Biology For Class IX - Chapter No.4 - Cells And Tissues - Questions and Answers

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CHAPTER 4
CELLS AND TISSUES

Questions and Answers

Q.1: What is microscope? Describe parameters of microscopy?
Ans: MICROSCOPE:
Definition:
Microscope was simply a tube with lenses at each end and its magnification ranged from 3X to 9X.
It is define as:
Microscopes are instruments designed to produce magnified visual or photographic images of objects too small to be seen with the naked eye.

Microscopy:
The use of microscope is known as microscopy.

PARAMETERS OF MICROSCOPY:
There are two parameters especially important in microscopy;

• Magnification
• Resolution.

Magnification:

• The enlargement of an image is called magnification.
• By combining a number of lenses in the correct manner, a microscope can be produced an image that will yield very high magnification values.

Resolution:

• The resolution of a microscope is defined as the smallest distance between two points on a specimen that can still be distinguished as two separate objects.
• It helps to measure clarity of object.

IMPORTANCE OF PARAMETERS (MAGNIFICATION AND RESOLUTION):

• Both magnification and resolution are very important if requires a clear large picture of something less than 0.1 µm.
• For example: if a microscope has high magnification but low resolution, than a bigger version of a blurry image is produced.

Q.2: Who invented the microscope?
Ans: Zacharias Janssen (1580-1638) is considered to be the first investigator to invent the compound microscope in the 1590. It was simply a tube with lenses at each end and its magnification ranged from 3X to 9X.
Robert Hooke had improved his version of the compound microscope to observe organisms.

Q.3: Describe the types of microscope?
Ans:TYPES OF MICROSCOPE:
There are two microscopes are used in microscopy i.e:

1. Light microscope (LM)
2. Electron microscope (EM)

(a) Light Microscope:

• Source:
  In a light microscope, visible light passes through the specimen (the biological sample under observation).
  A photograph of an image taken through a microscope is called micrograph.
  
  
• Visibility:
  A live cell can be imaged by light microscope.
  
  
• Resolution:
  The light microscope can magnify the object up to 1000 times
  
  
• Magnification:
  The magnification of a light microscope is formed by using a mixture of the powers of the eye piece and the objective lens.
  Total magnification of an image with a compound light microscope = power of the objective lenses X power of the eye piece.
  If the power of the objective lenses is at 4x, 10x, 40x and
  The power of the eye piece is (typically) 10x.
  That is the object can be magnified, 40x, 100x or 400x.
  Similarly, a 10x eyepiece used with a 10x objective lens will produce a magnification of 100x.

Electron Microscopes:

• Source:
  Electron microscopes are differ from light microscopes.
  They produce an image of a specimen by using a beam of electrons rather than a beam of light.
  Electrons have a much shorter wavelength than visible light, and this allows electron microscopes to produce higher-resolution images than standard light microscopes.
  
  
• Visibility:
  Electron microscopes can be used to examine not just whole cells, but also the subcellular structures and compartments within them.
  A live cell cannot be imaged by electron microscope.
  
  
• Resolution:
  Electron microscope has a resolution as small as 0.2 nanometer (nm)
   .
• Magnification
  Magnification upto 250,000 times.

Types Of Electron Microscopes:
There are two major types of electron microscopes.

1. Scanning electron microscopy (SEM)
2. Transmission electron microscopy (TEM)

1. Scanning electron microscopy (SEM):

• In scanning electron microscopy, a beam of electrons moves back and forth across the surface of a cell or tissue, creating a detailed image of the 3D surface.

2. Transmission electron microscopy (TEM):

• In transmission electron microscopy, in contrast, the sample is cut into extremely thin slices before imaging, and the electron beam passes through the slice rather than skimming over its surface.
• TEM is often used to obtain detailed images of the internal structures of cells.

Q.4: Define the following terms: (i) Specimen (ii) Micrograph.
Ans: (i) SPECIMEN:
It is a biological sample we are looking at.

(ii) MICROGRAPH:
A photograph of an image taken through a microscope is called micrograph.

Q.5: How can we calculate the total magnification of a compound microscope?
Ans: In order to ascertain the total magnification when viewing an image with a compound light microscope, take the power of the objective lenses, which is at 4x, 10x, 40x and multiply it by the power of the eye piece which is typically 10x. Therefore, a 10x eyepiece used with a 10x objective lens will produce a magnification of 100x. Thismeans that the object can be magnified, 40x, 100x or 400x.

Q.6: Distinguish between the following in tabulated form:

• (i) Light microscope (LM) and Electron microscope (EM)
• (ii) Resolution and Magnification
• (iii) Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM)

Ans: (i) Difference Between Light microscope (Simple and Compound) and Electron microscope

S.NO.	Light microscope (LM) (Simple And Compound Microscope)	Electron Microscope
1.	They produce an image of a specimen by using a beam of visible light.	They produce an image of a specimen by using a beam of electrons
2.	A live cell can be imaged by light microscope.	A live cell cannot be imaged by electron microscope.
3.	Magnification of light microscope is lower i.e. 1500 X	Magnification of electron microscope is higher i.e.  250,000 X
4.	It achieves a resolution above 0.2 µm (micrometer).	It  achieves a resolution of about 0.2 nm (nanometer), a thousand times improvement over light microscope
5.	Visible light have longer wavelength (400-700 nm). this allows LE to produce lower-resolution images.	Electrons have much a shorter wavelength (1 nm), this allows EM to produce higher-resolution images.
6.	Light microscopes are smaller and lighter, so its easier to move and set-up.	Electron microscopes are large and heavy, so its hard to move and set-up.
7.	Light microscopes are less expensive.	Electron microscope are very expensive.
8.	Light microscope uses glass lenses for magnification.	Electron microscope uses electromagnetic lenses instead of glass lenses.
9.	The images of the specimen is projected into the human eye.	The image can not focus in human eye, therefore, screen or photographic plates are used to review and focus the image.
10.	Simple and compound microscopes are example of light microscopes	SEM and TEM are examples of Electron microscope

