During cellular respiration, pyruvic acid is converted into lactic acid when oxygen is present in the cell.

False:Pyruvic acid is converted into lactic acid only under anaerobic conditions, when oxygen is insufficient for the mitochondria to carry out aerobic respiration. When oxygen is present, pyruvic acid enters the mitochondria and is converted into acetyl CoA, which then enters the Krebs cycle for aerobic respiration. Lactic acid formation does not occur under these oxygen-rich conditions.

A. synovial membrane:Synovial membranes line the cavities of freely movable joints and secrete synovial fluid for lubrication. They do not surround the heart or other internal organs.

B. serous membrane:The heart is surrounded by the pericardium, which is a serous membrane. This double-layered membrane produces serous fluid to reduce friction as the heart beats within the thoracic cavity.

C. cutaneous membrane:The cutaneous membrane refers to the skin, which covers the external surface of the body. It does not enclose internal organs like the heart.

D. mucus membrane:Mucus membranes line body cavities that open to the exterior, such as the respiratory and digestive tracts, and secrete mucus to protect and lubricate surfaces. They are not associated with the heart.