Sohana Akter, Lecturer, English Medium Day Shift
Chapter-1: Cell and its structure
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What is cell?
What do you mean by cell theory?
Write down the types of measurement of cell.
Mention the unit of measurement of cell.
Draw a labeled diagram of plant and animal cell.
Differentiate between plant cell and animal cell.
What is prokaryotic and eukaryotic cell?
Write down the function of cytoplasm.
Differentiate between prokaryotic and eukaryotic cell.
What do you mean by somatic and gametic cell?
Differentiate between somatic and gametic cell.
What is cell wall? Write down the structure and function of cell wall.
What is plasmodesmata?
What is unit membrane?
What is plasmalemma? Write down the structure of plasmamembrane according to modern
concept.
What is plasmalemma and cytoplasm?
What is cytosol?
Write down the names of membrane and non membrane bounded cellular organelles?
What is mitochondria? Write down the structure and functions of mitochondria.
Why mitochondria is considered as the power house of a cell? Explain.
Write down the molecular structure of Ribose and deoxyribose sugar.
What is plastid? Describe the types of plastid.
Write down the structure and function of plastid. (chloroplast).
Write down the structure and functions of ribosome.
Write down the structure and functions of golgi bodies.
Write down the structure and functions of endoplasmic reticulum.
Why lysosomes are considered as suicide bag? Explain.
Differentiate between ribosome and lysosome.
Differentiate between endoplasmic reticulum and golgibodies.
Differentiate nucleus and neucleolus.
Differentiate between centrosome and centromere.
What is cell vacuole? Write down the structure and functions of cell vacuole.
What is nucleus? Write down the structure and functions of nucleus.
What is chromosome? Write down the structure and functions of chromosome.
Classify chromosome on the basis of centromere.
Analyze the role of chromosome in cell division.
What is nucleic acid?
Write down the atomic structure of DNA and RNA.
Write down the physical and chemical structure of DNA.
Write down the replication process of DNA.
Analyze the role of DNA in heredity.
Write down the structure of RNA.
Differentiate between DNA and RNA.
What is transcription? Write down the transcription process.
What is gene?
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
Q-01: What is cell?
Ans:
Cell:
Definition:
According to Loewy and Siekeviz, (1963)“ A cell is a unit of biological activity, delimitated by a selective permeable membrane and capable of
self reproduction in a medium of other living system.”
Q-02: Write down the types of cell.
Ans:
Types of cell:
On the basis of the organisation of nucleus, cells can be divided into two typesa) Prokaryotic cell and
b) Eukaryotic cell.
On the basis of function, there are two other types of cells. These area) Somatic cell and
b) Gametic cell.
Q-03: Write down the difference between plant cell and animal cell.
Ans:
Difference between plant and animal cell:
Characters
Plant cell
Animal cell
1. Cell wall
1. Most plant cells are bounded by a 1. No cell wall is present in animal
non-living cell wall made of
cell. It is surrounded only by plasma
cellulose.
membrane.
2. Plastids
2. Different types of plastids are
2. Plastids are not available here.
present.
3. Vacuoles
3. Usually one or more vacuoles are
3. Except some lower group of
present.
animals most of the animal does not
have any vacuoles.
4. Centriole
4. Normally no centrioles are present 4. Animal cells always bear
in plant cell.
centriolke.
5. Golgi bodies
5. Golgi bodies are rarely seen in
Golgi bodies are frequently seen here
plant cell under micrscope.
under microscope.
6. Reserve food
6. In plant cell reserve food is mainly In animal cells reserve food is mainly
starch.
glycogen.
Q-4: What is prokaryotic and eukaryotic cell?
A). Prokaryotic cell:
Definition:
The cells in which the nucleus is not well organized that are nuclear membrane and nucleolus are
absent, chromosome contain only DNA are known are prokaryotic cell.
B). Eukaryotic cell:
Definition:
The cells in which the nucleus is well organized that are the nuclear membrane and nucleolus are
present, chromosome fibres are known as prokaryotic cell.
Chapter-1: Cell and its structure
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
Questions:
1. What is cell?
2. What do you mean by cell theory?
3. Write down the types of cell.
4. Mention the unit of measurement of cell.
5. Draw a labeled diagram of plant and animal cell.
6. Differentiate between plant cell and animal cell.
7. What is prokaryotic and eukaryotic cell?
8. Write down the function of cytoplasm.
9. Differentiate between prokaryotic and eukaryotic cell.
10. What do you mean by somatic and gametic cell?
11. Differentiate between somatic and gametic cell.
12. What is cell wall? Write down the structure and function of cell wall.
13. What is plasmodesmata?
14. What is unit membrane?
15. What is plasmalemma? Write down the structure of plasmamembrane according to modern
concept.
16. What is protoplasm and cytoplasm?
17. What is cytosol?
18. Write down the names of membrane and non membrane bounded cellullar organelles?
19. What is mitochondria? Write down the structure and functions of mitochondria?
20. Why mitochondria is considered as the power house of a cell? Explain.
21. Write down the molecular structure of Ribose and deoxyribose sugar.
22. What is plastid? Describe the types of plastid.
23. Write down the structure and function of plastid (Chloroplast).
24. Write down the structure and functions of ribosome.
25. Write down the structure and functions of endoplasmic reticulum.
26. Write down the structure and functions of endoplasmic reticulum.
27. Why lysosomes are considered as suicide bag? Explain.
28. Differentiate between ribosome and lysosome.
29. Differentiate between endoplasmic reticulum and golgibodies.
30. Differentiate between nucleus and neucleolus.
31. Differentiate between centrosome and centrosome.
32. What is cell vacuole? Write down the structure and functions of cell vacuole.
33. What is nucleus? Write down the structure and functions of nucleus.
34. What is chromosome? Write down the structure and functions of chromosome.
35. Classify chromosome on the basis of centromere.
36. Analyze the role of chromosome in cell division.
37. What is nucleic acid?
38. Write down the atomic structure of DNA and RNA.
39. Write down the physical and chemical structure of DNA.
40. Write down the replication process of DNA.
41. Analyze the role of DNA in heredity.
42. Write down the structure of RNA.
43. Differentiate between DNA and RNA.
44. What is transcription? Write down the transcription process.
45. What is gene?
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
Q-01: What is cell?
Ans:
Cell:
Definition:
According to Loewy and Siekeviz, (1963)“ A cell is a unit of biological activity, delimitated by a selective permeable membrane and
capable of self reproduction in a medium of other living system.”
Q-02: Write down the types of cell.
Ans:
Types of cell:
On the basis of the organisation of nucleus, cells can be divided into two typesa) Prokaryotic cell and
b) Eukaryotic cell.
On the basis of function, there are two other types of cells. These area) Somatic cell and
b) Gametic cell.
Q-03: Write down the difference between plant cell and animal cell.
Ans:
Difference between plant and animal cell:
Characters
Plant cell
Animal cell
1. Cell wall
1. Most plant cells are bounded by a
1. No cell wall is present in animal
non-living cell wall made of cellulose. cell. It is surrounded only by plasma
membrane.
2. Plastids
2. Different types of plastids are
2. Plastids are not available here.
present.
3. Vacuoles
3. Usually one or more vacuoles are
3. Except some lower group of
present.
animals most of the animal does not
have any vacuoles.
