JKBOSE 9th Class Science Solutions Chapter 11 The Fundamental Unit Of Life

◆  Nucleus contains chromosomes composed of DNA and protein.

◆  Functional segment of DNA are called gene.

◆  Protoplasm. It is the living material of cell, Purkinje coined the term protoplasm.

◆  Cytoplasm is the fluid content of cell present between nucleus and plasma membrane. It contains metabolites and organelles.

◆ Cells are of two types i.e. prokaryotic cell and eukaryotic cell.

◆  Prokaryotic cells lack well organised nucleus and membrane bound organelles.

They have 70 S type of ribosomes.

Prokaryotic cell	Eukaryotic cell
1. Found in bacteria, Blue-green algae and Mycoplasma.	1. Found in Protista, Fungi, Plantae and Animalia.
2. Primitive nucleus called nucleoid present. Chromosome is single, circular and double stranded DNA but no proteins (so naked), No nuclear membrane.	2. A true nucleus present. Chromosomes are two to many, linear and formed of DNA and histones. Nuclear membrane present.
3. Cell wall when present, it is formed of peptidoglycan.	3. Cell wall when present in plant cells it is formed of cellulose.
4. Membrane bound cell organelles absent.	4. Present.
5. Ribosomes 70 S type. Small sized (1-10 μm).	5. 80 S type. Large sized (5-100 μm).

◆ Endoplasmic reticulum is an electron-microscopic interconnected network of cisternae, vacuoles and tubules. It is of two types: RER (cisternae are studded with ribosomes and involved in protein synthesis) and SER (tubules are without ribosomes).

1. It is a passage way for intracellular and intercellular transport of materials.

2. It gives internal support to the cell.

3. SER is involved in synthesis of lipids and steroids

4. RER is concerned with protein synthesis.

◆ Ribosomes are composed of RNA and proteins, granular electron-microscopic particles without membrane.

Function.

These act as protein factories.

◆ Golgi body is formed of stacked cisternae with swollen ends, vacuoles and vesicles. Functions.

1. It is involved in cell secretions such as mucous, enzymes and hormones.

2. It helps in storage of secretory products.

◆ Lysosomes are electron-microscopic single membrane bound vesicular structures of animal cells and contain hydrolytic enzymes.

Functions. 1. These are centres of intracellular digestion and act as both digestive bags and suicidal bags.

2. They destroy foreign substances.

3. They remove cellular debris.

◆ Mitochondria are rod-shaped, double-membranous, light-microscopic, eukaryotic structures. Inner membrane is with cristae and oxysomes.

Functions. These act as power houses or ATP mills as they are site for cellular respiration and release energy.

◆ Plastids are the largest sized eukaryotic structures of plant cells. These are of three types :

(i) Leucoplasts (colourless and store the food). Primary function of leucoplast is less and store the food). Primar storage.

(ii) Chloroplasts (green coloured and are sites of photosynthesis, so called kitchens of cells) or los or

Each chloroplast is double-membranous structure having grana in its inner chamber.

Each granum is formed of many chlorophyll containing thylakoids present in stacks.

Functions. Chloroplasts are site for photosynthesis.

(iii) Chromoplasts (coloured and help in pollination of flowers and dispersal of seeds and fruits).

◆ Centrosome is a structure found in animal cells and is formed of two microtubular centrioles, each being formed of 9 triplet microtubules showing 9 + 0 arrangement.

Function. These help in cell division.

Basal bodies give rise to cilia or flagella.

◆ Cell inclusions include reserve food in the form of glycogen granules or lipid droplets or starch grains. Con to our angle

◆ Vacuoles and fluid filled membrane bound spaces each containing cell sap within a outonoplast, wastes, gases, secretions, etc.

Functions. They help in storage of food, water and other wastes.

◆ Contractile vacuoles are present in fresh water protozoans.

⇒ Robert Hooke (1665) discovered the cell for the first time. A.V. Leeunwenhoek observed living cell for first time.

