Please refer to The Fundamental Unit of Life Class 9 Science Notes and important questions below. The Class 9 Science Chapter wise notes have been prepared based on the latest syllabus issued for the current academic year by CBSE. Students should revise these notes and go through important Class 9 Science examination questions given below to obtain better marks in exams
The Fundamental Unit of Life Class 9 Science Notes and Questions
The below Class 9 The Fundamental Unit of Life notes have been designed by expert Science teachers. These will help you a lot to understand all the important topics given in your NCERT Class 9 Science textbook.
Refer to Chapter 5 The Fundamental Unit of Life Notes below which have been designed as per the latest syllabus issued by CBSE and will be very useful for upcoming examinations to help clear your concepts and get better marks in examinations.
1. All the living organisms are made up of fundamental unit of life called “ cell”.
2. The cell is a Latin word for “a little room”.
3. The scientist Robert Hooke saw a little room in the cork (the bark of a tree) resembled the structure of a honeycomb. The use of the word “Cell” to describe these units is used till this day in Biology as” Cell Biology”.
4. The Compound Microscope consist eye piece,objective lens and condenser to observe a cell after putting a drop of Safranin (for plant cell) and methylene blue (for animal cell). 5. The scientist Leeuwenhoek saw free living cells in the pond water for the first time (father of microbiology)
6. The scientist Robert Brown discovered the nucleus in the cell.
7. The cell theory states that all the plants and animals are composed of cells, it was proposed by Schleiden and Schwann.
8. The cell theory was further expanded by Virchow by suggesting that “all cells arise from the pre-existing cells”.
9. The cells differ in size, shape, structure (Please refer to Fig. 5.2/5.3: Onion peel/Various cells in Human body, NCERT Book Page-57/58): Types of cells: Onion cells, Smooth muscle cell, Blood cells, Bone cell, Fat cell, Nerve cell, Ovum, Sperm etc. Each kind of cell performs specific function.
10. A single cell may constitute a whole organism as in Amoeba, Chlamydomonas, Paramecium and Bacteria; these are called as unicellular organisms. Whereas in multi-cellular organisms (Human beings) division of labor is seen.
11. The feature in almost every cell is same: Plasma membrane, nucleus and cytoplasm.
12. Plasma membrane: It is the outermost covering of the cell.
- It is called as selective permeable membrane (because it prevents movement of some materials).
- It helps in diffusion and osmosis
- Diffusion: movement of substance from high concentration to low concentration.
Eg; exchange of carbon dioxide or oxygen with external environment.
Osmosis: it is the passage of water from the region of high water concentration to a region of low water concentration through a selective permeable membrane.
a) The cell gains water, if the medium surrounding the cell has a higher water concentration (Hypotonic solution) than the cell.
b) The cell maintains the same water concentration as the cell (Isotonic solution), water crosses the cell membrane in both directions.
c) The cell loses water, if the medium has lower water concentration (Hypertonic solution) than the cell.Note – The cell drinking is endosmosis;
omission of water is called ex-osmosis.
13. The cell engulfs food is called endocytosis and ejects solid is called exocytosis. Amoeba acquires food through endocytosis and excretion of solid is called exocytosis.
14. The cell wall is a rigid outer covering composed of cellulose. It provides structural strength to plant cells. When a living cell loses water, there is shrinkage of contents of a cell away from the cell wall. This phenomenon is called as plasmolysis. The cell walls permit the cells of plants, fungi and bacteria to withstand very dilute (Hypotonic) external media without bursting.
15. The Nucleus: It is a dark colored, spherical or oval, dot-like structure near the center of a cell called Nucleus. The nucleus plays a central role in cellular activities/reproduction. The chromatin material gets organized into chromosomes. The chromosomes containinformation for inheritance of features from parents to next generations in the form of DNA (Deoxyribo Nucleic Acid ) and protein molecules. The functional segments of DNA are called genes. 16. In some organisms like Bacteria nucleus is not covered by nuclear membrane. Hence it is called as prokaryote. (Pro= primitive; karyote = karyon = nucleus.) The organisms with cells having a nuclear membrane are called eukaryotes
17. Differences between prokaryotes and eukaryotes
|Size: generally small (1-10 µm)||Size: generally large. (5-500 µm)|
|Nuclear region: Not well defined and not surrounded by a nuclear membrane & known as nucleoids.||Nuclear region: Well defined and surrounded by a nuclear membrane|
|Chromosome: Single||Chromosome: More than one Chromosome|
|Membrane-bound cell organellesAbsent||Membrane-bound cell organellespresent|
|Eg- bacteria, blue green algae||Eg fungi, plant cell and animal cell.|
18. Cell organelles: Every cell has fluid matrix (other than nucleus) is called cytoplasm. The nucleus and cytoplasm is together called as protoplasm. The protoplasm term was coined by Purkinje. It has important cell organelles: Endoplasmic Reticulum (ER), Golgi apparatus, Lysosomes, Mitochondria, Plastids, and vacuoles.