(ii) Difference Between Resolution and Magnification

S.NO.	Resolution	Magnification
1.	Resolution is a capacity to separate adjacent objects	The enlargement of an image is called magnification.
2.	Resolution is maintained upto certain magnification	By increasing magnification, resolution is disturbed.
3.	Resolution improves with the wavelength of light..	Magnification improves with the focal length of lens
4.	It helps to measure clarity of object.	It helps to increase the size of object.
5.	It is distance which is represented in 'µm' or 'nm'.	Magnification is power of an instrument and is represented with 'x' times.

(iii) Difference Between Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM)

S.NO.	Scanning electron microscopy (SEM)	Transmission electron microscopy (TEM)
1.	A beam of electrons moves back and forth across the surface of a cell or tissue.	Electrons beam passed through the specimen rather than skimming over its surface.
2.	SEM creates a detailed image of the 3D (three dimension) surface.	TEM obtains 2D (two dimension) detailed images of the internal structures of cells.
3.	It is used to study the structure of cell surface.	It is used to study internal structure of a cell .
4.	SEM is based on scattered electrons	TEM is based on transmitted electrons.
5.	SEM shows the sample bit by bit.	TEM shows the sample as a whole.
6.	SEM samples can be vary in thickness.	TEM samples must be thin.
7.	In SEM, sample is mounted on an aluminium stub.	In TEM, sample is mounted by using grids and holders.
8.	Sample preparation is easy.	Sample preparation is complicated
9.	Image shows on TV monitor.	Image shows on fluorescent screen.

Q.No.7: Write about the scientists which have a historical working background in the development of cell theory? Or Describe the brief history of the development of cell theory?
Ans: HISTORY OF THE DEVELOPMENT OF CELL THEORY:
Ancient Greeks were the first to make comprehensive attempts to organize the data of the natural world. Aristotle presented an organized observation to support the idea that all animals and plants are somehow related. Later this idea gave rise to questions like 'is there a fundamental unit of structure shared by all organisms?” But before microscope was first used in 17th century, no one knew that living organisms do share a fundamental unit i.e. cell.

Year	Contribution Of Scientist
1665	Robert Hooke: (Discovered Cell) Cell was first observed by Robert Hooke, an English scientist. He discovered a honeycomb-like structure in a cork slice using a primitive compound microscope. He only saw cell walls as this was dead tissue. He coined the term "cell" for these individual compartments he saw.
1670	Anton van Leeuwenhoek:  (Observed First Living cell) First living cells were seen by Anton van Leeuwenhoek, a Dutch biologist, from pond water with a microscope.
1683	Anton van Leeuwenhoek: (Miniature animals) He made several more discoveries on a microscopic level, eventually publishing a letter to the Royal Society in which he included detailed drawings of what he saw. Among these was the first protozoa and bacteria discovered.
1833	Robert Brown: (Discovered Nucleus) The center of the cell was seen by Robert Brown, an English botanist. He discovered the nucleus in plant cells.
1839	Theodor Schwann: (Cell theory) a German zoologist reached the conclusion that not only plants, but animal tissue as well is composed of cells.
1839	This ended debates that plants and animals were fundamentally different in structure. He also pulled together and organized previous statement on cells into one theory, which states: 1- Cells are organisms and all organisms consist of one or more cells. 2 - The cell is the basic structure unit for all organisms.
1840	Albrecht von Roelliker: Where does life come from, he discovered that sperm and eggs are also cells.
1845	Carl Heinrich Braun: He reworked the cell theory, calling cells the basic unit of life.
1855	Rudolf Virchow: 3rd part to the cell theory added by Rudolf Virchow, a German physiologist/physician/pathologist. He added that cell is not Denovo structure. This translates mean that all cells develop only from existing cells.
1862	Louis Pasteur: Louis Pasteur was a French biologist; microbiologist and chemist provided the experimental proof of this idea.

Q.8: Define cell theory? Who purposed the cell theory? Write down the postulates of cell theory?
Ans: Cell Theory:
One of the most important concepts in biology is that:

"A cell is a basic structural and functional unit of living organism."

This is known as a cell theory.

Scientists Role In Development Of Cell Theory:

• In 1839 cell theory was proposed jointly by two scientists, A Belgian Botanist called Schleiden and the German zoologist called Schwan.
• In 1855 Rudolf Virchow, a German physicians proposed an important extension of cell theory-that all living cells arise from pre-existing.
  
  

Postulates Of Cell Theory:
The postulates of cell theory are:

1. All Living organisms are made of one or more cells.
2. The cell is the fundamental unit of structure and function in all living organisms.
3. The new cell is derived from pre-existing cells dividing into two by cell division.
4. The cell contains the hereditary material which is passed from generation to generation.

Q.9: Define sub-cellular and acellular particles? Why sub-cellular or acellular particles are not included in five kingdom of classification?
Ans: Sub-Cellular Particles:
They are particles smaller than the living cells and are found suspended in the cytosol (of a cell) like the nucleus, Golgi complex and the mitochondria. 

Acellular Particles:
Acellular particles / organism are particles that do not have a cell like viruses, viroids and prions. They are not alive or active outside a living environment but active immediately they are inside a living environment (like a cell).

