Fundamental
Unit Of Life
(Q.) Name two major
functional regions of a cell.
(Ans) The
two major functional regions of a cell are-
a) Nucleus b) Cytoplasm
(Q.) Cells
come from pre - existing cells. How?
(Ans) Cells
divide to produce cells of their own kind. Thus, all cells come from pre -
existing cells.
(Q.) Who discovered the nucleus in the cell?
(Ans) Robert
Brown in 1831 discovered the nucleus in the cell.
(Q.) Who discovered
the cell?
(Ans) Robert
Hooke discovered the cells.
(Q.) What
substances form cell membrane and cell wall?
(Ans) Cell
membrane is made up of proteins and lipids. Cell wall is made up of cellulose.
(Q.) Name two-cell
organelles, which have DNA apart from nucleus.
(Ans) 1)
Plastids (2) Mitochondria
(Q.) Name the cell
organelles that are found only in plant cell.
(Ans) Plastids
and cell wall.
(Q.) Name the cell
organelle that is found only in animal cell.
(Ans) Centriole
(Q.) On what
factors do shape and size of cell depend?
(Ans) The
shape and size of cell depend on the functions they perform.
(Q.) Who coined the
term protoplasm?
(Ans) J.E.
Purkinje
(Q.) What are
chromosomes? Where are they present in the cell?
(Ans) Chromosomes
are visible rod-shaped structures present in the nucleus. They are composed of
DNA and protein.Chromosomes contain information for inheritable features from
parents to next generation in the form of DNA molecules.
(Q.) Why is the
plasma membrane called a selectively permeable membrane?
(Ans) The
plasma membrane allows or permits the entry and exit of some materials in and
out of the cell. It also prevents movement of some other materials in the cell
membrane. Therefore, it is called a selectively permeable membrane.
(Q.) Why is the
cell called the structural and functional unit of life?
(Ans) Cell
is called structural and functional unit of life because -
(i) All the living organisms are made up of cells.
(ii) All the functions taking place in the body of organisms are also performed
by the cells within themselves.
(Q.) What are
multicellular organisms? Give examples.
(Ans) The
organisms which are made up of many cells and these cells perform various
functions of the body are known as multicellular organisms, e.g.fungi, plants,
animals.
(Q.) What are
unicellular organisms? Give examples.
(Ans) Some
organisms are made up of a single cell only. They are known as unicellular
organisms. e.g. Amoeba, Chlamydomonas, Paramecium and Bacteria.
(Q.) Who presented
the cell theory for the first time? What was it?
(Ans) Two
biologists, Schleiden (1839) and Schwann (1839) presented the cell theory.
This stated that all the plants and animals are composed of cells and the cell
is the basic unit of life.
(Q.) Who discovered
free-living cells and how?
(Ans) Leeuwenhoek
with the improved microscope discovered the free-living cells in pond water for
the first time.
(Q.) Name the non -
living parts of a cell.
(Ans) 1.Cell
wall (plants only) 2.Vacuoles 3.Granules (cell inclusions)
(Q.) Which cell
organelle is known as the kitchen of the cell? Why?
(Ans) Chloroplast
is known as kitchen of the cell as photosynthesis takes place resulting in
synthesis of food.
(Q.) How do
substances like CO2 and water move in and out of the cell?
(Ans) Gases
like CO2 and O2 move in and out of the cell by diffusion
from their higher concentration to lower concentration.
Water enters the cell by endosmosis through semi-permeable plasma membrane from
its higher concentration to lower concentration.
Similarly, water moves out of the cell by exosmosis when a cell is placed in a
hypertonic solution.
(Q.) Explain the
terms.
a) Endocytosis b) Plasmolysis
(Ans) a)
Endocytosis- The flexibility of the cell membrane
enables the cell to engulf food and other material from its external environment.
Such processes are known as endocytosis.
b) Plasmolysis- When a
living plant cell loses water through osmosis, there is shrinkage or
contraction of the contents of the cell away from the cell wall. This
phenomenon is known as plasmolysis.
(Q.) Write any four
differences between the plasma membrane and cell wall.
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(Ans) Plasma
Membrane
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Cell Wall
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1. It is made up of lipids and protein.
2. It is living.
3. Present in both plant and animal cell.
4. It regulates entry and exit of molecules in and
out of the cell.
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1. It is made up of cellulose.
2. It is dead.
3. Found exclusively in plant cell.
4. Cell wall provides structural strength to the
plants.
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(Q.) Define- a) Diffusion b) Osmosis
(Ans) a)
Diffusion -
It is the spontaneous movement of molecules from region of their high
concentration to their lower concentration leading finally to uniform
concentrations. It is faster in the gaseous phase than in liquids and solids.
b) Osmosis-
It is the movement of solvent (water) molecules from region of its higher
concentration to its lower concentration through a semi - permeable membrane.
