2 because animals do not have chloroplast or a cell wall
Answer:
I feel it's to easily differentiate the positive from the negative...... like in gram staining of bacteria, the colour tell us which bacteria is gram positive or gram negative...... I just feel that this is science and it is advisable to know what the opposite result of an experiment should look like.
Answer:
All the arteries except pulmonary artery carry pure blood..it is so because blood flows with a high pressure and speed And because Arteries are situated deeper under the skin have thick-walled with Narrow lumen(cavity) and pulmonary artery carries deoxygenated blood i.e without oxygen..
Explanation:
lumen means Empty space within an object(solid)
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