Meaning and types of reproduction

CONTENT

• Meaning and Types of Reproduction
• Forms of Asexual Reproduction
• Sexual Reproduction (Conjugation and Fusion of Gametes)
• Meiosis and Importance of Meiosis

MEANING AND TYPES OF REPRODUCTION

Reproduction is the ability of an organism to give rise to new individuals of the same species in order to ensure continuity of life.

There are two types of reproduction                                                      

a. asexual reproduction     

b. sexual reproduction

1. Asexual Reproduction: is the process whereby an organism produces an offspring by itself. I.e. only one parent is presence. No gametes involved thus there is no fusion of nuclei, but the cells that give rise to the offspring usually divide by means of mitosis. Offspring produced are identical to the parent in all respect and are called clones
   1. Sexual Reproduction: is a type of reproduction that involves two parents and the fusion of the male and the female gamete to form a zygote. Offspring produced show new variation. The sex cells (gametes) are produced by meiotic cell division and after fertilization the new individual continue to grow and produce new cells by mitosis.

EVALUATION

1. What is reproduction?
2. Why is reproduction necessary?
3. Differentiate between the two types of reproduction.

FORMS OF ASEXUAL REPRODUCTION

1. Binary Fission: Fission is the simplest form and involves the division of a single organism into two complete organisms, each identical to the other and to the parent. Fission is common among unicellular organisms such as bacteria, many protists and some algae.
2. Budding: The parent organism develops an outgrowth which subsequently forms the new individual organism. These buds break off from the parent without causing any injury and live an independent life. Budding is common in yeast and hydra
3. Spore Formation: Spores are DNA-containing capsules capable of sprouting into new organisms; unlike most seeds, spores are produced without sexual union of gametes, when dispersed, each spore is capable of developing into a new organism. Spores are common in lower organisms especially fungi such as rhizopus and penicillum.
4. Fragmentation: A part of the parent organism breaks up and develops into a new independent organism. This type of reproduction is also called regeneration. Fragmentation is common in spirogyra and coelenterates.
5. Vegetative Propagation: It occurs in higher plants. In this process, a new plant grows from any portion of an old one other than the seeds. There are two methods of vegetative propagation, this include natural and artificial vegetative propagations.

Natural vegetative propagation involves the use of vegetative parts such as stems, leaves, roots or buds. The part involved must have a store of food and sometimes able to act as a perennating organ i. e. enable the plant to survive from one growing season to the next. Organs of vegetative propagation include;

• Bulbil: Axillary buds growing from the veins of leaves e. g. Bryophyllum and Begonia.
• Runners or stolons: Stems that creep horizontally on soil surface. Buds and adventitious roots develop from the nodes of the parent plants e. g. sweet potato, grass.
• Rhizomes: Underground horizontal stem. It has scaly leaves which cover lateral buds at the nodes. Lateral buds grow into new aerial shoots e. g. ginger, canna lily.
•  Corms: Underground stems which grow vertically in the soil. Buds develop from the axils of scale leaves, grow upward and form leaves and flowers e. g. cocoyam.
• Stem tubers: Underground stems which have swollen tips. Axillary buds on tubers give rise to new aerial shoots e. g. yam, sweet potato
• Suckers: Short underground horizontal branches e. g. banana, pineapple
•  Bulb: Underground condensed shoots with compressed stems and scaly leaves e. g. onion, garlic.

Artificial propagation is the use of parts of the parent plant to multiply the plants. Budding, grafting, layering, cutting and marcotting are types of artificial propagation.

EVALUATION

1. List four types of asexual reproduction with examples.
2. Discuss spore formation in a named fungus.

GENERAL EVALUATION/REVISIONAL QUESTIONS

1. List four forms of asexual reproduction giving one example of organism that exhibit each.
2. List four common natural vegetative parts in plant giving one example of plant in each case.
3. Describe five types of artificial vegetative propagation.
4. Briefly describe fragmentation in spirogyra.
5. Describe sporulation in amoeba.

READING ASSIGNMENT

College Biology, chapter 16, page 292 – 301

WEEKEND ASSIGNMENT

1. Bacteria multiply rapidly by     A. fragmentation     B. binary fission    C. spore formation     D. budding
2. The type of reproduction that is common to both Hydra and Yeast is   A. conjugation  

B. binary fission   C. grafting   D. budding

• During asexual reproduction in paramecium, how many times does the zygote divide to produce eight nuclei     A. 1     B. 2     C. 3     D. 4
• Vegetative propagation is described asexual reproduction because    A. reproductive organs are not involved    B. many new plants are produced    C. there is no exchange of genetic materials    D. new individuals are not formed
• Which of these organs of vegetative propagation is not a perennating organ?                              A. Rhizome     B. Sucker     C. Bulbil     D. Bulb

THEORY

1. Describe two types of artificial propagation.
2. State three advantages and two disadvantages of asexual reproduction.