Chp 5 The Cell and Hierarchy of Life

• permeate the cytoplasm and are continuous with the cell membrane.
• Robert Hooke coined the term “cell” after observing thin slices of cork in the microscope.
• Robert Hooke referred to the cells he observed as “little boxes or cells,” after the barren cubicles of a monastery.
• Schleiden, Schwann, and Virchow concluded the “cell theory” in 1838, 1839, and 1858 respectively.
• The cell theory states that the cell is the basic unit of life wherein all living things are made up of and each cell comes from pre-existing cells.
• 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.
• The cell is considered as a unit of structure, function, heredity, and development.
• Bacteria, viruses, and paramecia have only one cell and are examples of unicellular organisms.
• Humans, monkeys, fish, lizards, birds, and trees are composed of more than one cell and are examples of multicellular organisms.
• Prokaryotes, such as bacteria and cyanobacteria, resemble one another in form, having little internal organization and a strong cell wall encasing their exteriors.
• Eukaryotes, such as humans, have more elaborate interior organization, where different organelles create separate compartments for cellular functions such as photosynthesis, respiration, and synthesis of proteins.
• The ER forms a continuous network that extends from the cell membrane to the nuclear membrane.
• Ribosomes are attached to the ER, giving it the rough appearance, thus, it is referred to as rough ER (RER) and is usually associated with active protein synthesis process.
• Smooth ER (SER) does not contain ribosomes and is associated with cellular regions and involved in the synthesis and transport of lipids or detoxification of a variety of poisons within the cell.
• The Golgi apparatus is a cluster of flattened membranous sacs that are continuous with the channels of the SER and is responsible for the storage, modification and packing of materials produced for secretory export.
• Mitochondria are double-walled membranous sacs with folded inner partitions called cristae and release energy from food molecules and transform energy into usable ATP which happens during cellular respiration.
• Chloroplasts are also double membrane organelles with inner folds called thylakoids and its characteristic is quite similar with the mitochondria, but it is responsible in the conversion of light energy to chemical energy of sugars in the photosynthesis process in plants.
• Lysosomes are single-walled membranous sacs responsible in digestion of nutrients, bacteria, and damaged organelles and are also used to destroy certain cells in the process known as apoptosis or programmed cell death during embryonic development.
• Peroxisomes are spherical membranous vesicles that contain enzymes which detoxify harmful molecules and the enzymes produced are involved in the oxidative deamination of amino acids and break down of hydrogen peroxide.
• Vacuoles are membranous sacs that store and release various substances within the cytoplasm and are also responsible for the cell’s enlargement and water balance.
• The plant cell’s vacuoles are normally large occupying almost the entire cytoplasmic area.
• Cytoskeletons are used in the maintenance of the cell shape and include the centrosomes, cilia, flagella, fibrils, and microtubules found in either plant or animal cells.
• Centrosomes are non-membranous mass of two rod like centrioles and can be found only in animal cells, which helps to organize spindle fibers and distribute chromosomes during mitotic cell division.
• Cilia and flagella are minute cytoplasmic projections that can be found in animal cells that extend from the cell surface and are responsible to move particles along cell surface or to move the cell itself.
• Fibrils and microtubules are thin, hollow tubes that support the cytoplasm and transport materials within the cytoplasm.
• The cell is made up of three components: the cell membrane, cytoplasm, and nucleus.
• The cell membrane is continuous with the cell’s internal membrane system and is a membrane composed of double-layer phospholipids in which proteins are embedded.
• In plants, the cell wall is found next to the cell membrane.
• Ribosomes occur as free particles suspended within the cytoplasm or sometimes attached to the membranous wall of the endoplasmic reticulum.
• Ribosomes are granular particles composed of protein and RNA molecules.
• The endoplasmic reticulum is a series of membranous channels that permeate the cytoplasm and are continuous with the cell membrane.