Chapter 5 ( Fertilisation and organogenesis)

Question 1

Function of fertilization

Answer 1

1. provides for the recombination of paternal and maternal genes, thus restoring the original diploid number of chromosomes
2. activates the eggs to begin development.

Question 2

What is fertilization

Answer 2

This is the union of male and female gametes to form a zygote.

Question 3

spermatozoa come into contact with the eggs by

Answer 3

random movement.

Question 4

What happens when the head of a spermatozoon hits the vitelline membrane

Answer 4

the acrosome at the tip of the head bursts open, releasing a substance (sperm lysin) which softens the vitelline membrane at the point of contact.

Question 5

What’s capacitation

Answer 5

This is an activating process involving the removal of a layer of glycoprotein and plasma proteins from the outer surface of the sperm.

Question 6

Capacitation takes how many hours?

Answer 6

7hrs

Question 7

membrane becomes more permeable to Ca** which have the dual effects of?

Answer 7

increasing the beating activity of the sperm tail and promoting the acrosome reaction.

Question 8

What’s acrosome reaction?

Answer 8

acrosome membrane fuses with the cell membrane, which starts the release of acrosomal enzymes which pierce the egg membranes.

Question 9

What enables the spermatozoon to penetrate into the cytoplasm of the egg?

Answer 9

Acrosome reaction

Question 10

Further sperms are prevented from entering the ovum by

Answer 10

cortical reaction

Question 11

What is cortical reaction?

Answer 11

cortical granules migrating through the plasma membrane and applying themselves to the inner surface of the vitelline membrane fluid which cause the thickening of the vitelline membrane

Question 12

What is fertilization membrane?

Answer 12

Thickened vitelline which appears to lift off from the egg surface

Question 13

How is the nucleus of the sperm and ovum fuse ?

Answer 13

Commonly the nuclear membranes break down, a spindle is formed, and the now visible sperm and egg chromosomes arrange themselves on the spindles as in mitosis.

Question 14

Development of zygotes starts with

Answer 14

cleavage,

Question 15

What is cleavage ?

Answer 15

zygote dividing repeatedly by mitosis into progressively smaller cells or blastomere.

Question 16

List and explain the different yolk distribution

Answer 16

1. Homolecithal or isolecithal: Even distribution of yolk
2. Telolecithal: yolk is concentrated towards one pole known as the vegetal pole
3. centrolecithal: The amount of yolk is large, and it is collected compactly in the centre of the egg cell.
4. Discoidal eggs: The amount of yolk is so enormous that the non-yolky part of the cell forms a mere microscopic spot, or blastodisk, on top of the yolk mass

Question 17

What is equal and holoblastic cleavage ?

Answer 17

(furrow extend completely through the egg).
little or no yolk, the cleavage divisions
are symmetrical, resulting in blastomeres of equal size

Question 18

What is a meroblastic cleavage

Answer 18

a moderate amount of yolk is concentrated towards the vegetal pole; this causes cleavage to be unequal, the cell at the animal pole being smaller than the ones beneath.

Question 19

The The small and large cells of meroblastic cleavage are called ___respectively

Answer 19

micromeres and
macromeres

Question 20

The mass of cells is known as the ____, and its cavity as the ______, and the cellular layer of the _____.

Answer 20

1. blastula
2. blastocoel
3. blastoderm

Question 21

What type of Cleavage is
superficial and meroblastic?

Answer 21

Centrolecithal

Question 22

What is a radial Cleavage example

Answer 22

Successive tiers of equal sized blastomere come to lie one directly over another, and the whole embryo may posses several mirror-image planes and cleavage is indeterminate e.g. sea star,

Question 23

What is Spiral Cleavage?
Example of organisms.

Answer 23

The newly formed blastomeres comes to lie over and between two earlier ones, and as a result, pack themselves tightly together rather than just lightly contacting each other as do many radially cleaving embryos e.g. molluscs, annelids, nemertean and some planarian, platyhelminthes.

Question 24

What is a Bilateral Cleavage?

Answer 24

Nematodes): The different sizes of blastomeres (usually two) are confirmed to separate areas in the blastula,

Question 25

The formation of organs occurs in the embryo after what process?

Answer 25

gastrulation

Question 26

What is gastrulation process.

Answer 26

rearrange until they reach the places they will occupy in the adult, and the three germ layers of ectoderm, endoderm and mesoderm characteristics of triploblastic animals are formed.

Question 27

The three basic layers
undergo ______ to give rise to the final organs.

Answer 27

morphogenetic movement

Question 28

What are epithelial cells?

Answer 28

These are cells in close formation adhering to one another, forming a sheet or compact mass)

Question 29

What are mesenchymal cells?

Answer 29

These are much more individually mobile cells

Question 30

Epithelial cells form organs in the following ways:

Answer 30

(1) by local thickening of the layer; forming for instance a neural plate
(2) by the separation of layers to leave a space; as in coelom formation
(3) by folding a layer; as in early neural tube formation
(4) by fusion of once separate masses; as in later neural tube formation;
(5) by breaking up of layers to produce mesenchyme cells; as in formation of gut wall and neural crest

Question 31

Mesenchyme forms organs in the following ways

Answer 31

(1)by aggregation into mass as in bone formation
(2) by attachment to another mass as in the formation of skeletal capsules.
(3)by secondary rearrangement into epithelia as in the formation of blood vessels.

Question 32

The ectoderm gives rise to?

Answer 32

Neural tube,sensory organs and epidermis

Question 33

The endodermis gives rise to

Answer 33

The epithelial lining of the intestine and the outgrowth (respiratory system, endocrine, digestive system and urinary tissues )

Question 34

The mesoderm is divided into 3 regions namely

Answer 34

Dorsal epimere, central mesomere and ventral hypomere

Question 35

The dorsal epimere forms the

Answer 35

Skeletal muscles and vertebrae

Question 36

The central mesomeres forms the

Answer 36

Kidney and gonads

Question 37

The ventral hypomere forms the

Answer 37

Heart: The muscular organ responsible for blood circulation.
Peritoneum: The lining of the abdominal cavity.
Mesenteries: Membranes that support and stabilize internal organs.
Smooth muscle: Found in various organs like the digestive tract and blood vessels.
Connective tissue: Supports and binds various tissues throughout the body.

Question 38

The ventral hypomere is divided into

Answer 38

Outer somatic, inner splanchnic and the cavity between them; coelom

Question 39

The epimere coelom segments to give

Answer 39

a series of somites, separated from the rest of the mesoderm

Question 40

The epimere migrate and differentiate into three cell types:

Answer 40

Sclerotome: Forms the cartilage and bone of the vertebrae.
Dermatome: Develops into the dermis of the skin.
Myotome: Gives rise to skeletal muscles of the body.