Chapter 4: Module in Botany PDF

Introduction Plants have evolved different reproductive strategies for the continuation of their species. Some plants reproduce sexually while others reproduce asexually, in contrast to animal species, which rely almost exclusively on sexual reproduction. Plant sexual reproduction usually depends o...

Introduction Plants have evolved different reproductive strategies for the continuation of their species. Some plants reproduce sexually while others reproduce asexually, in contrast to animal species, which rely almost exclusively on sexual reproduction. Plant sexual reproduction usually depends on pollinating agents, while asexual reproduction is independent of these agents. Flowers are often the showiest or most strongly-scented part of plants. With their bright colors, fragrances, and interesting shapes and sizes, flowers attract insects, birds, and animals to serve their pollination needs. Other plants pollinate via wind or water; still others self-pollinate. **CHAPTER OBJECTIVES**: - To enumerate and describe the reproductive organ and structure of a flower; - To describe the mechanism of development of these structures in relation to plant life cycle; - To describe and differentiate asexual from sexual reproduction and to identify plants exhibiting this two types of reproduction. **Introduction** [Plants are majorly classified](https://www.toppr.com/guides/biology/diversity-in-living-organisms/plant-kingdom/) on basis of presence or absence of flower into flowering and non- flowering plants. Flowers are important for sexual reproduction by plants. They produce male sex cells and female sex cells. These must meet for reproduction to begin, a process called pollination. A flower is a characteristic feature of flowering plants and is actually an extension of the shoot meant for [reproduction](https://www.toppr.com/guides/biology/how-do-organisms-reproduce/introduction-to-reproduction/). Flowers are attractive and appear in different colours and shapes to attract pollinators who help in [pollen transfer](https://www.toppr.com/guides/biology/sexual-reproduction-in-floweing-plants/outbreeding-devices-pollen-pistil-interaction/). Flowers are the reproductive structures produced by plants which belong to the group known as Angiosperms, or \'Flowering Plants\'.  This group includes an enormous variety of different plants ranging from buttercups and orchids to oak trees and grasses. There are about 250,000 known species. 8 - Discuss the vegetative parts of a flower - Discuss the male and female reproductive organ of a flower - Identify and describe the functions of the reproductive parts of a flower and illustrate the pollination process I. **VEGETATATIVE PARTS OF A FLOWER** Flowers are the reproductive part of a plant. They are not only involved in reproduction, but are also a source of food for other living organisms. They are a rich source of nectar. **Flowers can either be** - Complete - Incomplete. A complete flower is the one that consists of sepals, petals, stamens and pistil. On the contrary, an incomplete flower is the one that lacks one or more of these structures. A complete flower consists of two different parts: - Vegetative Part - Reproductive Part **Also read: **[Flowers and Inflorescence](https://byjus.com/biology/flowers-inflorescence/) **Vegetative Parts of a Flower** The vegetative part of a flower consists of the following: - **Petals: **This is a bright-coloured part that attracts bees, insects, and birds. Colour of petals varies from plant to plant; some are bright while some are pale coloured. Thus, petals help us to differentiate one flower from another. - **Sepals: **Sepal is the green-coloured part beneath the petals to protect rising buds**. **Some flowers have fused petals-sepals while a few have separated petals-sepals. II. **Reproductive Parts of a Flower** Flowers contain the plant's reproductive structures In different plants, the number of petals, sepals, stamens and pistils can vary. The presence of these parts differentiates the flower into complete or incomplete. Apart from these parts, a flower includes reproductive parts -- stamen and pistil.  A flower may have only female parts, only male parts, or both. +-----------------------------------+-----------------------------------+ | **Female Reproductive Organ** | | +===================================+===================================+ | flowfm.jpg (7768 bytes) | The female parts of a flower | | | consist of an ovary, which | | | contains one or more ovules, a | | | style and the stigma. The ovary | | | is at the base of the flower. | | | | | | From the ovary, extends a tubular | | | structure called the style and on | | | the top of the style is a surface | | | receptive to pollen called the | | | stigma. | | | | | | The stigma can take many | | | different forms, most of them | | | designed to help trap pollen. | | | There are many variations on this | | | basic structural theme. | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | **Male Reproductive Organ\ | | | A Stamen** | | +-----------------------------------+-----------------------------------+ |  | consist of one or more stamens. | | | Each stamen is made up of paired | | | anthers (sacs containing pollen) | | | on a filament or stalk. | | | | | | The anthers are the orange/yellow | | | structures often seen in the | | | centre of a flower. | | | | | | Pollen from the anthers of one | | | flower is transferred to the | | | stigma of another usually either | | | by wind, or by animals, | | | especially insects. | +-----------------------------------+-----------------------------------+ The reproductive parts of a flower consist of the following: - **Stamen: **This is the male reproductive organ and is also known as Androecium. It consists of two parts namely: anther and filaments. The anther is a yellowish, sac-like structure, involved in producing and storing the pollens. The filament is a slender, threadlike object, which functions by supporting the anther. - **Pistil: **This is the innermost part and the female reproductive organ of a flower which comprises three parts -stigma, style and ovary. This is collectively known as the pistil. Stigma: It is the topmost part or receptive tip of carpels in the gynoecium of a flower. Style: It is the long tube-like slender stalk that connects stigma and the ovary. Ovary: It is the ductless reproductive gland that holds a lot of ovules. It is the part of the plant where the [seed formation ](https://byjus.com/biology/seed-formation/)takes place. **Also Read: **[Artificial Hybridization in Plants](https://byjus.com/biology/artificial-hybridization-plants/) - **Whorls** Along with the vegetative and reproductive parts, a flower is also composed of four whorls, which is largely responsible for the radial arrangement of a flower. A typical flower has a circular section with a common centre, which can be clearly observed and distinguished from the top of the flower. There are four whorls: - **Calyx** The calyx is the outermost whorl of a flower. It comprises sepals, tiny leaves present at the base of a flower. These protect the flower whorls against mechanical injuries and desiccation. Some plants have coloured sepals the calyx and are called petaloid. If the sepals are free the calyx is called polysepalous, and if they are united it is called gamosepalous. In many flowers, the sepals fall off before the flower even opens fully. Such sepals are known as caducous. In some, the sepals fall off after fertilization. Such sepals are known as deciduous. The persistent sepals remain up to the fruiting stage. - **Corolla** This is the second whorl of a flower. It contains petals which serve two main functions: To attract pollinators. To protect the reproductive parts of a flower Petals are brightly coloured and scented to attract animals and insects for pollination. The calyx and corolla are collectively called the perianth. **Different forms of the corolla are found in the flowers.