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Lec 3

Biology is the science of living organisms, encompassing the study of evolutionary relationships and cellular structures. The Cell Theory, credited to Schwann, Schleiden, and Virchow, states that all life forms consist of cells, which arise from pre-existing cells and perform essential life functions. Organisms are classified as prokaryotic, lacking a nucleus, or eukaryotic, which contain a nucleus and organelles, with cells varying in size, shape, and number.

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7 views4 pages

Lec 3

Biology is the science of living organisms, encompassing the study of evolutionary relationships and cellular structures. The Cell Theory, credited to Schwann, Schleiden, and Virchow, states that all life forms consist of cells, which arise from pre-existing cells and perform essential life functions. Organisms are classified as prokaryotic, lacking a nucleus, or eukaryotic, which contain a nucleus and organelles, with cells varying in size, shape, and number.

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ahmedaliajil1997
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Lec 3

Biology :Is the science of living things


Biology come from the Greek bios means life and Logos means
word or knowledge Biology includes the study of evolutionary
relationships among organisms and the diversity of life on earth
,Cell s the basic structural functional and biological unit of all
living organisms
* Term cell come from Latin cella meaning ‘’small room ‘’

Cell Theory
Credit for the formation of this theory to Theodor
Schwann ,Matthias Schleiden , and Rudolph Virchow
The cell Theory states
 All form of life contain one or more cells
 All cells come from pre existing cells
 All functions that make life possible occure within the cells
 All cells have genetic material required to regulate cell
functions and replicate ,passing this genetic information to
new cell

Prokaryotic and Eukaryotic


Prokaryotic : are organisms without a cell nucleus or any other
membrane bound organelles, such as Archaea and Bacteria
Eukaryotic :Eukaryotic cells are ce
lls that contain a nucleus and
organelles, and are enclosed by a plasma membrane . Organisms
that have eukaryotic cells include protozoa, fungi, plants and
animals.
These organisms are grouped i nto the biological domain
Eukaryota.

Eukaryotic cells are larger and more complex than prokaryotic


cells .

Prokaryotes and Eukaryotes

prokaryotic have a larger surface area to volume ratio giving


them a higher metabolic rate a higher growth rate and
consequently a shorter generation time compared to Eukaryotes .

Unicellular organisms: organisms that have only one cell


such as Amoeba
Multicellular organisms: organisms that have many cells
this cell form the tissue and organs.
Cell are typically composed of
1. Cell membrane (Plasma membrane)
2. Cytoplasm and its organelles such as ( mitochondria,
endoplasmic reticulum , Ribosome's, Golgi complex etc,.
3. True nucleus

Cell shape:
There is no typical shape ,but generally the cells are rounded or
spherical , oval, cuboidal ,cylindrical ,flat etc,.
the shape of cells depending mainly on functional adaptation
and partly on the surface tension and viscosity of cytoplasim,the
mechanical action of adjoining cells and rigidity of the cell
membrane .
Cell Number
— Some organisms like protozoans are single cell andothers are
multicellularThe body of human being is composed of about 26
trillions of cells in human blood the number of erythrocytes is
about five million per cubic ml of blood .and about 10 billion
neurons constitute the nerves system in human being

Cell size
The size of different cells ranges within broad limits ,some plant and
animals cells are visible to the naked eye , such as eggs ,but the majority
of cells are visible only under microscope .the size of human RBC is 7-8
µ in diameter

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