Sub-cellular or Acellular Particles Are Not Include In Five Kingdom Classification:
According to the first principle of the cell theory all organisms are composed of one or more cells. The following organisms are sub cellular or acellular particles and are not composed of cells:

• Viruses
• Prions and
• Viroids

Non-Living Characteristics:
They are sub cellular or acellular particles rather they but do not run any metabolic activity inside them.

Living Characteristics:
They show some characteristics of living organisms i.e:

• They can increase in number.
• They can transmit their characteristics to the next generations.

Classification:
Such acellular particles are not classified in any of the five kingdoms of classification.

Q.10: What is cell? Define its different types? Also write down functions of a cell? Or Write few lines on cell?
Ans: Cell:
Definition: "Cells are the smallest form of life i.e cells are the basic structural and functional units of all living things and all tissues and organs are composed of cells." It is a set of organelles made up of proteins, carbohydrates, lipids and nucleic acids.
The contents of cells from similar species are basically the same. The activity of an organism depends on the total activity of independent cells.

Types Of Cells:
Our body contains several billion cells, organized into over 200 major types, with hundreds of cell-specific functions. Plant cells are generally a cubical shape while animal cells are usually spherical. On the basis of its structure and functions, there are two main type of cells:

1. Prokaryotic
2. Eukaryotic

Prokaryotes:
Organisms whose cells do not have a membrane bounded nucleus are called prokaryotes ( ‘pro’ means before).

OR

Prokaryotes are organisms without a  cell nucleus, or any other membrane bound organelles. Most are unicellular but some are multicellular.
e.g. Bacteria and Cyanobacteria

Eukaryotes:
Organisms whose cells have a membrane bounded nucleus are called eukaryotes (from the Greek words ‘Eu’ means well or truly and ‘karyon’ means kernel or nucleus. Plant and animal cells are eukaryotes.

OR

Eukaryotes are organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton; The most characteristic membrane bound structure is the nucleus. Animal, plants, fungi and protists are eukaryotes.

Function Of A Cell:

• Plant cells and animal cells have evolved different organelles to perform specific functions. The activity of an organism depends on the total activity of independent cells.
• Energy flow occurs in cells through the breakdown of carbohydrates by respiration.
• Cells contain the information necessary for the creation of new cells. This information is known as 'hereditary information' and is contained within DNA.
• DNA (the hereditary information of cells) is passed from 'parent' cells to 'daughter' cells during cell division.
• Some functions performed by cells are so vital to the existence of life  that all cells perform them (e.g. cellular respiration). Others are  highly specialized (e.g. photosynthesis in plant cell only).

Q.11: Compare prokaryotes and eukaryotes in tabulated form?
Ans: Difference Between Prokaryotes and Eukaryotes

Cellular Structure	Prokaryotic cell	Eukaryotic cell
Example	Bacteria and Cyanobacteria	Animals and plants
Nucleus	Without membrane	Proper Nucleus and Membrane bounded
Number of chromosomes	One but not true chromosomes	More than One
Number of cells	Unicellular	Unicellular and Multicellular Present
True membrane bound organelles	Absent	Present
Lysosomes and Peroxisome	Absent	Present
Microtubules	Absent or rare	Present
Endoplasmic reticulum	Absent	Present
Mitochondria	Absent	Present
Ribosomes	Smaller 70S	Larger 80S
Vesicles	Present	Present
Golgi Apparatus	Absent	Present
Chloroplasts	Absent	Present (in plants)
Plasma membrane with steroid	Usually no	Yes
Permeability of nuclear membrane	Not present	Selective
Vacuoles	Absent	Present
Cell Size	1-10 µm	1-1000 µm
Flagella	Submicroscopic in size, composed of only one fiber	Microscopic in size; membrane bound

Q.12: Differentiate between prokaryotic and eukaryotic cell.
Ans: Difference Between Prokaryotic And Eukaryotic Cell

S.No.	Prokaryotic Cell	Eukaryotic Cell
1.	Nuclear membrane is absent therefore prokaryotic cells do not possess distinct nucleus.	A double nuclear membrane is present. They have well defined nucleus.
2.	They do not have many membrane bound structures e.g. Mitochondria, endoplasmic Reticulum, Golgi apparatus etc.	They have membrane bounded structures (organelles).
3.	Ribosomes are of small size and freely scattered in cytoplasm.	Ribosomes are of large size and present either on endoplasmic reticulum or free in cytoplasm.
4.	Nucleoplasm is absent.	Nucleoplasm is present.
5.	Single chromosome is found.	Proper chromosomes in diploid numbers are present.
6.	Respiratory enzymes are located on the inner surface of the cell membrane.	Respiratory enzymes are present in mitochondria.
7.	These cells are simple and comparatively smaller in size i.e. average 0.5-10nm in diameter.	These cells are complex comparatively large in size i.e. 10-100nm in diameter average.
8.	Bacteria and cyanobacteria are examples of Prokaryotes.	Fungi, algae, animal and plants are examples of exkaryotes.

Q.13: Write down difference between animal and plant cell
Ans: Difference between animal and plant cell

S.No.	Animal Cell	Plant cell
1.	A cell wall is absent in animal cell but they have cell membrane which is made up of protein and lipid.	Plant cells have rigid cellulose cell wall in addition to the cell membrane.
2.	Plastids are absent in animal cells.	Almost all plants cells contain plastids such as chloroplasts, chromoplasts and leucoplasts.
3.	Animal cells usually have small vacuoles (if any).	Plant cells have a large central vacuole filled with cell sap in mature cells.
4.	Centrosomes are present in animal cell which help in cell division.	Centrosomes are absent in plant cell.
5.	The cytoplasm fills the cell.	Its cytoplasm is reduced to a thin lining.
6.	Animals do not have plasmodesmata or pits.	Plant cells contain plasmodesmata or pits
7.	Nucleus is generally found at the centre of the cytoplasm.	Nucleus is found near the edge or periphery of the mature cell.
8.	Animal cells possess Lysosomes which contain enzymes that digest cellular macromolecules.	Plant cells rarely contain Lysosomes as the plant vacuole handles molecule degradation.
9.	Animal cells contain centrioles (these cylindrical structures) that organize the assembly of microtubules during cell division.	Plant cells do not typically contain Centrioles.
10.	Animal cells are usually spherical.	Plant cells are generally a cubical shape.