19. Endoplasmic Reticulum (ER): It is a large network of membrane –bound tubules and vesicles.
- There are two types of Endoplasmic Reticulum
- Rough Endoplasmic Reticulum (RER) (It looks rough because Ribosome’s are attached to its surface. They are the sites of protein synthesis).
- Smooth Endoplasmic Reticulum (SER) (It looks smooth because Ribosome’s are not attached to its surface. They are the sites of fat molecules synthesis).
1. SER; help in the functioning of enzymes and hormones to carryout biochemical activities.
2. SER detoxifies many poisons and drugs from the cell.
3. ER serves as channel for the transport of material between various regions of the cytoplasm and the nucleus.
4. Proteins and fat molecules produced by ER helps in membrane biogenesis.
21. Lysosomes: They contain membrane-bound sacs with powerful digestive enzymes (enzymes are made by RER) to digest the worn-out cell organelles. When the cell gets damaged, lysosomes may burst and the enzymes digest their own cell, hence called as “Suicidal bags of a cell”. It is a waste disposal system of the cell.
22. Mitochondria: It is covered by a double membrane. Outer membrane is very porous and the inner membrane is deeply folded. These folds create a large surface area for ATP (Adenosine Triphosphate) molecule synthesis. ATP is the energy currency of a cell; hence the Mitochondria are called as Power House of a Cell. Mitochondria have their own DNA and Ribosome’s; therefore they can make their own proteins.
23. Plastids: They are present only in plant cells. They are of two types.
1. Chromoplasts (Colored Plastids: Chloroplasts – Green pigmented and useful in Photosynthesis and also contains various other pigments like yellow or orange)
2. Leucoplasts (White or colorless plastids; stores materials such as oils, proteins, fats etc. ) Plastids are also covered by a double membrane. The matrix is called Stroma, seat for enzymatic actions. Plastids have their own DNA and Ribosome’s; therefore they can make their own proteins.
24. Vacuoles: Storage sacs for solid or liquid contents. They are small in size in animals while plants have large, may occupy 50-90 % of the cell volume. Helps to provide turgidity and rigidity to the cell. Many substances like amino acids, sugars, organi acids and proteins are stored in vacuoles. In Amoeba food vacuole is specialized to play an important role.
25. Cell: It is the fundamental structural unit of living organisms, helps in respiration, obtaining nutrition and clearing waste material or forming a new protein.
Differences between Plant cell and Animal Cell
|ANIMAL CELL||PLANT CELL|
|Cell wall absent||Cell wall present|
|Plasma membrane is the outer layer which provides turgidity to the cell||Cell wall is the outer layer which gives rigidity and turgidity to the cell|
|Vacuoles are small in size||Vacuoles are big in size|
|Plastids are absent||Plastids are present|
|Nucleus lies in the centre.||Nucleus lies on one side|
Questions for Class 9 Science Chapter 5 The Fundamental Unit of Life
Question. What is the function of ribosome?
Ans : Ribosome helps in protein synthesis.
Question. What is the function of cell wall and plasma membrane?
Ans : Cell Wall : Gives rigidity, shape and protection to plant cell.
Cell Membrane : Allows only selected materials to move in and out of the cell.
Question. Give the function of nuclear membrane.
Ans : The nuclear membrane present as outer covering of nucleus allows transfer of material inside and also out of the nucleus to cytoplasm.
Question. Write the functions of cell wall in plant cell.
Ans : (i) It provides rigidity and strength to the cell.
(ii) It gives a definite shape to the cell.
(iii) It withstands the osmotic pressure which is developed by cell contents.
(iv) It protects the inner cell organelles bounding the cell from outside.
