hard to flow the oxygen through lungs and remove the carbon dioxide.
Therefore, it is good to have many tiny alveoli than one big one or the rib cage that protect the lungs could go through some damages.
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Answer:
plicae circulares and intestinal villi
Explanation:
The inner wall of the intestine is full of wrinkles, called villi. An enlargement of them under the microscope reveals that they are formed by cells whose surface has innumerable small "wrinkled" structures. The small intestine is the largest viscera of the body (about six meters). Intestinal villi and microvilli increase the area of contact with the intestine as well as the speed of absorption of food. Blood capillaries and lymph are in these villi to absorb nutrients.
The intestinal villi, have the function of increasing the absorption of nutrients after digestion. They are the folds of the intestines. The surface of the villi has an area of 12 cm² and the microvilli 240 cm².
Villi and microvilli increase the area of intestinal absorption by approximately 30 times and 600 times, respectively, providing exceptionally efficient absorption of nutrients in the lumen.
The entire small intestine has circular folds of mucosa, also called Kerckring valves and circular plicae. Most extend transversely around the small intestine cylinder for about half or two-thirds of its circumference, but some form complete circles, and some have a spiraling direction; The latter usually extend a little more than once around the bowel, but occasionally two or three times. Circular folds slow the passage of partially digested food along the intestines and provide an increased surface for absorption.
