Module 2: Plant Structure and Functions PDF

## MOULE 2: PLANT STRUCTURE AND FUNCTIONS | Topic No. | Topic Title | Time Duration | |---|---|---| | 7 | Cell Structure | Two Hour | | 8 | Transport Process | One Hour | | 9 | Growth and Division of the Cell | Two Hours | | 10 | Plant Tissues, Organs and Primary Growth | One Hours | | 11 | Sexual...

## MOULE 2: PLANT STRUCTURE AND FUNCTIONS | Topic No. | Topic Title | Time Duration | |---|---|---| | 7 | Cell Structure | Two Hour | | 8 | Transport Process | One Hour | | 9 | Growth and Division of the Cell | Two Hours | | 10 | Plant Tissues, Organs and Primary Growth | One Hours | | 11 | Sexual Reproduction | One Hour | **Learning Objectives:** 1. You must be able to describe the plant cell structure. 2. You must be able to discuss the various transport processes. 3. You must be able to describe the events in each phase of cell cycle. 4. You must be able to explain the morpho-anatomy of the different plant with their development, adaptations, modifications and pharmaceutical importance. 5. You must be able to explain the process of sexual reproduction in plants. **TOPIC 7 – CELL STRUCTURE** All organisms are composed of small structures called cells. In plants, each cell consists of a box-like cell wall surrounding a mass of protoplasm, which in turn contains its own smaller parts, the organelles, such as nuclei, mitochondria, and chloroplasts. Cells are also the physical framework within which a plant's metabolism occurs. Water and salts are absorbed from soil by root cells, they are transported throughout the plant by cells of the vascular tissues, and the energy of sunlight is used in leaf cells to convert carbon dioxide and water to carbohydrates. Plant reproduction is also based on cells and cell biology: Some cells in flowers produce pigments or nectar that attracts insects that carry pollen between flowers, allowing sperm cells to contact egg cells. **TABLE 3-1 Examples of Plant Cell Shapes and Sizes** | Cell | Shape | Dimensions | |---|---|---| | Dividing cell in shoot or root | Cube | 12 µm × 12 µm × 12 µm | | Epidermal cell of lily (Lilium) | Flat, paving stone | 45 µm × 143 µm × 15 µm | | Photosynthetic cell in leaf of pear (Pyrus) | Short cylinder | 7.4 µm diam × 55 μm | | Water-conducting vessel cell in oak (Quercus) | Short cylinder | 270 µm diam × 225 µm | | Fiber cell in hemp (Cannabis) | Long cylinder | 20 µm diam × 60,000 µm | **FIGURE 3-1** A plant metabolism, development, and survival depend on numerous cells working together in a coordinated, integrated fashion. - **(A)** These cells store water in the center of a sunflower stem; they are relatively large and filled mostly with water. - **(B)** Part of the system that conducts water and nutrients in a sunflower stem. Numerous types of cells occur in specific arrangements that permit efficient conduction. - **(C)** In this transverse section through a leaf of Ligustrum, you can see a variety of cells. **FIGURE 3-3** A micrograph made with a transmission electron microscope of leaf cells. Considering the large number of living organisms and the numerous types of metabolism that must be carried out, one might suspect that there are hundreds of types of cells, but actually, just a small number of cell types exist. Most differences between organisms are due to differences in associations of their cells, not in the cells themselves. Regardless of whether a root, stem, leaf, or flower is being constructed, the same basic units—cells—are required. **FIGURE 3-4** Transverse section of wood showing several cell types. Although only a few types of cells exist, their differences are important. Any organism composed of more than one cell (a multicellular organism rather than a unicellular one) always has several types, each specialized for different tasks. **TABLE 3-2** As a plant develops, the cells in various parts become especially adapted for specific tasks. This division of labor allows the entire