Question. How many types of proteins are present in cell structure?
Ans : There are two types of protein molecules : intrinsic proteins, which completely covers the lipid bilayer and extrinsic proteins, which occur either on the outer surface or on the inner surface of the lipid membrane.
Question. What are vacuoles?
Ans : Vacuoles are fluid-filled structures surrounded by a membrane. The fluid in the vacuoles is called cell sap.
In animal cells, either they are absent or are very small in size.
Question. List any six functions of nucleus of a cell.
Ans :(i) Nucleus plays a central role in cellular reproduction.
(ii) It plays an important role in determining the way the cell will develop.
(iii) It also determines what form the cell will exhibit at maturity.
(iv) It contains chromosome thus inherits characters.
(v) It is the control centre of the cell.
(vi) It directs chemical activities of the cell.
Question. Name some organelles which are found only in animal cells and those which occur only in plant cells.
Ans : (i) Structures found only in animal cells : centrosomes, lysosome.
(ii) Structures found only in plant cells : cell wall, plastids and big vacuoles.
Question. (i) What will happen when eukaryotic cells are placed in hypotonic solution?
(ii) What will happen if eukaryotic cells are placed in hypertonic solution?
(iii) What will happen if eukaryotic cells are placed in isotonic solution?
(i) When eukaryotic cells are placed in hypotonic solution, the water molecules will enter into the cell and the cell will swell up.
(ii) If eukaryotic cells are placed in hypertonic solution, the water molecules will come out of the cell and the cell will shrink.
(iii) If the eukaryotic cell is placed in isotonic solution, the amount of water molecule will remain the same; it will neither move out nor will go inside.
The cell will remain same sized.
Question. What is endoplasmic reticulum? Write its main functions.
Ans : Endoplasmic reticulum is a network, enclosing a fluidfilled lumen. Its main functions are :
(i) Synthesis of proteins (rough ER).
(ii) Synthesis of lipids and other metabolic products and their secretion (SER).
(iii) Helps in formation of cell plate and nuclear membrane during cell division.
(iv) ER also produces substance for new cellular parts (especially cell membrane).
(v) ER provides internal support to the colloidal cytoplasmic matrix of the cell.
Question. Write a note on the structure of cell.
Ans : (a) Cell is the basic unit of all living organisms. It is surrounded by an outer selectively permeable Plasma Membrane. Plant cells have an additional covering called “cell wall” outer to the Plasma Membrane.
(b) Inside the plasma membrane there is a translucent viscous substance the cytoplasm in which the organelles are embedded. The control centre of the cell is the nucleus; it contains all the information necessary for the cell to function and to reproduce. Surrounding the nucleus is the endoplasmic reticulum (ER) on which ribosomes may be embedded. Ribosomes are granular structures which are the site of protein synthesis.
(c) The powerhouse of cell is the mitochondria.It helps in releasing energy by the oxidation of food in cell. There are flat membranous secretory structures in the cell called the Golgi bodies. In plant cells, an additional structure located near the nucleus called the chloroplast, is also present. They are the site of photosynthesis.
(d) Cells also contain lysosomes which are also called suicide bags. They digest and remove the unwanted debris of the cell. Centriole located near the nucleus helps in cell division. Cytoplasm also contains vacuoles filled with the cell sap. In plant cells, vacuole is large and centrally placed.
Question. Describe the role played by the lysosomes. Why are these termed as suicidal bags? How do they perform
Functions of lysosomes :
1. Extracellular digestion. Sometimes lysosome enzymes are released outside the cell to break down extracellular material.
2. Digestion of foreign material. Lysosome also destroys any foreign material which enters inside the cell such as bacteria.
3. Cellular digestion. In damaged cells, ageing cells or dead cells lysosomes get ruptured and enzymes are released. These enzymes digest their own cell. Lysosomes contain about 40 hydrolytic enzymes.
When the cell gets damaged, lysosomes burst and their enzymes digest their own cell. So, lysosomes are called ‘suicide bags’.
Question. What types of enzymes are present in the lysosomes?
What is their function? Which organelle membranes manufacture these enzymes?
Ans : Lysosomes contain powerful digestive enzymes capable of breaking down all organic material.
Lysosomes help to keep the cell clean by digesting worn out cell organelles and foreign material such as bacteria or food.