OR

Q.14: What are cell organelles? Name the organelles which are present in a typical cell or eukarotic and prokaryotic cell.
Ans: CELL ORGANELLES:
The small structures that make a cell and perform specific functions are called cell organelle. They can be observed from micrographs. Some important cell organelles found in eukarotic or typical cells are:

1. Cell wall (only in plant cell)
2. Cell Membrane
3. Cytoplasm: It Contains 


1. Cytoskeleton
2. Nucleus
3. Mitochondria
4. Endoplasmic Reticulum
   a. Smooth E.R
   b. Rough E.R
5. Golgi bodies
6. Ribosomes
7. Centrioles (only in animal cell)
8. Vacuoles
9. Plastids (only in plant cell)
   a. Chloroplast
   b. Chromoplast
   c. Leucoplast

Q.15: Draw a neat and labelled diagram of:
(ii) Animal cell
(iii) Plant cell
Ans:Animal cell

Plant Cell

Q.16: Describe or explain the structures and the functions of cell wall with labeled diagrams? Or Write a note on cell wall of a plant cell?
Ans: CELL WALL:

• A cell wall is a tough, rigid non-living and permeable protective layer in some cell types.
• This outer covering is positioned next to the cell membrane (plasma membrane) in plant cells, fungi, algae and bacteria.
• It is absent in animal cell.

Chemical Composition:
Cell wall composition varies depending on the organism.

• Prokaryotes or Bacterial cell walls: are composed of a sugar and amino acid called peptidoglycan.
• Fungal cell walls The main components of cell walls are chitin, glucans, and proteins.
• Plants: The cell wall is composed mainly of strong fibers of cellulose.

Structure Of Cell Wall:
In plants, the wall is composed of cellulose. It may consist up to three layers that help to support the plant. These layers include:

• The Middle Lamella
• The Primary Cell Wall and
• The Secondary Cell Wall

(i) Middle Lamella:

• It separates one cell from another.
• It is a thin membranous layer on the outer side of the cell.
• It is made of a sticky substance called pectin and cellulose.

ii) Primary cell wall:

• It lies on the inside of the middle lamella.
• It is mainly composed of cellulose.

iii) Secondary cell wall:

• It lies along side of the cell membrane.
• It is made up of a thick and tough material of cellulose which is held together by a hard, water proof substance called lignin.
• It is only found in cells which provide mechanical support in plants, i.e., Some cells of xylem like tracheid and vessels.

Plasmodesmeta:

• The openings in the cell wall are called plasmodesmeta which contain strands of cytoplasm that connect adjacent cells.
• This allows cells to interact with one another, allowing molecules to travel between plant cells.

Functions:
The cell wall has many important functions in a cell including:

1. Protection: The main function of the wall is to protect the inner parts of the plant cell.
2. Definite Structure: It gives plant cells a more uniform and regular shape.
3. Support: It provides support for the plant body.
4. Permeable: The cell wall is completely permeable to water and mineral salts which allows distribution of nutrients throughout the plant.

Q.17: What is cell membrane? Explain the structure and function of cell membrane? OR Describe the fluid mosaic model of cell membrane?
Ans: CELL MEMBRANE:

• The cell membrane is the outer most living boundary of all cells. The cell membrane, also called the plasma membrane.
• It physically separates the intracellular space (inside the cell) from the extracellular environment (outside the cell).
• In plant cells, there is cell wall outside the cell membrane.

Chemical Composition Of Cell Membrane:
The cell membrane is composed of:

• A double layer (bilayer) of special lipids called phospholipids
• Protein
• Small quantities of carbohydrates

Structure of the cell membrane - the fluid mosaic model:
S.J. Singer and G.L. Nicolson proposed the Fluid Mosaic Model of the cell membrane in 1972.
This model describes that:

• Phospholipid acting like matrix and conjugated glycoproteins (glucose and protein together) may float freely in this matrix.
• This model describes the structure of the cell membrane as a fluid structure with various protein and carbohydrate components floating freely in the membrane. Therefore, it is also called unit membrane.

Functions

• Protect:
  The cell membrane surrounds and protects the cytoplasm.
• Perform Exchange of Substances:
  All the exchanges between the cell and its environment have to pass through the cell membrane.
  It performs many important functions within the cell such as osmosis, diffusion, transport of nutrients into the cell, processes of ingestion and secretion.
• Selective-permeable barrier:
  The cell membrane is selectively permeable to ions (e.g. hydrogen, sodium), small molecules (oxygen, carbon dioxide) and larger molecules (glucose and amino acids) and controls the movement of substances in and out of the cells.

The fluid- mosaic model of cell membrane

Q.18: Describe the composition (or structure) and functions of cytoplasm?
Ans: CYTOPLASM:
Structure & Composition:

• The cytoplasm is the jelly-like substance that fills the cell.
• It is present between the plasma (cell) membrane and the nucleus.
• It consists of up to 90% water.
• It also contains dissolved nutrients and waste products.

Function:

• Its main function is to hold together the organelles which make up the cytoplasm.
• It also nourishes the cell by supplying it with salts and sugars and provides a medium for metabolic reactions to occur.

