Class 12th, Chapter-1, Reproduction in organism, Lecture-3

Asexual reproduction in protists and monerans:-

#In protists and monerans, the organisms or the parent cell divides into two to give rise to new individual. This, in these organisms cell division is itself a mode of reproduction.

#many single celled organisms reproduce by binary fission where a cell divides into two two halves and each rapidly grows into an adults example Amoeba ,Paramecium.

#In yeast the division is unequal and small buds are produced that remains attached initially to the parent cell which, eventually gets separated and matures into new yeast organisms ( cells).

#Members of kingdom fungi and simple plants such as algae reproduce through special Asexual reproductive structures.

a) Zoospores :- These are microscopic flagellated and motile spores produced inside the zoosporangia. These are without resistant covering (naked) are dispersed by swimming . These are formed in certain algae example ulothrix, and fungi e.g. Albugo and chlamydomonas.

b) Conidia:- Conidia are non motile spores produced  singly or in chains by the constrictions of tips of special hyphal  branches called conidiophores. These are dispersed by wind. After dispersal, conidia germinate by giving out germ tubes. These are formed in Aspergillus and Penicillium.

c) Buds:- An outgrowth or ingrowth or a bud develop on a parent body which after attaining specific size detaches and grows independently. 

Example :- sponges ,coelenterates (Hydra) , Annelides (syllis), Tunicates (salpa) and yeast and fungi.

Budding is of two types:-

1. Exogenous budding

2. Endogenous budding

1) Exogenious budding:- When the bud grows on outer surface of the parent body. In Hydra the bud arises from the body surface as an outgrowth. It  enlarges and develops tentacles. The fully formed bud separates from parent body and starts an independent life.

2) Endogenous budding:- 

# When the bud is formed inside the parent body.

Example - Spongilla (fresh water sponge).

#Number of buds called gemmules are formed inside the body.

#Each gemmule is formed as a mass of undifferentiated archaeocytes surrounded by a protective coat of spicules. When the sponge body degenerates during unfavourable conditions, archaeocytes come out through micropile and organise to form the sponge.

While in animals and other simple organisms the term asexual is used unambiguously , in plants the term vegetative reproduction is frequently used. In plants, the units of vegetative propagation such as runners, rhizomes , suckers,  tuber,  offset, bulb are all capable of giving rise to new offspring. These structures are called vegetative propagules. Obviously, since the formation of these structures does not involve two parents, the process involved is asexual.

Class -12th, Chapter-1, Reproduction organism, lecture-2

Difference between juvenile phase and reproductive phase 

Reproduction :-

Reproduction is defined as a biological process in which an organism gives rise to young ones (offsprings) similar to itself. The offsprings grow mature and in turn produce new offspring .

#Reproduction enables the continuity of species generation after generation.

#The organisms habitat, its internal physiology and several other factors are collectively responsible for how it reproduces.

Reproduction is of two types

a) Asexual reproduction

b) Sexual reproduction

Asexual reproduction 

When offspring is produced by a single parent with or without the involvement of gamete formation the reproduction is asexual it is also known as Apomixis.

In a sexual reproduction 

a) Only one parent is required.

b)There is no formation or fusion of gametes.

c)It involves only mitotic division.

d)New organisms develops from somatic part of the parent. (somatogenic reproduction).

e)New organisms are genetically and morphologically identical and they are called clones.

f)It is a rapid and less energy consuming process.

g)lower organisms reproduce by formation of zoospores(chlamydomonas), conidia (penicillium)etc.

Class- 12th Biology, Chapter-1, Reproduction in organism, Lecture-1

Lifespan  - Each and every organism can live only for a certain period of time.The period from birth to the natural death of an organism represents its life span. It may vary from a day to thousand's of years.

Life span of few organisms are as follows:- 

Elephant 75 years

Rose 10 years

Dog 15 to 20 years

Butterfly 1 to 2 weeks

Crow 15 years

Banana tree 25 years

Cow 25 years

Parrot 140 years

Crocodile 60 years

Horse 50 years

Fruit fly one month

Rice plant 4 months

Tortoise 100 to 150 years

Banyan tree 300 to 500 years

Mayfly one day (shortest lifespan)

# lifespan of organisms are not necessarily correlated with their sizes.

example -the sizes of crows and parrots are not very different yet their lifespan shows a wide difference.

#Whatever be the lifespan,  death of every individual organism is a certainty, i.e. no individual is immortal except single celled organisms.

#In single celled organisms death does not occur because their single celled body divides by binary fission producing two identical daughter individual. Here no dead body is found so they are considered as immortal.

Phases of lifespan

1. Juvenile phase - It is the pre-reproductive phase during which only vegetative growth takes place.

2. Reproductive phase - During this phase the reproductive organs develop and become function.

3. Aging or senescence- This phase is characterized by gradual deterioration of vital capacity is the terminal stage of ageing before death is called senescence.

4. Death- It is the end of life of an organism.

My first blog post.....ABOUT ME

Hello and welcome to my blog. I created this blog as a way to share ideas, tips, notes and tricks for the science students.This blog will serve as a platform of discussion and hopefully as a source of inspiration, knowledge and education for the students as well as others who wish to continuously increase their effectiveness in the classroom.ln this blog I will provide science notes for class 9th, 10th and biology notes for class 11th and 12th and colleges students.

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