REPRODUCTION (D3.1)

What is reproduction?

Production of offspring by parents which can be sexual or asexual

What is asexual reproduction? What are the aspects of it? What is an advantage of it?

• One parent

• No meiosis- only mitosis

• Offspring are genetically identical to each other

• No genetic variation is generated as existing gene combinations pass unchanged from generation to generation

• Advantage: In an unchanging environment, well-adapted parents produced offspring that are also well adapted

What is sexual reproduction? What are the aspects of it? What is an advantage of it?

• Two parents

• Meiosis is part of every sexual life cycle

• Offspring are gentically different from each th

What are the causes of genetic variation in sexual reproduction?

• Crossing over in meiosis 1

• Separation of homologous pairs during meiosis 1

• The fusion of the male gamete with the female gamete results in a new combination of chromosomes in the resulting zygote.

What is fertilization?

The fusion of gametes

What are the differences between male and female sexes in sexual reproduction?

• The smaller of the two gametes which fuse together is the male gamete or the sperm, while the larger is the female gamete or the egg

• The male gametes is smaller, allowing faster movement

• The male gametes are produced in large numbers

• The female gametes are non-motile

• The female gametes are larger due to stores of food reserves

• The female gametes are produced few-sometimes only one

What are the parts of the male reproductive system and what do they do?

• Erectile tissue: fills with blood to enlarge and harden the penis

• Penis: penetrates the vagina so semen can be ejaculated near the cervix

• Urethra: transfers semen during ejaculation and urine during urination

• Testis: produces sperm and testosterone

• Sperm duct: transfers sperm during ejaculation

• Seminal vesicle and prostate gland: secrete fluid containing alkali, proteins and fructose that is added to sperm to make semen

• Epididymis: stores sperm until ejaculation

• Scrotum: holds testes at a lower than core body temperature to promote sperm development

What are the parts of the female reproductive system and what do they do?

• Ovary: produces eggs, estradiol and progesterone

• Uterus: provides for the needs of the embryo and then the foetus during pregnancy (protection, supply of food and oxygen, and removal of waste products)

• Vulva: protects internal parts of the female reproductive system

• Oviduct: collects eggs during ovulation, provides a site for fertilization and then moves the embryo to the uterus

• Cervix: protects the foetus during pregnancy and then dilates to provide a birth canal

• Vagina: stimulates the penis to cause ejaculation and forms the birth canal

• Bladder and urethra

What is the ovarian cycle?

The cyclic changes seen in the ovaries

What are the 3 phases of the ovarian cycle?

• The follicular phase

• The ovulation phase

• The luteal phase

What happens in the follicular phase of the ovarian cycle?

• The follicular phase lasts for approximately 14 days (in a 28-day cycle) and begins with the first day of the menstrual flow (bleeding).

• At this point, the levels of both ovarian and pituitary hormones are low.

• The anterior pituitary secretes follicle-stimulating hormone (FSH) and luteinising hormone (LH).

• FSH stimulates the growth of ovarian follicles, each containing one immature egg; these follicles are small sac-like fluid-filled structures inside each ovary.

• The growing follicle secretes oestradiol (the primary form of oestrogen in a human female), but usually only one follicle matures while the others regress.

What happens in the ovulation phase of the ovarian cycle?

• Around the middle of the cycle (around Day 12), a sharp rise in the level of oestradiol stimulates the anterior pituitary to secrete LH (to a greater extent) and FSH (to a lesser extent).

• The spurt of LH causes the follicle to rupture, releasing the mature egg.

• This is known as ovulation and occurs in the middle of the menstrual cycle (around Day 14 of a 28-day cycle).

• The egg begins its passage to the uterus.

• Ovulation marks the transition from the follicular phase to the luteal phase of the cycle.

What happens in the luteal phase of the ovarian cycle?

• Following ovulation, LH and FSH levels drop.

• Under the influence of LH, the ruptured follicle is converted into the corpus luteum (yellow body), which is filled with cells.