** - Polypetalous Regular - Polypetalous Irregular - Gamopetalous Regular - Gamopetalous Irregular - **Stamens ** Stamen is also known as the third whorl of the flower and is the male reproductive part. It consists of a filament which is a thread-like structure with a circular structure anther on the top. Pollen is produced by the anther which contributes to the male reproductive process of the plant. All the stamens do not bear fertile anthers. - **Carpels**  The carpel is the fourth whorl of the flower present in the centre. The carpels contain the pistil, the female reproductive part of the flower. It comprises the ovary, style, and stigma. The egg or the ovule is present in the ovary. After [fertilization](https://byjus.com/biology/fertilization-in-plants/), sometimes the ovary turns into the fruit to keep the seed. At the top of the ovary is a vertical structure called style that supports the stigma. The dispersed pollens stick to the stigma and travel down to the ovary through the style. This was an overview of the different parts of a flower. **Also Read: **[Sexual Reproduction in Flowering Plants](https://byjus.com/biology/sexual-reproduction-in-flowering-plants/) **Functions Of Flower** **The important functions of flowers are mentioned below:** - Gametophytes develop in the flowers. - The flowers can produce diaspores without fertilization. - After fertilization, the ovary of the flower develops into a fruit containing a seed. - The most important function of flowers is reproduction. They help in the union of male and female gametes. - Flowers provide nectar to certain birds and insects, which in turn help in the transfer of pollen from one flower to the other. - Flowers may promote selfing, i.e., the union of sperms and eggs from the same flower, or cross-fertilization, i.e., the union of sperms and eggs from different flowers. **Pollination** Pollination is the process in which the pollens are transferred from anther to stigma. The process of pollination can occur through a different medium. The table mentioned below describes the different types of pollination along with their pollinating agents. ** Pollination Process** **  Pollination Medium** -------------------------- --------------------------   Malacophilous   By snails   Chiropteriphilous   By bats   Hydrophilous   By water   Zoophilous   By animals   Anemophilous   By air   Entomophilous   By insects   Ornithophilous   By birds III. **PARTS AND FUNCTIONS OF THE STRUCTURES OF THE FLOWER AND THE PROCESS OF POLLINATION** Parts of a Flower Most flowers have four main parts: [sepals](https://www.toppr.com/guides/biology/sexual-reproductio-in-flowering-plants/sexual-reproduction/), petals, stamens, and carpels. The stamens are the male part whereas the carpels are the female part of the flower. Most flowers are hermaphrodite where they contain both male and female parts. Others may contain one of the two parts and may be male or female.  Illustration shows parts of a flower, which is called the perianth. The corolla is composed of petals, and the calyx is composed of sepals. At the center of the perianth is a vase-like structure called the carpel. A flower may have one or more carpels, but the example shown has only one. The narrow neck of the carpel, called the style, widens into a flat stigma at the top. The ovary is the wide part of the carpel. Ovules, or megasporangia, are clusters of pods in the middle of the ovary. The androecium is composed of stamens which cluster around the carpel. The stamen consists a long, stalk-like filament with an anther at the end. The anther shown is tri-lobed. Each lobe, called a microsporangium, is filled with pollen. *The four main parts of the flower are the calyx, corolla, androecium, and gynoecium. The androecium is the sum of all the male reproductive organs, and the gynoecium is the sum of the female reproductive organs. (credit: modification of work by Mariana Ruiz Villareal)*  *The corn plant has both staminate (male) and carpellate (female) flowers. Staminate flowers, which are clustered in the tassel at the tip of the stem, produce pollen grains. Carpellate flower are clustered in the immature ears. Each strand of silk is a stigma. The corn kernels are seeds that develop on the ear after fertilization. Also shown is the lower stem and root.* If both male and female flowers are borne on the same plant, the species is called monoecious (meaning "one home"): examples are corn and pea. Species with male and female flowers borne on separate plants are termed dioecious, or "two homes," examples of which are *C. papaya* and *Cannabis*. The ovary, which may contain one or multiple ovules, may be placed above other flower parts, which is referred to as superior; or, it may be placed below the other flower parts, referred to as inferior. Part A shows a lily, which has an ovary above the petals. The ovary sits above the teardrop-shaped petals. Part B shows several fuchsia flowers hanging down from a stem. The ovary is below the edge of the petals.  The (a) lily is a superior flower, which has the ovary above the other flower parts. (b) Fuchsia is an inferior flower, which has the ovary beneath other flower parts. (credit a photo: modification of work by Benjamin Zwittnig; credit b photo: modification of work by "Koshy Koshy"/Flickr)  **Pistil consists of four parts** http://k8schoollessons.com/wp-content/uploads/2013/05/pistil-parts-of-a-flower.jpg *(Source: Britannica)* Flower Did you know the largest flower found on earth weighs fifteen pounds and can grow up to three feet! It is called the Rafflesia Arnoldii. And the smallest is the Wolffia and it is the size of a grain of rice. Flowers are more than pretty things, they are responsible for the reproduction of plants and are absolutely essential. Enrichment: A. **Give what is being asked.** 1. If the anther is missing, what type of reproductive structure will the flower be unable to produce? 2. What term is used to describe an incomplete flower lacking the androecium? 3. What term describes an incomplete flower lacking a gynoecium? 4. What forms the androecium in a flower? 5. The flower is important to a plant because it helps in: 6. What flower contain both stamens and pistils? B. **Essay. Answer the questions briefly** 1. What are sessile and pedicellate flowers? Give examples. 2. Flowers, which are pollinated by insects, are? C. **Label the parts of a flower** Parts Of A Flower **Introduction** Early in their evolution, plants acquired a life cycle that alternates between a multicellular haploid organism, the gametophyte, and a multicellular diploid organism, the sporophyte. Angiosperms have both female and male gametophytes. The female gametophyte is critical to many steps of the angiosperm reproductive process, including pollen tube guidance, fertilization, the induction of seed development upon fertilization, and maternal control of seed development after fertilization. Gametophytes and sporophytes differ morphologically and functionally. The major function of diploid sporophyte generation is to produce haploid spores, which are the products of meiosis. Spores undergo cell proliferation and differentiation to develop into gametophytes. The major function of gametophyte generation is to produce haploid gametes. The fusion of egg and sperm gives rise to the zygote, which is the beginning of diploid sporophyte generation, thereby completing the life cycle ([**Gifford and Foster, 1989**](http://www.plantcell.org/content/16/suppl_1/S133#ref-24)). - Explain what is Gametophyte - Discuss the reproductive organ of female gametophytes and development of male gametophytes - Discuss the difference between Gametophyte and Sporophyte I. **What is Gametophyte?** The gametophyte is a stage in the life cycle that is found in all plants and certain species of algae. This process includes both multicellular diploid generation known as Sporophyte and a multicellular haploid generation known as Gametophyte. The word Diploid refers to two sets of chromosomes in the cells, and normally written as '2n'. Haploid to only one set of chromosomes in the cells and written as 'n'.  The primary job of gametophyte is the production of Gametes. The produced gametes are the haploid reproductive cells, such as sperm and eggs. II. **Reproductive Organs of Gametophyte** There are two types of reproductive organs found in a gametophyte: **Archegonium**: A multicellular sex organ in the female that creates eggs. It is like an ovary in females because both structures form haploid cells of the egg. **Antheridium**: A Multicellular sex organ in the male that produces sperm.  