Reproduction How Life Continues Class 9 Notes Science Chapter 11

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Class 9 Science Chapter 11 Reproduction How Life Continues Notes

Class 9 Science Exploration Chapter 11 Notes

Class 9 Science Chapter 11 Notes – Class 9 Reproduction How Life Continues

→ Reproduction: It is a biological process by which all living organisms give rise to new individuals of their own species.

• Offspring usually resemble their parents because genetic material, called genes, is passed down to guide development.
• Genes act like instructions inside every cell, directing how an organism grows and functions.
• Reproduction not only ensures the continuation of each species but also allows life to adapt and exist in new forms.

→ Two Types of Reproduction: sexual and asexual.

→ Asexual Reproduction: When a single parent is involved in the formation of a new individual, without the fusion of gametes, it is called asexual reproduction. It involves repeated mitotic divisions. Various types of asexual reproduction are: vegetative propagation, binary fission, fragmentation, budding, etc.

→ Vegetative propagation: It is a method of reproduction where new plants grow from vegetative parts like root, stem, or leaf.

→ Natural examples: Sweet potato (root), potato and ginger (stem), Bryophyllum (leaf).

→ Artificial methods: Cutting (sugarcane), layering (lemon, jasmine), grafting (rose), tissue culture.

→ This method is quick and easy, requires only one parent, produces many plants in a short time, ensures identical offspring, and saves energy as no seeds are needed.

→ Tissue Culture: A method of plant propagation using the shoot tip (apical meristem) to produce many healthy, disease-free plants (e.g., banana). It improves yield and is a form of asexual reproduction.

→ Budding: Asexual reproduction where a small bud forms on the parent by cell division, grows, and detaches to live independently, e.g., yeast, Hydra.

→ Rhizopus (bread mould): It grows on decaying bread as white cotton-like fuzzy patches. These organisms can survive harsh conditions (heat, dryness) and germinate into new organisms under favourable conditions like moisture and darkness.

→ Clones: Genetically identical offspring produced from a single parent through asexual reproduction, having the same DNA and characteristics as the parent.

→ Sexual Reproduction: It is the process in which male and female gametes fuse to form a new individual. It involves two parents of opposite sexes of the same species. During reproduction, DNA copies itself, but the copies are not exactly identical, which leads to variation.

→ In sexual reproduction, variation occurs due to the mixing of genes from two parents during meiosis and fertilisation. This makes offspring genetically different and helps in adaptation, survival, and evolution (e.g., lactose intolerance, high-altitude adaptation).

→ Chromosomes: Thread-like structures in the nucleus that carry genetic information. Humans have 23 pairs (46 total), with one chromosome in each pair inherited from each parent.

→ Gametes: Haploid reproductive cells formed by meiosis and used only for reproduction.

→ Meiosis: A special type of cell division that forms gametes by reducing the chromosome number from diploid to haploid. Each gamete receives 23 chromosomes (one from each pair).

→ In animals, the gametes are sperm (male) and egg (female), while in plants, pollen grains carry male gametes and the ovule contains female gametes.

→ Sexual Reproduction In Flowering Plants:
Flowering plants, known as angiosperms, are the most diverse group of plants on Earth. In these plants, flowers act as reproductive organs, while some non-flowering plants, such as pines, also reproduce sexually.

Parts of a flower: A flower has four main parts, which help in plant reproduction:
1. Sepals: Green outer part that protects the flower bud.
2. Petals: Colourful parts that attract insects for pollination.
3. Stamen (male part):

• Anther: produces pollen
• Filament: supports the anther

4. Pistil/Carpel (female part):

• Stigma: receives pollen
• Style: connects stigma to the ovary
• Ovary: contains ovules (develop into seeds)

→ Pollination: The transfer of pollen grains from the anther to the stigma of a flower by agents like wind, water, insects, etc. It is of two types:

• Self-pollination: Transfer of pollen grains from the anther of a flower to the stigma of the same flower.
• Cross-pollination: Transfer of pollen from the anther of one flower to the stigma of another flower of the same plant or a different plant of the same type.

→ Pollinators: Organisms that transfer pollen from one flower to another, helping in plant reproduction. They can be biotic and abiotic agents.

• Biotic agents like insects, birds, and animals ensure effective pollination by carrying pollen while feeding.
• Abiotic agents like wind and water help plants that lack bright flowers or nectar.
• Wind carries light pollen (e.g., maize), while water helps in aquatic plants like Vallisneria.

→ Fertilisation in plants and seed formation:

• Fusion of male and female gametes is called fertilisation, which occurs when the male gamete reaches the ovule through the pollen tube, forming a zygote (fertilised egg).
• After fertilisation, the zygote develops into an embryo. The ovule becomes a seed with a protective seed coat, and the ovary develops into a fruit.
• The seed contains the future plant (embryo), which develops into a seedling when environmental conditions are favourable. This process is called germination.

→ Sexual Reproduction in Animals: It involves fusion of male and female gametes and may occur by asexual or sexual methods in different organisms.

→ External Fertilisation: In aquatic animals like frogs and fish, fertilisation occurs outside the body in water. Eggs and sperm are released into water, but many offspring are lost due to external factors.

→ Internal Fertilisation: In reptiles, birds, and mammals, fertilisation occurs inside the female body, providing better protection and higher survival chances for the offspring.

→ IVF or In-vitro Fertilisation: Fertilisation takes place outside the body in a laboratory.