• This period is known as the luteal phase.

• The corpus luteum secretes progesterone and oestradiol.

• As the levels of oestradiol and progesterone rise, the secretion of FSH and LH is inhibited by a negative feedback mechanism.

• This stage lasts for about 14 days.

What is the uterine cycle?

Refers to the changes that occur in the uterus

What are the 3 stages of the uterine cycle?

• Proliferative phase

• Secretory phase

• Menstruation

What is the proliferative phase of the uterine cycle?

• The proliferative phase coincides with the follicular phase and continues till ovulation.

• Oestradiol secreted by the growing follicle causes a thickening of the endometrial lining of the uterus preparing it for a possible pregnancy.

What is the secretory phase of the uterine cycle?

• The secretory phase roughly corresponds to the luteal phase of the ovarian cycle.

• Under the influence of progesterone, the uterine lining thickens further and changes into a secretory layer, in preparation for a potential implantation.

What is menstruation in the uterine cycle?

• Towards the end of the luteal phase, the decrease in levels of FSH and LH causes the corpus luteum to break down.

• The subsequent decrease in the levels of progesterone and oestradiol causes the thickened lining of the uterus to break down.

• The sloughed off layers, the unfertilised egg, and blood are shed from the body through the vagina, resulting in menstrual bleeding.

• In response to the low levels of ovarian hormones, the anterior pituitary secretes FSH and LH, a new follicle develops and the next cycle begins.

• A typical menstrual cycle lasts for 28 days and begins with the first day of the menstrual flow; it marks the onset of puberty and continues until menopause

What is the role of positive and negative feedback in regulating hormone levels during the menstrual cycle?

• The menstrual cycle is controlled by both positive and negative feedback mechanisms.

• Negative feedback occurs when an increase in the level of one hormone inhibits the secretion of other hormones; for example, rising oestradiol levels during the follicular phase inhibit FSH secretion, causing other follicles to regress.

• Eventually, a surge in oestradiol levels in the middle of the cycle causes a rise in LH and FSH levels — this is an example of positive feedback, where the rise in one hormone stimulates the increase of others.

• Soon after ovulation, the follicle becomes the corpus luteum, which secretes progesterone and oestradiol (to a lesser extent).

• As progesterone levels increase, the release of FSH and LH is inhibited — this is negative feedback again.

Where does fertilisation occur in the human female reproductive system?

Fertilisation typically occurs in the oviduct (also called the fallopian tube).

What is the state of the egg at the time of fertilisation?

The egg is a secondary oocyte that has not yet completed meiosis II. It is surrounded by two layers: the zona pellucida (a jelly-like glycoprotein layer) and the corona radiata (a layer of nourishing follicular cells)

What is the structure of a sperm cell involved in fertilisation?

A sperm consists of:

• A head with a haploid nucleus and an acrosome containing hydrolytic enzymes

• A midpiece packed with mitochondria for energy

• A tail (flagellum) for movement

What changes must sperm undergo to be capable of fertilising the egg?

Sperm must undergo capacitation, a physiological process in the female reproductive tract that activates them for fertilisation.

What happens when the first sperm reaches the egg?

• The sperm binds to complementary receptors on the egg's plasma membrane.

• The membranes of the sperm and egg fuse, allowing the sperm nucleus to enter the egg.

• The sperm tail and mitochondria are destroyed and do not enter the egg.

What is "egg activation" and what changes occur during it?

Egg activation is a process triggered by sperm entry that includes:

• A rise in intracellular calcium

• Completion of meiosis II by the egg

• A cortical reaction, which hardens the zona pellucida to prevent polyspermy (entry of more sperm)

What happens to the nuclei of the sperm and egg after fusion?

• The sperm nucleus becomes the male pronucleus, and the egg nucleus becomes the female pronucleus, both with haploid genomes.

• The nuclear membranes dissolve, and the chromosomes from both pronuclei condense.

How is the diploid zygote formed and what happens next?

