Biology: Plant Reproduction Study Guide PDF

Kuala Lumpur, Malaysia SEMESTER I NAME: _______________________ REF: 2024- 25/ SCI /STD 10/ HO 08 CLASS: _______________ SUBJECT: Biology DATE: 16/08/2024 Topic:...

Kuala Lumpur, Malaysia SEMESTER I NAME: _______________________ REF: 2024- 25/ SCI /STD 10/ HO 08 CLASS: _______________ SUBJECT: Biology DATE: 16/08/2024 Topic: Sexual Reproduction in Plants Introduction: Flowers are responsible for seed development and reproduction. There are four main flower parts/whorls in angiosperms: sepals(calyx), petals (corolla), stamens (androecium), and carpels (gynoecium). The stamen is considered the male reproductive part of a plant, and the carpel is considered the female reproductive part. Pollen is produced in the stamen, and the female ovary is contained within the plant carpel. Pollen is transferred from stamen to carpel by plant pollinators such as bugs, birds, and mammals. When the ovule (egg cell) within the ovary becomes fertilized, it develops into a seed. The ovary, which surrounds the seed, becomes the fruit. Flowers that are missing either stamens or carpels are called imperfect flowers. The flowers which contain only one sex organ, either stamens or carpels are called unisexual flower. For example: papaya and watermelon, corn, mulberry plants. If a flower contains all four main parts (sepals, petals, stamens, and carpels), it is called a complete flower. The flowers which contain both the sex organs, stamens as well as carpel, are called bisexual flowers. For example: Hibiscus and mustard plants, rose, lily, sweet pea. Page 1 of 9 Copyright © Global Indian International School  Sexual Reproduction and Flower Parts Flowers are the sites of sexual reproduction in flowering plants. The stamen is considered the male portion of a plant because it is where male gamete is produced and housed within pollen grains. The carpel contains the female reproductive organs. 1. Receptacle: The base of a flower to which all the parts of a flower are attached is called receptacle. 2. Sepal: This typically green, leaf-like structure protects the budding flower. Collectively, sepals are known as the calyx. 3. Petal: This plant structure is a modified leaf that surrounds the reproductive parts of a flower. Petals are typically colorful and often scented to attract insect pollinators. 4. Stamen: The stamen is the male reproductive part of a flower. It produces pollen and consists of a filament and an anther. 1. Anther: This sac-like structure is located at the tip of the filament and is the site of pollen production. 2. Filament: A filament is a long stalk that connects to and holds up the anther. Page 2 of 9 Copyright © Global Indian International School  5. Carpel: The female reproductive part of a flower is the carpel. It consists of the stigma, style, and ovary. 1. Stigma: The tip of the carpel is the stigma. It is sticky so it can collect pollen. 2. Style: This slender, tube-like part of the carpel that provides a pathway for male gamete to the ovary. 3. Ovary: The ovary is located at the base of the carpel and contains the ovules Perianth = Calyx + Corolla Pollination Pollination is the transfer of pollen (male gamete) from the anther of a flower to a stigma. Pollination is the sexual method of reproduction in all plants by the process of transferring the pollen grains from the anther to the stigma of the gynoecium and thereby leading to the fertilization process. Pollination is brought about by various agencies like air (anemophily), water (hydrophily), insects (entomophily) and animals (zoophily). Cross-pollination: pollen is transferred from one flower to the stigma of another flower in another plant or the same plant. Advantage of cross pollination: Increases genetic variation, population develop more resistant to environmental change. Self-pollination: pollen transferred to the stigma of the same flower or a flower of the same plant. Page 3 of 9 Copyright © Global Indian International School Advantage of self-pollination: Guarantees reproduction if pollinating agent is absent or not efficient. Self-Pollination. Page 4 of 9 Copyright © Global Indian International School Self -Pollination Vs Cross Pollination Transfer pollen grains from the Transfer pollen grains from the anther to the stigma of the anther to the stigma of the same flower. different flower. This process can take place This process can take place between two flowers on the either in the same flower same plant or different plants. Self-pollination increases Cross-pollination decreases genetic uniformity and genetic uniformity and decreases genetic variation. increases genetic variation. Produces limited amounts of Produces large amounts of pollen