→ Test-tube Baby: Zygote formed by IVF is developed for a few days and then placed in the uterus, where full development occurs. Fish, amphibians, and insects lay many eggs with less yolk. Their larvae hatch early and feed on their own (e.g., frog, butterfly).

• Reptiles and birds lay eggs with enough yolk to nourish the embryo.
• In mammals, the embryo develops inside the mother’s body.
• Post-hatching/post-birth care is provided by parents. This care helps in the protection, nourishment, and survival of young ones.

→ Reproduction in Human Beings: After puberty is attained, in females, the ovaries exhibit a cycle of events at definite intervals. The ovarian follicles grow into mature follicles. Generally, one mature follicle develops to surround one ovum. While in males, organ mature and begin producing sperms.

→ Male Reproductive System: It produces male gametes (sperm) and transfers them to the female body.

• This system has a pair of testes (singular – testis), two sperm ducts called vas deferens, and a penis.
• The testes produce the male gametes called sperm, and a hormone that regulates the sperm production and the physical changes during puberty.
• The vas deferens carry sperm to the penis.
• The penis is used for ejecting sperm and also passing urine.
• The sperm consists of head containing genetic material and a tail that helps the sperm in movements towards the egg in female sex organ.

→ Female Reproductive System: It consists of a pair of ovaries, oviducts (fallopian tubes), uterus, and vagina.

• Ovaries: Produce female gametes called ova (eggs) and hormones that brings changes during puberty.
• Oviducts (fallopian tubes): These tubes connect each ovary to the uterus.
• Uterus: Part where the development of the foetus takes place.
• Vagina: The chamber after the cervix that receives semen during mating and also acts as the birth canal.

→ Gametogenesis: The process by which gametes (sperm and eggs) are formed through meiosis. It takes place in the testes and the ovaries.

• In humans, gametes have 23 chromosomes instead of 46 so that after fertilisation, the zygote has the correct chromosome number.
• In males, gametogenesis produces many small, motile sperm, while in females it produces a single large egg.

→ What happens when a sperm meets an egg?

• The maturing ovum is released from one of the two ovaries every month by the process of ovulation.
• In humans, internal fertilisation occurs. Sperms are highly active and mobile. Millions of sperms are released in the vagina, and they move up through the cervix and uterus.
• In the fallopian tube, only one sperm fertilises the ovum; as a result, a zygote is formed. Zygote begins to divide immediately in the fallopian tube. At the same time, changes occur in the uterus.
• The inner wall of the uterus thickens and becomes rich with blood vessels, prepared to receive the developing zygote.
• Embryo moves to the uterus and gets attached to its thickened inner wall. The close attachment of the embryo to the uterus is called implantation, marking the beginning of pregnancy.

→ What happens when an egg is not fertilised?

• If fertilisation does not occur, the thickened inner wall of the uterus breaks down along with its blood vessels and moves out of the vagina in the form of a bleeding called menstrual flow (Menstruation). This lasts for 3-7 days.
• The menstrual cycle includes ovulation, preparation of the uterus, and menstruation.
• It repeats every 21-35 days (average -28 days).
• It begins at puberty (10-14 years) in girls and continues throughout the reproductive age till menopause (around 50 years).

→ Pregnancy and childbirth:

• After implantation, special tissues develop between the uterine wall and the foetus called the placenta, through which the nutritional, excretory, and respiratory needs of the foetus are met.
• The development of the foetus inside the uterus till birth takes about 9 months.
• The birth of a fully developed foetus occurs as a result of rhythmic contraction of the muscles in the uterus. Post birth, a baby needs special care.
• Breastfeeding is essential as it provides complete nutrition and protects the baby from diseases. Both mother and baby need proper care, including good nutrition, rest, and timely health support.

→ Reproductive Health:

• It includes aspects like:
• Responsible, safe, and satisfying reproductive life.
• Awareness regarding fertility regulation methods, the right, freedom, and choice to control birth.
• Ability to prevent and control sexually transmitted diseases.

→ Sexual Maturity: It is the stage during adolescence when the body becomes capable of reproduction. In boys, sperm production begins, and in girls, menstrual cycles start. However, emotional maturity develops later and involves handling emotions and making responsible decisions.

→ Readiness for sexual activity requires responsible decision-making to avoid unplanned pregnancies and sexually transmitted infections (STIs).

→ Sexually Transmitted Infections (STIs):
Infectious diseases caused by bacteria, viruses, protozoans, and fungi that spread through sexual contact, e.g., gonorrhoea, herpes, genital warts, syphilis, and HIV, which eventually lead to AIDS. Use of condoms helps prevent STIs and also reduces the chances of pregnancy.

→ Methods to prevent unwanted pregnancy:

• Barrier Method: Physical devices such as condoms and vaginal covers are used. They prevent entry of sperm in the genital tract during copulation and also prevent sexually transmitted infections like AIDS, gonorrhoea, and syphilis.
• Chemical Method: Use of a specific drug by females. Oral pills are hormonal preparations. They inhibit the production of gametes by changing hormonal balances. They can cause side effects.
• Intra-Uterine Devices (IUDs): A copper-T is placed safely in the uterus by a doctor or a skilled nurse, which prevents implantation in the uterus. They may irritate the uterus.
• Surgical Methods: A small portion of the vas deferens in males, and the fallopian tube in females, is surgically removed or ligated (tied). It is called a vasectomy in males and a tubectomy in females.

→ Abortion: Removal of an unwanted pregnancy, usually within the first trimester, when the embryo is small. Prenatal sex determination and sex-selective abortion are illegal in India as they disturb the natural sex ratio in society.

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