Grade 8, Biology
“πΏ Welcome to Class 8 Biology! π Explore the wonders of life with these intriguing chapter headings:
- Introduction to Reproduction:
- Define Reproduction π
- Importance of Reproduction in Living Organisms π±
- Modes of Reproduction:
- Sexual Reproduction πΊ
- Asexual Reproduction π
- Differences Between Sexual and Asexual Reproduction π€
- Sexual Reproduction in Animals:
- Male Reproductive Organs πΉ
- Female Reproductive Organs πΊ
- Fertilization and its Types π₯π§¬
- Oviparous and Viviparous Animals π£πΆ
- Development Stages:
- From Zygote to Gestation and Parturition π€°πΆ
- The Need for Test Tube Babies π§ͺπΆ
- Cloning in Animals π§¬πΎ
- Asexual Reproduction Methods:
- Binary Fission πβ
- Budding π±π
- Fragmentation and Regeneration ππ
- Special Cases:
- Metamorphosis in Frogs πΈπ
- Unique Methods of Asexual Reproduction π‘π
- Fun Facts and Exploration:
- Cloning in Mammals π§¬π
- Discoveries in Reproductive Science π¬π
1. Define Reproduction?
The production of new individuals by their parents is known as reproduction
2. Why reproduction is essential?
- Reproduction is one of the most important characteristic of living organism
- It is essential for survival of species on the π Earth
- It ensures continuity of life on earth.
3. What are the two modes of reproduction?
- Sexual reproduction
- Asexual reproduction.
4. Difference between Asexual and Sexual reproduction??
Asexual reproduction | Sexual Reproduction |
Production of new animals by single parent without involvement of gametes is called asexual reproduction | Production of new animal by existing two parents, by fusion of their gametes is called sexual reproduction. |
No gametes are involved. | Gametes are involved |
No zygote is formed | Fusion of male and female gamete result in the formation of zygote |
The young ones are the exact copy of their parents. | The new individual may resemble the parent or may resemble not |
Ex: Amoeba, Hydra and Yeast | Ex: Fish, Frog, Dog, Horse |
Mostly single celled organism, plants undergo asexual reproduction. | Animals undergo sexual reproduction. |
Example for asexual reproduction is Binary fission, Budding, Vegetative Propagation | Sexual intercourse in animals and pollination in plants. |
5.Define sexual reproduction in animals?
- Mostly animals reproduce by sexual reproduction.
- Here, two parents are involved, one male and one female
- Both parent have reproductive organs.
- Adult male produces male gametes called as sperms.
- Adult female produces female gametes called as ovum/egg.
- The process of production of gametes is called Gametogenesis.
6. Define Fertilization?
- The fusion of male gamete (sperm) with female gamete (egg) to form zygote during sexual reproduction is called Fertilization.
- Zygote is a fertilised egg.
- It is the first cell of new organism.
7. What are the two types of Fertilization?
- External fertilisation
- Internal fertilisation.
8. Difference between External and Internal fertilization??
External Fertilization | Internal fertilization |
Fertilization that takes place outside the female body is called External fertilization | The fertilization that occurs inside the female body is called Internal fertilization. |
Ex: Amphibians, Fishes | Ex: Mammals, Birds, Reptiles, Insects |
During rainy seasons female frog lays hundreds of egg on the layer of water. Male releases large number of sperms. Each sperm swim and reach the egg and it result in fertilization | The male animal releases its sperms into the female body. These sperms move to egg and fertilized it. |
9. Difference between oviparous and viviparous animals??
Oviparous animals | Viviparous animals |
The animals that lays eggs after fertilization is called as Oviparous animals | The animals that give birth to young ones are called Viviparous animals |
Ex: Frog, Lizard, Hens, Butterfly etc. | Ex: Humans, Dogs, Cows, Cat etc. |
Male Reproductive Organs
It consist of pair of testes, two sperm ducts (Vas deferens) urethra and penis
Testes:
- Male have two testes
- They are oval in shape
- They are inside a small muscular pouch called scrotum, it lies outside the abdominal cavity.
Function of Scrotum:
- Scrotum is responsible for the production of sperms
- Scrotum acts as a thermo regulator they keep the temperature of the testis 1-3 degree lower than the body temperature
Function of Testes:
- It is responsible for the production of male gametes called as sperms.
- It is also responsible for the production of the sex hormone called Testosterone.
- Testes starts the production of the sperms are the age of 14 to 15
- Healthy male testes produce two billion sperms everyday
Structure of Sperm:
- Sperm has a head, middle piece and a tail
- Tail helps in locomotion
- A coiled tube-like structure called Epididymis is firmly attached to testes
- Sperms are temporarily stored in Epididymis
Vas deferens (sperm duct)
- It is narrow duct that starts from a testes and joins the urethra
- It carries the sperms to urethra by muscular action
- Seminal vesicles produce fluid that mixes with sperm
- It provides nourishment to the sperms
Urethra
- It is a long tube that arises from urinary bladder to carry urine
- Semen from vas deferens joins the urethra
- Urethra carries urine from bladder as well as the semen from vas deferens through the penis
Penis:
- It is a long thick muscular organ.
