Tiêu đề REPRODUCTION IN ORGANISMS.pdf ✅

 Digital www.allendigital.in [ 3 ] 1. Life Span : • Each and every organism can live only for a certain period of time. • It may be as short as a few days or as long as a few thousand years. • The life spans of organisms are not necessarily correlated with their sizes. • The period from birth to the natural death of an organism represents its life span. • Life spans of organisms are not necessarily correlated with their sizes for e.g. the sizes of crows and parrots are not very different yet their life spans show a wide difference. • Similarly, a mango tree has a much shorter life span as compared to a peepal tree. Whatever be the life span, death of every individual organism is a certainty, i.e., no individual is immortal, except single-celled organisms. Reproduction : • Reproduction is defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself. The offspring grow, mature and in turn produce new offspring. Thus, there is a cycle of birth, growth and death. • Reproduction enables the continuity of the species, generation after generation. • The organism’s habitat, its internal physiology and several other factors are collectively responsible for how it reproduces. 20-30 Years 15-25 Years 65-90 Years 100-150 Years 60 Years 5-7 Years 3-4 Months 15 Years 20-30 Days 1-2 Weeks 62 Years 20-25 Years Approximate life spans of some organisms Reproduction in Organisms 01
NEET : Biology [ 4 ] www.allendigital.in  Digital • When offspring is produced by a single parent with or without the involvement of gamete formation, the reproduction is asexual. When two parents (opposite sex) participate in the reproductive process and also involve fusion of male and female gametes, it is called sexual reproduction. 2. Asexual reproduction : • In this method, a single individual (parent) is capable of producing offspring. As a result, the offspring that are produced are not only identical to one another but are also exact copies of their parent. • Are these offspring likely to be genetically identical or different? Answer will be genetically identical. • The term clone is used to morphologically and genetically similar individuals • Many single-celled organisms (monerans and protists) reproduce by binary fission. • Member of kingdom fungi and algae reproduce through special asexual reproductive structures called zoospores. • Conidia (Penicillium) buds (Hydra) and gemmules (sponge) are other common asexual reproductive structures. Vegetative propagules in angiosperms : (a) Eyes of potato; (b) Rhizome of ginger; (c) Bulbil of Agave; (d) Leaf buds of Bryophyllum; (e) Offset of water hyacinth (Eichhornia) • The fleshy bud which produces new plants in hydrophytes is called Turion • Is vegetative reproduction also a type of asexual reproduction? Answer will be yes. • Is the term clone applicable to the offspring formed by vegetative reproduction? Answer will be yes. • While in animals and other simple organisms the term asexual is used unambiguously, in plants, the term vegetative reproduction is frequently used. • In plants, the units of vegetative propagation such as runner, rhizome, sucker, tuber, offset, bulb are all capable of giving rise to new offspring. These structures are called vegetative propagules. • ‘Water hyacinth’ (Terror of Bengal) which is one of the most invasive weeds found growing wherever there is standing water. It drains oxygen from the water, which leads to death of fishes. • This plant was introduced in India because of its beautiful flowers and shape of leaves. Since it can propagate vegetatively at a phenomenal rate and spread all over the water body in a short period of time, it is very difficult to get rid of them.
Reproduction in Organisms  Digital www.allendigital.in [ 5 ] Types: - (i) Binary Fission: e.g.: Amoeba, Paramecium 3. Sexual Reproduction : • Sexual reproduction involves formation of the male and female gametes, either by the same individual or by different individuals of the opposite sex. These gametes fuse to form the zygote which develops to form the new organism. It is an elaborate, complex and slow process as compared to asexual reproduction. • Because of the fusion of male and female gametes, sexual reproduction results in offspring that are not identical to the parents or amongst themselves. • Plants, animals or fungi differ greatly in external morphology, internal structure and physiology, when it comes to sexual mode of reproduction, surprisingly, they share a similar pattern in sexual reproduction. Different phases of life in sexual reproducing organisms: (a) Juvenile Phase: • All organisms have to reach a certain stage of growth maturity in their life, before they can reproduce sexually. • In animals, this period of growth is called the Juvenile phase, while in plants it is known as vegetative phase. • Juvenile phase is of variable durations in different organisms. • In some plants, where flowering occurs more than once, what would you call the inter-flowering period – juvenile or mature? Answer will be mature. • Plants–the annual and biennial types, show clear cut vegetative, reproductive and senescent phases, but in the perennial species it is very difficult to clearly define these phases. Daughter cells Nucleus Micropyle Spicules Archeocyte Outer membrane Inner membrane Fully formed bud Tentacles Bud (ii) Budding e.g. Hydra (iii) Gemmule e.g. Sponge
NEET : Biology [ 6 ] www.allendigital.in  Digital • A few plants exhibit unusual flowering phenomenon; some of them such as bamboo species flower only once in their life time, generally after 50-100 years, produce large number of fruits and die. • Another plant, Strobilanthus kunthiana (neelakuranji), flowers once in 12 years. As many of you would know, this plant flowered during September-October 2006. Its mass flowering transformed large tracks of hilly areas in Kerala, Karnataka and Tamil Nadu into blue stretches and attracted a large number of tourists. (b) Reproductive Phase: • The end of juvenile phase is marked by the beginning of the next phase called reproductive phase. • In animals, the juvenile phase is followed by morphological and physiological changes prior to active reproductive behaviour. • In several animals, including human beings, the reproductive maturity is marked by a number of changes that occur in their bodies. • The reproductive phase is also of variable duration in different organisms. • During reproductive phase, the females of placental mammals exhibit cyclical changes in the activities of ovaries and accessory ducts as well as secretion of hormones. • In non-primate mammals like cows, sheeps, rats, deers, dogs, tigers, etc. such cyclical changes during reproduction are called Oestrus cycle where as in primates (monkeys, apes and humans) it is called menstrual cycle. • Many mammals are reproductively active throughout their reproductive phase and hence are called continuous breeders. • The end of reproductive phase can be considered as one of the parameters of senescence or old age. • There are concomitant changes in the body (like slowing of metabolism, etc.) during this last phase of life span. old age ultimately leads to death. • In both plants and animals, hormones are responsible for the transitions between the three phases. Interaction between hormones and certain environmental factors regulate the reproductive processes and the associated behavioural expressions of organisms Breeding Seasons: - • In most of animals do not breed throughout the year, instead they are seasonal breeders. • For instance; birds living in nature lays eggs only seasonally. • However, birds in captivity (as in poultry farms) can be made to lay eggs throughout the years by hormonal treatment. In this case, egg laying is not related to reproduction but is a commercial exploitation for human welfare. (c) Senescence (Aging) Phase : After reproductive maturity all organisms enter into a senescent phase. Senescence may be defined as the period between reproductive maturity and death of the organism. In both plants and animals, hormones are responsible for the transitions between the three phases. Interaction between hormones and certain environmental factors regulate the reproductive processes and the associated behavioural expressions of organisms.