An antheridium is just like a testis in human males because both generate haploid sperm [[cells]](https://byjus.com/biology/cells/).  Both antheridia and archegonia are normally microscopic structures. Some of the gametophytes have both antheridia and archegonia. These are known as bisexual gametophytes since they consist of both female and male structures. A gametophyte that has only one kind of gametangium is known as a unisexual gametophyte. **Also Read: **[[Pteridophyta]](https://byjus.com/biology/pteridophyta/) **Haploid** A cell is said to be haploid if it possesses only one set of chromosomes. Haploid can also be used to refer to the number of chromosomes in the gametes which can either be eggs in females or sperm cells in males. The gametes in humans are haploid as they contain 23 chromosomes. Each of this chromosome exists in a pair which are present in diploid cells. The chromosome number that is present in a single set can be represented as 'n', where 'n' is also known as the haploid number. In the case of humans, n=23. Gametes possess half of the chromosomes that are present in normal diploid cells of the body. These diploid cells are referred to as somatic cells. During meiosis, haploid gametes are produced. It is a kind of cell division wherein the number of chromosomes is reduced in the parent diploid cell by half in number. Some entities such as algae contain haploid sections in their life cycle. Other entities such as male ants exist as haploid entities all through their life span. **Female Gametophyte: Embryo sac** The female gametophyte of gymnosperms is a large and multicellular structure that serves the double function of supporting the gametes as well as nurturing the growing embryo which is in contrast to the state in angiosperms, wherein female gametophyte is minute and typically eight-nucleated with a single operational gamete. The female gametophytes are responsible for the formation of female gametes and produce the molecular and physical basis for fertilization and origination of the seed development. These minuscule formations make up for the central hub for plant reproduction that depends on the molecular processes for its growth and development. It is not only sustained by gene functions but by cellular functions as well that are encoded by accessory cells which can turn active genetically if there is a failure in the gametes. **Development of Female Gametophyte** The whole process of female gametophyte development occurs in two different phases. The first phase involves the megasporogenesis, where a single diploid mother cell undergoes meiosis to form haploid megaspore tetrad out of which only one will survive and other three disintegrate. The functional megaspore grows into an embryo sac. Megagametogenesis is the second phase where the functional haploid megaspore undergoes mitosis to generate 7-celled, 8-nucleate gametophyte known as embryo sac. Out of the eight nuclei, polar nuclei move to the centre and fuse to produce a single diploid cell at the centre. This is the cell which fuses with the sperm to produce triploid endosperm. Three of the nuclei develop into antipodal cells and two will transform into synergid cells which eventually disintegrate. **Male Gametophyte: Pollen Grain** The first gametophytic structure is the modification of microspore mother cell into the pollen grain. The pollen grain grows into the male gametophyte on germination which is initiated before pollination takes place. Inside the microsporangium, Pollen mother cell (PMC) undergoes meiosis and results in four microspores which eventually mature into pollen grains. The inner layer called tapetum nourishes the developing microspores. The pollen grains consist of two cells- a vegetative cell and a generative cell. Once the microsporangium is matured it bursts and releases the pollen from the anther. The pollen grain consists of two layers. - the outer thick layer is called the exine, - the inner thin layer is called intine which protects the pollen from damage. Male gametophyte development can be classified into two stages: Pre-pollination development and post-pollination development. **Development of Male Gametophyte** Pollen grains display germination that is initiated in pollen sac which is referred to as precocious germination wherein a large central vacuole formation causes the nucleus to be pushed to one side post which the nucleus goes through mitosis that gives rise to two daughter nuclei. The small cell that is formed is known as the generative cell and the larger cell is known as the vegetative cell which has cytoplasm in sufficient amounts acting as a food reserve for the male gametophyte to develop, while the generative cell assembles at the mid-section of the pollen grain. At this phase, the pollen grains fall on the stigma wherein further development takes place. The falling of the pollen grains on the stigma causes the nutrient absorption through the germ pore from the stigma which causes the vegetative cell to enlarge. The enlargement causes the intine to move out via the germ pore for the formation of the pollen tube. The nuclei of the vegetative and generative cell travel to the pollen tube. The generative cell at this stage divides to produce two haploids, the non-motile and unicellular male gametes. For the deeper insertion of the tube, the size of the developed male gametophyte is diminished and derives the nutrition from the style's tissues. **Examples of Gametophytes** Following are the important examples of gametophytes: **Mosses** The gametophyte stage of moss is long-lived while sporophytes appear as long stalks that release spores by the wind. The sporophytes are formed by mixing the gametophyte sex cells. Therefore, they have twice the number of chromosomes compared to gametophytes. **Hornwort** The hornwort gametophyte is green, long-lived and low to the ground, while the sporophyte is a thin, long stalk from which the spores are released. Hornwort gametophytes and sporophytes are independent organisms with different chromosome numbers. **Gametophyte and Sporophyte** All plants reproduce both sexually and asexually due to variation in generations. Gametophytes and sporophytes consisting of genetic elements of the plant species. Some of the complex vascular plants spend more time as sporophytes, while mosses are not the same. The noticeable part of the plant is visible and is the gametophyte stage of these species. There is only one copy of every chromosome in Haploid gametophytes in their every cell; this is the reason why this life phase must produce asexually. Eventually, gametophytes create gametes that combine to produce a diploid zygote and grows into the sporophyte. Diploid sporophytes consist of two copies of every chromosome, hence it is able to support meiosis to produce haploid spores that grow into gametophytes, and brings the [[alternation of generations.]](https://byjus.com/biology/plant-life-cycle-and-alternation-of-generations/) III. **Difference Between Gametophyte And Sporophyte** Though the stages are common in different plant groups, their level of complexity and status across various groups is different. Following are the differences between both stages: 1. The gametophyte is the haploid(n) state in the life cycle whereas sporophyte is the diploid(2n) state in the life cycle. 2. Spore formation takes place post meiosis whereas gamete formation either occurs directly or through mitosis. 3. For the formation of spores, the mother cell goes through meiosis to produce haploids whereas gametes undergo fusion for the formation of diploid(2n), the zygote. 4. The meiospore grows to develop into the gametophyte. The zygote grows to produce sporophytes 5. The cells in sporophytes have two genomes or possess two sets of chromosomes. The cells of the gametophyte have a single genome or produce one set of chromosomes. **Also Read: **[[Pollination]](https://byjus.com/biology/what-is-pollination/) ***Watch this video:*** https://www.youtube.com/watch?v=K9kEvzH8FGg **Enrichment:** A. **Answer the following questions briefly:** 1. What is gametophyte? 2. What is a sporophyte? 3. How does a male gametophyte develop? 4. What is a female gametophyte?. 5. How is a gametophyte different from sporophyte? 6. What are the two different types of gametophytes? 7. What is the difference between gametophytes and gametangia? 