⇒ Electron microscope was discovered in 1942.

⇒ Water obeys laws of diffusion.

⇒ Diffusion of gases occur from high concentration to low concentration.

⇒ Nucleus plays a central role in cellular reproductions, the process by which a cell divides and forms two new cells.

⇒ Membrane biogenesis Building up of membrane from proteins and lipid is known as membrane biogenesis. CH

⇒ SER also plays role in detoxification.

⇒ Camillo Golgi discovered Golgi bodies and shared Noble Prize in 1906 with Santiago Ramony Cajal for their work on structure of nervous system.

⇒ Vacuoles are sacs storage for solid or liquid contents.

⇒ The large central vacuoles of plant cell occupy 50-90% of cell volume and are full of cell sap.

⇒ Vacuoles provide turgidity and rigidity to the cell.

⇒ Food vacuoles of single celled organisms (Amoeba, Paramecium) help in digestion of food.

⇒ Prokaryotes. The simple organisms called Monerans without proper nucleus.

⇒ Nucleoid. A primitive nucleus of prokaryotes, not covered by nuclear membrane.

⇒ Eukaryotes. Organisms with true nucleus.

⇒ Cyclosis. Streaming movements of cytoplasm.

⇒ Autolysis. Self digestion of cell by its lysosomal enzymes.

⇒ Cell. Structural and functional unit of living organism.

⇒ Protoplasm. Living material of cell is termed Protoplasm.

⇒ Cytoplasm. It is the material within a living cell, excluding cell nucleus. It comprises cytosol and organelles.

⇒ Nucleus. Controlling centre of cell.

⇒ Autophagy. Digestion of its own cell organelles or reserve food by the lysosome.

⇒ Cristae. Infolds of inner mitochondrial membrane.

⇒ Leucoplasts. Colourless plastids.

⇒ Chloroplast. Chlorophyll-containing green coloured photosynthetic plastids.

⇒ Chromoplast. A pigmented plastid.

⇒ Tonoplast. Vacuolar membrane present around cell sap.

⇒ Diffusion. It is net movement of molecules or atoms from a region of high and concentration to a region of low concentration.

⇒ Gene. Functional segment of DNA.

⇒ Pinocytosis. Intake of fluid material in the cell.

⇒ Phagocytosis. Intake of solid material.

Ans.— Robert Hooke (1665) discovered cell for the first time. He examined a thin slice of cork under the microscope. He observed that cork resembled the structure of a honey comb consisting of many hexagonal compartments and called these boxes ‘cells’.

Ans.— 1. Cells are arranged in proper and systematic order to form a body of living organism. Thus cells serve as basic building structural units for more complex organisms.

2. Cell is also functional unit of life because all the metabolic activities of life take place at cell level.

3. Vital functions such as respiration, digestion, excretion and reproduction occur at cell level.

4. Cells contain genetic material which regulate cell functions and pass on all information to the next generation.

Ans.— The substances like CO₂ and water move in and out of cell by the process of diffusion. There is spontaneous movement of substances from higher concentration to lower concentration. The movement of water across selectively permeable membrane is called osmosis.

Ans.— Plasma membrane permits the entry and exit of selected materials in and out of the cell. It also prevents movement of some other materials required within the cell. The membrane is called selectively permeable membrane.

Prokaryotic Cell	Eukaryotic Cell
1. Size : generally small (1 – 10 μm) = 10–6 m	1. Size: generally large 5 – 100 μm
2. Nuclear region ………………  and know as ………… .	2. Nuclear region well defined and surrounded by a nuclear membrane.
3. Chromosome single.	3. More than one.
4. Membrane bound cell organelles absent.	4. …………………………….. .

Ans.— 2. Nuclear region undefined due to absence of nuclear membrane and are a known as Nucleoid.

4. Membrane bound cell organelles such as mitochondria, Golgi bodies, chloroplast etc. present.

Ans.— 1. Chloroplasts 2. Mitochondria.

