Reproduction

Question 1

What are the types of asexual reproduction?

Answer 1

• budding
• parthenogenesis
• regeneration

Question 2

What is regeneration

Answer 2

• Repair of damage to body
• a form of reproduction in some species
• involves mitosis and differentiation

Question 3

What is budding?

Answer 3

• similar process to regeneration
• occurs without damage
• may give rise to individuals or colonies

Question 4

What is parthenogenesis?

Answer 4

• development of egg without fertilisation
• new individual may be haploid or diploid
• invertebrates and few vertebrates

Question 5

What does sexual reproduction involve?

Answer 5

• Gametogenesis - making sex cells/gametes
• spawning or mating
• fertilisation - getting sex cells to fuse

Question 6

What is gametogenesis?

Answer 6

• germ cells need to proliferate (
finite time for females, indefinite time for males)
• germ cells need to undergo meiosis in order to exchange genetic material and to half their chromosome complement

Question 7

What are the different stages of a sperm cell during spermatogenesis?

Answer 7

• spermatogonium divides mitotically
• MEIOSIS - prophase; primary spermatocyte
• after 1st division - primary spermatocyte
• secondary spermatocyte
DIFFERENTIATION
• spermatid
• spermatozoa

Question 8

What is the site of spermatogenesis?

Answer 8

Seminiferous tubules in the testis

Question 9

Describe the development of oocyets

Answer 9

• oogonia proliferate through mitosis
• but when they enter into primary oocytes they immediately enter prophase 1 of meiosis
• the primary oocyte stays in this phase until the female animal becomes sexually mature
• second meiotic division only occurs after fertilisation

Question 10

What is the difference between oogonia and oocytes?

Answer 10

Primordial germ cells migrate to the forming gonad and becomes oogonia.
After a period of mitotic proliferation oogonia differentiate into primary oocytes.

Question 11

What happens in the first division of meiosis?

Answer 11

In the first division, the homologous chromosomes separate into 2 daughter nuclei.
• cytoplasm divides asymmetrically - one is a small polar body and the other is large cell (containing all developmental potential)

Question 12

What happens in the second division of meiosis?

Answer 12

Two sister chromatids of each chromosome separate to form 2 haploid cells
• once again, the cytoplasm divides asymmetrically to form another small polar body and the mature ovum.

Question 13

Summarise gametogenesis in males

Answer 13

• each spermatogonium gives rise to four haploid sperm
• mitosis ceases in the embryo
• meiosis begins at puberty through to end of life

Question 14

Summarise gametogenesis in females

Answer 14

• each oogonium undergoes mitosis forming primary oocytes
• meiosis begins in the embryo but stays in prophase 1 until puberty
• oocyte remains at metaphase 2 until fertilisation occurs where second division occurs
• otherwise ovulation occurs

Question 15

What does internal and external fertilisation require?

Answer 15

External - aquatic habitat

Internal - mating

Question 16

What are the 2 categories of animals with internal fertilisation?

Answer 16

Oviparous - egg bearing

viviparous - live bearing

Question 17

What is oviparous?

Answer 17

• Egg bearing

* development occurs outside the mother’s body

Question 18

What is viviparous?

Answer 18

• live bearing

* development occurs inside the mother’s body

Question 19

What specific organelles does the mother and father provide?

Answer 19

• Sperm provides the centriole

* All of the mitochondria provided by the mother

Question 20

What is an acrosome?

Answer 20

• cap at the front of the sperm that stores protein

* this is the part that first contacts the egg

Question 21

What is the zona pellucida?

Answer 21

• the thick outer coating covering the egg

* it is a layer of carbohydrate-covered proteins that surrounds the plasma membrane

Question 22

What is the function of the zona pellucida?

Answer 22

• protects the egg

* responsible for mediating the initial meeting of the sperm and the egg

Question 23

Where are cortical granules found and what is their function?

Answer 23

• cortical granules are filled with enzyme and line the inside of the cell membrane
• help make sure that only one sperm can fertilise the egg

Question 24

What are the differences between the egg and the sperm right before fertilisation?

Answer 24

• sperm has completed meiosis
• egg has not completed meiosis - the chromatids are still attached
- once fertilisation has occurred
• size: sperm is 10,000 times bigger than the sperm

Question 25

Describe the steps involved in fertilisation

Answer 25

1. sperm bind to the zona pellucida
2. enzymes of the acrosome are freed and begin to digest the zona pellucida
3. sperm tunnels toward the egg’s plasma membrane and 2 membranes fuse allowing sperm to release genetic material into the egg (fertilisation has occurred)
4. this triggers a release of calcium ions which cause cortical granules to release their contents and digest the zona pellucida making it unable to bind more sperm

Question 26

How does the egg cell ensure that only one sperm enters the egg?

Answer 26

• the sperm enters and releases its genetic material into the egg
• sperm activation factors trigger cortical granules to fuse with membrane
• causes a release of calcium ions derived from the egg cell
• cortical granules duse with membrane and enzymes released digest the zona pellucida
• sperm can no longer bind