8. Write a few examples of gametophytes. B. **Explain the development of female gametophyte in angiosperms. Illustrate the answer with suitable diagrams.** Introduction In angiosperms, pollination is defined as the placement or transfer of pollen from the anther to the stigma of the same or a different flower. In gymnosperms, pollination involves pollen transfer from the male cone to the female cone. Upon transfer, the pollen germinates to form the pollen tube and the sperm that fertilize the egg. - Determine the differences between pollination and fertilization, and self-pollination and cross-pollination, and describe how plants have developed ways to avoid self-pollination - Explain how pollination by insects aids plant reproduction - Differentiate among the non-insect methods of pollination - Describe the process of double fertilization in plants I. **Pollination and Fertilization** **Key Points** - - - - **Key Terms** - - - - **Self-Pollination and Cross-Pollination** Pollination takes two forms: self-pollination and cross-pollination. Self-pollination occurs when the pollen from the anther is deposited on the stigma of the same flower or another flower on the same plant. Cross-pollination is the transfer of pollen from the anther of one flower to the stigma of another flower on a different individual of the same species. Self-pollination occurs in flowers where the stamen and carpel mature at the same time and are positioned so that the pollen can land on the flower's stigma. This method of pollination does not require an investment from the plant to provide nectar and pollen as food for pollinators. These types of pollination have been studied since the time of Gregor Mendel. Mendel successfully carried out self-pollination and cross-pollination in garden peas while studying how characteristics were passed on from one generation to the next. Today's crops are a result of plant breeding, which employs artificial selection to produce the present-day cultivars. An example is modern corn, which is a result of thousands of years of breeding that began with its ancestor, teosinte. The teosinte that the ancient Mesoamericans originally began cultivating had tiny seeds, vastly different from today's relatively giant ears of corn. Interestingly, though these two plants appear to be entirely different, the genetic difference between them is minuscule. image **Genetic Diversity** Living species are designed to ensure survival of their progeny; those that fail become extinct. Genetic diversity is, therefore, required so that in changing environmental or stress conditions, some of the progeny can survive. Self-pollination leads to the production of plants with less genetic diversity since genetic material from the same plant is used to form gametes and, eventually, the zygote. In contrast, cross-pollination leads to greater genetic diversity because the male and female gametophytes are derived from different plants. Because cross-pollination allows for more genetic diversity, plants have developed many ways to avoid self-pollination. In some species, the pollen and the ovary mature at different times. These flowers make self-pollination nearly impossible. By the time pollen matures and has been shed, the stigma of this flower is mature and can only be pollinated by pollen from another flower. Some flowers have developed physical features that prevent self-pollination. The primrose employs this technique. Primroses have evolved two flower types with differences in anther and stigma length: the pin-eyed flower and the thrum-eyed flower. In the pin-eyed flower, anthers are positioned at the pollen tube's halfway point, and in the thrum-eyed flower, the stigma is found at this same location. This allows insects to easily cross-pollinate while seeking nectar at the pollen tube. This phenomenon is also known as heterostyly. Many plants, such as cucumbers, have male and female flowers located on different parts of the plant, thus making self-pollination difficult. In other species, the male and female flowers are borne on different plants, making them dioecious. All of these are barriers to self-pollination; therefore, the plants depend on pollinators to transfer pollen. The majority of pollinators are biotic agents such as insects (bees, flies, and butterflies), bats, birds, and other animals. Other plant species are pollinated by abiotic agents, such as wind and water.  II. **Pollination by Insects** Plants have developed adaptations to promote symbiotic relationships with insects that ensure their pollination. **Bees** Bees are perhaps the most important pollinator of many garden plants and most commercial fruit trees. The most common species of bees are bumblebees and honeybees. Since bees cannot see the color red, bee-pollinated flowers usually have shades of blue, yellow, or other colors. Bees collect energy -rich pollen or nectar for their survival and energy needs. They visit flowers that are open during the day, are brightly colored, have a strong aroma or scent, and have a tubular shape, typically with the presence of a nectar guide. A nectar guide includes regions on the flower petals that are visible only to bees, which help guide bees to the center of the flower, thus making the pollination process more efficient. The pollen sticks to the bees' fuzzy hair; when the bee visits another flower, some of the pollen is transferred to the second flower. Recently, there have been many reports about the declining population of honeybees. Many flowers will remain unpollinated, failing to bear seeds if honeybees disappear. The impact on commercial fruit growers could be devastating. image **Butterflies and Moths** Butterflies, such as the monarch, pollinate many garden flowers and wildflowers, which are usually found in clusters. These flowers are brightly colored, have a strong fragrance, are open during the day, and have nectar guides. The pollen is picked up and carried on the butterfly's limbs. Moths, on the other hand, pollinate flowers during the late afternoon and night. The flowers pollinated by moths are pale or white and are flat, enabling the moths to land. One well-studied example of a moth-pollinated plant is the yucca plant, which is pollinated by the yucca moth. The shape of the flower and moth have adapted in a way to allow successful pollination. The moth deposits pollen on the sticky stigma for fertilization to occur later. The female moth also deposits eggs into the ovary. As the eggs develop into larvae, they obtain food from the flower and developing seeds. Thus, both the insect and flower benefit from each other in this symbiotic relationship. The corn earworm moth and *Gaura* plant have a similar relationship.  **Pollination by Bats, Birds, Wind, and Water** Non-insect methods of pollination include pollination by bats, birds, wind, and water. III. **Non-Insect Methods of Pollination** Plants have developed specialized adaptations to take advantage of non-insect forms of pollination. These methods include pollination by bats, birds, wind, and water. **Pollination by Bats** In the tropics and deserts, bats are often the pollinators of nocturnal flowers such as agave, guava, and morning glory. The flowers are usually large and white or pale-colored so that they can be distinguished from their dark surroundings at night. The flowers have a strong, fruity, or musky fragrance and produce large amounts of nectar. They are naturally-large and wide-mouthed to accommodate the head of the bat. As the bats seek the nectar, their faces and heads become covered with pollen, which is then transferred to the next flower. **Pollination by Birds** Many species of small birds, such as hummingbirds and sun birds, are pollinators for plants such as orchids and other wildflowers. Flowers visited by birds are usually sturdy and are oriented in a way to allow the birds to stay near the flower without getting their wings entangled in the nearby flowers. The flower typically has a curved, tubular shape, which allows access for the bird's beak. Brightly-colored, odorless flowers that are open during the day are pollinated by birds. As a bird seeks energy-rich nectar, pollen is deposited on the bird's head and neck and is then transferred to the next flower it visits. Botanists determine the range of extinct plants by collecting and identifying pollen from 200-year-old bird specimens from the same site. image **Pollination by Wind** Most species of conifers and many angiosperms, such as grasses, maples, and oaks, are pollinated by wind. Pine cones are brown and unscented, while the flowers of wind-pollinated angiosperm species are usually green, small, may have small or no petals, and produce large amounts of pollen. Unlike the typical insect-pollinated flowers, flowers adapted to pollination by wind do not produce nectar or scent. In wind-pollinated species, the microsporangia hang out of the flower, and, as the wind blows, the lightweight pollen is carried with it. The flowers usually emerge early in the spring before the leaves so that the leaves do not block the movement of the wind. The pollen is deposited on the exposed feathery stigma of the flower.  **Wind pollination**: These male (a) and female (b) catkins from the goat willow tree (*Salix caprea*) have structures that are light and feathery to better disperse and catch the wind-blown pollen. **Pollination by Water** Some weeds, such as Australian sea grass and pond weeds, are pollinated by water. The pollen floats on water. When it comes into contact with the flower, it is deposited inside the flower. **Pollination by Deception** Orchids are highly-valued flowers, with many rare varieties. They grow in a range of specific habitats, mainly in the tropics of Asia, South America, and Central America. At least 25,000 species of orchids have been identified. Flowers often attract pollinators with food rewards, in the form of nectar. However, some species of orchid are an exception to this standard; they have evolved different ways to attract the desired pollinators. They use a method known as food deception, in which bright colors and perfumes are offered, but no food. *Anacamptis morio*, commonly known as the green-winged orchid, bears bright purple flowers and emits a strong scent. The bumblebee, its main pollinator, is attracted to the flower because of the strong scent, which usually indicates food for a bee. In the process, the bee picks up the pollen to be transported to another flower. Other orchids use sexual deception. *Chiloglottis trapeziformis* emits a compound that smells the same as the pheromone emitted by a female wasp to attract male wasps. The male wasp is attracted to the scent, lands on the orchid flower, and, in the process, transfers pollen. Some orchids, like the Australian hammer orchid, use scent as well as visual trickery in yet another sexual deception strategy to attract wasps. The flower of this orchid mimics the appearance of a female wasp and emits a pheromone. The male wasp tries to mate with what appears to be a female wasp, but instead picks up pollen, which it then transfers to the next counterfeit mate. image **Pollination by deception in orchids**: Certain orchids use food deception or sexual deception to attract pollinators. Shown here is a bee orchid (*Ophrys apifera*). IV. **Double Fertilization in Plants** Angiosperms undergo two fertilization events where a zygote and endosperm are both formed. **Double Fertilization** After pollen is deposited on the stigma, it must germinate and grow through the style to reach the ovule. The microspores, or the pollen, contain two cells: the pollen tube cell and the generative cell. The pollen tube cell grows into a pollen tube through which the generative cell travels. The germination of the pollen tube requires water, oxygen, and certain chemical signals. As it travels through the style to reach the embryo sac, the pollen tube's growth is supported by the tissues of the style. During this process, if the generative cell has not already split into two cells, it now divides to form two sperm cells. The pollen tube is guided by the chemicals secreted by the synergids present in the embryo sac; it enters the ovule sac through the micropyle. Of the two sperm cells, one sperm fertilizes the egg cell, forming a diploid zygote; the other sperm fuses with the two polar nuclei, forming a triploid cell that develops into the endosperm. Together, these two fertilization events in angiosperms are known as double fertilization. After fertilization is complete, no other sperm can enter. The fertilized ovule forms the seed, whereas the tissues of the ovary become the fruit, usually enveloping the seed.  **Double fertilization**: In angiosperms, one sperm fertilizes the egg to form the 2n zygote, while the other sperm fuses with two polar nuclei to form the 3n endosperm. This is called a double fertilization. After fertilization, the zygote divides to form two cells: the upper cell, or terminal cell, and the lower, or basal, cell. The division of the basal cell gives rise to the **suspensor**, which eventually makes connection with the maternal tissue. The suspensor provides a route for nutrition to be transported from the mother plant to the growing embryo. The terminal cell also divides, giving rise to a globular-shaped proembryo. In dicots (eudicots), the developing embryo has a heart shape, due to the presence of the two rudimentary **cotyledons** . In non-endospermic dicots, such as *Capsella bursa*, the endosperm develops initially, but is then digested, and the food reserves are moved into the two cotyledons. As the embryo and cotyledons enlarge, they run out of room inside the developing seed, and are forced to bend. Ultimately, the embryo and cotyledons fill the seed, and the seed is ready for dispersal. Embryonic development is suspended after some time, and growth is resumed only when the seed germinates. The developing seedling will rely on the food reserves stored in the cotyledons until the first set of leaves begin photosynthesis. Enrichment: A. Answer the questions briefly but concisely. 1\. Why do some plants have flowers? 2\. How can you tell which flowers are pollinated by animals or the wind 3\. Are seeds the only way flowering plants have of making new plants? 4\. Does it matter if pollen gets carried between flowers on the same plant? 5\. Many flowers need animals to pollinate them, but what do these pollinators get out of it? 6\. Pollination is vital for flowers, but is it important to humans? 7\. What's the difference between pollination and fertilization? 8\. What's it like working with honey bees -- aren't they dangerous? 9.What are some unusual mechanisms flowers use to get pollinated? 10.Some plants are pollinated by native birds, so what happens if the birds aren't around? Introduction The seeds and fruits are the results of [fertilization](https://www.toppr.com/guides/biology/human-reproduction/fertilization-and-post-fertilization-events-in-humans/) or [sexual reproduction](https://www.toppr.com/guides/biology/reproduction-in-animals/sexual-reproduction/) in plants. The ovary in angiosperms develops into the [fruit](https://www.toppr.com/guides/biology/morphology-of-flowering-plants/the-fruit/) whereas the ovules become the seeds enclosed within the fruit. [Seeds](https://www.toppr.com/guides/evs/seeds-and-seeds/seed/) are found both in gymnosperms and angiosperms.  - Discuss the Seeds and Fruits - Explain the Development of a Fruit - Learn the Simple, Aggregate, Multiple and Accessory Fruits - Differentiate true from false fruit - Illustrate dicotyledon and monocotyledon I. **SEEDS AND FRUITS** **Fruits** One of the many healthy things available in the world today is fruits. They are mostly sweet to taste, are filled with [nutrients](https://www.toppr.com/guides/science/nutrition-in-animals/introduction-to-nutrition/) and some of them are like tomatoes are also eaten as vegetables. The fruit is broadly divided into the pericarp which is the various covering layers of the fruit and the seed or seeds which are present inside it. The pericarp of a fruit can be further divided into: Fruit *Image Source: en.wikipedia.org* *Exocarp*-- It is the outermost layer which is formed from the outer layer or the epidermis *Mesocarp*-- Is the second or the middle layer which is often juicy and varies in thickness in different fruits *Endocarp*-- It is the innermost layer and also is different in different kinds of fruits II. **DEVELOPMENT OF A FRUIT** As mentioned earlier, once [[pollination]](https://www.toppr.com/guides/biology/sexual-reproductio-in-flowering-plants/pollination/) and fertilization occur, the zygote is formed and the ovary begins to differentiate into the fruit. The outer wall of the ovary begins to differentiate into the pericarp whereas the seed develops within the fruit itself. **Types of Fruits** Fruits can be classified in many ways. True and False Fruits Simple, Aggregate, and Multiple Fruits Simple fruits are further classified as fleshy and dry fruits depending on their appearance IV. **TRUE AND FALSE FRUITS**  *Image Source: slideplayer* - - III. **SIMPLE, AGGREGATE, MULTIPLE AND ACCESSORY FRUITS** **Simple Fruits** These fruits are formed from a single pistil only. They are further divided into Fleshy and Dry fruits based on the [[nature]](https://www.toppr.com/guides/business-studies/business-services/nature-and-types-of-services/) of their pericarp and its layers. A. **Fleshy Fruits** Fleshy fruits, as the name mentions, have a fleshy and juicy pericarp. They are further of many different types: - - - I. Dry fruits Dry fruits do not have juicy or thick pericarps and are of two types. - These fruits burst on their own to release the seeds.  