Answer:
The diagram can be improved by:
Lungs
↓
oxygen
↓
Red blood cells (carrying oxygen)
↓
Organs (like stomach and liver etc) from where carbon
is taken and oxygen is supplied
↓
RBC's carrying Carbon dioxide to the lungs
The component which is missing in the diagram are the organs where exchange of gases occurs. The red blood cells carry oxygenated blood from the lungs to all parts of the body and carries the wast carbon dioxide gas from them back to the lungs. The carbon dioxide is then exhaled by the lungs.
This is where diffusion happens down the concentration gradient i.e. from high to low concentrations (just like simple diffusion) but facilitated diffusion requires a special and specific protein within the cell membrane. The substate binds to the receptor and the receptor itself changes conformation so that the substrate is now on the other side of the membrane. This is done for molecules that are too large to pass straight through the phospholipid bilayer (cell membrane) by simple diffusion e.g. glucose.
I believe the correct answer among the choices presented above is the last option. It is in the Sahara desert that most-likely there is physical water scarcity. This is because it is a desert and it is a characteristic of a desert to have very small or no amount of water. Also, the climate their is very hot.
The elements that are characterized by the presence of an incomplete d sublevel are called "Transition Elements". The general properties of Transition Elements are; first, they are commonly high melting point metals, second, they have many oxidation states, third, they commonly form colored compounds, lastly, they are also paramagnetic.
