Bio 110 Chapter 7 Plant PDF

General Biology Bio 110 Chapter 7 Plant Contents: PART V Microbiology Chapter 6 PART VI Plant Chapter 7 PART VII Animal Chapter 8 PART IX Genetic Basis of Life a. C...

General Biology Bio 110 Chapter 7 Plant Contents: PART V Microbiology Chapter 6 PART VI Plant Chapter 7 PART VII Animal Chapter 8 PART IX Genetic Basis of Life a. Cell Cycle and Genetic Disorders Chapter 9 b. Classical Genetics and Modern Chapter 10 Biotechnology Part VI: Plant Introduction: Plans are mainly multicellular organisms, predominantly photosynthetic eukaryotes of the kingdom Plantae. Green plants obtain most of their energy from sunlight via photosynthesis by primary chloroplast. There are about 320000 species of plants, of which the great majority, some 260-290 thousand, produce seeds. Green plants provide a substantial production of the world’s molecular oxygen and are the basis of most of Earth’s ecosystem. Plants that produce grain, fruits, and vegetables also form basic human foods and have been domesticated for millennia. Plants have many cultural and other uses, such as ornament, building material, and writing materials, and in great variety, they have been the source of medicine. The scientific study of plants is known as Botany , a branch of Biology.  Part VI a. Types of Plant Tissues  a. Tissues and Organization 7.1 Types of Plant Tissues a. Epidermal Tissue b. Ground Tissue c. Vascular Tissue 7.2 Organ Systems of Flowering Plants a. Roots b. Stems c. Leaves d. Monocot Versus Eudicot Plants  7.1 Types of Plant Tissues: A flowering plant has the ability to grow its entire life because it possesses meristematic (embryonic) tissue. Apical meristems are located at or near the tips of roots (Figure 7.1) and stems (Figure 7.2), where they increase the length of these structures. Figure 7.2 Apical shoot meristem. Figure 7.1 Root hairs and meristem.  7.1 Types of Plant Tissues In addition to apical meristems, monocots have a type of meristem called intercalary meristem, which allows them to re-grow lost parts. They account for why grass can so readily re-grow after being grazed by a cow or cut by a lawnmower. Figure 7.2 Apical shoot meristem. Figure 7.1 Root hairs and meristem.  7.1 Types of Plant Tissues Meristems develop into three types of specialized tissues and functions include: epidermal tissue to form the outer protective covering of a plant, ground tissue to fills interior of a plant vascular tissue to transport water and nutrients in a plant and provides support  7.1 Types of Plant Tissues a. Epidermal Tissue The entire body of plants is covered by a layer of epidermis. The walls of epidermal cells that are exposed to air are covered with a waxy cuticle to minimize water loss and protect the cell against bacteria and other organisms that might cause disease. In roots, certain epidermal cells have long, slender projections called root hairs. Hairs increase the surface area of the root for absorption of water and minerals (Figure 7.1). They also help anchor plant firmly in place. On stems, leaves and reproductive organs, epidermal cells produce hairs called trichomes (Figure 7.2) that have two important functions: 1- to protect the plant from too much sun and to conserve moisture. 2- trichomes help protect a plant from herbivores by producing a toxic substance.  7.1 Types of Plant Tissues a. Epidermal Tissue (continued): In leaves, the lower epidermis of eudicots and both surfaces of monocots contain specialized cells called guard cells (Figure 7.3). These cells surround microscopic pores called stomata (sing., stoma). When the stomata are open, gas exchange and water loss occur. Figure 7.3 Guard cells. In woody plants, the epidermis of the stem is replaced by periderm. The majority component of periderm is box-like cork cells. New cork cells are made by a meristem called cork cambium. These non-living cells make the plant resistant to attacks by fungi, bacteria and animals. Some cork tissues are commercially used for bottle corks Figure 7.3 Periderm and and other products. cork cambium.  7.1 Types of Plant Tissues a. Epidermal Tissue (continued): The cork cambium has cracks on the surface called lenticels that are important in gas exchange between interior of a stem and air (Figure 7.4). b. Ground Tissue Ground tissue forms the bulk of a flowering plant and contains parenchyma, collenchyma and sclerenchyma cells (Figure 7.5). Figure 7.4 Cork cells. Figure 7.5 Ground tissue cells.  