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REPRODUCTION

Sec 2 ScienceLecture 1

REPRODUCTION Reproduction is the process of

producing new offspring.

mother and baby

mother and baby

CELL DIVISION Cells are required for:

- growth.- replacement

New cells are exactly the same as the ‘parent’ (original) cell

Cell simply divides into two

ASEXUAL REPRODUCTION IN AMOEBA

ASEXUAL REPRODUCTION IN YEAST

SEXUAL REPRODUCTION IN Homo sapiens

SEXUAL REPRODUCTION IN Animals

ASEXUAL REPRODUCTION

The new organism has the same genetic material as the parent.

Only one parent required.

Cell simply divides into two.

Method used by most unicellular organisms.

The new organism does not have the same genetic material as the parent.

A male & a female required.

Involves a male & a female gamete (sex cells).

Method used by most multicellular organisms.

SEXUAL REPRODUCTION

ADVANTAGES OF ASEXUAL REPRODUCTION Quick – no need to find a mate Because the genetic material of the

new organism is the same as that of the parent, thus the new organism has the desirable qualities of its parent.

ADVANTAGES OF SEXUAL REPRODUCTION Genetic material of the new offspring

is a combination of the genetic material from the parents thus the new offspring may have good traits e.g. better looking than the parents.

A variety of new organisms are produced.

SEX CELLS (gametes) Male sex cell = sperm

(plural sperms) Female sex cell = ovum (egg)

(plural ova) Sex cells are made in the

reproductive system of a man and a woman.

NO. OF CHROMOSOMES No. of chromosomes in a normal

human cell (excluding sex cell) = 46 (23 pairs)

23

NO. OF CHROMOSOMES IN A NORMAL HUMAN CELL (EXCEPT SEX CELL) = 46

46

62

4856

1 200

380

NO. OF CHROMOSOMES IN A SEX CELL = 23

BOY OR GIRL?

XY

BOY

XX

GIRL

TYPE OF EGGS PRODUCED BY FEMALES

X X

TYPES OF SPERMS PRODUCED BY MALES

YX

SPERM

Make a guess … Which organism produces the

LARGEST sperm? The fruit fly!

A HUMAN SPERM

cytoplasm

nucleus

plasma membrane

HEAD

MIDDLE PIECE

TAIL

mitochondrion (singular)

flagellum (singular)

THE HUMAN SPERM Very small 23 chromosomes A nucleus Some cytoplasm Can swim (has a flagellum) Many mitochondria

What can go wrong?

OVUM

A HUMAN OVUMcytoplasm

nucleus

plasma membrane

outer membrane mitochondrio

n (singular)

THE HUMAN OVUM Larger compared to the sperm 23 chromosomes A nucleus More cytoplasm Cannot swim Less mitochondria

THE MALE REPRODUCTIV

E SYSTEM

kidney

ureter

urinary bladder

These 3 parts are

NOT part of the male

reproductive system

scrotum

testis

sperm duct

sex glands

urethra

penis

MALE REPRODUCTIVE SYSTEM

PARTS OF THE MALE REPRODUCTIVE SYSTEM TESTIS (plural TESTES)- Produce sperms & male sex

hormones. SCROTUM- A bag of skin which holds the testes

outside the body.- Testes are outside the body thus lower

temperature for production & storage of sperm.

PARTS OF THE MALE REPRODUCTIVE SYSTEM SEX GLANDS- Produce fluids in which the sperms

‘swim’.- Semen = mixture of sperms and

fluids

PARTS OF THE MALE REPRODUCTIVE SYSTEM SPERM DUCT- A tube that carries the sperms to the

penis. PENIS- The organ from which semen leaves

the body and is deposited in the vagina of the female.

PARTS OF THE MALE REPRODUCTIVE SYSTEM URETHRA- A tube which carries sperms &

urine at different times. URETER- A tube that links the kidney to the

urinary bladder.

THE FEMALE REPRODUCTIV

E SYSTEM

kidney

ureter

These 3 parts are

NOT part of the female

reproductive system

urinary bladder (displaced to right side)

oviduct

vagina

uterus

ovary

cervix

urethra

FEMALE REPRODUCTIVE SYSTEM

PARTS OF THE FEMALE REPRODUCTIVE SYSTEM OVARY- Produces eggs & sex hormones.- A young girl’s ovary contains about 70 000

ova (eggs). About 500 will become mature.

- An ovum (egg) is released from the ovary every 28 days.

- The ovaries take turns to release an ovum.

A hamster egg entering the funnel of the oviduct

PARTS OF THE FEMALE REPRODUCTIVE SYSTEM OVIDUCT- Also called fallopian tube.- Connects the ovary to the uterus.- Funnel of oviduct collects the ovum.- Fertilisation takes place in the oviduct. UTERUS- Also called womb.- Where the baby grows during pregnancy.

