2CELL THEORY All living things are composed of cells and cell products. New cells are formed only by the division of existing cells.The cell contains inherited information (genes) that are used as instructions for growth, functioning and development.
3CELL THEORY, continuedThe cell is the functioning unit of life; the chemical reactions of life take place within cells.
5The structure of skeletal muscle Bundle of muscle fibersSingle muscle fiber(cell)Plasma membraneMyofibrilLight bandDark bandZ lineSarcomereTEM0.5 mI bandA bandM lineThick filaments (myosin)Thin filaments (actin)H zoneNucleiMuscle consists of bundles of long cells called fibers.Each fiber has a membrane around the outside like a single cellBut each fiber has hundreds of nuclei.
6Figure 31.2: Structure of a multicellular fungus Reproductive structure. The mushroom produces tiny cells called spores.Hyphae. The mushroom and its subterranean mycelium are a continuous network of hyphae.Spore-producing structures20 mMycelium
8SOME (but not most!) biologists consider unicellular organisms to be acellular. Examples: Amoeba and Acetabulariainstead of separate cells for separate functions, cytoplasm must carry out all vital functionsusually much larger than typical cellsAmoeba proteus ~ µmAcetabularia > 7 cm in length
22Functions of the parts of a prokaryotic cell Cell wall – forms protective outer layer which prevents damage from outside and bursting if internal pressure is highPlasma membrane – controls entry and exit of substances, pumping some in by active transport
23Functions of the parts of a prokaryotic cell, cont’d. Mesosome – increases the area of membrane for ATP production; may move DNA to poles during cell divisionCytoplasm – contains enzymes that catalyze chemical reactions of metabolism; also contains cell’s DNA, in region known as nucleoid
24Functions of the parts of a prokaryotic cell, cont’d. Ribosomes – synthesize proteins by translating mRNA; some proteins remain in cell and others are exportedNaked DNA – stores genetic information that controls cell and is passed onto daughter cells.
25Metabolic activities in prokaryotes Photosynthesis – carried out by Cyanobacteria (sometimes called blue-green “algae”)
26Metabolic activities in prokaryotes, cont’d. Nitrogen fixation – nitrogen fixing bacteria convert nitrogen gas from the air into nitrogen compoundssome are free-living bacteriasome live in symbiosis with plants, such as Rhizobium, forming root nodules on legumes
27Metabolic activities in prokaryotes, cont’d. 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