Chapter 8: How do Organisms Reproduce Revision Notes

Reproduction is the process by which all creatures expand their population by multiplying in number.

ASEXUAL REPRODUCTION

• Asexual reproduction is a type of reproduction in which only one organism reproduces.
• On its own, a single creature may replicate two or more organisms.
• All unicellular species, several multicellular organisms, and a few plants have this trait.

Fission

• Fission is a type of asexual reproduction seen in most unicellular organisms.
• Binary fission occurs when the fission produces two daughter cells (e.g. paramecium).
• Multiple fission occurs when fission produces a large number of daughter cells (e.g. Plasmodium).
• Distinct organisms may have different fission planes.

Budding

• Budding is an asexual reproduction method in which a tiny cyst-like formation forms on the parent's body, resulting in the birth of a new person.
• Buds can stay tied to their parents (yeast) or they can detach and become their own person (hydra).

Fragmentation and regeneration

• Regeneration is the process through which the organism regrows a lost organ or bodily component (e.g. lizard).
• Fragmentation is the process of breaking down an organism into smaller parts, each of which develops into a new organism. Planaria, Hydra, etc.

Formation of spores

• Fungi, for example, produce spores that can be disseminated from their fruiting body and develop into new individuals.

Vegetative propagation

• In plants, this is a sort of asexual reproduction.
• The plant's vegetative parts, such as leaves, stems, and roots, produce new plants.
• Artificial or natural vegetative propagation is possible.
• Leaves (e.g. bryophyllum), stems (e.g. turmeric, ginger), runners/stolons (e.g. grass runners, strawberry), bulbs (e.g. onion, lily), and so on are all examples of natural vegetative propagation.
• Cutting, grafting, layering, and plant tissue culture are examples of artificial procedures.

SEXUAL REPRODUCTION

Cell Division Types

In eukaryotic organisms, there are two forms of cell division:

1) Mitosis

• It is a kind of cell division.
• It occurs in somatic cells.
• Maintains the number of chromosomes.
• Two diploid daughter cells are produced.
• Asexual reproduction, development, and growth, as well as cell replacement and regeneration, are all dependent on it.

**2) Meiosis **

• It occurs in sex cells.
• The number of chromosomes is cut in half.
• Four haploid daughter cells are produced.
• Gamete creation is required for sexual reproduction.

Male reproductive system

• A pair of testes is a male's primary reproductive organ.
• They generate sperm, which are male sex cells, as well as testosterone, a male sex hormone.
• Organs of male reproduction
• A pair of testes is a male's primary reproductive organ.
• Outside the body, they are found in scrotal sacs and include seminiferous tubules as the structural and functional unit.
• Seminiferous tubules create male sex cells, sperms, which develop in the epididymis.
• The hormone testosterone is secreted by Leydig cells, which are found between the seminiferous tubules.
• Male reproductive organs (accessory reproductive organs)
• Several reproductive organs that help in the process of reproduction.
• The seminal vesicles and the prostate gland are reproductive glands that produce semen and nurture sperm.
• The copulatory organ is the penis with the urethra going through it.

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Male Ducts

• The vas deferens and the urethra are the major ducts in men.
• The vas deferens transports sperm from each testis to the urethra in a single tube.
• The urethra serves as a conduit for both sperm and urine.

Female reproductive system

• A pair of ovaries, a pair of fallopian tubes/oviducts, and accessory organs like the uterus and vagina make up the female reproductive system.
• The female reproductive organ is the most important organ.
• A female's major reproductive organ is a pair of ovaries.
• They make female sex cells known as eggs or ova, as well as female sex hormones known as oestrogen and progesterone.

Female accessory reproductive organ

• In females, the uterus and vagina are accessory reproductive organs.
• The uterus is where the foetus develops, whereas the vaginal canal gets sperm from the male.

MENSTRUAL CYCLE

Menstruation

• When fertilisation does not occur, menstruation is the cyclic process of the ovum being released from the ovary and being removed from the body.
• The blood-rich endometrium of the uterus also breaks down during menstruation when the ovum is expelled from the body.
• LH and FSH, two pituitary hormones, and oestrogen and progesterone, two ovarian hormones, all have a role in menstruation.
• The cycle in humans repeats every 28 days.

REPRODUCTION IN PLANTS

Sexual reproduction in flowering plants

• Flowers are used by plants to reproduce sexually.
• Flowers with essential whorls, such as androecium and gynoecium, aid in plant sexual reproduction.

Flowers' non-essential components

• There are necessary whorls and non-essential whorls in the typical floral structure.
• Because they do not actively participate in reproduction, Sepals and Petals are referred to as non-essential whorls.
• When in bud condition, sepals shield the inner fragile whorl and, if green in colour, also perform photosynthesis.
• When petals are coloured, they attract pollinating insects.

Flowers' essential whorls

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• The essential/reproductive whorls of a flower are referred to as androecium and gynoecium.
• Androecium generates male gametes in pollen grains, whereas gynoecium produces female gametes in ovules.
• Bisexual flowers have both whorls, whereas unisexual blooms have only one.
• A stamen is a single androecium component that consists of an anther and filament.
• Pollen grains produced by the anther are haploid.
• The stigma, style, and ovary make up each unique gynoecium component, which is referred to as a pistil.

Pollination

• Pollination is the process of pollen grains being transferred from anthers to the stigma of a flower.
• It is required for fertilisation.
• Self-pollination (autogamy) and cross-pollination are the two forms of pollination (allogamy).
• Pollen grains are transferred from anthers to the stigma of the same flower or another bloom of the same plant in self-pollination.
• Pollen is transmitted from anthers to the stigma of another flower in cross-pollination.
• Cross-pollination is accomplished by a variety of pollinating agents. Water, wind, insects, birds, bats, and other natural phenomena are examples.

Fertilization

• Fertilization is the fusion of male and female gametes.
• Pollens germinate on the stigma surface of the pistil in blooming plants following pollination and produce two male nuclei.
• Ovules have two polar nuclei and an egg cell.
• Triploid endosperm is formed when one male nucleus unites with two polar nuclei.
• Another male nucleus joins the egg cell to create the zygote, which produces the embryo and future plant.
• The ovary forms a fruit after fertilisation, and the ovules become seeds. The rest of the body wilts away.

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