NCERT Exemplar Problems Class 9 Science – The Fundamental Unit of Life

Question 1:
Which of the following can be made into crystal?
(a) A bacterium (b) An Amoeba (c) A virus (d) A sperm
Answer:
(c) Viruses are considered as an intermediate between living and non-living cells because they cannot metabolise and reproduce on their own. They can reproduce only when enters in a host’s body. They are an exception to cell theory.
A virus crystal is a collection of thousands of viruses. A viral crystal is a pore collection used for chemical studies.

Question 2:
A cell will swell up if
(a) the concentration of water molecules in the cell is higher than the concentration of water molecules
in surrounding medium
(b) the concentration of water molecules in surrounding medium is higher than water molecules concentration in the cell
(c) the concentration of water molecules is same in the cell and in the surrounding medium
(d) concentration of water molecules does not matter
Answer:
(b) Osmosis is a spontaneous process where movement of solvent molecules occurs into a region of higher solute concentration from lower solute concentration through a partially permeable membrane, so as to tend to equalise the solute concentration on the two sides.
When movement of the solvent takes place from outside to inside the all (inward movement) the process is endosmosis. It occurs in hypotonic solution and causes the swelling of cell.

When the movement of solvent takes place from inside to outside of the cell (outward movement) the process is exosmosis. It occurs in hypertonic solution. It results the shrinkage of the cell.

When the concentration of water both in the surrounding medium and in the cell is same, the solution in the the surrounding medium is said to be isotonic and no movement of water molecule takes place.

Question 3:
Chromosomes are made up of
(a) DNA (b) Protein (c) DNA and protein (d) RNA
Answer:
(c) Chromosomes are thread-like structures usually present in the nucleus which becomes visible only during cell division. Each chromosome is made up of two components

(i) Deoxyribonucleic acid (DNA)
(ii) Proteins (e.g., histones and acidic proteins)
These consist of two (unreplicated) or four (duplicated) arms and a primary constriction or centromere which gives them a particular shape due to its position. The paired condition of chromosome is called diploid and unpaired chromosome are said to be haploid.

Question 4:
Which of these options are not a function of ribosomes?
I. It helps in manufacture of protein molecules.
II. It helps in manufacture of enzymes.
III. In helps in manufacture of hormones.
IV. In helps in manufacture of starch molecules.
(a) I and II (b) II and III (c) III and IV (d) IV and I
Answer:
(c) Ribosomes are dense, spherical and granular particles which remains freely in the matrix or remain attached to endoplasmic reticulum. They are not bound by membrane and are present in both prokaryotic and eukaryotic cells. They play important role in synthesis of proteins. All enzymes are proteins but all hormones are not proteins

Question 5:
Which of these is not related to endoplasmic reticulum?
(a) It behaves as transport channel for proteins between nucleus and cytoplasm
(b) It transports materials between various regions in cytoplasm
(c) It can be the site of energy generation
(d) It can be the site for some biochemical activities of the cell
Answer:
(c) Endoplasmic reticulum exists as a membranous network, which is connected to the outer membrane of nucleus from one side and plasma membrane to the other.
It occurs in three forms
(i) Cisternae-closed fluid filled sac
(ii) Vesicles
(iii) Tubules
It is of two types, smooth endoplasmic reticulum i.e., without ribosomes on its surface and rough endoplasmic reticulum with ribosomes on its surface.

Question 6:
Following are a few definitions of osmosis.
Read carefully and select the correct definition.
(a) Movement of water molecules from a region of higher concentration to a region of lower concentration through a semipermeable membrane.
(b) Movement of solvent molecules from its higher concentration to lower concentration.
(c) Movement of solvent molecules from higher concentration to lower concentration of solution through a permeable membrane.
(d) Movement of solute molecules from lower concentration to higher concentration of solution through a semipermeable membrane.
Answer:
(a) The movement of water molecules through selectively permeable membrane along concentration gradient is called osmosis.
It is the passage of water from region of high water concentration through semipermeable membrane to a region of low water concentration (only through semipermeable membrane).
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.