7.1 Types of Plant Tissues Parenchyma cells -the best typical plant cell- are found in all organs of a plant. They may contain chloroplasts (Figure 7.5a) and carry-on photosynthesis (chlorenchyma) or contain colorless plastids to store the products of photosynthesis (i.e., starch, Figure 7.5b). Collenchyma (Figure 8.5c) cells are like parenchyma cells except they have thicker primary walls. The thickness is uneven and usually involves the corners of the cell. Collenchyma cells often form bundles just beneath the epidermis and give flexible support to immature regions of a Figure 7.5 Ground tissue cells. plant body.  7.1 Types of Plant Tissues b. Ground Tissue (continued): Sclerenchyma (Figure 7.5d) cells have thick secondary walls filled with lignin; a highly resistant organic substance that makes the walls hard. Lignin is analogous to the cement. Most sclerenchyma cells are non-living with primary function to support the mature regions of a plant. Figure 7.5 Ground tissue cells.  7.1 Types of Plant Tissues c. Vascular Tissue: There are two types of vascular (transport) tissue. They are: 1- Xylem transports water and minerals from the roots to the leaves. 2- phloem transports sucrose and other organic compounds, including hormones, usually from the leaves to the roots. Both xylem and phloem are considered complex tissues because they are composed of two or more kinds of cells. https://www.sciencefacts.net/xylem-and-phloem.html 7.1 Types of Plant Tissues 1- Xylem contains two types of conducting modified sclerenchyma cells: tracheids and vessel elements (VE) (Figure 7.6). The tracheids, form a less means of transport. The vessel elements are larger and arranged to form a continuous vessel for water and mineral transport. Figure 7.6 Xylem structure. 7.1 Types of Plant Tissues 2- Phloem: The conducting cells of phloem are specialized parenchyma cells called sieve-tube members arranged to form a continuous sieve tube connected to a companion cell. The companion cell is also believed to be involved in the transport function of phloem (Figure 7.7). Vascular tissues extend from the root through stems to the leaves and vice versa. In roots, vascular tissues are shown as cylinders; while bundles in stems and veins in leaves. Figure 7.7 Phloem structure.  Part VIa 7.2 Organ systems of Flowering Plants  7.2 Organ systems of Flowering Plants An organ is composed of two or more types of tissues working together to perform particular functions. An organ system contains many different organs that cooperate to carry out a process. Flowering plants, or angiosperms, are extremely diverse in size and shape, but they share many common structural features. Most flowering plants possess root and shoot systems (Figure 7.8). The root system simply consists of the roots, while the shoot system consists of the stem and leaves. A typical plant features three vegetative organs; roots, stems and leaves. Figure 7.8 Organization of a plant body.  7.2 Organ systems of Flowering Plants Vegetative organs are concerned with growth and nutrition. Flowers, seeds and fruits are structures involved in reproduction. a. Roots: The root system in the majority of plants is located underground. The root system is equivalent in size and extent to the shoot system, i.e., an apple tree has a much larger root system than a corn plant. A single corn plant may have roots as deep as 2.5 m and spread out over 1.5 m, while trees that live in the desert may have roots that penetrate to a depth of over 20 m. Figure 7.8 Organization of a plant body.  7.2 Organ systems of Flowering Plants a. Roots (continued): Function: 1.  The extensive root system of a plant anchors it in the soil and gives it support. 2.  Root absorbs water and minerals from the soil for the entire plant.  The cylindrical shape of a root allows it to penetrate the soil as it grows and permits water to be absorbed from all sides.  The absorptive capacity of a root is dependent on its many branches.  Root hairs are the structures that absorb water and minerals. Figure 7.8 Organization of a plant  7.2 Organ systems of Flowering Plants a. Roots (continued): Function: 2.  Root hairs are so numerous that they tremendously increase the absorptive surface of a root.  Root-hair cells are constantly being replaced, so this same rye plant forms about 100 million new root- hair cells every day.  A plant roughly pulled out of the soil will not fare well upon transplantation because small lateral roots and root hairs are torn off. Figure 7.8 Organization of a plant  7.2 Organ systems of Flowering Plants a. Roots (continued): Function: 2.  