How Do Organism Reproduce | Class 10 Notes | Science | Term 2 |

How Do Organism Reproduce | Class 10 Notes | Science |

# How Do Organism Reproduce

Reproduction

How Do Organism Reproduce : Reproduction is a biological process of production of new organisms from the existing organisms of same species. 

• The existing organisms are referred as parent whereas the new organisms produced by them are called off springs.
• It involves continuation of characters from parents to daughter cells by copying of DNA molecules present in chromosomes of the cell.
• Copying of DNA is also not a foolproof exercise, even minute changes bring about variations in the blueprint of the offspring. These useful variations are retained while the harmful ones do not go beyond.
• These are variations only which help the species to withstand drastic environmental changes, the save the species from becoming extinct and promote its survival for longer time.

Importance of reproduction is discussed as below:

• Continuation of life for millions of years from the time of their origin.
  
• Reproduction increases the size of pollution and helps in existence of species.
  
• New individuals added to the population compensate for the loss of death.
  
• Reproduction introduces variations in the offspring and also helps in transfer of these variations in to their offspring.
  
• It is a bridge to hereditary transmission.

Adaptations- Changes which empower an organism in order to survive successfully in some cheese environment are called as adaptations.
DNA (Deoxyribose nucleic acid) molecular forms its copy and this process of duplication of DNA is called DNA Replication. 

Types of Reproduction

• Living organisms reproduce by the two ways
• Asexual and Sexual Reproduction
  

Asexual Reproduction

Asexual reproduction occurs without the formation and fusion of gametes.

Characteristics

• It is uniparental.
  
• The fusion of gametes is not involved in it.
  
• It is rapid method of multiplication.
  
• Daughter organisms are generally identical to the parent one.
  
• It is found in unicellular organisms such as plant and lower animals.

Different forms of Asexual Reproduction are as discussed below:

1. Fission– In fission, a unicellular organism splits to form two new organisms.

• Binary fission: In this the parent organism splits into two daughter cells. Example: Amoeba, Paramecium, Leishmania, bacteria reproduce by binary fission.
  
• Multiple fission: It occurred during unfavourable environmental condition. In multiple fission the parent organism splits into to many new organisms at the same time. Nucleus divide several times in order to form a large number of daughter nuclei.
  

2. Budding – A new organism that is produced as result of outgrowth of the parent body part.
Spore formation- Spores are small, bulb like structure which develop at the top of the erect hyphae of the fungus plant, when released into the air germinate, into new individuals after landing into food or soil.

3. Fragmentation – It is the accidental process when the broken pieces of an organism grows into a complete organism.

4. Regeneration – When the simpler animals such as hydra and planaria developer new individual from their broken old apart then it is referred as regeneration. It is carried out by specialised cells which grow larger number of cells.

5.Vegetative Propagation – It is that mode of reproduction in which parts like stem root and leaves develop into the new plant under favourable condition. The new plant would exactly resemble the parent. Seedless plant can also be grown.

Sexual Reproduction

It is that type of reproduction that involves that to individual belonging to two different sexes.

• Male organism for male gametes.
  
• Female organism from female gametes.
  
• Gametes are produced by meiotic division.
  
• Male and female gametes fusion takes place.
  
• A diploid zygote is formed as a result of fertilization.

Sexual Reproduction in Plants

In flowering plants flower is the reproductive part since it contains reproductive organ of male and female part.
A typical flower consists of
1. Sepals – group of sepals is called calyx
It protects of flower in its bud condition.

2. Petals – group of petals is called Corola.
When coloured these petals attract the biotic pollinating agents.

3. Carpel / Pistil / Gynoecium / Female reproductive organ
It further consists of three parts that is Stigma, Style and Ovary.
Stigma provides platform for the pollen to land on it. Stigma is an elongated tube like structure which provides a way for the pollen tube to reach inside ovary.
Ovary the swollen part contains one to many ovules attached through placenta.
Fertilized ovules converts into seeds.

4.Stamen / Androecium / Male reproductive organ
Stamen further has two parts Anther and Filament
Anther is the fertile part of stamen in which pollen grain develops. Each pollen grain consists of two male gametes.

Pollination

The transfer of the pollen grains from the anther to the stigma is referred as pollination.
It is of two types as discussed below

Self pollination

• When pollen grains are transferred from anther to the stigma of same or genetically similar flower.
• It occurs in bisexual flower.
• No abiotic agents are required.

Cross pollination

• When the pollen grains are transferred from anther to stigma of another flower borne on a a different plant of the same species.
• It occurs in unisexual flowers.
• Agents are required for pollination.

Fertilization in Flowering Plants

The male and female gamete fusion is referred as fertilization.
Pollen grain is deposited on the stigma of carpel as a result of pollination. It grows into a pollen tube. Pollen tube pierces the stigma and grows through the style. It enters ovary. Pollen tube contains male gamete. It releases the male gamete into embryo sac. Male gamete fuses with the egg in order to form a zygote.

Double fertilization- Out of the two male gametes present in pollen grain, fuses with egg in order to form zygote whereas another fuses with polar nuclei in order to form endosperm. Two fertilization takes place simultaneously hence this is called double fertilization.

Triple fusion- Fusion of polar nuclei and one male gamete in order to form endosperm. Endosperm provides nutrition to the developing zygote.

Post Fertilization Changes

Post fertilization changes results in the formation of seeds.

• Ovary changes into fruit.
• Ovule changes into seed.
• Zygote divides several time to form embryo which in turn develops into seedling.
• Wall of ovary form fruit wall.
• Sepals, petals, Style and stigma fall off.
• Radicle will give rise to root.
• Plumule will give rise to shoot.

