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Life Span and Asual reproduction,  Practice Problems and FAQs

Life Span and Asual reproduction,  Practice Problems and FAQs

Do you know that the life of every organism is limited? Every organism that is born, has to die too. But then, if every organism dies then how does a species continue? It continues through the process of reproduction.

But what is reproduction? Do you think all organisms reproduce in the same way? Humans have a very complex method of reproduction but what about simple organisms like an Amoeba or a yeast? Do you think they would also reproduce the same way a human does? Of course not, because they have a much simpler body organisation. These simple organisms usually reproduce asexually with the involvement of a single parent. Let us learn more about this process in this article.

Table of contents

  • Lifespan
  • Reproduction
  • Budding
  • Binary fission
  • Multiple Fission
  • Fragmentation
  • Practice problems
  • FAQs

Lifespan

Lifespan is the time period between the birth and natural death of an organism. Every living thing has a finite lifespan. Only a few people live to be a hundred years old. Lifespan varies from organism to organism.

Lifespan of some species have been listed below:

Name of the species

Lifespan

Butterfly

1-2 Weeks

Fruit fly

1 Month

Rice plant

4 Months

Rose bush

10 Years

Crow

15 Years

Cow

25 Years

Banana plant

15 Years

Dog

12 Years

Reproduction

A biological process in which an organism gives birth to offspring of its own kind is known as reproduction. The offspring develop, mature, and generate more offspring. Because every creature has a life span, reproduction is necessary for life to continue on Earth. The biological world is diverse, and each organism has developed its unique strategy for multiplying and producing children. The habitat of the creature, its internal physiology, and a number of other elements have a role in how it reproduces.

There are two types of reproduction based on whether reproductive cells or gametes are involved in the process: Asexual and Sexual reproduction occurs

Asexual reproduction

Asexual reproduction occurs when a single parent produces children without the involvement of gamete development. It is not always applicable to single-celled organisms. A few multicellular organisms such as Planaria also reproduces through asexual reproduction.

Asexual reproduction results in the production of clones which are genetically and morphologically identical to the each other and the parent. This is because there is no fusion of gametes from different parents involved. It is further of different types such as binary fission, budding, fragmentation, spore formation etc.

Sexual reproduction

Sexual reproduction occurs when two parents of opposite sex participate in the reproductive process. It includes the fusion of gametes produced by the male and female parents. The offspring formed are genetically unique and share some similarities with the parent and with siblings but are not identical to them.


                                                 Fig: Types of reproduction

Types of asexual reproduction

Budding

Budding is a process in which some cells of the parent body grow and form a mass of cells or outgrowth called bud. This bud grows to form a new organism. In some cases, a new organism remains attached to the parent body such as yeast while in other cases, it detaches from the parent body.

Budding in Yeast

In yeast, unequal division occurs between the new organism and the parent body. A small bud remains attached to the parent body and develops into an adult organism after detaching.


                                                                      Fig: Budding in Yeast

Budding in Animals (Exogenous)

In this process, a bud grows externally or outside the parent body, grows and develops into a new organism. For example: Hydra


                                                   Fig: Exogenous budding in Hydra

Budding in Animals (Endogenous)

In this process, a bud grows internally or inside the parent body. Each bud is called a gemmule which is released from the parent’s body and develops into a new organism. For example: Freshwater or marine sponges


                                   Fig: Gemmules in Sponges

Binary fission

Binary fission is a process in which a parent cell divides into two almost equal-sized daughter cells which further develop into individual adults. Binary fission is the mode of reproduction in unicellular organisms such as bacteria, Paramecium, Amoeba, etc. when the conditions are favourable.


                                                      Fig: Binary fission in Amoeba

When unicellular organisms such as Amoeba do not have the best possible conditions or face unfavourable conditions (nutrition, water, etc. ), they enter in a process known as encystation.

Encystation

When unicellular organisms such as Amoeba do not have the best possible conditions or face unfavourable conditions (lack of nutrition, water, etc. ), they enter in a process known as encystation. During encystation, Amoeba decides to withdraw its pseudopodia and forms a cyst around itself by secreting a three-layered hard covering.


                                              Fig: Encystation in Amoeba

The encysted Amoeba multiplies by multiple fission and creates many minute amoeba or pseudopodiospores. When favourable conditions return, the cyst wall bursts and disperses the spores in the surrounding media. Each spore develops into a new adult organism.


                                                  Fig: Multiple fission in Amoeba

Types of binary fission

Binary fission is of four types:

  1. Irregular binary fission occurs in any plane. Example Amoeba
  2. Longitudinal binary fission happens along the longitudinal axis of an organism's body. Example: Euglena
  3. Transverse binary fission happens through the transverse axis of an organism’s body. Example: Paramoecium
  4. Oblique binary fission occurs in the oblique axis of the animal. Example: Ceratium

Multiple fission

Multiple fission is a process in which a parent cell divides into multiple daughter cells. In this process, the first nucleus divides to form multiple nuclei, eventually forming multiple daughter cells.

For example : Amoeba, Plasmodium


                                           Fig: Multiple fission in Plasmodium

Sporulation

Sporulation is the process by which organisms produce several haploid or diploid reproductive structures known as spores. Spores can be both sexual or asexual.

