4/6/2008 DMA: 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. • 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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CHAPTER VIII- The Cell- Review...4/6/2008 DMA: Chapter 8 Hartmann's Plant Science, 4th edition 1 THE CELL • The plant cell is the basic structural and physiological unit of plants,
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• The plant cell is the basic structural and physiological unit of plants, in which most reactions characteristic of life occur.
• 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.
• 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.
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, and endoplasmic reticulum (Fig. 8-5).
• Mitochondria are cytoplasmic bodies that are smaller than plastids.
• The mitochondria are sites of respirationand are also involved in protein synthesis. They produce energy-rich compounds such as adenosine triphosphate (ATP).
The Nucleus• The nucleus is a prominent organelle within the cell,
enclosed by a double membrane and containing one or more bodies called nucleoli.
• Within the nucleus are the chromosomes, long lengths 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.
• Unlike nuclear DNA, mitochondrial DNA and chloroplastic DNA are inherited only from the female parent. (There is no sexual segregation of genetic traits).
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 pecticcompounds that hold adjacent cell walls together.
• 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.