(a) In the process of respiration, state the function of alveoli.

(b) Rate of breathing in aquatic organisms is much faster than that in terrestrial organisms. Give reasons.

(c) Complete the following pathway showing the breakdown of glucose :

Glucose in cytoplasm (6-carbon molecules) $\rightarrow$ (i) (3-carbon molecules + energy) $\xrightarrow{\text{Presence of } O_2 \text{ in mitochondria}}$ (ii) + $H_2O$ + energy

(a) Function of Alveoli: Alveoli provide a very large, thin-walled surface area where the exchange of gases ($O_2$ and $CO_2$) can take place between the lungs and the blood capillaries. Their walls contain an extensive network of blood vessels to facilitate this exchange.

(b) Breathing Rate in Aquatic vs. Terrestrial Organisms: The amount of dissolved oxygen in water is fairly low compared to the amount of oxygen in the atmosphere. Therefore, aquatic organisms must breathe much faster to obtain sufficient oxygen, whereas terrestrial organisms can breathe at a slower rate because of the high concentration of oxygen in the air.

(c) Completed Pathway:

• (i) Pyruvate (3-carbon molecule)
• (ii) Carbon dioxide ($CO_2$)

$$\text{Glucose (6-carbon molecule)} \xrightarrow{\text{In cytoplasm}} \text{Pyruvate (3-carbon molecule)} + \text{Energy} \xrightarrow{\text{Presence of } O_2 \text{ in mitochondria}} CO_2 + H_2O + \text{Energy}$$