Presentation on theme: "CELLS Cell Theory, Microscopy, Prokaryotes. CELL THEORY 1.All living things are composed of cells and cell products. 2.New cells are formed only by the."— Presentation transcript:
CELLS Cell Theory, Microscopy, Prokaryotes
CELL THEORY 1.All living things are composed of cells and cell products. 2.New cells are formed only by the division of existing cells. 3.The cell contains inherited information (genes) that are used as instructions for growth, functioning and development.
CELL THEORY, continued 4.The cell is the functioning unit of life; the chemical reactions of life take place within cells.
Possible Exceptions to the Cell Theory
The structure of skeletal muscle Muscle Bundle of muscle fibers Single muscle fiber (cell) Plasma membrane Myofibril Light band Dark band Z line Sarcomere TEM 0.5 m I bandA band I band M line Thick filaments (myosin) Thin filaments (actin) H zone Sarcomere Z line Nuclei Muscle consists of bundles of long cells called fibers. Each fiber has a membrane around the outside like a single cell But each fiber has hundreds of nuclei.
Figure 31.2: Structure of a multicellular fungus Hyphae. The mushroom and its subterranean mycelium are a continuous network of hyphae. Reproductive structure. The mushroom produces tiny cells called spores. Spore-producing structures 20 m Mycelium
SOME (but not most!) biologists consider unicellular organisms to be acellular. Examples: Amoeba and Acetabularia –instead of separate cells for separate functions, cytoplasm must carry out all vital functions –usually much larger than typical cells Acetabularia > 7 cm in length Amoeba proteus ~ µm
The animal cell
The plant cell
Task Look at the diagram and list similarities and differences between the two cells.
Pro – before Karyon – nucleus Comprise domains Bacteria and Archaea (Archaebacteria)
Electron microscope views of prokaryotic cells
Functions of the parts of a prokaryotic cell Cell wall – forms protective outer layer which prevents damage from outside and bursting if internal pressure is high Plasma membrane – controls entry and exit of substances, pumping some in by active transport
Functions of the parts of a prokaryotic cell, contd. Mesosome – increases the area of membrane for ATP production; may move DNA to poles during cell division Cytoplasm – contains enzymes that catalyze chemical reactions of metabolism; also contains cells DNA, in region known as nucleoid
Functions of the parts of a prokaryotic cell, contd. Ribosomes – synthesize proteins by translating mRNA; some proteins remain in cell and others are exported Naked DNA – stores genetic information that controls cell and is passed onto daughter cells.
Metabolic activities in prokaryotes Photosynthesis – carried out by Cyanobacteria (sometimes called blue-green algae)
Metabolic activities in prokaryotes, contd. Nitrogen fixation – nitrogen fixing bacteria convert nitrogen gas from the air into nitrogen compounds –some are free-living bacteria –some live in symbiosis with plants, such as Rhizobium, forming root nodules on legumes
Metabolic activities in prokaryotes, contd. Fermentation - process by which an sugar is broken and energy released. –occurs during times of low oxygen supply and is therefore known as a type of anaerobic respiration