Which one of the two multicellular organisms — Spirogyra and Planaria reproduces by regeneration and why ? Give an example of any other organism which can also reproduce by the same process.
Which one of the two multicellular organisms — Spirogyra and Planaria reproduces by regeneration and why ? Give an example of any other organism which can also reproduce by the same process.
Planaria reproduces by regeneration.
Why:
Planaria is a fully differentiated organism with specialised cells that have the capacity to proliferate and make large numbers of cells. From this mass of cells, different cells undergo changes to become various cell types and tissues in an organised sequence referred to as development. Thus, if Planaria is cut into pieces, each piece can grow into a complete new individual.
In contrast, Spirogyra has a very simple multicellular body design and reproduces by fragmentation, where it simply breaks up into smaller pieces upon maturation, and these pieces grow directly into new individuals without requiring specialised regenerative cells.
Other Organism:
Hydra is another organism that can also reproduce/regenerate by the same process.
Marking Scheme
- 1Identifying Planaria as the organism that reproduces by regeneration. (0.5 marks)
- 2Explaining the mechanism of regeneration (specialised cells, proliferation, and organized development/differentiation). (1 mark)
- 3Providing Hydra as another example of an organism capable of regeneration. (0.5 marks)
Hint
Think about which organism has specialized regenerative cells that proliferate and differentiate. Remember that Spirogyra simply breaks into fragments upon maturation.
Quick Oral Answer
Planaria reproduces by regeneration because it contains specialised cells that can proliferate and differentiate into all the required cell types. Another example is Hydra.
Analysis & Explanation
Regeneration and fragmentation are often confused.
- Fragmentation occurs in simple multicellular organisms like Spirogyra where the body simply breaks into pieces upon maturation, and each piece grows into a new filament. No specialized cells are involved.
- Regeneration occurs in more complex, fully differentiated organisms like Planaria and Hydra. It relies on specialized regenerative cells that proliferate and undergo a structured developmental pathway to recreate lost tissues and organs. However, as noted in the text, regeneration is not the same as normal reproduction because organisms do not typically rely on being cut up to reproduce.
Common Mistakes
- 1Stating that Spirogyra reproduces by regeneration instead of fragmentation.
- 2Failing to mention the role of 'specialised cells' and 'differentiation/development' when explaining why Planaria undergoes regeneration.
Interesting Facts
If a Planaria is cut lengthwise or crosswise into multiple pieces, each piece retains the polarity of the original body and grows a new head and tail in the correct orientation!
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2022?
This question carries 2 marks in the CBSE Class 10 Science 2022 examination.
Which chapter does this question come from in Science?
This question is from the chapter "How do Organisms Reproduce?" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Regeneration" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2022 paper?
This is a Short Answer question from Section A in the CBSE Class 10 Science 2022 paper.