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Selina Concise Biology Class 9 ICSE Solutions Cell: The Unit Of Life

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Selina Concise Biology Class 9 ICSE Solutions Cell: The Unit Of Life

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 9 Biology Chapter 2 Cell: The Unit Of Life. You can download the Selina Concise Biology ICSE Solutions for Class 9 with Free PDF download option. Selina Publishers Concise Biology for Class 9 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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ICSE SolutionsSelina ICSE Solutions

Selina ICSE Solutions for Class 9 Biology Chapter 2 Cell: The Unit Of Life

Exercise 1

Solution A.

(a) Ribosomes → Synthesis of proteins
(b) a single cell
(d) cell membrane
(a) absence of centrosome
(c) Cellulose
(a) Mitochondria

Solution B.1.

(a) Mitochondria
(b) Ribosomes
(c) Chromosomes
(d) Centrosome
(e) Lysosomes
(f) Cell membrane

Solution B.2.

(a) F (False). Animal cells do not contain a cell wall.
(b) F (False). A cell wall is made up of cellulose.
(c) T (True)
(d) T (True)
(e) F (False). In eukaryotes, cytoplasm is the part of the cell which surrounds the nucleus.
(f) T (True)
(g) T (True)

Solution B.3.

23 pairs of chromosomes are found in human cells.

Solution B.4.

DNA (Deoxyribonucleic acid)

Solution B.5.

Column A Column B
    (a) Vacuoles(iii) Covered by tonoplast
    (b) Nucleolus(v) Forms RNA
    (c) Lysosomes(i) Intracellular digestion
    (d) Anthocyanin(iv) Dissolved in the cytoplasm
    (e) Cristae(ii) Respiratory enzymes

Solution B.6.

(a) Lysosome
(b) Centriole
(c) Plasma membrane
(d) Insects
(e) Genes
(f) Leucoplast

Solution C.1.

Protoplasm is the living matter of the cell. Protoplasm cannot be analysed chemically because the chemical composition of protoplasm is very complex. It varies slightly from one cell to another, although the common elements included in the composition of protoplasm such as carbon, hydrogen, oxygen, nitrogen, sulphur, iron and phosphorus are still the same in all the cells.

Solution C.2.

Organs of an organism are the parts of the body which have a definite shape and structure and perform specific functions. Cell organelles are also parts of the cell which have a definite shape and structure and perform specific functions. Organelles have the same status in a cell as the organs have in the entire body of an animal or a plant performing specific functions.

Solution C.3.

The cells of an elephant would be of the same size as the cells of a rat. The size of cells does not vary within the organisms, however, the number of cells varies from one organism to another. A larger animal like an elephant will have more number of cells as compared to a smaller animal like a rat. However, the size of the cell will be the same.

Solution C.4.

(a) Protoplasm and cytoplasm

ProtoplasmCytoplasm
(i) It is the living matter, the total substance of a living cell, i.e. the cytoplasm and the nucleus.(ii) It is a mixture of water and soluble organic and inorganic compounds, in which various cell organelles are embedded.

(b) Nucleolus and nucleus

NucleolusNucleus
(i) It is a round-shaped nucleoli present inside the nucleus.(ii) It is a dense spherical structure present in the cell that contains a network of thread-like structures called chromatin fibres.

(c) Centrosome and chromosome

Centrosome Chromosome
(i) It is a clear area of cytoplasm close to the nucleus, from which spindle fibres develop during cell division.

(ii) Centrosome is found only in an animal cell.

(i) Chromosomes carry hereditary information or genes which transmit genetic characters from parents to offspring.

(ii) Chromosomes are found in the nucleus of both, animal and plant cells.

(d) Cell wall and cell membrane

Cell wallCell membrane
(i) It is a non-living rigid layer.(i) It is a living, thin, flexible membrane.
(ii) It is made of cellulose.(ii) It is made of lipoproteins.
(iii) It is freely permeable.(iii) It is semi-permeable.

(e) Plant cell and animal cell

Plant cellAnimal cell
(i) Cell wall is present.(i) Cell wall is absent.
(ii) Centrosome is absent.(ii) Centrosome is present.
(iii) Vacuoles are large and prominent.(iii) Vacuoles are small and temporary.
(iv) Plastids are present.(iv) Plastids are absent.