Ans.— Cell will stop performing basic functions and result in its death.

Ans.— Lysosomes are membrane-bound sacs filled with enzymes and these enzymes may digest their own contents if burst. They carry out autolysis (auto= self; lysis – break down) hence called “suicidal bags.”

Ans.— Proteins are synthesised on the ribosomes which are attached to the surface of ER or lie freely in the cytoplasm. Ribosomes are also called “protein factories” of cell.

Ans.— 1. The Golgi apparatus performs the function of storage, modification and packaging of materials synthesised in the cell. These materials will not be able to perform their function in its original form.

2. The formation of lysosomes will be affected.

Ans.— Mitochondria are known as ‘power house’ of the cell. They are sites for synthesis, storage and transport of ATP (Adenosine triphosphate) commonly called energy currency.

Ans.— 1. Proteins are synthesised by ribosomes.

2. SER is site for synthesis of lipid.

3. These proteins and lipids are modified by Golgi apparatus to form plasma membrane.

Ans.— Plasma membrane is flexible and it enables the cell to engulf in food and other materials from the external environment. Such a process is termed endocytosis.

Ans.— Osmosis. It is a special case of diffusion of water through a selectively permeable membrane. It is a passage of water from a region of higher concentration through a semipermeable membrane to a region of low water concentration.

Take four peeled potatoes halves and hollow 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 this setup 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.

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

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

Ans.— (1) The water gathers in hollowed portion of potato cups B and C due to osmosis.

(ii) Cup A acts as control experiment and indicates that cavity of potato will not induce any type of movement.

(iii) Cup A does not contain hypertonic solution hence water does not rise. In cup D, cells of potato cup being boiled cells are dead and no osmosis occurs.

Ans.— 1. The prokaryotes have a single membrane.

2. Cells which have respiratory enzymes associated with plasma membrane.

3. Circular DNA without proteins, forming a single prochromosome called nucleoid and lying in direct contact with cytoplasm.

4. They have 70 S ribosomes.

5. They lack membrane-bound organelles, sap vacuoles.

6. They do not show cyclosis, phagocytosis, pinocytosis and exocytosis.

7. Cell division by fission or budding.

Examples. Bacteria, Blue-green algae and Mycoplasma.

Ans.— 1. The eukaryotic cells have double membrane and plasma membrane devoid of respiratory enzymes.

2. These cells have linear DNA associated with proteins forming two to many chromosomes enclosed by a nuclear envelope. Thus proper well defined nucleus is present.

3. There are present 80 S ribosomes.

4. Many membrane-bound organelles such as mitochondria, chloroplasts, lysosomes etc., and sap vacuoles present.

5. Form mitotic apparatus in cell division and undergo meiosis.

6. They may show cyclosis, phagocytosis, pinocytosis and exocytosis.

Examples. Plant cell, Animal cell, Amoeba, Euglena.

Ans.— Structure of prokaryotic cells 

Ans.— Refer to Basis and Basics.

Ans.— (i) Cylindrical (ii) (1) Nucleus (2) Cytoplasm (3) Cell Well.

(iii) Function of cytoplasm. It is ground substance and site for various metabolic reactions.

Ans.— A generalized plant cell consists of three distinct parts viz, cell wall, cell membrane or plasma membrane and protoplasm.

1. Cell wall. It is the outermost covering of a cell made up of a non-living substance called cellulose.

2. Cell membrane or Plasma membrane. It is thin, delicate and elastic protoplasmic covering lying internal to the cell wall.

The plasma membrane controls the entrance and exit of molecules and ions.

3. Cytoplasm. It consists of a number of living and non-living structures. The living structures are called cytoplasmic organelles or cell organelles and include structures like endoplasmic reticulum, ribosomes, Golgi apparatus, mitochondria, lysosomes, plastids, vacuoles etc.

