Fundamental unit of life

1. A cell will swell up if
(a) the concentration of water molecules in the cell is higher than the concentration of water
molecules in surrounding medium
(b) the concentration of water molecules in surrounding medium is higher than water molecules
concentration in the cell
(c) the concentration of water molecules is same in the cell and in the surrounding medium
(d) concentration of water molecules does not matter.
Solution:
(b) If a cell is placed in a solution containing higher concentration of water molecules than the
concentration of water molecules in the cell (hypotonic solution), the cell will gain water by the
process of osmosis (endosmosis). Although water molecules freely cross the cell membrane in both
the directions but more water enters into the cell than leave and thus the cell swells up.
Which of these is not related to endoplasmic reticulum?
(a) It behaves as transport channel for proteins between nucleus and cytoplasm.
(b) It transports materials between various regions in cytoplasm.
(c) It can be the site of energy generation.
(d) It can be the site for some biochemical activities of the cell.
Solution:
(c) Endoplasmic reticulum (ER) is a membranous network which almost fills up the intracelluar cavity.
ER serves as channel for the transport of materials (especially proteins) between various regions of
the cytoplasm or between the cytoplasm and the nucleus. ER also functions as a cytoplasmic
framework providing the site for some biochemical activities of the cell.
Mitochondria is the site of energy generation.
What is plasmolysis?
When a cell is placed in a hypertonic solution i.e., a solution in which concentration of water
molecules outside the cell is lesser than the concentration of water molecules inside the cell, the cell
will loss water by the process of osmosis (exosmosis). Although water crosses the cell membrane in
both directions, but more water leaves the cell than enters resulting in the shrinkage of cell
cytoplasm. This phenomenon of shrinkage of cell cytoplasm when put in a hypertonic solution is
called plasmolysis.
How does amoeba acquire its food?
Amoeba acquires its food through a process, termed as endocytosis.
Imp. Point- Organelle other than nucleus, containing DNA are mitochondria and chloroplast.
What are the two postulates of cell theory? Who gave the cell theory.
The cell theory says that-
that all the plants and animals are composed of cells and that the cell is the basic unit of life.
New cells arise from the pre-existing cells.
The cell theory was presented by two biologists, M.J. Schleiden (1838) and Theodore Schwann
(1839).
Why are lysosomes known as suicidal bags a cell?
Solution:

2. Lysosomes are known as ‘suicide bags’ of the cell because they contain digestive enzymes capable to
digest the whole cell when the situation demands. When the cell gets damaged during some
disturbance in cellular metabolism, lysosomes may burst and digestive enzymes thus released digest
r their own cell. This is a mechanism of self-defence by the cell.
Why does the skin of your finger shrink when you wash clothes for a long time?
Solution:
Soap solution is a hypertonic solution i.e., it is more concentrated than the cells of our skin. As we
know when a cell is immersed in a hypertonic solution, water leaves the cell by the process of
exosmosis resulting in shrinkage of the cell. In the same way, while washing clothes for a long time,
exosmosis occurs in the skin cells resulting in the shrinkage of skin cells of our fingers.
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.
Solution:
(c) Cells of onion peel are surrounded by a cell wall whereas the RBCs (red blood cells) do not have
cell wall. When the cells of onion peel and RBCs are separately kept in hypotonic solution, RBCs will
first swell up and then burst due to endosmosis. However, cell wall in the cells of onion peel exerts a
counter wall pressure when the cells become fully turgid. This stops further entry of water into the
cells and thus the cells do not burst.
Why do plant cells possess large sized vacuole?
Solution: In mature plant cells, a large central vacuole occupying most of the cell space is present. It
is because in the plant cells, vacuole does not only store food material and waste products, rather it
also contains cell sap. The cell sap helps to keep the cell turgid and provides rigidity and support to
it. Vacuole also helps in maintaining water balance of the cell. Thus plant cells possess large sized
vacuole.
Difference between nucleus and nucleoid are:
Nucleus Nucleoid
1. It is larger in size. 1. It is smaller in size.
2. It is bounded by double membrane. 2. It is not bounded by any membrane.

3. 3. It contains nucleolus. 3. It does not contain nucleolus.
4. It contains DNA associated with histone proteins.
4. It contains naked DNA i.e., DNA is not associated w
histone proteins.
5. It is present in eukaryotic cells. 5. It is present in prokaryotic cells.
6. Plastids are present. 6. Plastids are absent.
In brief state what happens when
(a) dry apricots are left for sometime in pure water and later transferred to sugar solution?
(b) a red blood cell is kept in concentrated saline solution?
(c) the plasma membrane of a cell breaks down?
(d) rheo leaves are boiled in water first and then a drop of sugar syrup is put on it?
(e) Golgi apparatus is removed from the cell?
Solution:
(a) When dry apricots are left in pure water, they swell up due to endosmosis and when they are
kept in sugar solution, they shrink due to exosmosis.
(b) When a red blood cell is kept in concentrated saline solution, it loses water due to exosmosis and
shrinks.
(c) If plasma membrane of a cell breaks down, all the protoplasmic materials including cells
organelles will come out of the cell resulting in their non-functioning and hence death of the cell.
Plasma membrane is a selectively permeable membrane which regulates transport of certain specific
substances into and out of cell maintaining the identity of the cell. If plasma membrane of a cell
breaks down, there may occur loss of some essential components of the cell and the substances
which are not required by the cell may enter into it. This would ultimately lead to death of the cell.
(d) Cells of the rheo leaves will die on boiling, hence no plasmolysis will occur. If we will put sugar
solution on it there will be no effect of putting sugar syrup over the leaves.

