Asexual Reproduction

Asexual reproduction is the process resulting in the production of genetically identical offspring

Examples include:

Binary Fission (amoeba/bacteria)
Budding (sponges/anemones)
Spore Formation (ferns/mosses/fungi)

	Advantages	Disadvantages
to a population of species in the wild	Rapid increase in population under correct conditions Time/Energy efficient Can exploit suitable environments Faster than sexual as only parent is required Isolated organisms can reproduce	Limited genetic variation Population is vulnerable to changes in environment – may be suited to one habitat only Disease can affect the entire population
to crop plants	All offspring show same characteristics are parents, which can be good (high yield, disease- resistant)	If the parent plant has weak characteristics (low yield, not disease-resistant), the offspring would have the same traits

Sexual Reproduction

Sexual reproduction is a process involving the fusion of the nuclei of two gametes (haploid) to form a zygote (diploid) and the production of offspring that are genetically different from each other
Fertilisation is the fusion of gamete nuclei

	Advantages	Disadvantages
to a population of species in the wild	Genetic variation Can adapt to environmental change, giving survival advantage Disease won’t usually affect the whole population (due to variation)	Takes time and energy to find mates Difficult for isolated members of a species to reproduce
to crop plants	Higher yield Increase in variation allows the crops to cope with weather changes	Variation may lead to offspring being less successful than parents at growing well or good harvest

Reproduction in Flowering Plants

Parts of a Flower

Sepal: protects flower in bud form
Petal: attracts insects
Stigma: collects pollen grain
Ovary: produces female gamete
Ovule: inside the ovary; has female gamete
Anther: produces and releases pollen which has male gamete

Insect and Wind Pollinated Flowers

Insect Pollinated Flower	Wind Pollinated Flower
Large and bright petals to attract insects	Dull and drab petals, often green/brown
Nectar guides draw insect to nectar	No nectar or scent
Lower number of pollen grain produced as there is a high rate of successful pollination	High number of pollen grain produced as there is a low rate of successful pollination
Large, sticky and thorny pollen grains to attach to insects to be carried away	Smooth, small and light pollen grains so they are easily blown away with wind
Anthers are inside flower, stiff and firmly attached so that insects brush against them	Anthers are outside flower, swinging lose on long filaments for easy pollen release
Stigma is inside flower, sticky so pollen grain sticks to it when insects brush past	Stigma is outside flower, feathery to catch drifting pollen grain

Pollination

Pollination is the transfer of pollen grains from the anther to the stigma
Self-pollination as the transfer of pollen grains from the anther of a flower to the stigma of the same flower or different flower on the same plant
Cross-pollination as transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species
Cross-pollination improves genetic variation as there are 2 parent plants
Lack of variation is bad as the offspring may not survive in different conditions
Insect pollination relies of a vector, whereas wind pollination relies on the wind only.

Fertilisation

Fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule
The male gamete in the pollen germinates and forms a pollen tube from the stigma through the style. It then makes its way through the pollen tube and enters through a gap in the ovule called the micropyle
Once the male gamete reaches the end of the pollen tube the end disintegrates and then the male gamete enters inside. Then the 2 gametes will fuse together and end up forming a zygote
The zygote divides via mitosis and forms the embryo. The ovule swells up to form the seed seed. The integument of the ovule becomes hard and dry to form the testa. Water ends up being withdrawn from the seed making it dormant. The ovule became the seed and the ovary becomes 2 parts – radicle and tubule. The radicle ends up becoming the root and the tubule becomes the chute. The cotyledon is formed out of starch and amino acids to act as a food source. The micropyle becomes the hilum.

Factors Affecting Germination of the Seed

Germination is the start of growth in the seed
The factors that affect this are:
- Water – allows seed to swell up and the enzymes in the embryo to start working so that growth can occur. The starch and protein cotyledon are digested by enzymes to form glucose and amino acids suitable for the seeds nutrient need. Vacuoles expand allowing the root and chute to grow. Turgor pressure is maintained in the cells.
- Oxygen – Early stages of germination is anaerobic. When the testa splits open, oxygen is allowed to permeate through and aerobic respiration occurs.
- Warmth – germination improves as temperature rises (till the optimum point) as the reactions which take place are controlled by enzymes. Ideal temperature varies depending on the seed itself.

Sexual Reproduction in Humans

Sex Cells and Fertilisation

Fertilisation is the fusion of the nuclei from a male gamete (sperm cell) and a female gamete (egg cell).

Sperm	Egg
Very small	Large
Flagellum	No flagellum
Can move	Can’t move
Produced daily in large numbers after puberty	Present from birth, one matures and is released each cycle after puberty

Gamete	Feature	Reason
Sperm	Flagellum (tail)	Enables it to swim to the egg
	Enzymes in head (acrosome)	To digest jelly coat and cell membrane of egg
	Many mitochondria	Provides energy for locomotion
Egg	Cytoplasm with energy store	Provides energy for dividing zygote after fertilisation
Egg	Jelly coat that changes after fertilisation	Forms an impenetrable barrier after fertilisation to prevent other sperm nuclei entering the cell

Male Reproductive System

Testis: produces sperm and testosterone
Scrotum: sac supporting testes, to ensure sperm is kept at a tempereature slightly lower than the body’s
Epididymis: stores sperm
Sperm Duct: pathway of the sperm in which it mixes with seminal fluid
Seminal Vesicle: produces seminal fluid to help sperm swim (fluid + sperm = semen)
Prostate Gland: secretes an alkaline fluid to help sperm swim and to neutralise acid in vagina

Urethra: carries semen and has a muscle that prevents semen mixing with urine
Penis: allows semen to pass into the vagina of a woman during intercourse

Female Reproductive System

Ovary: contains egg which will mature and develop when hormones are released; produces oestrogen and progesterone.
Oviduct: egg moves through this by cilia (present on the lining) movement and peristalsis; fertilisation occurs here
Uterus: muscular bag with soft lining where the zygote will be implanted into the endometrial lining to develop into a foetus
Cervix: ring of muscle below uterus to keep the baby in place during pregnancy
Vagina: sperm deposited here; muscular tube that leads to the inside of the woman’s body. Passageway for exit of menstrual blood. Passage for exit of foetus during labour.

Sex Hormones in Humans

Puberty

Hormonal changes in humans:

Testosterone in males
Oestrogen in females

Gonads are the reproductive structures (testes and ovaries) in which hormones are produced and are the hormone’s target organs.

Males	Females
Sperm produced (main characteristic)	Maturation of egg (main characteristic)
Growth of hair	Maturation of egg (main characteristic)
Development of muscles	Hips become broader as pelvis widens
Voice cracks as larynx changes shape	Hips become broader as pelvis widens
Broadening of shoulders	Vagina becomes larger
Penis becomes larger	Breasts develop and nipples become larger
Scrotum expands to contain larger testes	Breasts develop and nipples become larger
Formation of acne as skin becomes oily	Menstrual cycle begins

The Menstrual Cycle

28 days long on average
Controlled by hormones
Ovulation (release of an egg) occurs about halfway through the cycle
Menstruation (breaking of the uterus lining) lasts around 5-7 days and signals the start of the next cycle

Hormones Involved in the Menstrual Cycle

Follicle Stimulating Hormone (FSH)
- produced in the pituitary gland
- stimulates 1 follicle to mature
- follicle becomes a Graafian follicle
- stimulates ovary to produce oestrogen
Oestrogen
- stops FSH secretion (so only 1 egg matures)
- stimulates pituitary gland to produce LH
- stimulates repair in lining of uterus
Luteinising Hormone (LH)
- stimulates ovulation
- stimulates formation of the corpus luteum
Progesterone
- released by corpus luteum
- prepares uterus for pregnancy and implantation
- prevents FSH and LH secretion so another egg doesn’t mature

Ovulation occurs once the follicle matures and oestrogen level is at its peak
If the egg isn’t fertilised the corpus luteum breaks down and progesterone level falls
If pregnancy occurs progesterone production continues until the placenta is developed, preventing the uterus lining from breaking down and aborting the pregnancy

Growth and Development of the Foetus

Growth and Development

In early development, the zygote divides by mitosis to form the embryo, which will implant into the wall of the uterus. The gestation period is 9 months. In the first 12 weeks, development of the organs occur and after that, the foetus grows in size.

The Foetus in the Uterus

Amniotic Sac: membrane made out of mother’s blood plasma, that encloses the amniotic fluid
Amniotic Fluid: protects the foetus against mechanical shocks and prevents it from drying out and prevents temperature fluctuations
Umbilical Cord: connects mother to the foetus and contains blood vessels for transfer of materials

The Placenta

The placenta has several important functions in during the gestation period:

Involved in the exchange of nutrients (like glucose) from the mother to the baby
Involved in the exchange of wastes (like CO₂ and urea) from the baby to the mother
Protection to the foetus is provided by the mother’s immune systems
Protects against dangerous fluctuations in the mother’s blood pressure
Secretes progesterone to maintain uterus lining (corpus luteum breaks down by 3^rd month)

The placenta also develops finger-like projections called villi, which extend into the wall of the uterus. This increases the surface area for diffusion of wastes and nutrients.

There is no direct contact between maternal and foetal blood as their blood groups may be different. This also makes sure that pathogens do not reach the baby.

Some toxins (nicotine) and pathogens (HIV and Rubella virus) are small enough to pass across the placenta and reach the foetus.

There are 2 blood vessels in the umbilical cord:

Umbilical artery: carries deoxygenated blood and wastes away from the foetus to the placenta
Umbilical vein: carries oxygenated blood and nutrients to the foetus from the placenta

Towards the end of pregnancy, even antibodies cross the placenta so that the baby has immunity to certain diseases. This is an example of passive immunity.

Antenatal Care and Labour

Antenatal Care

Antenatal care is the care provided during the pregnancy period.

Dietary needs include:

Sufficient proteins
Calcium and Iron
Folic acid (prevents birth defects of the brain and spine)

The mother should avoid smoking as it has severe effects:

Low birth weight
Birth defects related to the brain, heart and lungs

The mother should avoid alcohol consumption as it has severe effects:

Increased risk of miscarriage
Increased risk of premature birth
Affects brain development – leads to learning disability and behavioural problems later

Labour

The process of labour is:

Breaking of the amniotic sac
Contraction of the muscles in the uterus wall (stimulated by oxytocin)
Cervix dilates (stimulated by oxytocin)
Baby passes out through the vagina
Umbilical cord is cut and tied (so that there is no blood loss)
Delivery of the afterbirth (placenta)

Breast Milk vs Formula Milk

	Advantages	Disadvantages
Breast Milk	Free At correct temperature Has antibodies Has all nutrients in right proportions Baby develops bond with mother Less risk of contamination Easy to digest No additives	Can lead to postnatal depression if it doesn’t come out of the mother easily Only the mother is responsible for feeding the baby
Bottle Feeding using Formula Milk	Father can be involved Baby gets hungry less often Mother doesn’t need to be worried about their diet	Expensive Risk of infections if bottle isn’t sterilised properly

Methods of Birth Control

Artificial Insemination (AI)

Treats fertility by inserting semen directly into uterus close to ovulation. The sperm may be obtained by from the partner or a donor. This is done if:

Sperms aren’t motile enough
Male has erectile dysfunction

In Vitro Fertilisation (IVF)

Treats infertility by containing eggs and sperms outside the body within a petri dish.

Woman is given fertility drugs
Eggs are obtained
Kept in a petri dish and fertilised with sperms
Grown in an incubator
Healthy embryos are transferred into the uterus

Methods of Birth Control

Natural:

Abstinence: refrain from having intercourse
Monitoring Body Temperature: body temperature rises near ovulation (not effective)
Rhythm Method: woman keeps track of her ovulation (not effective)
Monitoring Cervical Mucus: woman knows when mucus is thick enough to block sperm (not effective)

Barriers:

Condom: placed on penis and prevents sperm from reaching egg (and HIV)
Femidom: placed in vagina and prevents sperm from reaching egg (and HIV)
Diaphragm: cervical cap that prevents sperm from reaching egg, but is usually effective when used with a spermicidal

Chemical:

Spermicidal: kills sperm (applied on the vagina)
Intra Uterine Device: placed in uterus, acts as a barrier and breaks down endometrium, so the embryo doesn’t get implanted and is removed from the body
Intra Uterine System
Contraceptive Pill: contains high levels of oestrogen and progesterone so that uterus lining is maintained and so that new egg doesn’t develop and get released
Implant: releases progesterone which will restrict ovulation
Injection: injects progesterone which will restrict ovulation

Surgical:

Vasectomy: sperm duct is cut and tied so it doesn’t mix with seminal fluid
Tubectomy: oviduct is cut and tied so the egg doesn’t reach the site of fertilisation

Social Implications of Contraception and Fertility

Fertility treatments are very expensive
Can lead to overpopulation
IVF can lead to multiple pregnancies, risking life of foetus and mother
Can cause emotional and financial loss as these can cause miscarriages
Children born through this are prone to mental retardation, lung problems and learning disabilities
Women are obtaining professional degrees so they can focus on their work

Sexually Transmitted Infections (STI)

STIs

STIs are infections that are transmitted via body fluid through sexual contact
Human Immunodeficiency Virus (HIV) is an STI

Methods of Transmission

Transmitted through body fluids, especially semen:

Unprotected sex
Sharing needles
Unsterilised surgical instruments
Blood transfusion
From infected mother to foetus via blood or milk

HIV

Viruses attack some types of lymphocytes; hence the number of lymphocytes are reduced and therefore there is a reduced ability to produce antibodies. HIV can cause AIDS.