Science Chapter 6 Reproduction in Animals Class 8 PDF Notes Download for FREE
Reproduction in animals is the process by which animals create new individuals of the same species. This can happen in two main ways: sexual reproduction, where a male and female animal produce offspring by combining their genetic material, and asexual reproduction, where a single animal creates offspring without the need for another animal. Reproduction ensures that a species can continue to exist and grow over time.
Modes of Reproduction:
The different ways animals reproduce, are known as "modes of reproduction." There are two main types:
1. Sexual reproduction and
2. Asexual reproduction
Sexual Reproduction: This is when two animals, a male and a female, come together to produce offspring. They each contribute genetic material (sperm and egg) that combines to create a new animal. This method results in offspring that are genetically different from their parents. Examples include humans, birds, and fish.
Male Reproductive Organ: The male reproductive system includes:
Testes: A pair of organs that produce male gametes called sperm.
Sperm Ducts: Two tubes that transport sperm from the testes.
Penis: The external organ that delivers sperm into the female reproductive system.
Sperm Production:
The testes generate millions of sperm.
Each sperm is very small but consists of three parts: a head, a middle piece, and a tail.
Despite its small size, a sperm is a single cell with all the usual cell components.
Female Reproductive System:
Ovaries: A pair of organs that produce female gametes called ova (eggs).
Oviducts (Fallopian Tubes): Tubes through which the mature egg travels from the ovary to the uterus.
Uterus: The organ where the baby develops during pregnancy.
Egg Release: In humans, one mature egg is released from an ovary into the oviduct each month.
Single Cell: An egg, like a sperm, is also a single cell.
Female Reproductive Organs in Humans
Fertilisation:
The reproduction process begins with the fusion of a sperm cell and an ovum (egg cell).
When sperm comes into contact with an egg, one sperm may combine with the egg.
This fusion is called fertilisation.
During fertilisation, the nuclei of the sperm and egg merge to form a single nucleus.
This results in the formation of a fertilised egg, or zygote.
Fertilisation involves the meeting of an egg cell from the mother and a sperm cell from the father.
The new individual inherits traits from both parents.
For example, you might notice characteristics in your siblings that resemble those of your parents.
When fertilisation occurs inside the female body, it is known as internal fertilisation.
Internal fertilisation happens in many animals, including humans, cows, dogs, and hens.
Fertilisation
Development of Embryo
Fertilisation results in the formation of a zygote, which begins to develop into an embryo.
The zygote divides repeatedly, forming a ball of cells.
These cells group to develop into different tissues and organs, creating the embryo.
The embryo embeds itself into the wall of the uterus for further development.
Inside the uterus, the embryo gradually forms body parts such as hands, legs, head, eyes, and ears.
When the embryo has developed all identifiable body parts, it is called a foetus.
Upon the completion of the foetus's development, the mother gives birth to a baby.
In hens, internal fertilisation occurs, but hens do not give birth to live chicks like humans and cows.
After fertilisation, the zygote divides and travels down the oviduct, forming protective layers around it.
The hard shell of a hen's egg is one of these protective layers.
Once the hard shell forms, the hen lays the egg. The embryo develops into a chick over about 3 weeks.
The hen sits on the eggs to provide warmth, allowing the chick to develop inside the eggshell.
Once fully developed, the chick breaks out of the eggshell.
In animals with external fertilisation, the embryo develops outside the female body within its egg.
Viviparous and Oviparous Animals
Viviparous Animals
Give Birth to Live Young: Viviparous animals give birth to live offspring rather than laying eggs.
Internal Development: The embryo develops inside the mother’s body.
Examples: Humans, cows, and dogs are viviparous animals.
Nourishment: The developing embryo receives nutrients from the mother through the placenta.
Oviparous Animals
Lay Eggs: Oviparous animals lay eggs, which develop and hatch outside the mother’s body.
External Development: The embryo develops inside the egg, which has a protective shell.
Examples: Birds, reptiles, and amphibians are oviparous animals.
Nourishment: The embryo gets its nutrients from the yolk inside the egg.
Young Ones to Adults
New individuals born or hatched from eggs continue to grow until they reach adulthood.
In some animals, the young ones look very different from the adults.
For example, look at the chart given is a life cycle of a frog where tadpoles change into adult frogs that can jump and swim.
This drastic change from larva to adult is called metamorphosis.
Humans also experience changes as we grow, but unlike animals undergoing metamorphosis, we have body parts similar to those of adults from birth.
Life Cycle of a Frog
2. Asexual Reproduction: In this method, a single animal can reproduce without needing a mate. The offspring are genetically identical to the parent. This means the new animal is a clone of the original one. Examples include some insects and simple organisms like bacteria and hydra.
In a hydra, you might see one or more bulges. These bulges are developing into new hydras and are called buds.
Similar to how yeast forms buds, hydras also create new individuals from these buds.
This process, where only one parent is involved, is known as asexual reproduction.
Since new hydras develop from buds, this type of asexual reproduction is specifically called budding.
