BIOLOGY
THE
FUNDAMENTAL UNIT OF LIFE
Q.1. Who discovered cells and how?
Answer: Robert Hooke in 1665 discovered the cells. He examined a thin slice of cork
under a self-designed crude microscope and observed that the cork resembled the
structure of a honey comb. The latter consisted of many tiny compartments.
Hooke called them cellulae (singular cellula), now termed cells. Cellula
is a Latin name which means ‘a little room’. Such rooms were also present in
monastries.
Q.2. Why is the cell called the structural and functional unit of
life?
Answer: All living organisms are made up of cells. Thus, cell is the
structural unit of life. Each living cell has the capacity to perform certain
basic functions that are characteristics of all living forms. Each cell
acquired distinct structure and function due to the organization of its
membrane and cytoplasmic organelles in specific way. Each kind of cell
organelle performs a special function, such as making new materials in the cell
(e.g., chloroplast, ribosomes), clearing up the waste materials from the
cells (e.g., lysosomes), utilisation of oxygen in oxidation of food and
energy production (e.g., mitochondria), movement (microtubules
containing spindle, cilia, flagella), etc. A cell is able to live and perform
all its functions because of these organelles. These organelles together
constitute the basic unit of structure and function called the cell.
Q.3. How do substances like CO2
and water move in and out of the cell?
Answer: Carbon dioxide (CO2)
moves in and out of the cells by the process of diffusion. Diffusion involves
movement of molecules from higher concentration to lower concentration across
the plasma membrane.
Water moves in and out of the cells by osmosis. Osmosis is
the movement of water or solvent through a semipermeable membrane from a
solution of lower concentration of solutes to a solution of higher
concentration of solutes to which the membrane is relatively impermeable.
Both diffusion and osmosis are physical or mechanical processes
and do not require spending of energy for their performance by the cells.
Q.4. Why is plasma membrane called a selectively permeable
membrane?
Answer: Plasma membrane is called selectively permeable membrane because
it allows the movement of only selected molecules across it and not all of
them.
Q.5. Fill in the gaps in the
following table illustrating differences between prokaryotic and eukaryotic
cells
|
|
|||
|
|
Answer:
2. It lies in the cytoplasm and not covered with a nuclear membrane, nucleoid.
2. It lies in the cytoplasm and not covered with a nuclear membrane, nucleoid.
4. Membrane-bound cell organelles such as mitochondria, plastids,
Golgi apparatus, lysosomes, etc., are present in the cytoplasm.
Q.6. Can you name the two organelles we have studied that contain
their own genetic material?
Answer: (a) Mitochondria; (b) Chloroplasts (plastids).
Q.7. If the organization of a cell is destroyed due to some
physical and chemical influence, what will happen?
Answer: A well organized cell maintains homeostasis, i.e., constant
internal chemical composition. It is, therefore, able to perform basic
functions such as respiration, obtaining nutrition, clearing of waste, forming
new proteins, etc. If the organization of a cell is destroyed, it will not be able
to maintain homeostasis and thus will not be able to perform above said basic
functions and such a cell will ultimately die.
Q.8. Why are lysosomes are known as suicide bags?
Answer: Lysosomes contain digestive enzymes for almost all types of
organic materials. If their covering membrane breaks as it happens during
injury to cell, the digestive enzymes will spill over the cell contents and
digest the same. As lysosomes are organelles which on bursting can kill cells
possessing them, they are called suicide bags.
Q.9. Where are proteins synthesized inside the cell?
Answer: Proteins are synthesized in the ribosomes.
Exercises
Q.1 Make a comparison and write down ways in which plant cells are different from animal cells.
Answer: Differences between plants and animal cells are as follows:
|
|
||
|
|
||
|
|
||
|
|
||
|
|
||
|
|
Q.2. How is a prokaryotic cell different from a eukaryotic cell?
