A cell posses hydrophobic layer called plasma membrane which contains transmembrane proteins to transport the molecules in and out of the cells. These trans-membrane proteins allow only the passage of small molecules like ions, glucose.
But the macro-molecules having high molecular weight cannot pass the plasma membrane so they can enter the cell by a complex process called endocytosis.
The endocytosis helps engulf the large molecule by surrounding the particle and then invagination of the plasma membrane inside the cell-mediated by clathrin-coated proteins.
Cellular respiration takes place in the cells of all organisms. It occurs in autotrophs such as plants as well as heterotrophs such as animals. Cellular respiration begins in the cytoplasm of cells.
