SS1 Biology Lesson Note on Reproduction in Unicellular Organisms and Invertebrates

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TOPIC: REPRODUCTION IN UNICELLULAR ORGANISMS AND INVERTEBRATES

CONTENT:

• Reproduction in Amoeba by Asexual Reproduction by
  • Binary fission
  • Multiple fission
• Reproduction in Paramecium by
  • • Asexual reproduction
    • Sexual reproduction
• Reproduction in spirogyra by
  • • Asexual or vegetative reproduction or conjugation
• Reproduction in the earthworm by
  • • Sexual reproduction

SUB – TOPIC1: REPRODUCTION IN AMOEBA

Amoeba is a unicellular protozoa. Its mode of reproduction is asexual by fission and multiple fission.

Binary Fission

It occurs under normal condition in water when the organism grows to a particular size, the nucleus divides into two equal daughter nucleus divides nuclei and each of the daughter nuclei become enclosed by half of the protoplast leading to the production of two daughter cells. The cell division is simply mitotic.

Multiple fission

In some unicellular organisms such as Amoeba, the cells rounds up to a cyst-like structure. The protoplasm undergo fission as the nucleus of the parent divides into several daughter nuclei by amitosis (repeated divisions). This is followed by the enclosing one nucleus. Several cells are released from the cyst. The type of asexual reproduction occurs under adverse condition.

EVALUATION

1. Define asexual reproduction.
2. Name two forms of asexual reproduction in amoeba;
3. State two difference between binary fission and multiple fission.

SUB-TOPIC 2 : REPRODUCTION IN PARAMECIUM

Paramecium is a protozoa that is more developed than Amoeba. It reproduces both sexually and asexually. Asexual reproduction is by binary fission and sexual reproduction is by conjugation.

Binary fission in paramecium

At maturity the cell stops moving. The two nuclei (macro nucleus and micro nucleus divide mitotically to give four nuclei). This is followed by the movement of the daughter nuclei in opposite direction to the anterior and posterior ends respectively, of a now elongated cell. After this the cell divides transversely along the region of the oral groove and the daughter cells become separated under normal condition this occurs after 8 to 12 hours.

Sexual reproduction in Paramecium

Sexual reproduction by conjugation takes in Paramecium in the following steps:

1. Two individuals called conjugant come together and lie side by side.
2. The meganucleus of each conjugants disintegrate.
3. The micronucleus of each conjugants divides into two parts twice, forming four micronuclei. Three of the four micro – nuclei in each conjugant disintegrate. The remaining micronucleus again divides into two.
4. One micronucleus from each conjugal migrates into the other conjugant. In other words, the conjugants exchange nuclear material.
5. The migratory nucleus of one conjugant and the stationary nucleus of the other conjugant fuse in each individual to form a fusion nucleus in each ex-conjugal divides into four new individuals, each with a new
6. The fusion nucleus in each ex-conjugant divides into four individuals each, with a new meganucleus and micronucleus.

 

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