grains. pollen grains. In self-pollination, both the In cross-pollination, both the stigma and anther mature at the stigma and anther mature at same time. the different time. This process is carried out even For cross-pollination to happen when the flowers are closed. flower should be open. No need of pollinators to Require pollinators to transfer transfer pollen grains. pollen grains. Do it Yourself What is the significance of Pollination in plants? Fertilization (Syngamy) Fertilisation is the union of the male and female gametes to form a zygote. Since the male and female gametes are haploid (n) when the two unite the zygote is diploid (2n). Fertilisation starts when a pollen grain lands on the stigma. The pollen grain then germinates forming a pollen tube. The pollen tube is an example of chemotropism since it is growing toward chemicals produced from the ovule. The male gametes travel down the pollen tube. The pollen tube enters the ovule by way of the micropyle (small pore). The two male gamete nuclei are released into the embryo sac. Page 5 of 9 Copyright © Global Indian International School Double Fertilization Since there are 2 sperm nuclei that have reached the embryo sac both nuclei will fuse with female gametes. One sperm nucleus will fuse with the egg cell to form the zygote (2n) while the other sperm nucleus fuses with the 2 polar nuclei in the embryo sac to form an endosperm nucleus (3n). Post Fertilization Events: 1. Seed Formation The fertilized ovule becomes the seed. The integuments become the wall of the seed called the testa. The endosperm nucleus leads to the formation of triploid endosperm, a food tissue. The diploid zygote develops into a plant embryo. The developing embryo draws nourishment from the endosperm. The embryo ceases development and goes dormant. The ovule becomes a seed, which contains a dormant plant embryo, food reserve, and the protective coat called the testa. a. The Embryo The embryo is made up of the radicle or future root and the plumule or future shoot. The endosperm is the nutrition (mainly fats, oils and starch) for the embryo. There are 2 types of seeds b. Monocots and Dicots Monocots have one cotyledon in the seed while dicots have two cotyledons. The cotyledons are food reserves for the young plant after it germinates from the soil. It uses these food reserves until it is capable of making its own food. In monocots the food is absorbed from the endosperm while in dicots the food is stored in the cotyledons. Page 6 of 9 Copyright © Global Indian International School  A. Fruit Development The ovary becomes a fruit. The wall of the ovary becomes the wall of the fruit called the pericarp. The fruit protects the developing seeds and plays an important role in seed Page 7 of 9 Copyright © Global Indian International School dispersal. Once the fruit forms the rest of the flower parts die and fall away. Seed Dormancy Dormancy is a period of inactivity. There is very little cellular activity and no growth. One or many of the following reasons that bring about seed dormancy: Hormones that inhibit growth- Growth Inhibitors The testa is impermeable to water and oxygen- The testa will eventually break down and allow water and oxygen into the seed. The testa may be too hard for the embryo to germinate. An Auxin (Growth Regulator) may be absent until suitable environmental conditions develop. Germination The embryo will germinate from the seed if the proper environmental conditions are present. When this occurs, the embryo resumes its growth. In order for germination to occur the following conditions must be present: Water must be present. This allows the seed to swell and enzymes to function. Oxygen must be present in the soil. The temperature must be suitable for the species of plant. Optimum temperatures are usually between 5-30 degrees Celsius depending on the species. The dormancy period must be complete. Some seeds need light and others need darkness. Page 8 of 9 Copyright © Global Indian International School Events of Germination When germination begins the first thing that happens is water is absorbed by the seed through the micropyle and through the testa. Enzymes in the seed now digest the foods stored in the seeds: These digested foods are absorbed by the embryo. The stored food of the seed is being used up as the embryo grows larger. The radicle grows larger and breaks through the testa. It becomes the roots of the new plant. The plumule grows larger and emerges above the ground. Leaves form. Germination occurs differently in different plants. In some plants the cotyledon remains underground while in other plants the cotyledon emerges above ground. Page 9 of 9 Copyright © Global Indian International School