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Transcript
UNIVERSITY OF NAIROBI FACULTY OF EXTERNAL DEGREE STUDIES AND FACULTY OF SCIENCE Plant Structure and Function (SBT 204) Written By Dr. Norman C. Njoroge and Dr. Nelson O. Amugune Lecturers: Department of Botany University of Nairobi Reviewed By Dr. Elijah M.W. Akunda Senior lecturer: Department of Botany Lecture 1 Lecture outline Plant Cell Structure Page 1.0 Introduction 1.1 Plant cell components 1.2 Cell Size 1.3.0 Cell Compartmentation 1.3.1 The significance of compartmentation of a plant cell 1.3.2 Integration and coordination of cell metabolism 1.4.0 Structure of the cell wall 1.4.1 Middle lamellae 1.4.2 Primary cell wall 1.4.3 Secondary cell wall 1.4.4 Further modifications of the secondary cell wall 1.4.5 Simple and bordered pits 1.4.6 Plasmodesmata 1.4.7 Functions of the cell 1.5.0 Protoplast 1.5.1 Organelles 1.5.2 Nucleus 1.5.3 Nuclear membrane 1.5.4 Nucleoplasm 1.5.5 Chromatin 1.5.6 Nucleolus 1.6.0 Cytoplasm 1.6.1 Ground substance 1.6.2 Organelles bounded by two membranes 1.6.2.1 Plastids 1.6.2.1.1 Chromoplasts 1.6.2.1.2 Leucoplasts 1.6.2.1.3 Chloroplasts 1.6.2.2 Mitochondria 1.7.0 Organelles bounded by one membrane 1.7.1 Microbodies 1.7.1.1 Peroxisomes 1.7.1.2 Glyoxysomes 1.7.2 Vacuoles 1.8.0 Endomembrane system 1.8.1 Endoplasmic reticulum 1.8.2 Golgi bodies 1.8.2.1 Relationship between Golgi apparatus and endoplasmic reticulum 1.8.3 Plasma membrane 1.9.0 Cytoskeleton 1.9.1 Microtubules 1.9.2 Microfilaments 2.0 Ribosomes 2 3 5 6 6 7 7 7 8 10 10 10 12 13 13 14 14 14 15 15 15 15 16 16 16 16 16 16 18 19 19 19 20 20 20 20 21 22 22 22 22 23 23 Introduction We shall begin the study of this unit by reviewing the structure of the different parts of a plant cell and how the structures of those parts are suited to the function they perform. As we have already learned, the cell is the basic unit of structure and function. A good understanding of cell structure and function is essential because it will help us understand how a particular tissue is able to carry out its functions. For example, when we study the structure of a pallisade cell in a leaf, we are then able to understand how its structure enables it carry out photosynthesis. In our study of cell structure and function in the unit on “Introductory biochemistry and genetics” we simply stated the function of various organelles, but throughout this unit we are going to relate the structure of what we study to its function. Let us consider the example of glucose and fructose mentioned in the introduction of the unit. Both sugars contain exactly the same kinds and number of atoms (C6H12O6), but the atoms are arranged differently (figure 1). The two monosaccharides differ in the position of the C=O group. This small difference in position of the C=O group, distinguishes glucose that a cell can use directly in production of energy during respiration, from fructose that cannot be used directly as a source of energy. Glucose Fructose Figure 1 The structure of glucose and fructose. Both glucose and fructose contain the same kind and number of atoms, but the C=O group is on carbon 1 in glucose and on carbon 2 in fructose. So in this unit our main focus is to describe the structure of a plant part and explain how that structure enables that part carry out the task or tasks it is supposed to perform. In this lecture, we begin by identifying the plant cell components. We shall then discuss the size and shape of a plant cell and how the components of the cell are organized inside into organelles or compartments. We shall then review the advantages of having such an organizational set up with respect to some different chemical reactions that take place in the cell. Once we finish looking at the organization of a plant cell, we shall look at the cell wall, the outermost part of a plant cell, and then move into the interior of the cell for study of the relationship between structure and function of the cell organelles.