How Do Organisms Reproduce

Animals and plants reproduce as a law of nature. It is a means of ensuring the survival of the species and in the context of evolution. Organisms choose among different methods to reproduce. Sexual and asexual reproductions are two major classifications, having its own advantages and disadvantages. Each method is appropriate for different species.
Vertebrates, such as humans, are almost exclusively reproduce sexually. Many simpler animals reproduce asexually.

ASEXUAL REPRODUCTION

• Asexual reproduction is the production of a new organism from a single parent without the involvement of sex cells (or gametes).
• It is quick, simple and the genes of the parent will not be diluted by those of another individual.
• Offspring is a direct clone of the parent, both physically and genetically, for all kinds of asexual reproduction.
• So, the purpose of reproduction which is to propagate one’s own genes makes asexual reproduction a good bet for the species evolutionarily.
• Also, an organism that reproduces asexually can reproduce about twice as fast as one that reproduces sexually.

FEATURES OF ASEXUAL REPRODUCTION

1. Single parent involved
2. No gamete formation or fertilization
3. The whole process takes place in a small period of time
4. Rapid multiplication and growth
5. Limited variation (genetically similar)

TYPES OF ASEXUAL REPRODUCTION

Asexual Reproduction could be classified into many kinds:

(i)Binary fission in amoeba
(ii)Budding in Hydra
(iii) Spore formation in Rhizopus fungus (or bread mould)
(iv) Regeneration in Planaria (flatworm)
(v)Fragmentation in Spirogyra
(vi) Vegetative propagation in flowering plants (like rose plants)

It is observed in both unicellular and multicellular organisms.

SEXUAL REPRODUCTION

• Combination of special reproductive cells i.e. sex cells results in sexual reproduction.
• It is the type of reproduction in which both male and female sexes are needed to propagate new generation.
• So, offspring has a different combination of genes which could be an adaptive advantage in an unpredictable environment and plays an important role in evolution.
• Sexual reproduction is a lot more complex than asexual reproduction.
• In sexual reproduction male and female gametes fuse with each other to form a zygote.
• Gametes are the cells involved in sexual reproduction.
• The gametes are specialized cells which have only half the number of chromosomes of all other cells in the organism…
• Gametes are of two types : male gametes and female gametes.
• The process of meiosis, which produces haploid cells from diploid cells.
• So there is possibility of two copies of a single chromosome crossing over to create a completely new chromosome that contains a new combination of genes.
• Sexual reproduction allows more variation than asexual reproduction.
• Unlike in asexual reproduction where a single cell is divided to produce offspring simple cell-by-cell division is not possible in multicellular organisms.
• This is because most of the multicellular organisms have a complex body design and a higher level of organization like tissues, organs and organ system. So, they need a special mode for reproduction.
• However, if two reproducing cells simply join, the chromosome number in the new organism will be doubled which is not possible because the number of chromosomes in each cell of every organism is fixed.
• The same is true for the reproducing cell.
• Reproducing cells from both parents reduce their chromosome number into the half before fusion and are called gametes (germ cells).
• The gametes are produced in a specialized system called the reproductive system.
• Size and shape of gametes are almost the same in simple organisms but a male gamete is small and mobile while female gamete is large, immobile and they stores food for the fetus in higher organisms.

Features of Sexual Reproduction

1. Two parents are involved (both male and a female).
2. Gamete formation and fertilization take place.
3. The whole process is slow and lengthy.
4. The variation occurs; offspring are different from parents, genetically and physically.