(f) Prokaryotes and eukaryotes

ProkaryotesEukaryotes
(i) Organisms with cells containing a primitive, undefined nucleus are called prokaryotes.(i) Organisms with cells containing a well-defined nucleus with a nuclear membrane are called eukaryotes.
(ii) They contain small ribosomes.(ii) They contain larger ribosomes.
(iii) They lack other cell organelles.(iii) They contain other cell organelles.
(iv) Examples: Bacteria, blue-green algae(iv) Examples: Euglena, Human beings

Solution C.5.

Features found only in plant cells:

  1. Presence of cell wall
  2. Presence of large vacuoles. The liquid contained in vacuoles is called cell sap
  3. Presence of plastids

Features found only in animal cells:

  1. Presence of centrosome

Solution C.6.

Cells generally remain small in size because:

  1. To enable different regions of the cell to communicate with each other rapidly for the cell to function effectively
  2. To have a large surface area is to volume ratio for greater diffusion of substances, in and out of the cell

Solution D.1.

Postulates of cell theory:

  1. Cell is the smallest unit of structure of all living things.
  2. Cell is the unit of function of all living things.
  3. All cells arise from pre-existing cells.

Cell theory was propounded by Theodor Schwann and Matthias Schleiden in the year 1839 and was modified by Rudolf Virchow in 1858.

Solution D.2.

Living cellBrick in a wall
1. Non-rigid living structure1. Rigid non-living structure
2. Mainly composed of cellulose2. Mainly composed of soil
3. Freely permeable3. Impermeable

Solution D.3.

CellsPlastidPigment
(a) petals of sunflowerChromoplastsXanthophyll
(b) ripe tomatoChromoplastsCarotene
(c) skin of green mangoChloroplastsChlorophyll
(d) cells of potatoLeucoplastsNo pigment

Solution D.4.

(a) Plasma membrane:

  1. Separates contents of the cell from its surroundings
  2. Regulates the entry of certain solutes and ions
  3. Maintains the shape of animal cell

(b) Ribosome:

  1. Protein synthesis

(c) Lysosomes:

  1. Intracellular digestion
  2. Destroy foreign substances
  3. When the cell is old or injured, lysosomes rapidly destroy cell organelles and hence, are called suicide bags.

(d) Mitochondria:

  1. Synthesis of respiratory enzymes
  2. Release of energy from pyruvic acid produced in cytoplasm in the form of ATP

(e) Golgi apparatus:

  1. Synthesis and secretion of enzymes, hormones, etc.
  2. Formation of acrosome of sperm

(f) Cytoplasm:

  1. Different organelles contained in it perform different functions.
  2. All metabolic activities occur in it.

(g) Asters of centrosome:

  1. Initiates and regulates cell division
  2. Forms spindle fibres

(h) Chromosomes:

  1. Carry genetic characters from parents to offspring

(i) Glycogen granule:

  1. Serves as food for the cell

(j) Vacuoles:

  1. Gives turgidity to the cells
  2. Storage of water and other substances, food, pigments and waste products

Solution D.5.

Common features found in both plant and animal cells:

  1. Presence of cell membrane
  2. Presence of liquid matrix called cytoplasm in the cell
  3. Presence of mitochondria which produces energy
  4. Presence of ribosomes that synthesize proteins
  5. Presence of Golgi body
  6. Presence of a prominent nucleus

Solution E.1.

(a) Fig. B is a plant cell. It has a cell wall and a large vacuole which pushes the nucleus towards the periphery.
(b) Cell membrane, ribosomes, nucleus, endoplasmic reticulum, lysosomes, Golgi body and mitochondria are common to both the types.
(c) Plastids and cell wall are found only in plant cell. Centrosome is found only in animal cell.

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Describe The Structure Of A Generalized Cell

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Structure Of A Generalized Cell

Though cells may differ in shape and size, all of them have the same basic structure, referred to as the generalized cell structure or generalized cell. A cell has both living and non-living parts. The living parts of the cell that have a definite shape, structure, and function are called organelles.

The main parts of a generalized cell are cell membrane, cytoplasm, and nucleus.

Cell membrane: It is the outer covering of a cell. It is a porous membrane through which selected substances can enter or leave the cell. The cell membrane is also called plasma membrane.

Cytoplasm: It is a jelly-like fluid that fills up the part of the cell between the cell membrane and the nucleus. Several organelles are embedded in the cytoplasm.

Nucleus: It is considered to be the brain of the cell. Nucleus is surrounded by a membrane called the nuclear membrane and is filled with a semi-solid substance called the nucleoplasm. Thread-like structures called chromosomes are present in the nucleoplasm. Chromosomes carry genes, which transfer the characteristics of a cell to the new cells that are formed during cell division. Also present inside the nucleus is a round granule called nucleolus, which contains a network of fibrous material called chromatin fibres.

