8. How Do Organisms Reproduce

 8. How Do Organisms Reproduce

  DNA is present in the chromosomes of the nucleus and carries the information for making all of the cell’s proteins which determine the organism’s characteristics.

For a cell to grow, divide and reproduce, it needs to create copies of its DNA so that it can pass on the information to its daughter cells. This process is called DNA replication.

The generated DNA copies might be similar but not identical to the original, which lead to variation in the species. Such variation is the basis of evolution.

Creation of DNA Copy 

 

Modes of Reproduction  

There are two modes of reproduction: Asexual Reproduction and Sexual Reproduction.

Asexual Reproduction:

Occurs in lower invertebrates and plants with simple organisation

Involves no formation and fusion of gametes

Requires a single parent

Involves only mitosis division

Reproductive unit is somatic cells of the parent

Offspring are genetically identical to parents

Often result in rapid production of a large number of offspring

Sexual Reproduction:

Occurs in almost all types of animals and higher plants

Involves formation and fusion of gametes

Requires two parents

Involves meiosis division during gamete formation

Reproductive unit is a gamete

Offspring resemble, but are not genetically identical to their parents

Less rapid increase in number

There are six types of asexual reproduction methods. They are:

Binary Fission: It involves the replication of DNA and division of the cell into two identical daughter cells.

Fragmentation: It involves splitting up of organisms into fragments. Each of these fragments develops into a fully mature individual.

Regeneration: It involves breaking of body into distinct pieces, each of which can produce an offspring.

Budding: It involves the formation of outgrowth or shoots which grow and mature to become new organisms.

Vegetative Propagation: It involves the formation of offspring in plants without the production of seeds or spores.

Spore Formation:  It involves the formation of haploid spores which grow into multicellular individuals without the event of fertilization.

Types of Asexual Reproduction 

 

Parts of a Flower 

Parts of a Flower  

The diagram shows different parts of a flower:

Petal: It is the brightly coloured structure of the flower which is used to attract insects by its colour and scent

Sepals: These are the green leaves around the outside of the flower which are used to protect the flower while it is still in bud

Stamen: It is the male reproductive part of the flower which consists of two parts: the filament and the anther

Filament: Thin stalk which is the male reproductive organ of a flower

Anther: Part of the stamen that produces the pollen

Carpel: Sometime also known as the pistil, it is the female reproductive part of the flower which contains the ovary, stigma and style.

Stigma: Part of the pistil or carpel that receives pollen

Style: Central part of the pistil/carpel

Ovary: Lower part of the pistil that contains ovules, which later develop into seeds

Receptacle: It is the swollen base of the flower that attaches it to the stem 

Sexual Reproduction in a Flowering Plant 

 

Sexual Reproduction in Human Beings 

 The fusion of a male germ-cell produced by the pollen grains with the female gamete present in the ovary is known as Fertilisation.

Once the pollen lands on the stigma, it needs to reach the ovary for fertlisation. It does this with the help of a pollen tube which grows out of the pollen grain and travels through the style to reach the ovary.

After fertilization, the fertilized egg cell (zygote) divides many times and forms an embryo. The embryo forms a hard wall around it and is then known as a seed.

The ovary swells up and ripens to form a fruit surrounding the seed. After fertilization, the parts of a flower such as petals, sepals, stamens, style and stigma wither and die.

Male Reproductive System 

  The reproductive organs of a male body are:

Penis: It is the male sex organ which develops completely at puberty. A boy experiences ejaculation, the release of semen from the penis, for the first time during puberty.

Scrotum:  It is a sack of skin behind penis which holds the testes. It acts as a temperature control system for the testes.

Testes: These are the round glands that develop during puberty and produce sperm, which contain the male's reproductive cells.

Vas Deferens: It is the duct which carries sperm away from the testes towards the penis.

Prostate Gland:  It is a gland located between the bladder and the penis and secretes fluid to nourish and protect the sperm.

Female Reproductive System  

The reproductive organs of a female body are:

Vagina: Muscular tube connected to the uterus that enables sexual intercourse, flow of menstrual fluids and through which a baby is delivered during childbirth.

Uterus: Also known as the womb, it is the female organ in which the baby develops prior to birth.

Ovary: A part of the reproductive system. In plants, it is the lower part of the pistil in a flower that contains ovules which later develop into seeds. In animals, it is the egg-producing organ of a female.

Cervix: The cervix is the lower part of the uterus. The cervical canal is a passage through which sperm travels to fertilise an egg cell.

Fallopian Tube: The Fallopian tube carries an egg from the ovary to the uterus.

What Happens When the Egg is Not Fertilised

The ovary releases one egg every month, which is fertilised and received by the uterus. The uterus develops a thick and spongy blood lining for the nourishment of the embryo.

If the egg is not fertilised, this thick lining is not required. In that case, the blood lining slowly breaks and the blood comes out through the vagina. This cycle takes place every month and is called menstruation.

  

Reproductive Health  

Reproductive health refers to the physical, mental, and emotional well-being of adolescents. It includes nutritious diet, personal hygiene and physical activities.

Nutritious Diet: A healthy or nutritious diet for adolescents provides enough calories and nutrients for growth and good health.

Personal Hygiene: Personal hygiene is important to keep the body and mind healthy. It includes taking care of body odour, hair hygiene, oral hygiene and menstrual hygiene.

Physical Activities: Adolescents should make sure they get plenty of exercise and fresh air to stay fit and healthy - at least 30 minutes a day is recommended.

Sexually Transmitted Diseases

Sexually transmitted diseases (STDs) are infections that spread through sexual contact between two persons. Sexually transmitted diseases are caused by bacteria, parasites and viruses.  These diseases can be prevented if proper precautions are taken. Some preventive measures include:

Using condoms

Getting vaccinated for Hepatitis B

Avoiding sexual contact with a known infected person

Avoiding excessive alcohol and drugs