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Reproduction - Asexual Reproduction

Grade 9CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Asexual reproduction involves a single parent without the fusion of gametes. The offspring produced are genetically identical to the parent and are often referred to as 'clones'.

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Binary Fission: The parent organism splits into two equal halves. In Amoeba, splitting can occur in any plane, whereas in Leishmania, it occurs in a definite orientation in relation to the whip-like structures.

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Multiple Fission: The parent cell divides into many daughter cells simultaneously. This is seen in organisms like Plasmodium (the malarial parasite) during unfavorable conditions.

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Fragmentation: Multicellular organisms with relatively simple body organization (e.g., Spirogyra) simply break up into smaller pieces upon maturation, each growing into a new individual.

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Regeneration: If an organism like Hydra or Planaria is cut into pieces, each piece can grow into a complete organism using specialized cells that proliferate and make large numbers of cells.

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Budding: A small outgrowth or 'bud' forms on the parent body due to repeated cell division at one specific site. In Hydra, this bud matures and detaches to become an independent individual.

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Vegetative Propagation: New plants are developed from vegetative parts like roots, stems, or leaves. Examples include Bryophyllum (leaves), Money Plant (stem), and Sweet Potato (roots).

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Spore Formation: In Rhizopus (bread mould), thick-walled structures called spores are produced within sporangia. These spores are resistant to harsh environments and germinate when they find a moist surface.

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Tissue Culture: This involves removing tissues or cells from the growing tip of a plant and placing them in an artificial medium containing nutrients and hormones to grow a large number of plants (clones) in disease-free conditions.

📐Formulae

N=N0×2nN = N_0 \times 2^n

where N=Total number of individuals after n generations\text{where } N = \text{Total number of individuals after } n \text{ generations}

N0=Initial number of individualsN_0 = \text{Initial number of individuals}

n=Number of cycles of binary fissionn = \text{Number of cycles of binary fission}

💡Examples

Problem 1:

If a single Amoeba undergoes binary fission every 2020 minutes, calculate the total number of individuals produced after 22 hours.

Solution:

n=120 minutes20 minutes=6n = \frac{120 \text{ minutes}}{20 \text{ minutes}} = 6 N=1×26=64N = 1 \times 2^6 = 64

Explanation:

In binary fission, the population doubles every cycle. Since 22 hours equals 120120 minutes, there are 66 cycles of division. Using the formula N=2nN = 2^n, we get 26=642^6 = 64.

Problem 2:

A scientist observes a culture of 10001000 bacteria. If the population doubles through asexual reproduction every hour, how many bacteria will be present after 33 hours? Show the calculation using vertical addition for the growth steps.

Solution:

Initial=1000\text{Initial} = 1000 After 1 hour: 1000+1000=2000\text{After 1 hour: } 1000 + 1000 = 2000 After 2 hours: 2000+2000=4000\text{After 2 hours: } 2000 + 2000 = 4000 After 3 hours: 4000+4000=8000\text{After 3 hours: } 4000 + 4000 = 8000 4000+40008000\begin{array}{r} 4000 \\ + 4000 \\ \hline 8000 \end{array}

Explanation:

Since asexual reproduction (binary fission) results in doubling, we add the current population to itself for every hour elapsed. After 33 hours, the population reaches 80008000.