Figure shows a generalized cell. It is important to note that some of the organelles shown in figure may be present only in plant cells and not in animal cells and vice versa.

Structure of a Generalized Cell 1
Structure of a Generalized Cell

Let us learn about the cytoplasmic organelles shown in figure.

Golgi apparatus (or Golgi body): It is made up of tubules (long tube-like structures), vesicles (small vessels), and vacuoles and is responsible for the secretion of chemical substances like enzymes, hormones, and proteins.

Vacuole: It is a fluid-filled space enclosed in a membrane. Vacuoles store excess water, useful minerals, pigments, and many other substances.

Lysosome: Lysosomes contain chemical substances called enzymes that are capable of digesting cells and a variety of intra- and extra-cellular materials [intra, internal (inside); extra, external (outside)]. In times of emergency, lysosomes burst and destroy the cell. Hence, they are also called suicide bags of the cell.

Endoplasmic reticulum :It is a network of tubules and channels and is involved in the synthesis, storage, and transport of cell products.

Ribosomes: These are small granular structures scattered in the cytoplasm that act as sites of protein synthesis.

Centrosome: This structure is present only in animal cells. The main function of centrosomes is to initiate and regulate cell division.

Plastids: These are present only in plant cells. Plastids contain certain pigments that have a specific role to play in the functioning of the plant. Depending on the pigment colour, plastids are of three kinds: chloroplasts, chromoplasts, and leucoplasts.

  • Chloroplasts contain the green pigment chlorophyll, which helps plants in making food.
  • Chromoplasts contain non-green pigments that give colour to flowers and fruits.
  • Leucoplasts are colourless and store food in the form of carbohydrates, fats, and proteins.

Mitochondria (singular mitochondrion): These are tiny spherical or rod-shaped bodies. They act as sites of energy production and are, therefore, called the powerhouses of the cell.

Structural Variations in Cells

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Cells: Variation in Number, Shape, and Size

All living things carry out certain basic functions with the help of different sets of organs. Cells are called the structural unit of an organ. These may be compared to the bricks of a wall. As bricks are assembled to make a wall, similarly, cells are assembled to form an organism. Let us find out more about cells.

The smallest structural and functional unit of an organism is called a cell. Cells of organisms show variation in terms of their number, shape, and size. Let us discuss each of these variations in detail.

Variation in Number
All living organisms are made up of one or more cells. On the basis of cell number, organism are grouped into 2 categories. Bodies of organisms may consist of one or many cells. Organisms whose body consists of a single cell are called unicellular organisms. Examples of unicellular organisms are Amoeba, Paramoecium, Euglena, and bacteria. Thus, in a unicellular organism, a single cell performs all vital activities like feeding, movement, respiration, and reproduction. Organisms whose body consists of many cells are called multicellular organisms. For example – Plants, animals & fungi. Most plants and animals (including human beings) are multicellular organisms.

Variation in Size
Most cells are microscopic and cannot be seen with the naked eye. Cell size may vary from a micrometre (a millionth of a metre) to a few centimetres. The smallest cells are bacteria, which generally range in size from 0.1 to 0.5 micrometre. The largest cell is the egg of an ostrich, which is 170 millimetre in diameter. Human nerve cells are believed to be the longest cells.

  1. The size of different cells ranges between broad limits.
  2. Some plants and animals cells are visible to the  naked eye.
  3. Most cells are visible only with microscope.
  4. The prokaryotic cells usually range between 1 to 10 mm.
  5. The eukaryotic cells usually range between 10 to 100 mm.
  6. Amoeba proteus may reach a diameter of 0.5 mm.
  7. The smallest cells are those of Mycoplasma laidlawiil (0.1µ in dimeter) or PPLO (pleuro pneumonia like organism).
  8. The largest cell is egg of an Ostrich.

Variation in Shape
Cells exist in different shapes. They can be disc-shaped, polygonal, rectangular, branched, or even irregular. The shape of a cell depends on the specific function it performs. Here are a few examples that illustrate this.

Structural Variations in Cells 1

  1. The shape of cell may be variable or fixed.
  2. Variable shape occur in Amoeba, WBC etc.
  3. Fixed shape occur in most plant and animals.
  4. Cells may be diverse shapes such as polyhedral (8, 12 or 14 sides) spherical (e.g. eggs of mainly animals), spindle shaped (Smooth muscle fibres), elongated (e.g. Nerves cells) so on.