Q.19: Describe the composition (or structure) and function of cytoskeleton?
Ans: CYTOSKELETON:
Structure & Composition:
Cytoskeleton is a microscopic network of protein consists of microtubules and various filaments. Microtubules are made of tubulin while filaments made up of active protein.
Function:
They are spread out through the cytoplasm, providing both structural support and means of transport within the cell.

Q.20: Describe the structure and function of Nucleus? Draw a labelled diagram also?
Ans: NUCLEUS:
The nucleus is the largest organelle in the cell and contains the entire cell's genetic information in the form of DNA.

Occurrence:

• The presence of a nucleus is the primary factor that distinguishes eukaryotes from prokaryotes. A prominent nucleus occurs in eukaryotic cell.
• In animal cell, it is located in the center.
• In plant cell due to presence of a large central vacuole, it is push towards cell membrane.

Structure:

• Nuclear Envelope:
  Nucleus is covered by two phospholipids membranes known as nuclear envelope that separates the nucleus and its contents from the cytoplasm.
• Nuclear pores:
  Nuclear pores are found in the nuclear envelope and help to regulate the exchange of materials (such as RNA and proteins) between the nucleus and the cytoplasm.
• Nucleoplasm:
  Inside nuclear envelope, a granular fluid is present called nucleoplasm.
• Nucleolus:
  In nucleus an aggregation of RNA is also present called nucleolus.
  It is a dark spot. 
• Chromatin Net Work:
  In non-dividing cell the genetic material is found in the form of net work in the nucleus called chromatin net work.
• Chromosomes:
  Chromosomes are visible only during cell division. They are composed of DNA and protein.

Function:

• It stores the cell's hereditary material, or DNA.
• It controls all the activity of a cell.

Q.21: Describe structure and function of mitochondria and draw labelled diagram also?
Ans: MITOCHONDRIA:
(Singular; Mitochondrion)
A mitochondrion is a double membrane bound organelle found in eukaryotic cells only.
Structure:

• The compartment of mitochondria contain two phospholipid bilayers, there is an outer membrane, and an inner membrane.
• The outer membrane is smooth.
• The inner membrane contains many folds called cristae which contain specialized membrane proteins that enable the mitochondria to synthesize ATP.
• Inside the inner membrane is a jelly-like matrix.

Function:

• Mitochondria is the site of aerobic respiration. 
• During aerobic respiration energy is produced in the form of ATP (Energy flow occurs in cells through the breakdown of  carbohydrates by respiration). Therefore the Mitochondria is also called ‘Power house’ of cell.

Q.22: Describe the structure and function of endoplasmic reticulum with labelled diagram?
Ans: ENDOPLASMIC RETICULUM:
(Endo = inside, Plasma = protoplasm, reticulum = network)
The endoplasmic reticulum (ER) is an organelle found in eukaryotic cells only.
Structure:

• The ER has a double membrane consisting of a network of hollow tubes, flattened sheets, and round sacs. These flattened sheets, hollow folds and sacs are called cisternae.
• The ER is located in the cytoplasm and is connected to the nuclear envelope.

Types Of Endoplasmic Reticulum:
There are two types of endoplasmic reticulum:

1. Smooth Endoplasmic Reticulum (SER) and
2. Rough Endoplasmic Reticulum (RER)

Smooth Endoplasmic Reticulum:
It does not have any ribosomes attached.
Function:

• It is involved in the synthesis of lipids, including oils, phospholipids and steroids.
• It is also responsible for metabolism of carbohydrates, regulation of calcium concentration and detoxification.

Rough Endoplasmic Reticulum:
It is covered with ribosomes giving the endoplasmic reticulum its rough appearance.
Function:

• It is responsible for protein synthesis and plays a role in membrane production.
• The folds present in the membrane increase the surface area allowing more ribosomes to be present on the ER, thereby allowing greater protein production.

Q.23: Describe the structure and function of ribosomes with labelled diagram?
Ans: RIBOSOMES:
Structure:

• Ribosomes are tiny granular structures.
• They are composed of RNA and protein.
• Ribosomes may occur singly in the cytoplasm or in groups or may be attached to the endoplasmic reticulum thus forming the rough endoplasmic reticulum.

Function:

• They occur in the cytoplasm and are the sites where protein synthesis occurs. Hence they are called protein factories of  cell.

Q.24: Describe the structure and function of golgi bodies with labelled diagram?
Ans: GOLGI BODIES:
Discovery:
The Golgi body was discovered by the Italian physician Camillo Golgi. It was one of the first organelles to be discovered and described in detail because its large size made it easier to observe.
Structure:

• The Golgi body is the sorting organelle of the cell.
• The Golgi body consists of a stack of flat membrane-bound sacs called cisternae.
• The cisternae within the Golgi body consist of enzymes which modify the packaged products of the Golgi body.

Function:

• It is important for proteins to be transported through Golgi body from where they are synthesized to where they are required in the cell.
• Proteins are transported from the rough endoplasmic reticulum (RER) to the Golgi.
• In the Golgi, proteins are modified and packaged into vesicle. The Golgi body therefore receives proteins made in one location in the cell and transfers these to another location within the cell where they are required. For this reason the Golgi body can be considered to be the 'post office' of the cell.

Q.25: Describe the structure and functions of vesicles and lysosomes?
Ans: VESICLES AND LYSOSOMES:
VESICLES:
Structure:

• Vesicles are small, membrane-bound spherical sacs. Many vesicles are made in the Golgi body and the endoplasmic reticulum, or are made from parts of the cell membrane.
• Vesicles can be classified according to their contents and function, such as Transport vesicles.

Function:

• Vesicles facilitate the metabolism, transport and storage of molecules.
• Transport vesicles transport molecules within the cell.