(a) Plastids. Plastids are spherical or discoid bodies containing different types of pigments in them. They are of three types viz. chloroplasts, chromoplasts and leucoplasts. The chloroplasts contain a green pigment in them, called chlorophyll. They play a vital role in the process of photosynthesis. Leucoplasts are colourless plastids. They are Popul concerned with the storage of starch.

(b) Vacuoles. These are fluid-filled bubble-like structures bounded by a membrane, called tonoplast. They are mostly found in plant cell. Vacuoles provide turgidity and rigidity to cell.

4. Nucleus. It is a dense spherical body bounded by a membrane, called nuclear membrane. Embedded within the nuclear sap are found a number of thread-like structures called chromosomes with genes on them. The nucleus controls the various metabolic activities of the cell.

Ans.— Ultrastructure of plant cell. Refer to Basis and Basics. (Fig)

Ans.— (i) Position. It is a thin, transparent, electron microscopic, elastic, regenerative and semipermeable membrane present outside the protoplasm. It is also called cell membrane or plasmalemma.

(ii) Structure. The plasma membrane is a lipoproteinaceous and trilaminar membrane in which outer and inner layers are formed of globular protein molecules which move as icebergs in lipid layers. Carbohydrates are present only on outer surface of plasma membrane.

(iii) Functions. Plasma membrane is a semipermeable or selectively permeable membrane which regulates the exchange of materials between the cytoplasm and environment. It is a dynamic membrane whose permeability varies.

Ans.— Refer to Basis and Basics. (Fig)

Ans.— (i) Structural and functional unit of life is called cell.

(ii) A cell is mass of protoplasm formed of different types of inorganic and organic biomolecules and externally bounded by a thin and semipermeable plasma membrane.

Ans.— A cell which is very active cannot have a very large volume because the amount of nutrients needed for various metabolic reaction depends on the cell volume. Small bodies have more surface per unit volume than the large bodies.

Ans.— Compound microscope. There are two main types of microscopes-light (optical) and electron.

1. Light or optical microscopes employ visible light for illumination.

2. Glass lenses are used in combination to increase magnification. Therefore, these microscopes are also called compound microscopes.

3. They have a maximum magnification of 2000-4000 times.

4. Light microscopes cannot resolve objects smaller than 0.25-0.30 μm.

1. Shapes of the cells differ not only in different organisms but also in different parts of same organism. They may be oval, spherical, discoid, cuboidal, columnar, spindleshaped etc..

2. The shape of the cell is usually related with its location and function.

3. Amoeba and leucocytes go on changing their shapes to enable them to engulf the

materials.

Ans.— M.J. Schleiden and Theodore Schwann (1938-39) proposed cell theory. The cell theory can be stated as follows :

(a) The body of all living organisms is composed of cells. Cell is a unit of structure and function of life.

(b) New cells are formed from the pre-existing cells only. (R. Virchow).

(c) The life is passed from one generation to the next generation through a single cell.

Ans.— Three major functional regions of a cell are:

1. Plasma membrane 2. Nucleus 3. Cytoplasm

Ans.— Unicellular organism. In such organisms, a single cell carries out all life processes with the help of organelles. They are also called acellular organisms.

Multicellular organism. A multicellular organism is made up of large number of cells. The cells are differentiated to share varied functions performed by unicellular organisms. Whatever the case may be, all multicellular organisms start their life from a single cell. The multicellular organism represents itself in two forms – as an individual and as a member of assembly of cells.

1. The division of labour in a multicellular organism increases the efficiency of the organism.

2. It promotes the chance of survival.

Ans.— Differences between cell wall and cell membrane 

Cell wall	Cell membrane
1. It is present only in plant cells where it lies outside the cell membrane.	1. It occurs in animal cells and plant cells.
2. Dead in nature and permeable.	2. Living membrane and is semi – permeable.
3. Composed of cellulose.	3. Composed of lipids and proteins.
4. It is thick in nature.	4. Comparatively very thin.