RER (Rough Endoplasmic Reticulum) makes the digestive enzymes present in the lysosomes.
Question. Name the cell organelle which are known as :
1. Control centre of the cell
2. Demolition squads/suicidal bags of the cell
3. Export firms
4. Powerhouse of the cell
5. Kitchen of the cell
6. Internal transport system
3. Golgi bodies
6. Endoplasmic reticulum
Question. Give brief introduction of Prokaryotic and Eukaryotic cell.
Ans : Prokaryotic cell :
1. Cell size is generally small.
2. Only a single chromosome is present.
3. Nucleolus is absent.
4. Cell division takes place by fission or budding.
Eukaryotic cell :
1. Cell is generally large.
2. More than one chromosome is present.
3. Nucleolus is present.
4. Cell division takes place by mitotic or meiotic.
Question. Explain endocytosis.
Ans : Endocytosis is the ingestion of material by the cells through the plasma membrane. It is a collective term that describes three similar processes : phagocytosis (cell eating), potocytosis (cell drinking) and receptormediated endocytosis. These processes are pathways to specifically internalize solid particles, small molecules and macromolecules, respectively.
74. Why do plant cells have more in number and big-sized vacuoles as compared to the animal cells?
Ans : Plants cells attain turgidity and rigidity due to the more number of vacuoles as well as large-sized vacuoles help the plant cells to withstand the wear and tear, external environmental conditions. They also help in the storage of essential material required by plants for their growth like amino acids, sugar and various organic substances.
Question. Give difference between ribosome and centrosome.
(i) It is found in both animal cell and plant cell.
(ii) These are dense, spherical and granular particles which occur freely in the matrix or remain attached to the endoplasmic reticulum.
(i) Centrosome is found only in animal cells.
(ii) It consists of two granules like centrioles.
Question. (i) Name the organelle which provides turgidity and rigidity to the plant cell. Name any two substances which are present in it.
(ii) How are they useful in unicellular organisms?
Ans : (i) Plant cells have big vacuoles full of cell sap that provide them turgidity and rigidity. Plant vacuoles store amino acids, sugars, various organic acids and some proteins.
(ii) In unicellular organism they may serve the following purposes :
1. Forming food vacuoles : In single celled organisms like amoeba, the food vacuole contains the food items that the amoeba has ingested. The food items are digested by the enzymes later on.
2. Removal of excess water and wastes : In some unicellular organisms, specialized vacuoles play important roles in expelling excess water and some wastes from the cell.
Question. Give difference between light and electron microscope.
Light microscope :
(i) It uses glass lenses.
(ii) It uses a beam of light to illuminate the object.
(iii) Internal vacuum is not required.
Electron microscope :
(i) It uses electromagnets.
(ii) It uses a beam of electrons instead of light.
(iii) Internal vacuum is essential.
Question. What are genes?
Ans :ene is a part of DNA. They are located on chromosomes in linear fashions. One gene may perform one or more function. Genes are carrier of genetic character.
Question. Name the cleaning organelle in the cell.
Ans : Lysosomes.
Question. What is the full form of DNA?
Ans : DNA (Deoxyribose Nucleic Acid).
Question. Name the cell organelle which helps in the formation of lysosome.
Ans : Golgi apparatus.
Question. Why are plasma membrane called selectively permeable membrane?
Ans : Plasma membrane allows to go in and out some materials to and from the cell. It also prevents movement of some other materials. So, it is called selectively permeable membrane.
Question. What are ribosomes? Where are ribosomes located in the cell? What is their function?
Ans : Ribosomes are spherical organelles present in the cell which are either freely distributed in the cytoplasm or may be attached to the endoplasmic reticulum. It has ribosomal RNA (Ribonucleic acid) and proteins. It helps in protein synthesis.
Question. What is a eukaryotic cell?
Ans : Eukaryotic cells are much larger and more complex than prokaryotic cells. Their complexity is reflected in their DNA content. These cells contain a membrane bound nucleus containing nucleolus. A eukaryotic cell contains many membrane bound cell organelles like the mitochondria, the endoplasmic reticulum and the Golgi bodies. These cells have more than one chromosome and the cell division is by meiotic mode.
Question. Explain the structure and function of Golgi bodies.
Ans : Structures : Golgi bodies consist of a system of membrane-bound vesicles arranged in stacks parallel to each other called cisterns. These membranes have connections with the membrane of endoplasmic reticulum (ER).