Nerve cells carry messages between different parts of the body. Hence, they are elongated in shape. Muscle cells help in movement through contraction and expansion. Hence, they are thin and long. Skin cells cover a large area. Hence, they are flat in shape.

Activity

Aim: To observe a single cell (hen’s egg).
Materials needed: A hen’s egg, a boiling pan, and water.
Method: Boil the egg and remove the shell. Cut the boiled egg into two halves.
Observation: The boiled egg has a yellow part and a white part surrounding it. The white part is called albumin while the yellow part is called yolk. In an unboiled egg, the albumin is a jelly-like transparent liquid. The yolk looks like a thicker yellow jelly.
egg

PREPARING A SLIDE TO VIEW CELLS

Most cells are viewed with the help of a compound microscope. To view a specimen under a microscope, it has to be first placed Inanimate Not alive on a glass slide. Placing the specimen on the slide is called mounting. Two types of mounts are generally prepared in the laboratory: dry mount and wet mount.

A dry mount is generally used for viewing inanimate objects. As the term suggests, a dry mount does not require water. Wet mounts are generally prepared using water and are used for viewing living specimens like organisms and cells. In a wet mount, a small piece of the specimen is placed at the centre of the slide with one or two drops of water. The specimen is then covered with a coverslip and viewed under a microscope. In case of permanent slides (i.e., slides that need to be preserved for later use), materials other than water need to be used as the specimens have to be preserved for a longer duration.

The specimen to be viewed under a microscope is often stained (i.e., coloured) with a dye. Staining highlights biological tissues and specific regions in the cells, which makes it easier for us to view the details. Some of the commonly used staining dyes are safranin, methylene blue, and crystal violet.

Prokaryotic and Eukaryotic Cells
Cells that lack a well-defined nucleus surrounded by a nuclear membrane are called prokaryotic cells. Organisms that have such cells are called prokaryotes (pro, primitive; karyon, nucleus). Examples of prokaryotes are bacteria and blue-green algae. Cells that have a well-defined nucleus are called eukaryotic cells. Organisms that have such cells are called eukaryotes (eu, true; karyon, nucleus). All organisms apart from bacteria, blue-green algae, and viruses are eukaryotes.

Cell Division and Growth
The food that we eat leads to an increase in the size of cells. After reaching a certain size, a cell divides into two by a process known as cell division. Increase in the number of cells in the body as a result of cell division is responsible for growth in organisms. Cell division also replaces the dead or damaged cells with new ones and is, thus, responsible for healing wounds.

Selina Concise Biology Class 9 ICSE Solutions Tissues: Plant And Animal Tissues

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Selina Concise Biology Class 9 ICSE Solutions Tissues: Plant And Animal Tissues

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 9 Biology Chapter 3 Tissues: Plant And Animal Tissues. You can download the Selina Concise Biology ICSE Solutions for Class 9 with Free PDF download option. Selina Publishers Concise Biology for Class 9 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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ICSE SolutionsSelina ICSE Solutions

Exercise 1

Solution A.

  1. (c) Parenchyma
  2. (a) Fibrous connective tissue
  3. (a)Meristem- Actively dividing cells

Solution B.1.

(a) Apical or terminal meristematic tissue
(b) Protective tissue
(c) Columnar epithelium (Epithelial tissue)
(d) Ligament (Connective tissue)
(e) Conducting tissue
(f) Sclerenchyma (Supporting tissue)

Solution B.2.

Sclerenchyma composed of long, narrow and thick cells, which have become dead, forms the least specialized tissue in plants. This tissue forms the walls and boundaries of plant cells and provides strength to tissue plant parts.

Solution B.3.

(a) Tissue
(b) Permanent tissue cells
(c) Cambium

Solution B.4.

(a) Tips of roots
(b) Nose
(c) Lining of mouth
(d) Veins of leaves
(e) Lining of trachea
(f) Bones

Solution B.5.

(a) Squamous epithelium
(b) Cuboidal epithelium
(c) Neuron
(d) Ciliated columnar epithelium

Solution C.1.

Ciliated columnar epithelium is found in the lining of trachea. This epithelium has thread-like projections called cilia at their free ends. The cilia constantly keep lashing and move the materials which enter this organ.

Solution C.2.

Nervous tissue or neurons are specialized group of cells. This tissue is concerned with perception and responses of animals.
The nervous tissue constitutes the nervous system, which is an organ system. It controls and coordinates all the systems of the body.

Solution C.3.