Asexual spores in algae are microscopic and motile and are known as zoospores.

Fungi produce many asexual spores such as zoospores, aplanospores, conidiospores, etc for asexual reproduction.

Fragmentation

When the body of some organisms splits into separate pieces (fragments), each of which develops into an adult, capable of producing new progeny.

For example: Planaria, Spirogyra


                                                                              Fig: Fragmentation

Fragmentation vs Regeneration

Fragmentation

Regeneration

Fragmentation is a method of asexual reproduction in which an organism reproduces by splitting into fragments, each of which matures into a separate organism.

Regeneration occurs in multicellular organisms when an organism regrows parts or limbs that have been lost due to predation or accident.

Example: Spirogyra, Planaria

Fig: Fragmentation

Example: Limbs of Salamanders, Tail of lizards

Fig: Regeneration

Practice Problems

1. Your teacher gave you X organism to study ways of asexual reproduction. This organism can reproduce by forming a bud on its body which grows to form a new individual. You named this method of asexual reproduction as A. When you cut the same organism into small fragments, each fragment forms new individual and you named this method of asexual reproduction as B. Identify X, A and B.

Solution: The process of reproduction in which an outgrowth develops on the body of an organism and develops to a new individual is called budding. Thus, A is budding.

The process of formation of new organisms from a cut fragment is known as fragmentation. Thus, B is fragmentation. Hydra is an animal that belongs to phylum Coelenterata and can reproduce both by budding and fragmentation. Thus, X is Hydra.

2. Read the given assertion and reason and select the correct option.

Assertion: Amoeba generally reproduces by binary fission.

Reason: Amoeba switches the method of reproduction as multiple fission during unfavourable conditions.

  1. Both assertion and reason are correct, reason is the correct explanation of assertion.
  2. Both assertion and reason are correct but reason is not the correct explanation of assertion.
  3. Assertion is correct, Reason is incorrect.
  4. Both assertion and reason are incorrect.

Solution: Amoeba is a protozoan which reproduces generally by binary fission, that is, the parent body divides into two daughter cells. During unfavourable conditions, it forms a cyst. As soon as conditions become favourable, the cyst wall breaks out and multiple daughter cells are released. This suggests that during unfavourable conditions, Amoeba reproduces by multiple fission. Hence, option b is correct.

3. Match the following:

Column I

Column II

  1. Transverse binary fission

I. Planaria

  1. Fragmentation

II. Marine sponges

  1. Endogenous budding

III. Paramoecium

  1. A - III, B - I, C - II
  2. A - II, B - I, C - III
  3. A - I, B - III, C - II
  4. A - III, B - II, C - I

Solution: Paramoecium reproduces by means of binary fission along the transverse axis of its body.

In Planaria reproduction occurs by means of fragmentation in which the body breaks into small fragments and each fragment develops into an adult individual.

In marine sponges a bud grows internally or inside the parent body. Each bud is called a gemmule which is released from the parent’s body and develops into a new organism. This is known as endogenous budding.

4. What are the differences between sexual and asexual reproduction?

Answer: The differences between sexual and asexual reproduction are -

Sexual reproduction

Asexual reproduction

  1. Generally two parents of opposite sex are involved.

1. Only a single parent is involved.

  1. Reproduction occurs by means of fertilisation, i.e., fusion of the male and female gametes contributed by each parent.

2. No gamete formation or fusion is involved.

  1. Offspring are genetically unique and are not identical to the parents.

3. Offspring are genetically identical to the parent.

FAQs

1. Why are unicellular organisms considered to be biologically immortal?

Answer: Unicellular organisms are said to be biologically immortal because they do not grow old and die (under normal conditions). Instead, they reproduce by cell division and divide into two daughter cells, each of which again grow into adult cells and divide. An example is Amoeba.

2. Why is asexual reproduction more economic?

Answer: Asexual reproduction is more economic because it is faster compared to sexual reproduction and hence can help the population size to increase rapidly when the conditions are favourable. As only one parent is needed, it saves the time and energy needed to find a mate.

3. How is binary fission different from mitosis?

Answer: Binary fission is a type of amitotic cell division in which the nucleus elongates and constricts followed by the constriction of cytoplasm to form daughter cells. There is no involvement of spindle fibres or chromosome division. It mostly occurs in prokaryotic organisms and few unicellular eukaryotes.

Mitosis is a type of cell division that serves as a mode of asexual reproduction in eukaryotes only. It involves spindle fibre formation and proper duplication and separation of chromosomes.

4. If asexual reproduction is more economic, why does sexual reproduction occur?

Answer: Sexual reproduction is of utmost significance because it helps to bring variations in a population. Accumulation of variations over a long period of time is majorly responsible for evolution and formation of new species (speciation). Variations also provide more adaptability to changing environments and resistance against diseases. Thus, sexual reproduction is essential.

Youtube Link: https://youtu.be/A2z2yLYbam0 

Related Topics

Post-fertilisation events in plants and animals: Introduction, Events in plants, Events in animals, Difference in Asexual and sexual reproduction, Parthenogenesis

Sexual reproduction: Overview; Phases of sexual reproduction, Types of breeders, Types of cycles (menstrual and oestrus cycle)

Vegetative propagation

 

 

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