Transplantation is more apt to be successful if you take a part of the surrounding soil along with the plant, leaving as much of the lateral roots and the root hairs intact as possible. 3.  Roots produce hormones that stimulate the growth of stems and coordinate their size with the size of the root. Figure 7.8 Organization of a plant  7.2 Organ systems of Flowering Plants b. Stems: The shoot system of a plant is composed of the stem, the branches and the leaves. A stem, the main axis of a plant, has a terminal bud that allows the stem to elongate and produce new leaves (Figure 7.8). A node occurs where leaves are attached to the stem; the region between nodes is called an internode (Figure 7.8). An axillary bud, located at a node, can produce new branches of the stem (or flowers). A horizontal underground stem, called a rhizome, sends out roots below and shoots above at the nodes as it grows. Figure 7.8 Organization of a plant  7.2 Organ systems of Flowering Plants Stem function: 1. Stem supports leaves to be exposed to as much sunlight as possible. 2. Stem has vascular tissue that transports water and minerals from roots through stem to leaves and transports the products of photosynthesis, usually in opposite direction. 3. As trees grow, they accumulate woody tissue to add to strength of their stems. 4. In some plants (e.g., cactus), the stem is the primary photosynthetic organ. 5. Stem is a water Cactus reservoir in juicy plants, while under- ground branches store nutrients. Figure 7.8 Organization of a plant  7.2 Organ systems of Flowering Plants c. Leaves Leaves are the major part of a plant that carries on photosynthesis, a process that requires water, CO2 and sunlight. Leaves receive water from the root system by way of the stem. The size, shape, color and texture of leaves are highly variable. These characteristics are fundamental in plant identification. Leaves of some aquatic weeds may be less than 1 mm in diameter, while some palms may have leaves that exceed 6 m in length. The shape of leaves can vary from cactus spines to white oak leaves. Leaves can exhibit a variety of colors from Figure 7.8 Organization of a plant various shades of green to deep purple.  7.2 Organ systems of Flowering Plants c. Leaves (continued): The texture of leaves varies from smooth (Solomon's seal) and waxy like a magnolia to coarse like a sycamore. Plant bearing leaves the entire year is called evergreen and that losing its leaves every year is called deciduous (seasonal). Solomon's Broad and thin plant leaves have the Seal maximum surface area for the absorption of carbon dioxide and the collection of solar energy needed for photosynthesis. The wide portion of a foliage leaf is called Magnoli the blade. a The petiole is a stalk that attaches the blade to the stem. Some leaves are specialized to protect buds, attach to objects (tendrils), store food (bulbs), or capture insects (vinus).  7.2 Organ systems of Flowering Plants d. Monocot Versus Eudicot Plants: Flowering plants are divided into two groups, depending on the number of cotyledons in the seed (Figure 7.9). Some embryos have one cotyledon, monocots and other have two, eudicots. Cotyledons of eudicots supply nutrients for seedlings, but the cotyledon of monocots acts as a transfer tissue and the nutrients are derived from the endosperm before the first true leaves begin photosynthesizing (Figure 7.9). The vascular (transport) tissue is organized differently in monocots and eudicots. In the monocot root, vascular tissue occurs in a ring (Figure 7.9). In the eudicot root, the xylem (red) is star-shaped; and the phloem (blue) is located between the points of the star. In monocot stem, the vascular tissue are scattered, while occur in ring in eudicot stem. Leaf veins are vascular tissues within a leaf.  7.2 Organ systems of Flowering Plants d. Monocot Versus Eudicot Plants (continued): Figure 7.9 Monocots versus eudicots..  7.2 Organ systems of Flowering Plants Monocots exhibit parallel venation and eudicots exhibit netted venation, which may be either pinnate or palmate. Pinnate venation means that major veins originate from points along the centrally placed main vein and palmate venation means that the major veins all originate at the point of attachment of the blade to the petiole. Monocots have their flower parts arranged in multiples of three and eudicots have their flower parts arranged in multiples of four or five. Eudicot pollen grains usually have three pores and monocot pollen grains usually have one pore (Figure 7.10). The eudicots are the larger group and include some of our most familiar flowering plant. The monocots include grasses, lilies, orchids and palm trees, among others. Some of most significant food sources are monocots, including rice, wheat and Figure 7.10 An eudicot pollen grain. corn.  