Sexual Reproduction in Human Being

Human beings are unisexual that is the sexes are separate.
There is sexual dimorphism, i.e., male and females are visibly different from each other.
Cells involved in sexual reproduction is gamete or reproductive cells.
Male gamete- Sperm
Female gamete- Ovum or egg

Puberty- The age at which reproductive organs become functional, i.e., gonads start producing gametes and sex hormones. Boys attain puberty at the age of 13-14 years while girls attain puberty at 10-12 years.

Gametes- A sperm contains genetic material and has long tail. Tail helps sperm in order to move towards the female gamete (ovum). Ovum is non mobile. It is thousand times longer than sperm. It contains water and stored food.

Male Reproductive System

Male reproductive system in human beings is associated with the formation and transfer of sperms to ovum. It consists of-

• A pair of testes: It produces sperms. ( Spermatogenesis).
  It produces and secretes testosterone hormone.
• Scrotum: Deep pigmented pouch like structure wherein testes are located.
  It keeps testes temperature 2-2.5° less then the body temperature so that sperms production starts.
• Vas deference: It is a long tube which starts from testes and ends up to penis. Sperms formed in testes are delivered through vas deference.
• Prostate and seminal vesicles glands: These glands and their secretions which makes the sperm transport easier and provides nutrition to sperms.

Female Reproductive System

• A pair of Ovaries: It producers egg. It secretes estrogen and progesterone hormone.
• Fallopian tube or Oviduct: These are the paired tubes originating from uterus one on either side of it. Here, the fusion of ovum and sperm takes place that is fertilization.
• Uterus: It is a single, pear shaped, highly muscular hollow structure present in pelvic cavity. Hair the placenta is formed and embryo gets its nutrition.
• Vagina: It is a short and wide muscular tube and is also known as birth canal. Menstrual blood comes out through vagina.

Fertilization

Internal fertilization takes place in humans. Millions of sperms are released into vagina during mating. The sperms moves up through cervix into uterus then to oviducts. Fertilization takes place inside the upper part of the fallopian tube.

Implantation

Zygote is formed after fertilization. The zygote divides by mitosis and moves slowly into fallopian tube. The process of attachment of embryo with uterine wall is called implantation. New embryo is called foetus.

Placenta

It is the psychological connection between the embryo and uterine wall of mother. It carries the following functions
It provides nutrition and oxygen to the foetus from mother’s blood.
It removes carbon dioxide and nitrogenous waste from the blood of foetus.
It produces hormone progesterone for maintaining pregnancy.

Gestation Period

The total time taken for the development of an embryo into the mother’s uterus is called gestation period. In humans it is of 9 months.

Parturition- The of a child is called parturition. The walls of the uterus contracts repeatedly under the influence of hormone oxytocin, which forces the foetus to come out.

Sexually Transmitted Disease

The disease which can be spread through sexual contact are known as STDs.
Bacterial STDs:- Gonorrohea and Syphilis
Viral STDs:- HIV AIDS and Warts

Contraception / Birth Control

It is the prevention of pregnancy in women.

Contraceptive devices: The devices used to avoid pregnancy.

1.Mechanical Barrier: In this condoms on the penis or similar covering worn in vagina. Mum does not reach the egg and hens prevent fertilization. This method also helps to prevent STDs.

2.Oral Contraception: In this drugs (medicine) are taken which helps to prevent ovulation and fertilization by changing hormone level. Since the drugs change hormone balance they can cause side effects too.

3.IUCDs (Intra Uterine Contraceptive Devices)
In this devices such as loop are placed in uterus in order to prevent pregnancy. They can cause irritation to the uterus.

4.Surgical Method

• Vasectomy- Vas-deferens is blocked and hence sperms transfer will be prevented.
• Tubectomy- Fallopian tube is blocked and hence sperm and egg fusion will be prevented.

How Do Organisms Reproduce Questions

Question: What happens if the egg is not fertilized?

Answer: When the end is not fertilized then the thick and vascular endometrium wall of the uterus which is formed of tissue and blood shades of and along with mucus comes out through vagina in the form of vaginal bleeding. This is known as menstruation.

Question: What is Menopause?

Answer: The sexual cycle in a woman continuous up to the age of 45 to 50 years. Eggs are not released by ovaries after that. This stage is called menopause. It also marks the end of mensuration in the woman.

Question: What would happen fertilization of eggs does not take place?

Answer: When egg is fertilized the zygote is formed. The zygote divides many times mitotically to form embryo. The embryo gets implanted to the inner uterine wall and a lady is now said to be pregnant.

Question: Define implantation.

Answer: Implantation simply defined as the attachment of embryo to the inner uterine wall.

Question: What is semen?

Answer: The secretions of male accessory ducts, i.e., seminal vesicles and prostate gland along with the sperms.

Question: Differentiate between sperm and ova.

Answer: 

Sperm	Ova
Male sex cell	Female sex cell
Motile	Non motile
Produce in large numbers	Produce in small number usually one per cycle.
Contains only genetic material	Contains ooplasma and genetic material both.

Question: List about the changes which are common in both boys and girls on the onset of puberty.

Answer: Thick hair growing in new parts of the body such as armpits.
The growth of thinner hair can also be seen on legs and arms as well as on the face.
The skin frequently becomes oily and individual might begin to develop pimples.

Question: In human female reproductive system, determine the part where the following functions takes place.
(a) Production of egg
(b) Site of fertilization
(c) Site of implantation
(d) Entry of the sperm

Answer: (a) Ovary
(b) Oviduct
(c) Uterus
(d) Vagina

# How do Organism Reproduce

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