Title SP-3_Ch-13_Reproduction in Organisms _ Sexual Reproduction in Flowering Plants.pdf ✅

Chapter Contents Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Life Span Types of Reproduction Asexual Reproduction Sexual Reproduction Events in Sexual Reproduction Flower - A Fascinating Organ of Angiosperms Pre-fertilisation : Structures and Events Double Fertilization Post-fertilization : Structures and Events Apomixis and Polyembryony The "biological process" which allows the production of new organism from the existing organism is called "reproduction". Reproduction is one of the most fundamental attributes of all living organisms as it is essential for the survival of a species. LIFE SPAN The period from birth to the natural death of an organism represents its life span. Life span is a specific trait of each organism. Life span varies from few days to several thousand years. Life spans are not necessarily correlated with size or complexity of organisms. As for example, crow and parrot are of almost equal size, but crow has a life span of only 15 years while parrot lives for about 140 years. Similarly mango tree lives for 200 years while peepal has a life span of about 2500 years. Whatever be the life span, the death of every organism is sure. Hence living organisms are mortal. However, single celled organisms are considered as immortal because they simply get larger and then divide which is not considered as death. TYPES OF REPRODUCTION There are two types of reproduction, asexual and sexual. ASEXUAL REPRODUCTION Features of asexual reproduction are : 1. As there is involvement of only one parent so it is uniparental. 2. It can occur with or without gamete formation but gametic fusion is absent. Chapter 13 Reproduction in Organisms & Sexual Reproduction in Flowering Plants
2 Reproduction in Organisms & Sexual Reproduction in Flowering Plants NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 3. The individuals produced are exact copies of each other and their parents because the new organisms produced inherit all of its chromosomes from one parent. Such a group of morphologically and genetically similar individuals is called clone. 4. It can occur through unspecialised or specialised parts of parent. 5. It is common method of reproduction in organisms that have a relatively simple organisation like single celled organism of monera, protista as well as plants and animals with relatively simple organisation like algae, fungi, sponges. Higher plants also exhibit this type of reproduction where it is known as vegetative reproduction. 6. Simple and quick method. Rose (5-7 years) Elephant (60-90 years) Butterfly (1-2 weeks) Banana tree (25 years) Parrot (140 years) Horse (60 years) Tortoise (100-150 years) Fruitfly (2 weeks) Rice plant (3-4 months) Banyan tree (200-300 years) Crocodile (60 years) Cow (20-25 years) Dog (25-30 years) Crow (15 years) Fig. : Approximate life spans of some organisms Let us discuss different ways of asexual reproduction : (i) Binary fission (ii) Budding (iii) Sporulation (iv) Fragmentation (v) Vegetative reproduction/propagation
NEET Reproduction in Organisms & Sexual Reproduction in Flowering Plants 3 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 (i) Binary Fission Nucleus Nucleus enlarge Karyokinesis Cytokinesis Daughter cells Fig. : Binary fission in Amoeba Occurrence : It occurs in many single celled organisms belonging to kingdom Monera (Bacteria), and Protista (Amoeba and Paramecium). Mechanism : In this process, the parent organism divides into two halves, each half forming an independent daughter organism. It means, the parent body as a whole forms reproductive unit and the parent continues living as two daughter individuals. It involves amitosis in bacteria and mitotic division of nucleus in yeast and amoeba i.e., karyokinesis followed by division of cytoplasm i.e., cytokinesis. Depending upon the plane of division, binary fission is of the following types : (a) Simple Binary Fission (Irregular Binary Fission) : Divi- sion can occur through any plane, e.g., Amoeba. (b) Longitudinal Binary Fission : The plane of fission passes along the longitudinal axis of the organism, e.g., Euglena. (c) Transverse Binary Fission : The plane of this division runs along the transverse axis of the individual, e.g., Bacteria, Paramoecium, Diatoms. (ii) Budding : Occurrence : Occurs in single celled organisms Parent cell Bud Fig. : Budding in yeast like yeast. Mechanism : In this process unicellular structure develops an outgrowth (bud) on one side. Daughter nuclei produced through karyokinesis shifts into the bud. The bud grows, constricts at the base, separates and eventually mature into new organism (cell). Unlike binary fission, cytoplasmic division is unequal and parental cell exists. (iii) Sporulation : Asexual reproduction can also occur through formation of specialised reproductive structure like spores by members of the kingdom fungi and simple plants such as algae. The most commonly produced spores are zoospores and conidia. Zoospores : These are microscopic motile endogenous spores. Zoosporangium Zoospore They are most common asexual structures formed in algae. In unicellular green alga, Chlamydomonas zoospore is pyramid shaped, anteriorly flagellated, resembling parent cell. Fig. : Asexual structure: Zoospores of Chlamydomonas
4 Reproduction in Organisms & Sexual Reproduction in Flowering Plants NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Conidia : These are non-motile spores produced on conidiophores. These are most common asexual spores produced by fungi. Conidia Fig. : Asexual structure : Conidia of Penicillium Under unfavourable condition the Amoeba withdraws its pseudopodia and secretes a three layered hard covering or cyst around itself. This phenomenon is termed as encystation. When favourable conditions return, the encysted Amoeba divides by multiple fission and produces many minute Amoeba. (iv) Fragmentation: Fragmentation is a form of asexual reproduction where an organism splits into fragments. Each of these fragments develops into mature fully grown individual followed by mitosis, e.g some algae (Spirogyra), filamentous fungi, Hydra, etc. (v) Vegetative Reproduction/Propagation : In this method somatic part of the plant detaches from the body of the mother and develops into a new independent plant under suitable environmental conditions. The detachable somatic part involved in vegetative propagation is called vegetative propagule. There are two types of vegetative propagation. A. Natural methods of vegetative propagation B. Artificial methods of vegetative propagation A. Natural methods of vegetative reproduction : Natural methods of vegetative reproduction in plants Stem Leaves Root eg. Dahlia Sweet potato eg. (walking fern) Adiantum Begonia Bryophyllum Underground stem Subaerial Stem Aerial Stem eg. Sugarcane, Opuntia Bulbils eg. Lily, Agave, Oxalis, Ananas Dioscorea Tuber eg. Potato Rhizome eg. Banana, Ginger Bulb eg. Onion, Garlic Offset eg. Eichhornia Pistia Sucker eg. Chrysanthemum Pineapple Runner eg. Grasses