(i) The material synthesized near the ER is packaged and dispatched to various targets inside and outside the cell through Golgi apparatus.
(ii) It also stores, modifies and helps in the packaging of products in vesicles.
(iii) In some cases, complex sugars may be made from simple sugars in it.
(iv) It also helps in the formation of lysosomes.
Question. What are the types of cell on the basis of type oforganization?
Ans : (i) Prokaryotic cells : Cells which have less developed nucleus and without nuclear membrane and nucleolus. These are primitive and incomplete cells. E.g. bacteria.
(ii) Eukaryotic cells : Cells which have well developednucleus with nuclear membrane and nucleolus. E.g. plants and animals.
Question. What is lacking in a virus which makes it dependant on a living cell to multiply?
Ans : Viruses look selectively permeable process membrane and cell organelles. Thus, they lack a basic structural organization to perform various life processes effectively and in their own way. After entering in a living cell, a virus utilizes its own genetic material and machinery of host cell to multiply.
Question. What would happen if when we put an animal cell into a solution of sugar or salt in water?
Ans : The following three things could happen : (i) If the solution surrounding the cell is very dilute than cytoplasm, the water will move into the cell, i.e., the cell will gain water.
(ii) If the solution has exactly similar water concentration as that of cytoplasm of cell, there will be no net movement of water across the cell membrane, i.e., no gain or loss of water from the cell.
(iii) If the medium (solution) has a lower concentration of water than the cell, i.e., the solution is concentrated, the cell will lose water by osmosis. How do all cells look alike in terms of shape and size?
Ans : Cells vary in shapes and sizes according to the fusion. Generally, cells are spherical but they may be long and branched as in nerve cell, Kidney shaped as guard cell in plant’s leaves, discoid as RBC, spindle shaped as muscle cell, etc. Size of cell varies from 0.2 mm to 18 cm in diameter. Some are microscopic while some are visible with naked eyes.
For example :
(i) Size of a typical cell in a multicellular organism ranges from 20-30 mn.
(ii) The largest cell is ostrich egg (15 cm in diameter with shell and 8 cm in diameter without shell).
(iii) The longest cell is nerve cell (up to 1 m. or more) and red blood cells are the smallest cell in our body.
(iv) Smallest cells so far known are PPLOs, e.g. mycoplasma (0.1 mm in diameter).
Question. Who gave the cell theory? What does it state? Which organism is an exception of cell theory?
Ans : Two biologists; “Schleiden and Schwann” gave the “Cell theory” which expanded by “Rudolf Virchow”.Cell theory states that :
(i) All plants and animals are composed of cells.
(ii) Cell is the basic unit of life.
(iii) All cells arise from pre-existing cells. Viruses are the exceptions of cell theory.
Question. Do vacuoles store material? If so, name them.
Ans : Yes, vacuoles store some important substances required in life of the plant cell. These are amino acids, sugars, various organic acids and also some proteins.
Example : Amoeba, vacuoles also store food.
Question. How do substances like CO2 and water move in and out of the cell?
Ans : The substances like CO2 move in and out of a cell by diffusion from the region of high concentration to low concentration. Water also obey the law of diffusion.
The movement of water molecule through such a selective permeable membrane is called osmosis.
Question. How does fungi and bacteria can withstand much greater changes in the surrounding medium than animal cells?
Ans : The cell wall present in fungi and bacteria permits these cells to resist very dilute external medium without bursting. Water is taken up by osmosis.
Hence, cells swell and build the pressure against the cell wall. The wall exerts an equal pressure against the swollen cell. It is because of the cell wall, such cells can resist much greater changes in the surrounding medium than animal cells.
Question. Give difference between diffusion and osmosis.
1. Diffusion can occur in any medium.
2. The diffusing molecules may be solids, liquids or gases.
3. Semipermeable membrane is not required.
4. An equilibrium in the free energy of diffusion molecules is achieved in the system.
1. It occurs only in liquid medium.
2. It involves movement of solvent molecules only.
3. Semipermeable membrane is required.
4. Equilibrium in the free energy of solvent molecules is never achieved.
Question. What are the function of endoplasmic reticulum and lysosome.
(a) Functions of endoplasmic reticulum :
(i) It forms supporting skeletal framework of the cell.
