plant tissues

• The epidermis is the outermost layer of cells that covers all above-ground parts of plants.
• Our earth is inhabited by different kinds of living organisms, who look very different from each other.
• These living organisms include archaebacteria, eubacteria, protista (Amoeba, Chlamydomonas), fungi, plants and animals.
• The bodies of living organisms are made up of microscopic units called cells.
• The cell has the same central position in biology as an atom in the physical sciences.
• The cell is the basic structural and functional unit of living organisms.
• Present-day cells share common fundamental properties, such as employing DNA as their genetic material, being surrounded by a plasma membrane, and using the same basic mechanisms for energy metabolism.
• Present-day cells have evolved a variety of different life-styles, with many organisms, such as bacteria (both archaebacteria and eubacteria), protozoa (e.g., amoeba) and yeasts, consisting of single cells (called unicellular organisms) that are capable of independent self-replication.
• More complex organisms, called multicellular organisms, are composed of collections of cells that function in a coordinated manner, with different cells specialized to perform the particular tasks.
• The human body, for example, is composed of more than 200 different kinds of cells, each specialized for such distinctive functions as memory, sight, movement and digestion.
• The diversity exhibited by the many different kinds of cells is striking; for example, consider the differences between bacteria and the cells of human brain.
• All cells, whether they exist as one-celled organisms (unicellular organisms) or as a part of multicellular organisms, are capable of carrying out certain basic functions such as nutrition, respiration, growth and reproduction.
• These functions are essential for the survival of the cells.