Part VIb b. Nutrition and Transport  Part VI b: Nutrition and Transport 7.3 Plant Nutrition: a. Essential Inorganic Nutrients  Hydroponics b. Soil 1. Mineral Particles 2. Humus 3. Living Organisms c. Water and Mineral Uptake 7.4 Transport Mechanisms in Plant a. Water Transport  Cohesion-Tension Model of Xylem Transport (Upward Movement) b. Organic Nutrient Transport  Pressure-Flow Model of Phloem Transport (Downward Movement)  7.3 Plant Nutrition The ancient Greeks believed that plants were “soil-eaters” and somehow converted soil into plant material. In the seventeenth-century, scientists believed that the increase in weight of trees was due to the addition of water. Water is a vitally important nutrient for a plant, but scientists were unaware that water and carbon dioxide (taken in at the leaves) combine in the presence of sunlight to produce carbohydrates (photosynthesis). a. Essential Inorganic Nutrients: Approximately 95% of a typical plant’s dry weight (weight excluding free water) is carbon, hydrogen and oxygen. In addition, plants require certain other nutrients that are absorbed as minerals by the roots. A mineral is an inorganic substance usually containing two or more elements.  7.3 Plant Nutrition A- Essential Inorganic Nutrients: Why are minerals from the soil needed by a plant ? Nitrogen is a major component of nucleic acids and proteins. Phosphorus is a major component of nucleic acids. Magnesium is a component of chlorophyll. Iron is a building block of cytochrome molecules. A nutrient is essential if: It has an identifiable role. No other nutrient can substitute and fulfill the same role. A deficiency of this nutrient causes a plant to die without completing its life cycle.  7.3 Plant Nutrition Essential nutrients are divided into macronutrients (eg., C, H, O, N, P, K, S, Ca and Mg) and micronutrients (eg., Fe, B, Mn, Cu, Zn, Cl and Mo) according to their relative concentrations in plant tissue. Beneficial nutrients are another category of elements taken up by plants. They are required for the growth of a particular organism or organism's part (eg., horsetails require silicon as a mineral nutrient and sugar beets show enhanced growth in the presence of sodium). Hydroponics: Hydroponics is of interest as a way to grow crops. Hydroponic culture allows plants to grow well if they are supplied with all the nutrients they need, while plant growth will suffer if a particular mineral is omitted (Figure 7.11). In hydroponics, plant pests, weeds and diseases are eliminated. Solution lacks an essential nutrient Complete nutrient solution Figure 7.11 Nutrient deficiencies.  7.3 Plant Nutrition B- Soil Oxygen can enter from the air, but all of the other essential nutrients are absorbed by roots from the soil, eg., plant's life is dependent on the quality of the soil and the ability of soil to provide nutrients it needs. Soil is defined as a mixture of mineral particles, decaying organic material (humus), living organisms, besides, air and water. 1. Mineral Particles: It is best if the soil contains particles of different sizes to allow spaces for air. Sand particles are the largest (0.05–2.0 mm in diameter) and clay particles are the smallest (less than 0.002 mm). Because sandy soils have many large particles, they have large spaces, and the water drains readily through the particles. In contrast, a soil composed mostly of clay particles has small spaces that fill completely with water.  7.3 Plant Nutrition 1. Mineral Particles: Because clay particles are unable to retain negatively charged NO3-, the nitrogen content of soil is low. Legumes are sometimes planted to provide nitrogen to the soil. 2. Humus Humus, which mixes with the top layer of soil particles, increases the benefits of soil. Humus is acidic; therefore, it retains positively charged minerals until plants take them up. When the organic matter in humus is broken down by bacteria and fungi, inorganic nutrients are returned to plants.  7.3 Plant Nutrition 3. Living Organisms: Small plants play a major role in the formation of soil. The roots of larger plants penetrate soil and opens up soil layers, allowing water and air to spread. There are many different types of soil animals. The largest of them, such as toads, snakes and rabbits, disturb and mix soil by burrowing. Smaller animals like ants, construct colonies with massive chambers and tunnels. The microorganisms in soil, such as protozoans, fungi, algae and bacteria, are responsible for the final decomposition of organic remains in humus to inorganic nutrients.  