Maharashtra Board Class 10 Science Part 2 Chapter 3 Life Processes in Living Organisms Part 2 PDF Download

Life Processes in Living Organisms Part - 2

Reproduction: Asexual and Sexual reproduction.

Reproduction and modern technology

Reproductive health

Population Explosion

Important Questions

1. Which are the important life processes in living organisms?

2. Which life processes are essential for production of energy required by body?

3. Which are main types of cell-division? What are the differences?

4. What is the role of chromosomes in cell-division?

We have studied various life processes in previous classes. All those life processes i.e. nutrition, respiration, excretion, sensation and response (control and co-ordination), etc. are essential to each living organism to remain alive. Besides these life processes, one more life process occurs in living organisms; it is reproduction. However, reproduction does not help the organism to remain alive but it helps to maintain the continuity of the species of that organism.

Can You Tell?

1. What do we mean by maintenance of species?

2. Whether the new organism is genetically exactly similar to earlier one that has produced it?

3. Who determines whether the two organism of a species will be exactly similar or not?

4. What is the relationship between the cell division and formation of new organism of same species by earlier existing organism?

Formation of new organism of same species by earlier existing organism is called as reproduction. Reproduction is one of the various important characters of living organisms. It is also one of the various reasons responsible for evolution of each species. In living organisms, reproduction occurs mainly by two methods. Those two methods are- asexual and sexual reproduction.

Asexual Reproduction

Observe

Observe the pictures and tell the life process which you identified.

Process of formation of new organism by an organism of same species without involvement of gametes is called as asexual reproduction. As this reproduction does not involve union of two different gametes, the new organism has exact genetic similarity with the reproducing organism. This is uniparental reproduction and it occurs by mitotic cell division. Absence of genetic recombination is a drawback whereas fast process is advance of this reproductive method.

Teacher's Note

Asexual reproduction is like making copies. When a potato grows eyes, each eye can grow into a new potato plant - just like one potato becomes many potatoes without needing a second plant.

Exam Trick

Remember: Asexual = one parent. Sexual = two parents. Think of it like this - one parent alone can do asexual reproduction, but sexual reproduction needs a couple.

Points to Remember

Asexual reproduction needs only one parent.

New organisms are exactly like the parent organism.

It happens through mitosis, not meiosis.

No mixing of genes happens in asexual reproduction.

A. Asexual Reproduction in Unicellular Organisms

1. Binary Fission

Try This

Activity 1: Take a conical flask and collect the water in it from a pond having stagnant water and aquatic plants. Add some wheat grains and aquatic plants to it. Keep it for 3 to 4 days so that wheat grains and plants will decompose. Early in the morning on fourth day, take a glass slide and put a drop of that water over it. Carefully, put a cover-slip on that drop and observe under compound microscope.

You will be able to see many paramecia performing the binary fission.

Prokaryotes (Bacteria), Protists (Amoeba, Paramoecium, Euglena, etc.) and eukaryotic cell-organelle like mitochondria and chloroplasts perform asexual reproduction by binary fission. In this process, the parent cell divides to form two similar daughter cells. Binary fission occurs either by mitosis or amitosis.

Axis of fission or division is different in different protists. For example: Amoeba divides in any plane due to lack of specific shape; hence it is called as simple binary fission. Paramoecium divides by transverse binary fission whereas Euglena by longitudinal binary fission.

Binary fission is usually performed by living organisms during favorable conditions i.e. availability of abundant food material.

2. Multiple Fission

Asexual reproduction by multiple fission is performed by Amoeba and other similar protists. Amoeba stops the formation of pseudopodia and thereby movements whenever there is lack of food or any other type of adverse condition. It becomes rounded and forms protective covering around plasma membrane. Such encysted Amoeba or any other protist is called as cyst.

Many nuclei are formed by repeated nuclear divisions in the cyst. It is followed by cytoplasmic division and thus, many amoebulae are formed. They remain encysted till there are adverse conditions. Cyst breaks open on arrival of favorable conditions and many amoebulae are released.

Teacher's Note

Binary fission is like splitting one amoeba into two amoebas. When food is plenty, the amoeba divides quickly - just like one cell becomes two cells in a few hours.

Exam Trick

Remember: Binary = two. One cell becomes two cells. Binary fission = cell cuts into two halves.

Points to Remember

Binary fission means one cell divides into two cells.

Different organisms divide in different ways.

Multiple fission makes many daughter cells at once.

Cyst helps organisms survive in bad conditions.

3. Budding

Try This

Activity 2: Bring the active dry yeast powder from market. Take 50 ml lukewarm water in a conical flask. Add 5 gm of active dry yeast powder and 10 gm table sugar to that water and mix well the mixture. Keep the flask in warm place and after an hour take a drop of that mixture on a clean glass slide. Put a cover-glass on that drop and observe it under the compound microscope.

You will see the yeast cells performing budding i.e. a small bud coming out of many parent cells. Asexual reproduction occurs by budding in yeast- a unicellular fungus. Yeast cell produces two daughter nuclei by mitotic division, so as to reproduce by budding. This yeast cell is called as parent cell. A small bulge appears on the surface of parent cell. This bulge is actually a bud. One of the two daughter nuclei enters this bud. After sufficient growth, bud separates from the parent cell and starts to live independently as a daughter yeast cell.

Teacher's Note

Budding is like a balloon growing from yeast. A small bump forms on the yeast cell and grows bigger until it becomes a new yeast cell - like how a baby grows from its parent.

Exam Trick

Remember: Budding = like grapes on a vine. A small bud grows out and then falls off to become a new organism.

Points to Remember

A small bud grows out from the parent cell.

Yeast cells reproduce by budding.

The bud gets one daughter nucleus.

The bud separates and lives as a new cell.

B. Asexual Reproduction in Multicellular Organisms

1. Fragmentation

This type of asexual reproduction occurs in multicellular organisms. In this type of reproduction, the body of parent organism breaks up into many fragments and each fragment starts to live as an independent new organism. This type of reproduction occurs in algae like Spirogyra, and sponges like Sycon.

Whenever there is plenty of water and nutrients are available to Spirogyra, its filaments grow up very fast and break up into many small fragments. Each fragment starts to live independently as a new Spirogyra fiber. If the body of Sycon breaks up accidentally into many fragments, each fragment develops into new Sycon.

2. Regeneration

You may know that the wall lizard breaks up and discards some part of its tail in emergency. Discarded part is regenerated after a period. This is an example of limited regeneration. However, under certain situations, an animal- Planaria breaks up its body into two parts and thereafter each part regenerates remaining part of the body and thus two new Planaria are formed. This is called as regeneration.

Teacher's Note

Fragmentation is when a starfish loses an arm and the arm grows back into a new starfish. In India, when a plant piece falls in soil, it can grow into a new plant.

Exam Trick

Remember: Fragmentation = breaking into pieces. Each piece becomes a new organism. Like breaking a chocolate bar into pieces - each piece is still chocolate.

Points to Remember

Body breaks into many small pieces.

Each piece grows into a new organism.

Spirogyra and sponges use this method.

It needs favorable conditions like water and food.

This is a preview of the first 3 pages. To get the complete book, click below.