Reproduction PDF

PERPETUATION OF LIFE  ANIMAL REPRODUCTION There are varieties of organism in animal kingdom that means they possess different modes of reproduction depending on the complexity of their morphology and physiology. Through reproduction, animals ensure that there are other indivi...

PERPETUATION OF LIFE  ANIMAL REPRODUCTION There are varieties of organism in animal kingdom that means they possess different modes of reproduction depending on the complexity of their morphology and physiology. Through reproduction, animals ensure that there are other individuals of their kind that can take their place on Earth when they die.  SEXUAL REPRODUCTION  During sexual reproduction in animals, a haploid sperm cell and a haploid egg cell unite to form a diploid zygote. The process wherein a sperm and egg unite is called fertilization.  Most animals exhibit cross-fertilization, which involves two separate individuals of the same species (a male and a female) in reproduction. Even earthworms, which have two sexes (hermaphrodite), do cross-fertilization.  Frogs, crabs, corals, and most fishes undergo external fertilization. In external fertilization, the meeting of gametes does not occur inside the body of the female animal. but in the open environment or outside the body.  Oviparous vs. Vivaparous Oviparous- egg laying Viviparous- gives birth HUMAN REPRODUCTION Most fertilization happens inside the body of the female species, wherein the male deposits the sperm in the female's reproductive organ during mating. This is called internal fertilization.  ASEXUAL REPRODUCTION  Some animals are also capable of asexual reproduction whenever sexual reproduction is not possible. Asexual reproduction in animals occurs in invertebrates and can be done through budding or fragmentation.  Asexual reproduction has certain advantages over sexual reproduction. It enables animals living in isolation to reproduce even without a mate, and it can produce numerous offspring quickly. This will help the organism perpetuate and continue its species for generations. Budding Budding involves the splitting of new individuals from an existing organism by forming small projections, called buds, from the parent's body. Animals such as Hydra undergo this type of asexual reproduction. Small buds arise on their bodies and then later on detach from the parent's body and settle to the ground where they become mature individuals Fragmentation Fragmentation and regeneration is a type of asexual reproduction wherein a single parent breaks into parts that give rise to new individuals. Sponges, Planaria, and starfish are examples of animals that exhibit this type of asexual reproduction Parthenogenesis Parthenogenesis is a form of asexual reproduction in some animals that give rise to the growth and development of an embryo without fertilization. Parthenogenesis occurs in some insects (bees, aphids), crustaceans (water fleas, crayfish), flatworms, some snails, few reptiles, and certain species of fish.  Transverse Binary Fission The cell divides along the horizontal axis.  PLANT REPRODUCTION  Plant reproduction is the process of generating new plant individuals or offspring. Plants reproduce in two ways: sexual and asexual. Sexual Reproduction Sexual reproduction in plants involves the fusion of the parents' gametes. This fusion gives rise to an individual that has the genes of both parents. Thus, the offspring is not genetically identical with either parent-rather, the offspring carries a combination of both parents' genes.  Flower A flower consists of highly specialized male and female reproductive organs. The female reproductive part of the flower, called pistil, has stigma, style, and ovary. The ovary contains the ovule that has the egg nuclei. The stamen, on the other hand, is the male part of the flower. It has the anther that produces pollen grains, which contain the sperms.  Pollination is the transfer of pollen from the anther to the stigma of the flower.  Seed The seed usually consists of a seed coat, embryo, and endosperm. The seed coat protects the internal parts of the seed against external factors. Thus, it ensures that the seed remains dormant until conditions are right.  The endosperm serves as the food for the growing embryo. Eudicot seeds such as beans, mango, and jackfruit have two cotyledons, while monocots such as corn, wheat, and rice have one cotyledon.  The embryo has three parts: hypocotyl, epicotyl, and radicle. The hypocotyl becomes the lower part of the stem. The radicle or embryonic root becomes the primary root and the first organ to emerge in plants. The epicotyl becomes the upper part of the stem and gives rise to the shoot.  After the seeds are formed and become matured, they are usually scattered in the environment where they can grow as new plants. The scattering of seeds is known as seed dispersal. This process is very important in the survival and distribution of the plant species. There are different ways by which seeds are dispersed. External factors Buch as wind, animals, humans, and water help in the successful dispersal of seeds. Some seeds, such as dandelion and mahogany, have specialized structures intended for easy dispersal.  Some have thorns or sticky surface that can cling on to some animals.  Most humans and animals eat fruits. They throw the seeds on the ground where they become new plants.  Germination is the early growth stage of a plant embryo. Germination leads to maturity, which leads to reproduction. Asexual Reproduction Asexual reproduction is a type of reproduction that creates genetically identical offspring. The offspring that arise from asexual reproduction are considered clones off the parent. In most plants, asexual reproduction is an advantageous adaptation. Stolons Stolons or runners are specialized stems of some plants, such as the strawberry.  Rhizomes Rhizomes are stems that grow horizontally under the ground like the ginger. Tubers Tubers are used both for starch storage and give rise to new plants. An example is potato plant.  Bulbs Bulbs are underground stems that give rise to a new plant, such as in the case of onions and lilies.  Corm Corm differs from the bulb since it is also used for storage of food of the plant. It sometimes referred to as the bulbotuber. Corms give rise to new small corms in their nodes called cormels.  Compare the two advantages and two disadvantages of sexual and asexual reproduction in plants.