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Chapter 2 science test (Cell theory (States That (All living organisms are…

- - - - Nucleus
        
        All plant and animal cells, which are eukaryote organisms, contain a true nucleus bounded by a nuclear membrane. (Prokaryotes such as bacteria and archaea don't have a nucleus.) This structure contains a eukaryotic cell's DNA and directs cell activities.
        
        Endoplasmic reticulum
        
        The cell membrane is double-layered in animals, and forms the outer cell boundary that protects the cell contents and regulates what goes in and out of cells. In plants, a plasma membrane lies just underneath the tough cell wall that supports plant tissue. The endoplasmic reticulum is an extensive membrane complex extending throughout the cytoplasm from the outer membrane of the nuclear envelope. It contains about half of the cell's membranous tissue. Rough endoplasmic reticulum contains ribosomes that produce proteins. Smooth endoplasmic reticulum manufactures lipids.
        
        Golgi Apparatus
        
        Also called the Golgi complex or Golgi body, this organelle looks like a stack of flattened water balloons. It processes the proteins produced by the endoplasmic reticulum and ribosomes, modifying and storing them until it packages them in vesicles. Lysosomes also come from the Golgi apparatus. These are sacs containing enzymes capable of breaking down cell macromolecules.
        
        Storage Organelles
        
        Vesicles are membranous sacs that transport or store a variety of compounds. Produced primarily in the membrane systems of the plasma membrane, endoplasmic reticulum and Golgi apparatus, they move throughout the cell along cytoplasmic filaments to discharge their contents to other organelles or outside the cell. Vacuoles are large in plant cells. One large vacuole takes up much of the cell space and functions in maintaining cell size and turgor pressure (the pressure the cell's contents exert on the wall). Animal cell vacuoles are smaller. They store compounds and help with water and waste regulation.
        
        Energy-Producing Organelles
        
        Mitochondria are peanut-shaped organelles found in both plants and animals. The sites of cellular respiration, they break down sugar to fuel the cell. Chloroplasts occur in plant cells. They contain chlorophylls, and photosynthesis occurs within them, allowing plant cells to form sugar from air and water in the presence of sunlight. Both mitochondria and chloroplasts are thought to have originated from free-living prokaryotic organisms that were engulfed by eukaryotic cells and developed symbiotic relationships with those cells early in the history of life.
- - - - Prokaryotic cells are not as complex as eukaryotic cells. They have no true nucleus as the DNA is not contained within a membrane or separated from the rest of the cell
- - - - Membrane transport system is the transport system by which various molecules enter into and out of cell across cell membrane.
      - Passive transport
        
        Passive transport mechanism does not require cellular energy to transport molecules across cell membrane. So it is a passive process.
        
        In this transport system, molecules are transported from its higher concentration to the lower concentration until concentration gradient is diminished.
        
        Passive transport does not work against concentration gradient.
        
        Active Transport
        
        Active transport requires transporter protein and continuous supply of cellular energy for the transport of molecules across concentration gradient of the membrane.
        
        Active transport is very important to transport the molecules which are present in very low concentration in the medium.
        
        In active transport permease or transporter protein carries the molecules across the membrane and the energy required to transport is obtained by ATP or Ion gradient.
        
        The substances transported by active transport are glucose, aminoacids, organic acids and inorganic ions (SO4–, PO4–, K+ etc).