1. subtopics 9.1 - asexual reproduction in plants & animals 9.2 - sexual reproduction in...

CHAPTER 9:Reproduction & Development

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Subtopics

9.1 - Asexual reproduction in plants & animals9.2 - Sexual reproduction in flowering plant9.3 - Human reproductive system9.4 - Fertilization & foetal development9.5 - Roles of hormones

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After studying this topic, students should be able to:

a) Explain the following terms & give examples of each:

1. Parthenogenesis (plant & animal)2. Sporulation (plant)3. Budding (plant and animal)4. Binary fission (animal)5. Fragmentation (animal)6. Vegetative propagation (in plant)

Learning outcomes

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One of the fundamental characteristics of living organisms is the ability to reproduce a new generation of individuals of the same species.

A new individual normally has to go through a period of growth & development before it reaches the adult stage at which it can reproduce itself.

Reproduction involves the transmission of genetic material from the parental generation to the next generation.

Introduction to Reproduction

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The significance of reproduction in a given species is to replace those members of the species that have died, due to predation, disease & accidental death.

This ensures the continuity of the species & when conditions are favourable, it also allows the increase in the number of individuals of the species.

Types of reproduction

Asexual reproduction

Sexual reproduction

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i. SEXUAL REPRODUCTION Involves two parents; the female produces

eggs or ova & male produces spermatozoa to fertilize the eggs.

ii. ASEXUAL REPRODUCTION Does not involve the production of gametes

& only one parent is required. Different ways are evolved for asexual reproductions & the young are genetically identical to the parent.

Type of Reproduction

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Asexual reproduction is the production of offspring from organism without the fusion of gametes.

Asexual reproduction used by many unicellular organisms, plants & lower animals.

Involves only mitotic cell division - each offspring has exactly the same heredity as its parent.

Learning Outcome : 9.1 - Asexual reproduction in plants and animals.

Asexual Reproduction

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The parent individual may split, bud or form

fragments to produce offspring that is genetically identical (and has the same adaptive capabilities as parent).

No variation among the progenies that produced.

Asexual reproduction is also capable of producing a large number of progeny in rapid time compared to sexual reproduction.

Learning Outcome : 9.1 - Asexual reproduction in plants and animals.

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1. Parthenogenesis[Gk : parthenos, virgin : gamos, marriage]

The development of a female gamete (egg) forming a new individual without being fertilized

by a male gamete (spermatozoon)

It happens naturally in some insects. E.g. : honey bee (n) & aphids (2n), Rotifer sp.

In plants, a form of parthenogenesis called apomixis. E.g. : some citruses, certain grasses (Kentucky bluegrass) & dandelions.

Learning Outcome : 9.1 - Asexual reproduction in plants and animals.

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Honey bee

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Aphid Kentucky bluegrass

11Rotifer sp.Dandelions

Learning Outcome : 9.1 - Asexual reproduction in plants and animals.

• Recently, the Komodo dragon discovered to reproduce by parthenogenesis.

• The ability to reproduce both sexually & parthenogenetically probably resulted from the Komodo dragon's isolated natural habitat, living as it does on islands in the Indonesian archipelago.

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Komodo dragon

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Spore - A reproductive cell that can develop into an individual without first fusing with another reproductive cell. Spores are produced by plants, fungi, bacteria & some protists.

E.g.: Plasmodium sp. which causes malaria, produces a special kind of spore called sporozoite.

Learning Outcome : 9.1 - Asexual reproduction in plants and animals.

2. Spore Formation (Sporulation)The formation of spores or microscopic

unicellular reproductive units that each containing cytoplasm & nucleus.

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Dryopteris sp.15

Parent organism divides into two approximately equal parts. Each daughter cell becomes a new individual. E.g.: Amoeba sp., Paramecium sp.

The advantage of binary fission is its speed in reproduction when the environmental factors are good.

Learning Outcome : 9.1 - Asexual reproduction in plants and animals.

3. Binary FissionA process in which an unicellular organism divides into two identical cells (same as the

parent cell).

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Amoeba sp.17

Paramecium sp.

Is the ability to form the new whole individual when original organism cut into pieces (in term of reproduction).

Flatworm (Planaria sp.), Tapeworm (Taenia saginata) & Filamentous algae (Spirogyra sp.).

Learning Outcome : 9.1 - Asexual reproduction in plants and animals.

4. Fragmentation

A single parent breaks into parts that regenerate into whole new individuals.

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Cut Planaria sp. worm in two

Growsnew head

Anteriorhalf with

no tail

Growsnew tail

Some flatworm species reproduce by dividing across the middle.Then each offspring regenerates the missing half of its body.

Planaria sp. 19

Plan

aria

sp.

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21Taenia saginata

Learning Outcome : 9.1 - Asexual reproduction in plants and animals.

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Many animals can also replace lost appendages by regeneration but this is not reproduction because new individuals are not created.

E.g.: lizard can grow new tail when injured.

E.g.: Yeast, Hydra sp., Obelia sp.& some plants

Learning Outcome : 9.1 - Asexual reproduction in plants and animals.

5. Budding

The formation of an outgrowth/ bud from a parent’s cell or body which later is released

& becomes another new cell or individual.

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24Yeast

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Hydra sp.

Occurs in plants

E.g.: The production of strawberry plants from runners & gladioli from daughter corms.

Learning Outcome : 9.1 - Asexual reproduction in plants and animals.

6. Vegetative Propagation

New individuals develop from leaves, stems or roots or by specialized multicellular

structures [e.g. tubers (potato), corms, rhizomes, suckers, bulbs (onion), stolons &

adventitious plantlets] that become detached from the parent plants.

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Learning Outcome : 9.1 - Asexual reproduction in plants and animals.

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Strawberry plants form stolons in their asexual reproduction.

Stolons are horizontal stems with long internodes, points where adventitious buds form.

The strawberry plant grows horizontal stolons over the soil, sprouting new strawberry plants where nodes touch the soil.

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stolon

Some plants have special underground stems called rhizomes.

They resemble roots but are really stems, indicated by the presence of scale-like leaves, buds & nodes.

They grow by branching in different directions & forming new plants as they grow.

Learning Outcome : 9.1 - Asexual reproduction in plants and animals.

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rhizome

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Vegetative reproduction from a stem cutting less than a

week old

stem cutting

Learning Outcome : 9.1 - Asexual reproduction in plants and animals.

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• Some plants are capable of producing young plants along their leaf margin.

• These miniature plants are called plantlets.

• These little structures grows a short stem & roots before they drop to the ground & grow into independent new plant.

• These plants have meristematic tissue along the margins of their leaves capable of producing plantlets at each notch of the leaf.

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Bryophyllum daigremontianum produces plantlets along the margins of its leaves. When they are mature enough, they drop off and root in any

suitable soil beneath.

plantlets

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Potato tuber

rhizome

36onion bulbs

corm

suckers

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