Answer: Differences between prokaryotic and eukaryotic cells:
|
|
||
|
|
||
|
|
||
|
|
||
|
|
Q.3. What would happen if the plasma membrane ruptures or break
down?
Answer: Plasma membrane is a selectively permeable membrane of the cell
that maintains its homeostasis, i.e., constant internal composition of
the cell. If it ruptures or breakdown the constant internal chemical
composition of the cell will be lost and it will not be able to perform its
basic functions. Such a cell with ruptured plasma membrane is killed.
Q.4. What would happen to the life of a cell if there was no Golgi
apparatus?
Answer: There would not be any lysosome for intracellular digestion and
cleansing, not complexing of molecules, no exocytosis and no formation of new
plasma membrane.
Q.5. Which organelle is known as the powerhouse of the cell? Why?
Answer: Mitochondrion is known as the powerhouse of the cell because it
contains enzymes that are needed for stepwise oxidation of food stuffs
(carbohydrate, fats or lipids and proteins) present in the cells to CO2 and water. Oxidation of
food releases energy which is used to form high-energy ATP (adenosine
triphosphate) molecules. ATP is known as energy currency of the cell and
it is used as cellular fuel. Energy stored in ATP is used to bring about energy
requiring activities of cell such as photosynthesis, protein synthesis and
muscle contraction.
Q.6. Where do the lipids and proteins constituting the cell
membrane get synthesized?
Answer: Proteins are synthesized in ribosomes of rough ER while lipids are
synthesized over smooth ER.
Q.7. How does an Amoeba obtain its food?
Answer: Amoeba is unicellular animal. It acquires its food by the process of
endocytosis. Plasma membrane of Amoeba is flexible with its help Amoeba
engulfs food particles. The engulfed food particle passes into the body of
organism as a phagosome. Phagosome combines with lysosome to produce digestive
or food vacuole. Digestion occurs in food vacuole. The digested food
passes into surrounding cytoplasm. The undigested matter is thrown out of the
cell.
Q.8. What is osmosis?
Answer: Osmosis is diffusion of water from the region of its higher
concentration (pure water or dilute solution) to the region of its lower
concentration (strong solution) through a semipermeable membrane.
Q.9. Carry out the following osmosis experiment:
Take four peeled potato halves and scoop each one out to make
potato cups. One of these potato cups should be made from a boiled potato. Put
each potato cup into a trough containing water.
Now
(a) keep cup A empty;
(b) put one teaspoon sugar in cup B;
(c) put one teaspoon salt in cup C;
(d) put one teaspoon sugar in the boiled potato cup D;
Keep these for 2 hours. Then observe the four potato cups and
answer the following:
(i) Explain why water gathers in the hollowed portion of B and C.
(ii) Why is potato A necessary for this experiment?
(viii) Explain why water does not gather in the hollow out portion of A
and D?
Answer:
(i) When unboiled potato cups B and C were put into a trough containing water, the cells of potatoes gained water by endosmosis. When a teaspoon of sugar and salt were added later in the hollowed portion of B and C cups respectively, water movement occurred through the plasma membranes of the cells from within the cells of potato into the hollowed portion of both B and C cups because of exosmosis (i.e., exit of water molecules through permeable plasma membranes from within the cells of unboiled potatoes into the hollowed portions having hypertonic sugar and salt, respectively).
(i) When unboiled potato cups B and C were put into a trough containing water, the cells of potatoes gained water by endosmosis. When a teaspoon of sugar and salt were added later in the hollowed portion of B and C cups respectively, water movement occurred through the plasma membranes of the cells from within the cells of potato into the hollowed portion of both B and C cups because of exosmosis (i.e., exit of water molecules through permeable plasma membranes from within the cells of unboiled potatoes into the hollowed portions having hypertonic sugar and salt, respectively).
(ii) Potato cup A is necessary in the experiment as a
‘control’ for providing comparison with situations created in potato cups B, C
and D. It indicates that the potato cavity alone does not induce movement of
water.