• The chromosomes from both pronuclei come together and participate in a joint mitosis, forming two diploid nuclei.

• This marks the first cell division of the diploid zygote.

What are the parts of a flower?

• Pistil ( which comprises of the stigma, style and ovary)

• Ovary

• Stigma

• Style

• Petal

• Receptacle

• Stamen

• Anther

• Filament

• Ovule

• Sepal

What are the parts of a stamen?

Each stamen includes a filament (stalk) and an anther (pollen sac).

What is inside the anther?

The anther contains pollen grains, each with a generative cell and a tube cell, surrounded by exine (outer layer) and intine (inner layer).

What are the parts of a pistil (carpel)?

• Stigma – sticky surface that receives pollen.

• Style – connects the stigma to the ovary.

• Ovary – contains ovules, each with an embryo sac made up of seven cells and eight haploid nuclei.

What is pollination?

Pollination is the transfer of pollen from the stamen to the pistil. It can occur via insects, animals, wind, or water.

What happens after a pollen grain lands on the stigma?

It germinates, forming a pollen tube that grows down the style into the ovary.

What happens inside the pollen tube?

The generative cell divides to form two sperm cells, which travel to the ovule through the micropyle.

What is double fertilisation?

• One sperm fuses with the egg to form a diploid zygote (embryo).

• The second sperm fuses with the central cell (which has two polar nuclei) to form a triploid endosperm.

• This process is unique to flowering plants.

How is pollination carried out by insects

Insects transfer pollen while feeding on nectar or visiting flowers, leading to pollination.

What are some adaptations of insect-pollinated flowers?

• Production of nectar to attract insects.

• Bright colours or white petals.

• Strong scents.

• Sticky, heavy pollen that adheres to insects

Why do some flowers attract specific insects?

To improve pollination efficiency and avoid wasting pollen on the wrong species, flowers evolve features that appeal to specific pollinators (e.g., scent and colour attract bees).

What type of flowers are found in plants like tomato, mango, and lily?

These plants have hermaphroditic flowers, which contain both male and female reproductive parts.

If these flowers can self-pollinate, why do they still rely on pollinators?

Although pollen can be transferred within the same flower (self-pollination), many plants depend on pollinators to transfer pollen to flowers on other plants. This promotes cross-pollination, which increases genetic diversity and enhances species survival.

What are the two main types of pollination?

• Cross-pollination – Pollen is transferred from a flower on one plant to a flower on a different plant.

• Self-pollination – Pollen is transferred to the same flower or another flower on the same plant.

What are the advantages of cross-pollination?

It increases genetic variation, which helps plants adapt to changing environments and ensures evolutionary success.

What agents help in the process of cross-pollination?

• Animals such as insects, birds, and bats (see Figure 1).

• Wind (especially for grasses and cereals).

• Water (in some aquatic plants).

What are the features of animal-pollinated flowers?

• Bright colours, scents, and nectar to attract animals.

• Sticky pollen that clings to animal bodies.

What are the features of wind-pollinated flowers?

• Small, unscented flowers.

• No nectar.

• Lightweight pollen.

• Feathery stigmas to catch airborne pollen

What are some plant adaptations that prevent self-pollination and encourage cross-pollination?

• Separate male and female plants (e.g., date palm, papaya) – ensures pollen must travel between plants.

• Different maturation times of male and female flowers on the same plant (e.g., avocado) – prevents simultaneous fertilization.

• Time differences in anther and pistil maturity in the same flower – seen in plants like arum lily, ivy, carrot, and salvia.

• Structural differences in hermaphroditic flowers – such as two forms of primrose flowers

What is self-incompatibility?

It is the inability of a plant to produce zygotes after self-pollination due to genetic or structural barriers.

Why is self-incompatibility important?

It prevents inbreeding, promotes genetic variation, and results in seeds of better quality and vigour.

How does self-incompatibility work?

• It may prevent pollen germination, pollen tube growth, fertilisation, or embryo development.

