Reproduction:

It is the process by which living beings produce new organisms like themselves.

Importance of Reproduction

• It is necessary to maintain the continuity of life on Earth.
• Reproduction balances birth rate and death rate on Earth.
  
  

DNA (Deoxyribonucleic Acid)

The molecules of DNA (Deoxyribonucleic Acid) in the chromosomes found in the nucleus of a cell contain genetic traits.

Importance of DNA Replication

• DNA duplication acts as a carrier of genetic information and transmits all genetic traits from one generation to another.
• It contains instructions for the formation of other cell components, such as proteins and RNA molecules.
• If DNA is not copied during reproduction, the correct proteins will not be formed, and the structure of an individual will be completely different.
• DNA replication preserves the traits of one generation in the next, which can be used for the development of the next generation.

Reproduction

Reproduction is of two types:

• Asexual reproduction
• Sexual reproduction

(i) Asexual Reproduction

• A single organism produces a new organism.
• Gametes are not formed.
• The new organism is identical to the parent organism.
• It is a very useful method for continuous multiplication.
• It is more commonly found in lower organisms.
  
  

(ii) Sexual Reproduction

• Two organisms (one male and one female) together produce a new organism.
• Male and female gametes are formed.
• The new organism is genetically similar to the parent organisms but not identical.
• It helps in generating variations in a species.
• Found in higher organisms.
  
  

Various Forms of Asexual Reproduction

(1) Fission

• In this process, a single cell divides into two or more cells.
• Fission is observed in unicellular organisms.

It is of two types:

(a) Binary fission – A unicellular organism divides into two cells. Example: Amoeba.

(b) Multiple fission – The original cell divides into multiple offspring cells. Example: Plasmodium.

(2) Budding

In this process, a bulge appears on the organism's body, which is called a bud.

This bud first grows small, then develops into a full organism and separates from the parent.

Example: Hydra (multicellular organism), Yeast.

 

(3) Regeneration

• In this process, if an organism breaks into pieces due to some reason, each piece develops into a new organism.
• Example: Planaria, Hydra.
  
  

(4) Fragmentation

In this reproduction method, a simple structured multicellular organism splits into small pieces.

These pieces grow and develop into a new organism.

Example: Spirogyra.

 

(5) Spore Formation

At the tips of some organisms' filaments, spore cases are formed, which contain spores.

Spores are spherical structures protected by a thick wall.

When favorable conditions are met, spores start growing.

(6) Vegetative Propagation

In some plants, new plants are formed from their vegetative parts like roots, stem, or leaves. This is called vegetative propagation.

(a) Natural Methods (Natural Vegetative Propagation)

• Through roots – Dahlia, Sweet potato.
• Through stem – Potato, Ginger.
• Through leaves – In Bryophyllum, buds on leaf margins develop into new plants.

(b) Artificial Methods (Artificial Vegetative Propagation)

• Cutting – Rose.
• Layering – Jasmine.
• Grafting – Mango.

Advantages of Vegetative Propagation

• Plants that do not produce seeds, such as banana and rose, can be propagated.
• New plants are genetically identical to the parent plant.
• It is a cheap and easy way to grow plants.
  
  

Sexual Reproduction

Reproduction in Plants

• The flower is the reproductive organ of a plant.
• Flowers are of two types:

(i). Unisexual Flowers:

• Flowers that have only male or female reproductive organs. These are called incomplete flowers.
• They contain either stamens or pistils.
• They perform cross-pollination.
• Examples: Papaya, White mulberry, Watermelon.
  
  

(ii). Bisexual Flowers:

• Flowers that contain both male and female reproductive organs.
• They have both stamens and pistils.
• They perform both self-pollination and cross-pollination.
• Examples: Tulip, Sunflower, Lily.
  
  

Structure of a Flower

(i) Sepals

• Green and leaf-like.
• Protects the bud before blooming.

(ii) Petals

• Usually large and colorful.
• Some have fragrance.
• Attract insects for pollination.

(iii) Stamens

• The male reproductive part of the flower.
• Each stamen consists of two parts:
• Filament – Supports the anther.
• Anther – Contains pollen grains.

(iv) Carpels or Pistil (Gynoecium)

• The female reproductive part of the flower.
• Each pistil has three parts:
• Stigma – Receives pollen grains.
• Style – Tube-like structure that supports the stigma.
• Ovary – Swollen part containing ovules (female gametes).
  
  

Four Main Stages of Reproduction in Plants

1. Pollination
2. Fertilization
3. Seed Formation
4. Germination

(i) Pollination

The transfer of pollen grains from the anther to the stigma is called pollination.

Types of Pollination:

1. Self-Pollination –

• Transfer of pollen within the same flower.
• Usually does not require an external agent.

2. Cross-Pollination –

• Transfer of pollen from one flower to another flower of the same species.
• Requires external agents like wind, water, or insects.
  
  

(ii) Fertilization

The process of fusion of male and female gametes.

Steps:

• After pollination, pollen grains land on the stigma and enter the style through pollen tubes.
• Each pollen tube contains two male gametes.
• The pollen tube reaches the ovary where the ovules are located.
• The pollen tube enters the ovule through a small opening called the micropyle.