LYSOSOMES:
Structure:

• Lysosomes are single-membrane bounded organelles.
• They are formed by the Golgi body and contain powerful digestive enzymes that can potentially digest the cell.

Function:

• These powerful enzymes can digest cell structures and food molecules such as carbohydrates and proteins.
• Lysosomes are abundant in animal cells that ingest food through food vacuoles.
• When a cell dies, the lysosome releases its enzymes and digests the cell.

Q.26: Describe the structure and function of vacuoles with labelled diagram?
Ans: VACUOLES:
Structure:

• Vacuoles are fluid-filled spaces that occur in the cytoplasm of plant cells, but are very small or completely absent in animal cells.
• Plant cells generally have one large vacuole that takes up most of the cell's volume in mature cell.
• A selectively permeable boundary called the tonoplast, surround the vacuole.
• The vacuole contains cell sap which is a liquid consisting of water, mineral salts, sugars and amino acids.

Function:

• The vacuole plays an important role in hydrolysis, excretion of cellular waste, storage of water, organic and inorganic substances.

Q.27: Describe the structure and function of vacuole with labelled diagram?
Ans: CENTRIOLES:
Structure:

• Animal cells contain a special organelle called a centriole.
• The centriole is a cylindrical tube-like structure that is composed of 27 microtubules arranged in a very particular pattern of triplets in rows.
• The site where two centrioles arranged perpendicular to each other are referred to as a centrosome.

Function:

• Centrosome: 
  The centrosome plays a very important role in cell division.
  
  
• Centrioles: 
  The centrioles are responsible for organizing the microtubules that position the chromosomes in the correct location during cell division.

Q.28: Define plastids and its types?  Also write thier functions?
Ans: PLASTIDS:
Plastids are large cytoplasmic and major organelles found in the cells of plants and algae.
Function:

• Plastids are the site of manufacture and storage of important chemical compounds used by the cell. 
• Plastids often contain pigments used in photosynthesis.
• The types of pigments present can change or determine the cell's colour.                          

Types Of Plastids:
There are three different types of plastids:

1. Chloroplasts:
   * These are green coloured plastids found in plants and algae.
   * The chloroplast is a double membrane organelle. Within the double membrane is a gel-like substance called stroma which contains enzymes for photosynthesis.
   * Suspended in the stroma are stack-like structures called grana (singular = granum) which is a stack of thylakoid discs. The chlorophyll molecules (green pigments) are found on the surface of the thylakoid discs.
   Function:
   Chloroplast contain green pigments called chlorophyll, which absorbs energy from the sun for photosynthesis and manufacture carbohydrates..
   
   
2. Chromoplasts:
   The colour of plant flowers such as an orchid is controlled by a specialized organelle in a cell known as the chromoplast. Chromoplasts contain colour pigments such as  red, orange or yellow, which are common in ripening fruit, petals of flowers or autumn leaves and other colored parts of plants.
   Function:
   They give the colours to petals of flowers and to fruits, thus attracts insects and help in pollination and dispersal of fruits.
   
   
3. Leucoplasts:
   Colour less. triangular or tubular or of any other shape plastids. They are found in the cells of underground parts of plants.
   Function:
   They store starch, proteins and lipids in roots.

Q.29: Describe the structure and function of chloroplast with labelled diagram?
Ans: CHLOROPLAST:
Structure:

• These are green coloured plastids found in plants and algae.
• The chloroplast is a double membrane organelle.
• Within the double membrane is a gel-like substance called stroma. Stroma contains enzymes for photosynthesis.
• Suspended in the stroma are stack-like structures called grana (singular = granum).
• Each granum is a stack of thylakoid discs.
• The chlorophyll molecules (green pigments) are found on the surface of the thylakoid discs.

Function:

• Chloroplast contain green pigments called chlorophyll, which absorbs energy from the sun for photosynthesis.

Q.30: Discuss transport of molecules which occurs in cell membrane? OR How does movement of molecules across the cell membrane occur?
Ans: Movement or Transport of Molecules across the cell membrane:
Movement of substances across cell membranes is necessary as:

• It allows cells to acquire oxygen and nutrients.
• Excrete waste products and,
• Control the concentration of required substances in the cell (e.g oxygen, water, hormones, ions, etc).

Types of Transport or Movement Of Molecules Across The Cell Membrane:
This movement or transport molecules occurs by:

1. Diffusion
2. Osmosis
3. Facilitated diffusion and
4. Active Transport

1. Diffusion:
Definition:

"Diffusion is the movement of substances or molecules from a region of high concentration to a region of low concentration. It is therefore said to occur down a concentration gradient."

Passive Transport:
Diffusion is a passive process which means it does not require any energy input. It can occur across a living or non-living membrane and can occur in a liquid or gas medium.
Examples:
Diffusion of carbon dioxide, oxygen, water and other small molecules that are able to dissolve within the lipid bilayer.

2. Osmosis:
Definition:

"Movement of water always occurs down a concentration gradient, i.e., from dilute solution to concentrated solution through a semi permeable membrane."

Passive Transport:
Osmosis is also a passive process and does not require any input of energy.
Example:
Cell membranes allow molecules of water to pass through, but they do not allow molecules of most dissolved substances, e.g. salt and sugar, to pass through it.
Importance Of Osmosis:
In biological systems, osmosis is vital to plant and animal cell survival.

1. Osmosis maintains cell turgidity.
2.  It causes the transportation of nutrients and discharge of metabolic waste products.
3.  It preserves the interior environment of a living entity to maintain an equilibrium between the intracellular fluid levels and water, as:
   a) Osmosis affects red blood cells and plant cell. It helps the cell volume remains constant.
   b) Osmosis in the kidneys keeps the water and salt levels in the body and blood at the correct levels.