Osmosis is a purely mechanical process by which cells absorb water without
spending any amount of energy.
(Q.) When and how
the cells were discovered?
(Ans) In
1665, Robert Hooke observed a thin slice of cork(part of the bark of a
tree)under a self - designed microscope and observed astructure like a
honeycomb consisting of many little compartments. Robert Hooke called these
boxes as cells. Cell is a Latin word usedfor a little room.
(Q.) Name the
living parts of a cell.
(Ans) 1.
Plasma Membrane 2.Cytoplasm 3. Endoplasmic
reticulam (ER) a)Smooth ER (b) Rough ER
4.Mitochondria 5.Golgi apparatus 6.Ribosomes 7.Lysosomes 8.Centrioles
(animals only) 9.Plastids
(plants only)
(Q.) Why are
Mitochondria known as power house of the cell?
(Ans) Mitochondria
are called power house of cell because respiration takes place in them and
energy is released in the form of adenosine tri-phosphate (ATP). The cell uses
this energy to perform various functions such as mechanical work and making of
new chemical compound .
(Q.) What are the types of plastids? Write their names and fuctions.
(Ans) Plastids
are of three types -
i) Leucoplasts- Leucoplasts store starch, protein and fat.
ii) Chromoplasts- Chromoplasts provide colour to fruits and flowers.
iii) Chloroplasts- Green coloured chloroplast is the site of photosynthesis as
it contains chlorophyll.
(Q.) Differentiate
between prokaryotic and eukaryotic cell.
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(Ans) Feature
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Prokaryotic
cell
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Eurkaryotic
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1. Nucleus
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Lacks
true nucleus. Circular DNA lies naked in the cytoplasm. No chromosomes,
nucleolus or nuclear membrane.
Nuclecoplasm
undifferentiated from cytoplasm.
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True
nucleus bound by nuclear membrane contains DNA, chromosomes, nucleolus and
nuclear membrane present, Nucleoplasm differentiated from cytoplasm.
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2. Organelles
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Membrane
– bound organelles like Golgibodies, plastids, mitochondria and endoplasmic
reticular (ER) are absent.
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Membrane
– bound organelles present.
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3. Cell division
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Divides
by simple fission, spindle is not formed, no mitosis and meiosis.
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Divides
by mitosis or by meiosis.
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4. Examples
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Bacteria
and cyanobacterica (blue – green algae).
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All
other organism.
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(Q.) Differentiate
between diffusion and osmosis.
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Diffusion
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Osmosis
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1. Diffusion can occur in any
medium.
2.The diffusing molecules may be solvent.
3. Semi permeable membrane is not required.
4.It is dependent upon the free energy of the diffusing molecules and
independent of molecules of other substances in the system.
5. An equilibrium in the free energy of diffusion molecules is achieved in
the system.
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1.
It occurs only in liquid medium.
2. It involves movement of solvent
molecules only.
3. Semi permeable membrane is required.
4. Though it is the diffusion of solvent molecules
only yet influenced by the presence of other substances (solutes) in the
system.
5.Equilibrium in the free energy of solvent
molecules is never achieved.
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(Q.) How
does an Amoeba obtain its food?
(Ans) Amoeba
engulfs its food by forming pseudopodia around the food particle.
These pseudopodia are projections of cell membrane.
Once surrounded by pseudopodia the food becomes part of cell and it forms a
food vacuole. This method of engulfing food is termed as endocytosis (phagocytosis).
(Q.) How will you
relate nucleus with DNA?
(Ans) Nucleus
is located in the center of the cell. It is the main cell organelle and
controls all the activities of cell. A membrane having pores surrounds it. Its
chief compounds are chromatin material and nucleolus. Chromatin material when
condenses form knot like structures called chromosomes. Chromosomes contain
hereditary units called genes, which in turn are made up of DNA. These DNA are
carriers of characters from one generation to another.
(Q.) Write one functions
of each of the following cell organelles.
a) Plasma membrane b) Mitochondria c) Lysosomes d) Endoplasmic reticulum e)
Vacuoles
(Ans) a)
Plasma membrane or cell membrane: It controls
the entry and exit of material from the cell to outside and from outside to
inside. It also protects the cell.
b) Mitochondria: Cellular respiration takes place
resulting in release of energy. Hence, they are also known as powerhouse of the
cell.
c) Lysosomes: They contain powerful enzyme that can
digest and remove worn out cell organelles.
d) Endoplasmic Reticulum (ER):
Rough Endoplasmic Reticulum (RER)-It synthesizes proteins.
Smooth Endoplasmic Reticulum (SER)- It synthesizes fats and lipids. They are
filled with a liquid called cell sap and provide turgidity and rigidity to
plant cells.