organism to become more efficient. Unicellular organization has a significant consequence: It does not allow division of labor or specialization. **FIGURE 3-5** - **(A)** Cells located at the growing tip of Pinus are specialized for cell growth and division. - **(B)** These "stone cells" provide strength in a coconut shell and therefore protect the seed. **MEMBRANE** All cells contain at least some membranes, and cells of eukaryotes (plants, animals, fungi, and protists) contain numerous organelles composed of membranes. Membranes perform many important tasks in cell metabolism. Like whole individuals, cells have a life span. During their life cycle (cell cycle), cell size, shape, and metabolic activities can change dramatically. A cell is “born” as a twin when its mother cell divides, producing two daughter cells. Each daughter cell is smaller than the mother cell. **FIGURE 3-11** Generalized plant cell. ## **PROTOPLASM** All cells, either prokaryotic or eukaryotic, are made of a substance called protoplasm (Figure 3-5). The protoplasm of a single cell is called its protoplast. **FIGURE 3-12** - **(A)** A healthy, growing cell. - **(B)** These cells have been treated with salt to draw water out of the cell. ## **NUCLEUS** The nucleus (plural, nuclei) serves as an archive, or permanent storage place, for the organism's genetic information. **FIGURE 3-13** A preparation called a freeze-fracture. The cell is frozen and then tapped to cause it to break. The lipids of the membranes are weak when frozen. **FIGURE 3-14** Nucleoli usually stain more intensely than the rest of the nucleus In cells undergoing rapid cell division (e.g., cells in root tips, shoot tips, young leaves, and flower buds), the DNA, histones, and duplicating enzymes may dominate the nucleoplasm; however, in mature cells that are not dividing, messenger molecules and reading enzymes may be more abundant. Inside every nucleus is one, two, or rarely several bodies called nucleoli (singular, nucleolus), areas where the components of ribosomes are synthesized and partially assembled. **FIGURE 3-17** ThtilWlfl mltodloodrial metNOlt is folded Into platt-1 aistJe, gi'ling It a largts..toKt ⚫rea;many!!SplratOI)' tnzymturt intrinsic p,0 1111 tilt aim mtmballt. **TABLE 3-5** The Relative Volumes of Organelles in Plant Cells | Organelle | Young Cell | Mature Cell | |---|---|---| | Nucleus | 32.4 | 0.23 | | Vacuole | 4.93 | 83.3 | | Mitochondria | 5.35 | 1.01 | | Plastids | 3.72 (proplastids) | 3.16 (chloroplasts) | | Dictyosomes | 0.40 | 0.04 | | Hyaloplasm | 52.9 | 12.1 | | Lipid | 0.23 | 0.00 | **FIGURE 3-15** Azalea flower buds open overnight, the petals and stamens expanding rapidly as each cell fills its central vacuole with water. **TABLE 3-6** Concentrations of Nutrients in Vacuoles Isolated from Barley (Hordeum) Leaf Cells | Nutrient | Concentration (mM) | In Our Blood | |---|---|---| | Cr | 56.1 | 101 to 111 | | NO3- | 42.9 | not typically measured | | HPO42- | 64.5 | 0.25 to 0.43 | | SO42- | 25.1 | not typically measured | | K+ | 142.2 | 3.7 to 5.2 | | Na+ | 42.2 | 136 to 144 | **FIGURE 3-16** A system to excrete wastes never evolved in plants; instead, metabolic waste products are pumped across the vacuole membrane and stored permanently in the central vacuole. ## **CYTOPLASM** If the nucleus and vacuole are excluded from the protoplasm, the remaining material is referred to as cytoplasm and contains the following structures. **FIGURE 3-18** Mitochondrial membranes are folded, forming large sheets or tubes known as cristae (pronounced CHRIS tee; singular, crista). This folding provides room for large numbers of enzymes. **FIGURE 3-26** Electron micrograph showing two chloroplasts with two peroxisome-type microbodies next to them. ## **MICROBODIES** Viewed by electron microscopy, cells are seen to contain numerous small, spherical bodies approximately 0.5 to 1.5 µm in diameter. ## **MITOCHONDRIA** Cells store energy as highly energetic but