(ii) ER provides a pathway for the distribution of nuclear material from one cell to the other.
(b) Functions of lysosomes :
(i) Lysosomes serve as intracellular digestive system. They destroy any foreign material which enters the cells such as bacteria and virus.
(ii) Lysosomes also remove the worn out and poorly working cellular organelles by digesting them to make way for their new replacements.
Question. Explain the functions of various cell organelles.
Ans : Functions of cell organelles :
(i) Endoplasmic Reticulum : It forms the supporting skeletal framework of the cell.
(ii) Ribosomes : It synthesises proteins.
(iii) Golgi Apparatus : It produces vacuoles which contain cellular secretion.
(iv) Lysosomes : It serves as intracellular digestive system as it digest the foreign materials which enter the cell.
(v) Mitochondria : These are the sites of cellular respirations.
(vi) Plastids : These are present only in plants and trap solar energy to manufacture food for plants.
(vii) Vacuoles : They help to maintain the osmotic pressure in a cell.
(viii) Peroxisomes : They carry-out some oxidative reactions.
(ix) Centrosome : It helps in cell division in the animal cell.
Question. Which cell organelle is known as the ‘suicidal bags’ of a cell? Why?
Ans : Lysosomes are known as suicidal bag of cell. During the disturbance in cellular metabolism, lysosome may burst and the enzymes digest their own cell. Hence, lysosome are called ‘suicide bags’ of a cell.
Question. What is nucleoid?
Ans : The nuclear region in some cells are poorly defined due to the absence of a nuclear membrane, it contains only nucleic acid. This undefined nuclear region with nucleic acid in it is called nucleoid.
Question. (i) Name the largest animal cell.
(ii) Name the smallest cell.
Ans : (i) An ostrich egg.
(ii) Pleuro pneumonia bacterium.
Question. What is osmosis?
Ans : The movement of water molecules through a selectively permeable membrane is called osmosis. This takes place from higher water concentration to lower water concentration.
Question. What are cisterns?
Ans : The Golgi bodies consist of a system of membranebound vesicles arranged in stacks called cisterns.
Question. Name the cell organelles that have their own DNA and ribosomes. Name the autonomous organelles in the cell.
Ans : The cell organelles with their own DNA and ribosomes are mitochondria and plastids. Chloroplast and mitochondria are the autonomous organelles in the cells.
Question. What is the role of cell organelles in the cell?
Ans : Each kind of cell organelles performs a specific function such as making new material, clearing of the waste, transporting material, etc.
Question. Name the type of organism in which a single cell constitutes the whole organism.
Ans : Organism in which a single cell constitutes the whole organism is unicellular organism.
Question. What is the function of chromosome?
Ans : Chromosomes contain information for the hereditary pattern of features from parents to next generation in the form of DNA molecules.
Question. What is plasma membrane made up of?
Ans : Plasma membrane is made up of proteins and lipids.
Question. What is diffusion?
Ans : The process when gases like CO2 and O2, move across the cell membrane, is called diffusion.
Question. Name the cell organelle due to which leaves, flowers and fruits get their colour.
Ans : Chromoplast.
Question. State two conditions required for osmosis.
Ans : (i) The difference in the concentration of water, one should have higher concentration than the other.
(ii) Semi-permeable membrane is also required through which water will flow.
Question. What is a prokaryotic cell?
Ans : A cell in which there is absence of a defined nuclear region and a nuclear membrane is called a prokaryotic cell. Prokaryotic cells are generally small in size. They lack membrane bound cell organelles. They have a single chromosome.
Question. Which cell organelle transmits the heredity information from parents to offspring?
Ans : Genes are the functional units of chromosomes which transmit the heredity information from parents to offspring. These are located on chromosomes.
Question. Give difference between organs and organelles.
Ans : Organs :
They are found in multicellular organisms.
They are large sized.
They may be external or internal to the body of organisms.
1. They are found in all eukaryotic cells.
2. They are very small sized.
3. They are mostly internal.
Question. Give difference between Chloroplasts and Chromoplasts.
(i) They are green plastids.
(ii) They contain chlorophylls and carotenoids.
(iii) Lamellae are present.
(iv) Chloroplasts are sites of photosynthesis.
(i) They are non-green coloured plastids.
(ii) Chlorophylls are absent.
(iii) Lamellae are absent.
