5/20/2015DMA: Chapter 8 Hartmann's Plant Science, 4th edition 1 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.

5/20/2015DMA: Chapter 8 Hartmann's Plant Science, 4th edition 2 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 % as water.

3 Electron microscope Enhanced light microscope

5/20/2015DMA: Chapter 8 Hartmann's Plant Science, 4th edition 4 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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5/20/2015DMA: Chapter 8 Hartmann's Plant Science, 4th edition 8 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 وسطى that has pectic material مواد هلامية 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.

5/20/2015DMA: Chapter 8 Hartmann's Plant Science, 4th edition 9 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.

5/20/2015DMA: Chapter 8 Hartmann's Plant Science, 4th edition 10 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. Primary and Secondary wall

5/20/2015DMA: Chapter 8 Hartmann's Plant Science, 4th edition 11 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.

5/20/2015DMA: Chapter 8 Hartmann's Plant Science, 4th edition 12 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).

5/20/2015DMA: Chapter 8 Hartmann's Plant Science, 4th edition 13 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.

5/20/2015DMA: Chapter 8 Hartmann's Plant Science, 4th edition 14 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).

5/20/2015DMA: Chapter 8 Hartmann's Plant Science, 4th edition 15 The Nucleus The nucleus is a prominent organelle عضو بارز within 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).

5/20/2015DMA: Chapter 8 Hartmann's Plant Science, 4th edition 16 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.