Maharashtra Board Class 12 Biology Chapter 1 Reproduction in Lower and Higher Plants PDF Download

Reproduction In Lower And Higher Plants

Reproduction is the production of young ones like parents. Reproduction is an essential process as it leads to continuation of species as well as to maintain the continuity of life. Each organism has its own particular method of reproduction. All these methods generally fall into two categories:

i. Asexual reproduction

ii. Sexual reproduction.

1.1 Asexual Reproduction

Asexual reproduction does not involve fusion of two compatible gametes or sex cells. It is the process resulting in the production of genetically identical progeny from a single organism and inherits the genes of the parent. Such morphologically and genetically identical individuals are called clones. Organisms choose to reproduce asexually by different modes or ways:

i. Fragmentation: Multicellular organisms can break into fragments due to one or the other reasons. e.g. Spirogyra. These fragments grow into new individuals.

ii. Budding: It is the most common method of asexual reproduction in unicellular Yeast. Usually it takes place during favourable conditions by producing one or more outgrowths (buds). These buds on seperation develop into new individual.

iii. Spore formation: In Chlamydomonas asexual reproduction occurs by flagellated, motile zoospores which can grow independently into new individuals.

Other methods of asexual reproduction include - Binary fission which occurs in Amoeba, Paramoecium; Conidia formation in Penicillium and Gemmules formation in Sponges.

The capacity to reproduce by vegetative propagation:

Root - Sweet potato, Asparagus, Dahlia.

Leaf - Bryophyllum, Kalanchoe, Begonia, etc.

Stem - rhizome (turmeric), tubers (potato), bulbs (onion), etc.

Teacher's Note

Budding in yeast is like how our body makes new cells. In India, we use potato buds to grow new potato plants in farms.

Exam Trick

Remember: Asexual = one parent only. Buds from yeast are like making copies of a photocopy machine.

Points to Remember

Asexual reproduction needs only one parent plant.
All new plants made this way look exactly like their parent.
Fragmentation, budding and spore formation are three main types.
Yeast uses budding to make new yeast cells.

1.2 Sexual Reproduction

It involves fusion of two compatible gametes or sex cells. All organisms reach to the maturity in their life before they can reproduce sexually. In plants, the end of juvenile or vegetative phase marks the begining of the reproductive phase and can be seen easily in the higher plants at the time of flowering. The flower is specialized reproductive structure of a plant in which sexual reproduction takes place. The function of flower is to produce haploid gametes and to ensure that fertilization will take place. Typical flower consists of four different whorls viz. calyx, corolla androecium and gynoecium.

Sexual reproduction involves two major events viz. meiosis and fusion of gametes to form diploid zygote and the production of genetically dissimilar offsprings. Variations are useful from the point of view of the survival and the evolution of species, over the time.

Sexual reproduction is characterised by fusion of the male and female gametes (fertilization), the formation of zygote and embryogenesis. Sequential events that occur in sexual reproduction are grouped into three distinct stages viz, Pre-fertilization, Fertilization and the Post-fertilization.

Vegetative Reproduction

Plants reproduce asexually through their vegetative parts. Hence, the new plants formed are genetically identical to their parents. There are also few methods which would not occur naturally in the plants. Agriculture and horticulture exploit vegetative reproduction in order to multiply fresh stocks of plants. Artificial methods are used to propagate desired varieties according to human requirements. The various methods are as follows:

a. Cutting: The small piece of any vegetative part of a plant having one or more buds is used for propagation viz. Stem cutting - e.g. Rose, Bougainvillea; leaf cutting - e.g. Sansvieria; root cutting e.g. Blackberry.

b. Grafting: Here parts of two plants are joined in such a way that they grow as one plant. In this method, part of the stem containing more than one bud (Scion) is joined onto a rooted plant called stock, is called grafting. Whereas budding is also called bud grafting in which only one bud is joined on the stock, e.g. Apple, Pear, Rose, etc.

c. Tissue culture: It is a method by which a small amount of plant tissue is carefully grown to give many plant lets. Micropropagation method is also used now a days.

Teacher's Note

Grafting is like joining two different fruit trees together. In India, farmers graft mango trees to grow better mangoes.

Exam Trick

Remember: Cutting = one piece. Grafting = two pieces joined together. Easy way - think of grafting as a tree surgery.

Points to Remember

Cutting means taking one piece of a plant with buds.
Grafting joins two different plant parts together.
Both methods make plants that are exactly like the parent plant.
Tissue culture uses tiny pieces of plant to grow many new plants.

This is a preview of the first 3 pages. To get the complete book, click below.