(iii) Water does not gather in the hollowed portion of
potato cup A because it does not possess higher osmotic concentration than the
cells of potato.
Potato cup D is boiled potato cup. On
boiling, potato cells die and the membranes of the potato cells lost their
permeability. As a result, when teaspoon of sugar is added into the hollowed
portion of boiled potato cup D, water does not come out from within the potato
cells into the hollowed portion.
Questions Based on Question Bank.
Q.1. Why are lysosomes known as “suicide bags” of a cell?
Answer: The lysosomes are suicide bags of a cell because they have
hydrolytic enzymes that help in degrading waste materials produced within the
cells. Some time cells also digest itself. Therefore, lysosomes are known as
suicide bags of a cell.
Q.2. Do you agree that “A cell is a building unit of an organism”?
Answer: Yes, cell is a building unit of every living organism as every
living being is made up of one or more cells. For example, in unicellular or
acellular organisms, the single cell performs all the functions of life.
In multicellular organisms all the cells have a similar basic structure
and perform a similar basic life activities. However, they become specialised
to form components of different structures that perform different functions.
Cells are first organised into tissues, each with a specific function,
e.g., contraction by the muscular tissue. Tissues are organised to form organs
with each organ performing a specific task, e.g., heart, kidney, lung,
stomach, eyes. Organs are grouped into organ systems, each with a major
function, e.g., circulatory system, excretory system, respiratory system,
digestive system, skeletal system. A living organism has a number of organ
systems. Thus, in all such organisational complexity, cell remains the basic
building unit of the organism.
Q.3. Why does the skin of your fingers shrink when you wash
clothes for a long time?
Answer: Clothes are washed with soap or detergent solution. This solution
is hypertonic as compared to osmotic concentration of our skin cells.
The washing solution, therefore, results in exosmosis in the skin cells
that come in contact with it for some time. Due to this reason, the skin over
the fingers shrinks while washing clothes for a long time.
Q.4. Why is endocytosis found in animals only?
Answer: Endocytosis is swallowing up of food and other substances
(bacteria, viruses) from external medium by the plasma membrane. This is
possible only when plasma membrane is in direct contact with external medium.
It occurs only in animal cells. In plant cells, a cell wall is present over the
plasma membrane. Therefore, their plasma membrane cannot perform endocytosis.
Q.5. A person takes concentrated solution of salt. After some time
he starts vomiting. What is the phenomenon responsible for such a situation?
Explain.
Answer: Concentrated salt solution is a hypertonic solution so
causes irritation and excessive dehydration in the wall of alimentary canal due
to exosmosis. There is uncomfortable stretching which causes reverse
movements and hence vomiting.
Q.6. Name any cell organelle which is nonmembranous.
Answer: Ribosome.
Q.7. We eat food composed of all the nutrients such as
carbohydrates, proteins, fats, vitamins, minerals and water. After digestion, they
are absorbed in the form of glucose, amino acids, fatty acids, glycerol, etc.
What mechanisms are involved in the absorption of digested food and water?
Answer: Digested food is taken in the intestinal cells by the following
process:
(i) Glucose, amino acids and some ions—Active transport.
(ii) Fatty acids, glycerol—Diffusion (Passive transport)
(iii) Water—Osmosis.
Q.8. If you are provided with some vegetables to cook, you
generally add salt into vegetables during cooking process. After adding salt,
vegetables release water. What mechanism is responsible for this?
Answer: On adding salt, vegetables release water due to exosmosis. Exosmosis
occurs whenever the external medium is hypertonic as compared to the osmotic
concentration inside living cells.
Q.9. If cells of onion peel and RBC are separately kept in
hypotonic solution what among the following will take place? Explain the reason
for your answer. (a) Both the cells will swell (b) RBC will burst
easily while cells of onion peel will resist the bursting to some extent. (c)
a and b both are correct (d) RBC and onion peel cells will behave
similarly.
