Class 12 ||Reproduction in Organism

1. CHAPTER -1Reproduction in Organism BY: Nikhil Gaurav M.Sc. Zoology

2. Reproduction • Reproduction is a fundamental feature if living organisms which involves the transmission of genetic material from one generation to next ensuring the survival of species over a longer period of time. • Reproduction (or breeding) is the biological process by which new individual organisms  – "offspring" – are produced from their "parents "of their own kind. • Reproduction is a fundamental feature of all known life ; each individual organism exists as the result of reproduction.

3. Characteristic feature of Reproduction All mode of reproduction have some basic features: • Synthesis of RNA , proteins and other biomolecules. • Replication of DNA. • Cell division and growth of cells. • Formation of reproductive units. • Development of new individual from reproductive units.

4. Purpose of Reproduction • CONTINUITY OF SPECIES :- Reproduction maintains the continuity of species. • POPULATION ORGANISATION :- It maintains population of young, adults and aged individuals of a species. • REPLACEMENT :- It replaces individuals dying due to ageing. • VARIATION :- It introduces variations in the organisms . Useful variations help in adaptations and evolution. • LIFE :- Existence of life on the Earth is possible only due to reproduction.

5. Life span • The period from birth to natural death of an organism is called its life span. • Life span of an organism may be from few minutes to several thousand years.

6. Life Span of Living Organism

7. Phases of Life • Life of an Organism usually include four Phases:- • Birth • Juvenile Phase or Vegetative Phase • Reproductive or Maturation Phase • Ageing or senescent Phase. • Natural Death.

8. Types of Reproduction

9. ASEXUAL REPRODUCTION • In this reproduction only one/Single parent is involved. • Formation and fusion of gametes doesn’t take place. • The offspring produced are genetically and morphologically similar to parents. So , they are also known as CLONE. • In asexual reproduction only one type of cell division take place i.e. Mitosis. • Asexual reproduction doesn't take part in evolution. • It generally takes place from the somatic part of the body of an organism. • Example:- Euglena,Paramecium,Amoeba.

10. Types of Asexual Reproduction. • Fission ----------- a) Binary Fission b) Multiple Fission • Budding ---------- a) Exogenous Budding b) Endogenous Budding • Spore formation • Regeneration • Fragmentation • Plasmotomy • Vegetative Propagation • Tissue Culture/ Micropropagation • Cloning

11. Asexual reproduction takes place in various ways. These are as follows:- • Fission:- It is the division of the parent body in to two or more daughter individuals identical to the parents. It is of two types:- • Binary Fission:- In this, parent organism divides in to two halves, each half forms an independent daughter organism. Ex- Bacteria , Protozoa. • Multiple Fission:- In this, the parent body divides in to many daughter organisms . It occurs in Amoeba and Plasmodium.

12. Euglena Paramecium Amoeba

13. Budding • Formation of daughter individual from a small projection , the bud ,arising on the parent body is called Budding. • It occurs in some lower animals such as sponges, Hydra. • On the basis of location of bud budding may be of two types:- • Exogenous Budding :- When the bud grows on outer surface of the body. Ex-Hydra. The bud is identical to the parent. When the bud is large enough , can break off of the parent body and lives on its own. • Endogenous Budding :- When the bud grows on inner surface of the body. Ex- Sponges.

14. Exogenous Budding Endogenous Budding Sponge Yeast Hydra

15. Spore Formation Spores • Spores are usually thick or thin walled haploid and unicellular propagule which under favorable conditions can give rise to new organism using mitotic division. • There are several kinds of spores. These are zoospores, sporangiospores, conidia, chlamydospores etc. • Sporulation refers to the formation of spores from vegetative cells during unfavorable environmental conditions. • Ex- Rhizopus.

16. Conidia Zoospores • Conidia are asexually produced spores that are borne externally in chains to the cells that produce them. • A zoospore is a motile asexual spore that uses a flagellum for locomotion and able to swim in water. Penicillium

17. Regeneration • Regeneration is the formation of the whole body of an organism from a small fragment (Morphallaxis) or the replacement of lost part (Epimorphosis).

18. Fragmentation Spirogyra • Fragmentation in multicellular organisms is a form of asexualreproduction  in which an organism is split into fragments. • Each of these fragments develop into matured, fully grown individuals that are identical to their parents. • Ex- Spirogyra, Sponges.

