Question

how are the following structure modified for their specific functions- root hair cell, xylem vessel, red blood cell

Answer 1

root hair absorbs ions from soil
xylem transport water
red blood cell transport oxygen and other nutroents

Answer 2

Root hair cells have to absorb water so :
1) They have enormous surface area.
2)They contain cell sap ,of a higher concentration than that of the surrounding water.
3)They have thin walls.The call wall is thin and permeable as it allows movement of water molecules and dissolved substances freely in and out of the cell. The cell membrane is very thin and semi permeable which means it only allows water molecules to pass through it but not larger molecules of dissolved salts.

Red cells have no nucleus , no mitochondria and no endoplasmic reticulum and because of this they are more efficient in carrying out their task. The absence of nucleus makes the cells biconcave thus increasing the surface area volume ratio for absorbing more oxygen.Loss of mitochondria means that red blood cells cannot use oxygen for themselves (as we know cellular respiration occurs there) thus all the oxygen absorbed from lungs is transported and delivered to tissues unconsumed. Also there is full transport of glucose in blood plasma that also unconsumed.Lastly , no endoplasmic reticulum means increased flexibility of RBCs for their movement through narrow capillaries.

Xylem vessels have long and narrow lumen to facilitate capillarity and are made of dead cells to ensure the movement of water and they are also thick to prevent collapsing.