(iv) They add colour to the organs for attracting animals to perform pollination and fruit dispersal.
Question. How do lysosomes perform their function?
Ans : Functions of lysosomes :
(i) Extracellular digestion : Sometimes lysosome enzymes are released outside the cell to break down extracellular material.
(ii) Destruction of foreign material : Lysosome also destroys any foreign material which enters inside the cell such as bacteria.
(iii) Cellular digestion : Enzymes are released in damaged cells, ageing cells or dead cells. These enzymes digest their own cell.
Lysosomes contain about 40 hydrolytic enzymes.
Lysosomes burst and their enzymes digest their own cell when the cell gets damaged. So, lysosomes are called ‘suicide bags’.
Foreign materials entering the cell, such as bacteria or food, as well as dead old organelles in the lysosomes break up into small pieces.
Question. Describe an activity to demonstrate endosmosis and exosmosis. Draw a diagram also.
Ans : 1. Endosmosis : The movement of water in the cell or a body through a semipermeable membrane is called endosmosis. It can be demonstrated as follows :
(i) Take some raisins with stalks and put them in plain water in a beaker.
(ii) Observation : Raisins absorb water and swell. Raisins have high concentration of sugar than surrounding plain water. Because of this, water from the outside passing through
semipermeable membrane enters into the cell. This is endosmosis.
Question. How does a living cell perform basic functions?
Ans : A living cell perform basic functions by division of labour among specific components within it is known as cell organelles.
Question. What could happen if nucleus is removed from the cell?
Ans : If nucleus is removed from a cell, the protoplasm will ultimately dry up and the cell will die because the nucleus controls all the metabolic activities of a cell.
Question. Name the organelles present in liver of animals which detoxifies many poisons and drugs.
Ans : In the liver of animal cells, smooth endoplasmic reticulum helps in detoxifying many poisons and drugs.
Question. How are new cells reproduced?
Ans : Cells multiply by dividing themselves again and again. Cells divide to produce cells of their own kind.
Question. Give example of working of chromoplasts.
Ans : Spinach looks green due to the presence of chloroplasts, papaya is yellow and edible part of watermelon is red due to the presence of chromoplasts.
Question. What is plasmolysis?
Ans : When a living plant cell loses water through osmosis there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is known as plasmolysis.
Question. What would happen to the life of a cell if there was no Golgi apparatus?
Ans : Golgi apparatus plays an important fusion of storage, modification and packaging of the products in vesicles. If there were no Golgi bodies, packaging and dispatching of materials synthesised by the cell will be stopped.
Question. What is the function of vacuoles?
Ans : Vacuoles are the storage sacs for solid or liquid content. In plant cells, it provides turgidity and rigidity to the cell. In single-celled organisms, vacuoles store food, e.g. amoeba.
Question. Explain the following terms :
(a) Plasma membrane,
Ans : (a) Plasma membrane : It is a thin membrane which controls the passage of materials in and out of the cell. It is also called selectively permeable membrane. It makes the outer oundary of the cell and is made up of protein.
(b) Cytoplasm : It is transparent jelly-like thick substance present in the cell. It makes the ground of the cell in which all the cell organelles are suspended.
(c) Nucleus : It is a double-layered membrane structure which contains chromosomes required for the inheritance of characteristics from one generation to the other.
Question. What is lacking in a virus which makes it dependant on a living cell to multiply?
Ans : Viruses do not have a basic structural organization to perform various life processes in their own as they look selectively permeable process membrane. After
entering in a living cell, a virus utilizes its own genetic material and machinery of host cell to multiply.
Question. Expand the term ATP. What is use of ATP?
Ans : ATP stands for Adenosine Tri-phosphate Application : ATP molecules are rich in chemical energy. The body cells use this energy for synthesis of new chemical compounds, and for mechanical work done by cells.
Question. What is the function of nucleus in a cell?
Ans : The nucleus plays a very important role in the reproduction of cells. It also helps the single cell to divide and form two new daughter cells. It also helps in an important role in determining how cell will develop.
Question. Name various cell organelles.
Ans : The cell organelles are : Endoplasmic Reticulum, Ribosomes, Golgi apparatus, Lysosomes, Mitochondria, Plastids, Vacuoles, Peroxisomes and Centrosome.
Question. (a) Name the organelle which provides turgidity and rigidity to the plant cell. Name any two substances which are present in it.
