fertilisation

Question 1

define a zygote

Answer 1

the fertilised egg from which a new individual develops

Question 2

define cleavage

Answer 2

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

Question 3

define chiasma

Answer 3

the point at which crossing over occurs between chromatids

Question 4

define morula

Answer 4

solid mass of blastomeres resulting from a number of cleavages of a zygote, or fertilized egg

Question 5

define blasocyst

Answer 5

a hollow ball of cells formed during early embryonic development

Question 6

what’s the trophoblast

Answer 6

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.

Question 7

what’s the blastocoele

Answer 7

the primordial, fluid-filled cavity inside the early forms of embryo

Question 8

what’s an inner cell mass

Answer 8

the group of cells in the blastocyst that develop into the embryo, also called the embryoblast

Question 9

what is the order from outside in of the three germ layers

Answer 9

1. ectoderm
2. mesoderm
3. endoderm

Question 10

what does the ectoderm form

Answer 10

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

Question 11

what does the mesoderm form

Answer 11

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

Question 12

endoderm

Answer 12

the endoderm is the innermost germ layer. it forms the lining of the digestive system as well as the lungs and thyroid

Question 13

define the amniotic fluid

Answer 13

the fluid contained within the amnion. it protects the embryo against injury

Question 14

define amnion

Answer 14

the membrane that forms a cavity around the embryo. it secretes a fluid (amniotic fluid) into the cavity to protect the embryo

Question 15

what is the yolk sac

Answer 15

a small, membranous structure situated outside of the embryo with a variety of functions during embryonic development.

Question 16

what is the chorion

Answer 16

one of the embryonic membranes that eventually forms part of the placenta

Question 17

what is the chorionic villi

Answer 17

finger like projections that develop from the outer layer of cells of the early embryo. they grow to form part of the placenta

Question 18

Relate a zygote to the stages of embryonic development

Answer 18

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.

Question 19

describe the embryonic cycle

Answer 19

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

Question 20

Discuss how the roles of the placenta establish viable pregnancy during the embryonic cycl

Answer 20

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.

Question 21

what does the yolk sac and allantois form

Answer 21

the outside of the umbilical cord

Question 22

draw diagrams to explain

Question 23

what is crossing over

Answer 23

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