3. Facilitated Diffusion :
Definition:

"Facilitated diffusion is a special form of diffusion which allows rapid exchange of specific substances. Particles are taken up by carrier proteins which change their shape as a result. The change in shape causes the particles to be released on the other side of the membrane."

Passive Transport:
Facilitated diffusion is also a passive process and does not require any input of energy.

4. Active transport:
Definition:

"Active transport is the movement of substances against a concentration gradient, from a region of low concentration to high concentration using an input of energy."

In biological systems, the form in which this energy occurs is adenosine triphosphate (ATP). ATP and ADP are molecules involved with moving energy within cells.
Examples: of substances moved include sodium and potassium ions.

Q.31: demonstrates how osmosis affects red blood cells and plant cell, when they are placed in three different solutions with different concentrations?
Ans: Osmosis Affects Red Blood Cells And Plant Cell:

a) Osmosis Affects Red Blood Cells:
Experiment:
a) Red Blood Cells:
Placed cells in different beakers with different types of solution.
Observations:

1. A Hypotonic Solution (Solution has relatively less solute): 
   When a cell is placed in a hypotonic solution, water enters and cell swells and may rupture like an over-filled balloon.
   
   
2. Isotonic Solution (Solution has equal concentrations of solutes):
   When an animal cell, such as red blood cell, is placed in an isotonic solution, the cell volume remains constant because the rate at which water is entering cell is equal to the rate at which it is moving out.
   
   
3. Hypertonic Solution (Solution has relatively more solute):
   Similarly, an animal cell placed in a hypertonic solution (has relatively more solute in solution) will lose water and will shrink in size.

b) Osmosis Affects Plant Cells:
Experiment:
Plant cells use osmosis to absorb water from the soil and transport it to the leaves. Placed cells in different beakers with different types of solution. 
Observations:

1. A Hypotonic Solution (Solution has relatively less solute): 
   In hypotonic solution, water tends to move first inside cell and then inside vacuole. When vacuole increases in size, cytoplasm presses firmly against the interior of cell wall, which expands a little. Due to strong cell wall, plant cell does not rupture but instead becomes rigid. This condition is known as turgor in plants.
   
   
2. Isotonic Solution (Solution has equal concentrations of solutes):
   In isotonic environment, the net uptake of water is not enough to make the cell turgid and it is not firm.
   
   
3. Hypertonic Solution (Solution has relatively more solute):
   In hypertonic conditions a plant cell loses water and cytoplasm shrinks and shrinkage of cytoplasm is called plasmolysis.

Q.32: Predict the the direction of osmosis with the help of an experiment? And answer:

1. What do you observe happening to the level of the solution inside the potato?
2. What conclusion can you draw based on your observation?
3. What conditions were met in this experiment that makes this type of transport different to diffusion?

Ans: Predicting the direction of osmosis

"Osmosis is a process in which movement of water always occurs from dilute solution to concentrated solution through a semi permeable membrane."

To prove the direction of osmosis, we perform potato osmoscope process.

Apparatus:

• Beaker
• Potato peeler/scalpel
• Pins
• Large potato
• Concentrated sucrose/sugar solution

Procedure:

1. To obtain concentrated sucrose / sugar solutions, add 100g of sugar to 200ml of water.
2. Peel off the skin of a large sized potato with a scalpel/potato peeler.
3. Cut its one end to make the base flat.
4. Make a hollow cavity in the potato almost to the bottom of the potato.
5. Add the concentrated sugar solution into the cavity of the potato, filling it about half way. Mark the level by inserting a pin at the level of the sugar solution (insert the pin at an angle into the cavity at the level) (A).
6. Carefully place the potato in the beaker containing water.
7. After 15 to 20 minutes, mark the level by inserting the second pin at the level of the sugar solution (insert as the first pin) (B).

i) Observation:
After a period of time, within the osmoscope, the sugar solution rises and is seen coloured.

ii) Conclusion:
An increase in the level of sucrose solution is observed in the cavity in the potato. It is because of the entrance of water due to endosmosis from the beaker.
Also, a water potential gradient is built between the sucrose solution in the external water and the cavity in the potato.

ii) Direction Of Movement Of Water Molecules:
Though both the liquids are divided by living cells of the potato, which allow the entrance of water into the sugar solution.
The cells of potato serving as a selectively permeable membrane. This demonstrates the entrance of water into the potato osmoscope which contains concentrated sugar solution.
Result:
Hence, Osmosis is the phenomena in which water molecules moves from area of higher concentration to the area of lower concentration through semi or selective permeable membrane.

Q.33: Write a note on cell size and surface area to volume ratio? OR Explain the cell size and shape and relate them with its surface area and volume ratio?
Ans: Cell Size:
Cells are microscopic mostly and they are incredibly small. They are vary greatly in size. Most cells lie between these extremes.

• The Smallest Cell:
  The smallest cells are bacteria called mycoplasmas, with diameter between 0.1 μm to 1.0 μm.
• The Bulkiest Cells:
  The bulkiest cells are bird eggs.
• The Longest Cells:
  The longest cells are some muscle cells and nerve cells.

RELATIONSHIP BETWEEN SIZE, SHAPE AND CELL FUNCTION:
Cell size and shape are related to cell function.

• Bird's Eggs:
  Bird's eggs are bulky because they contain a large amount of nutrient for the developing young.
• Muscle Cells:
  Long muscle cells are efficient in pulling different body parts together.
• Nerve cells:
  Lengthy nerve cells can transmit messages between different parts of body.
• Red Blood Cells: Small cell size also has many benefits.
  For example: Human red blood cells are only 8 μm in diameter and therefore can move through our tiniest blood vessels i.e. capillaries.