Question 7:
Plasmolysis in a plant cell is defined as
(a) break down (lysis) of plasma membrane in hypotonic medium
(b) shrinkage of cytoplasm in hypertonic medium
(c) shrinkage of nucleoplasm
(d) None of the above
Answer:
(b) When a cell is immersed in hypertonic (very concentrated) solution, water diffuses out of the cell by the process of osmosis. This is because there is a lower concentration of water outside the cell.
Although water molecules pass the cell membrane in both direction but more amount of water goes out of the cell than the amount of water which enters it. As a result of this the cell shrinks. This process is called exosmosis. If exosmosis continues in a plant cell, the cytoplasm appears to be shrunken. This is called plasmolysis and the cell Is said to be plasmolysed.

Question 8:
Which of the following are covered by a single membrane?
(a) Mitochondria (b) Vacuole (c) Lysosome (d) Plastid
Answer:
(c) Lysosomes are simple, tiny spherical sac-like structures evenly distributed in the cytoplasm each lysosome is surrounded by a double membrane and contains powerful enzymes capable of digesting or breaking down all organic material. These enzymes are made by rough endoplasmic reticulum.
They perform following functions in our body

1. They help in breaking down (digesting) large molecules of the cell.
2. They help in defence against bacteria and viruses.
3. During starvation, lysosomes act on their own cellular organelles and digest them. This results in cell death. The lysosomes are also called suicide bags or demolition squads of the cell.

Question 9:
Find out the false sentences.
(a) Golgi apparatus is involved with the formation of lysosomes.
(b) Nucleus, mitochondria and plastid have DNA; hence they are able to make their own structural proteins.
(c) Mitochondria is said to be the power house of the cell as ATP is generated in them.
(d) Cytoplasm is called as protoplasm.
Answer:
(d) Along with the function of secretion of various enzyme proteins and producing vacoules, Golgi apparatus is also involved in the synthesis of cell wall, plasma membrane and lysosome.
Nucleus, mitochondria and plastids have their own genome (f.e., DNA) and ribosomes. They are self replicating organelles /. e., they have power to divide and are able to synthesise their own structural protein (semi autonomous organelles). Mitochondria is site of cellulose respiration and synthesis of energy rich compounds (ATP). Therefore it is called as power house of the cell. The part of cell which between the plasma membrane and nuclear envelope is called the cytoplasm.

Question 10:
Find out the correct sentence
(a) Enzymes packed in lysosomes are made through RER (Rough Endoplasmic Reticulum)
(b) Rough endoplasmic reticulum and smooth endoplasmic reticulum produce lipid and protein
respectively
(c) Endoplasmic reticulum is related with the destruction of plasma membrane
(d) Nucleoid is present inside the uncleoplasm of eukaryotic nucleus
Answer:
(a) The undefined nuclear region is the cytoplasm of prokaryotic cells is called nucleoid.
The prokaryotic cells consist of a single chromosome, which is direct content of the cytoplasm /.e., there is no nuclear membrane in a eukaryotic cell, the nuclear envelope separates the nucleus from the cytoplasm.
The nuclear envelope contains many pores (the nuclear pores) and encloses the liquid ground substance, the nucleoplasm. Within nucleoplasm two types of nuclear structures are embedded—the nucleolus and chromatin material.
The nucleolus may be one or more in number and is not bounded by any membrane. It is rich in protein and RNA (Ribonucleic Acid) molecules and acts as the site for ribosome formation, hence are also known as factory of ribosomes.

Question 11:
Which cell organelle plays a crucial role in detoxifying many poisons and drugs in a cell?
(a) Golgi apparatus (b) Lysosomes
(c) Smooth endoplasmic reticulum (d) Vacuoles
Answer:
(c) Smooth endoplasmic reticulum in liver cells of vertebrates helps in detoxification. It metabolises various toxic or poisonous substances such as drugs, aspirin, insecticides (DDT), petroleum products and pollutants. These toxic substances make their entry in animal’s body through food, air or water.

Question 12:
The proteins and lipids, essential for building the cell membrane, are manufactured by
(a) endoplasmic reticulum
(b) Golgi apparatus
(c) plasma membrane
(d) mitochondria
Answer:
(a) The endoplasmic reticulum performs the following functions
(i) It increases the surface area of the cytoplasm for various metabolic activities of the cell.
(ii) It gives internal support to the colloidal matrix e., cytoplasm.
(iii) It is associated with the synthesis, storage and transport of metabolic products.
(iv) It helps in the formation of the cell plate and nuclear membrane during cell division.
(v) Routh Endoplasmic Reticulum (RER) is associated with the synthesis of proteins.
(vi) Smooth Endoplasmic Reticulum (SER) secretes lipids which along with proteins constitute cell membrane by a process called membrane biogenesis.

