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CELL THEORY
The development of the cell theory: Robert Hooke was the first to
describe cells after looking at cork under a microscope.
Anton van Leeuwenhoek was observing living things in pond water.
Schleiden (a German botanist) was observing cells in plants, while Schwann (a German biologist) was observing cells in animals.
Conclusion:All plants and animals are made of cells.
Virchow observed and concluded that new cells came from other cells.
The Cell Theory was developed based on the work of these and other scientists…
The cell theory states that : the cell is the basic unit of life; all living organisms are made of one or
many cells. all cells come from pre-existing cells.
Cells can be Prokaryotic or Eukaryotic :
Prokaryotic cells:
are smaller and simpler do not have nuclear membrane. their genetic information is not contained in a
nucleus, rather it is spread throughout the cytoplasm. Bacterial cells are an example of prokaryotic cells.
Eurkaryotic cells:
are larger and more complex have a nucleus surrounded by a nuclear
membrane. are found in higher life forms such as plant
cells and animal cells.
STRUCTURE OF A TYPICAL CELL
CELL MEMBRANE/ PLASMA MEMBRANE
Sometime called plasmalemma Thin envelope, semi – permeable and elastic. Functions:a. Maintains the integrity of the cell.b. Holds the cell content.c. prevents the contents of one cell from mixing with those
of other cells.d. Controls the entrance and exit of materials in the cell.
NUCLEUS
Direct cell division Contain the hereditary information in
the form of gene. Control protein synthesis and other
metabloic activities of the cell.
CYTOPLASM
Living substance of the cell. Contains the cytoplasmic organelles.
RIBOSOMES
Small spherical in structure . Site of protein synthesis.
GOLGI BODIES
Manufacturing, processing, and packaging macromolecules like protein and other products.
ENDOPLASMIC RETICULUM
ENDOPLASMIC RETICULUM Network of membranous canals that
are continuous with nuclear envelope. Serves as passageway for substances
between the cytoplasm and the nucleus.
SMOOTH ENDOPLASMIC RETICULUM Devoid of ribosomes. Lipid synthesis, carbohydrate
metabolism, and helps in detoxification of drug and poison.
ROUGH ENDOPLASMIC RETICULUM Studded with attached ribosomes. Synthesis of protein.
LYSOSOMES
LYSOSOMES Encloses strong hydrolitic enzymes that can
break down all large macromolecules. Helps in digesting bacteria and other foreign
substances taken in by phagocytic cells Engulfs another organelle specially the damage
one.
VACUOLES
VACUOLES Fluid- filled cavities that are
sorrounded by membranes. Named according to the specific
functions they play within the cells.
Food vacuole – contains food particles ingested by
phagocytic cells. Contractile vacuole – pumps out excess water from the
cells of freshwater protist. Central vacuole – found mainly in plant cells and used to
store nutrients, metabolites and waste products.
MITOCHONDRIA
MITOCHONDRIA Converts the potential energy of food
molecules into molecules. Powerhouse of the cell.
CHLOROPLAST
CHLOROPLAST Contains the green pigment chlrophyll
that that captures light energy from the sun and converts it into chemical energy through the process of photosynthesis.
PEROXISOMES
PEROXISOMES Hydrolysis of fatty acids into simple
units. Contains enzymes that can detoxify
alcohol and other harmful substances and convert poisonous peroxides to water.
CYTOSKELETON
CYTOSKELETON Network of filaments that extend in entire
region of the cytoplasm. Give support and maintain the structure and
shape of the cell. Microfilaments, intermediate filaments,
microtubles.
MICROFILAMENTS – found just beneath the cell membrane providing support and maintaining cell shape, formation of cleavage furrow in animal cells.
Intermediate filaments – meaintain cellular shape. Microtublues – play important roles in intracellular
transport, formation of mitotic spindle needed for cell division, and formation of cell wall in plant cells.
CELL WALL
Found outside the cell membrane of plant cells, fungi and bacteria.
Provides rigidity and structural support to cells.