They are of many types: - - - - http://cdn.biologydiscussion.com/wp-content/uploads/2016/02/clip\_image002\_thumb-69.jpg *Image Source: Toppr.com* - These fruits do not dehisce or burst to release the seeds.  They are of many types: - - - - -  *Image Source: ficcio* Aggregate Fruits These fruits are developed from an aggregate or cluster of multiple separate pistils that are borne on a single [[flower]](https://www.toppr.com/guides/biology/anatomy-of-flowering-plants/flower/). This aggregate or group of fruits that are developed from a single flower are known as an etaerio. Example: Raspberry. Multiple Fruits When an entire inflorescence develops into a single fruit, it is called a multiple fruits.  Example: Pineapple, figs, mulberry, jackfruit. V. **DICOTYLEDON AND MONOCOTYLEDON SEEDS** Once fertilization occurs, the mature ovule begins to differentiate into a seed. A seed contains many parts, namely: https://4.bp.blogspot.com/-KRLzOrAfPdM/V1-BaPSlGkI/AAAAAAAAAIA/jX6aGnN2\_M4faL2aUoC5a0UOEjRJNVBWwCLcB/s1600/Untitled.png *(Image Source: societynatureo.blogspot)* - - - - - **Enrichment:** A. **Short answer essay.** 1. **Where do fruits and seeds come from?** 2. **How seeds move?** 3. **Why do fruits have seeds?** **Introduction** Though we often consider seeds to be the first stage of new plant life, seeds are only containers, and not all plants reproduce by using them. Like with animals, the foundations of new plant life have less to do with the container, be it an egg or a womb, and more to do with what\'s *inside* that container: the embryo. The embryo in plants, whether it\'s found in a seed or a bud, contains the early form of the organs the plant needs to live. When conditions are right, the embryo bursts out of its container and becomes a seedling -- beginning the process of growing into an adult plant. - Discuss the Plant Embryo development - Illustrate the origins, development and diversity of plant embryos. - Explain how seeds develop I. **PLANT EMBRYO DEVELOPMENT** When a plant is fertilized, its male and female cells form a zygote -- a combined cell that can divide itself and grow into a new organism. That zygote will eventually form the plant embryo, which the parent plant protects by forming a container around it, whether it be a seed, a bud, a shoot or something similar, which is filled with endosperm -- food that the embryo can use during the early stages of germination. When this container is subjected to the correct conditions, the embryo can then complete its function. **Plant Embryo Function** The plant embryo function is effectively as a sort of \"starter kit\" for the new plant\'s life: It contains the earliest forms of the plant\'s roots, leaves and stem, and is capable of sensing, often through the use of its container, whether the correct conditions for growth are present. When the embryo detects an adequate amount of water, oxygen and other minerals in its environment, it begins to consume the endosperm in its container in order for the new plant to start growing.  II. **ORIGINS, DEVELOPMENT AND DIVERSITY OF [[PLANT EMBRYOS]](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/embryo-plant).** \(A) Various cells (grey cell in dashed red box) can generate plant embryos. Zygotic embryos form from the egg cell but [microspores](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/microspores), [somatic cells](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/somatic-cells) and in vitro-generated [callus](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/callus) cells can also start [embryogenesis](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/embryogenesis). (B) Two sequential processes define plant embryogenesis: its initiation from a non-embryonic precursor, followed by the development of a multi-cellular embryo. (C) Embryos in land plants are diverse. While the multicellular [bryophyte](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/bryophyte) embryo generates single-celled [spores](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/bacterial-spore), multicellular bodies with different organs (color legend below) are formed in, for example, [gymnosperms](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/gymnosperm), [monocots](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/monocotyledon) and [dicots](https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/magnoliopsida). III. **SEED & FRUIT DEVELOPMENT** The number of seeds within a fruit is also tightly linked to fruit size and shape in species with multiple fused carpels. If only one ovule, or a subset of the total ovules, is fertilized, it can result in abnormal development close to the unfertilized ovules and fruit asymmetry. Additionally, fruit size has been shown to be positively correlated with seed number in strawberry, kiwifruit, and apple. Generally, the more seeds a fruit contains, the bigger it is. *The relationship between fertilization, seed development, fruit development, fruit size, and fruit shape explain why growers of some tree fruit crops bring in supplemental pollinators to ensure that the maximum number of ovules within each flower are pollinated.* **Carpel number determines the relationship between pollination, seed development & fruit development** A **carpel* ***is the structure which includes both the ovary and its associated ovule(s) in a flower. The number of carpels, and the degree of fusion between carpels, varies among plant species. The common tree fruit crops grown in California generally contain either a single carpel, or multiple fused carpels. For example, flowers of walnut, pistachio, and all crop species within the genus *Prunus* contain a single carpel, while female kiwifruit flowers contain at least 30 fused carpels. After pollination and fertilization, carpels develop into the fruit tissue we eat (ovary) and the seeds within (ovules). Fruit development is initiated by growth regulating hormones produced by developing seeds. Because carpels ultimately develop into fruit tissue, the number of carpels in a flower determines the degree to which pollination and seed development is required to produce fruit. Flowers with one carpel only require fertilization of one of the two ovules to produce fruit. In contrast, species with multiple fused carpels require fertilization of a smaller proportion of the total ovules within a flower for fruit development. The growth regulating hormones produced by a subset of the total possible seeds are sufficient to initiate the development of fused carpels into fruit. As a result, normal fruit development is less dependent on seed development in species with multiple fused carpels. **Seeds Into Plants** The first major step of plant growth is called germination. When the embryo in a container has grown enough, using water and oxygen from its environment and consuming endosperm for energy, it bursts out of its container. Roots begin form, and the new plant\'s stem and leaves push up out of the ground. Once it has burst from its container, the embryo is officially deemed a \"seedling,\" and will grow into an adult plant. **Enrichment:** A. **Answer the questions exhaustively** 1. How significant is plant embryology in our modern society? 2. What does change have to do with plants' development? 