Question 13:
The undefined nuclear region of prokaryotes are also known as
(a) nucleus (b) nucleolus
(c) nucleic acid (d) nucleoid
Answer:
(d) The prokaryotic cells lack true nucleus and a circular DNA lies naked in the cytoplasm.
The unidentified nuclear region of the cell is called nucleoid. The prokaryotic cell lacks chromosomes and nucleolus or nuclear membrane and nucleoplasm remains undifferentiated from the cytoplasm.

Question 14:
The cell organelle involved in forming complex sugars from simple sugars are
(a) endoplasmic reticulum
(b) ribosomes
(c) plastids
(d) Golgi apparatus

Answer:
(d) Golgi body was first discovered by Camillo Golgi. Golgi bodies, or Golgi complex are formed by stacks of flattened (saucer-shaped) membranes or flattened sacs called cisternae. Golgi bodies are usually called dictyosomes in plants.
Golgi apparatus is absent in bacteria, blue-green algae, mature sperms and red blood cells of mammals and other animals.
The Golgi apparatus arises from the membrane of the smooth endoplasmic reticulum, which in turn originates from the rough endoplasmic reticulum.
The proximal Golgi saccules (cisternae at cis face) are formed by fusion of ER-derived vesicles, while distal saccules (cisternae at trans face) “give their all” to vesicle formation and disappear. Thus, Golgi saccules are constantly and rapidly renewed.
The main functions of Golgi apparatus are
(i) They store, modify, package and condense the proteins synthesised in the ribosomes.
(ii) They form the cell plate during the cell division.
(iii) They set aside digestive enzymes in tiny membrane bound vesicles which later become lysosomes.
(vi) They synthesise some polysaccharides for the cell membrane.

Question 15:
Which out of the following is not a function of vacuole?
(a) Storage
(b) Providing turgidity and rigidity to the cell
(c) Waste excretion
(d) Locomotion
Answer:
(b) Vacuoles may be small or large. These are filled with liquid or sap and are membrane-bound organelles. In animal cells, vacuoles are smaller in size and lesser in number than in plant cells. In some plant cells, only one large vacuole is present. The major portion of a plant cell is occupied by vacuoles.
The (approx 90% in some cases) either may be contractile (can contract) or non-contractile. When the pressure of the contents of a contractile vacuole increases, it contracts and releases its contents. In unicellular organisms like Amoeba, food particles are present inside food vacuoles. But are not associated with locomotion.
The main functions of vacuoles are

1. In animals, vacuoles are often associated with the maintenance of water balance.
2. They work in osmoregulation, e., the maintenance of internal pressure.
3. They store various substances including waste products.

(b) Endocytosis is the ingestion of material by the cells through their plasma membrane. It is a collective term that describes three similar processes phagocytosis (cell eating), potocytosis (cell drinking) and receptor-mediated endocytosis.
These processes are pathways to specifically internalise solid particles, small molecules and ion, and macromolecules, respectively. All of them require energy, so they may be regarded as different forms of active transport.
Out of these phagocytosis is the common method of feeding among the Protozoa (e.g., Amoeba) and lower Metazoa (e.g., sponges). In pseudopodial movement the phagocyte enguls the particle lysosomes, join with the vacoule containing ingested particle and pour their contents into the vacoule to destroy the particle.

Question 16:
Amoeba acquires its food through a process, termed
(a) exocytosis (b) endocytosis
(c) plasmolysis (d) Both exocytosis and endocytosis both
Answer:
(b) Endocytosis is the ingestion of material by the cells through their plasma membrane. It is a collective term that describes three similar processes phagocytosis (cell eating), potocytosis (cell drinking) and receptor-mediated endocytosis.
These processes are pathways to specifically internalise solid particles, small molecules and ion, and macromolecules, respectively. All of them require energy, so they may be regarded as different forms of active transport.
Out of these phagocytosis is the common method of feeding among the Protozoa (e.g., Amoeba) and lower Metazoa (e.g., sponges). In pseudopodial movement the phagocyte enguls the particle lysosomes, join with the vacoule containing ingested particle and pour their contents into the vacoule to destroy the particle.