fairly unreactive compounds, such as sugars and starches. Mitochondria (singular, mitochondrion) are the organelles that carry out this cell respiration. **FIGURE 3- 27** (A) Microtubules that are part of a dividing nucleus and are involved in pulling chromosomes to the ends of the cells. (B) Alpha- and beta-tubulin associate into a dimer called tubulin. **FIGURE 3-28** Microtubules (depicted here in purple) are often located next to the plasma membrane. ## **RIBOSOMES** Immersed in the protoplasm are ribosomes, particles responsible for protein synthesis. **FIGURE 3-22** (A) Ribosomes only rarely occur free in the cytoplasm; instead, they are usually attached to membranes such as the type shown here, called endoplasmic reticulum (ER). **FIGURE 3-23** (A) With rapid dictyosome activity, as in these mucilage-secreting cells, the cytoplasm may almost fill with dictyosome vesicles, and fusion of vesicles with the plasma membrane is so abundant that the plasma membrane appears scalloped. **FIGURE 3-24** (A) Vesicles derived from ER migrate a short distance to a dictyosome-forming face. **FIGURE 3-25** This is a mucilage cell. ## **DICTYOSOMES** Much of the material secreted by a cell must first be modified by a dictyosome, a stack of thin vesicles held together in a flat or curved array. **FIGURE 3-29** (A) The two members of a pair of centrioles are always located perpendicular to each other. **FIGURE 3-30** Flagella occur on many algal and fungal cells, especially the unicellular organisms. This is the alga Dunalliela. ## **PLASTIDS** Plastids are a group of dynamic organelles able to perform many functions. **FIGURE 3-19** All plastids have an outer and an inner membrane, but in chloroplasts, the inner membrane is extensive and highly folded. **TABLE 3-7** Types of Plastids | Amyloplasts | Store starch; considered to be leucoplasts | |---|---| | Chloroplasts | Carry out photosynthesis | | Chromoplasts | Contain abundant colored lipids; in flowers and fruits | | Etioplasts | A specific stage in the transformation of proplastids to chloroplasts; occur when tissues are grown without light | | Leucoplasts | Colorless plastids; synthesize lipids and other materials | | Proplastids | Small, undifferentiated plastids | **FIGURE 3-20** (A) Cells from a developing bean seed. The large pink bodies are starch grains; the small bluish-red ones are protein bodies. ## **THE PLANT CELL STRUCTURE** Although various parts of a plant – roots, wood, bark, leaves, and flower parts appear to be quite diverse, virtually all of their cells have all of the following organelles; exceptions are rare. ## **CENTRAL VACUOLE** Within young, small cells are organelles, vacuoles, that have just a single membrane, the vacuole membrane. **FIGURE 3-15** Azalea flower buds open overnight, the petals and stamens expanding rapidly as each cell fills its central vacuole with water. **TABLE 3-8** Subunits of the Cell | Whole cell | |---|---| | Cell wall | | Protoplasm | | Nucleus | | Vacuole | | Cytoplasm | | All remaining organelles | | Cytosol | **FIGURE 3-27** (A) Microtubules that are part of a dividing nucleus and are involved in pulling chromosomes to the ends of the cells. (B) Alpha- and beta-tubulin associate into a dimer called tubulin. **FIGURE 3-29** (A) The two members of a pair of centrioles are always located perpendicular to each other. **FIGURE 3-30** Flagella occur on many algal and fungal cells, especially the unicellular organisms. ## **TOPIC 8 – TRANSPORT PROCESS** One fundamental aspect of life itself is the ability to transport specific substances to particular sites, moving molecules against the direction in which they would diffuse if left alone. **FIGURE 12-1** - **(A)** Xylem is a means of long-distance transport, carrying water from the tips of this plant's long roots. - **(B)** Xylem of an Opuntia cactus. ## **TOPIC 9 – GROWTH AND DIVISION OF THE CELL** The life cycle of individual organisms includes stages of