|
|
Development
After fertilization a diploid cell forms which is called zygote.
Zygote develops into new organism in anywhere.
This process is called development.
In plants after fertilization each ovule develops into seed and pistil develops into fruits.
Fruits protect seeds.
SEED
Seeds contain 3 main parts these are Testa, Endosperm and Embryo.
Testa protects the seed that is very hard.
Endosperm is a tissue which stores foodstuffs for embryo.
Embryo is a small model f new offspring.
It develops into adult organism.
A seed needs three factorsfor germination;
H2O, O2 and temperature
Seed use oxygen for respiration because it is non-green.
Seed lost weight during germination. Because embryo use carbohydrate, proteins and lipids from endosperm.
In animal development, there are four steps. These are:
Cleavage
Morula
Blastula
Gastrula
After fertilization, zygote starts the first of mitotic cell division.
Formation of two cell from zygote is known as cleavage.
These cells are called blastomers.
Each blastomere divides repeatedly until 32 cells are formed.
This group of cells is called morula.
After morula, cells continue divide mitotically and forms ball like structure which is called blastula.
In blastula several hundered cells are formed around a cavity filled with fluid.
After blastula some cells migrate. Inner portion of ball and 3 different layer are formed.
This three layered structure is called gastrula.
These layers: Endoderm, Ectoderm and Mesoderm
After formation of these layers each layer differentiate into organs and tissues.
This process is called differentiation
During differentiation
Ectoderm develops into ; Endocrine glands, Nervous system, Skin.
Mesoderm develops into;
Blood, Skeletal system, Muscles, Circulatory system, Excretory system, Gonads
Endoderm develops into; Digestive system, respiratory system, pancreas and liver
1. Shell: Some animals lay egg with shell. Shell contains CaCO3 and it protects the embryo.
It forms in oviduct after fertilization which is impermeable to water but permeable to gases.
Shell is seen in reptiles, and birds.
The Chorion
It is located under the shell
Chorion allows gas exchange.
3. The Allantois: It is a sac which stores excretory substances.
It is large in reptiles and birds and small in mammals.
Vitellus (Yolk Sac)
Yolk sac store protein, lipid and carbohydrates.
It is large in reptiles and birds. But small in mammals. Because mammals embryo take nutrients from its mother.
The Amnion:
Amnion is filled by amniotic fluid.
It supports the embryo.
6. Placenta: Placenta is a link between embryo and mother which nutrient, and hases may pass.
It has rich small blood vessels.
In human fertilization occurs in fallopian tube.
After fertilization, zygote starts division mitotically. However it is moved toward uterus by cilia.
MULTIPLE BIRTHS
A)FRETERNAL TWINS: In some woman both of two ovary produce egg in month.
If there are sperms in oviduct at ovulation time. Two egg are fertilized by two different sperm.
They implant at different sites of uterine wall and develops indepently.
IDENTICAL TWINS
After formation of zygote from one egg and sperm. It divides mitotically.
Group of cell split into two parts in blastula stage.
Each group of cells develops into a child indepently.
Identical twins have identical properties.
The offspring of Black Bear is about 300 grams at birth.
The haviest offspring is African Elephant, 110 kilograms.
The smallest offspring is Kangaroo; 0,75 grams.
The longest gestation periods of development is seen in Indian Elephant, 607-641 days.
The least gestation periods of development is seen in Opossum; 13 days.
The mouses reach the ability to reproduce 35-49 days after birth.
The whale can reach the ability to reproduce 6-12 years after birth.
Human can reproduce 12-15 years after birth.
The highest number of offspring in one birth is seen in rabbits;
15 offsprings in one birth.