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.