initiation, growth, and death. **FIGURE 4-1** The cell cycle consists of division and growth phases. **FIGURE 4-2** For example, leaf cells stop dividing when the leaf is only a few millimeters long; they continue to grow as the leaf expands and then function for the rest of the leaf 's life. **FIGURE 4-3** Some cells live for many years, even hundreds of years, but others die shortly after they mature. **FIGURE 4-4** In contrast to palms, this conifer has many groups of dividing cells. **FIGURE 4-5** When a cambial cell divides, one of the new daughters becomes a wood or bark cell, and the other remains part of the dividing layer. ## **GROWTH PHASE OF CELL CYCLE** In the 1800s, when the cell cycle was first being studied intensively, researchers gave the greatest attention to the division activities because many events could be identified. **FIGURE 4-6** Comparison of cell cycles of different tissues or species. ## **G1 PHASE** In G1 (or gap 1), the first stage after division, the cell is recovering from division and conducting most of its normal metabolism. **FIGURE 4-7** If each gene were a distinct piece of DNA, ensuring replication of each would be difficult, and ensuring that each daughter nucleus received one copy of each would be even more difficult. **TABLE 4-1** Cell Cycle Phase Durations in Root Tip Cells and Cell Cultures | Species | Total | G1 | S | G2 | M | |---|---|---|---|---| | Daucus carota (carrot) Root tip | 7.5 | 1.3 | 2.7 | 2.9 | 0.6 | | Daucus carota Cell culture | 51.2 | 39.6 | 3.0 | 6.2 | 2.4 | | Haplopappus gracilis Root tip | 10.5 | 3,5 | 4.0 | 1.4 | 1.6 | | Zea mays (corn) Root tip | 9.9 | 1.7 | 5.0 | 2.1 | 1.1 | | Allium cepa (onion) | 17.5 | 1.5 | 10 | 4.0 | 2.0 | **FIGURE 4-8** Each nucleus in the cells of Arabidopsis thaliana has two of each of these five types of chromosomes. **FIGURE 4-9** Histone proteins associate into short cylinders and then DNA winds around each cylinder. **FIGURE 4-10** This chromosome was taken from a cell during division. **FIGURE 4-11** (A) Before S phase, each chromosome has one chromatid and one copy of each gene. ## **S PHASE** During S (or synthesis) phase, the genes in the nucleus are replicated. **FIGURE 4-12** In this root of Scirpus (bulrush, sedge), cells in the central column have enormous nuclei that have undergone endoreduplication. **FIGURE 4-13** Egg cells of pines and other conifers become enormous. ## **G2 PHASE** After S phase, the cell progresses into G2 phase (G2), during which cells prepare for division. **FIGURE 4-14** During mitotic nuclear division, one chromatid from each chromosome is pulled to one end of the cell, and the other chromatid of each chromosome goes to the other end. ## **M PHASE** Mitosis is duplication division. It is the more common type of karyokinesis. ## **TOPIC 10 – PLANT TISSUE, ORGANS AND PRIMARY GROWTH** The body of an herb contains just three basic parts: leaves, stems, and roots. **FIGURE 5- 1** - **(A)** The primary body of an herb like this geranium consists of roots, stems, and leaves - **(B)** This Iris is also an herb and never produces wood or bark. **FIGURE 5- 2** This prickly pear shows that one plant can have two types of shoot. **FIGURE 5-3** This orchid carries out photosynthesis by means of roots that contain chlorophyll. **FIGURE 5-4** Most epiphytic orchids resist the stresses of temporary drying because their shoots are fibrous and have a thick cuticle composed of cutin and wax. **FIGURE 5-5** These bromeliads are not rooted into the coastal sand dunes ## **TOPIC 11 – SEXUAL REPRODUCTION** Sexual reproduction of flowering plants is the result of the male sperm in the pollen uniting with the female egg in a flower. **FIGURE 1** Birds, insects, bats, and other animals are attracted to scented or brightly colored flowers. **FIGURE 2** Pollination of a flower **FIGURE 3** Fertilization of a flower. **FIGURE 4** One sperm nucleus fertilizes the egg, and the other sperm nucleus fuses with the