7.3 Plant Nutrition C- Water and Mineral Uptake in plant: Pathways for water and mineral uptake and transport in plant are the same. Water and minerals can enter the root of a plant from the soil simply by passing between the porous cell walls or through root hairs when they have a higher osmotic pressure (or lower water potential) than the soil solution (Figure 7.12). Plants possess the ability to actively (by expending energy) take up and concentrate minerals. Plants can take up minerals until they are See more concentrated (sometimes 10,000x Figure 9.3 greater) in the plant than in the surrounding medium. Following their uptake by root cells, minerals move in cells across selectively permeable plasma membrane. By what mechanism do minerals cross plasma membranes ? Figure 7.12 Pathways of water and minerals.  8.3 Plant Nutrition C-Water and Mineral Uptake in plant: Recall that a plant cell absorbs minerals in the ionic form; nitrogen is absorbed as nitrate (NO3-), potassium as potassium ions (K+). Ions cannot cross the plasma membrane because they are unable to enter the non-polar phase of the lipid bilayer (Figure 7.13). The energy of ATP is indirectly required for mineral ion transport. Mineral Ion Transport : 1. A plasma membrane pump, called a proton pump, hydrolyzes ATP and uses energy released to transport hydrogen ions (H+) out of the cell. 2. This sets up an electrochemical gradient that drives positively charged ions such as K+ through a channel protein into the cell. 3. Negatively charged ions are Figure 7.13 Minerals uptake. transported, along with H+.  Part VI b 7.4 Transport Mechanisms in Plant  7.4 Transport Mechanisms in Plant When leaves carry on photosynthesis, carbon dioxide enters leaves at the stomata, but water, the other main requirement for photosynthesis, is absorbed by the roots. Then, water must be transported from the roots to the stem to the leaves through a vascular transport tissue called xylem. The process of photosynthesis results in sugars, which are used as a source of energy and building blocks for other organic molecules throughout a plant. On the other hand, phloem is the type of vascular tissue that transports organic nutrients to all parts of the plant requiring a source of energy in order to carry on cellular metabolism and/or will store them for future use.  7.4 Transport Mechanisms in Plant a. Water Transport: Numerous experiments were done to determine how water and minerals rise to the tops of very tall trees in xylem and how organic nutrients move in the opposite direction in phloem ? Upward movement is described in the following model of xylem transport. Cohesion-Tension Model of Xylem Transport (Upward Movement) The cohesion-tension model (Figure 7.14) describes a mechanism for xylem transport that requires no expenditure of energy by the plant and is dependent on two properties of water; cohesion and adhesion. Figure 7.14 Cohesion-tension model of xylem transport.  7.4 Transport Mechanisms in Plant a. Water Transport (continued): Cohesion-Tension Model of Xylem Transport (Upward Movement) The term cohesion refers to the tendency of water molecules to come together due to hydrogen bonding that forms a continuous water column in xylem, from the roots to the leaves. Adhesion refers to the ability of water, a polar molecule, to interact and fill up the walls of the vessels in xylem and prevents water from slipping back. When the stomata of a leaf are open, the cells of the spongy layer are exposed to the air, which can be quite dry. Figure 7.14 Cohesion-tension model of xylem transport.  7.4 Transport Mechanisms in Plant a. Water Transport (continued): Cohesion-Tension Model of Xylem Transport (Upward Movement) Water then evaporates as a gas or vapor, a process called transpiration, from the spongy layer into the intercellular spaces. Over 90% of the water taken up by the roots is eventually lost by transpiration. Then, water molecules from the leaf veins replace those in the spongy layer. Because water molecules are cohesive, transpiration exerts a pulling force, or tension, that draws the water column through the xylem upward to replace the water lost from leaf veins. Figure 7.14 Cohesion-tension model of xylem transport.  