3. Tissue culture is a very valuable tool for study plant development. Are the results from tissue culture experiments on plant development completely applicable to normal development? Explain. **Introduction** Many plants reproduce asexually as well as sexually. In asexual reproduction, part of the parent plant is used to generate a new plant. Grafting, layering, and micropropagation are some methods used for artificial asexual reproduction. The new plant is genetically identical to the parent plant from which the stock has been taken. Asexually reproducing plants thrive well in stable environments. - Describe characteristics of plants that reproduce asexually - Discuss the mechanisms, advantages, and disadvantages of natural and artificial asexual reproduction - Discuss plant life spans I. **CHARACTERISTICS OF ASEXUAL PLANTS** Many plants are able to propagate themselves using asexual reproduction. This method does not require the investment required to produce a flower, attract pollinators, or find a means of seed dispersal. Asexual reproduction produces plants that are genetically identical to the parent plant because no mixing of male and female gametes takes place. Traditionally, these plants survive well under stable environmental conditions when compared with plants produced from sexual reproduction because they carry genes identical to those of their parents. Many different types of roots exhibit asexual reproduction. The corm is used by gladiolus and garlic. Bulbs, such as a scaly bulb in lilies and a tunicate bulb in daffodils, are other common examples. A potato is a stem tuber, while parsnip propagates from a taproot. Ginger and iris produce rhizomes, while ivy uses an adventitious root (a root arising from a plant part other than the main or primary root), and the strawberry plant has a stolon, which is also called a runner. Shown are photos of various roots. Part A shows bulbous garlic roots. Part B shows a tulip bulb that has sprouted a leaf. Part C shows ginger root, which has many branches. Part D shows three potato tubers. Part E shows a strawberry plant. Different types of stems allow for asexual reproduction. (a) The corm of a garlic plant looks similar to (b) a tulip bulb, but the corm is solid tissue, while the bulb consists of layers of modified leaves that surround an underground stem. Both corms and bulbs can self-propagate, giving rise to new plants. (c) Ginger forms masses of stems called rhizomes that can give rise to multiple plants. (d) Potato plants form fleshy stem tubers. Each eye in the stem tuber can give rise to a new plant. (e) Strawberry plants form stolons: stems that grow at the soil surface or just below ground and can give rise to new plants. (credit a: modification of work by Dwight Sipler; credit c: modification of work by Albert Cahalan, USDA ARS; credit d: modification of work by Richard North; credit e: modification of work by Julie Magro) Some plants can produce seeds without fertilization. Either the ovule or part of the ovary, which is diploid in nature, gives rise to a new seed. This method of reproduction is known as **apomixis**. An advantage of asexual reproduction is that the resulting plant will reach maturity faster. Since the new plant is arising from an adult plant or plant parts, it will also be sturdier than a seedling. Asexual reproduction can take place by natural or artificial *(assisted by humans) means.* II. **NATURAL METHODS OF ASEXUAL REPRODUCTION** Natural methods of asexual reproduction include strategies that plants have developed to self-propagate. Many plants---like ginger, onion, gladioli, and dahlia---continue to grow from buds that are present on the surface of the stem. In some plants, such as the sweet potato, adventitious roots or runners can give rise to new plants. In *Bryophyllum* and kalanchoe, the leaves have small buds on their margins. When these are detached from the plant, they grow into independent plants; or, they may start growing into independent plants if the leaf touches the soil. Some plants can be propagated through cuttings alone.  A stolon, or runner, is a stem that runs along the ground. At the nodes, it forms adventitious roots and buds that grow into a new plant. **Artificial Methods of Asexual Reproduction** These methods are frequently employed to give rise to new, and sometimes novel, plants. They include grafting, cutting, layering, and micropropagation. Illustration shows the trunk of a sapling, which has been split. The upper part of a different sapling is wedged into the split and taped so that the two parts can grow together. Grafting has long been used to produce novel varieties of roses, citrus species, and other plants. In **grafting**, two plant species are used; part of the stem of the desirable plant is grafted onto a rooted plant called the stock. The part that is grafted or attached is called the **scion**. Both are cut at an oblique angle (any angle other than a right angle), placed in close contact with each other, and are then held together Figure 3. Matching up these two surfaces as closely as possible is extremely important because these will be holding the plant together. The vascular systems of the two plants grow and fuse, forming a graft. After a period of time, the scion starts producing shoots, and eventually starts bearing flowers and fruits. Grafting is widely used in viticulture (grape growing) and the citrus industry. Scions capable of producing a particular fruit variety are grated onto root stock with specific resistance to disease. **Cutting** Plants such as coleus and money plant are propagated through stem **cuttings**, where a portion of the stem containing nodes and internodes is placed in moist soil and allowed to root. In some species, stems can start producing a root even when placed only in water. For example, leaves of the African violet will root if kept in water undisturbed for several weeks. **Layering**  In layering, a part of the stem is buried so that it forms a new plant. **Layering** is a method in which a stem attached to the plant is bent and covered with soil. Young stems that can be bent easily without any injury are preferred. Jasmine and bougainvillea (paper flower) can be propagated this way. In some plants, a modified form of layering known as air layering is employed. A portion of the bark or outermost covering of the stem is removed and covered with moss, which is then taped. Some gardeners also apply rooting hormone. After some time, roots will appear, and this portion of the plant can be removed and transplanted into a separate pot. **Micropropagation** **Micropropagation** (also called plant tissue culture) is a method of propagating a large number of plants from a single plant in a short time under laboratory conditions. This method allows propagation of rare, endangered species that may be difficult to grow under natural conditions, are economically important, or are in demand as disease-free plants. Photo shows a plant growing in a test tube. To start plant tissue culture, a part of the plant such as a stem, leaf, embryo, anther, or seed can be used. The plant material is thoroughly sterilized using a combination of chemical treatments standardized for that species. Under sterile conditions, the plant material is placed on a plant tissue culture medium that contains all the minerals, vitamins, and hormones required by the plant. The plant part often gives rise to an undifferentiated mass known as callus, from which individual plantlets begin to grow after a period of time. These can be separated and are first grown under greenhouse conditions before they are moved to field conditions. III. **PLANT LIFE SPANS**  The length of time from the beginning of development to the death of a plant is called its life span. The life cycle, on the other hand, is the sequence of stages a plant goes through from seed germination to seed production of the mature plant. Some plants, such as annuals, only need a few weeks to grow, produce seeds and die. Other plants, such as the bristlecone pine, live for thousands of years. Some bristlecone pines have a documented age of 4,500 years. Even as some parts of a plant, such as regions containing meristematic tissue---the area of active plant growth consisting of undifferentiated cells capable of cell division---continue