4. Centriole
4. Normally no centrioles are present
4. Animal cells always bear
in plant cell.
centriolke.
5. Golgi bodies
5. Golgi bodies are rarely seen in plant Golgi bodies are frequently seen here
cell under microscope.
under microscope.
6. Reserve food
6. In plant cell reserve food is mainly
In animal cells reserve food is mainly
starch.
glycogen.
Q-4: What is prokaryotic and eukaryotic cell?
Ans:
A). Prokaryotic Cell:
Definition:
The cells in which the nucleus is not well organized that are the nuclear membrane and nucleolus
are absent, chromosome contain only DNA are known as prokaryotic cell.
B). Eukaryotic cell:
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
Definition:
The cells in which the nucleus is well organized that are the nuclear membrane and nucleolus are
present, chromosome fibres are known as prokaryotic cell.
Q-5: Differentiate between Prokaryotic and eukaryotic cell.
Ans:
Difference between Prokaryotic and eukaryotic cell:
1. Nucleus
2. Internal
structure
3. Cell wall
4. Ribosome
type
5. Mitochondra
6. Number of
cell
7. Cell division
8. Size of cell
9. Organisms
1. Not well organized, nuclear
membrane, neucleolus is absent, only
chromatin fibre is present.
2. No membrane bounded organelles,
Ribosomes are smaller.
3. Always present
3.70s type.
1. Well organized, nuclear membrane,
neucleolus, chromatin fibre are
present.
2. Plastids, mitochondria,
Endoplasmic reticulum and large
ribosomes are present.
3. Except animals cell wall is present.
4.80s type.
5. Not present.
4. Always uncicellular
5. One to several thousands.
4.Unicellular or multicellular
5. Amitosis or Binary fission
6. Small in size
7. Bacteria, blue green algae
5. Mitosis and meiosis
6. Much greater in volume.
7. Plants, animals, fungi.
Q-6: What is somatic and gametic cell?
Ans:
A). Somatic cell:
Definition:
The cells which are takes part in the organisaton of the body of an organism and normally divide
through the process of binary fission and mitotic division is known as somatic cell.
B). Gametic cell:
Definition:
A reproductive cell or sex cell that contains the haploid set of chromosomes, produced from the
primordial germ cells through meiosis cell division and take part in sexual reproduction but do not
construct the main body is known as gametic cell.
Q-7: Differentiate between somatic and gametic cell.
Ans:
Difference between Somatic and Gametic cell:
Characters
1. Origin
Somatic cell
1. Originated from previous somatic cell
2. Chromosome
number
2. Chromosome number is diploid (2n)
Chapter-1: Cell and its Organization.
Gametic cell
1. Originated from primordial germ
cell
2. Chromosome number is haploid
(n)
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
3. Cell division
4. Function
3. Somatic cells are produced through
binary fission or mitosis cell division.
4. Takes part in the growth of the body
only.
3. Gametic cell produced through
meiosis cell division
4. Takes part in the reproduction
only.
Q-8: What is cell wall? Write down the structure and functions of cell wall.
Ans:
A) Cell wall:
Definition:
In each plant cell protoplast is covered by a non-living layer made of cellulose. This nonliving layer is known as cell wall.
Cell wall is the unique and outstanding feature of a plant cell. Cell wall is absent in animal cell.
B). Structure of cell wall:
i). Physical Structure:
A typical mature cell wall is made of three different layers. Namely1. Middle lamella,
2. Primary cell wall and
3. Secondary cell wall.
1). Middle lamella:
a. The first layer of cell wall is middle lamella.
b. During cytokinesis the formation of cell wall begins. Initially pectose particle in the name of
fragmoplast are being deposited and then these particle coalesced to each other forms a thin cell
plate.
C. Due to physical and chemical changes this cell plate converted to middle lamella. The middle
lamella is the common layer between two cells.
2). Primary cell wall:
a. On the middle lamella, by the deposition of cellulose, hemicelluloses and glycoprotein a thin layer
is formed. This is called primary cell wall.
b. This is formed on the inner surface of middle layer.
3). Secondary cell wall:
a. In some cell (Trachid fibres etc) another layer develops on the primary wall. Generally it occurs
after full maturation of the cell.
b. This layer is thicker, generally cellulose and lignin is deposited on it. This layer is known as
secondary cell wall.
c. Secondary cell wall is three layered.
d. This layer is not formed in the meristematic and highly active cells.
e. In this case some scientist designate the third layer of the second cell wall as tertiary cell wall.
Pit fields:
a. This is the thinnest region of the cell wall.
b. A pit is common in between the two cells positioned side by side and opposite to each other.
c. In between two pit fields only middle layer is present. This middle layer is known as pit
membrane.
d. Pit facing one another are known as pit pair.
e. Actually primary layer is not developed in the pit fields. After the formation of secondary wall pit
can be bordered with or without border.
ii). Chemical structure:
a) Chemical composition of a cell wall is much complex. Cellulose, hemicelluloses, lignin,
pectin, suberin are the chemical components of a plant cell wall.
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
b) But, bacterial cell wall is composed of protein and lipid.
The cell wall of fungi is made of Chitin.
C). Functions:
The functions of cell wall are-
a.
b.
c.
d.
Gives mechanical strength to the cells and to the plant as a whole.
Shape up the appearance of the cell.
Protects the inner living active material from the external pressure.
Being rigid and registant to expansion, allows the cells to build a turgor pressure which
further helps to support the herbaceous plants.
e. Trasnsportation, absorption of mineral salts and water are also carried out by the cell wall.
f. Maintains connection with adjacent cell through plasmodesmata.
g. Protects the plasmamembrane.
h. Prevents the osmotic bursting of the cell
i.
Q-09: What is plasmodesmata?
Ans:
Plasmodesmata:
Definition:
Although each cell appears to be enclosed in a box of cellulose it is by no means isolated from
its neighbours. The cellulose wall is interupted at intervals by narrow pores carrying fine strands of
cytoplasm which join the living cells to one another. These are called plasmodesmata.
Q-9: What is plasma membrane? Write down the structure and function of Plasma membrane.
Ans:
A). Plasma membrane:
Definition:
In each cell there is a thin, living elastic semiepermeable membrane inside the cell wall,
surrounding the protoplasm is known as plasma membrane.
B). Structure of plasma membrane according to the modern concept:
Regarding the structure of plasma membrane many model have been hypothetically proposed
by different scientists. Among the entire model the Fluid Mosaic Model by S.J. Singer and G.L.
Nicolson in 1972, is considered as the modern concept about the structure of plasma membrane and
still now it is most accepted model.
According to the Fluid Mosaic Model the structure of plasma membrane isThe plasma membrane is of two layers and made of phospholipid. The plasma membrane is
actually composed of two types of components. These are1). Phospholipid and
2). Protein.
1). Phospholipid:
The phospholipids are arranged by two layers. It is known as lipid by layer. Each
phospholipid consists of one molecule of glaycerol with two non-polar fatty acid tails and a polar
phosphate head. The head is hydrophilic and the tail is hydrophobic in nature. The heads are remain
opposite to each other and the two fatty acid tail layers remain face to face.
