Cells, Tissues, Organs and Systems
All living things are made up of one or more cell(s). CElls are the most basic units of life and aggregate in order to make higher units of life as follows:
cells+cells=tissues
tissues+tissues=organs
organs+organs=systems
systems+systems=life form
All cells have internal parts that keep them alive. These parts are called organelles:
Nucleus: Largest and darkest body in a cell, it is the control center or the cell which controls all cell functions.
Mitochondria: Energy factory of the cell that keeps cell functions active.
Vacuoles: Serving as storage spaces in a cell, it is a clear space that holes waste products or any excess food, water, or gases.
Cytoplasm: It is the watery jelly-like substance that surbounds the organelles, it is 70% water.
Cell membrane: This allows only certain materials in or out of the cell.
Cell wall: (plant cells only) It is a rigid "skin-like" layer that surrounds the cell.
Animal and Plant Cells
A simple diagram of animal and plant cells:

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