(b) How are they useful in unicellular organisms?
Ans : (a) Plant cells have big vacuoles that provide them turgidity and rigidity. Plant vacuoles store amino acids, sugars, various organic acids and some proteins.
(b) In unicellular organism they can serve the following works :
(i) Forming food vacuoles : In single celled organisms like amoeba, the food vacuole contains the food items that the amoeba has engulfed. After that the food items are digested by the enzymes.
(ii) Removal of excess water and wastes : In some unicellular organisms, vacuoles play important roles in egesting excess water and some wastes from the cell.
Question. What is membrane biogenesis?
Ans : The endoplasmic reticulum helps in the manufacture of proteins and fat molecules or lipids which are important for the cell function. These proteins and lipids helps in the building of the cell membrane. This process is known as membrane biogenesis.
Question. All cells come from pre-existing cells. Justify?
Ans : All organisms around are made up of one or more cells. There are single cells organism called unicellular like amoeba whereas some single body are made up of many cells called multicellular organism. Cells divide to produce cells of their own kind. Hence, all cells come from pre-existing cells.
Question. What are chromosomes? What are they made of?
Ans : The compact rod-like bodies inside the nucleus are called chromosomes. These are seen at the time of cell division. They are made up of deoxyribonucleic acid or DNA and proteins.
Question. What is the cell wall composed of ?
Ans : The cell wall is composed of cellulose.
Question. Name two cells with cell wall.
Ans : Onion cell (plant cell) and fungi are two cells with cell wall.
Question. Which organelle makes the digestive enzyme of lysosome?
Ans : Rough endoplasmic reticulum makes the digestive enzyme of lysosomes.
Question. Where are genes located in the cell?
Ans : Genes are located in the chromosomes in the nucleus of the cell.
Question. Why does mitochondria have largely folded inner membrane?
Ans : Mitochondria have largely folded inner membrane which provides the increased surface area for ATPgenerating chemical reactions. Mitochondria is the site for cellular respiration and provides energy to the cell.
Question. Name the autonomous organelles in the cell.
Ans : Chloroplast and mitochondria are the autonomous organelles in the cells.
Question. What is the energy currency of the cell?
Ans : ATP—Adenosine Triphosphate.
Question. Name the cell organelle that helps in packaging?
Ans : Golgi apparatus.
Question. What is cell wall?
Ans : Cell wall is the rigid outer covering of plasma membrane in plant cells.
Question. What would happen if the plasma membrane breaks down?
Ans : If plasma membrane breaks down then molecules of some substances will freely move in and out.
Question. Where are proteins synthesized inside the cell?
Ans : The proteins are synthesised in the ribosomes, known as protein factories too.
Question. Who discovered cells in living organisms? Give an example of unicellular organism.
Ans : Leeuwenhoek (1674) was the first to observe the free living cells in pond water. Example of unicellular organisms : Amoeba, Chlamydomonas, Paramoecium, Bacteria, etc.
Question. What is the function of plastids?
Ans : Plastids are present only in plant cells. There are two types of plastids chromoplasts (coloured plastids) and leucoplasts (white or colourless). Chromoplast : Consists of coloured pigments andgiven different colours to flowers, fruits and leaves. The green colour pigment present in leaf is called chlorophyll which helps in the photosynthesis and a plastid with chlorophyll is called chloroplast. Leucoplast : It stores starch, oil and protein granules in it.
Question. Where do lipids and proteins get synthesized?
Ans : Lipids get synthesized in the smooth endoplasmic reticulum and proteins get synthesised in the ribosome and rough endoplasmic reticulum.
Question. Write a function of cell membrane.
Ans : Its major function is to hold cellular contents and control passage of materials in and out of the cell.
Question. What is the function of DNA?
Ans : They are responsible for storing and transmitting hereditary information from one generation to another. They contain the information necessary for constructing and organizing cells.
Question. List two similarities between mitochondria and plastids.
Ans : Plastids are similar to mitochondria in external structure. Like the mitochondria, plastids also have their own DNA and ribosome.
Question. Name the cell organelle which helps in the transporta tion of material.
Ans : Endoplasmic reticulum.
Question. Name the smallest cell and the longest cell in human body.
Ans : The smallest cell is the red blood cell or sperm cell in male. The longest cell is the nerve cell.