Surface area of cells:
Most cells are small in size. In relation of their volumes, large cells have less surface area as compared to small cells.

For Example:
1 large cell and 27 small cells.
Calculation Of volume:
In both cases, the total volume is same:

3 Volume = 30 μm X 30 μm X 30 μm = 27,000 μm³.

Calculation Of Surface Area:
In contrast to the total volume, the total surface areas are very different. Because a cubical shape has 6 sides, its surface area is 6 times the area of 1 side.
The surface areas of cubes are as follows:

• 2 Surface area of 1 large cube = 6 X (30 μm X 30 μm) = 5400 μm²
• 2 Surface area of 1 small cube = 6 X (10 μm X 10 μm) = 600 μm²
• 2 Surface area of 27 small cubes = 27 X 600 μm = 16, 200 μm²
• 2 Surface area of one large cube = 5400 μm²
• Total surface area of 27 small cubes = 16,200 μm²

RELATION BETWEEN CELL SIZE AND VOLUME RATIO:

• Waste production and demand of nutrients are directly proportional to cell volume.
• Cell takes up nutrients and excretes wastes through its surface cell membrane.
• So a large volume cell demands large surface area but, a large cell has a much smaller surface area relative to its volume than smaller cells have.
• Each internal region of the cell has to be served by part of the cell surface.
• As a cell grows bigger, its internal volume enlarges and the cell membrane expands.
• Unfortunately, the volume increases more rapidly than does the surface area, and so the relative amount of surface area available to pass materials to a unit volume of the cell steadily decreases.

CONCLUSION:
Hence we conclude that the membranes of small cells can serve their volumes more easily than the membrane of a large cell.
A structure has an increased surface area, there is an increase in the functioning of that structure.

Q.34: Examine the plant cells and animal cells under the microscope. And answers the following questions:
1. What are the shapes of epidermal cells of the onion peel and the human cheek cells?
2. Why is iodine used to stain the onion peel?
3. What is the difference between the arrangement of cells in onion cells and in human cheek cells?
4. Why is a cell considered the structural and functional unit of living things?

Ans: Examining Plant cells Under The Microscope:
To study the microscopic structures of plant cells.
Apparatus:

• Onion
• Blade
• Slides and cover slips
• Brushes
• Tissue paper
• Compound microscope
• Forceps
• Dropper
• Iodine solution
• Watch glass
• Petri dish containing water

Procedure:

1. Peel off the outer most layer of an onion carefully, using a pair of forceps.
2. Place the peeled layer in a watch glass containing water. Make certain that the onion peel does not roll or fold.
3. Using a scalpel or a thin blade, cut a square piece of the onion peel (about 1cm ).
4. Remove the thin transparent skin from the inside curve of a small piece of raw onion and place it on a drop of iodine solution on a clean slide.
5. Cover the peel with a cover slip ensuring that no bubbles are formed.
6. Using a piece of tissue paper wipe off any excess iodine solution remaining on the slide.
7. Observe the onion skin under low power of the microscope and then under high power.
8. Draw a neat diagram of 5-10 cells of the typical cells you can see. Onion cells stained with methylene blue.

Examining Animal Cells Under The Microscope:
To study the microscopic structures of human cheek cells under a compound microscope.
Apparatus:

• Cotton bud
• Clean slide
• Methylene blue
• Dropper
• Water
• Tissue paper
• Forceps
• Microscope

Procedure:

1. Place a drop of water on a clean glass slide.
2. Using a clean ear bud, wipe the inside of your cheek. The ear bud will collect a moist film.
3. Spread the moist film on a drop of water on a clean glass slide, creating a small smear on the slide.
4. Use a cover slip to cover the slide gently.
5. Place one or two drops of stain on the side of the cover slip.
6. Use a piece of tissue to remove the excess dye.
7. Observe the cheek cells under low power magnification and then under high power magnification.

Answers:
1. What are the shapes of epidermal cells of the onion peel and the human cheek cells?
Ans: Both onion and human cheek cells are epithelial cells. Onion peel cells are brick-like or rectangular in shape, having distinct cell walls whereas human cheek cells have undefined shape. They are rounded or flat polygonal cells with a prominent nucleus.

2. Why is iodine used to stain the onion peel?
Ans: Onion cells are naturally transparent, so it is difficult to properly examine their cells without using a solution to increase contrast. Although onions may not have as much starch as potato and other plants, the stain (iodine) reacts with the starch present in onion cells, producing a coloration that makes the cells easily visible under a microscope.

3. What is the difference between the arrangement of cells in onion cells and in human cheek cells?
Ans: Onion cells are compactly arranged and without any intercellular spaces. Each cell has a distinct cell wall, a prominent nucleus and a vacuole.
Human cheek cells are also compactly arranged to form a continuous layer. The cells are without cell wall. Cell membrane encloses a distinct nucleus and a vacuole.

4. Why is a cell considered the structural and functional unit of living things?
Ans: A cell is considered as the basic structural and functional unit of organisms:
Structural unit of organisms:
Microscopic studies reveals that all living organisms are made of one or more cells. Therefore, cell is the fundamental unit of structure of all living organisms.
Functional unit of organisms:
Cells are of different shapes and sizes, as they have to perform different functions. All basic functional activities, characteristics of living things, occur in the cell. Therefore, cell is also a unit of function in all living organisms.

Q.35: Draw a neat and labelled diagram of:
The structure of Bacterial Cell

Ans:

(i) The structure of Bacterial Cell

Q.36: Animal and Plant Tissues
Ans: Click Here for Question-Answer