Answer:
(b) RBC will burst as there is no mechanism to resist entry of water into them. Onion peel cells do not burst. Endosmosis causes some initial swelling in such onion peel cells but cell wall puts a mechanical barrier to promote entry of water. Therefore, these cells do not burst.
(b) RBC will burst as there is no mechanism to resist entry of water into them. Onion peel cells do not burst. Endosmosis causes some initial swelling in such onion peel cells but cell wall puts a mechanical barrier to promote entry of water. Therefore, these cells do not burst.
Q.10. Bacteria do not have chloroplasts but some bacteria are
photoautotrophic in nature and perform photosynthesis. Which part of bacterial
cell perform this?
Answer: Photoautotrophic bacteria posses photosynthetic pigments inside
small vesicles which may be attached to the plasma membrane.
Q.11. Match the items of A
and B.
|
|
||
|
|
||
|
|
||
|
|
||
|
|
||
|
|
Answer: a - iv; b-v; c-iii; d-i; e-ii.
Q.12. Write the name of different plant parts in which
chloroplast, chromoplast and leucoplasts are present.
Answer:
1. Chromoplast: Flower (petals) and fruits.
1. Chromoplast: Flower (petals) and fruits.
2. Chloroplast: Green leaves and green parts.
3. Leucoplast: Root and underground stem.
Q.13. Name the organelles which show analogy written as under
(a) Transporting channels of the cell .........
(b) Power house of the cell ........
(c) Packaging and dispatching unit of the cell ......
(d) Digestive bag of the cell ......
(e) Storage sac of the cell ........
(f) Kitchen of the cell .......
(g) Control room of the cell .......
Answer:
(a) Endoplasmic reticulum; (b) Mitochondria; (c) Golgi apparatus; (d) Lysosome; (e) Vacuole; (f) Chloroplasts; (g) Nucleus.
(a) Endoplasmic reticulum; (b) Mitochondria; (c) Golgi apparatus; (d) Lysosome; (e) Vacuole; (f) Chloroplasts; (g) Nucleus.
Q.14. How is bacterial cell different from an onion peel cell?
Answer: Differences between bacterial cell
and an onion peel cell:
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
Q.15. How do substances such as carbon dioxide and water move in
and out of the cell?
Answer: By diffusion and osmosis respectively.
Q.16. How does Amoeba obtain its food?
Answer: Amoeba obtains its food through the
process of endocytosis. When Amoeba is near food or senses food, it
extends its pseudopodia around the food and engulfs it. When the food enters
its body the Amoeba forms a food vacuole around it which contains
enzymes that help in digesting the food particles.
Q.17. Name two organelles in plant cell that contain their own
genetic materials and ribosomes.
Answer:(i) Plastids; (ii) Mitochondria.
Q.18. Why are lysosomes also known as “scavengers of the cell”.
Answer: Lysosomes are called scavengers of the cell because they remove
cell debris consisting of dead and worn out cell organelle by digesting the
same. Rather they nourish the cells by sending out digesting nutrients into the
cytoplasm.
Q.19. Which cell organelle control most of the activities of the
cell?
Answer: Nucleus, by controlling metabolism and cell activities. Genes
express their effect through RNAs. RNAs control synthesis of proteins and
enzymes.
Q.20. Which kind of plastid is more common in (a) Root of
the plant, (b) Leaves of the plant, (c) Flowers and fruits.
Answer: (a) Leucoplasts in roots; (b) Chloroplasts in
leaves; (c) Chromoplasts in flowers and fruits.
Q.21. Why do plant cells possess large sized vacuole?
Answer: Vacuole of plant cells is large in size because it has to take
part in following activities:
1. It stores salts, sugar, amino acids, organic acids and some
proteins.
2. Metabolic wastes of the cell are dumped in the vacuole.
3. Lysosomal enzymes occur in the vacuole of plant cell.
4. The vacuole contains cell sap and helps in maintaining
turgidity of the cell.