Ans.— Functions of cell wall

1. It provides shape and rigidity to the cell.

2. It protects the protoplast.

3. It is involved in the movement of materials in and out of the cell.

Ans.— The plasma membrane is flexible made of three layers consisting of a central lipid layer, sandwiched between two protein layers. From this it is obvious that the main constituents of the plasma membrane are lipids and proteins.

Ans.— Functions of plasma membrane

1. It provides shape to the cell.

2. It protects the contents of cell.

3. It protects the cell from injury.

4. It regulates the flow of material into and out of cell. It allows only the selected substances to move across it.

5. It forms organelles of cell.

Ans.— Viruses lack any kind of membrane and hence do not show characteristics of life until they are present a living body and use its cell machinery to multiply.

Ans.— Diffusion. Transport of metabolites across the membrane along the concentration gradient and without the use of carrier molecule and energy is called simple diffusion.

Movement of substances takes place from a high concentration to a low concentration region. Exchange of gases also occurs by diffusion.

Illustration. The simple diffusion canno be demonstrated by keeping crystals of copper sulphate wrapped in a cloth in a beaker of water.

Observation. The water just outside the SWALORY bag turns blue shortly. The colour then spreads progressively until all the water turns uniformly blue.

Conclusion. Evidently, the dissolved copper sulphate diffuses out through the of the cloth from the area of high concentration to an area of low concentration until it attains an identical concentration in the entire volume of water.

Ans.—  Mitochondrion Structure. Mitochondria are power house’ of cells. It has two mitochondrial membranes and two chambers. Inner mitochondrial membrane is produced into finger-like processes called cristae to increase the surface area for the distribution of respiratory enzymes of electron transport chain. Cristae are studded with regularly placed knob-like oxysomes which take part in energy releasing reactions. Inner chamber is filled with a granular matrix respiratory enzymes. Matrix present in inner chamber also contains DNA, ribosomes.

1. These are called power houses or power plants or ATP mills as these are site aerobic oxidation (cellular respiration) of glucose to produce energy-rich ATP molecules.

2. They store and transport ATP molecules.

Ans.— Plastids. These are double membrane bound organelles found in plant cell. These are of three types: 1. Chromoplasts 2. Chloroplasts 3. Leucoplasts.

Ans.— Functions of plastids.

1. Chloroplasts are the site of photosynthesis so called as kitchen of the cell.

2. Chromoplasts provide colour to flowers and fruits.

3. Leucoplasts are site of storage of food.

Ans.— (i) Structure. A chloroplast is formed of two membranes and two chambers, so resembles a mitochondrion. Outer membrane is freely permeable while inner membrane is semipermeable. Inner chamber is filled with a denser and granular proteinaceous (about 50%) ground substance called stroma or matrix. It is site of dark reaction of photosynthesis and has a number of grana, 70 S ribosomes and DNA molecules (circular and naked)

Grana are site for light reactions of photosynthesis.

(ii) Function of Chloroplasts. These are sites of photosynthesis, so are called “kitchens of cell.”

Ans.— A true nucleus is present in all the eukaryotic cells except mammalian RBCs, sieve tube cells, tracheids and vessels. It directs life processes of cells. It is formed of four components :

(a) Nuclear membrane. It is a two-layered envelope around the nuclear sap. It is porous (with nuclear pores) and semipermeable membrane. It regulates exchange of materials between nucleoplasm and cytoplasm.

(b) Nucleoplasm. It is a semifluid colloidal substance in which nucleoli and chromatin fibres are present.

(c) Nucleolus. It is dense, spherical, naked and darkly stained structure and is the site of formation and store house of rRNAs.

(d) Chromatin fibres. These are long, fine and darkly stained threads which collectively form nuclear reticulum. During cell division, these condense to form a species specific number of rods, called chromosomes. Chromosomes are composed of DNA and proteins. Functional segments of DNA are called genes and act as units of heredity and variations.

