Sunday, April 12, 2015

Class9 Biology chapter Cell the Fundamental unit of life :Assignment solved

1. What is plasma membrane? What are their functions?

Ans:
  • Plasma membrane also called as cell membrane, is the outer covering of a cell that separates the cell contents (protoplasm) from the surrounding medium.
  • It is made up of proteins and lipids.
  • It gives form (shape and size) to the cell
  • It maintains the individuality of the cell (i.e. seperates cells)
  • It keeps the cell contents in place
2. What are cell organelles ?

Ans: The certain specific living parts of a cell with a definite function are celled Cell organelles. All cell are found to have same organelles and together these constitute to the basic unit of life.

3. What is cellulose and its functions?

Ans: Cellulose is the main component of a plant cell wall. It is responsible for giving structural shape to the cell and also to protect the protoplasm.

4.  What is a Prokaryotic cell? Give an Example.

Ans: The cells that do not have a nuclear membrane and membrane bound cell organelles (i.e. well-defined nucleus) are known as Prokaryotic Cells.  Example:-  Blue green algae, Bacteria, Mycoplasma etc.

5. What are the advantages of multicellularity ?

Ans:
  • The division of labour in a multicellular organism increases the efficiency of the organism.
  • It increases the Chance of survival.
6. What are vacuoles? What are their functions?

Ans:
  • Vacuoles are clear fluid/gas filled spaces in the cytoplasm.
  • In plant cells, it is larger and less in number as compared to the animal cells.
  • Vacuoles help in the storage of water, food and other waste substances.
7.  What is ER ? Name two types of ER. Write its main functions.

Ans:
  • Endoplasmic Reticulum or ER, is a network of tube like structures found in the cytoplasm.
  • The two types of ER are Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER).
  • It provides channel for quick transport of materials
  • It provides materials (i.e. lipids and proteins) for membrane biogenesis.
8. Write the Function of Chromatin material.

Ans: The Chromatin material mainly consists of DNA’s, therefore plays an important role in storing and transmitting hereditary information (DNA) from one generation to another.

9. Name a cell that lacks membrane. Where is it prepared?

Ans: Ribosomes is  a cell organelle which lacks membrane and is prepared in the Nucleolus.

10. What is plasmolysis? What happens to a plasmolysed cell when it is placed in water ?

Ans:
  • The detachment of  cell membrane of the plant cell from the cell wall when put in Hypertonic Solution is known as Plasmolysis.
  • The cell that has undergone plasmolysis i.e. plasmolysed cell when placed in water, the water moves into the cell from the solution due to the higher concentration of water in the solution (Endosmosis) and therefore the cell swells.

11. What do yo mean by nucleoid?

Ans: The undefined nuclear region of prokaryotic cells like blue green algae are known as nucleoid. The nucleoid contains nucleic acid but does not have any membrane covering it.

12. What are the factors which restrict the size of the cell?

Ans: The factors which restrict the size of the cell are:
  • Functions of cell.
  • Cell’s requirement of oxygen and other materials from the environment.
  • Regulating ability of the nucleus of the cell.
13. Name the two nucleic acids present in the cell and their functions.

Ans:
  1. Ribose Nucleic Acid (RNA) – It helps in protein synthesis.
  2. Deoxyribo Nucleic Acid (DNA) – It stores heriditary information.
14. Give any two functions of plastids.

Ans:
  • Chloroplast is the site of photosynthesis  and helps in preparing food (in case of plant cells).
  • Leucoplast are the site of storage of food.
  • Chromoplast provide colour to various flowers and fruits.
15. Write down the main functions of cell wall.

Ans:
  • Cell wall provides shape as well as rigidity to the cell.
  • It protects the protoplasm.
  • It is involved in the movement of materials in and out of the cell.
  • It prevents the cell from bursting even in very dilute solution.
16. Describe in short the chief components of a nucleus.

Ans:
  • Nucleoplasm – the semi-fluid part of protoplasm lying inside the nucleus, in which nucleoli and Chromatin fibers are found.
  • Nucleolus – a dense, spherical, darkly stained structure, which the site of formation and store house of RNA’s.
  • Nuclear Membrane-  The membrane that bounds the nucleus, which semi-permeable, double layered and porous.
17.  What role does a nucleus play in cellular reproduction?

Ans: The nucleus plays the central role in the cell division/reproduction. Nucleus carry the hereditary information and it divides to form two new cell by the process of cellular reproduction. Apart from that, nucleus also plays a vital role in determining when the cell will divide.

18. Write functions of lysosomes?

Ans:
  • They take part in intracellular digestion of foreign particles.
  • They provide energy during starvation.
  • They help in defence against bacterial and viral infections.
  • They remove cellular debris.
19. Define Osmosis. In what ways it is different from diffusion?

Ans:

Diffusion

Diffusion is defined as the movement of particles from a region of high concentration to a region of low concentration.

Osmosis

Osmosis is defined as the passage of water from a region of high water concentration to a region of low concentration through a Semi-permeable membrane.

 20. Write one function each of – Ribosomes, Vacuole, Plasma Membrane

Ans:
  • Ribosomes : It helps in Protein Synthesis
  • Vacuole : They help in the storage of water, food and other waste substances.
  • Plasma Membrane : It regulates the flow materials in and out of the cell.

2 comments:

  1. Thanks for your valuable information.I found it very useful.Keep posting amazing content like this.

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    ReplyDelete
  2. Very informative for the students about Fundamental units of life.
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    ReplyDelete

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