Question 17:
The cell wall of which out of these is not made up of cellulose
(a) bacteria (b) Hydrilla (c) mango tree (d) lactus
Answer:
(a) Plant cells, in addition to the plasma membrane, have another rigid outer covering called the cell wall. The cell wall lies outside the plasma membrane. The plant cell wall is mainly composed of cellulose. Cellulose is a complex substance and provides structural strength to plants. Bacteria is not a plant therefore its cellwall is made up of peptidoglycan.

Question 18:
Silver nitrate solution is used to study
(a) endoplasmic reticulum
(b) Golgi apparatus
(c) nucleus
(d) mitochondria
Answer:
(d) Camillo Golgi, discovered the revolutionarily method of staining individual cell structures. This method is raftered to as black reaction. It uses weak solution of silver nitrate and is valuable in tracing the processes and most delicate ramifications of cells.

Question 19:
Organelle other than nucleus, containing DNA is
(a) endoplasmic reticulum
(b) Golgi apparatus
(c) mitochondria
(d) lysosome
Answer:
(c) Other than nucleus mitochondria contains DNA and are able to synthesis their own proteins they are regarded as semiautonomous organelles.

Question 20:
Kitchen of the cell is
(a) mitochondria
(b) endoplasmic reticulum
(c) chloroplast
(d) Golgi apparatus
Answer:
(c) Chloroplasts are present in green algae and higher plants. They have a green pigment called chlorophyll and they are involved in the photosynthesis of food. Therefore they are also known as the ‘kitchens of the cells’. Each chloroplast is bounded by two unit membranes like the mitochondria. It shows two distinct regions
(i) Grana are the main functional units of chloroplast. They are stacks of membrane bounded, flattened
discoid sacs (called thylakoids) containing the molecules of chlorophyll.
(ii) Stroma is the homogeneous matrix in which grana are embedded. It contains a large variety of photosynthetic enzymes, starch grains DNA and ribosomes.

Question 21:
Lipid molecules in the cell are synthesised by
(a) smooth endoplasmic reticulum
(b) rough endoplasmic reticulum
(c) Golgi apparatus
(d) plastids
Answer:
(a) Lipid molecules in the cell are synthesised by the smooth endoplasmic reticulum present is the cell. (Also, refer to G. 12)

Question 22:
Cell arises from pre-existing cell was stated by
(a) Haeckel (b) Virchow (c) Hooke (d) Schleiden
Answer:
(b) In 1938 Schleiden proposed the idea that plants consist of cells. Later in the year 1839, Schwann independently asserted that all animals and plants are made up of cells. This joint finding forms the basis of cell theory.
The cell theory was refined further in 1855, when R. Virchow presented the idea that all cells arise from pre-existing cell. His amorphism was (Omnis Cellula-e-Cellula).

Question 23:
Cell theory was given by
(a) Schleiden and Schwann (b) Virchow
(c) Hooke (d) Haeckel
Answer:
(a) Schleiden (1836) and Schwann (1834) gave the cell theory, which was further refined by R. Virchow (1855). The main postulates of cell theory are
(i) All organisms are composed of cells and cell products.
(ii) All metabolic reactions take place in cells. Thus cell are structural and functional units of life.
(iii) All cell arise from pre-existing cells only. No cell can originate spontaneously but they comes into being only by division of pre-existing cells.
(iv) Every organism starts its life as a single cell.

Question 24:
The only cell organelle seen in prokaryotic cell is
(a) mitochondria (b) ribosomes (c) plastids (d) lysosomes
Answer:
(b) Unlike eukaryotic cell, a prokaryotic cell lacks membrane-bound organelles like plastids, mitochondria and endoplasmic reticulum but smaller and randomly scattered ribosomes are seen

Question 25:
Organelle without a cell membrane is
(a) ribosome (b) Golgi apparatus (c) chloroplast (d) nucleus
Answer:
(a) Nucleus is sorrounded by two nuclear membranes both forming a nuclear envelope;
Golgi apparatus is a set of membrane-bounded, fluid filled visicles, vacuoles and flattened cisternae. Plastids are also membrane bound organelle but ribosomes moves freely in the matrix or remain attached to the endoplasmic reticulum.

