Reproduction (DP IB Biology)

Male gametes are sperm cells, and female gametes are ova (eggs).

Male plant gametes are carried in pollen grains, and female plant gametes are held in the ovules within the ovary.

Fertilisation is the fusion of a male and female gamete, producing a zygote with new combinations of alleles, leading to genetic variation.

Males produce many thousands of sperm per ejaculation to increase chances of fertilisation, while females typically release only one egg per menstrual cycle.

The male gamete is smaller than the female gamete because the male gamete travels to the female gamete, with less food reserves than the egg.

The ovaries produce ova (eggs) and female sex hormones like estrogen and progesterone.

The fallopian tubes transport the egg from the ovary to the uterus and are the site where fertilisation typically occurs.

The uterus is where a fertilised egg implants and develops into a fetus.

The cervix is the lower part of the uterus that opens into the vagina; it allows the passage of sperm into the uterus and, during childbirth, dilates to allow the baby to pass through.

The testes produce sperm cells and male sex hormones like testosterone.

The sperm duct transports sperm from the testes to the urethra during ejaculation.

The prostate gland produces a fluid called semen, which contains nutrients required for the sperm cells to swim.

The urethra is a tube that transports urine from the bladder out of the body. Both males and females have a urethra.

The menstrual cycle consists of the ovarian and uterine cycles. It is the sequence of events that includes the thickening of the uterus lining, ovulation and menstruation; it is controlled by a series of hormones.

Oestradiol causes the uterus lining to thicken during the first part of the menstrual cycle. It also interacts with other hormones to bring about the maturation of an egg cell.

Oestradiol levels rise from day 1 and peak just before day 14. The peak in oestradiol occurs just before the egg cell is released.

False.

A decrease in progesterone levels at the end of the cycle results in the loss of the lining during menstruation.

Progesterone levels are low from day 1 – 14 and starts to rise once ovulation has occurred. Levels then decrease towards the end of the cycle.

FSH is released by the pituitary gland and causes an egg to start maturing in the ovary. It also stimulates the ovaries to start releasing oestrogen.

When oestrogen levels reach their peak the pituitary gland is stimulated to release LH (luteinising hormone).

Oestrogen and FSH interact in a negative feedback loop. When oestrogen levels are high enough, it inhibits the secretion of FSH.

OR

Progesterone, FHS and LH interact in a negative feedback loop. Progesterone thickens and maintains the endometrium but also inhibits the secretion of FSH and LH from the pituitary gland.

Oestrogen and LH interact in a positive feedback loop. After ovulation, LH causes the wall of the follicle to develop into the corpus luteum, which secretes more oestrogen.

The hormones FSH, LH and progesterone are given during IVF.

• FSH and LH stimulate the development of follicles

• Progesterone is given to ensure the endometrium is maintained

Superovulation is when many more follicles than normal begin to mature due to artificial doses of FSH given at a much higher concentration than is present during a normal menstrual cycle.

Fertilisation is the fusion of gamete (haploid) nuclei, resulting in the formation of a zygote (diploid nucleus).

Fertilisation in humans involves the fusion of a sperm cell with an egg cell, and entry to the egg by the sperm nucleus which has its tail and mitochondria destroyed in the process.

The result of fertilisation is the formation of a zygote/fertilised egg cell.

A zygote is a diploid cell formed by the fusion of a sperm and an egg cell during fertilisation.

The sperm's enzymes digest the egg cell's glycoprotein layer to allow the sperm to reach the egg's membrane.

False.

Vesicles released from the egg destroy the sperm's flagellum (tail) and mitochondria upon entry.

False.

The sperm's mitochondrial DNA is destroyed, so it is not inherited by the zygote.

True.

During fertilisation dissolution of nuclear membranes of both sperm and egg nuclei occurs.

After the nuclear membranes dissolve, all condensed chromosomes participate in joint mitosis to produce two diploid nuclei.

The purpose of joint mitosis is to produce two diploid nuclei which become the zygote.

The main stages of sexual reproduction are the production of gametes inside ovules and pollen grains, pollination, pollen development and fertilisation to produce an embryo.

