Concept:

• Muscle cramps happen when anaerobic respiration takes place in our muscle cells.
• When we are doing heavy physical work/exercise n re is a lack of oxygen as demanded by muscles cause this.

Explanation:

The below figure explains flow of conversion of glucose to energy -

• When Pyruvate converted into lactic acid instead of CO₂ + Energy + H₂O
• Muscle cramps occur.
• A hot water bath or a massage can help in getting relief from muscle cramps. These two things improve blood circulation, reby increasing supply of oxygen to muscles.

Hence, after doing physical work we get muscle cramps are due to  conversion of pyruvate to lactic acid.

The correct answer is Alveoli.

Key Points

• Alveoli are an important part of respiratory system whose function it is to exchange oxygen and carbon dioxide molecules to and from bloodstream.
  • These tiny, balloon-shaped air sacs sit at very end of respiratory tree and are arranged in clusters throughout lungs.
  • The respiratory system is network of organs and tissues that help you brea.
  • It includes your airways, lungs, and blood vessels. The muscles that power your lungs are also part of respiratory system.
  • These parts work toger to move oxygen throughout body and clean out waste gases like carbon dioxide.

The correct answer is Alveoli.

Key Points

• The alveoli are where lungs and blood exchange oxygen and carbon dioxide during process of breathing in and breathing out.
  • These are tiny air sacs at end of bronchioles (tiny branches of air tubes in lungs).
  • Oxygen bread in from air passes through alveoli and into blood and travels to tissues throughout body.
  • Carbon dioxide travels in blood from body's tissues and passes through alveoli to be bread out.