polar nuclei. ## **THE SEED** A seed is a living entity that serves as a bridge between generations of a plant. **FIGURE 5** The major parts of seeds are common to dicots and monocots. ## **PLANT STRUCTURE and FUNCTIONS** The flowering plants discussed here are formally classified as the division Magnoliophyta, but they are known informally as angiosperms. ## **PLANT TISSUES** The individual cells of multicellular organisms are arranged into groups that function collectively as tissues. ## **MERISTEMATIC OR EMBRYONIC TISSUES** These group of young cells. The new cells produced are typically small, each with a proportionately large nucleus in the center and tiny vacuoles. ## **PERMANENT TISSUES** These are usually non-dividing cells, with a few exceptions. ## **KINDS OF SIMPLE PERMANENT TISSUES** **FIGURE 4.2** Types of parenchymal cells. **FIGURE 4.6 (left)** Section of marigold (Caledula officinalis) stem showing pink-stained collenchyma cells. **FIGURE 4.7** Schlerenchyma. ## **XYLEM** This is composed of four cell types, namely: ## **PHLOEM** As complex permanent tissue composed of: **FIGURE 4.8.** Xylem tissue and cells. **FIGURE 4.13.** Phloem tissue from a stem, showing cell types. ## **THE PLANTS OUTER COVERINGS** ## **EPIDERMIS** The epidermis is the outer covering of the plant. It is a complex tissue composed of epidermal cells, guard cells, and trichomes. **FIGURE 4.16.** Epidermis and epidermal cells. **FIGURE 4.17.** Cross section of leaf of pincushion tree (Hakea sp.). Note the thick cuticle and small channels crossing the cuticle. **FIGURE 4.18.** Stomata. **FIGURE 4. 19.** Glandular hairs of tobacco (Nicotiana tabacum). ## **PERIDERM** The periderm is a protective layer that forms in older stems and roots after those organs expand and the epidermis splits and is lost. It is a secondary tissue. **FIGURE 4.20** Diagram of periderm, showing the layers: phellem, cork cambium, and phelloderm. ## **SECRETORY TISSUE PRODUCE AND SECRETE MATERIALS** Secretory structures occur mostly in leaves and stems. **FIGURE 4.19** Glandular hairs of tobacco (Nicotiana tabacum). **FIGURE 4.21** Laticifer cells in spurge (Euphorbia sp.) stems. ## **MERISTEMS** We now know the tissues and cell types making up the vascular plant, but how do these tissue and cells come to be? **FIGURE 4.22.** Diagram of a tomato plant showing the relative positiions of the root apical meristem (RAM) and shoot apical meristem (SAM), the primary meristems (protoderm, ground meristem, and procambium), and the secondary meristems (vascular cambium and cork cambium) in both the shoot and root systems. **FIGURE 4.23** Shoot and root tips. ## **ROOT AND SHOOT MERISTEMS** The vascular plant body is polar, meaning that it has a shoot end and a root end. ## **PRIMARY MERISTEMS** A shoot tip and a root tip of a representative plant are shown in Figures 4.22 and 4.23. **FIGURE 4.22** Diagram of a tomato plant showing the relative positiions of the root apical meristem (RAM) and shoot apical meristem (SAM), the primary meristems (protoderm, ground meristem, and procambium), and the secondary meristems (vascular cambium and cork cambium) in both the shoot and root systems. **FIGURE 4.23.** Shoot and root tips. ## **SECONDARY MERISTEMS** The secondary meristems are responsible for cell division, initiation of cell differentiation, and growth in a lateral direction, thereby increasing the thickness and circumference of stems and roots. **FIGURE 4.24** Summary of meristems and the tissues they generate. ## **TOPIC 11 – SEXUAL REPRODUCTION** Sexual reproduction of flowering plants is the resuilt of the male sperm in the pollen uniting with the female egg in a flower. **FIGURE 1** Birds, insects, bats, and other animals are attracted to scented or brightly colored flowers. **FIGURE 2** Pollination of a flower **FIGURE 3** Fertilization of a flower. **FIGURE 4** One sperm nucleus fertilizes the egg, and the other sperm nucleus fuses with the polar nuclei.