CLASS: SS1

SUBJECT: BIOLOGY                                PERIOD(3)

TOPIC: REPRODUCTION

SUBTOPIC 1: REPRODUCTION IN UNICELLULAR ORGANISMS

SUBTOPIC 2: REPRODUCTION IN INVERTEBRATES

PREVIOUS KNOWLEDGE: Students are familiar with the topic

OBJECTIVES: At the end of the period

  1. The students should be able to
  2. Define reproduction
  3. State the types of reproduction

iii.      Explain in details the types of asexual and sexual reproduction

Period 2:

  1. Describe reproduction in Amoeba
  2. Describe reproduction in Paramecium

iii.      Describe reproduction in spirogyra

 

Period 3:

  1. Describe reproduction in earthworm
  2. Describe reproduction in cockroach

iii.      Describe reproduction in Housefly

  1. Describe Reproduction in snail.
  2. Describe reproduction in toad
  3. Differentiate between complete and incomplete metamorphosis

References

Essential Biology for Senior Secondary Schools 1-3, by M.C Michaels pg 244 – 251.

 

Content

Reproduction is the process by which living organisms produce offspring (new individuals) of their type. Reproduction is of 2 types namely.

  1. Asexual reproduction – an individual produces an offspring by itself, that is, a single parent without production of gamates or fusion of nuclei. Closes (offspring which are identical to the parent) are produced. Asexual reproduction is common among single organisms, flowering plants and in organisms which can produce both sexually and asexually depending on certain conditions (food availability, favorable environmental conditions for growth) the types of asexual reproduction include:
  2. Binary fission: The parents organisms simply divides into 2 or more parts by mitosis, each of which can exist by itself. If the cells divides into more than 2 cells, it is referred to as fission e.g. in bacteria and  protists e.g. of Binary fission Amoeba, Paramecium.
  3. Budding: In this types, the offsprings develops as an outgrowth of the parent. The bud may form an external or internal surface of the parents. Internal buds are formed in some sponges and are released when the parents dies. External buds occur in Hydra, coral polyps and yeast. These buds break off from the parent without causing any injury and lead an independent life.

iii.      Spore formation: Spores are small unicellular bodies which are produced in large numbers. They are small light and dispersed by the wind. Spores are usually produced by fungi, mosses, ferns, algae, protists and bacteria.

  1. Fragmentation – a part of an organisms breaks up or fragments and give rise to a new organism. It occurs in algae, coelenterates and sponges e.g. planaria, spirogyra
  2. Vegetative propagation – occurs mainly in higher plants. A new plant grows from any portion of an old one other than the seeds e.g. stems and roots.
  3. Patogenesis – is a natural form of asexual reproduction in which growth and development trof embryos occur without fertilization, that is developed from an unfertilized egg cell e.g. aphids, honey bee, ants, wasps. Some scorpions, some plants, nematodes, water flies, some mites, some fish, amphibians and reptiles.

vii.     Schizogony – this is the asexual reproduction of a sporozoite by multiple fission within the body of the host giving rise to merozoites. This type is found in some protozoa especially parasitic sporozoans e.g. malaria parasite  plasmodium

  1. Sexual reproduction: Offsprings are produced by the fusion of 2 different sex cells which usually come from 2 different parents.

 

Reproduction in Amoeba

Amoeba reproduces asexually by splitting or dividing into two equal parts by mitosis to produce 2 new daughter cells (binary fission)

 

REPRODUCTION IN PARAMECIUM

Paramecium reproduces asexually (binary fission) and sexually (conjugation). Conjugation in Paramecium involves the pairing of a whole cell with another whole cell both of which as a gamete and exchange nuclei.

 

REPRODUCTION IN SPIROGYRA

Spirogyra reproduce sexually (conjugation) and asexually fragmentation) in conjugation, 2 filaments (conjugants) lie side by side and produce outgrowths which meet and form the conjugation tube. The cell cytoplasm shrinks away from the cell walls and round up to form a gamete. One acts as the male and migrates through the conjugation tube into the other cell and fuse forming a zygote or zygosphere which germinates and forms a new filament. It also occurs  in mucor rhizopus and paramecium.

 

Fragmentation in spirogyra occurs when a filament reaches a certain length, parts of its break away and grow into new filaments.

 

REPRODUCTION IN EARTHWORM

Earthworm reproduces sexually and the fertilization is internal. Matured male and female earthworms came together and mate. The male injects sperm into the female reproductive organs. After fertilization, the female lays numerous eggs which hatch into small and tiny baby earthworms which develop into adulthood.