2). Protein:
There are three types of proteins in the plasma membrane. These arei). Peripheral protein: This is present in the surface of the plasma membrane,
ii). Integral protein: This extends one surface to another
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
iii). Lipid combined protein: This is confined in the core of the lipid.
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
Glycocalyx:
Glycoprotein and glycocalyx combinedly known as glycocalyx. It is a sugar layer over the membrane.
The glycocalyx attached with most of the protein molecule is known as Glycoprotein while the
glycocalyx attched with some of the phospholipid molecules is known as the while the glycocalyx
attached with some of the phospholipid molecules is known as the Glycolipids. The glycocalyx is
present only at the external surface of the plasmamembrane.
Cholesterol: It is found mostly in animal cell in between the two phospholipids at the internal portion
of the cell membrane.
Recent research supports that the biomembrane is not solid rather it is highly fluid. It is found that the
lipid particle has internal motion and they can diffuse sidewise. These can rotate along their axis, even
can transfer from one layer to another layer. This type of movement is known as flip-flop movement.
Moreover the constituents of the membrane remain free floating making a mosaic pattern of different
component. This information supports fluid-mosaic model. Considering all these things the model is
known as fluid mosaic model.
B). Functions:
The functions of plasmamembrane area) To protect the inner components from the outer adverse condition.
b) The plasmamembrane surrounds the cytoplasm of living cells, physicall separating the
intra cellular components from the extra cellular environment.
c) It is also plays a role in anchoring the cytoskeleton to provide shape to the cell, and in
attaching to the extra cellular matrix and other cells to help group cells together to form
tissues.
d) The plasmamembrane functions as a barrier that makes it possible for the cytoplasm to
maintain a different composition from the material surrounding the cell.
e) In animal cell, it is involved in the formation of vesicles, cilia, flagella, microvilli etc.
f) The cell membrane contains numerous receptor molecules that are involved in
communication with other cells and the outside world in general. These respond to
antigens, hormones, and neurotrasnmiter in various ways.
g) The cell membrane also allows cell identification.
h) It enhances the absorbing area by producing microvilli in animal cells.
i) It controls the molecular activity of the cell.
j) The cell membrane contain different types of enzymes.
k) It plays an important roles in developing different cell organelles.
l) Trasnportation of material from outside to inside and vice versa.
m) To act as a source of various information.
n) Synthesis of micromolecules and
o) In some case it helps pinocytosis and phagocytosis process of taking food materials etc.
Q-9: What is Protoplast, Protoplasm and cytoplasm?
Ans:
A). Protoplast:
Definition:
All the materials inside the cell surrounded by cell wall is called protoplast.
Protoplast is divided into two parts. These area. Living protplasm and
b. Non-living substance.
B). Protoplasm:
Definition:
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
The total mass of the materials inside the plasma membrane bounded living cell is called
protoplasm.
There are three parts of protoplasm. These area. Plasmamembrane,
b. Cytoplasm and
c. Nucleus
C). Cytoplasm:
Definition:
All the materials except the nucleus surrounded by cell membrane of a cell are called
cytoplasm.
It has three parts. These area. Cytoploasmic matrix.
b. Cytoplasmic organelles and
c. Ergasti substance
Q-10: Write down the names of membrane bounded and non-membrane bounded cellular organelles.
Ans:
A). Names of membrane bounded cellular organelles:
a. Mitochondria
b. Endoplasmic reticulum,
c. Golgi bodies,
d. Lysosome,
e. Cell vacuole,
d. Peroxysome and
g. Vessicle.
B). Name of non-membrane bounded cellular organelles:
a. Ribosome,
b. Centroile,
c. Proteosome and
d. Microtubules etc.
Q-11: What is mitochondria? Write down the structure and function of mitochondria.
A). Mitochondria:
Definition:
The cytoplasmic organelle covered by two layered membrane, related with the production
of energy of a cell is known as mitochondria.
Though first observation of mitochondria were made in 1840s, Richard Altman in 1894
established them as cell organelles, and in 1998 Carl Benda first coined the term ‘mitochondria’.
B). Structure:
The number of mitochondria in a cell may vary on the cell types and species. Generally there are
300-400 mitochondria in a single cell. The structure of mitochondria is written as bellows:
1. Shape and size: The shape of mitochondria may be filamentous, granular or oval.
2. Membrane: Actually, mitochondria are organelles that have a double unit membrane structure. One
of them is called outer membrane and other is inner membrane. The outer membrane defines the
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
external shape of mitochondria while the innermembrane has many folds called cristae. The
volume between the inner membranes is called intermembrane space (wide approx 70A) and the
volume enclosed by the inner membrane is called the matrix of the mitochondria.
3. Mitochondrial matrix: The mitochondrial matrix contains a highly concentrated mixture of hundreds
of enzymes. These include most of the enzymes that participate in the TCA Cycle.
The matrix also contains other structures and molecules including ribosomes, matrix granules and
mitochondrial DNA.
4. Cristae: Cristae are folds of the inner mitochondrial membrane. The quantity and shape of the cristae
may vary. For example, although the shape of cristae within mitochondria is often either flat or tubular,
in some cases (e.g. in certain never cells) they have whorl-like shape. While in other cases (e.g. in some
photoreceptor come cells) they have a whorl-like shape. While in other cases (e.g. in some
photoreceptor cone cells) they have a whorl-like shape.
5. Oxisome or F1 perticels: Cristae are covered with many tiny ‘stalked particles’ called inner membrane
spheres of the F1 particles. Each stalked particle has a head diameter of 8-9 nm and a stalk 30-35A wide
and 45-50A long.
6. ETS and ATPase complex: The inner membrane of mitochondria contains the electron transport
system (ETS) and ATPase complex. The ETS generates a proton gradient and the ATPase complex
uses porton gradient to produce adenosine triphopsphate (ATP) from adenosien diphosphate (ADP).
Chemical structure: The chemically mitochondria composed of the following components:
(i) Protein 60 to 70%
(ii) Lipid-25 to 35%
(iii) DNA, RNA 0.5% and
(iv) Trace amount of sulphur, iron, copper, vitamins etc.
Fig-Mitochondria
C). Function:
The functions of mitochondria area. The main function of the mitochondria is the production of energy, in the form of
adenosine triphosphate (ATP). So, mitochondria are considered as power house of the
cell as their main function is to provide energy to the cell.
b. Mitochondria are involved in building, breaking down, and recycling products needed
for proper cell functioning. For example, some of the building blocks of DNA and RNA
occur within the mitochondria.
c. They are required for cholesterol metabolism, neurotransmitter metabolism, and
detoxification and ammonia in the urea cycle.
d. Mitochondria help to maintain proper concentration of calcium ions within the various
compartments of the cell.
e. Mitochondria storage the ions of Ca2+ , S2+ , Fe2+ , Mn2+
f. Mitochondria help in the regulation of membrane potential, cell proliferation and cell
metabolism.
g. Mitochondria cause apoptosis or programmed cell death.
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
h. Mitochondria help in the biosynthesis of haeme and steroids.
i. Mitochondria synthesis DNA and RNA. According to scientist Benda the mitochondria
contribute in heredity.
Q-12: Why mitochondria is considered as the power house of a cell? Explain.