True.

Pollen grains contain male gametes.

The anther is the part of the stamen that produces the male gametes.

After fertilisation, the ovule becomes a seed (an embryo) and the ovary develops into the fruit.

The stigma is the part of the female reproductive organ that receives the pollen.

The ovary contains the ovules where female gametes develop.

The pollen tube grows from the pollen grain down the style to the ovary, allowing male nuclei to travel to the ovule.

True.

Some flowering plants are hermaphroditic which means they contain both male and female parts. However, reproduction in flowering plants is sexual, even if a plant species is hermaphroditic.

Cross-pollination occurs when pollen from one plant is transferred to the stigma of another plant of the same species.

True.

Cross-pollination increases genetic variation.

Self-pollination occurs when pollen from a flower lands on its own stigma or on the stigma of another flower on the same plant.

Nectar attracts insects to the flower, aiding in the transfer of pollen.

True.

Pollen from insect-pollinated flowers is sticky to adhere to insects.

Wind-pollinated plants produce large amounts of light, non-sticky pollen that can be carried by the wind.

A self-incompatibility mechanism is a genetic process that prevents self-pollination by inhibiting pollen tube growth or fertilisation from the same plant.

Adaptations to prevent self-pollination, and promote cross-pollination include different maturation times for pollen and stigma, separate male and female flowers or male and female plants.

True.

Wind-pollinated plants are less likely to self-pollinate due to the random dispersal of pollen by the wind.

A disadvantage of self-pollination is that it reduces genetic variety in the offspring, leading to inbreeding and less adaptability to environmental changes.

Seed dispersal is the process of distributing seeds away from the parent plant to reduce competition.

False.

Pollination is the transfer of pollen from anther to stigma, while seed dispersal is the distribution of mature seeds.

Methods of seed dispersal include wind, water, animals, and explosions.

Animals help in seed dispersal by eating fleshy fruits and dispersing seeds through egestion or by carrying sticky seeds on their fur.

Germination is the start of growth in a seed after dormancy when conditions become favourable.

True.

Water is required for seed germination to allow the seed to swell, burst the seed coat, and activate enzymes.

The radicle is the first structure to emerge from the seed and forms the initial root that grows downward into the soil.

The three factors required for germination are water, oxygen, and warmth.

The hypocotyl is the curved portion of the plant shoot that appears above ground and grows upwards, helping the seedling to emerge.

Food reserves provide energy and nutrients for the growth and development of the embryo during germination.

Cotyledons are early leaf structures in a seed that help transfer food reserves to the embryo during germination.

During germination, food reserves in the seed, mainly endosperm, are mobilised and transferred to the growing embryo to support its development.

Secondary sexual characteristics are physical features that develop during puberty under the control of reproductive hormones, but are not directly involved in reproduction.

The two main types of sex hormones involved in puberty are gonadotropin-releasing hormone (GnRH) and steroid sex hormones like oestrogen and testosterone.

True.

The onset of puberty is triggered by the release of GnRH from the hypothalamus, which is detected by the pituitary gland.

The release of GnRH triggers the onset of increased luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release.

The increase in sex hormone production during puberty leads to the development of secondary sexual characteristics.

LH and FSH are hormones produced by the pituitary gland that enhance the effects of the sex hormones oestrogen and testosterone during puberty.

Gametogenesis is the process of gamete (sperm or egg) formation, involving both mitosis and meiosis.

Sperm cells are produced in the testes in males.

Spermatogonia are the diploid cells in the germinal epithelium of the seminiferous tubules that divide by mitosis to produce new germ cells.

Sertoli cells form the inner lining of the seminiferous tubules and provide support and nourishment to the developing sperm cells.

False.

Spermatogenesis involves both mitosis and meiosis.

Ova (eggs) are produced in the ovaries of females.

Oogonia are the diploid cells in the germinal epithelium of the ovaries that divide by mitosis to produce new germ cells.

During the first 7 months of fetal development, the oogonia in the ovaries divide by mitosis to form several million primary follicles.