7.4 Transport Mechanisms in Plant b. Organic Nutrient Transport: As plants transport water and minerals from the roots to the leaves through xylem, they transport organic nutrients to all parts of plants that need them through phloem as in the following process. Pressure-Flow Model of Phloem Transport (Downward Movement) The pressure-flow model (Figure 7.15) is a current explanation for the movement of organic materials in phloem. Consider the experiment in which two bulbs are connected by a glass tube. First bulb contains solute at a higher concentration than the second bulb. Bulb are bounded by a differentially permeable membrane and the entire apparatus is submerged in distilled water. Distilled water flows into the first bulb because it has the higher solute concentration. Figure 7.15 The pressure-flow model.  7.4 Transport Mechanisms in Plant b. Organic Nutrient Transport (continued): Pressure-Flow Model of Phloem Transport (Downward Movement) The entrance of water creates a positive pressure and water flows toward the second bulb. This flow not only drives water toward the second bulb, but it also provides enough force for water to move out through the membrane of the second bulb—even though the second bulb contains a higher concentration of solute than the distilled water. In plants, sieve tubes are analogous to the glass tube that connects the two bulbs as they form a continuous pathway for organic nutrient transport throughout a plant. Figure 7.15 The pressure-flow model.  7.4 Transport Mechanisms in Plant b. Organic Nutrient Transport (continued): Pressure-Flow Model of Phloem Transport (Downward Movement) 1. Photosynthesizing leaves (the source) are producing sugar that is actively transported into sieve tubes in which sugar is carried across the membrane in conjunction with hydrogen ions (H+) (Figure 7.16). 2. After sugar enters sieve tubes, water follows passively by osmosis. 3. The buildup of water within sieve tubes creates the positive pressure that accounts for the flow of phloem contents. The roots (and other growth areas) are a sink for sugar, meaning that they are removing sugar and using it for cellular respiration. Figure 7.16 Pressure-flow model of phloem transport.  7.4 Transport Mechanisms in Plant b. Organic Nutrient Transport (continued): Pressure-Flow Model of Phloem Transport (Downward Movement) 4. After sugar is actively transported out of sieve tubes, water exits phloem. 5. Then, water is taken up by xylem (sink). 6. The latter transports water to leaves, where it is used for photosynthesis. 7. Most water is transpired; some is used for photosynthesis and some reenters phloem by osmosis. Now, phloem contents continue to flow from the leaves (source) to the roots (sink). Figure 7.16 Pressure-flow model of phloem transport..  Part VIc Plant Reproduction  Part VI: Plant Reproduction 7.5 Plant Reproduction a. Sexual Reproductive Strategies in Plant  Life Cycle Overview b. Asexual Reproductive Strategies in Plant 1. Tissue Culture of Plant 2. Cell Suspension Culture 7.5: Plant Reproduction Introduction: Sexual Reproduction Flowering plants reproduce sexually through a process called pollination. The flowers contain male sex organs called stamens, and female sex organs called carpel( pistils) The anther is the part of the stamen that contain pollen. This pollen needs to be moved to a part of the carpel(pistil) called the stigma. Figure 7.17 Sexual reproduction in flowering plants.  7.5 Plant Reproduction a. Sexual Reproductive Strategies: Sexual reproduction is the way to generate polymorphism among the offspring through the process of meiosis (see Chapter 10) and fertilization. In a changing environment, new hybrids may be better adapted for survival and reproduction than either parent. Life Cycle Overview When plants reproduce sexually, they go through two stages; sporophyte (diploid, 2n) and gametophyte (haploid, n). 1. In flowering plants, the diploid sporophyte is the generation that bears flowers (Figure 7.17). Figure 7.17 Sexual reproduction in flowering plants. 7.5 Plant Reproduction 2. A flower; the reproductive structure of angiosperms, produces two types of spores by meiosis; micro-spores and megaspores. 3. A microspore undergoes mitosis and becomes a pollen grain, which is either wind-blown or carried by an animal to the female gametophyte. 4. In the meantime, the megaspore has undergone mitosis to become the female gametophyte, an embryo sac located within an ovule found within an ovary. 5. At maturity, a pollen grain travels through pollen tube to the embryo sac. Figure 7.17 Sexual reproduction in flowering plants.  7.5 Plant Reproduction 6. Once a sperm fertilizes an egg, the zygote becomes an embryo. 