 

REPRODUCTION IN COCKROACH

Metamorphosis is the series of gradual changes of form and shape of certain organisms from the fertilized egg (immature stage) to adult (mature stage) and there are 2 types Complete (Egg – larva-pupa – adult) e.g. mosquito, housefly, wasp, beetles, bees, butterfly and incomplete (egg – nymph – adult) e.g. grasshopper, termites, dragonfly, aphis, cockroach, prayingmatis, locust etc.

 

Reproduction in cockroach, is sexual and internal fertilization occurs. The male introduce sperms into the female where it is stored in sperm pouch from which the sperm fertilizes the eggs. The eggs of cockroach are laid in a horny egg case called ootheca which is chitinous in nature. The case contains 10-15 egg and are arranged in 2 rows of 5-8 eggs per row. These egg cases are deposited in a dark, warm and humid place where they hatch after about 30 – 100days into nymphs (very small, wingless and colourless organisms) Nymptial  life lasts for 10 – 16 days during which series of moulting occur to develop wings and grow bigger.

 

The appearance of wings shows adulthood. An adult cockroach has well developed parts. The lifecycle is about 11 – 20 months.

 

 

REPRODUCTION IN HOUSEFLY

Housefly breeds on any decomposing organic material and it exhibits complete metamorphosis. The life cycle is short about 3-4weeks. After fertilization, the female lays 2-7 batches of eggs (100 – 150 eggs per batch) in moist decomposing matter and these hath out in 8 hours to 3 days into which larvae maggot). The Larval body is made up of 12 segments and it possess the head which has a pair of hooks for tearing food dn to draw it along and 2 pairs of spiracles (on the 2nd and 12th segments. It moults, shedstis skin) several times and last for about 5 -14 days to begin pupal stage. The maggot shortes and theskin forms the puparium (pupal case). It doesn’t feed or move at this stage because internal reorganization of the body is taking place. The pupal stage takes 3-10 days after which the adult emerges from the puparium using a sac-like organ (ptilinum) on its head.

 

 

REPRODUCTION IN SNAIL

Snail reproduces sexually and its fertilization  is internal. The female lays the eggs in a cool dry place. Baby snails hatch and emerge from the eggs after some days.

 

Reproduction in toad

Snail reproduces sexually and the fertilization is internal. The female lays the eggs in a cool dry place. Baby snail hatch and emerge from the eggs after some days.

 

RERPODUCTION IN TOAD

Toad reproduces sexually and fertilization is external. As the female lays her eggs, the male releases its sperms on them. The eggs are surrounded in strings of jelly (the jelly separates the eggs to receive enough oxygen, protect mechanical injury, prevent bacterial  and fungal attack and from drying-up. Toad undergo metamorphosis from egg to adult stage the tadpole emerge from the egg after 1-2 days and grow. It feeds on the egg yolk at first due to the absence of  mouth and breathes through the skin. It attaches itself to a water weed using a sticky substance secreted by a V-shaped cement gland.

 

The tadpole develops 3 external gills on either side of the head and horny jaws for feeding on water weeds(herbivore) After 6-10 days after hatching, the external gills disintegrate and the internal gills develop. A gill cover (operculumO avers the gills leaving an opening called spout on the left side through which water flows out. The limbs develop, mouth replaces horny jaws and the tadpole starts eating small animals. A young toad develops after reabsorption of the tail. The process takes a total of about 40-45days. Thyroid gland at the region of the head and turn a hormone called thyroxine which controls metamorphosis in amphibians. Absence of this hormone / iodine deficiency prevents or inhibits metamorphosis.

 

INSTRUCTIONAL MATERIALS: Textbooks, pictures; videos showing reproduction.

Teaching methods procedures

Step I: teacher revises the topic and introduce the new logic

Step II: Teacher explains metamorphosis in insects and toad

Step III: Teacher explains reproduction in unicellular organisms and invertebrates

Step IV: Teacher allows students to ask questions and writes notes under content on the board.

CLASSROOM (ACTIVITIES)

PERIOD 1: Students discuss reproduction types

PERIOD 2: Students discuss reproduction in unicellular animals.

PERIOD 3: Students discuss reproduction and metamorphosis in invertebrates

EVALUATION:

PERIOD 1: What is reproduction?

PERIOD 2: Explain conjugation in paramecium

PERIOD 3: Explain courtship in toad

 

SUMMARY/CONCLUSION: Teacher summarizes the topic, makes the students notes and makes corrections where necessary.

 

ASSIGNMENT(S)   

PERIOD 1: In a tabular form, differentiate between sexual and asexual reproduction

PERIOD 2: Differentiate between complete and incomplete metamorphosis.