Download - Lower Secondary - Sexual Reproduction
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This presentation was produced by the Science department of Temasek Secondary School. Redistribution or reproduction of this resource is prohibited by copyright regulations. This resource should be used for educational purposes.
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REPRODUCTION
Sec 2 ScienceLecture 1
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REPRODUCTION Reproduction is the process of
producing new offspring.
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mother and baby
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mother and baby
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CELL DIVISION Cells are required for:
- growth.- replacement
New cells are exactly the same as the ‘parent’ (original) cell
Cell simply divides into two
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ASEXUAL REPRODUCTION IN AMOEBA
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ASEXUAL REPRODUCTION IN YEAST
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SEXUAL REPRODUCTION IN Homo sapiens
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SEXUAL REPRODUCTION IN Animals
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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
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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.
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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.
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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.
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NO. OF CHROMOSOMES No. of chromosomes in a normal
human cell (excluding sex cell) = 46 (23 pairs)
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23
NO. OF CHROMOSOMES IN A NORMAL HUMAN CELL (EXCEPT SEX CELL) = 46
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46
62
4856
1 200
380
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NO. OF CHROMOSOMES IN A SEX CELL = 23
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BOY OR GIRL?
XY
BOY
XX
GIRL
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TYPE OF EGGS PRODUCED BY FEMALES
X X
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TYPES OF SPERMS PRODUCED BY MALES
YX
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SPERM
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Make a guess … Which organism produces the
LARGEST sperm? The fruit fly!
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A HUMAN SPERM
cytoplasm
nucleus
plasma membrane
HEAD
MIDDLE PIECE
TAIL
mitochondrion (singular)
flagellum (singular)
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THE HUMAN SPERM Very small 23 chromosomes A nucleus Some cytoplasm Can swim (has a flagellum) Many mitochondria
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What can go wrong?
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OVUM
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A HUMAN OVUMcytoplasm
nucleus
plasma membrane
outer membrane mitochondrio
n (singular)
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THE HUMAN OVUM Larger compared to the sperm 23 chromosomes A nucleus More cytoplasm Cannot swim Less mitochondria
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THE MALE REPRODUCTIV
E SYSTEM
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kidney
ureter
urinary bladder
These 3 parts are
NOT part of the male
reproductive system
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scrotum
testis
sperm duct
sex glands
urethra
penis
MALE REPRODUCTIVE SYSTEM
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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.
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PARTS OF THE MALE REPRODUCTIVE SYSTEM SEX GLANDS- Produce fluids in which the sperms
‘swim’.- Semen = mixture of sperms and
fluids
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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.
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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.
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THE FEMALE REPRODUCTIV
E SYSTEM
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kidney
ureter
These 3 parts are
NOT part of the female
reproductive system
urinary bladder (displaced to right side)
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oviduct
vagina
uterus
ovary
cervix
urethra
FEMALE REPRODUCTIVE SYSTEM
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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.
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A hamster egg entering the funnel of the oviduct
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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.
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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.
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REVISIONLabel the parts in the male & female reproductive system.
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kidney
ureter
urinary bladder
scrotum
testis
sperm duct
sex glands
urethra
penis
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kidney
ureter
oviduct
vagina
uterus
ovaryurinary bladder (displaced to right side)
cervix
urethra
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FERTILIZATION
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THE AMAZINGR A C E
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oviduct
cervix.
oviduct
cervix.
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Where is the egg?(see video clip)
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FERTILIZATION Fertilization takes place in the
oviduct.
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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.
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2323
46
ovum sperm
FERTILISATION
zygote
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2323
46
ovum sperm
FERTILISATION
zygote
parent cell
46meiosis
parent cell
46meiosis
mitosis46
46 46
4646
46
embryo
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FERTILIZATION The sperm and egg each have 23
chromosomes. The zygote formed will have 46
chromosomes. Then the zygote divides by normal
cell division.
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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.
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AFTER FERTILIZATION
When it reaches the uterus, it is a ball-like structure consisting of many cells – an embryo.
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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).
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THE AMNION The amnion (a membrane) encloses
the embryo in the amniotic cavity, which is filled with amniotic fluid.
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amnion
amniotic cavity
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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.
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AMNIOCENTESIS
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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).
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AMNIOCENTESIS
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amniotic fluidplacenta
foetus
uterus
cervix
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HOMEWORK What is amniocentesis used for?
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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)
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DOWN’S SYNDROME
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DOWN’S SYNDROME 3 instead of 2 chromosome no. 21
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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.
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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
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WHAT MAKES UP THE PLACENTA The blood vessels of the fetus & the
blood vessels of the mother in the wall of the uterus.
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FOETUS MUMWALL OF THE UTERUS
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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.
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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
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amnion
amniotic cavity
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5 weeks 6 weeks 7 weeks
10 weeks 3 months
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4 months 5 months
6 months 7 months 8 months
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zygote
embryo
foetus
baby
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A 10mm,
5 week old embryo from an ectopic pregnancy, still in the oviduct.
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A 6 week old embryo.
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HOW LONG BEFORE THE BABY IS BORN? For humans, it takes 9 months.
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9 mths
About 9 mths
1 yr
2 mths
12 days
Didelphis marsupialis
1 yr 10 mths
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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.
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TWINS
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IDENTICAL TWINS
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FRATERNAL TWIN BOYS
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IDENTICAL TWINS
FRATERNAL TWINS
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From The TimesMarch 26, 2008
Thomas Beatie, a married man who used to be a woman, is pregnant with a baby girl