Download 2. CHAPTER VIII- The Cell

THE CELL
• The plant cell is the basic structural and physiological
unit of plants, in which most reactions characteristic of
life occur + cells division → plant tissues.
• Cytology is the branch of biology involved in the study
of the components of cells and their functions.
• Cells vary greatly in size. The smallest must be
measured in micrometers (1/1,000 of a millimeter), but
some wood fiber cells are several centimeters long.
• Early cytological studies were conducted with light
microscopes, which can demonstrate general cellular
features but which cannot resolve all the fine details
within cells.
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DMA: Chapter 8 Hartmann's Plant
Science, 4th edition
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• Electron microscopes and enhanced light
microscopes have revealed that living cells are
not empty chambers but highly organized
complexes of subcellular compartments with
specialized metabolic functions.
• In the living cell, these complexes are distributed
through a dynamic and orderly flow of materials
within the cytoplasm that mainly formed of 8590% as water.
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DMA: Chapter 8 Hartmann's Plant
Science, 4th edition
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Electron microscope
Enhanced light microscope
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CELL STRUCTURE
There are two types of cells:
• Prokaryotic cells have no separate subcellular units; for
example, nuclear material is not enclosed in a
membrane. (These cells, considered primitive, are found
in bacteria).
• Eukaryotic cells are made up of compartments
bounded by membranes, with specialized structures and
functions.
• These units, called organelles, include the nucleus,
mitochondria, plastids, microbodies, vacuoles,
dictyosomes (Golgi bodies), and endoplasmic
reticulum (Fig. 8-5).
• Plant cells are eukaryotic cells.
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DMA: Chapter 8 Hartmann's Plant
Science, 4th edition
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DMA: Chapter 8 Hartmann's Plant
Science, 4th edition
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Science, 4th edition
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Science, 4th edition
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Cell wall: Dead part of the plant that protect
protoplast (‫ (الخلية الواحدة الحية‬, mainly of cellulose →
over which, with time lignin material precipitates
→strengthen the stand of plant through keeping the
structure of cells that also support by middle lamella
‫ صفيحة رقيقة وسطى‬that has pectic material ‫مواد هالمية‬
‫ مقوية‬. Aslo strengthen realized by secondary wall
layer of cellulose that has ↑ % of lignin, suberin and
cutin.
Also cells are connected together by cytoplasmic
material = Plasmadesmata which extend through
plasma membrane.
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DMA: Chapter 8 Hartmann's Plant
Science, 4th edition
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The Cell Wall
• The cell wall functions:
1. Protects the protoplast,
2. Provides an external structure,
3. In some tissues (e.g., bark, wood) may act as a strong
support for the plant.
• The cell wall is nonliving, made up of
1. Cellulose,
2. Pectic substances, and
3. Lignins.
• Between cells lies an intercellular layer called the middle
lamella, which contains many of the mucilaginous pectic
compounds that hold adjacent cell walls together.
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DMA: Chapter 8 Hartmann's Plant
Science, 4th edition
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Primary and Secondary wall
• Adjacent to the middle lamella is the primary wall, which
is composed mostly of cellulose.
• The secondary wall layer, which lies within the primary
wall and is laid down only after the primary wall is
complete, is usually thicker than the primary wall when
fully developed.
• Individual cells in a tissue are connected to one another
via strands of cytoplasmic material, called
plasmodesmata, which extend through the plasma
membrane.
• Water and dissolved materials can move from cell to cell
through these connections.
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DMA: Chapter 8 Hartmann's Plant
Science, 4th edition
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The Protoplast: is membrane that bounded the plasma
membrane which in turn is encased within a cell
wall. All the living organelles of the plant cell are
contained within it. It is surrounded by a living
cytoplasm membrane that show differentially
permeability (‫) نفاذية اختيارية‬
• The plasma membrane, also called the
plasma-lemma, is a lipid bilayer surrounding
the cytoplasm →important for selective
absorption + generation of energy+ protein
and act as enzyme + determine the uptake
and efflux of ions +Surface receptors, both
on the inside surface and in communication
with the cell environment.
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DMA: Chapter 8 Hartmann's Plant
Science, 4th edition
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Cytoplasm
• The cytoplasm is a viscous fluid composed of
matrix proteins in which organelles of cell swim,
bounded by the semi-permeable plasma
membrane.
• The flow of organelles within the cytoplasmic
matrix, called cytoplasmic streaming.
• Also within the cytoplasm is a very important
network of membranes, the endoplasmic
reticulum (ER).
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DMA: Chapter 8 Hartmann's Plant
Science, 4th edition
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• Proteins are synthesized on the surfaces of the ER
throughout the cell, on small discrete structures called
ribosomes (Ribo-Nucleic Acid =RNA are on its
surface connected together→polypeptides→protein).
• Plastids of several types are located within the
cytoplasm.
1- Leucoplasts (colorless) serve as storage bodies for oil,
starch, and proteins.
2- Chromoplasts contain the various plant pigments,
including chlorophyll.
• Chromoplasts with chlorophyll are called chloroplasts
and are responsible for photosynthesis in leaves and in
some stems + store for protein and lipids + has DNA.
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DMA: Chapter 8 Hartmann's Plant
Science, 4th edition
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• Mitochondria: are cytoplasmic bodies
that enclosed by a double membrane and
are smaller than plastids.
• The mitochondria are sites of respiration
and are also involved in protein synthesis.
They produce energy-rich compounds
such as Adenosine Triphosphate (ATP).
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DMA: Chapter 8 Hartmann's Plant
Science, 4th edition
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The Nucleus
• The nucleus is a prominent organelle ‫ عضو بارز‬within the
cell, enclosed by a double membrane and containing
one or more bodies called nucleoli.
• Within the nucleus are the chromosomes that carries
genes + long lengths mollecules of deoxyribonucleic
acid (DNA) and associated proteins that contain the
genetic information.
• DNA is also found outside the nucleus in the
mitochondria and in the chloroplasts, thereby giving
these bodies a role in heredity independent of the
nucleus. ‫يعطيها دورا الوراثة مستقل عن النواة‬
• Unlike nuclear DNA, mitochondrial DNA and
chloroplastic DNA are inherited only from the female
parent. (There is no sexual segregation of genetic
traits).
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DMA: Chapter 8 Hartmann's Plant
Science, 4th edition
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Vacuoles: surrounded by membrane = Tonoplast
• Vacuoles may occupy a major portion of the interior of
plant cells:
1. In actively dividing cells, vacuoles are very small,
2. But in mature cells, vacuoles account for up to 90% of
the cell volume).
• The membrane surrounding the vacuole is called the
tonoplast, and it serves an important role in:
1. Regulating ion flow within the cell,
2. Maintaining cell turgor, and
3. Other functions as:
The vacuole serves as a storage reserve for water and
salts, sugar, starch, protein, oil and pigments (blue and
red) as well as for toxic products.
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DMA: Chapter 8 Hartmann's Plant
Science, 4th edition
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