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NCERT Class 10 Science Textbook Chapter 8 With Answer PDF Free Download
Chapter 8: How do Organisms Reproduce
Before we discuss the mechanisms by which organisms reproduce, let us ask a more basic question – why do organisms reproduce?
After all, reproduction is not necessary to maintain the life of an individual organism, unlike the essential life processes such as nutrition, respiration, or excretion.
On the other hand, if an individual organism is going to create more individuals, a lot of its energy will be spent in the process.
So why should an individual organism waste energy on a process it does not need to stay alive? It would be interesting to discuss the possible answers in the classroom!
Whatever the answer to this question, it is obvious that we notice organisms because they reproduce.
If there were to be only one, nonreproducing member of a particular kind, it is doubtful that we would have noticed its existence. It is the large numbers of organisms belonging to a single species that bring them to our notice.
How do we know that two different individual organisms belong to the same species?
Usually, we say this because they look similar to each other. Thus, reproducing organisms create new individuals that look very much like themselves.
8.1 Do Organisms Create Exact Copies OF Themselves?
Organisms look similar because their body designs are similar. If body designs are to be similar, the blueprints for these designs should be similar.
Thus, reproduction at its most basic level will involve making copies of the blueprints of body design.
In Class IX, we learned that the chromosomes in the nucleus of a cell contain information for the inheritance of features from parents to the next generation in the form of DNA (Deoxyribose Nucleic Acid) molecules.
The DNA in the cell nucleus is the information source for making proteins. If the information is changed, different proteins will be made. Different proteins will eventually lead to altered
Therefore, a basic event in reproduction is the creation of a DNA copy. Cells use chemical reactions to build copies of their DNA.
This creates two copies of the DNA in a reproducing cell, and they will need to be separated from each other.
However, keeping one copy of DNA in the original cell and simply pushing the other one out would not work because the copy pushed out would not have any organized cellular structure for maintaining life processes.
Therefore, DNA copying is accompanied by the creation of an additional cellular apparatus, and
then the DNA copies separate, each with its own cellular apparatus. Effectively, a cell divides to give rise to two cells.
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NCERT Solutions Class 10 Science Chapter 8 How do Organisms Reproduce
1. What is the importance of DNA copying in reproduction?
DNA – Deoxyribonucleic acid is the genetic material that is present in the cells of all organisms. DNA carries genetic information from one generation to the other and this helps in producing organisms of its own types. DNA copying is a must for inheriting the traits from parents. Any variations in DNA copying will give rise to the origin of new species.
2. Why is the variation beneficial to the species but not necessarily for the individual?
The reason why the variation is more beneficial to the species than individuals is that sometimes the climatic changes have a drastic effect on the species, which makes their survival difficult.
For example, if the temperature of the water body increases, then there might be certain species of microorganisms that might die. This may result in a disturbance in the environment. So, variation is beneficial to species and not for individuals.
1. How does binary fission differ from multiple fission?
When a single cell divides into two equal halves, it is known as binary fission. Bacteria and amoeba are examples of binary fission.
When a single cell divides into multiple daughter cells at the same time, it is known as multiple fission. Algae and sporozoans are examples of multiple fission.
2. How will an organism be benefit if it reproduces through spores?
Following are the ways through which an organism will be benefited if it reproduces through spores:
- The number of spores produced in one sporangium would be large.
- In order to avoid competition in one place, spores can be distributed to faraway places with the help of air.
- In order to prevent dehydration under unfavorable conditions, the spores are covered by thick walls.
3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Organisms at higher complex levels cannot give rise to new individuals through regeneration because they have an organization of their organs system at different levels.
All these organ systems are interconnected and work in full coordination. They can regenerate a few of their lost body parts like skin, blood, muscles, etc. but can’t give rise to new individuals.
4. Why is vegetative propagation practiced for growing some types of plants?
Following are the advantages of practicing vegetative propagation for growing some types of plants:
- Crops like orange, banana, and pineapple do not have viable seeds, so vegetative propagation can be used.
- It is a rapid, cheap, and easier method to grow crops.
- It can be used in places where seed germination fails.
- Good quality variety can be preserved.
5. Why is DNA copying an essential part of the process of reproduction?
DNA copying is an essential part of the process of reproduction because it carries the genetic information from the parents to the offspring.
A copy of DNA is produced through some chemical reactions resulting in two copies of DNA. Along with the additional cellular structure, DNA copying also takes place which is then followed by cell division into two cells.
How do Organisms Reproduce NCERT Textbook With Solutions PDF Free Download