Sexual Reproduction in Plants

Science > Biology > Botany > Reproduction in Plants > Sexual Reproduction in Plants

Sexual reproduction is also called amphimixis (Gk. amphi – both, mixis – union) or syngenesis (Gk. syn – together, genesis – origin) or amphigony (Gk. amphi – both, gony – marriage). In this article, we shall study sexual reproduction in plants.

When two parents (opposite sex) participate in the reproductive process and also involve fusion of male and female gametes, it is called sexual reproduction. Sexual reproduction involves formation of the male and female gametes, either by the same individual or by different individuals of the opposite sex. These gametes fuse to form the zygote which develops to form the new organism.

It is an elaborate, complex and slow process as compared to asexual reproduction. Because of the fusion of male and female gametes, sexual reproduction results in offspring that are not identical to the parents or amongst themselves.

Preparation for Sexual Reproduction:

All organisms have to reach a certain stage of growth and maturity in their life, before they can reproduce sexually. That period of growth is called the juvenile phase. It is known as vegetative phase in plants. This phase is of variable durations in different organisms. The end of juvenile/vegetative phase which marks the beginning of the reproductive phase can be seen easily in the higher plants when they come to flower.

In animals, the juvenile phase is followed by morphological and physiological changes prior to active reproductive behaviour. The reproductive phase is also of variable duration in different organisms. In non-primate mammals like cows, sheep, rats, deers, dogs, tiger, etc., such cyclical changes during reproduction are called oestrus cycle. Whereas in primates (monkeys, apes, and humans) it is called menstrual cycle.

Characteristics of Sexual Reproduction:

• It takes place with the help of gametes.
• It is biparental in origin i.e. two parents are involved (both male and female).
• A male gamete and a female gamete fuse together and fertilization takes place.
• It involves both meiosis and mitosis,
• It is a slower and lengthy method of reproduction.
• Variations occur in sexual reproduction. Offspring are different from parents, genetically and physically. It is important for evolution.
• It occurs more frequently in higher organisms than in prokaryotes. 

Advantages of Sexual Reproduction:

• Sexual reproduction is biparental in origin i.e. two parents are involved (both male and a female). Thus during sexual reproduction fusion of gametes from different parents occur. It results in genetic recombination causing variations. Offspring produces in this type is different from parents, genetically and physically. Thus, it ensures the survival of species in a population and helps in evolution.
• Since both the parents are involved, the newly formed individual (offspring) has characteristics of both the parents.
• The genetic variations produced during sexual reproduction help offspring to adapt to different environments. It also provides vigour and vitality to the offspring. Offspring can adapt better to changing environmental conditions. Hence, the species produced by sexual reproduction survive more than those produced by asexual reproduction.

Disadvantages of Sexual Reproduction:

• Sexual reproduction is usually bi-parental. Hence in sexual reproduction, the two genders must find each other to be able to reproduce. It takes time and energy to locate a suitable mate with the preferred traits that are desired so that the offspring produced by the union can thrive. 
• Fertilization has a chance factor. Sexual reproduction is not a 100% successful method of creating offspring. Some chosen mates may be infertile. Others may not have the gametes come together, despite numerous attempts at creating offspring.
• Sexual reproduction involves the first mating of suitable mates. The fusion of gametes and fertilization. It involves both meiosis and mitosis. Hence it is a slow and lengthy process and requires a lot of time.
• Sexual reproduction can produce numerous offspring at one time. Humans may typically have one child through reproduction, but twins, triplets, and larger multiples are possible. Horses may typically have one foal, but cats and dogs may have more than a dozen in a litter. Compared to asexual reproduction, however, there are usually fewer offspring produced over time. 

Sexual Reproduction in Plants:

Plants can reproduce asexually or sexually. But the majority of the flowering plants reproduce sexually. The flower is the reproductive part of a plant i.e., both male and female gametes are produced by flowers. Sexual reproduction in plants takes place in flowers.  During sexual reproduction, they produce seeds. Plants in their lifetime produce seeds that germinate, grow and develop into new plants. These new plants flower, scatter their seeds and die.

Sexual Reproduction in lower plants:

Bryophytes e.g. Moss:

Moss plants grow in damp places because they depend on moisture to sexually reproduce.  They need water for the sperm to swim towards the eggs for fertilization. Mosses reproduce by spores, which are analogous to the seeds of flowering plants. The spores are single celled.  Spores are housed in the brown capsule that sits on the seta. The spores ripen and are dispersed from the capsule, and some land in areas where there is enough moisture for them to grow.

Some mosses have cups on their tops that produce sperm, these are male plants. The female plants has eggs between overlapping leaves. As the sperm become mature they swim through water to the eggs and fertilize them. The fertilized egg then produces the stalked brown capsule.

Algae e.g. Spirogyra:

In spirogyra, sexual reproduction takes place by conjugation. Two filaments lie side by and produce short tubes that grow and connect the opposite cells. During this time the protoplasts of conjugating cells (gametangia) recede, round up and function as gametes. At the point of contact, the tips of these processes dissolve (bycytase) to form conjugation tube between opposite cells. This structure looks like ladder. Hence, the conjugation is called scalariform or H-shape conjugation. The contents then move from male cell (male gametangia) to female cell (female gametangia) and their nuclei combine, forming a zygote. This process is known as conjugation. The zygote secretes a thick wall to become zygospore. Therefore, in the late stage of conjugation, male gametangia remain empty and the female gametangia contain zygospores.

Science > Biology > Botany > Reproduction in Plants > Sexual Reproduction in Plants