Chapter 1 reproduction in organisms
Channel: ISHTA’s BIO ACADEMY
Date: 2023-04-30

1. Reproduction in organism. • Introduction: • The period of birth to natural death of an organism is called life span. No individual is immortal except unicellular organism. Because it continue its life in progeny by fission.
2. Approximate life span of some organism. .
3. The continuity of life on earth is achieved by the process of reproduction.
4. • Reproduction: It is a biological process in which an organism gives rice to young ones or offspring. • Reproduction enables the continuity of species generation after generation. • Types of reproduction: • Asexual reproduction: It is the reproduction by single parent with out formation of gametes. • Sexual reproduction: It is the reproduction in which two parents of opposite sex involves with the formation and fusion of gametes.
5. Asexual reproduction. • The offspring developed by asexual reproduction are exact copy of heir parents. They are genetically identical. Hence they are termed as clones. • Asexual reproduction is common in unicellular organism. In plants and in animals having simple organisations. • Binary fission: The single cell organism of kingdom Monera and Protista reproduce by simple cell division called binary fission. The cell divides in to two half. Each half develops in to new an adult.

38. • In diplontic plant (Gymnosperms and angiosperms) zygote undergoes mitosis to develops into diploid dominant sporophyte.
39. • In haplo diplontic ( Bryophytes and pteridophytes) zygote undergoes mitosis to develops into diploid sporophyte.
40. • Embryogenesis: It is the process of development of embryo from zygote. The zygote undergoes division and differentiation into embryo. • Oviparous (egg laying animals): The reptiles and birds lay egg in safe environment. After incubation young one hatches out. • In oviparous embryogenesis takes place outside the body.
ed ovarian cavity (locule). • The megasporangia commonly called ovules arises from the placenta. • The number of ovules in an ovary may be one (wheat, paddy, mango) or many (papaya, water melon, orchids).
56. Megasporangium (Ovule) : • The ovule is a small structure attached to the placenta with stalk called funicle. • The body of the ovule fuses with funicle in the region called hilum.
57. • Each ovule has one or two protective envelopes called integuments. • Integuments encircle the ovule except at the tip. • the small opening present at tip called micropyle. • Opposite to the micropylar end the chalaza is present. • It represents the basal part of the ovule.
58. • The integument Encloses a mass of cells called the nucellus. • These cells have abundant reserve food materials. • The embryo sac or female gametophyte is located in the nucellus. • An ovule generally has a single embryo sac formed from a megaspore through reduction division.
59. Megasporogenesis • The process of formation of megaspores from the megaspore mother cell is called megasporogenesis. • Ovules generally differentiate a single megaspore mother cell (MMC) in the micropylar region of the nucellus. • The MMC undergoes meiotic division.
60. • The majority of flowering plants, one of the megaspores is functional while the other three degenerate. • Only the functional megaspore develops into the female gametophyte. • Note- the nucellus is diploid. • MMC is diploid, • the functional haploid • female gametophyte is haploid.
61. • The nucleus of the functional megaspore divides mitotically to form .