to grow, some parts undergo programmed cell death (apoptosis). The cork found on stems, and the water-conducting tissue of the xylem, for example, are composed of dead cells. Plant species that complete their lifecycle in one season are known as annuals, an example of which is *Arabidopsis*, or mouse-ear cress. Biennials such as carrots complete their lifecycle in two seasons. In a biennial's first season, the plant has a vegetative phase, whereas in the next season, it completes its reproductive phase. Commercial growers harvest the carrot roots after the first year of growth, and do not allow the plants to flower. Perennials, such as the magnolia, complete their lifecycle in two years or more. In another classification based on flowering frequency, **monocarpic** plants flower only once in their lifetime; examples include bamboo and yucca. During the vegetative period of their life cycle (which may be as long as 120 years in some bamboo species), these plants may reproduce asexually and accumulate a great deal of food material that will be required during their once-in-a-lifetime flowering and setting of seed after fertilization. Soon after flowering, these plants die. **Polycarpic** plants form flowers many times during their lifetime. Fruit trees, such as apple and orange trees, are polycarpic; they flower every year. Other polycarpic species, such as perennials, flower several times during their life span, but not each year. By this means, the plant does not require all its nutrients to be channelled towards flowering each year. As is the case with all living organisms, genetics and environmental conditions have a role to play in determining how long a plant will live. Susceptibility to disease, changing environmental conditions, drought, cold, and competition for nutrients are some of the factors that determine the survival of a plant. Plants continue to grow, despite the presence of dead tissue such as cork. Individual parts of plants, such as flowers and leaves, have different rates of survival. In many trees, the older leaves turn yellow and eventually fall from the tree. Leaf fall is triggered by factors such as a decrease in photosynthetic efficiency, due to shading by upper leaves, or oxidative damage incurred as a result of photosynthetic reactions. The components of the part to be shed are recycled by the plant for use in other processes, such as development of seed and storage. This process is known as nutrient recycling. The aging of a plant and all the associated processes is known as **senescence**, which is marked by several complex biochemical changes. One of the characteristics of senescence is the breakdown of chloroplasts, which is characterized by the yellowing of leaves. The chloroplasts contain components of photosynthetic machinery such as membranes and proteins. Chloroplasts also contain DNA. The proteins, lipids, and nucleic acids are broken down by specific enzymes into smaller molecules and salvaged by the plant to support the growth of other plant tissues. The complex pathways of nutrient recycling within a plant are not well understood. Hormones are known to play a role in senescence. Applications of cytokinins and ethylene delay or prevent senescence; in contrast, abscissic acid causes premature onset of senescence. Enrichment: a. **Select the correct answer** 4. During \_\_\_\_\_\_\_\_, an ovule or ovary can give rise to a seed without fertilization occurring. a. grafting b. adventitious rooting c. apomixis B. Grafting is commonly used in the \_\_\_\_\_\_\_\_ industry. a. potato b. floral c. grape C. \_\_\_\_\_\_\_\_ have a lifecyle of two years or more. a. Biennials b. Perrenials c. Annuals D. Asexual reproduction works best in \_\_\_\_\_\_\_\_. a. stable environments b. temperate climates c. stressful conditions E. The kalanchoe can reproduce asexually by \_\_\_\_\_\_\_\_. a. adventitious roots b. stolons c. bud-bearing leaves F. The aging process in plants is known as \_\_\_\_\_\_\_\_. a. senescence b. ripening c. maturing G. \_\_\_\_\_\_\_\_ requires a laboratory environment for plant propagation. a. Layering b. Micropogagtion c. Cutting H. **Asexual Reproduction means** b. Involves sex cells and fertilization c. There is variation in the offspring. d. Does not involve sex cells and fertilization. e. Offspring are not genetically identical to one another. I. **Algae, the simplest green plants, reproduce by an asexual method known as \_\_\_.** a. sowing b. budding c. fragmentation d. vegetative propagation J. **Placing seeds on or in the ground for future growth is called** a. Fragmentation b. Reproduction c. Sowing d. Budding - Flowers are the reproductive structures produced by plants which belong to the group known as Angiosperms, or \'Flowering Plants\'. This group includes an enormous variety of different plants ranging from buttercups and orchids to oak trees and grasses. There are about 250,000 known species. The vegetative part of a flower consists of petals and sepals. - Flowers contain the plant's reproductive structures. In different plants, the number of petals, sepals, stamens and pistils can vary. The presence of these parts differentiates the flower into complete or incomplete. Apart from these parts, a flower includes reproductive parts -- stamen and pistil. A flower may have only female parts, only male parts, or both. - The gametophyte is a stage in the life cycle that is found in all plants and certain species of algae. This process includes both multicellular diploid generation known as Sporophyte and a multicellular haploid generation known as Gametophyte. - All plants reproduce both sexually and asexually due to variation in generations. Gametophytes and sporophytes consisting of genetic elements of the plant species. - Pollination takes two forms: self-pollination and cross-pollination. Self-pollination occurs when the pollen from the anther is deposited on the stigma of the same flower or another flower on the same plant. Cross-pollination is the transfer of pollen from the anther of one flower to the stigma of another flower on a different individual of the same species. The plants depend on pollinators to transfer pollen. The majority of pollinators are biotic agents such as insects (bees, flies, and butterflies), bats, birds, and other animals. Other plant species are pollinated by abiotic agents, such as wind and water. - The fruit is broadly divided into the pericarp which is the various covering layers of the fruit and the seed or seeds which are present inside it. Fruits can be classified in many ways. True and False Fruits, Simple, Aggregate, and Multiple Fruits. - Once fertilization occurs, the mature ovule begins to differentiate into a seed. A seed contains many parts, namely: the seed coat, the cotyledons, the endosperm and the embryo. - Plant Embryo Develops when a plant is fertilized, its male and female cells form a zygote -- a combined cell that can divide itself and grow into a new organism. That zygote will eventually form the plant embryo, which the parent plant protects by forming a container around it, whether it be a seed, a bud, a shoot or something similar, which is filled with endosperm -- food that the embryo can use during the early stages of germination. When this container is subjected to the correct conditions, the embryo can then complete its function. - Many plants are able to propagate themselves using asexual reproduction. Artificial Methods of Asexual Reproduction includes grafting, layering, cutting and micropropagation. - The length of time from the beginning of development to the death of a plant is called its life span. References: Berg, (1997).Introductory Botany. Saunders College Publishing, Harcourt Brace College Publishers Capili, N. L. (2013). General botany laboratory manual. C & E Publishing, Inc. Evangleista, E. and Evangelista L. (2009).Worktext in General Botany. C & E Publishing, Inc. Stern, K.R., J.E. Bidlack, & S.J.H. Jansky. (2008). Introductory plant biology. 11th ed. The McGraw-Hill Companies, Inc. [[http://biology.kenyon.edu/courses/biol114/Chap12/Chapter\_12A.html]](http://biology.kenyon.edu/courses/biol114/Chap12/Chapter_12A.html) [[https://courses.lumenlearning.com/boundless-biology/chapter/asexual-reproduction/]](https://courses.lumenlearning.com/boundless-biology/chapter/asexual-reproduction/)