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CELL STRUCTURE
Cell Structure
• Cell wall
• Cell membrane
• protoplasm - the living contents within the
cell: nucleus and cytoplasm
Cell membrane
• Chemical
components :consists
of protein and lipid
• Structure: Two layers
of lipid sandwiched
between two protein
layers
Function of cell membrane
• Act as a partially permeable barrier controlling the
movement of substances between the cell and the
surrounding
• Act as support
• Act as enzyme which catalyzes the chemical
reaction within the cell membrane
• Act as carriers in transporting substance across the
membrane
• Act as recognition center
The Structure of Cell membrane
Nucleus
• Contains chromatin which is involved in
nuclear division
• Contains a nucleolus
Structure of Nucleus
• Enclosed by and
envelope of two
membranes that is
perforated by nuclear
pores
Function of Nucleus
• Necessary for survival of a cell
• Controls all the activities of the cell, cellular
function, cell division and heredity
Nuclear membrane
• Doubled layer
• Similar structure as
cell membrane
• Continuous with E.R.
• With microscopic
pores for exchange of
materials between
nucleus and cytoplasm
Nucleoplasm
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Nuclear sap
Gel-like
Denser than cytoplasm
Contains proteins, nucleotides and ions
Chromatin
• Consists of DNA and protein ( histone )
• Condense to rod-shape chromosome just prior to
nuclear division
• Carry genetic materials which determine
organisms’ characteristics and transmit these
characteristics to next generations
Nucleolus
• Composed of DNA mainly
• Act as the manufacturing site of ribosomal DNA
(rDNA) and ribosomes
Ribosomes
• Particles synthesis in
nucleolus and then
pass through the
nuclear pores to the
cytoplasm
• Made of protein and
rDNA
• The site for protein
synthesis
Endoplasm Reticulum ( E.R.)
• A system of parallel flattened membranebounded sacs called cisternae
• Continuous with the outer membrane of the
nuclear envelope
• Act as an intracellular transport system
• There are two types of E.R - Rough ER and
smooth ER
Rough E.R.
• Ribosomes are
attached to its surface
• Transports proteins
made by the
ribosomes through the
cisternae to smooth
ER and then to Golgi
appartus for futher
modification
Smooth E.R.
• Without ribosomes
attached to its surface
• Transport lipids
• Synthesis of lipids and
steriod
Diagram of Golgi
Golgi Apparatus
• Usually located near the nucleus
• consists of stacks of flattened membrane bounded
sacs called cisternae and many vesicles
• At one end of the stacks new cisternae are
constantly formed by fusion of vesicles pinched
from smooth ER; at the other end, small Golgi
vesicles are pinched off constantly
• Transport in vesicles of many cell materials, such
as enzymes form ER
• Involved in secretion and lysosome formation
Lysosomes
• A spherical sac bounded by a
single membrane
• Contain digestive (hydrolytic)
enzymes
• Intracellular digestion of food
materials eg. Amoeba
• Destroy the worn-out
organelles inside cell
• For self-destruction of cells in
developmental process
Mitochondrion I
cristae
matrix
outer
membrane
inner membrane
• Surrounded by an envelope
of two membranes, the inner
being folded to form cristae
• Contains a matrix with
respiratory enzymes for the
Kreb’s cycle
• Rich in cell which require
large amont of energy such as
sperm tail, muscle cell
Mitochondion II
• The cristae increase the
surface area for attachment
of respiratory enzymes for
the electron transfer
reactions
• In aerobic respiration,
cristae are the sites of
oxidative phosporylation
and electron transport
Function of Mitochondrion
• Act as power house of a cell
• The energy releasing reactions of
respiration occur in matrix and on the
cristae
Centrioles
• Adjacent to nucleus
• Internal structure of a centriole is similar to that of
basal body of a cilium, with 9 micotubules
• Forming the spindle fibres and microtubules during
nuclear division to control the separation of
chromatids and chromosome
Microtubule
• Act as cytoskeleton which
support the cell
• Involves in the movement
of substances inside the
cell
• Forming the spindle fibres
which involve in the
separation of chromatids
and chromosome
Cell wall
• Only found in plant cells
• Rigid and rather
permeable
• Made of cellulose
• Usually modified by
lignin
• with pores which are
penetrated by
plasmmodesmata
Function of Cell wall
• Provides mechanical support and protection
of the cell
• Allows a pressure potential to be developed
which aids in support
• Prevent osmotic bursting of the cell
Chloroplast
• Large plasmid
containing chlorophyll
which absorb light for