Follicle cells develop around the oogonia as they enter meiosis I, forming primary follicles.

The secondary oocyte formed after meiosis I does not complete meiosis II until after a sperm cell enters it, at which point the oocyte becomes an ovum.

Polyspermy is the entry of more than one sperm cell into a single oocyte during fertilisation.

The zona pellucida is the layer of glycoproteins surrounding the secondary oocyte that sperm cells must digest to reach the oocyte's cell surface membrane.

The acrosome reaction is the process where sperm cells release digestive enzymes from the acrosome structure to digest through the zona pellucida.

The fusion of the sperm and oocyte cell membranes triggers the movement of cortical granules to the cell surface, releasing enzymes that harden the zona pellucida and prevent polyspermy.

True.

Fertilization is completed when the male and female nuclei fuse inside the ovum.

A blastocyst is the hollow ball-shaped structure that forms after the fertilized ovum undergoes several mitotic divisions.

The blastocyst is located in the oviduct before it reaches the uterus and implants in the endometrium around 7 days after fertilisation.

The zona pellucida that surrounded the fertilized ovum breaks down and is lost by the time the blastocyst reaches the uterus.

The finger-like projections allow the blastocyst to penetrate and implant into the endometrium of the uterus.

After implantation, there is an exchange of nutrients and oxygen between the blastocyst and the mother's blood.

hCG stimulates the corpus luteum to maintain production of oestrogen and progesterone, and it also stimulates growth of the placenta and uterus during early pregnancy.

True.

hCG levels decline after 12 weeks as the placenta takes over production of oestrogen and progesterone.

Pregnancy tests detect the presence of hCG in the mother's urine or blood to confirm a positive pregnancy. Monoclonal antibodies with attached dyes will react with hCG hormone (from the mothers urine) causing a colour change in the results window.

Pregnancy tests use monoclonal antibodies that bind to the hCG antigen.

In addition to preparing and maintaining the lining of the uterus, progesterone inhibits uterine contractions and the production of oxytocin, preventing premature labour.

At the end of pregnancy, fetal oestrogen levels increase, signalling for the placenta to stop producing progesterone. At this point, the pituitary gland increases production of oxytocin beginning the onset of labour.

Oxytocin stimulates contractions of the uterine muscles, which strengthen and increase in a positive feedback loop.

Uterine contractions cause the cervix to dilate and the amniotic sac to rupture, allowing the baby to be pushed out through the vagina.

The positive feedback loop refers to how uterine contractions trigger the release of more oxytocin, which in turn causes stronger contractions.

In placental mammals, the placenta is responsible for the exchange of substances between the mother and fetus, as well as the production of pregnancy hormones.

False.

The mother's and fetus's blood never mix directly, but are separated by the placental barrier.

The placental barrier is a selectively permeable membrane that allows the exchange of certain substances between the mother's and fetus's blood while restricting the passage of others.

From mother to fetus: oxygen, antibodies, water, glucose.

From fetus to mother: carbon dioxide, water, urea.

The large surface area of the placental villi increases are area and therefore the efficiency of the exchange of substances.

The placenta has a large surface area (of the placental villi) to maximise the exchange of substances between the mother and fetus.

It also has a good blood supply to maintain concentration gradients for exchange.

Menopause is when a female stops having periods for longer than 12 months, typically occurring between 45 and 55 years old as a natural part of ageing.

HRT is a treatment that replaces the hormones oestrogen and progesterone to relieve the symptoms of the menopause.

False.

Early epidemiological studies showed that HRT decreased the risk of coronary heart disease. However, later randomised controlled trials showed an increased risk.

A cause-and-effect relationship refers to a connection between two events where one event (the cause) directly influences or produces a change in the other event (the effect).

This suggests that HRT would be directly responsible for reducing the risk of heart disease, rather than merely being associated with it by chance or due to other factors.

The timing hypothesis is the concept that HRT started in the early years of menopause provides benefit to the heart with reduced risk of CHD, whereas starting HRT several years post-menopause may increase risk.