Biology Chapter 4: Reproduction and Growth

Reproduction: Production of new individuals of the same species for the continuation of the species.

Types of reproduction:

Sexual reproduction Asexual reproductionThe production of new individuals involving sex cells or gametes

The production of new individuals without involving sex cells

Gametes are formed by meiotic division The process relies entirely on mitotic division

Involves 2 individuals Involves only one individual (single parent)New individual inherit genes from both parents

New individuals get their genes from one parent

Occur in humans, other mammals, birds, reptiles, amphibians, fish, flowering plant

Occurs in simple organism like Amoeba sp., Paramecium sp., Hydra sp.

Produces offspring that are genetically different from their parentsEnsure the survival of the species if the environmental conditions undergo changes constantly

Produces offspring that are genetically identical from their parentsEnsure the adaptations of the parent for survival are pass downed unchanged to the offspring

Necessity for the formation of gametes:

1) Formation of gametes happens in reproductive organs (gonads)2) Male gonads are known as testes and female gonads are known as ovaries3) Formation of gametes is through meiosis in which 46 chromosomes are halved to 23.4) During fertilisation, a fusion of a sperm and an ovum which has 23 chromosomes

each produces a zygote with 46 chromosomes

The male reproductive system

1) Testis: produce both the male gametes (sperms) and male sex hormones. Has thousands of seminiferous tubules inside.

2) Scrotum: hold the testes and located outside the main body cavity. Has lower temperature (2-3 C lower than normal temp) for development of healthy sperm.

3) Epididymis: Combination of thousands of seminiferous tubules coiled together outside the testis. Sperms are formed in the seminiferous tubules and mature within the epididymis. The functions is to store and mature the sperm.

4) Vas deferens or sperm duct: Connected to epididymis. Stores the sperm and transfer the sperm from the apididymis to the ejaculatory duct. The vas deferens leaves the scortum and enters the abdominal cavity

5) The 2 sperm ducts are joined to urethra which connects the urinary bladder to the penis.

6) Seminal vesicles: secrete a thick, clear fluid containing nutrients for the sperms7) Prostate gland: secretes a milky white fluid that activates or increase the mobility of

the sperm.

Spermatogenesis

1 2 3 4 5

1) Primordial germ cells undergo mitosis to form many spermatogonia (spermatogomium) (2n)

2) Each spermatogonium (2n) develops into primary spermatocytes3) Upon puberty, primary spermatocyte undergoes meiosis I and form 2

secondary spermatocyte (n)-haploid4) These spermatocytes undergo second meiosis and form 4 spermatids5) Spermatids differentiate to form spermatozoa (sperm cells)

mitosis mitosis Cell growth Meiosis I

Meiosis II differentiation

The female reproductive system

1) Ovaries: produce the female gametes (ova/ovum) and secrete female sex hormones; oestrogen an progesterone

2) Fallopian tube: Move the ovum along. Has fimbriae which surround ovaries.3) Uterus: thick-walled, muscular organ that holds the developing embryo and foetus

Oogenesis

1) Embryonic gonads of foetus contains primordial germ cells that undergo mitosis to produce oogonia

2) At the 5th month of fetal development, these ooginia (2n) develop into primary oocyte (2n). Each primary oocyte is surrounded by the follicular cells known as primary follicle.

3) A baby girl is born with all the primary follicles which then mature after puberty.4) Primary oocyte undergoes first meiosis to form secondary oocyte and a polar body.5) During ovulation, secondary oocyte is released into Fallopian tube by ruptured

Graffian follide.6) If sperm penetrate the secondary oocyte during fertilization, meiosis II will be

completed and ovum and second polar body are formed.

The formation of twins:

Identical twins Differences Fraternal twins or non-identical twins

One ovum is fertilised by one sperm to form a zygote

The zygote then split into 2 separate embryos

The division complete

Fertilisation Two ova are released at the same time during menstrual cycle, each ovum is fertilised by a sperm

Two zygotes are formed which divide and develop into 2 seperate embryos

Both twin have same genetic constitution

Genetic constitution

Both twin do not share the same genetic constitution

Share one placenta Numbers of placentas

Each embryo has its own placenta and umbilical cord

Have same sex Sex May have same or different sexesSame physical characteristics Physical

characteristicsDo not share same physical characteristics

The functions of placenta in foetal development:

The placenta:

(a) Is the site of the exchange of nutrients, respiratory gas and waste between mother and foetus

(b) Secretes oestrogen and progesterone: help to maintain the thick blood enriched endometrium

The placenta is connected to the foetus by the umbilical cord

The umbilical cord is a tube with one umbilical vein and 2 umbilical arteries

(a) Umbilical arteries: carry blood rich in carbon dioxide and nitrogenous waste products from the foetus to placenta

(b) Umbilical vein carries blood rich in oxygen and nutrients from placenta to the foetus.

Sexual reproduction in flowering plants

Sexual reproduction in flowering plants (angiosperms) takes place in the distinctive reproduction structure called the flower.

There are 4 flower parts, namely sepals, petals, stamens and carpel.

The male reproductive structure are the stamens which consists of: Filament: a long stalk which support the anther Anther: the structure that produces pollen grains. Pollen grains contain the

male gamete The female reproductive structures are the carpels. Several carpels fuse together to

form a pistil. Pistil has 3 parts: Stigma: a sticky structure at the apex of the style to which pollen grain adhere Style: a stalk that joins the stigma to the ovary Ovary: contains ovule

The formation of pollen grains in the anther:

(1) Pollen is produce in the anther which consists of four pollen sacs.

(2) In each pollen sacs, are hundred of pollen mother cells (2n) or microsporocyte

(3) Each pollen mother cell undergoes meiosis to produce four haploid microspores (n)

(4) The nucleus of each microspore then divides by mitosis to form a tube nucleus and a generative nucleus. The microspores develop into pollen grains.

Formation of the embryo sac in the ovule: