1
Reproduction
y Reproduction is one of the seven characteristics of living organisms
y Reproduction is defined as the ability of an organism to produce new
individuals of its own kind
y There are two types of reproduction namely:
1. Sexual reproduction Æ involves two parents and gives variety in offspring
2. Asexual reproduction Æ involves one parent and offspring are copies of parent
2
Sexual reproduction
3
Asexual reproduction
4
Sexual reproduction
y Reproduction is one of the fundamental characteristics of life
y Every individual member of a species has a definite lifespan – death is
inevitable
y Reproduction is defined as the formation of new individuals of the same
species thus ensuring the continuation of the species into future
generations
y New living organisms can only be produced by living organisms
5
The female reproductive system
y
The major functions of the female reproductive system are as follows:
1.
2.
3.
To produce the female gamete (egg or ovum)
To provide a safe environment inside the female body for the baby to
develop
To produce the female sex hormones (oestrogen and progesterone)
6
The female reproductive system
Fig. 39.2
7
The female reproductive system
1.
y
y
Ovaries
The ovaries are responsible for producing the female gametes
(egg cells)
The ovaries are also responsible for production of the female sex
hormones (oestrogen and progesterone), which are involved in
controlling the reproductive process
8
The female reproductive system
1.
Ovaries
9
The female reproductive system
2.
y
y
y
3.
y
Fallopian tubes
The open funnel end close to the ovary captures the egg cell
Fertilisation of the egg cell usually occurs in the Fallopian tube
The fertilised egg is carried to the uterus or womb Æ for this
reason, the Fallopian tubes are also sometimes referred to as
oviducts
Uterus (womb)
The function of the uterus is to provide a suitable environment for
the baby to develop in over the course of the 40 week pregnancy
10
The female reproductive system
3.
Uterus (womb)
11
The female reproductive system
4.
y
5.
y
y
y
Cervix
The cervix is a narrow opening between the uterus and the vagina Æ
the cervix acts as the entrance to the womb
Vagina
The vagina is a muscular tube receives the penis during sexual
intercourse
The sperm, in the semen, are deposited in the vagina
The vagina is also the passageway for childbirth at the end of
pregnancy Æ for this reason, the vagina is also sometimes referred
to as the birth canal
12
The female reproductive system
5.
y
y
y
y
y
Vagina
The vagina is the female copulatory organ and is also referred to as
the birth canal
The vagina is a muscular tube receives the penis and semen during
sexual intercourse
The sperm, in the semen, are deposited in the vagina, referred to as
insemination
The vagina is also the passageway for menstrual flow and childbirth
The acidity of the vagina helps protect against infection by
microorganisms such as bacteria
Table 39.2
13
The menstrual cycle
y
y
y
y
When a girl is born, she already has all of her eggs present in her
ovaries Æ however, at this stage, all of the eggs are in an immature
form
From the age of approximately 12-13 onwards, one egg develops to
maturity each month or so
Other changes in a woman’s reproductive system also occur each
month, referred to as the menstrual cycle
On average, the menstrual cycle is a 28 day cycle, however, the
menstrual cycle can vary from female-to-female and also from monthto-month
14
The menstrual cycle
15
Events of the menstrual cycle
y For simplicity, we will deal with the events of the menstrual cycle as a
series of four consecutive steps differentiated on the basis of hormone
levels (oestrogen, progesterone, follicle stimulating hormone, and
luteinising hormone)
y Day 1 – Day 5
y Day 6 – Day 13
y Day 14
y Day 15 – Day 28
The Menstrual Cycle - teenwire.com
BBC - GCSE Bitesize - Biology | Humans | Hormones in the menstrual cycle
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Events of the menstrual cycle
y Day 1 - Day 5
y Day 1 is the first day of menstruation
y Menstruation is often referred to as a period
y Menstruation is defined as the detachment, breakdown, and
discharge of the lining of the womb through the vagina
y The discharge of the lining of the womb through the vagina usually
lasts from 3-5 days
y Day 6 – Day 13
y The lining of the womb begins to build up with blood once more
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Events of the menstrual cycle
y Day 14
y Ovulation occurs Æ ovulation is defined as
the release of the egg cell from the ovary’s
surface into the body cavity
y Once in the body cavity, the egg cell is
drawn into the Fallopian tube
y The egg cell is capable of being fertilised for
up to 24 hours after ovulation
„
„
„
Day 15 – Day 28
Initially, the lining of the womb continues to fill with blood, however,
after day 26 the lining of the womb begins to break down
The next menstrual cycle can now commence once again, i.e. day 1
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Pregnancy stops the menstrual cycle
y Failure of menstruation (‘missed period’) is
usually a sign that the female has become
pregnant
y The developing embryo within the womb of the
mother releases a hormone into the mother’s
blood which prevents the lining of the womb from
disintegrating, i.e. menstruation does not occur
y Note, poor physical condition and/or mental
stress may also result in a failure of menstruation
(‘missed period’)
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Male and female reproductive systems
y Sperm journey
seminiferous tubule of testis Æ epididymis Æ vas deferens Æ
urethra Æ vagina Æ cervix Æ uterus Æ Fallopian tube
y Egg cell journey
ovary Æ body cavity Æ Fallopian tube
20
Fertilisation
y
Fertilisation is the fusion of the male gamete (sperm) and the female
gamete (egg) to form a zygote