Question 26:

Answer:
(a) The micrometre commonly known as micron is SI derived unit of length equalling to 10^-6 of a metre.

Question 27:
Lysosome arises from
(a) endoplasmic reticulum
(b) Golgi apparatus
(c) nucleus
(d) mitochondria
Answer:
(b) The Golgi apparatus is involved in formation of lysosome. (Also, refer to Q. 8)

Question 28:
Living cells were discovered by
(a) Robert Hooke (b) Purkinje (c) Leeuwenhoek (d) Robert Brown
Answer:
(c) In the year 1670, Anton Van Leeuwenhoek, a Dutch biologist discovered the living cell when he looked at the pond water under the microscope, he made of lenses.

Question 29:
Select the odd one out
(a) The movement of water across a semi permeable membrane is affected by the amount of substances dissolved in it.
(b) Membranes are made of organic molecules like proteins and lipids
(c) Molecules soluble in organic solvents can easily pass through the membrane.
(d) Plasma membranes contain chitin sugar in plants.
Answer:
(d) Each cell is bounded by an extremely delicate, thin elastic living membrane, called the plasma membrane. The plasma membrane is made up of two layers of lipid (fat) molecules with protein molecules which is sandwitched between lipid layer.
The structure of plasma membrane can be observed under an electron microscope only. It is a selectively permeable membrane which allows the flow of only some substances into the cell and out of the cell. Viruses do not have any membranes.
Functions

1. It gives a definite shape to the cell.
2. It provides protection to the in contents of the cell.
3. It regulates entry and exit of substances in to and out of the cell.
4. It can internalise solid and liquid materials by infolding or extending around them. This is the process of active intake of materials.
5. In animal cells, it is involved in adhesion, recognition and in the formation of vesicles, cilia, flagella, microvilli etc.

Short Answer Type Questions

Question 30:
Why are lysosome known as suicidal-bags of a cell?
Answer:
During the breakdown of cell structre, when the cells gets damaged, the lysosomes may break and enzymes, which are capable of digesting or breaking down all organic nutrients may release into the cell.
Due to their capabilty of digestion they may eat up or digest or break down other cell organelles leading to hampered metabolic activities and finally death of the cell.
This is the reason why lysosome are also known as suicidal bags of cell.

Question 31:
Do you agree that ‘A cell is a building unit of on organism’. If yes, explain why?
Answer:
A cell is composed of various organelles which perform different function. A cell is structural, functional and smallest unit of life capable of all living functions.
The number of cells vary from organism to organism. An Ameoba is single celled or unicellular, where all the basic functions are performed in one cell.
On the contrary, a human is multicellular having as many as 60 x 10¹⁵ cell (weight about 60 kg). In a multicellular organism, cell form tissues, which in turn together form organs and? different functions are performed by different organs i.e., they have well-developed division of labour.

Question 32:
Why does the skin of your finger shrink when you wash clothes for a long time?
Answer:
Soap solution is a hypertonic solution i.e., more concentrate than our skin cells. As we know, when the cell is immersed in a hypertonic solution, water diffuse out of the cells by osmosis (diffusion of water across semipermeable membrane), due to lower concentration of water outside the cell. As a result, the cell shrinks. The process is called exosmosis. During washing of clothes, exosmosis takes place in the skin cells. This leads to shrinkage of skin over the fingers while washing clothes for a long time.

Question 33:
Why is endcytosis found in animals only?
Answer:
Endocytosis refers to invagination of a small region of plasma membrane, forming an interacellular membrane-bound vesicle. It has been observed in many kinds of animal cells, where the plasma membrane is in direct contact with external medium.
Endocytosis is not shown by plant cells because a rigid cell wall is present over the plasma membrane in them.
Thus, this process is found in animals only.

Question 34:
A person takes concentrated solution of salt, after sometime, he starts vomiting. What is the phenomenon responsible for such situation? Explain.
Answer :
Concentration salt solution is a hypertonic solution (water concentration lower as compared to the cell) therefore it causes exosmosis. The outward movement of water from the cell results in irritation and excessive dehydration. This results in reverse movements and hence, vomiting. {Also, refer to Q. 2 )

Question 35:
Name any cell organelle which is non-membranes.
Answer:
A non-membranous cell organelle is ribosome.
Ribosomes are extremely small, round bodies found either in the free state in the cytoplasm or attached to the surface of the ER. They are composed of ribonucleoproteic (ribonucleic acid and protein).
The main function of ribosomes is to act as a platform for the synthesis of proteins.
(Also, refer to 0.4).