Ans.— The nucleus performs the following important functions :

(i) The nucleus controls all the cellular activities of the cell. UN nislas.03

(ii) It contain genetic material. The nucleus plays an important role in transmission of hereditary characters from parents to offsprings.

(iii) The nucleus plays a vital role in cell division (cell reproduction).

Ans.— There are two forms of endoplasmic reticulum. They are the following :

1. Rough type (RER) : Ribosomes are associated with rough endoplasmic reticulum.

2. Smooth type (SER): Golgi apparatus are associated with smooth endoplasmic reticulum.

Ans.— Components of ER.

Ans.— Cell.

Ans.— Robert Hooke (1665)

Ans.— Robert Hooke.

Ans.— A.V. Leeuwenhoek (1667).

Ans.— Discovered nucleus in the cells of orchid.

Ans.— M.J. Schleiden and Theodore Schwann.

Ans.— He stated “omnis cellula e cellula” which means new cells are formed by the growth and division of pre-existing cells.

Ans.— A eukaryotic (Eu = good, Karyon = nucleus) cell has a true nucleus (with nuclear membrane), 80 S ribosomes, membrane bound cell organelles like ER, Golgi body, mitochondria, etc. and cytoplasm shows cyclosis.

Ans.— (i) Plasma membrane. (ii) nucleus and (iii) cytoplasm.

Ans.— Ribosomes.

Ans.— Lysosome.

Ans.— Power houses or ATP mills.

Ans.— ATP. Adenosine triphosphate

Ans.— Respiratory enzymes.

Ans.— Plastid (chloroplast).

Ans.— Leucoplasts, chloroplasts and chromoplasts.

Ans.— Chloroplast. It is site of photosynthesis in green plants. During this process plant prepare their own food by trapping solar energy and use CO₂ and water as raw materials.

Ans.— Cell secretion and acts as condensation membrane.

Q. 19. Which organelle plays central role in cellular reproduction ?

Ans.— Nucleus.

(A) Robert Hooke

(B) Antony Von Leeuwenhoek

(C) Purkinjee

(D) Hertwig.

Ans.— (C) Purkinjee

(C) swell up and finally burst

(D) become sickle shaped.

Ans.— (B) shrink and become wrinkled

(A) controlling volume

(B) intake of materails

(C) its selective permeability

(D) protection against bursting.

Ans.— (D) protection against bursting.

(A) cellulose

(B) proteins

(C) lipids

(D) all above.

(A) water

(B) organic substances only

(C) inorganic substances only

(D) inorganic substances only.

Ans.— (D) inorganic substances only.

(A) Cell wall

(B) Mitochondria

(C) Ribosome

(D) Golgi apparatus.

Ans.— (A) Cell wall

(A) Respiration

(B) Protein synthesis

(C) Fat synthesis

(D) Photosynthesis.

Ans.— (B) Protein synthesis

(A) Protein synthesis

(B) nucleotide synthesis

(C) Lipid synthesis

(D) Secretory functions.

Ans.—  (A) Protein synthesis

(A) residual bodies

(B) suicidal bags

(C) autophagic vacuoles

(D) All of these.

Ans.— (B) suicidal bags

(A) Batteries

(B) power house

(C) plasmosomes

(D) Both (A) and (B).

Ans.— (D) Both (A) and (B).

(A) cytoplasm

(B) plasmalemma

(C) mitochondria

(D) Both (A) and (B)

Ans.— (C) mitochondria

(A) lipid synthesis

(B) proteolysis

(C) peptide bond formation

(D) chlolesterol synthesis

Ans.— (A) lipid synthesis

(A) lipid-protein-lipid

(B) protein-lipid-protein

(C) single unit membrane

(D) only steroids.

Ans.— (B) protein-lipid-protein

(A) nucleolus

(B) mitochondrion

(C) nucleus

(D) ribosome.

Ans.— (C) nucleus

(A) plasmalemma

(B) cell wall

(C) tonoplastive

(D) plasmodesmata.