5. Plant cell vacuole contains an osmotic concentration which is
required for the process of osmosis through plasma membrane.
Q.22. How are chromatin, chromatid and chromosome related to each
other.
Answer: Chromatin is intertwined mass of fine thread-like structures made of DNA and
protein. During cell division (mitosis or meiosis), chromatin condenses to form
thicker rod-like structures called chromosomes. Each chromosome consists
of two similar halves called chromatids. Formation of chromosomes having
two similar halves or chromatids is meant for equitable distribution of
chromatin which is hereditary material.
Q.23. What are consequences of the following conditions?
(a) A cell having higher water concentration than the
surrounding medium.
(b) A cell containing low water concentration than the
surrounding medium.
(c) A cell having equal water concentration to its
surrounding medium.
Answer: High water concentration occurs in hypotonic solution, low water
concentration in hypertonic solution while equal water concentration in
isotonic solution.
(a) A cell having higher water
content or hypotonic cell sap will undergo exosmosis and, therefore, lose
water. It may undergo plasmolysis.
(b) A cell having low water concentration or hypertonic
cell sap will undergo endosmosis and absorb water from outside. It would become
turgid.
(c) A cell having isotonic cell sap will neither gain nor
lose water to the external medium.
Q.24. Illustrate only a
plant cell as seen under electron microscope. How is it different from animal
cell
|
|
||
|
|
||
|
|
||
|
|
||
|
|
Q.28. Mention the differences between Nucleus and
Nucleoid.
|
|
||
|
|
||
|
|
||
|
|
||
|
|
TISSUES
Q.1.
What is a tissue?
Answer: A tissue is a group or collection of similar cells which work
together to achieve a particular function and have common origin. Blood, phloem
and muscles are all examples of tissues.
Q.2.
What is the utility of tissues in multicellular organisms?
Answer: In multicellular organisms there are millions of cells. Most of
these cells are specialised to carry out a few functions. Each specialized
function is taken up by a different group of cells or tissues. Since these
cells of a tissue carry out only a particular function, they do it very
efficiently. For example, in human beings, muscle cells contract and relax to
cause movement, nerve cells carry messages and blood flows to transport oxygen,
food, hormones and waste materials and so on. Likewise, in plants, vascular
tissues (xylem, phloem) conduct water and food from one part of the plant to
other parts. So, multicellular organisms show division of labour.
Q.3.
Name three types of simple tissues.
Answer: Three types of simple tissues of plants are:
1.
Parenchyma; 2. Collenchyma; and 3. Sclerenchyma.
Q.4.
Where is apical meristem found?
Answer: Apical meristem is found in shoot apex and root apex of an
angiospermic plant.
Q.5.
Which tissue makes up the husk of coconut?
Answer: Sclerenchymatous fibres.
Q.6.
What are constituents of phloem?
Answer: Phloem is a complex tissue of the angiosperm plants. It serves as
a conducting tissue and is made up of four types of elements: (i) Sieve
tube; (ii) Companion cells; (iii) Phloem fibres (bast fibres),
and (iv) Phloem parenchyma.
Q.7.
Name the tissue responsible for the movement in our body.
Answer: Muscular tissue.
Q.8.
What does a neuron look like?
Answer: Neuron or nerve cell is a unit of nervous tissue (brain, spinal
cord and nerves) which serves to transmit messages in our body. A neuron
consists of cell body with a nucleus and cytoplasm, from which long thin
hair-like parts arise. Usually, each neuron has a single long part called the axon,
and many short branched processes (parts) called dendrites.
Q.9.
Give three features of cardiac muscle.
Answer: (i) Cardiac muscles are involuntary.
(ii)
Cardiac muscle cells are cylindrical, branched and uninucleate.
(iii)
Cardiac muscles show rhythmic contraction and relaxation throughout the life.
Q.10.
