Here we have given NCERT Solutions for Class 9 Science Chapter 5 The Fundamental Unit of Life .
|Chapter Name||The Fundamental Unit of Life|
|Number of Questions Solved||18|
NCERT Solutions for Class 9 Science Chapter 5 The Fundamental Unit of Life
Who discovered cells, and how ?
Robert Hooke discovered the cell in 1665. He examined a thin slice of cork through a self designed primitive microscope and saw that the cork resembled the structure of a honey comb consisting of many tiny compartments. He called them cells which is derived from the Latin word “cellula” meaning ‘a little room’.
Why is the cell called the structural and functional unit of life ?
All living organisms are made up of cells. Thus, cell is the structural unit of life. Each cell acquires distinct structure and function due to the organisation of its membrane and cytoplasmic organelles in the specific way. Such an organisation enables the cells to perform basic functions such as respiration, obtaining nutrition, clearing of waste material, forming new proteins etc. The cell is, therefore, the basic functional unit of living organisms.
How do substances like CO2 and water move in and out of the cell? Discuss.
CO2 moves in and out of the cells by the process of diffusion which involves movement of molecules from higher concentration to lower concentration across the cell membrane.
Water moves in and out of the cells by osmosis. Osmosis is the movement of water or solvent through a semi-permeable membrane from a solution of lower concentration of solutes to a solution of higher concentration of solutes.
Why is the plasma membrane called a selectively permeable membrane?
Plasma membrane permits the entry and exit of only selected materials in the cell. It also prevents movement of selected materials. Therefore, the plasma membrane is called a selectively permeable membrane.
Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells
The differences between prokaryotic cell and eukaryotic cell are as follows:
Can you name the two organelles we have studied that contain their own genetic material?
If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?
If the organisation of a cell gets destroyed due to any reason then lysis of the whole cell will occur due to the enzymes released by lysosomes.
Why are lysosomes known as suicide bags?
Lysosomes contain digestive enzymes that are capable of digesting the whole cell. During breakdown of cell structure, when the cell gets damaged, lysosomes digest their own cells by releasing own enzymes. Therefore, they are known as suicide bags of a cell.
Where are proteins synthesised inside the cell?
The ribosomes attached to the endoplasmic reticulum as well as present freely in the cytoplasm of all active cells are the site for the synthesis of proteins.
Make a comparison and write down ways in 2. which plant cells are different from animal cells.
Differences between plant cells and animal cells are as follows:
|Character||Plant cells||Animal cells|
|1.||Cell wall||Present outside the plasma membrane.||Absent. Outermost covering is plasma membrane.|
|3.||Vacuole||Single, large central vacuole||Many and small vacuoles|
|6.||Mitochondria||Less in number||More in number|
|7.||Golgi body||Many and scattered||Single and near the nucleus|
How is a prokaryotic cell different from a eukaryotic cell?
Differences between prokaryotic and eukaryotic cells are as follows:
|Character||Prokaryotic cell||Animal cell|
|1.||Occurrence||Found in Kingdom Monera: bacteria, blue- green algae and mycoplasma.||Found in Protista, Fungi, Plantae and Animalia.|
|2.||Incipient nucleus called nucleoid present. No nuclear membrane and nucleolus.||A true nucleus is present. Nuclear membrane and nucleolus present.|
|3.||Chromosome||Single chromosome||More than one chromosome|
|4.||Membrane bound cell organelles||Absent||Present|
|5.||Ribosomes||70 S type||80 S type|
|7.||Size||Small sized (1-10 pm)||Large sized (5-100 pm)|
|8.||Cyclosis (Streaming movement of cytoplasm)||Absent||Present|
What would happen if the plasma membrane ruptures or breaks down?
The plasma membrane acts as a mechanical barrier to the protoplasm which regulates transport of materials into and out of cell maintaining the identity of the cell. In case of rupturing of the plasma membrane, the protoplasmic contents will get dispersed in the surrounding medium and thus cell will disintegrate.
What would happen to the life of a cell if there was no Golgi apparatus?
In the absence of Golgi apparatus, the following problems will arise:
- The secretory activities. of the cell will cease to occur.
- The broken membranes like those of lysosomes, cell wall, plasma membrane, etc. will not get repaired.
- In case of sperms, acrosome formation will not take place, causing inability of sperms to enter the egg.
Which organelle is known as the power house of the cell? Why?
Mitochondrion is known as the power house of the cell. It is because the mitochondrion is the site of cellular respiration where energy in the form of ATP (adenosine triphosphate) is generated as a consequence of oxidation of carbohydrates and fats (lipids).
Where do the lipids and proteins constituting the cell membrane get synthesised?
Smooth endoplasmic reticulum (SER) helps in the manufacturing of lipids which are important for the formation of cell membrane. Ribosomes are the site for protein synthesis. The manufactured proteins are then sent to different places in the cell depending upon the need by the endoplasmic reticulum (ER).
How does an Amoeba obtain its food?
Amoeba acquires its food through endocytosis. Endocytosis involves invagina-tion of a small region of the plasma membrane and ultimately forming an intra cellular membrane bound vesicle. This process is generally involved in the ingestion of food materials. Intake of solid particles by a cell through its cell membrane is called phagocytosis or cell eating. In this process, cell membrane of Amoeba puts up protoplasmic processes around the food particle. The processes join and fuse to form phagosome.
What is osmosis?
Osmosis involves the passive flow of water or any other solvent from a region of higher water, concentration to a region of lower water concentration through a semi- permeable membrane.
Carry out the following osmosis experiment. Take four peeled potato halves and scoop 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
- Explain why water gathers in the hollowed portion of B and C.
- Why is potato A necessary for this experiment?
- Explain why water does not gather in the hollowed out portions of A and D.
1. Water gathers in B and C because in both the situations there is difference in the concentration of water in the trough and water in the potato cup. Hence endosmosis (i.e. water enters into the cell) takes place as the potato cells act as a semi-permeable membrane.
2. Potato cup A is necessary in the experiment as a ‘control’ for providing comparison with situations created in potato cups B, C and D. It indicates that the potato cavity alone does not induce any movement of water.
3. Water does not gather in hollowed out portions of A. This can be explained as follows. For osmosis to take place, a concentration gradient is necessary to develop between the two solutions on either side of a semi- permeable membrane (in this case potato strip). Here water is present only on one side i.e., convex side of potato cup whereas concave side of the cup is empty. Water will fill in the concavity only on account of endosmosis that can take place when some solution having concentration higher than that of water is present it. Hence, the hollowed out portion of A remained empty. In cup D cells become dead due to boiling, hence semi permeability of membrane is lost so no osmosis will take place in it.