The answer is B. a nucleus.
Prokaryotic cells do not have a nucleus. They have ribosomes, a cell membrane, a cell wall, and DNA, but lack a nucleus. Prokaryotes also don't have mitochondria or chloroplasts and generally lack organelles.
The circulatory system - hemoglobin in the blood transports oxygen :)
Distance is the length of the path travelled
displacement is the shortest length of the path travelled
distance does not have direction, hence, it is a scalar quantity
displacement has direction, hence, it is a vector quantity
<span>As humans change the way we live on the planet, the way that nitrogen moves around the Earth also changes. Nitrogen atoms may seem small enough to be easily overlooked. We look right through the ones in the air, do we not? Yet recent changes in the nitrogen cycle are causing a very noticeable effect on natural environments and human health. Lakes are clogged with aquatic weeds. Dead zones have formed in areas of the oceans where animals can not survive. Air pollutants that contain nitrogen are decreasing air quality and greenhouse gases that contain nitrogen are becoming more common.</span>