Question 36:
We eat food composed of all the nutrients like carbohydrates, proteins, fats, vitamins, minerals and water. After digestion, these are absorbed in the form of glucose, amino acids, fatty acids, glycerol, etc.
What mechanisms are Involved in absorption of digested food and water?
Answer:
The mechanisms involved in absorption of digested food and water are diffusion and osmosis respectively.
(i) Digested food-through diffusion, e., the process in which molecules move from their region of higher concentration to their region of lower concentration till they are uniformly distributed throughout the available space.
(ii) Water-through osmosis, e., the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
In this case, from small intestine (high concentration) to blood low concentration.

Question 37:
If you are provided with some vegetables to cook. You generally add salt into the vegetables during cooking process. After adding salt, vegetables release water. What mechanism is responsible for this?
Answer:
On adding salt, the external medium is made hypertonic, i.e., concentration of water is lowered as compared to the concentration of water inside the cell. Thus, water is released from the vegetables due to exosmosis (water molecules goes out of the cell resulting in shrinkage of cell). (Also, refer to Q. 34)

Question 38:
If cells of onion peel and RBC are separately kept in hypotonic solution, what among the following will take place? Explain the reason for your.
(a) Both the cells will swell.
(b) RBC will burst easily while cells of onion peel will extent.
(c) Both (a) and (b) are correct.
(d) RBC and onion peel cells will behave similarly
Answer:
(c) The solution with higher concentration of water as compared to the cell is termed as hypotonic solution.
When the cells are kept in a hypotonic solution endosmosis occurs i.e., the inward movement of water takes place.
This results in the swelling up of cells. When kept in hypotonic solution the RBCs burst easily because they are animal cells and do not possess cell wall, while the onion peel possess cell wall which makes it resistant to the bursting due to swelling caused by endosmosis.
Therefore, option (c) is correct.

Question 39:
Bacteria do not have chloroplast, but some bacteria are photoautotrophic in nature and perform photosynthesis. Which part of bacterial cell performs this?
Answer:
Bacterial cell do not have chloroplast but yet some photoautotrophic bacteria perform photosynthesis due to the presence of chlorophyll in coperated in the membrane. Embedded in the cell membrane are reaction centers which specifically absorb light energy. These reaction centre exist in forms of sacs-tubes or sheets depending on the amount of surface area needed.

Question 40:
Match the following columns

Answer:
The correct matching is A.→ (4) B. → (5) C.→(3) D. → (1) E. → (2)
One of the special function of smooth endoplasmic reticulum of liver of vertebrate is detoxification.
{Also, refer (o 0.11)
Lysosomes are called the suicidal bags of cell as they digest the organelles of their own cell. {Also, refer to Q. 30)
Nucleoid is the undifferentiated nuclear region of a prokaryotic cell and bacteria are prokaryote.
{Also, refer to Q. 13)
Food vacuoles are present in Amoeba to store the food trapped by endocytosis.
{Also, refer to Q. 16)
Nucleus is composed of two membrane called nuclear membrane, nucleoplasm, nucleolus and chromatin material.

Question 41:
Write the name of different plant parts in which chromoplast, chloroplast and leucoplast are present.
Answer:
Plastids occur in most plant cells, but are absent in animal cells. Like mitochondria, plastids also have their own genome {l.e., DNA) and ribosomes. They are self-replicating organelles like the mitochondria, i.e., they have the power to divide. Plastids are of following three types

1. Chromoplasts Coloured plastids (except green colour). They add colour to organs e.g flowers fruits, for attracting animals to perform pollination and fruit dispersal.
2. Chloroplasts Green-coloured plastids. These are the sites of photosynthesis and are present in the leaves of the plant.
3. Leucoplasts The colourless plastids. Leucoplasts takes part in storage of food and can be present anywhere in an organism.

