The blood leaving the tissues becomes richer in

After a vigorous exercise,you may experience cramps in your leg muscles. Why does this happen?

Name the energy currency in the living organisms. When and where is it produced?

Which of the following statement$(s)$ is (are) true about respiration?
$(i)$ During inhalation,ribs move inward and diaphragm is raised
$(ii)$ In the alveoli,exchange of gases takes place i.e.,oxygen from alveolar air diffuses into blood and carbon dioxide from blood into alveolar air
$(iii)$ Haemoglobin has greater affinity for carbon dioxide than oxygen
$(iv)$ Alveoli increase surface area for exchange of gases

Which of the following is most appropriate for aerobic respiration?

How are the lungs designed in human beings to maximize the area for exchange of gases?