CBSE Class IX ( 9th) Science | Chapter 5. THE FUNDAMENTAL UNIT OF LIFE | Lesson Exercises

CBSE Class IX ( 9th) Science | Chapter 5. THE FUNDAMENTAL UNIT OF LIFE | Lesson Exercises

Question 1. Make a comparison and write down ways in which plant cells are different from animal cells.

Answer :

Comparison Between Plant Cells & Animal cells
Plant Cells	Animal Cells
Plant cells have one, large central vacuole occupying almost 90% of cell volume. Plant cells have Plastids. Plant cells have Cell wall and a cell membrane. In plant cells, Lysosomes usually not evident. Plant cells generally do not have Cilia. Plant cells have round (irregular) Plant cells have chloroplasts because they make their own food	Animal cells have one or more small vacuoles (much smaller than plant cells). Animal cells do not have Plastids Animal cells have a cell membrane only In Animal cells, Lysosomes occur in cytoplasm. Animal cells have Cilia Animal cells have rectangular (fixed shape) Animal cells don't have chloroplasts

Question 2. How is a prokaryotic cell different from a eukaryotic cell?

Answer :

Difference Between Prokaryotic Cell & Eukaryotic Cell
Prokaryotic Cell	Eukaryotic Cell
Prokaryotes cell lacks a nuclear membrane Prokaryotic cell has no membrane-bound cytoplasmic organelles.  Prokaryotes cell does not have Golgi            apparatus Prokaryotes cells does not have endoplasmic reticulum In Prokaryotes cells, Chloroplasts is absent Prokaryotes cells does not have Cytoplasmatic structure Prokaryotes cells are usually single cells, examples bacteria, archaea In Prokaryotic cells many of the functions of such organelles are also performed by poorly organised parts of the cytoplasm The chlorophyll in photosynthetic prokaryotic bacteria is associated with membranous vesicles In Prokaryotic cells reproduction is always asexual.	Eukaryotic cell has a nuclear membrane Eukaryotic cell has a membrane-bound cytoplasmic organelles. Eukaryotic cell has a Golgi apparatus Eukaryotic cell has an endoplasmic reticulum  In Eukaryotic cell,  Chloroplasts is present Eukaryotic cell has cytoplasmatic structure Eukaryotic cell can be single cells, colonies, higher multicellular organisms with specialized cells, examples protists, fungi, plants, animals etc In Eukaryotic cells many of the functions of such organelles are also performed by well organised parts of the cytoplasm The chlorophyll in photosynthetic Eukaryotic cell is associated with plastids  In Eukaryotic cells reproduction may be sexual or asexual

Question 3. What would happen if the plasma membrane ruptures or breaks down?

Answer : This is the outermost covering of the cell that separates the contents of the cell from its external environment. The plasma membrane allows or permits the entry and exit of some materials in and out of the cell. It also prevents movement of some other materials. Thus, the cell membrane, acts like a selectively permeable membrane which regulates the movement of materials between the ordered interior of the cell and the outer environment.

In case, if it gets ruptured and broken, lysosomes may burst and the enzymes digest their own cell. Structurally, lysosomes are membrane-bound sacs filled with digestive enzymes. Lysosomes are a kind of waste disposal system of the cell. Lysosomes help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles.

Question 4.  What would happen to the life of a cell if there was no Golgi apparatus?

Answer : The Golgi apparatus consists of stacks of membrane-bound vesicles that function in the storage, modification and packaging of substances manufactured in the cell. The material synthesised near the endoplasmic reticulum is packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus. In the absence of Golgi apparatus, a cell would have no network to processed nutrition and use it for growth, hence no cellular life.

Question 5. Which organelle is known as the powerhouse of the cell? Why?

Answer : Mitochondria are known as the powerhousesof the cell. Because, the energy required for various chemical activities needed for life is released by mitochondria in the form of ATP(Adenosine triphopshate) molecules. ATP is known as the energy currency of the cell. The body uses energy stored in ATP for making new chemical compounds and for mechanical work. Mitochondria have two membrane coverings instead of just one. The outer membrane is very porous while the inner membrane is deeply folded. These folds create

a large surface area for ATP-generating chemical reactions. Mitochondria are strange organelles in the sense that they have their own DNA and ribosomes. Therefore, mitochondria are able to make some of their own proteins.

Question 6. Where do the lipids and proteins constituting the cell membrane get synthesised?

Answer : The lipids and proteins constituting the cell membrane get synthesised by the process of membrane biogenesis at smooth endoplasmic reticulum (SER) and rough endoplasmic reticulum (RER) respectively. Both are a large network of membrane-bound tubes and sheets. It looks like long tubules or round or oblong bags (vesicles). The SER helps in the manufacture of fat molecules, or lipids, important for cell function .The RER contains particles called ribosomes attached to its surface The ribosomes, which are present in all active cells, are the responsible for manufacturing of protein.The manufactured proteins are then sent to various places in the cell depending on need, using the ER (endoplasmic reticulum).

Question 7. How does an Amoeba obtain its food?

Answer : An Amoeba obtain its food by using the process of endocytosis in which the flexibility of the cell membrane enables the cell to engulf in food and other material from its external environment.

Question 8. What is osmosis?

Answer : Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration. Through osmosis, the plasma membrane allows or permits the entry and exit of some materials in and out of the cell. It also prevents movement of some other materials. Unicellular freshwater organisms and most plant cells tend to gain water through osmosis. Absorption of water by plant roots is also an example of osmosis.

Osmosis is of great importance in biological processes where the solvent is water. The transport of water and other molecules across biological membranes is essential to many processes in living organisms. The energy which drives the process is usually discussed in terms of osmotic pressure

Question 9. Carry out the following osmosis experiment:

Take four peeled potato halves and scoos each one out to make potato cups. One of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water.

Now,

(a) Keep cup A empty

(b) Put one teaspoon sugar in cup B

(c) Put one teaspoon salt in cup C

(d) Put one teaspoon sugar in the boiled potato cup D.

Keep these for two hours. Then observe the four potato cups

and answer the following:

(i) Explain why water gathers in the hollowed portion of B and C.

Answer : Water gathers in the hollowed portion of B and C due to process of Osmosis in which outside water with high concentration make a passage through a semi-permeable membrane of potato to mix with salt or sugar with low water concentration inside the potato.

(ii) Why is potato A necessary for this experiment?

Answer : Because its cells have a selectively permeable membrane, which allows or permits the entry and exit of some materials in and out of the cell using the process of Osmosis.

(iii) Explain why water does not gather in the hollowed out portions of A and D.

Answer : Water does not gather in the hollowed out portions of A and D because cup A is empty and there is no difference in concentration of water hence no osmosis will take place. Where as in in cup D, due to boiling of potato, its selectively permeable membrane has been destroyed so there will be no water accumulation due to osmosis.