 

(iii) Formation of Seeds

After fertilization, the zygote divides multiple times within the ovule to form an embryo. The ovule develops a hard coat and gradually transforms into seeds.

 

(iv) Germination

Under favorable conditions, the process by which seeds develop into new plants is called seed germination.

 

Human Reproduction

Common Changes in Boys and Girls During Puberty

(i) Sudden increase in height.

(ii) Change in body shape.

(iii) Change in voice:

• Boys develop a deeper voice.
• Girls develop a high-pitched voice.

(iv) Reproductive organs start maturing.

 

Changes in Boys During Puberty:

(i) Development of facial hair such as beard and mustache.

(ii) Growth of hair under the armpits, on the chest, and in the groin area.

(iii) Voice becomes deeper.

(iv) Development of muscles, broadening of shoulders, and increase in weight.

 

Changes in Girls During Puberty:

(i) Development of breasts.

(ii) Growth of hair under the armpits and in the pubic region.

(iii) Onset of the menstrual cycle.

(iv) Deposition of fat around the hips.

Puberty: Puberty is the stage at which boys and girls become sexually mature.

 

Male Reproductive System

 

The main organs involved in the human male reproductive system are the testes, scrotum, sperm ducts, urethra, and penis.

 

Testes: The testes produce sperm and the male hormone testosterone.

 

Scrotum: The scrotum provides an appropriate temperature for sperm production, which is 1-3°C lower than the body’s normal temperature.

 

Sperm Duct: The sperm duct is a long, muscular tube that transports mature sperm from the epididymis to the pelvic cavity, passing just behind the bladder.

 

Seminal Vesicles and Prostate Gland:

The seminal vesicles and prostate gland secrete fluids into the sperm duct, making sperm motile by providing a liquid medium. This secretion also nourishes the sperm.

 

Urethra:

The urethra is a tube that extends from the bladder to the external body, allowing the passage of urine and sperm. It serves as a common passage for both.

 

Penis:

The penis is the external male reproductive organ that transfers sperm into the female’s vagina during intercourse.

 

Female Reproductive System

 

(i) Ovaries:

• The female gametes or ova are produced in the ovaries.
• At birth, a girl’s ovaries contain thousands of immature eggs. At puberty, some of these eggs begin to mature.
• One of the two ovaries releases a mature egg every month.
• The ovaries also produce the hormones estrogen and progesterone.

 

(ii) Fallopian Tubes:

• The fallopian tube carries the egg from the ovary to the uterus.
• Fertilization of the egg by sperm occurs here.

 

(iii) Uterus:

• The uterus is a sac-like structure where the embryo develops.
• It opens into the vagina through the cervix.

 

Sexual Reproduction in Humans

 

(i) The male parent produces sperm, while the female parent produces eggs.

(ii) During intercourse, sperm travel upward and reach the fallopian tube, where fertilization occurs. This leads to the formation of a zygote in the uterine lining, which marks the beginning of a new life.

(iii) The zygote undergoes division to form an embryo.

(iv) The embryo gradually moves down and gets implanted in the uterus.

 

How Does the Embryo Receive Nutrition in the Mother’s Womb?

Placenta:

It is a specialized tissue with a disc-shaped structure present in the uterus. Its main functions include:

(i) Supplying glucose, oxygen, and other nutrients from the mother’s blood to the embryo.

(ii) Removal of waste materials produced by the embryo.

The period from fertilization to birth is called gestation, which lasts for about 9 months.

 

What Happens If the Egg Is Not Fertilized?

If the egg is not fertilized, it remains alive for about a day. Since the ovary releases one egg each month, the uterus also prepares itself every month to receive a fertilized egg by thickening its lining. If fertilization does not occur, the thickened layer is no longer needed, and it gradually breaks down and is discharged from the vagina along with blood and mucus. This cycle occurs approximately every month and is known as menstruation or the menstrual cycle, lasting about 2-8 days.

 

Reproductive Health

Reproductive health means maintaining physical, mental, social, and behavioral well-being related to reproduction.

Sexually Transmitted Diseases (STDs): Many diseases can be sexually transmitted, such as:

(a) Bacterial STDs – Gonorrhea, Syphilis

(b) Viral STDs – Warts, HIV/AIDS

Using condoms can help prevent the spread of such diseases to some extent.

 

Contraception – The prevention of pregnancy is called contraception.

Types of Contraception:

(a) Mechanical Barriers – Prevent sperm from reaching the egg.

Examples:

• Condoms worn over the penis.
• Cervical caps placed inside the vagina.
  
  

(b) Chemical Methods – Prevent egg production in females by taking hormonal pills, which may have side effects.

 

(c) IUCD (Intrauterine Contraceptive Device) – A device such as a loop or Copper-T is placed inside the uterus to prevent pregnancy.

 

(d) Surgical Methods:

(i) Vasectomy – Cutting or blocking the sperm ducts in males to prevent sperm transport.

 

(ii) Tubectomy – Blocking the fallopian tubes in females to prevent egg transport.