أحياء لغات – Reproduction in livings للصف الثالث الثانوى 2016

 Reproduction in livings

.All livings depend on various sources for supplying them with energy that is necessary for their life

,However

.They stay living on this Earth for a limited period which eventually ends by death

,So

They should perform the function of nutrition, respiration, excretion, and sensation in order to succeed in staying alive even shortly on Earth

:Importance  of  the reproductive function

?GR) The reproductive function is less important to the individual life than the above mentioned functions

  Because , Any non breeding organism can maintain life naturally. Moreover, the removal of genital organs from some organisms didn’t affect their normal life 

And  If any of these functions was impeded, the individual perishes immediately. Accordingly, reproduction depends on all the other functions, and not the reverse

What is the result   If   Rrproduction  is impeded at the population level? extinction of the species occurs Because , it is the function that assures the continuity of species on Earth after death of the individuals

N.B ) All the organisms start life acting to secure their existence as individuals, they save the necessary energy for growing up to certain stage. Then, they begin acting for maintenance of species through reproduction, to which most of their energy and behavior become directed.

GR) The reproductive capacities differ among organisms

:due to                                                   

.The various ambient.                    - Prevalent hardships.     - Life nature -

.Life duration (their ages).             - The size of the living -

The reproductive capacities among livings

GR) Aquatic organisms produce much more progeny than their land relatives. Also, parasites produce much more progeny than other organisms why? In order to compensate their loss

GR) The production of primitive or short-aged organisms’ progeny’s is much more than higher or long-aged ones since the production of the latter is less endangered, Why ? due to the provided care and protection

NB) The species and individuals seen around at present, express the success of their ancestors in reproduction and in overcoming the hardships they face throughout their consecutive generations. Conversely, many of the extinct forms had failed to continue up till now, from these we recall the dinosaurs and other giant reptiles that did not continue in reproduction, and so, became in the record of geological history. Similar fossil forms are known in the animal and plant kingdoms

Methods of reproduction in livings 

Livings reproduce by many ways and modes in order for species to continue. These modes can be grouped into two main methods

:First: Asexual reproduction

  The isolation of a body part either a spore cell, or many cells, or tissues and their growth into a new organism that fully resembles the original from which the above part has been isolated, So, the features of   the

.following generations remain the same even if the surrounding conditions change

  At any change in the environment most of the offspring become exposed to destruction ,,,,,,,, unless their parents had been adapted for that change

This kind of reproduction is common in the plant kingdom, but is limited to some primitive forms of the animal kingdom

This reproduction depends on mitotic division of cells where cells resulting from this division receive complete copy (2n) of the original cell’s chromosomes

The capacity for regeneration

.Decreases in higher animals

In some Crustaceans and Amphibians, it is limited to restoration of the cut parts only

In higher vertebrates regeneration never exceeds healing of wounds especially those located in skin, blood vessels, and muscles

.NB) If the body of some animals is cut into several parts, each part can grow to a new individual

:Adaptation of  spore

.It   of cytoplasm with little amount of water -

.A nucleus -

.A thick coat -

?When the spore matures, What will happen 

.It liberates from the mother plant to be disseminated into air

Upon reaching to a suitable medium for growth, its coat ruptures while it absorbs water and divides several times by mitosis and grows to a new individual

:Advantages of reproduction by Sporogony

.a. Quick propagation

.b. Tolerance to hard conditions

.c. Distribution to distant region

.NB) Many Fungi such as Bread mould, Mushroom and some Algae and Ferns reproduce by Sporogony

Natural Parthenogenesis

Parthenogenesis occurs in some worms, Crustaceans, and Insects

Honey bee

.It reproduces this way as the queen produces some eggs

.(That develop without fertilization forming drones  (Drones are haploid (N

.(Some others develop after fertilization to queen and workers, (diploid (2N

.This dependes on the type of food provided

Aphid insect

Artificial parthenogensis

Parthenogenesis has been induced artificially by egg activation as in case of frogs and sea stars through

 It exposure to heat, electric shock, irradiation, some salts, agitation, or pricking with a needle

These stimuli lead to ………duplication of their chromosomes and so develop without fertilization to individual that are totally identical with the mother

By similar stimuli, early embryonic stages of rabbits were obtained from their eggs

In an exciting experiment a scientist separated small pieces of Carrot plant into conical flasks containing Coconut

?milk,WHY

.which comprises the whole plant hormones and nutrient elements

Changes in plant

.They began to grow and develop into a full Carrot plant

 .He separated single cells from the same plant and cultivated them by the same method and obtained full plants

,Similarly

.Tobacco plants were obtained from isolated cells of Tobacco leaves that have been treated by the same method

These experiments confirmed that any somatic cell in the plant comprises the whole genetic information that can be translated a whole developed organism if cultivated in a proper nutrient medium containing plant hormones with certain ratio

Importance of tissue culture

These methods are now applied in

.Propagating rare plants or -

.Propagating  desirable strains -

.Propagating strains more resistant to diseases -

Scientists foresee hopes on the progress of these techniques nearly in order to solve food problems, and to shorten -

.the time needed for growing desirable crops

NB) Selected tissues for such culture can be preserved in liquid Nitrogen for a long period while remaining alive till cultivation