part i: cell theory and structures of cell

• The term cell was first coined after Robert Hooke (1665) observed thin slices of cork in the microscope. He called them “little boxes or cells,” after the barren cubicles of a monastery.
• The importance of cells in the living matter was fully understood after Schleiden (1838), Schwann (1839) and Virchow (1858) concluded the “cell theory.”
• In its modern form, cell theory states that “all organisms are made up of one or more cells, within which the life process of metabolism and heredity occur.” In other words, cell is considered as a unit of structure, function, heredity, and development.
• Bacteria, viruses, and paramecia have only one cell (unicellular organisms) while humans, monkeys, fish, lizards, birds and trees are composed of more than one cell (multicellular organisms).
• Prokaryotes resemble one another in form, having little internal organization and a strong cell wall encasing their exteriors.
• Bacteria and cyanobacteria (blue-green algae) are examples of prokaryotes.
• Eukaryotes have more elaborate interior organization, where different organelles create separate compartments for cellular functions such as photosynthesis, respiration and synthesis of proteins.
• Among eukaryotes, plants and fungi have evolved with strong exterior cell walls.
• Simply speaking, the absence of nuclear membrane distinguishes prokaryotes from eukaryotes.
• The cell is basically made up of three components namely: cell membrane, cytoplasm and nucleus.
• Cell Membrane - It separates the contents of the cell from its surroundings
• The membrane is continuous with the cell’s internal membrane system
• The cytoplasm is the living matter within the cell, excluding the nucleus, and has fluid and jellylike substance.
• Hyaloplasm is a jelly-like substance. It is found in the uterus and is the site of implantation.
• The nucleus is separated by a porous nuclear membrane within the hyaloplasm.
• Nucleus has liquid portion called karyolymph where chromatin materials and nucleolus are found.
• Chromatin is the thread-like materials that form a network within the nucleus.
• Chromatin is rich in deoxyribonucleic acid that controls the formation of the enzymes in the cell, thus controlling all its chemical reactions.
• Nucleolus is an aggregate of granules made of ribonucleic acid and located inside the nucleus.
• The cell membrane is the outer layer of the living cell. It is a membrane composed of double layer phospholipids in which proteins are embedded.
• Cell membrane gives form to the cell and controls the passage of materials in and out of cell.
• In plants, cell wall is found next to the cell membrane. It is composed of cellulose and a variety of complex carbohydrate and amino acid combinations
• The cell wall provides support and may even keep the plant cells from bursting in hypoosmotic environments.