The bacterium that converts milk into yogurt is: MCQ with Answer and Explanation

Explanation:
Mitochondria and chloroplasts contain circular DNA and 70S ribosomes, enabling them to transcribe and translate some proteins independently, though they rely on nuclear genes for most proteins. This partial autonomy supports the endosymbiotic origin hypothesis. The presence of their own genetic material and protein synthesis machinery qualifies them as semi-autonomous. Thus, both assertion and reason are correct, and the reason correctly explains the assertion.

Explanation:
The 'lub' sound occurs at the beginning of ventricular systole when the atrioventricular valves (mitral and tricuspid) close to prevent backflow of blood into the atria. The 'dub' sound occurs at the beginning of diastole due to closure of the semilunar valves (aortic and pulmonary). Valve closure is passive, resulting from pressure gradients.

Explanation:
Salivary amylase (ptyalin) hydrolyzes starch into maltose and dextrins, initiating carbohydrate digestion. The reason explains the presence of amylase in saliva.