Science 101-Biology -the story

chap.3 the building blocks of life
"Don't be so quick Mirale." said her father. "We are going to thank our destiny for giving you-Michael and  Mirale, the chance to study biology."
  "Well, you can answer the question first and tell things later." Michael scowled. But his father had already started talking:
Cells are the building blocks of life. Our body is made up of approximately 10 trillion cells and there are a lot of amazing things that they can do.
 Inside a cell, there a lot of smaller organells, as you see right now. The nucleus controls the cell's activities. They send signals to other organells in the cell. Also, they have chromosomes, which contains DNA, the nucleic acid that makes up an organism's genes.
 A mitochondrion is the powerhouse of the cell. It has enzymes that converts the chemical energy in food into another form of energy that a cell can use.
The ribosome alters protein that has been secreted by the cell as residue into hormones or digestive enzymes.
 A lysosome contains enzymes which breaks down food or foreign particles. White blood cells' lysosome can destroy bacteria.
Now as a finale, the cell membrane could be called as a 'gatekeeper'. The gatekeeper may let water molecules or molecules dissolved in water to pass through the cells, but they would not allow bigger molecules or molecules of certain chemical composition. If we call this 'transportation', it could be divided into passive transportation and active transportation. Passive transportation does not use energy to move molecules. Instead, the molecules dissolve in water and move by themselves, following the current of the ordinary concentration gradient. Whereas the active one is against concentration gradient. In an effort to move from a lesser concentration to greater concentration, they expend out energy. The carrier molecules combine with a molecule bigger than water molecule, and it leads it in or out from the cell.(White blood cell expends out energy to engulf an invading bacteria.)
 And here comes out a question:'If we grow taller and bigger, do the cells also grow bigger too?' The answer is 'no'. Instead, they increase in numbers. But.....how? They divide themselves of course!