CHAPTER

UNIT-VI Reproduction

REPRODUCTION IN ORGANISMS

Syllabus

Reproduction in Organisms: Reproduction, a characteristic feature of all living organisms for continuation of their species; modes of reproduction-asexual and sexual reproduction; asexual reproduction-binary fission, sporogenesis, budding, gemmule formation, fragmentation; vegetative propagation in plants.

Chapter Analysis

2016 2017 2018

List of Topics OD D OD D/OD

Asexual • Vegetative propagule 1 Q

reproduction • Three stages in life cycle of plants (3 M)

Sexual • Significance of meiocyte 1Q 1 Q 1 Q

reproduction • Sexuality in plants (2 M) (2 M) (3 M)

• Difference between parthenogenesis and parthenocarpy

• On the basis of above analysis, it can be concluded that vegetative propagule in angiosperms, concept of meiocyte, sexuality in plants and concept of parthenogenesis and parthenocarpy are the most important topics of the chapter.

TOPIC-1 Asexual Reproduction

TOPIC - 1

Asexual Reproduction .... P. 01

TOPIC - 2

Sexual Reproduction .... P. 05

Revision Notes

Life Span: It is the period from birth to the natural death of an organism.

> Reproduction: It is a process in which an organism gives rise to young ones (offspring) through which cycle of life is maintained.

> Types of Reproduction : Asexual reproduction and Sexual reproduction.

> Asexual Reproduction : The production of offspring by a single parent is known as asexual reproduction. The offspring produced asexually are identical to one another and also to their parent. Such morphologically and genetically similar individuals are known as clones. It is usually seen in unicellular organisms and in plants and animals which has simple body organization.

> Different Methods of Asexual reproduction

1. Fission: In this, the parent cell divides into two or more individuals. Examples - Protists and Monerans. Fission is of two types:
2. Binary fission: It is the division of parent cell into two individuals. Examples - Amoeba, Paramecium.

(b) Multiple fission: It is the division of parent cell into many individuals. Example – Plasmodium.

1. Budding: The formation of a daughter individual from a small projection, the bud, arising on the parent body is called budding. It occurs in Yeasts (Fig: 1.1), sponges and Hydra (Fig: 1.3).
2. Other Reproductive Structures:
3. Zoospores (motile spores)—Found in some algae, fungi and protists.

2 Oswaal CBSE Chapterwise & Topicwise Question Bank, BIOLOGY, Class – XII

1. Conidia (non-motile spores)—Penicillium.
2. Gemmules (internal buds of sponges)—Sponges (Spongilla).

1. Vegetative Propagation: In certain plants, vegetative propagules (the units of vegetative propagation such as runner, rhizome, sucker, tuber, offset and bulb) arise from the nodes of modified stems. When the nodes come in contact with damp soil or water, they produce roots and new plants. Examples,

1. Eyes in potato—Emergence of small plants from the buds ('eyes') of the potato tuber.
2. Rhizomes of banana and ginger.
3. Adventitious buds—Arise from the notches present at margins of leaves of Bryophyllum.
4. Bulbil—Fleshy bulb in Agaves which function as vegetative propagules.

1. Sporulation: During unfavourable conditions, some organisms get surrounded by a resistant, three layered, hard covering called cyst. The cyst consists of number of spores. These spores get liberated during favourable conditions and this process is called sporulation. e.g., Amoeba (Fig: 1.2).

1. Fragmentation: A type of asexual reproduction, where an organism splits into fragments and each fragment develops into a new organism e.g., Spirogyra, sponges, etc.

<math>\triangleright</math> Terror of Bengal: Water hyacinth is known as terror of Bengal because it grows rapidly and enormously and hampers the growth of the native species and eliminates them. It is also known as "blue devil".

IMPORTANT DIAGRAMS:

Bud Nucleus divides itself and forms daughter nuclei

ughter yeast

Nucleus

Parent yeast

Vacuole Formation of separate daughter cells

Bud is formed from parent cell and parental nucleus is copied Fig 1.1: Budding in Yeast

Mouth

Daughter

cells

Nucleus Búd Parent Cell Nucleus divides Cytoplasm divides

Fig 1.2: Budding Hydra

Fig 1.3: Binary fission in Amoeba

(1 mark each)

Very Short Answer Type Questions

1. 1. Identify 'A' in the given diagram and state its function. R [Delhi Set-I, Comptt. 2016]

Ans. 'A'—Adventitious buds

Function — Vegetative propagation <math>\frac{1}{2} + \frac{1}{2}</math>

[CBSE Marking Scheme, 2016] ·A Q. 2. Identify 'A' in the given diagram and state its

function. R [Delhi Set-II, Comptt. 2016]