Ans:
Mitochondria is considered as the power house of a cell becauseThe main function of mitochondria is to help organism produce energy from food through
cellular respiration. The process has mainly three stages.
a. Glycolysis.
b. Kreb’s cycle and
c. Electron transport system.
The first stage glycolysis doesnot occur in mitochondria, but it occurs in cytoplasm with or without
oxygen. A series of biochemical reactions of Kreb’s cycle occur in mitochondria of a cell. Lastly,
another series of biochemical reactions occur through the electron transport chain, a series of electron
carrier in the inner membrane of mitochondria. In the process, energy is, ultimately, produced. An
organisum uses the energy to perform different functions.
This is why a mitochondria is called ‘the power house’ of a cell.
Q-13: What is plastid: Write down the types of plastid.
Ans:
A). Plastid:
Definition:
The biggest cell organelle made of lipid and protein membrane contains stroma and grana,
scattered in the cytoplasm of a plant cell in known as plastid.
In 1885 scientist Schimper deiscovered and named plastid.
B). Chloroplast:
Green coloured plastids are called chloroplast. They are found in the cells of leaves, young stems
and other green parts of a plant.
2. Chromoplast:
Though the chromoplasts are coloured, they are not green. The photosynthetic pigment
xanthophylls, carotene, phycoerythrin, phycocyanin etc. are present in them, and so some of them are
yellow, some others are blue and red. The flowers, leaves and other parts of a plant assume their
attractive colourful appearance from the mixture of those pigments.
They are found in colourful flowers, leaves and roots of carrots. Their main purpose is to make
flower attractive for pollination. Moreover, they synthesize and store different types of
photosynthetic pigments.
3. Leucoplast:
Leucoplasts are non-pigmented in contrast to other plastids. They are usually found in the cells of
the plant parts where usually sunlight does not reach; for example, root, ovaries and embryo. Their
main function is the storage of food. Leucoplast can be transformed into chromoplast or chloroplast in
contact with sunlight.
Q-14: Write down the structure and function of chloroplast.
Ans:
A). Chloroplast:
Definition:
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
The plastid which is responsible for green color in plant parts is known as chloroplast.
Every cell may contain one or more chloroplast. In higher plants the shapes of chloroplast is
lanceolate.
B). Structure:
The structure of chloroplast is written as bellows:
a) A bi-layered semipermiable membrane surrounds the whole chloroplast. It is composed of
protein and lipid. This is called lipoprotein.
b) A hygroscope matrix surrounded by a membrane is there. This matrix is called stroma.
c) In the stroma, 40-80 well-arranged barrel shaped grana are present.
d) In one granum there are 5-25 granum disc. Inside the granum disc, there are spaces.
Probbably chlorophyll and other photosynthetic materials are present in this chamber.
e) Some granum discs of two adjacent grana are connected by minute tubular bodies, which are
called stroma lamelli.
f) Many crystalline bodies are arranged in the membrane of grana disc. These are called
quantosome. In the dark phase of photosynthesis, carbon-di-oxide is assimilated mainly in the
quantosome.
Fig: Structure of Chloroplast
C). Function:
The functions of chloroplast area)
To prepare carbohydrate food through photosynthesis.
b)
Solar energy converted into chemical energy.
c)
To produce protein and fats with the help of enzymes.
Q-15: Write down the difference between mitochondria and Plastid.
Ans:
Difference between Mitochondria and Plastid:
Characters
Mitochondria
Plastid
1. Location
1. Present in both plant and animal cell
1. Only found in plant cell.
2. Activity
2. It is the respiratory organelle of the plant 2. It is food synthesis organelles of
and animal cell.
higher plant cell.
3. Pigments
3. There is no pigment
3. There are different types of
pigments.
4. Membrane
4. The inner membrane becomes folded
4. There is no folded membrane
known as cristae
5. Chamber
5. There is incomplete chambers due to fold 5. There is no chamber.
of inner membrane
6. Storage of
6. There is not storage of food materials.
6. Colorless plastids i.e
food
leucoplastids store different types
of foods.
Q-16: Write down the structure and functions of centrosome.
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
Ans:
A). Centrosome:
Definition:
A cell organelle located near to the nucleus made of centriole and centrosphere is known
as centrosome.
In 1887 Van Benden discovered centrosome in the cell. Later on named Boveri.
B). Structure:
a) The liquid materials with which the centrosome is formed is called centrospheres. Aster rays are
produced from centrospheres during cell division.
b) The two dumble-shaped or cylindrical bodies are found in the centre of the centrospheres known as
centriole.
c) During cell division the two centrioles become separated and move to the two opposite poles.
d) Each centriole consists of three parts. These arei. Cylinder wall,
ii. Triplets and Linkers.
e) The wall of the centriole is composed with triplets tube.
f) Each triplet again divided into triple microtubules marked as ABC.
g) The centrioles are chemically composed of protein, lipid and ATP.
h) Generally it is found the animal cell.
Fig : Centriole.
C). Function:
The functions of centrosomes area) To indicate poles during cell division.
b) To produce aster rays.
c) To assist in cell division and
d) To form cilia of flagella in some specialized cells
Q-17: What is ribosome? Write down the structure functions of ribosome.
Ans:
A). Ribosome:
Definition:
Very minute, spherical bodies remain attached with endoplasmic recticulum or occur
freely in the cytoplasm, synthesized protein are known as ribosome.
B). Structure and functions of ribosome:
a) The ribosome are tiny particles without a covering membrane and have oblate spheroid structure of
150A0-200A0 A in diameter.
b) Each ribosome consists subunits of 70S ribosome are respectively 50s and 30S.
Chapter-1: Cell and its Organization.
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Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
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c)
d)
e)
f)
Similarly the and smallar subunits of 80S ribosome are respectively 60S and 40S.
The smaller subunits of ribosome occurs the large subunits like a cap.
The subunits of ribosome occur separately when ribosomes are not involved in protein synthesis.
The two subunits join when proteins synthesis start, and undergo dissociation when proteins
systhesis stops.
g) Many ribosomes line up on the mRNA chain during proteins synthesis, Such a group of active
ribosomes is called a polyribosome, or a polysome.
According to the size and the sedimentation coefficient (S) two types of ribosome have been
recognized, 70S ribosome and 80S ribosomes.
A) 70S Ribososme:
These are comparatively smaller and havesedimentation coefficient 70S. They occur in all
prokaryotic cells and in mitochondria and chloroplast of eukaryotic cells.
B) 80S Ribosome:
These are comparatively larger and have sedimentation coefficient 80S. They occur in all
eukaryotic cells.
Function:
a) Ribosomes are the sites in a cell in which protein synthesis takes place.
b) The produced cytochrome, which transports electrons during cellular respiration.
c) According to Laninger the phosphorilation of glucose held in ribosome.
Q-18: What is golgi body? Write down the structure and function of golgi body.
Ans:
A). Golgi body:
Definition:
The organelle which have flat, long, tube like structure, remain united together near the
nucleus is known as golgi body.