- It injects the sperm into the vagina of the female body
Accessory gland of male reproductive system:
- Seminal vesicles
- Prostate gland
- Bulbo urethral gland
- These glands secretes seminal plasma that is rich in fructose, calcium and certain enzymes
Female Reproductive Organs
It consist of pair of ovaries, oviducts, fallopian tubes, uterus and vagina
Ovaries
- Ovaries are present in the abdominal cavity just below the kidneys
- Function of the ovaries is to make the female gametes called ova/ eggs
- It also secrets sex hormones called oestrogen and Progesterone
- Ovaries are attached to uterus by fibroid chord called ovarian ligament
- Ovaries start producing eggs at the time of puberty
- In humans, single mature egg is released into Ovi duct each month
- Like sperms, egg is also a single cell that is much bigger than sperms
Fallopian tubes
- It is also called as oviduct
- It is a thin coiled muscular tube with funnel shaped opening near ovaries
- This joins the uterus to ovary
- The egg released from ovaries passes through this fallopian tube
- Fertilization of egg takes place in fallopian tube
Uterus
- Two fallopian tubes connect to a bag like organ called Uterus
- Uterus is also called as womb
- Growth and development of the fertilized egg (zygote) into a baby takes place in the Uterus
- Uterus has muscular tissues that gets expanded during pregnancy to hold the baby and contract after the baby birth.
Vagina
- The uterus opens into a wide muscular tube called vagina
- It opens outside the body
- In females vaginal opening and urinary openings are separate
Accessory organs
Female reproductive system has accessory glands like
- Mammary glands ( nourishment of infants)
- Bartholin gland ( secretion of lubricant)
Fertilization in Human:
- Fertilization is internal in humans
- During sexual intercourse millions of sperms are introduced into the vagina of the female through the penis
- The process of releasing the sperms into vagina is called Ejaculation
- Sperms are highly active and motile
- The reach the fallopian tubes through uterus
- One of the sperm fuses with ovum in the fallopian tube to forms zygote
- After fertilization covering is formed the around the fertilized egg to prevent other sperms entering it
- If the ovum is not fertilized then it is expelled from the vagina along with some muscular tissues and blood. This is known as Menstruation
Write the development of the zygote in detail??
- Zygote divides rapidly and repeatedly to form a group of cells
- Cells then group and begin to form different tissues and organs of the body. This developing structure is called embryo
- For further development embryo gets embedded in the walls of the uterus. This is called Implantation
- Embryo developed in uterus and the body parts are formed
- The stage of embryo where all the body parts can be identified is called as Foetus
- The foetus is attached to uterus by placenta
- Placenta provides Oxygen and nutrients to the foetus and remove the waste
- When the development of foetus is complete mother gives birth to the babies
- The complete development of foetus from fertilization till the birth of the baby is called Gestation period
- It is about 9 months or 40 weeks
- The act of giving birth to a baby is called Parturition.
Why there is a need for test tube babies??
- Due to some reasons in few women fallopian tubes are blocked
- These women are unable to bear babies
- This is because sperm cannot reach the Ovi duct were fertilization takes place.
How test tube babies are formed??
- Doctors collect freshly released egg and sperm and keep together for few hours invitro or IVF
- In vitro means fertilization outside the body
- Here zygote is allowed to develop for about a week and then placed in the mother’s uterus
- Then complete development of baby takes place in the uterus and the test tube baby is formed like other babies.
How the development of embryo in hen takes place??
- In hens internal fertilization takes place
- Hens lay eggs so they are oviparous animals
- After fertilization zygote divides repeatedly
- It travels to Oviduct
- During its travel it forms many protective layer that is hard shell of the egg
- After this the hen lays eggs
- Hen sits on the egg to provide sufficient warmth. This is called Incubation
- Development of chick takes place inside the egg shell.
- Hatching π£- the process by which the completely developed chick comes out of the egg shell by breaking is called hatching.
What are the changes from young one’s to adult??
Animals like frog, mosquito, butterfly have different stages of development between hatching eggs and formation of adult.
Write about the development of frogs??
- Female frog lays large number of eggs in water
- After sometime egg hatch into larva called tadpoles
- They feed on algae and bits of plants
- Tadpole grows hindlimbs
- After the development of hindlimbs frog crawls to the land
- Tail is removed gradually during the development
- That transformation of larvae into adult through drastic changes is called Metamorphosis.
List the various methods of asexual reproduction??
- Binary fission
- Budding
- Fragmentation
- Regeneration
Write the difference between the Binary fission and Budding??
Binary fission | Budding |
It takes place in organisms like Amoeba, Paramecium, Euglena etc. | It takes place in hydra, sea anemones, sponges and corals |
Here the parent organism split to form two organism of same kind | A small outgrowth called bud is formed on the body of the parent organism that grows in size and get detached to form new organism |
Here the parent itself divides to form a daughter amoebae | Here bud is formed from the parent and get detaches to form new organism |
Note:
In corals and sponges buds do not separate the stay attached to the parent reproduce again and form colony
Facts:
- Cloning is the production of the exact copy of the cell any body part or a complete organism
- Animals that are genetically identical are called as Clones
- First successful cloning in mammals was done by Lan wilmut at Roslin institute in Edinburg
- First successfully clonedΒ mammal is sheep βThe Dollyβ
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