• In some plants, self-sterility genes prevent pollen with the same allele (e.g., 's1') from succeeding.

In which plants is self-incompatibility found?

It is observed in white clover (Trifolium repens) and cabbage (Brassica oleracea)

What happens after fertilisation in plants?

• The zygote forms the embryo.

• The triploid cell forms the endosperm.

• The ovule wall becomes the seed coat, and the ovary becomes the fruit

Why is seed dispersal necessary?

To avoid competition with the parent plant for resources like water, soil, and sunlight.

What are the main methods of seed dispersal?

• Wind – seeds are lightweight and may have wings/hairs (e.g., dandelion, maple, drumstick).

• Water – seeds are buoyant (e.g., coconut, water lily).

• Animals – seeds may be eaten and excreted, hoarded, or attached to fur (e.g., burdock)

What is germination?

Germination is the process by which a seed develops into a seedling, beginning with water uptake and ending when the radicle emerges.

What is seed dormancy?

A state of low metabolic activity where the seed waits for favourable conditions to germinate.

What are the three essential conditions for germination?

• Water – activates metabolism.

• Oxygen – required for respiration.

• Temperature – optimal range is 25–30°C.

What happens during seed germination?

• Imbibition – seed absorbs water and swells.

• Respiration resumes – metabolic activity increases.

• Mobilisation of food – enzymes break down food reserves into usable nutrients.

• Embryo development – radicle (root) emerges, followed by the plumule (shoot), forming a seedling.

• Light response – after emergence, light helps orient the seedling and straighten the plumule.

How are pollination and seed dispersal connected?

Both involve wind, water, or animals. However, pollination enables fertilisation, while seed dispersal spreads the offspring.

Where does fertilisation occur in the human body?

Fertilisation takes place in the oviduct.

What is the state of the egg at the time of fertilisation?

The egg released from the follicle has not yet completed meiosis II and is referred to as the secondary oocyte.

What is the structure that prevents entry of more than one sperm into the egg?

The zona pellucida is a jelly-like, non-cellular layer composed of glycoproteins that prevents the entry of sperm.

What happens to the sperm once it binds to the oocyte?

. The head of the sperm enters the cytoplasm of the egg, while the midpiece and tail are destroyed.

Describe what happens after the sperm nucleus enters the egg.

The sperm nucleus undergoes a series of changes to form the male pronucleus. The male pronucleus and the female pronucleus both have a haploid genome. The nuclear membranes of the male and female pronuclei dissolve, chromatin from both nuclei condense to form chromosomes resulting in a single-celled diploid organism. The diploid zygote now undergoes mitotic division.

What is the purpose of hormone treatment at the beginning of IVF?

The normal menstrual cycle is suppressed using medicines. This treatment takes about 2 weeks and helps the healthcare worker to control the timing of ovulation.

What hormone is used to stimulate multiple egg production during IVF?

The person undergoing treatment is given fertility drugs. These drugs contain FSH which stimulates follicles, resulting in superovulation or the production of multiple eggs.

What hormone causes the follicles to mature, and when is it administered?

The person undergoing treatment is injected with the hormone human chorionic gonadotropin (hCG), which causes the follicles to mature.

What is the procedure for collecting the eggs during IVF called?

Before the follicles rupture, the eggs are collected by a technique called follicular aspiration.

How is fertilisation achieved in IVF?

The eggs are put into a petri dish and the sperm from the donor is transferred to the dish.

How is successful fertilisation assessed in IVF?

After 16–18 hours, the sample is assessed to see whether fertilisation has occurred.

What happens after successful fertilisation in IVF?

If fertilisation has occurred, the fertilised eggs are allowed to grow in a specially formulated culture medium in the laboratory.

When are embryos implanted and what can be a result of this step?

Healthy embryos are selected and transferred to the uterus. This can happen on Day 3 or Day 5. This is known as implantation. Often, multiple embryos are transferred to improve chances of implantation and this may lead to multiple births.