Question 42:
Name the organelles which show the analogy written as under
(a) Transporting channels of the cell
(b) Power house of the cell
(c) Packaging and dispatching unit of the cell
(d) Digestive bag of the cell
(e) Storages sacs of the cell
(f) Kitchen of the cell
(g) Control room of the cell
Answer:
(a) Transporting channel of the cell. Endoplasmic reticular is the transporting channel of the cell as it connects the cell membrane to the nuclear membrane.
(b) Mitochondria are called the power house of the cell because, they generate energy in the form of ATP (Adenosine Triphosphate).
(c) Packaging and dispatching unit of the cell is golgi complex as they store, modify, package and condense the proteins synthesised by ribosomes.
(d) Lysosomes are known as the digestive bags of the cell due to the presence of enzymes in them which are capable of degrading any organic material.
(e) Vacoules are termed as storage sacs of the cell as they store the food.
(f) Chloroplast are termed as kitchen of cell due to their function of performing photosynthesis.
(g) Nucleus is the control room of the cell as it regulates almost all the activities of the cell.

Question 43:
How is bacterial cell different from onion pell?
Answer:
The major differences between bacterial cell (prokaryotic) and onion peel (eukaryotic) are tabulated below

Question 44:
How do substances like carbon dioxide (C0₂) and water (H₂0) move in and out of the cell?
Answer:
When (C0₂) accumulates in high concentration inside the cell, diffusion occurs. C0₂ moves out of the cell from the region of higher concentration to a region of lower concentration.
When a cell is placed in a solution with a different solute concentration the water tends to move either in or out of the cell according to its concentration gradient by the process of osmosis.

Question 45:
How does Amoeba obtain its food?
Answer:
Amoeba obtain its food by the process of phagocytosis. It literally means ‘cell eating’. It is a common method of feeding among the Protozoa and lower Metazoa .
It is also the way in which white blood cells (leucocytes) engulf cellular debris and uninvited microbes (viruses and bacteria) in the blood. In the phagocytosis, an area of the plasma membrane, coated initially with actin-myosin, forms a pocket and engulfs the solid material (e.g., bacteria, debris).
The membrane-enclosed vesical, phagosome, then detaches form the cell surface (plasma membrane) into the cytoplasm where its contents are digested by lysosomal enzymes.

Question 46:
Name the two organelles in a plant cell that contain their own genetic material and ribosome.
Answer:
Mitochondria and plastids have their own DNA and ribosome and hence can synthesise their own protein and genetic material.(Also, refer to Q. 9)

Question 47:
Why are lysosomes also known as scavengers of the cells?
Answer:
Lysosomes contain hydrocitic enzymes synthesised by endoplasmic reticulum. These enzymes remove the worn out and poorly working cell organelles by digesting them so that, new replacements can be made. They remove the cell debris therefore, they are known as scavenger, cellular house keepers and demolition squads of the cell.(Also, refer to Q. 8)

Question 48:
Which cell organelle controls most of the activities of the cell?
Answer:
Nature and occurrence The nucleus is a large, centrally located spherical cellular component. It is bounded by two nuclear membranes, both forming a nuclear envelope. Nuclear envelope encloses a space between two nuclear membranes and is connected to a system of membranes called the ER (Endoplasmic Reticulum).
It encloses nucleolus, nuclear pore and nucleoplasm.

Nucleus has very important functions as listed below

1. The nucleus controls all metabolic activities of the cell. If the nucleus is removed from a cell, the protoplasm ultimately dries up and dies.
2. It regulates the cell cycle.
3. It is concerned with the transmission of hereditary traits form the parent to offspring.

Question 49:
Which kind of plastid is more common in
(a) roots of the plant (b) leaves of the plant
(c) flowers and fruits
Answer:
(a) Roots of plant contain leucoplast which are colourless plastids and act as storage of food.
(b) Leaves of plant contain green coloured chlorophyll for photosynthesis
(c) Flowers and fruits contain multicoloured chromoplast to attract pollinators.
(Also, refer to Q. 41)

Question 50:
Why do plant cells possess large sized vacuole?
Answer:
Plant cells are known to have bigger vacuoles than that of animal cells as they need to store food and water. This is because the plant don’t possess the ability to move freely like that of animals. Thus, they possess large vacuoles as a reservoir in unfavourable conditions.