Scientist Camilo Golgi at first observed the presence of golgi body in the cell. It is also known
as Lipochondria. It is composed of stacks of membrane-bound structure known as cisternae and
vesicles
B). Structure and function:
Function:
Golgi apparatus is metabolically very active and many functions have been assigned to it. The
main functions of golgi apparatus are as below:
a) Its acts to process and package the macromolecules such as proteins and lipids that are
synthesized by the cell.
b) It is also involved in the transport of lipids around the cell, and the creation of lysosomes.
c) The golgi apparatus synthesizes some simple carbohydrate such as galactose, sailic acid and
certain polysaccharides, pectin compounds from simple sugars.
d) The golgi apparatus links carbohydrates with proteins coming from ER to form glycol
proteins. This process is called glycolsylation.
e) Lipidsa and proteins coming from the ER or complexes into lipoproteins in the golgi
apparatus. The production of hormones by endocrine glands is mediated through golgi
apparatus.
f) In many mammalian tumour and cancer cells the golgi apparatus has been described as the
site or origin of pigment granules (melanin).
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
g) Golgi apparatus takes part information of sperm’s acrosome in mammals. It accelerates
mitochondria to synthesize ATP.
Q-19: What is endoplasmic reticulum? Write down the structure and function of endoplasmic
reticulum.
Ans:
A). Endoplasmic reticulum:
Definition:
The net like structures, tubular, having hollow cavities seen in the cytoplasm is known as
endoplasmic reticulum.
In 1945 scientist Porter discovered endoplasmic reticulum in the cell. Endoplasmic
reticulum is found in both the plant and animal cells.
B). Structure:
a) Endoplasmic reticulum is two types. These are-smooth and rough endoplasmic reticulum.
b) The reticulum which bears ribosomes is known as rough endoplasmic reticulum and the reticulum
where ribosomes is known as rough endoplasmic reticulum and the reticulum where ribosome
absent is called smooth endoplasmic reticulum.
c) It consists of two layered semipermeable membrane.
d) Generally they are branched and lie in parallel.
e) They may stretch from the cell membrane upto nuclear membrane.
f) The chemical composition of this membrane is lipid and proteins.
C). Function:
a) The ER acts as an intra cellular supporting framework that also maintains the form the cell.
b) If facilities transport of materials from one part of the cell to another, thus forming the cells
circulatory systems.
c) It keeps the cell organelles proper stationed and distributed in relation to one another.
d) It provides space for temporary storage of synthetic products such as glycogen.
e) Tubular ER extensions called desmotubules extend to the plasmadesmata to make ER continue in
the two adjacent plant cells.
f) In muscle cells ER helps in music contraction by regulating calcium ions concentration in the
sarcoplasm.
g) The smooth ER is responsible for a variety of vital cell processes that include carbohydrate
metabolsim, lipid synthesis, calcium storage, and poison detoxification.
h) The smooth ER is responsible for hydroxylating drug or poison molecules to increase their
solubility and aid removal of these harmful molecules from the system.
i) Ribosomes attached to the ER synthesize proteins that are secreted b a wide variety of cells
including pancreatic cells, which produce and export insulin.
j) The smooth ER is responsible for hydroxylating enzymes that important in lipid synthesis.
k) The rough ER is responsible for the covalent attachment of certain carbohydrate to specific
proteins to form glycoprotein.
l) The rough ER is responsible for a great deal of membrane production in the cell and continues to
grow by adding phospholipids and proteins to itself.
Q-20: Why Lysosome is considered as the suicide bag?
Ans:
The cytoplasmic organelles similar to vesicles covered by thin membrane where various hydrolytic
enzymes are present is known as lysosome. Lysosome is considered as the suicide bag becauseChapter-1: Cell and its Organization.
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Lecturer in Botany, EMDS
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University of Dhaka
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Sohana Akter, Lecturer, English Medium Day Shift
It destroys the germs by the process of phagocytosis and helps in cellular digestion. Incase of absent
of enough food in the cell, the enclosed enzymes come out rupturing the wall of lysosome and
destroy all other organelles of the cell. This is known as autophagy. In this way the whole cell may
be digested. Due to the role of autolysis the lysosome is considered as suicide bag.
Q-21: What is nucleus? Write down the structure and function of nucleus.
Ans:
A). Nucleus:
Definition:
The compact, comparatively thicker clear, round organelles surrounded by a membrane in
the protoplasm is known as nucleus.
It is roughly round or spherical in stucture. Mature sieve cells and red blood cells lack nucleus. A
nucleus houses the heredity information in it. It controls the metabolic functions of the cell. In 1831
scientist Robert Brown discovered nucleus.
B). Structure:
A nucleus is composed of the following partsa) Nuclear membrane,
b) Nucleoplasm,
c) Nucleolus and
d) Chromatin fibre.
These are describes as bellows in details:
a). Nuclear membrane:
The membrane that encloses the nucleus is called nuclear membrane. It is a double layered
membrane, and composed of lipids and proteins. In this membrane, there are some channels called
nucleopores. Substances get in and out of a nucleus through the pores.
Function:
a. To keep the nuclear substances apart from the cytoplasm.
b. To perform the function of transportation and communication between internal materials and
outer cytoplasm.
b). Nucleoplasm:
The jell-like fluid enveloped by nuclear membrane is called nucleoplasm. It is similar to the
cytoplasm of a cell. The viscous fluid contains nucleic
b). Nucleoplasm:
The jell-like fluid enveloped by nuclear membrane is called nucleoplasm. It is similar to the
cytoplasm of a cell. The viscous fluid contains nucleic acids, proteins, enzymes and some other
substances dissolved in and mixed with it.
Function:
a. It contains chromosome, nucleolus, enzymes and minerals and
b. It helps in various metabolic functions of nucleus.
c). Nucleolus:
In a nucleus round shaped structure attached with a chormosome is called nucleolus. This non
membrane bound structure is composed of RNA and proteins.
Function:
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
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Sohana Akter, Lecturer, English Medium Day Shift
a. Synthesis of different types of proteins and RNA in a eukaryotic cell is the main function of
nucleolus.
d). Chromatin fibre:
A mass of genetic material, composed of thread like coiled structures, is called chromatin reticulum.
Chromatin fibers get super coiled during neclear division and become more condensed, and then they
are called chromosomes. Chromosomes are individually more distinct. They are the units of heredity,
and pass genetic information from generation to generation. The normal members of a group of identical
organisms have the same number of chromosomes.
Function:
a. Chromosomes contain genes, and thus carry hereditary trait from generation to
generation.
Fig: Structure of Nucleus.
Q-22: Analyze the roles of different cells in conducting nerve, muscles, blood, skin and bones in human
body.
Ans:
The roles of different cells in conducting nerve, muscles, blood, skin and bones in human body:
Animal tissue cell in the structural and functional unit of organisms. Functions of unicellular or
multicellular animals are performed in different ways. From the very appearance of the ancient world
till today species of phylum protozoa performs their biological functions, such as: taking of food,
growth and reproduction by the single cell.
In multicellular animals there are differences and variations in cells. In human body there are
different types of cells which are engaged in different activities which as nerve cells spread within the
human body and forms a net work. These cells are to receive stimuli and send it to the brain and again,
sends motor impulses from the brain to the definite organ.
Both nerve cells in the ear and eye help in vision and hearing. Due to the lack of different kinds of
nerve cells most of the animals can not differentiate the exact colour of the objects just like
human being. Many animals can see only at day time some at night. Muscle cells are used in writing.
