fertilisation Flashcards
define a zygote
the fertilised egg from which a new individual develops
define cleavage
at stage when the zygote is dividing by mitosis. the process of mitosis results in the formation of two cells. these two cells divide again by mitosis into four, eight then 16 and so on
define chiasma
the point at which crossing over occurs between chromatids
define morula
solid mass of blastomeres resulting from a number of cleavages of a zygote, or fertilized egg
define blasocyst
a hollow ball of cells formed during early embryonic development
what’s the trophoblast
A thin layer of cells that helps a developing embryo attach to the wall of the uterus, protects the embryo, and forms a part of the placenta.
what’s the blastocoele
the primordial, fluid-filled cavity inside the early forms of embryo
what’s an inner cell mass
the group of cells in the blastocyst that develop into the embryo, also called the embryoblast
what is the order from outside in of the three germ layers
- ectoderm
- mesoderm
- endoderm
what does the ectoderm form
the outermost germ layer. this will form the outer layers of the body such as the skin, hair and mammary glands, as well as the nervous system
what does the mesoderm form
the mesoderm is the middle germ layer. the skeleton, muscles, connective tissue, heart, blood and urogenital also allows the formation of the stomach and intestines
endoderm
the endoderm is the innermost germ layer. it forms the lining of the digestive system as well as the lungs and thyroid
define the amniotic fluid
the fluid contained within the amnion. it protects the embryo against injury
define amnion
the membrane that forms a cavity around the embryo. it secretes a fluid (amniotic fluid) into the cavity to protect the embryo
what is the yolk sac
a small, membranous structure situated outside of the embryo with a variety of functions during embryonic development.
what is the chorion
one of the embryonic membranes that eventually forms part of the placenta
what is the chorionic villi
finger like projections that develop from the outer layer of cells of the early embryo. they grow to form part of the placenta
Relate a zygote to the stages of embryonic development
A zygote goes through many divisions after fertilisation during the cleavage stage. 2 cells - 4 cells - 8 cells - 16 cells. A solid ball of cells will form called a morula. The morula moves down the fallopian tubes and changes to a blastocyst. The blastocyst will embed itself into the endometrium through implantation.
describe the embryonic cycle
After the cleavage stage, the blastocyst will embed itself into the endometrium. The embryonic knot will transform into the primary germ cells. The germ layer can now grow and differentiate by absorbing nutrients. The amniotic membrane and yolk sac will form. The germ layer will bend to form a cylinder shape, which causes the amniotic membrane to increase in size and the yolk sac to decrease in size. A body stalk forms which attaches to the germ layer.
this structure is now called a chorion. Chorionic villi develop from the chorion membrane and contain blood vessels which will extend out into the females endometrium
Discuss how the roles of the placenta establish viable pregnancy during the embryonic cycl
The placenta is an organ that supplies nutrients and removes wastes from the foetus. Chorionic villi develop from the chorion membrane and contain blood vessels. As the baby’s chorionic villi penetrate the endometrium, it becomes surrounded by the mother’s blood. The placenta is attached to the foetus via the umbilical cord, which consists of umbilical veins and arteries. The arteries release wastes and CO2 and absorb nutrients and O2 through the veins, all by diffusion and active transport.
what does the yolk sac and allantois form
the outside of the umbilical cord
draw diagrams to explain
what is crossing over
the interchange of the parts of the chromatids of a homologous pair of chomosomes during the first stage of meiosis. it creates new combinations of alleles