  1. Muscular tissue (Cardiac muscles)
  2. Epithelial tissue (Lining of blood vessels of the heart)
  3. Connective tissue (Fluid connective tissue in the form of red blood corpuscles)

Solution C.4.

A tissue is a group of similar cells from the same origin that together carry out a specific function. An egg is a zygote or a cell but a cluster of eggs cannot be considered as a tissue as it does not form an organ like a tissue. Instead it gives rise to a new individual organism if gets fertilised.

Solution C.5.

  1. Striated muscles: Provide the force for locomotion and all voluntary movements of the body. These muscles are found in the limbs.
  2. Unstriated muscles: Provide movements for the passage of food in the intestines. These muscles are found in iris of the eye, lining of blood vessels, urinary bladder, etc.
  3. Cardiac muscles: Provide rhythmic contraction and relaxation movements. These muscles are found only in the heart.

Solution D.1.

(a) Cell and tissue

CellTissue
A cell is the structural and functional unit of all living beings.
E.g. epithelial cell

A tissue is a group of similar cells which perform a specific function.
E.g. nervous tissue

(b) Organ and organism

OrganOrganism
Several tissues together contribute to specific functions inside the body and constitute an organ.
E.g. stomach

Several organ systems together constitute the organism.
E.g. human being

(c) Organ and organelle

OrganOrganelle
Several tissues together contribute to specific functions inside the body and constitute an organ.
E.g. stomach

Parts of the cell that have a definite function in the cell.
E.g. mitochondria

(d) Organ and organ system

OrganOrgan system
Several tissues together contribute to specific functions inside the body and constitute an organ.
E.g. stomach

Many organs act together to perform a specific life process and constitute an organ system.
E.g. digestive system

Solution D.2.

(a) Parenchyma and Collenchyma

ParenchymaCollenchyma 
(i)  Consists of large thin-walled living cells with a single large vacuole
(ii)  Intercellular spaces may or may not be present

(i)  Consists of elongated cells having thickening in their cell walls
(ii)  Intercellular spaces are totally absent

(b) Meristematic tissue and Permanent tissue

Meristematic tissuePermanent tissue
(i)  Have the capacity to divide
(ii)  Do not have intercellular spaces

(i)  Have lost the capacity to divide
(ii)  Have large intercellular spaces

(c) Sclerenchyma and Parenchyma

Sclerenchyma Parenchyma
(i)  Consist of dead cells
(ii)  Have thick cell walls

(i)  Consist of living cells
(ii)  Have thin cell walls

(d) Cells of involuntary muscle and voluntary muscle

Cells of involuntary muscleCells of voluntary muscle
(i) Small and spindle-shaped(i) Long and cylindrical
(ii) Uninucleate(ii) Multinucleate
(iii) Lack stripes or striations(iii) Show stripes or striations
(iv) Found in the walls of the intestine and lining of blood vessels(iv) Found in the arms, legs, face and neck

(e) Fibres of voluntary muscle and cardiac muscle

Fibres of voluntary muscleFibres of cardiac muscle
(i) Long and cylindrical(i) Short and branched
(ii) Multinucleate(ii) Uninucleate
(iii) Under the control of one’s own will or volition(iii) Not under the control of one’s own will or volition
(iv) Found in the arms, legs, face and neck(iv) Found in the heart

Solution E.1.

(a) The given diagram is of the phloem tissue because the cells show cellular contents unlike the xylem tissue which contains hollow cells without any cellular contents.
(b)
1 → Sieve cell
2 → Phloem parenchyma cell
3 → Companion cell
4 → Sieve plate
(c) The phloem is a food-conducting tissue and is likely to be found in the leaves and stem of plants to carry the food manufactured in the leaves to various parts of the plant.
(d)
1 → Sieve cells: Help in the transport of food from leaves to storage organs and other parts of the plant.
2 → Phloem parenchyma cells: Storage of starch, fat and other organic food material.
3 → Companion cells: Help in the functioning of the sieve tube cells.
4 → Sieve plate: Perforations in the sieve plates allow water and dissolved organic solutes to flow along the sieve tube.

Solution E.2.

(a) The given diagram shows a nerve cell or neuron.
(b)
1 → Dendrites/Dendrons
2 → Axon
3 → Nucleus
4 → Cyton/Perikaryon
5 → Neurolemma
6 → Axon endings
(c) The nerve cell is likely to be found in the nervous system of the human body. The function of the nerve cell is to transmit messages from one part of the body to another. It is associated with perception and responses of animals.

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