CELL STRUCTURE Cell Structure Cell wall Cell membrane
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 • • 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 (r. DNA) and ribosomes
Ribosomes • Particles synthesis in nucleolus and then pass through the nuclear pores to the cytoplasm • Made of protein and r. DNA • 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 • • • 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 • • 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
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