Answer:
Question: Two requirements for gas exchange which are accomplished by the gills in a fish include:
1. Water flowing in opposite directions across the gill lamellae for gas exchange, in other words, respiration is experienced by the fish.
2. The fish allows water through its mouth, then forces the water to drain through the gills supporting gill lamellae, and enhancing gas exchange.
Question: How does their structure help to satisfy these requirements?
1. The rows of gill filaments with numerous folds through diffusion makes sure oxygen from the water moves from a place of more concentration to the blood of the fish which has less concentration causing the removal of carbon dioxide.
2. The large surface area of the gill means it has to maximize the low percentage of dissolved oxygen in the water compared to the higher percentage of oxygen in the air makes it possible for water to pass through the mouth and empty through the gills after the mouth is closed.