Question 51:
How are chromatin, chromatid and chromosomes related to each other?
Answer:
Inside the nucleoplasm a tangled mass of thread-like structures is called chromatin. They are formed of an acid called Deoxyribonucleic Acid (DNA) and proteins. When a cell starts to divide, the tangled mass of chromatin condense into long threads and finally, rod-like bodies called chromosomes. The chromosomes contain stretches of DNA which carry information for protein synthesis.
A gene is called the hereditary unit and DNA is called the hereditary material.
A chromatid is one copy of duplicated chromosome which is generally joined to the other copy by a centromere.

Question 52:
What are the consequences of the following conditions?
(a) A cell containing higher water concentration than the surrounding medium
(b) A cell having low water concentration than the surrounding medium.
(c) A cell having equal water concentration to its surrounding medium.
Answer:
(a) When a cell possess higher water concentration than the surrounding medium then exosmosis occurs in the cell due to the difference in water concentration in the cell and surrounding medium and cells shrinks.
(b) When a cell has low water concentration than surrounding medium then, endosmosis occurs leading
the swelling of the cell.
(c) A cell having equal concentration to its surrounding medium will not show any changes as isotomic conditions persist in the solvent.

Long Answer Type Questions

Question 53:
Draw a plant cell and label the parts which
(a) determines the function and development of the cell.
(b) packages materials coming from the endoplasmic reticulum.
(c) provides resistance to microbes to withstand hypotonic external media without bursting.
(d) is site for many biochemical reactions necessary to sustain life.
(e) is a fluid contained inside the nucleus.
Answer:
A plant cell and its parts is as below

Question 54:
Illustrate only a plant cell as seen under electron microscope. How is it different from animal cell?
Answer:
A plant cell as seen under electron microscope

Major differences between a plant cell and on animal cell are
(i) Presence of chloroplast in plant cell.
(ii) Presence of large central vacuole in plant cell.
(iii) Presence of cell wall.

Question 55:
Draw a neat labelled diagram of an animal cell.
Answer:
A diagram of an animal cell is as given below

Question 56:
Draw a well labelled diagram of an eukaryotic nucleus. How is it different form nucleoid?
Answer:
A diagram of an eukaryotic nucleus is as given

The major differences between eukaryotic and prokaryotic nucleus is that a prokaryotic nucleus
(i) is undifferentiated
(ii) is not bound by nuclear membrane
(iii) does not contain chromosome
(iv) does not possess nucleolus and nucleoplasm.

Question 57:
Differentiate between rough and smooth endoplasmic reticulum. How is endoplasmic reticulum important for membrane biogenesis?
Answer:
The major differences between rough and smooth endoplasmic reticulum are

Endoplasmic reticulum synthesises lipids (smooth endoplasmic reticulum) and proteins (rough endoplasmic reticulum) which are responsible for formation of membrane. Thus, they help in membrane biogenesis.

Question 58:
In brief state what happens when
(a) Dry apricots are left for sometime in pure water and later transferred to sugar solution?
(b) A red blood cell is kept in concentrated saline solution?
(c) The plasma-membrane of a cell breaks down?
(d) Rheo leaves are boiled in water first and then a drop of sugar syrup is put on it?
(e) Golgi apparatus is removed from the cell?
Answer:
(a) Dry apricots when placed in pure water swell due end osmosis (inward movement of water) and later when are transferred sugar solution exosmosis (outward movement of water) occurs and they shrink again.
(b) When a Red Blood Cell is placed in concentrated saline solution exosmosis occurs and the RBCs shrink due to excess loss of water.
(c) Breaking of the plasma membrane leads to the scattering of the cell organelles as it forms the basic supporting unit of the cell.
(d) When Rheo leaves are boiled in water first and then a drop of sugar syrup is put on it, osmosis does not occurs, due to the death of the cells of the leaf. This shows that selective premeability is property of living plasma membrane.
(e) Golgi complex helps in the package, storage and transfer of proteins synthesised by ribosomes. Thus, when ribosomes are removed the cell will not function properly.

Question 59:
Draw a neat diagram of plant cell and label any three parts which differentiate it from animal cell.
Answer:

(i) Cell wall in the characteristic feature of plant cell.
(ii) Chloroplast is found in plant cell which helps in photosynthesis in plants. Animals cannot synthesise their own food because chloroplast is not found in the animal cell.
(iii) Large vacuoles are found in plant cell which contains excretory waste of plant cell. Animal cell do not possess vacoules, if present these are of small size.