Alternation of Generation

Introduction

In this article, you will find all the essential concepts related to alternation of generation. We have introduced the Alternation of Generation from CBSE Class 11 Biology Notes. Alternation of generations in plants is a kind of life cycle in which the two generations of plants alternate between diploid and haploid organisms. Here we will discuss Alternation of Generation and its life cycle, Stages of Alternation of Generations—Sporophyte Generation and Gametophyte Generation.

Let us start with defining the alternation of generations in plants.

About Alternation of Generation

Alternation of generations defines the life cycle of a plant which alternate between two phases i.e sexual and asexual phases or haploid and diploid generations.

Alternation of generations definition

“Alternation of generations in plants is a kind of life cycle in which two distinct generations of plants oscillate between haploid and diploid organisms.”

The alternation of generations can be compared with the animals’ sexual reproduction where diploid and haploid cells can be found in both the generations.

Plants fungi and algae oscillate between the haploid gametophyte and diploid sporophyte, and between sexual and asexual reproduction. Hence the life cycle of a fungi, an algae, bryophyta and Pteridophyta is called alternation of generations. The capability in the plants to reproduce asexually and sexually assits them in adapting to various surroundings.

The alternation of generations varies with the kind of plant, fungi and algae. The haploid is the dominant generation and the gametophyte consists of the main plant in the alternation of generations in bryophytes. In the tracheophytes, the diploid is the dominant generation and the sporophyte consists of the main plant.

The life cycle of the plant fungi and algae in one of the two generations is dominant over the non-dominant generation. The plants from the dominant generation live for longer and grow larger, in the form of other plants, trees, and ferns. The plants from the generations that are non-dominant are hardly visible and are small.

The sporophyte is the dominant generation in vascular plants, while the generation that is dominant is the gametophyte in the plants that are non-vascular.

Stages of Alternation of Generations

There are two phases of alternation of generations:

• Sporophyte Generation

A sporophyte is the result of two haploid gametes fusing together to make a diploid zygote. Zygote undergoes a series of mitosis resulting in a multicellular organism. Upon maturity, the sporophyte forms sporangia, which is the reproductive organ. The spore mother cells in sporangia undergo meiosis to make haploid spores. The spores are let out and carried by water and air and in favorable conditions, they form into a gametophyte.

• Gametophyte Generation

Gametophyte is the next generation in the alternation of generations. The spores are newly created and possess half of the parent organism’s DNA. The spore undergoes mitosis many times to make a gametophyte. The gametes are made during the gametophyte generation by the gametangia. Then the gametes are sent out into the environment or transferred between the plants. When a gamete comes in contact with a gamete of the opposite sex, they merge to create a zygote, which then becomes a sporophyte.

Alternation of generation in Vascular and Nonvascular Plant

Both Vascular and Nonvascular plants have alternation of generation. Let’s discuss them.

1. Vascular plant: there are two types of vascular plants i.e. seedless and seed bearing vascular plants. In seedless plants like ferns both the sporophyte and gametophyte are independent while in seed bearing vascular plants gametophyte is dependent on the sporophyte for survival.
2. Non vascular plants: these plants require moist habitats for survival unlike vascular plants. Gametophyte is the primary phase of the vascular plant life cycle. This phase consists of green mossy vegetation while the elongated stalks are the sporophyte phase of the plant.

Conclusion

Alternation of generations refers to the life cycle that is generally seen in fungi, algae, and plants in which they alternate between haploid and diploid organisms. The two stages of alternation of generations are called Sporophyte Generation and Gametophyte Generation. Plants oscillate between the haploid gametophyte and diploid sporophyte, and between sexual and asexual reproduction. Hence, a plant’s life cycle is called alternation of generations. The capability of the plants to reproduce asexually and sexually assits them in adapting to various surroundings.