7. Ovule develops into a seed, which contains the embryo and stored food surrounded by a seed coat and ovary becomes a fruit. 8. When a seed germinates, a new sporophyte emerges and through mitosis and growth becomes a mature organism. Figure 7.17 Sexual reproduction in flowering plants. It worth mentioning that the sexual life cycle of flowering plants is adapted to a land existence. Pollen grains (male gametophytes) are not released until they develop a thick wall.  7.5 Plant Reproduction a. Sexual Reproductive Strategies (con’d): The microscopic female gametophytes develop completely within the sporophyte and are thereby protected from desiccation. Aside from producing the spores and protecting the gametophytes, flowers often attract pollinators, which aid in transporting pollen from plant to plant. Flowers also produce the fruits that enclose the seeds. Flowering is often a response to environmental signals such as the length of the day and temperature. Figure 7.17 Sexual reproduction in flowering pollinators plants.  7.5 Plant Reproduction b. Asexual Reproductive Strategies: Asexual reproduction is the production of an offspring identical to a single parent. It is less complicated in plants because pollination and seed production are not required. Therefore, it can be advantageous when the parent is already well- adapted to a particular environment and the production of genetic variations is not a necessity. Rhizomes are underground stems that produce new plants asexually. Irises are examples of plants that have no aboveground stem because their main stem is a rhizome that grows horizontally underground. Potatoes are expanded portions of a rhizome branch and each eye is a bud that will produce a new potato plant if it is planted with a portion of the swollen tuber. Sweet potatoes are modified roots propagated by planting root sections. As a discovery, the plant hormone auxin can cause roots to develop and allows plants to be propagated from stem cuttings.  7.5 Plant Reproduction b. Asexual Reproductive Strategies (con’d): I. Tissue Culture of Plant: Tissue culture is growth of a tissue in an artificial liquid or solid culture medium. Somatic embryogenesis, meristem tissue culture and anther tissue culture are three methods of cloning plants due to the ability of plants to grow from single cells; a process called totipotency. Figure 7.18 Asexual reproduction through tissue culture.  7.5 Plant Reproduction 1. Somatic Embryogenesis: During somatic embryogenesis, hormones are added to the medium to cause leaf or other tissue cells to generate small masses of cells namely callus (pl. calli) and little “plantlets” (Figure 7.18). Many crop plants, e.g., tomato, and ornamental plants, e.g., lilies, have been produced using somatic embryogenesis. They can vary because of mutations that arise during production process. These mutations, called somaclonal variations, are another way to produce new plants with desirable traits.. Figure 7.18 Asexual reproduction through tissue culture. 7.5 Plant Reproduction 2. Meristem Tissue Culture: Meristem tissue can also be a source of plant cells and the resulting plants are identical; e.g., with the same traits If the correct proportions of hormones are added to liquid medium, many new shoots develop from a single shoot tip. Another advantage to producing identical plants from meristem tissue is that the plants are virus-free. Figure 7.18 Asexual reproduction through tissue culture.  7.5 Plant Reproduction 3. Anther Tissue Culture: Anther tissue culture is a technique in which the haploid cells within pollen grains are cultured in order to produce haploid plantlets. A diploid (2n) plantlet can be produced if chemical agents; colchicine, to encourage chromosomal doubling are added to the anther culture. Anther tissue culture is a direct way to produce plants that are homozygous. Asexual reproduction method: Anther Tissue Culture https://propg.ifas.ufl.edu/09-tissue-culture/01- types/01-tctypes-anther.html  7.5 Plant Reproduction II. Cell Suspension Culture A technique called cell suspension culture allows scientists to extract chemicals (i.e., secondary metabolites) from plant cells in high concentration and without having to over-collect wild-type plants growing in their natural environments. These cells produce the same chemicals the entire plant produces. For example, cell suspension cultures of Digitalis species produce digitoxin, which are useful in the treatment of heart disease. In this way, endangered wild plants in the original habitat can be saved. https://www.sciencedirect.com/ Thank you