What are functions of areolar tissue?
Answer: Areolar tissue is a
connective tissue. It fills the space inside the organs, supports internal
organs and helps in repair of tissues.
Exercises
Q.1.
Define the term “tissue”.
Answer: A tissue is a group or collection of similar or disimilar cells
which work together to achieve a particular function. Cells of a tissue have
common origin.
Q.2.
How many types of elements together make up the xylem tissue? Name them.
Answer: Xylem is a complex tissue. It is made up of following four kinds
of cells (= elements): (i) Tracheids; (ii) Vessels; (iii)
Xylem parenchyma; (iv) Xylem fibres.
Q.3.
How are simple tissue different from complex tissue in plants?
Answer: A simple tissue is made up of only one type of cells where as
complex tissue is made up of different types of cells.
Q.4.
Differentiate between parenchyma, collenchyma and sclerenchyma on the basis of
their cell wall.
Answer: The differences between cell
walls of parenchyma, collenchyma and sclerenchyma are given in following table:
Q.5.
What are the functions of the stomata?
Answer: The important functions of stomata are:
(i)
Exchange of gases with atmosphere, e.g., entry of carbon dioxide for
photosynthesis and of oxygen for
respiration.
(ii) Transpiration, i.e., loss
of water in the form of water vapour.
Q.6. Diagrammatically show
the difference in three types of muscle fibres.
Q.7
What is the specific function of the cardiac muscle?
Answer: Cardiac muscle is present in the heart. It contracts and relaxes
rapidly and continuously with a rhythm, but it never gets fatigued.
Q.8.
Differentiate between striated, unstriated and cardiac muscles on the basis of
their structure and site/location in the body.
Answer: Differences between striated, unstriated and cardiac muscles are
as follows:
Q.9 Draw a labelled diagram
of a neuron.
Answer:
Q.10.
Name the following:
(a)
Tissue that forms inner lining of our month.
(b)
Tissue that connects muscle to bone in humans.
(c)
Tissue that transports food in plants.
(d)
Tissue that stores fat in our body.
(e)
Connective tissue with a fluid matrix.
(f)
Tissue present in the brain.
Answer: (a)
Squamous epithelium; (b) Tendon;
(c)
Phloem; (d) Adipose tissue;
(e)
Vascular tissue (Blood and lymph); (f) Nervous tissue.
Q.11.
Identify the type of tissue in the following: skin, bark of tree, bone, lining
of kidney tubule, vascular bundle.
Answer: Skin: Epithelial tissue (squamous epithelium);
Bark
of tree: Cork (protective tissue);
Bone:
Skeletal tissue (connective tissue);
Lining
of kidney tubules: Cuboidal epithelial tissue;
Vascular
bundle: Complex permanent tissue — xylem and phloem.
Q.12.
Name the regions in which parenchyma tissue is present.
Answer: Parenchyma is a simple permanent tissue of
angiospermic plants. It is present in cortex and pith of stem and roots. It is
also present in the mesophyll of leaves.
Q.13.
What is the role of epidermis in plants?
Answer: Epidermis is a protective tissue of angiospermic plants. It provides
protection to underlying tissues. Epidermis forms outer covering of various
plant organs such as roots, stem, leaves and flowers and remains in direct
contact with the environment. Any substance, whether solid, liquid or gas can
enter into the plant or move outside only after passing through this layer.
Epidermis helps in absorption, secretion, excretion, gaseous exchange and
transpiration. It helps in preventing the entry of pathogens.
Q.14.
How does cork act as a protective tissue?
Answer: The cork cells are dead and do not have any intercellular spaces.
The cell walls of the cork cells are coated with suberin (a waxy substance).
Suberin makes these cells impermeable to water and gases. Cork is protective in
function; it protects underlying tissues from desiccation (loss of water from
plant body), infection and mechanical injury.
Q.15. Complete the table:
Answer:
0 comments:
Post a Comment