19. Plasmotomy • Plasmotomy is a type of asexual reproduction in which a multinucleate protozoan cell divided into two or more multinucleate daughter-cells without the occurrence of mitosis. • Generally, Single-celled organisms undergo reproduction through a process called binary fission in which karyokinesis is followed by cytokinesis which means that nuclear division is followed by cytoplasmic division but here cytokinesis is followed by karyokinesis. • Ex- Opalina,Pleomyxa,Plasmodium.

20. Vegetative Reproduction Bryophyllum • Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment of the parent plant or a specialized vegetative structures like roots,stems,leaves. • It is the formation of new plants from vegetative units such as bud , tuber, rhizomes etc. • These vegetative units are called as vegetative propagule. • Vegetative reproduction may occur naturally or artificially as induced by farmers. Stem cutting

21. STEM 1)RUNNER :- Runners are a special kind of hard stem that lie along the ground horizontally and bears several nodes and internodes and when node part comes in contact with soil, it send new roots into the soil. Ex :- Dhoob grass (Cynodon),Oxalis. Oxalis

22. 2) Offset An offset is a short thick runner like the branch on the surface of water which produces a new plant at its tip. The offsets grow in all directions from the main stem of the parent plant. Ex- Water Hyacinth propagates by offsets. Eichhornia crassipes

23. Eichhornia crassipes(Weed) • Water hyacinth( Eichhornia crassipes) is known as the “Terror of Bengal” because it is an exotic shrub which is fastest growing weed found in standing water of ponds and lakes. • It floats in water with the help of spongy stem and inflated petioles of leafs • It grows asexually by means of offsets which bear leaves and roots in cluster at the nodes. Once it start growing, its eradication become very difficult. • It was introduced in India for its broad and attractive leaves and showy flowers. • As Fish is a supplement food in Bengal and Water hyacinth makes water oxygen and solar energy deficient and results in decline in number of fishes and because of the fish scarcity in Bengal caused by Eichhornia, the water hyacinth is also called "Terror of Bengal”.

24. 3) Rhizome 4) Tuber • Buds in the Rhizomes of Banana, Ginger and Turmeric give rise to aerial shoots which develop in to new plants under favorable conditions. • The eyes (buds) present in tuber of potato give rise to aerial shoots.

25. 5) Bulb 6) Corm • The bulb of Onion, Tulip are modified shoots. Each bulb has more terminal buds which grows into new shoots and grows into a new bulb. • The Corm of Colocasia has swollen bases of stem which have buds for vegetative propagation.

26. 7) Sucker 8) Stolon • Suckers are plant stems that arise from buds on the base of parent plants stems. • Ex- Banana, Chrysynthamum • Stolon is a horizontal branch of a plant that forms a base for buds to develop into identical plants. • Ex- Strawberry

27. ROOTS Roots of some plants bears radical buds which give rise to new plants. Ex- Dalbergia Sisso (Indian Rosewood)

28. LEAVES In Bryophyllum pinnatum and kalanchoe , the leaves have small buds on their margins. When these are detached from the plant, they grow into independent plants; they may also start growing into independent plants if the leaf touches the soil. 

29. Artificial Vegetative Propagation • Artificial methods of asexual reproduction are frequently employed to give rise to new plants. They include :- • Grafting • Cutting • Layering • Micropropagation.

30. 1)Grafting Grafting has long been used to produce novel varieties of roses, citrus species, and other plants. In grafting, two plant species are used: part of the stem of the desirable plant is grafted onto a rooted plant called the stock. The part that is grafted or attached is called the scion. Both are cut at an oblique angle , placed in close contact with each other, and are then held together. Matching up these two surfaces as closely as possible is extremely important because these will be holding the plant together. The vascular systems of the two plants grow and fuse, forming a graft. After a period of time, the scion starts producing shoots, eventually bearing flowers and fruits. Grafting is widely used in viticulture (grape growing) and the citrus industry. Scions capable of producing a particular fruit variety are grafted onto root stock with specific resistance to disease.

31. 2)Cutting Plants such as money plant are propagated through stem cuttings where a portion of the stem containing nodes and internodes is placed in moist soil and allowed to root. In some species, stems can start producing a root even when placed only in water.

