AP BIOLOGY

Detailed explanation-1: -Like us, fish also need to take in oxygen and expel carbon dioxide in order to survive. But instead of lungs, they use gills. Gills are branching organs located on the side of fish heads that have many, many small blood vessels called capillaries.

Detailed explanation-2: -The respiratory system. Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills.

Detailed explanation-3: -Gills contain many filaments, each with thousands of tiny folds called lamellae, which greatly increase the surface area that comes into contact with water. Dissolved oxygen in seawater passes through thin membranes in the lamellae and enters the fish’s blood, and carbon dioxide is eliminated.

Detailed explanation-4: -Respiration in fish takes place with the help of gills. Most fish possess gills on either side of their head. Gills are tissues made up of feathery structures called gill filaments providing a large surface area for exchange of gases.

Detailed explanation-5: -The gill is where fish absorb oxygen from the surrounding water into their blood. However, oxygen can only diffuse into the blood at the gills if the oxygen level is higher in the water than in the blood – that is, oxygen needs to flow from an area of high levels to an area of low levels.