4. (e) If Golgi apparatus is removed from the cell, modification, sorting and packaging of materials
coming from ER or synthesised in the Golgi apparatus itself, will not take place. Other functions
carried out by the Golgi apparatus such as synthesis of complex sugars, formation of lysosomes,
membrane biognesis etc. will also not take place, resulting in non-functioning and hence death of
the cell.
Intestine absorbs the digested food materials. What type of epithelial cells are responsible for
that?
Columnar epithelium consists of pillar-like cells that are much taller than wide. The nuclei are
generally elongated along the long axis of cells. It lines the intestine . Columnar epithelium of
intestine is specialised for the absorption of water and digested food.
While doing work and running, you move your organs like hands, legs etc. Which among the
following is correct?
(a) Smooth muscles contract and pull the ligament to move the bones.
(b) Smooth muscles contract and pull the tendons to move the bones.
(c) Skeletal muscles contract and pull the ligament to move the bones.
(f) Skeletal muscles contract and pull the tendon to move the bones.
Solution:
(d) Skeletal muscles or striated muscles are found in the body wall and the limbs (biceps and triceps
of arms, legs). The contraction and relaxation of these muscles are under the control of organism, so
they are also called voluntary muscles. These are attached to the bones by tendons. When they
contract, they pull the tendon to move the bones and help in the movement of limbs.
Nervous tissue is not found in
(a) brain
(b) spinal cord
(c) tendons
(d) nerves.
Solution:
(c) The nervous tissue, which contains densely packed nerve cells, called neurons (Gk. neuro =
nerve), is present in the brain, spinal cord and nerves. The neurons are specialised for conduction of
nerve impulses. Tendon is a type of connective tissue.
ln desert plants, rate of water loss gets reduced due to the presence of
(a) cuticle
(b) stomata
(c) lignin
(d) suberin.
Solution:
(a) Cuticle is the continuous waxy layer that covers the aerial parts of a plant. Composed mainly of
cutin, it is secreted by the epidermis and its primary function is to prevent water loss.
A nail is inserted in the trunk of a tree at a height of 1 metre from the ground level. After 3 years
the nail will
(a) move downwards
(b) move upwards
(c) remain at the same position

5. (d) move sideways.
Solution:
(c) The nail will remain at the same position after 3 years, but will appear to have sunk into the tree.
This is because of the secondary growth of the tree which increases the girth of a tree. The increase
in height of the plant will occur due to primary growth which occurs only in the regions of the apical
meristems i.e. at the tips of the main stem or branches. As increase in height of the tree takes place
from top only, therefore the nail will remain at the same position as it is inserted near the ground
level.
Which structure protects the plant body against the invasion of parasites?
Solution:
Epidermis is a layer of parenchymatous cells that forms the outermost covering of plant body.
Epidermis consists of compactly arranged cells without any intercellular spaces. On the aerial plant
parts, it secretes a thick, waxy, water-resistant layer called cuticle on its outer surface. These
features .make the epidermis protective against loss of water, mechanical injury and the invasion of
parasites.
Give reasons for:
(a) Meristematic cells have a prominent nucleus and dense cytoplasm but they lack vacuole.
(b) Intercellular spaces are absent in sclerenchymatous tissues.
(c) We get a crunchy and granular feeling, when we chew pear fruit.
(d) Branches of a tree move and bend freely in high wind velocity.
(e) It is difficult to pull out the husk of a coconut tree.
Solution:
(a) Meristematic cells have a prominent nucleus and dense cytoplasm because they are
metabolically highly active and are in continuous state of division. Meristematic cells lack vacuole
because they do not store food material, waste material, sap etc.
(b) Sclerenchyma cells have lignified cell walls which makes them compact and leaves no
intercellular spaces.
(c) Pear fruit contains sclerenchymatous stone cells or sclereids which provide gritty texture to the
fruit. Thus, when we chew pear fruit, we get a crunchy and granular feeling.
(d) Collenchyma tissue present in the branches of a tree provides flexibility to them and allows their
easy bending without breaking. Thus the branches move and bend freely in high wind velocity.
(e) The husk of a coconut is made up of sclerenchymatous fibres which consist of compactly
arranged cells with thick lignified cell walls and no intercellular spaces. So, they are tightly joined
together. Thus, it is difficult to pull out the husk of a coconut.
Define the process of differentiation.
Differentiation can be defined as the phenomenon of transformation of unspecialised cells into
specialised cells by the loss of ability to divide and by taking up permanent shape, size, structure and
function.