Which of these statements are correct?
(i) All vertebrates have four-chambered hearts.
(ii) Deoxygenated and oxygenated blood are separated in animals with high energy needs.
(iii) Fishes have double circulation.
Birds and mammals have four-chambered hearts. They have high energy needs, and four chambers ensure a complete separation of oxygenated and deoxygenated blood, which is essential to cater to their high oxygen requirements. Lower vertebrates have less chambers in their heart. In higher vertebrates, blood goes through the heart twice, once to and from the lungs, and the other time to and from other parts of the body. In fishes, the blood passes through the heart only once and goes to the gills. Also, fishes have a two chambered heart.