The method of reproduction where a single parent organism splits into two identical daughter organisms is called Binary Fission.
Binary Fission in Amoeba
5 Important Topics of Science Class 8 Chapter 6 Reproduction in Animals
Importance of Science Chapter 6 Reproduction in Animals Class 8 Notes
Revision notes help us quickly understand and remember key concepts before exams.
They save time by focusing on essential information and skipping unnecessary details.
These notes simplify complex topics, making them easier to understand and use.
They provide practical examples that show how theoretical knowledge is used in real-life situations. Revision notes ensure thorough preparation by covering all important topics in a structured manner.
They increase confidence by clearly understanding what to expect in exams.
Accessible formats like PDFs allow for easy studying anytime and anywhere.
Tips for Learning the Class 8 Science Reproduction in Animals Notes
Understand the basic terms like sexual and asexual reproduction. Knowing these helps in understanding how animals reproduce.
Learn about how different reproduction methods work. For example, learn how sexual reproduction differs from asexual reproduction.
Compare and contrast sexual and asexual reproduction. This helps you understand the advantages and differences between these methods.
Learn the names and functions of reproductive organs in different animals, such as ovaries and testes. Understanding these structures helps you grasp how reproduction happens.
Study the life cycles of animals, from birth to reproduction. Knowing stages like embryonic development and growth can help you understand how animals reproduce and develop.
Use examples of various animals to see how reproduction occurs in real life. Examples like frogs, insects, and mammals can show you different reproductive strategies and processes.
Conclusion
In Vedantu’s Class 8 Science Chapter 6 Notes on Reproduction in Animals covers the important topics of how animals reproduce. We’ve explored both sexual and asexual reproduction, including the processes and structures involved. Our notes have simplified these concepts to make them easier to understand and remember. By focusing on key topics such as reproductive methods, organs, and life cycles, you should now have a clearer grasp of how different animals bring new life into the world. Use these notes to review, and you’ll be well-prepared for your exams.
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FAQs on Reproduction in Animals Class 8 Notes: CBSE Science Chapter 6
1. What are the main topics to revise in Class 8 Science Chapter 6, Reproduction in Animals?
For a quick revision of this chapter, you should focus on the core concepts. These include the two primary modes of reproduction, sexual and asexual, the male and female reproductive organs, the process of fertilisation and subsequent development of the zygote into an embryo, the distinction between viviparous and oviparous animals, and the concept of metamorphosis as seen in frogs.
2. How can you quickly summarise the two main modes of reproduction in animals?
The two modes of reproduction can be summarised as follows:
- Sexual Reproduction: This process involves two parents, a male and a female. It requires the fusion of their respective gametes (sperm and egg) to form a zygote, resulting in offspring with genetic traits from both parents.
- Asexual Reproduction: This process involves only a single parent. The offspring produced are genetically identical to the parent, as there is no fusion of gametes. Examples include budding and binary fission.
3. Why do offspring from sexual reproduction show variation, while those from asexual reproduction are identical to the parent?
Offspring from sexual reproduction show variation because they inherit a unique combination of genes from two different parents through the fusion of sperm and egg. In contrast, asexual reproduction involves only one parent passing on its exact genetic material to the offspring, resulting in a genetically identical clone.
4. What is the correct sequence of development from fertilisation to foetus in humans?
The development follows a specific sequence. First, the fusion of a sperm and an ovum, called fertilisation, results in the formation of a single cell known as a zygote. The zygote undergoes repeated cell division to form an embryo, which then embeds in the uterus wall. The embryo continues to develop until its body parts are identifiable, at which stage it is called a foetus.
5. For revision, what is the main difference between internal and external fertilisation?
The key difference lies in the location where the fusion of gametes occurs. Internal fertilisation takes place inside the female's body, as seen in humans, cows, and hens. External fertilisation happens outside the female's body, typically in an aquatic environment, as seen in frogs and fish where eggs and sperm are released into the water.
6. How do viviparous and oviparous animals differ in their reproductive strategy?
The primary difference is in how they bring forth their young. Viviparous animals, such as humans and dogs, give birth to live young that have developed inside the mother's body. In contrast, oviparous animals, like birds and reptiles, lay eggs. The embryo develops inside the egg, drawing nourishment from the yolk, and hatches outside the mother's body.
7. What does 'metamorphosis' mean in the life cycle of a frog, and why is this concept important?
Metamorphosis refers to the drastic transformation an animal undergoes from its larval stage to its adult form. In a frog's life cycle, the aquatic larva, known as a tadpole, changes into an adult frog. This concept is important because it highlights that the young of some animals can look completely different from the adults, unlike in humans where babies are born with the same basic body structure as adults.
8. How can you distinguish between budding and binary fission for your exam revision?
The main distinguishing factor is the method of division. In budding, a new organism develops from an outgrowth or 'bud' on the parent's body, as seen in Hydra. In binary fission, a single-celled organism, like an Amoeba, splits into two equal, identical daughter cells. Budding involves an outgrowth, while binary fission is a complete split of the parent organism.
