AlTamayuz in Science

1st Prep First Term

Prepared by
Dr/ Zeinab Salah
‫للتواصل وحجز مجموعات اﻷونﻼين‬
Tel: 01014731686

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 Unit 3: Living organisms, their structure and processes
Lesson 1: Cells and life

Cell
 The bodies of most living organisms are composed of several simpler
structural units, as following:
 Human body is composed of a group of systems.
 Each system is composed of a group of organs.
 Each organ is composed of a group of tissues.
 Each tissue is composed of a group of cells.
 The cell: is the unit of function in any living organism.
 The cell is the smallest structural unit in any living organism, which
performs various vital processes necessary for the continuation of life,
such as nutrition, growth and respiration.

Classification of Living Organisms

 All living organisms are similar in that the cell is the basic unit of
structure and function, as well as in the vital processes they perform,
but they differ in many other characteristics.
 As the result of the enormous diversity of living organisms, many
attempts have been made to classify them.
 Classification: is the arrangement of living organisms into groups based
on their similarities and differences, to facilitate their study and
identification.
 Classification attempts: There are multiple bases for classifying living
organisms, such as:
 Classification according to the type of their cells into:
1) Eukaryotes: divided according to the number of cells to unicellular
and multicellular organisms.
2) Prokaryotes: all of them are unicellular organisms.

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Unicellular and Multicellular Organisms
Unicellular Organisms Multicellular Organisms
Their body consists of a single cell. Their body consists of many cells.
Unspecialized, meaning that the cell 1) Their cells are differentiated (they
performs all vital processes vary in their shape and structure).
necessary for life. 2) Their cells are specialized in their
function (each group of cells
performs specific vital processes).
Microscopic organisms that can’t be Relatively large in size and can be
seen by the naked eye, but can be seen by the naked eye.
observed under a light microscope.
Examples: Examples:
 Prokaryotes: such as bacteria. All of them are eukaryotes such as
 Eukaryotes: such as Euglena. plants, animals and some fungi.
Prokaryotes and Eukaryotes
Prokaryotes Eukaryotes
Unicellular living organisms, which Unicellular or multicellular
are simple in structure and relatively organisms with more complex body
small in size. and relatively large in size.
Their genetic material in the cell is Their genetic material in the cell is
found in the cytoplasm and not surrounded by a nuclear membrane,
surrounded by a nuclear membrane. separating it from the cytoplasm.
(True nucleus)
Examples: Examples:
 Bacteria. Plants, animals, some fungi and
protozoa (such as Amoeba and
Paramecium).

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Cell structure of Prokaryotes and Eukaryotes
Prokaryotes Eukaryotes
Bacterial cell Plants cell Animal cell
All share the presence of plasma membrane (cell membrane), cytoplasm and
ribosomes.
The bacterial and plant cells share the presence of Animal cell doesn’t
cell wall. have cell wall.
Bacterial cell doesn’t Plant cell has Animal cell doesn’t
have chloroplasts. chloroplasts. have chloroplasts.
Bacterial cell doesn’t Plant cell has one large Animal cell has Small
have vacuole. vacuole. vacuoles.
Bacterial cell doesn’t Plant cell doesn’t have Animal cell has
have centrosome. centrosome. centrosome.
Many cell organelles are Plant and animal cells contain many cell
missing such as: Golgi organelles such as: Golgi apparatus, endoplasmic
apparatus, endoplasmic reticulum and mitochondria.
reticulum and
mitochondria.

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Stem Cells
 Stem cells: are undifferentiated cells that have the ability to be
transformed and differentiated into all the differentiated cells of the
body that perform specialized functions.
 Stem cells, are characterized by many properties, including:
1) Their ability to renew themselves through division and produce more
stem cells.
2) Their ability to differentiate into specialized types of cells found in the
body such as muscle cells, liver cells, intestinal cells, and nerve cells.
 The function of the cell differs depending on its structure.
 Example: the composition of muscular tissue from long muscle cells
(fiber) allows it to perform the functions of contraction and relaxation.
 Stem cells have great importance in scientific research as they help to:
1) Increase understanding of how diseases occur.
2) Generate healthy cells to replace cells infected by disease.
3) Test new drugs before use to determine their safety and effectiveness.
 Scientific experiments have proven the effectiveness of stem cell therapy
in certain diseases, such as:
1) Bone marrow failure.
2) Heart and vascular diseases.
3) Diabetes and burns.
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 Give reasons for
1) The cell is the basic unit of function in living organisms.
 Because it performs various vital processes necessary for the
continuation of life such as nutrition, growth and respiration.
2) The importance of classifying living organisms.
 To facilitate their study and identification.
3) Amoeba is unspecialized.
 Because its body consists of one cell that performs all vital processes
necessary for life.
4) Bacteria, Amoeba and Paramecium are classified as microorganisms.
 Because they are unicellular organisms that can’t be seen by the naked
eye, but can be observed under a light microscope.
5) Human cells are both differentiated and specialized.
 Because they vary in their shape and structure and each group of cells
performs specific vital processes.
6) Bacteria are classified as prokaryotes.
 Because their genetic material in the cell is found in the cytoplasm and
not surrounded by a nuclear membrane.
7) Mushroom fungus is classified as eukaryote.
 Because their genetic material in the cell is surrounded by a nuclear
membrane, separating it from the cytoplasm.
8) Stem cells can produce more of themselves.
 Because they have the ability to renew themselves through division.
9) Stem cells can be used to increase understanding of how diseases occur.
 Because by observing cell differentiation, it is possible to understand
when they turn into healthy or diseased cells.
10) Stem cells can be used to test new drugs before they are used.
 Because stem cells can be grown in the laboratory, and treated with the
tested drug to determine their safety and effectiveness.
11) Prokaryotes can’t form stem cells.
 Because they consist of one unspecialized cell that performs all vital
processes, but stem cells are undifferentiated cells.
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