Walking and movement.
Three kinds of blood cells are engaged in different activities. Red blood corpuscles absorbs
oxygen from lung and transports oxygen by the heart to different cell’s of the body through arteries and
capillaries. While blood corpuscles prevents from disease. Platelets are responsible for starting the
process of blood clotting. As a result bleeding is stopped from the wound.
Besides making body covering integumentary cells performs different functions according to its
location. Hair grows from the integumentary cells of the head. Sweat secretes from the sweat gland in
particular space.
Bone cell constitutes bone with deposition of minerals or cartilage and makes structure and
supports the body. Bone cell are very much important to build structure, shape, growth of the bones etc.
Q-23: Differentiate between cytoplasm and Neucleoplasm.
Ans:
Difference between cytoplasm and neocleoplasm:
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
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Sohana Akter, Lecturer, English Medium Day Shift
Cytoplasm
1. This is the part of the protoplasm remains
outside the nucleus.
2. It is bounded by plasma membrane.
3. This does not carry heredity materials-DNA
4. Cytoplasm is comparatively less dense.
5. It contains cytoplasmic organelles like
mitochondria, golgi bodies, endoplasmic
reticulum etc.
Nucleoplasm
1. This is the part of the protoplasm remains
inside the nucleus.
2. This is bounded by nuclear membrane.
3. It carries heredity materials-DNA.
4. Nucleoplasm is comparatively denser.
5. It contains chromosomes, nucleolus etc.
Q-24: Write down the functions of cell vacuole.
Ans:
Functions of cell vacuole:
The function and important of cell vacuole varies greatly according to the type of cell in which they are
present. In general, the function of the vacoule includes:
a) Isolating materials that might beharmful or a threat to the cell.
b) Containing waste products.
c) Containing water in plant cells.
d) Maintain internal hydrostatic pressure or turgor within the cell.
e) Maintaining an acidic internal pH.
f) Containing small molecules.
g) Allows plants to support structures such as leaves and flowers due to the pressure of the central
vacuole.
h) In seeds, stroed protienn nedded for germination are kept ‘protiens bodies’, which are modified
vacuoles.
Q-25: Differentiate between Golgi bodies and endoplasmic reticulum.
Ans:
Difference between golgi bodies and endoplasmic reticulum:
Golgi bodies and endoplasmic reticulum are two very important organelles inside cells. The two
organelles are responsible for different but very important functions for the survival of the cells.
However, the main difference in between them are-
Features
1.Definition
2. Structure
3. Types
4. Functions
Golgi bodies
1. The organelle which have flat,
long, tube like structure, remain
united together near the nucleus is
known as golgi body.
2. Golgi bodies are an arragement of
few fluid-filled dishes in a cell.
3. One type and smooth
4. It produces lysosome and secrets
enzymes and metabolic substances.
Take part to form cell plates and
plasma membrane
Chapter-1: Cell and its Organization.
Endoplasmic reticulum
1. The net like structures, tubular, having
hollow cavities seen in the cytoplasm is
known as endoplamic reticulum.
2. Endoplasmic reticulum is a network of
tubules and vesicles.
3. It is two types smooth and rough.
4. It acts as a framework of protoplasm.
Tubule work as internal carrier of lipid and
proteins.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
Q-26: Differentiate between nucleus and nucleolus.
Ans:
Difference between Nucleus and Nucleolus:
Features
1. Definition
2. Structure
3. Types
Nucleus
1. It locates in the cytoplasm.
2. It controls all functions of the cell
3. It does not take part in protein synthesis.
4. Functions
4. It bears heredity characters.
Nucleolus
1. It locates inside the nucleus.
2. It synthesizes ribosome
3. It takes part in protein and
RNA synthesis.
4. It is not related with heredity
characters.
Q-27: Differentiate between nucleus and nucleolus.
Ans:
Difference between Ribosome and Lysosome:
Features
1. Location
2. Structure
3. Membrane
4. Types
5. Functions
Nucleus
1. It is attached to the endoplasmic.
Nucleolus
1. It is spreaded all over the
cytoplasm almost same
quantity.
2. It is composed of RNA and Histone protein. 2. There are many enzymes in
it.
3. It is not covered by any membrane
3. It is covered by a membrane.
4. Mainly it is two types-70S and 80s. They 4. There are not types and units.
have two units-50S and 30S; 60s and40s
respectively.
5. It is related with the synthesis of protein.
5. It helps endocellular
digestion process.
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
Q-27: Differentiate between nucleus and nucleolus.
Ans:
Difference between centrosome and centromere:
Features
Nucleus
1. Location
1. Found in animal cell only.
2. Structure
3. Site
4. Types
5. Functions
Nucleolus
1. Found in chromosome both
plant and animal cell.
2. It is composed of protein and RNA.
2. It is composed of protein and
DNA.
3. It is observed the cytoplasm near the 3. It is observed at chromosome
nucleus.
in the nucleus.
4. Centriole present in it in the middle.
4. There are centriole.
5. It plays a vital role to form astar rays and 5. Traction fibre attached to the
spindle apparatus.
centrosome during anaphase
stage of cell division.
Q-28: What is chromosome? Write down the structure and functions of chrosome.
Ans:
A). Chromosome:
Definition:
The thread like structure found in the nucleus, composed of nucleoprotein bears the heredity
characters is called chromosome.
In 1875 Strarsbarger discovered first time the chromosome in the nucleus. In 1902, Bovery opined that
“Chromosome is the bearer of heredity characters”.
B). Physical Structure:
A typical chromosome is composed of seven parts. These are1) Pellicle,
2) Matrix,
3) Chromonema,
4) Centromere,
5) Arm
6) Secondary constriction and
7) Satellite.
These are describe as bellows in details.
1). Pellicle:
The outer covering membrane of chromosome is known as pellicle. It is the outer thin but
Darlington and Novikoff deny the exixtane of such coating.
2). Matrix:
The fluid materials bounded by the pellicle of a chromosome is known as matrix. Matrix or
ground substance of the chromosome is made up of proteins, small quantities of RNA and lipid. Many
scientist including Darlington deny the presence of matrix, as it is not proved by electron microscope.
3). Chromonemata:
Each chromosome is consist of one pair of chromatids, which are attached to a point by
centromere. Each chromatids again consists of longitudinally arranged one, two or more fine chromatin
threads. These threads are called chromonemata (sing. chromonema). All the chromonema remain
twisted with each other. Each chromonema or coil filament may be following two types:
(i) Paranemic coils:
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
When the chromonemal threads are easily separable from coils then such coils are known as
paranemic coils.
(ii) Plectonemic coils:
When the chromonemal threads remain inter-twined so intimately that they cannot be separate
easily is known as pectonemic coils.
4). Centromere:
Centromere is an indispensable part of the chromosome. It attaches two chromatids at a point.
This is about rounded and a clear zone containing one or more chromosomere and spindle fibre. The
location of the centromere produces a constriction. This constriction is called primary constriction or
arm. Arm may be equal or unequal.
Generally a single centromere is present in one chromosome. But sometimes more than one
centromere is present. According to the location of centromere, the chromosomes may be different
types.