During sexual intercourse, the man positions the erect penis within
the vagina of the female Æ this results in ejaculation, i.e. the release
of semen from the penis
The sperm in the semen swim through the cervix and into the womb,
and then onto the Fallopian tube
If an egg is present in the Fallopian tube, then the sperm may fuse
with the egg, i.e. fertilisation occurs, to form a zygote
y
y
y
y
y
Note, successful fertilisation may only occur in the Fallopian tube
Note, in humans fertilisation is also referred to as conception
21
Fertilisation
y
y
y
y
The fertilised egg (zygote) continues to travel down the Fallopian
tube towards the womb
As it travels towards the womb, the zygote divides several times to
form a ball of cells Æ after approximately one day, this ball of cells
reaches the womb and then attaches itself to the lining of the wall of
the womb, referred to as implantation
Once implantation has occurred, the woman is said to be pregnant
Usually, a woman first realises that she may be pregnant when her
monthly period does not occur
22
Fertilisation
23
Implantation
The embryo implants in the wall of the womb on about the 7’th day of development
24
Pregnancy and birth at end of week nine Æ
foetus
25
Pregnancy and birth Æ foetus
y A foetus is an embryo that resembles a developed individual,
normally evident after week nine onwards of development
26
Pregnancy and birth Æ foetus
y Third month Æ
27
Pregnancy and birth Æ foetus
y Fourth month Æ
28
Pregnancy and birth Æ foetus
y Fifth month Æ
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Pregnancy and birth Æ foetus
y Sixth and seventh months Æ
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Pregnancy and birth Æ foetus
y Eight and ninth months Æ
31
Human foetus at ten weeks Æ placenta
Fig. 39.5
32
Pregnancy and birth
y The placenta also prevents the mother’s blood from coming into
contact with the foetus’ blood Æ if this were to happen,
antibodies in the mother’s blood would destroy the foetus
y Instead, the placenta allows the exchange of materials between
the mother’s blood and the foetus’ blood but does not allow actual
mixing of the mother’s blood and the foetus’ blood
y The placenta is a temporary organ formed from maternal and embryo tissue
which enables exchange between maternal and foetal blood
y The functions of the placenta are as follows:
1. Protection
2. Gas exchange
3. Nutrient supply
4. Excretion
5. Hormonal
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Pregnancy and birth
y A tube called the umbilical cord, containing two umbilical arteries and
one umbilical vein connects the foetus to the placenta
y The two arteries carry blood from the foetus to the placenta
y The vein carries blood from the placenta to the foetus
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Pregnancy and birth
y Inside the womb, the foetus is surrounded by amniotic fluid Æ
amniotic fluid helps to cushion the foetus against physical injury
Table 39.3
35
Pregnancy and birth
y
The length of time from conception to birth is referred to as
pregnancy Æ typically, a human pregnancy lasts for approximately
40 weeks (or nine months)
At this stage the foetus is fully developed and ready to be born Æ the
infant is born just as the structure and efficiency of the placenta
begins to deteriorate
Prior to birth, the infant will normally have turned and be facing headdown, with its face near the cervix
When the mother goes into labour, the wall of the womb begins to
contract in spasms Æ the baby is pushed out of the womb, via the
vagina, to the exterior
y
y
y
y
Labour may happen quite quickly or can last for several hours
36
Genetics
y
y
y
The nucleus is the control centre of cells
The nucleus of a cell contains structures referred to as genes
Genes are involved in controlling the activities of the cell, and also in
passing information on during cell division
37
Genetics
y
y
Genetics is the study of the way that characteristics are passed from
one generation to the next Æ in other words, genetics is the study of
heredity
All of us possess two different types of characteristics namely:
1.
2.
Inheritable characteristics
Non-inheritable characteristics
38
Genetics
y
Inheritable characteristics are determined by our genes, i.e. they
are passed on to us from our parent’s gametes
Inheritable characteristics include:
y
y
y
y
y
y
y
Hair colour
Eye colour
Shape of nose
Height
Gender (male or female)
Etc.
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Genetics
y
Non-inheritable characteristics are not determined by your genes,
instead, these characteristics are learned throughout the course of
your life (aka acquired characteristics)
Non-inheritable characteristics include:
y
y
y
y
y
Ability to play a game or musical instrument
Ability to drive a car or ride a bike
Accent you speak with
Etc.
40
Chromosomes and genes
y
The nucleus of a cell contains thread-like structures referred to as
chromosomes
A chromosome consists of a molecule of DNA, which is wrapped
around a protein
Genes are found along the length of the chromosome molecule Æ in
reality, a gene is just a small section of the DNA
y
y
y
One chromosome may contain hundreds of genes
41
Chromosomes and genes
y
Human cells usually contain 23 pairs of chromosomes (i.e. a total
of 46 altogether)
The only cells that do not contain 46 chromosomes are the gametes
(sperm and egg cells) which only contain a total of 23 chromosomes
each
At fertilisation, the male and female gametes fuse to produce a new
cell with a total of 46 chromosomes Æ the new cell will therefore
have all the genes needed to grow into a new individual
y
y
½
+ ½
= 1
42
Basic lifecycle of sexually
reproducing organisms
43
Chromosomes and genes
y Nine months later, you come out kicking and screaming (and
dancing)
y To which parent do you look exactly alike?
y How about your siblings?
y Do you look exactly alike them?
44