photosynthesis
• Bounded by two
membrane
• Consists of chloroplast
envelope, stroma,
lamella and granum
Vacuole
• Absence or small in animal cells
• Common and large in plant cells
• The enclosing membrane is called
tonoplast
• Contain the internal cell sap which
is a concentrated solution consists
of water, sugar, salts, fat, oils,
proteins and pigment
Function of Vacuole
• Store various substances eg. Food and
wastes
• Maintenance of turgor for support
• Contain hydrolytic enzymes to acts as
lysosomes during life and cause autolysis
after death
Plant Histology
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Parenchyma
Collenchyma
Sclerenchyma
Xylem Tissue
Phloem Tissue
Parenchyma
• Plant cells with thin cell
wall and living protoplasm
• Roughly isodiametric with
intercellular spaces
• Found in cortex and pith of
stems and root, mesophyll
of leaves and packing
tissues in xylem and
phloem
Function of Parenchyma
• Act as packing tissues between more specialized
tissues
• Turgidity of these cells can provide support in
herbaceous plant
• Store food
• Intercellular air spaces allow gaseous exchange
• Metabolically active
• Their cell walls are important pathway for the
water and mineral salts through the plant
Collenchyma
• Characterized by the
deposition of extra cellulose at
the corners of the cells so have
thickening cell wall of their
corners
• They are living cells
• Found in regions beneath the
epidermis of stem (hypodermis)
and near the vascular tissues,
eg, midrib of leaves
Sclerenchyma
• Plant cells with
uniformly thickened
cell wall which is
usually lignified
• They are dead cells
• Support the cells
• There are two types:
fibres and Sclerids
Fibre
• Long narrow cell shape with tapering ends,
wall with few piths
• Found in cortex, pericycle, vascular tissues,
surrounding vascular bundles
Sclereids
• Shorter, vary much in shape, may be
spherical, polyhedral, elongated or branched
with numerous pits
• Found in almost everywhere in plant body,
especially in cortex, phloem of stems and
roots, in fruit wall and seed coat
• Act as main cell type for mechanical
support
Xylem Tissue
• Tracheary elements
(tracheids, vessels)
which are dead and
empty cells for
conducting water and
support
Tracheids
• Narrow elongated cell with finely tapering ends,
without protoplasm at maturity, with heavily
lignified and pitted secondary cell wall
• Passage of water from cell to cell is facilitated
through pit-pairs which allow lateral transport of
water
• Act as the only water conducting elements in
gymnosperms and primitive vascular plant;
small amount in angiosperms
Vessel I
• Long, pipe-like cell shape, with complete or
incomplete perforation at the end wall
• Without protoplasm at maturity
• Join each other at perforated end walls to
form longitudinal conducting tubes
• Shorter, greater in diameter than tracheids
Vessel II
• Water moves from cell to cell through
perforations and pit pairs
• Cell wall lignified and strengthened to
prevent collapse
• More specialized for water conducting than
tracheids
• Only present in angiosperms
Diagram of Phloem
Phloem Tissue
• Sieve elements (sieve cells, sieve tube elements)
for conduction of food materials
• Sieve elements are elongated cells, cell wall with
sieve areas
• Sieve elements is absence of nucleus, tonoplast,
decrease in number of ER and ribosomes, with
thin layer cytoplasm to facilitate the translocation
of food
Sieve Cell
• With sieve areas evenly distributed
• Present in gymnosperms and lower vascular
plant
Sieve Tube Element
• Located on the end walls called sieve plates
• Connected by sieve plates with each other
to form sieve tube
• Present in angiosperms
• With companion cell to help translocation
of food
Blood cell
• Is a specialized connective tissue for
transportation of materials and body
defence
• include fluid medium (plasma 55%) and
cellular constituents (erythrocytes,
leukocytes and thrombocytes 45%)
Skeletal muscle
• Innervated by the voluntary part of nervous
system
• contraction is neurogenic required nervous
stimulation
• contract and fatigue rapidly
• attached to the skeleton
• long, cylindrical with tapering or rounded
ends
Functions of skeleton muscle
• for the maintenance of posture
• for locomotion and movements of body
parts
Neurones
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Including cell body and nerve fibres
located in C.N.S
cell body is stellate in shape
nerve fibres are protoplasmic extensions of
cell body, including dendrons and axon
Nerve
• a group of nerve fibres bound together by
connective tissues lying outside C.N.S
• including sensory nerve, motor nerve and
mixed nerve