5) The secondary constrictions:
Besides the primary constriction, that is the centromere, chromosome may possess on or more
secondary constriction on both the arms at any point. Secondary constriction is also known as the
nuclear organizer.
6) Satellite:
Sometimes the chromosomes bear round or knob like structure at one end which are known as
satelite. Satellite is connected with the chromosomes by thin chromatin filament. Chromosomes wit
satellite is known as SAT-Chromosomes.
7) Telomeres:
According to Muller, Each extremity of the chromosomes has specialized regions, which are
known as telomere.
C). Chemical structure of chromosome:
Chemically chromosomes are mainly composed of nucleic acids and protein. There are trace
amount of lipid, enzymes, Ca2+ are exist in the chromosome.
1. Nucleic acid: The largest molecule of the cell is the cucleic acid. Chromosomes have tow
types of nucleic acids viz; (i) Deoxyribo Nucleic Acid or DNA and (ii) Ribo Nucleic Acid
Or RNA.
(i)
DNA: This is the permanent component of chromosome. Among all components
DNA contribute 45%
(ii)
RNA: This is temporary component of eukaryotic chromosome but permanent
genetic components of some virus. Among all components RNA contribute 0.21.4%. Actually this is a single-strand polymer of nucleotide molecules.
2. Protein: The main structure of chromosome made by protein. Nucleic acid remain linear
arranged within protein. Two types of proteins are found in chromosome.
Q-29: Analyze the role of chromosome in cell division and heredity.
Ans:
Role of chromosome in Cell division and heredity:
A) Role of chromosome in cell division:
1. Chromosomes are essential for the process of cell division and are responsible for the replication,
division and creation of daughter cells that contain correct sequences of DNA and proteins.
2. Proteins make up for one of the most important components of the human body. They are
responsible for building muscles and tissues, growth and repair, as well as the synthesis of thousands
of enzymes, like DNA replication enzymes produced by the body. Proteins synthesis steps and their
successful completion is the responsibility of genes that are contained in chromosomes.
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
3. Cell division is a continuous process that must occur for an organism to function, whether for growth,
repair, or reproduction. During cell division stages, the chromosome is responsible for the replication
and distribution of DNA amongst new cells.
4. It is also crucial that reproductive cells, such as eggs and sperm, contain the right number of
chromosomes and that those chromosomes have the correct structure. If not, the resulting offspring
may fail to develop properly. For example, people with Down syndrome have three copies of
chromosomes 21, instead of the two copies found in other people. In humans, defective
chromosomes made up of joined pieces of broken chromosome cause one type of leukemia and some
other cancers.
5. For an organism to grow and function properly, cells must constantly divide to produce new cells to
replace old, worn-out cells. During cell division, it is essential that DNA remains intact and evenly
distributed among cells. Chromosomes are a key part of the process that ensures DNA is accurately
copied and distributed in the vast majority of cell divisions.
B). Role of Chromosome in heredity:
Nucleic acids are the naturally occurring long chain polymers present in the chromosomes of nucleus
in the cell, capable of being broken down to yield phosphoric acid, sugars and a mixture of organic
bases and play the prime role on inherited characteristics of every living organisms by direction the
process of protein synthesis.
Q-30. Define: Nucleic acid, Nucleoside, Nucleotide, Dinucleotide and polynucleotide.
Ans:
A). Nucleic Acid:
A big organic acid composed of numerous nucleotides found in the nucleus which control all the
metabolic function of a cell is known as nucleic acid.
There are two types of nucleic acid. These are
1. Deoxyribonucleic Acid (DNA),
2. Ribonucleic Acid (RNA)
The basic components of nucleic acids of nucleic acids are1. Pentose sugar,
2. Inorganic phosphate and
3. Nitrogenous base.
B). Nucleoside:
Definition:
The compound which is composed of one molecule of pentose sugar and one molecule of
nitrogenous base (adenine, guanine, thyamine, cytosine and uracil) is called nucleoside.
Fig: Nucleoside
C). Nucleotide:
Definition:
The compound which is composed of nucleoside and inorganic phosphate is called
nucleotide.
Fig: Nucleotide
Chapter-1: Cell and its Organization.
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Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
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Sohana Akter, Lecturer, English Medium Day Shift
C) Dinucleotide:
Definition:
When two nucleotides combine together to form a compound by phosphediester bond is called
dinucleotide.
E) Polynucleotide:
When many nucleotides combine one after another to form a chain like compound is called
polynucleotides.
Each molecule of DNA is made of poly nucleotide chain.
Q-31: What is DNA? Write down the physical and chemical structure of DNA.
Ans:
Definition:
"The nucleic acid of living cell having deoxyribose sugar in its nucleotide, carrying hereditary traits,
controlling all biological activities of cell and capable or replication and mutation is known as
deoxyribonucleic acid or DNA”.
It is the main chemical structure of chromosome of eukaryotic cells. It is also found in mitochondria,
chloroplasts of eukaryotes and cytoplast of prokaryotes and in some viruses.
In 1953 Watson and Crick made a model Of DNA. This model is known as Watson and Crick Double
Helix Model of DNA. They awarded Nobel Prize in the year 1962 for their work.
A) Physical Structure:
According to Double Helix Model of DNA of Watson and Crick, the physical structure of DNA isa) DNA looks like a double helical, spiral ladder like.
b) The frames or helix of two side of the ladder are formed by the alternate sugar phosphate
connection.
c) In between the frame or helix of each side, at the inner side a pair of nitrogenous base present.
d) The two bases are connected by hydrogen bond. As such the outer side of the ladder of
phosphate and nitrogenous bases remain parallel to each other.
e) The two sides at long direction of the ladder remain opposite to each other, one side 3'-5'
directions and at the other side 5'-3' direction. This type of arrangement is known as
Antiparallel arrangement.
f) Guanine of one side of helix connected with cytosine of the other side helix by three hydrogen
bond (G
C) and Adenine of one helix get connected with thymine by two hydrogen bond
(A=T).
g) The distance of each spiral of the ladder is 34A and consists of ten mononucleotides in per
complete turn, so the length of each mononucleotide is 3.4A.
h) The diameter of the helix is 20A.
B). Chemical structure:
According to Double Helix Model of DNA of Watson and Crick, the chemical structure of DNA isDNA molecule is a polymer of deoxyribonucleotide. Each deoxyribonucleotide composed of the
following molecules.
1) Deoxyribose pentose sugar,
2) Nitrogenous base and
3) Inorganic phosphoric acid.
These are describe as bellows in details.
1). Deoxyribose pentose sugar:
Chapter-1: Cell and its Organization.
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Lecturer in Botany, EMDS
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a) DNA contains 2- -D type deoxyribose pentose sugar in which an oxygen atom is lacking in
carbon 2 position of pentose structure.
b) The nitrogenous bases are attached with the first carbon of the pentose sugar while the inorganic
phosphoric acid is attached with fifth carbon of the pentose sugar.
c) The third carbon or pentose sugar is attached with the fifth carbon of the next pentose sugar.
