أحياء لغات-Sexual & asexual reproduction للصف الثالث الثانوى

Compare between Sexual & asexual reproduction

:Sexual Reproduction -

.it takes place by  2 parents *

.fusion between gametes occurs *

.divided by meiosis to give gametes *

.it is the source of gentic variations *

.the offspring are different *

.they can adapt to new conditions *

 .it takes place in higher organisms *

.it need  long time&high amount of energy for maturation and pregnancy *

.it need high biological cost because females only can reproduce *

:Asexual Reproduction -

.it takes place by one parent only *

.there are no gametes *

.divided by mitosis to give 2 cells *

.there is no genetic variations *

.all offspring are similar *

.they can not *

.it takes place in lower organisms *

.it need short time and samll amount of energy *

.it not need high biology cost because all individuals reproduce *

Sexual Reproduction in living organisms

.Sexual Reproduction needs the presence of two individuals, male and  female to produce sexual gametes

 .Gametes fused during fertilization to form the zygote

.Zygote then divides and grows to the embryo then to young & adult

.Sexual reproduction needs more time and energy

.(The production of new individuals takes place by the half number of individuals (by females only

Sexual reproduction provides genetic variations for  facing the  changes in the environmental

.conditions

      Sexual reproduction occurs after elapse of certain age and need the proper nest before mating , they may alternate in guarding

the eggs and protection of the youngs

Types of Sexual Reproduction

:Sexual reproduction occurs by 2 main methods

:Conjugation -

,In primitive organisms such as some Protozoa, Algae and Fungi

                                  :Reproduction by sexual gametes -

.Higher plants and animals reproduce by means of sexual gametes

.Male and female gametes,are Produced  from meiosis that takes place in gonads

:Types of conjugation

                   .a) Scalariform conjugation.                    b)Lateral conjugation

at suitable conditions, but they turn to sexual reproduction by conjugation if subjected to drought or a change in water temperature or purity

a) Scalariform conjugation

Spirogyra is common in the green scum of standing water where its filaments float, each filament is formed of one *

.row of cells

When two filaments contact parallel to each other, a protrusion grows inwards between them, then walls *

 .in-between disappear forming a conjugation tube

 .The protoplasm of one cell moves across the conjugation tube to cell of the opposite filament to form zygote *

.Zygote is coated by a thick wall forming zygospore to protect it along unsuitable conditions *

b) Lateral conjugation

.This conjugation occurs between the adjacent cells of the same filament *

.The protoplasm of one cells moves to the adjacent cell through an opening in the wall in between them *

Compare between Scalariform conjugation and Lateral conjugation