PARTS OF THE FEMALE REPRODUCTIVE SYSTEM CERVIX- The narrow opening of the uterus.- Becomes wider during the birth of the baby. VAGINA- Also called birth canal.- A muscular tube where sperms from the

penis are deposited.- Becomes wider during the birth of the baby.

REVISIONLabel the parts in the male & female reproductive system.

kidney

ureter

urinary bladder

scrotum

testis

sperm duct

sex glands

urethra

penis

kidney

ureter

oviduct

vagina

uterus

ovaryurinary bladder (displaced to right side)

cervix

urethra

FERTILIZATION

THE AMAZINGR A C E

oviduct

cervix.

oviduct

cervix.

Where is the egg?(see video clip)

FERTILIZATION Fertilization takes place in the

oviduct.

FERTILIZATION Fertilization is the fusion of a sperm

& an ovum to form a zygote. Out of the 100 million sperms

released into the vagina during intercourse, only one of these will fertilize the egg.

2323

46

ovum sperm

FERTILISATION

zygote

2323

46

ovum sperm

FERTILISATION

zygote

parent cell

46meiosis

parent cell

46meiosis

mitosis46

46 46

4646

46

embryo

FERTILIZATION The sperm and egg each have 23

chromosomes. The zygote formed will have 46

chromosomes. Then the zygote divides by normal

cell division.

AFTER FERTILIZATION As the zygote divides by normal cell

division, it moves along the oviduct towards the uterus with the help of: cilia sweeping the fertilised egg

(zygote) along the oviduct. peristaltic movements in the

oviduct.

AFTER FERTILIZATION

When it reaches the uterus, it is a ball-like structure consisting of many cells – an embryo.

DEVELOPMENT OF THE EMBRYO It takes about 5 days for the embryo

to reach the uterus. Implantation: Eventually the embryo

sinks or becomes embedded in the uterine lining (wall of the uterus).

THE AMNION The amnion (a membrane) encloses

the embryo in the amniotic cavity, which is filled with amniotic fluid.

amnion

amniotic cavity

FUNCTIONS OF THE AMNIOTIC FLUID

1) A shock absorber - protects the foetus against mechanical injury because it is incompressible.

2) Allows the foetus to move freely during growth.

3) Lubricates and reduces friction in the vagina (birth canal) during birth.

AMNIOCENTESIS

WHAT IS AMNIOCENTESIS? A hollow needle inserted into the

uterus through the abdomen. Remove a small amount of amniotic

fluid (about 2 tbsps, 20 ml). Carried out during the middle

trimester (3rd to 6th month).

AMNIOCENTESIS

amniotic fluidplacenta

foetus

uterus

cervix

HOMEWORK What is amniocentesis used for?

WHY AMNIOCENTESIS?The amniotic fluid around the foetus contains skin cells shed by the foetus. These skin cells contain DNA.

From this genetic material, we can determine:

Genetic diseases e.g. Down Syndrome (Gender of the foetus)

DOWN’S SYNDROME

DOWN’S SYNDROME 3 instead of 2 chromosome no. 21

THE MAKINGS OF A PLACENTA... Blood capillaries grow from the fetus

into the uterine wall. The fetus’ blood capillaries are in

close contact with the mother’s blood spaces.

THE MAKINGS OF A PLACENTA... Note: The fetus’ blood capillaries are

not joined to the mother’s blood capillaries.

Why?- high blood pressure of mother- different blood type of mother and foetus

WHAT MAKES UP THE PLACENTA The blood vessels of the fetus & the

blood vessels of the mother in the wall of the uterus.

FOETUS MUMWALL OF THE UTERUS

FUNCTIONS OF THE PLACENTA

1) Allow food, oxygen & water to pass from the mother’s blood to the fetus.

2) Allow waste substances produced by the fetus to pass back into the mother’s blood for removal.

3) Prevents some harmful substances in the mother’s blood from reaching the fetus.

THE UMBILICAL CORD The umbilical cord attaches the

foetus to the placenta. The umbilical cord contains the

blood vessels of the foetus, namely: 2 umbilical arteries 1 umbilical vein

amnion

amniotic cavity

5 weeks 6 weeks 7 weeks

10 weeks 3 months

4 months 5 months

6 months 7 months 8 months

zygote

embryo

foetus

baby

A 10mm,

5 week old embryo from an ectopic pregnancy, still in the oviduct.

A 6 week old embryo.

HOW LONG BEFORE THE BABY IS BORN? For humans, it takes 9 months.

9 mths

About 9 mths

1 yr

2 mths

12 days

Didelphis marsupialis

1 yr 10 mths

HEREDITY Characteristics of the parents are

passed on to their children. During fertilisation, half the

chromosomes are from the father & the other half from the mother.

TWINS

IDENTICAL TWINS

FRATERNAL TWIN BOYS

IDENTICAL TWINS

FRATERNAL TWINS

From The TimesMarch 26, 2008

Thomas Beatie, a married man who used to be a woman, is pregnant with a baby girl