2). Nirgogenous base:
a) The nitrogenous base form the base structure between the two strands of DNA.
i. Adenine (A),
ii. Guanine (G),
iii. Cytosine (C) and
iv. Thymine (T).
c) The scientist later on divided these four types of nitrogenous bases into two main groups. These are
Purine and Pyrimidine base.
d) Adenine and Guanine are known as Purine base while the Cytosine and Tymine is known as
Pyrimidine base.
e) If one strand of DNA contain Purine base the opposite strand must have to contain Pyrimidine
Tymine and if one strand of DNA contain Guanine base then the opposite strand contain Cytosine
base.
f) Adenine always connected with Tymine by two hydrogen bond (A=T) and Guanine always
connected with Cytosine with Three hydrogen bond (G=C).
g) These Nitrogenous bases are attached with the first carbon of pentose sugar.
3). Inorganic phosphoric acid:
The other part of DNA is a phosphoric acid. It is attached to the sugar molecule in place of the
–OH group on the 5' carbon.
One molecule of pentose sugar and one molecule of nitrogenous base together form nucleoside
and one molecule of nucleoside with one molecule of inorganic phosphoric acid together form
nucleotide. DNA is the polymers of this nucleotide.
Q-32. Write down the replication process of DNA.
Ans:
DNA replication:
Definition:
The process by which a new DNA helix is formed from old DNA double helix is known as
DNA replication.
DNA replication is the precondition of cell division. This process takes place at the interphase
stage of cell division . In the newly formed daughter DNA molecule, one strand will be old (that
comes conservative DNA. About 20 proteins and some enzymes are related in this process. These
This process is complete by three consecutive stages. The stages are1. Separating of strands:
The first major step for the DNA replication to take place is the breaking of hydrogen bonds
between bases of the two anti parallel strands. The unwindsing of the two strands is the starting point.
The spiliting happens in place of the chains which are rich in A-T. That is because there are only two
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
bonds between adenine and thymine. Helicas is the enzyme that splits the two strands. The initiation
point where the spliting stars is called ‘ origin of replication’. The Y shaped structure that created is
known as replication fork.
2. Creation of complementary strands:
Separated each strand of DNA serves as a template to guide the synthesis of its complementary strand
of DNA. The essential mucleotide of DNA are existing in nucleoplasm. With the help of DNA
polymerase and Mg2+ these nucleotide attach to each template by phosphodiaster bonds. One of the
most important steps of DNA replication is the binding of RNA premise in the initiation point of the 3'5' parent chain. RNA premise can attract RNA nucleotides which bind to the DNA nucleotides of the
3'-5' strand due to the hydrogen bonds between the bases. RNA nucleotides are the primers (starters)
for binding of DNA nucleotides.
3. Creation of ne DNA:
DNA nucleotides are arrange and bound to the complementary strand according to the sequence
of templates. Thymine and guanine arranged in complementary strand against the adenine and cytosine
of template. Purine and pyrimidine bases of template and complementary strand bound together by
hydrogen bonds as specific rules. Thus each strand of parent DNA used as template and finally forms
two new DNA each of which have one new and one old strand.
Q-33: Write down the significance of DNA replication.
Ans:
Significance of DNA replication:
(a) DNA replication needs to occur so that during cell division, new cells will also have a copy of the
organism’s DNA.
(b) DNA is necessary to make all the RNA and proteins needed for cells carry out necessary reactions
and cellular processes in order for them to survive.
c) Semi-conservative nature of DNA replication ensures the species specific traits that pass through
generation to generation unchanged.
Q-34: Differentiate between DNA and RNA.
Ans:
Difference between DNA and RNA:
Features
DNA
RNA
1. Helix
1. DNA is double helix, ladder like 1. RNA is single stranded chain
structure
like structure.
2. Sugar
2. Deoxyribose sugar
2. Ribose sugar
4.
Pyrimidine 3. Cytosine and Thymine
3. Cytosine and Uracil
base
5. Formation
4. Formed by DNA replication
4. Formed by transcription from
DNA.
6.
Genetic 5. Generally it bears gene this is why it 5. Generally it never carries the
material
carries the heredity characters from one heredity characters but in some
generation another generation.
plant viruses (eg: TMV) it carries
the heredity materials.
Example: gRNA
7. Types
6. Basically DNA is one type
6. Basically RNA is 4 types. These
areChapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
8. Location
9. Lognevity
10. Nucleotide
a. mRNA,
b. tRNA and
c. rRNA
8. Mainly found in the chromosomes of 8. Mainly found in the cytoplasm,
nucleus.
cytoplasmic
organelles
(eg:
mitochondria) and nucleus. Also
found in chromosome in small
quantity.
9. It is a permanent component of a 9. Functionally it is temporary.
chromosome
10. Numerous polynucleotide are present
10. Number of polynucleotide is
in DNA.
less than the DNA.
Q-35: What do you mean by genetic RNA?
Ans:
Genetic RNA (gRNA):
Definition:
Some plant virus and bateriophages contain no DNA, where RNA contains the genetic material and
carry heredity features from generation to generation. This type of RNA is called genetic RNA of
gRNA.
For example: Tobacco Mosaic Virus (TMV), yellow Mosaic Virus etc.
Q-36. What do you mean by gene?
Ans:
Gene:
Definition:
Genes are the fundamental units of heredity which transmits information from cells to cells and hence
one generation to the next.
Genes consists of specific sequence of DNA nucleotides which can code for the structure of polypetide
chains, tRNA molecules and rRNA molecules. Genes are arranged in linear series along the
chromosomes, determining specific characters of the organisms.
Q-36: What is transcription? Write down the process of transcription.
A) Transcription:
Definition:
“ With the help of polymerase enzyme, production of a RNA transcript of a gene from DNA is
called transcription. So, the process by which a complementary RNA strand is produced from a DNA
is called transcription.”
In this process, two strands of a double helix DNA get apart from each other by being untwisted
as the hydrogen bonds between complementary nucleotides are broken by enzyme. So, from any one of
two parted DNA strand, a mRNA strand is synthesized.
This involves following consecutive processes:
1. A specific region of the DNA molecule, called a criston, unwinds. This unwinding is the result of
hydrogen bonds between base pairs in the DNA double helix being broken with action of RNA
polymerase enzyme. This exposes the bases along each strand.
2. Each base along one strand attracts its complementary RNA nucleotide, i.e. a free guanine base on
the DNA will attracts an RNA nucleotide with a cytosine base and a uracil (not thymine) is attracts
to adenine.
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College
Sohana Akter, Lecturer, English Medium Day Shift
3. The enzyme RNA polymerase moves along the DNA adding one complementary RNA nucelotide
at a time to the newly unwound of DNA.
4. The region of base pairing between the DNA and the RNA is only is only around 12 base pairs at
any one times as the DNA helix reforms behind the RNA polymerase.
5. The DNA thus acts as a template against which mRNA is constructed. A number of mRNA
molecules may be formed before the RNA polymerase leaves the DNA, which closes up reforming
its double helix.
6. Being too large to diffuse across the nuclear membrane, the mRNA leaves instead through the
nuclear pores. In the cytoplasm it is attracted to the ribosomes. Along mRNA is a sequence of triplet
codes which have been determined by the DNA. Each triplet is called a codon.
Chapter-1: Cell and its Organization.
Sohana Akter
Lecturer in Botany, EMDS
B.Sc (Hons). M.Sc (First Class), 3rd
University of Dhaka
Rajuk Uttara Model College