32. 3) Layering Layering is a method in which a stem attached to the plant is bent and covered with soil. Young stems that can be bent easily without any injury are the preferred plant for this method. Jasmine and Bougainvillea (paper flower) can be propagated this way. In some plants, a modified form of layering known as air layering is employed. A portion of the bark or outermost covering of the stem is removed and covered with moss, which is then taped. After some time, roots will appear; this portion of the plant can be removed and transplanted into a separate pot. Ground Layering

33. 4) Micropropagation • Micropropagation (also called plant tissue culture) is a method of propagating a large number of plants from a single plant in a short time under laboratory conditions. This method allows propagation of rare, endangered species that may be difficult to grow under natural conditions, are economically important, or are in demand as disease-free plants. • To start plant tissue culture, a part of the plant such as a stem, leaf, embryo, anther, or seed can be used. The plant material is thoroughly sterilized using a combination of chemical treatments standardized for that species. Under sterile conditions, the plant material is placed on a plant tissue culture medium that contains all the minerals, vitamins, and hormones required by the plant. The plant part often gives rise to an undifferentiated mass, known as a callus, from which, after a period of time, individual plantlets begin to grow. These can be separated; they are first grown under greenhouse conditions before they are moved to field conditions.

34. Advantages of Vegetative Propagation • It is cheaper, rapid and convenient method of growing plants. • Plants like Banana, Grape, Pineapple, Orange, Rose, Jasmine etc do not produce viable seeds. These are grown only by vegetative propagation. • Desirable characters of fruits and flowers can be maintained in plants grown by vegetative propagation. • Grafting helps in combining good traits from two varieties in a single plant. • Good qualities of a species or variety can be maintained. • Plants grown by vegetative propagation have exact qualities of the parent plant.

35. Disadvantages of Vegetative propagation. • It does not produce new varieties. • Plant lose physical strength and good health when grown repeatedly. • Plants so produced are genetically alike, hence they are susceptible to the same diseases. • Undesirable Character persist in the species generation after generation.

36. Sexual reproduction • Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete (such as a sperm or egg cell) with a single set of chromosomes (haploid) combines with another to produce a organism composed of cells with two sets of chromosomes (diploid). •  Sexual reproduction is termed as biparental. • Sexual reproduction involves meiosis during gamete formation and mitosis during development of offspring from zygote. • Offspring's are neither genetically identical to the parents nor to each other.

37. Sexual reproduction involves formation of male and female gametes, either by the same individual or by the different individual of opposite sex. • In animals, the male gamete is formed by the process of spermatogenesis while the female gamete is formed by the process of oogenesis. • Spermatogenesis and oogenesis is collectively known as Gametogenesis. • The process of fusion of both these gametes is known as fertilization. • After fertilization a diploid zygote is formed which results in to formation of a new individual organism.

38. Reproduction in flowering plants • Monocarpic Plants :- These plants produce flowers only once in their life. After flowering, they produce fruits and die. All annuals (Wheat , Rice) and biennials (Radish, Carrot) are monocarpic. A few perennial plants like certain species of Bamboo and Neelakuranji are also monocarpic. Bamboo flowers only once in their lifetime. This plant dies after it sets seeds. This plant usually flowers after 50-100 yrs, produces a large number of fruits and dies. Strobilanthus kunthiana ( Neelakurinji) flower once in 12 yrs. Its mass flowering transformed large tracts of hilly areas in Kerala, Karnataka and Tamil Nadu (Nilgiri).

39. Polycarpic Plants These are perennial plants that flowers repeatedly at intervals every year. Ex- Apple, Orange, Mango etc. A few perennial plant bear flower throughout the year. Ex- China Rose. These plants do not die after flowering.

40. Breeding of animals • On the basis of breeding, animals are of two types:- • SEASONAL BREEDERS :- They reproduce at a particular period of the year. Such as Frog, Lizard, most birds, deer etc. • CONTINUOUS BREEDER :- These animals continue to breed throughout their sexual maturity. Such as rabbit, mice, cattle etc. • The females of placental mammals shows cyclic changes in the activities of ovaries and accessory ducts as well as hormones during the reproductive phase.

41. CYCLIC CHANGES DURING REPRODUCTION • In non-primate mammals like cows, sheep, rats, deers etc., such cyclic changes during reproduction are called Oestrus cycle. • In primates (Monkeys, apes and humans) such cyclic changes during reproduction are called Menstrual cycle.

42. Events in sexual reproduction • The event of sexual reproduction follow a regular sequence. • For convenience these sequential events are grouped into three distinct stages as follow :- • 1) Pre-fertilization events/changes. • 2) Fertilization. • 3) Post-fertilization events/changes.

43. Pre-fertilization events • It includes all the event which are prior to fusion of gametes. • The two main pre-fertilization events are as follow:- • 1) Gametogenesis :- The process of formation of male and female gametes. Gametes are haploid (n) cells. Gametes may be :- • Homogametes or Isogametes :- The two gametes are similar in appearance and can not be differentiated into male and female gametes. Ex- Cladophora. • Heterogametes :- The two gametes are morphologically different and can be distinguished in to male and female gamete. The male gamete is called Antherozoid or Sperm and female gamete is called egg or ovum.

44. Sexuality in organisms In Plants, • Homothallic and Monoecious :- These terms are used to describe the bisexual condition of plant and some fungi. • Heterothallic and Dioecious :- These terms are used to describe the unisexual condition of plant and some fungi. • Staminate:- Those flowers which bears only stamens. • Pistillate :- Those flowers which bears only pistil or carpel. Dioecious Monoecious Ex- Maize, Pine, Spruce Ex- Papaya, Dates, Kiwifruit

45. In Animals, • Unisexual :- Individuals of all species either male or female. Ex- cockroach. • Bisexual or Hermaphrodite :- Species which possess both male and female reproductive organ in same body. Ex- Earthworm, leech ,Sponge ,Tapeworm. Several organism belonging to monera ,fungi and bryophytes have haploid plant body but organisms belonging to pteridophyte, gymnosperms, angiosperms and most of the animals including human being, the parental body is diploid. In diploid organisms , specialized cells called meiocytes (gamete mother cell) undergoes meiosis which results in the formation of haploid gamete. Dioecious Plant: Marchantia Monoecious plant: Chara Bisexual animal: Earthworm

46. 2) Gamete Transfer • In majority organisms, male gamete is motile where as female gamete is non-motile or stationery. • Exceptions, in few fungi and lower algae both types of gametes are motile. • A medium is required through which male gamete can move. • In algae, bryophytes and pteridophytes water is the medium for gamete transfer. • To compensate loss of male gametes during transport, the number of male gametes produced is several thousand times the number of female gamete produced.

47. Pollination • The transfer of pollen grains from the anther to the stigma is called pollination. • Pollen grains germinate on the stigma and the pollen tube carrying the male gametes reaches up to the ovule and discharge the gametes near the egg. Pollen grain showing pollen tube.

48. fertilization • This process is also called Syngamy in which fusion of two gametes takes place and results in the formation of zygote. • Parthenogenesis :- In some organisms like rotifers, honey bees and even some lizard and birds (turkey) the female gamete undergoes development of new organism without fertilization. This phenomenon is called parthenogenesis. Honey Bee Turkey Rotifer The smallest animal on the Earth

49. Fertilization are of two types:- • 1) External fertilization :- In aquatic organisms, like algae, fishes as well as amphibians Syngamy / fertilization takes place outside the body of the organism in an external medium (water). Its major disadvantage is that offsprings are extremely exposed to predators who threats their survival up to adulthood. Spawn

50. 2) Internal fertilization :- In many terrestrial animals like fungi and other higher animals and majority of plants, they develop a special mechanism in which male deposits its gamete inside the female body and Syngamy/fertilization takes place. In this case, the male gamete is motile and has to reach to female gamete in order to fuse with it. • Chances of survival of offsprings are more. Therefore a small number of egg is produced. POST FERTILIZATION CHANGES • Events in sexual reproduction after the formation of zygote are called post fertilization events/changes. In organisms with external fertilization the zygote is formed outside the body while with internal fertilization the zygote is formed inside of the body. • The development of zygote depends on type of lifecycle and environment. • In organisms like fungi and algae, zygote develops a thick coat which is resistant to damage. It undergoes a period of rest before germination. • In organism with haplontic life cycle, zygote divides by meiosis to form haploid spores that grow into haploid individual.