NCERT Grade 9-The Fundamental Unit of Life-Answers – MySchoolPage

NCERT Grade 9-The Fundamental Unit of Life-Answers

NCERT Solutions for Class 9 Science

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1.     Plant cell:

(a) Cell wall is present.

(b) Plastids are present.

(c) They have dictyosomes instead of golgi body.

(d) Centrosomes and centrioles are absent.

(e) Vacuoles are larger in size.

(f) Daughter cells separate from each other due to formation of cell plate.

Animal cell

(a) Cell wall is absent.

(b) Plastids are absent.

(c) They have golgi apparatus.

(d) Centrosomes and centrioles are present.

(e) Vacuoles are smaller in size.

(f) Daughter cells separate from each other due to contrition or furrow formation.

2.    Prokaryotic cell

(a) Nuclear region is not surrounded by a nuclear membrane.

(b) Nucleolus is absent.

(c) Only one chromosome.

(d) Membrane bound cell organelles are absent.

Eukaryotic cell

(a) A double layered nuclear envelope is present around the nuclear region.

(b) Nucleolus is present.

(c) More than one chromosomes are present.

(d) Membrane bound cell organelles are present.

3.    The rupture or break down of cell’s plasma membrane indicates that cell is damaged and in such condition the lysosomes of the damaged cells may burst and the digestive enzymes present inside those lysosomes would digest their own cell. This will result into death of the cell.

4.    The functions of golgi apparatus includes storage, modification and packaging of products in the vesicles. If there was no golgi apparatus for a cell then all sort of storage, modification, packaging and dispatch of materials within and outside the cell would be impossible.

5.    It is Mitochondria of the cell also k own as the power house of the cell because it synthesizes energy in the form of ATP during respiration which is vital for various life activities.

6.    The endoplasmic reticulum is of two types:

(i) Smooth endoplasmic reticulum (SER) : It is responsible for the synthesis of lipids constituting cell membrane.

(ii) Rough endoplasmic reticulum (RER) : It bears the ribosomes and is therefore responsible for the synthesis of proteins constituting cell membrane.

7.    Amoeba feeds on microorganisms (like planktons) which float on water. It develops false feet or pseudopodia to surround the food finally captures the food within a sac like structure called the food vacuole inside which digestion of food takes place.

8.    Osmosis is the movement of water(solvent) from a region of high water concentration through a semipermeable membrane to a region of low concentration of water. It can take place only in liquid medium and not in solid or gases. Example is absorption of water from soil by plant roots

9.    (i) When we put one teaspoon sugar in cup B and one teaspoon salt in cup C, the
hypertonic solution is formed inside so through osmosis water from outside enters inside and collects in the hollowed portion of cups B & C.

(ii) Potato A is necessary to observe osmosis.

(iii) In hollowed out portion of A & D there is no solution (liquid medium) present therefore osmosis cannot take place and as a result water does not gather.Potato A is necessary to observe osmosis.

10.  In 1665, an English scientist named Robert Hooke discovered cells. When he saw honey comb like structure while observing thin slice of cork under his self-designed microscope.

11.  All living organisms are made up of cells so cell is the basic building unit of a living organism and all the activities performed by a living organism are sum total of activities performed by its cells hence cell is called the structural and functional unit of life.

12.  The exchange of gases (CO2 & O2) between cells takes place by diffusion process. Diffusion is defined as movement of a substance from a region of higher concentration to lower concentration. CO2 is formed inside cell due to respiration and it accumulates in the cell so its concentration is high in the cell as compared to the surroundings. On the other hand O2 is utilized inside cell during respiration and therefore its concentration decreases inside the cell while remains comparatively high in the surroundings. As a result CO2 diffuses out and O2 diffuses into the cell.

13.  Plasma membrane is a highly specific structure. It is made up of lipids and proteins who selectively allow the entry of substance into cell and exit of some other substances from the cell i.e. selectively permeable.

14.   Prokaryotic Cell:

(i) Size: generally small (1 – 10 μm) 1 μm = 10 – 6 m

(ii) Nuclear region: not defined and known as nucleoid.

(iii) Chromosome: single

(iv) Membrane-bound cell organelles Absent.

Eukaryotic Cell

(i) Size: generally large (5 – 100 μm)

(ii) Nuclear region: well defined and surrounded by a nuclear membrane

(iii) More than one chromosome

(iv) membrane bound cell organelles are present.

15.  Chloroplast and Mitochondria.

16.  If the organisation of a cell is destroyed due to some physical or chemical influence then such cell would not survive any more as all components of that cell are digested up by its lysosomes.

17.   Lysosomes are cell organelles filled with hydrolytic (digestive) enzymes. When a cell is damaged, its lysosomes may burst out and its enzymes digest up its own cell. Due to this, we can say that lysosomes are suicide bags.

18.  Ribosomes are the sites for protein synthesis inside the cell.

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