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Q1. Name the processes by which CO2 and H2O move in and out of the cell?
Solution
CO2 and H2O
move in and out of the cell by the process of diffusion and osmosis respectively.
Q2. What will happen
if: (a) Ribosomes are removed from the cell. (b) Golgi apparatus is removed
from the cell.
Solution
(a) If ribososmes are
removed from the cell, proteins will not be synthesized. (b) If Golgi apparatus
is removed from the cell, packaging of materials, synthesis of complex sugars
and formation of lysosome will be adversely affected.
Q3. Distinguish between
chloroplast and leucoplast with respect to their pigments and function.
Solution
Differences between
chloroplast and leucoplast: Chloroplast Leucoplast Green pigment
Colourless pigment Helps in photosynthesis Helps in the
storage of proteins and starch
Q4. Which cell
organelles are called the powerhouses of the cell and why? Why is ATP called
energy currency of the cell?
Solution
Mitochondria are called
the powerhouses of the cell. During oxidation of food, a large amount of energy
is released by mitochondria which gets stored in the form of energy-rich
compound called adenosine triphosphate (ATP). This energy stored in the form of
ATP is used for making new chemical compounds and for performing mechanical
work, therefore ATE is called energy currency of the cell.
Q5. What will happen if
plasma membrane ruptures or breaks down?
Solution
Plasma membrane is a
selectively permeable membrane of the cell that maintains homeostasis, i.e.
a constant internal composition of the cell. If it ruptures or breaks
down, the constant internal composition of the cell will be lost and the cell
will not be able to perform its basic functions. Such a cell with a ruptured
plasma membrane gets killed.
Q6. What would happen
to a cell if its nucleus is removed?
Solution
The nucleus controls all
the metabolic activities of the cell. If the nucleus is removed from a cell,
its protoplasm dries up and the cell dies. Therefore, the nucleus is paramount
to a cell's survival.
Q7. What did A.
Leeuwenhoek discover in 1674?
Solution
In 1674, with the help of
an improved microscope, A. Leeuwenhoek discovered the free-living cells in pond
water for the first time.
Q8. State two reasons
for plant cells to have a large central vacuole.
Solution
Plant cells have a large
central vacuole because: (i) They help in maintaining the osmotic pressure
of the cell. (ii) They store important substances like amino acids and
proteins. (iii) They also store metabolic wastes of the cell.
Q9. Define diffusion.
Solution
Diffusion is the
spontaneous movement of molecules from a region of high concentration to a
region of low concentration.
Q10. Give one function
each of the following nuclear parts: a) Nuclear pore b) Nuclear membrane c)
Chromosomes
Solution
a) Nuclear pore: It
allows the transfer of materials from inside the nucleus to the cytoplasm. b)
Nuclear membrane: It gives a distinct identity to the nucleus by keeping its
contents inside and separate from the cytoplasm. c) Chromosomes: They contain
DNA, which carries the information necessary for constructing and organizing
cells.
Q11. When can you call a
single cell as an organism?
Solution
A single cell is called
an organism when it carries out all the functions needed to sustain its life.
Amoeba and bacteria are single-celled organisms.
Q12. List six functions
of nucleus of a cell.
Solution
Functions of nucleus:
(i) Nucleus has a double layer covering called nuclear membrane which has
pores which allow the transfer of materials from inside the nucleus
to its outside. (ii) It directs the chemical activities of the cell.
(iii) It determines the way, the cell will develop and the form it will
exhibit at maturity. (iv) It plays an important role in cell division.
(v) It plays a central role in cellular reproduction. (vi) Nucleus
has chromosomes which contain information for the inheritance of features from
parents to the next generation.
Q13. What are cell
organelles? Give four examples.
Solution
Within the cytoplasm of a
cell, there are various minute but distinct structures which perform
special functions. These structures are called cell organelles. Examples:
Mitochondria, endoplasmic reticulum, golgi apparatus and ribosomes.
Q14. (a)Differentiate
between: (i)Functions of RER and SER. (ii)Plasma membrane and cell wall.
(b)What is endocytosis?
Solution
(a) (i) RER helps in
protein synthesis whereas SER helps in the synthesis of fat molecules and
detoxifies poisons and drugs. (ii) Plasma membrane is semi-permeable, flexible
and made up of lipids and proteins. It is found in the animal cell as well as
plant cell whereas cell wall is found only in plant cell. It is rigid in nature
and made up of cellulose. (b) The ability of the plasma membrane to engulf
food particles from the external environment is called endocytosis.
Q15. Name the three
basic parts of a cell. Of these, which forms the outer boundary of the cell?
Solution
The three basic parts of
a cell are cell membrane, cytoplasm, and nucleus. The cell membrane forms the
outer boundary of the cell.
Q16. Differentiate
between cell wall and cell membrane.
Solution
Cell membrane Cell
wall 1. Cell membrane is thin and flexible. Cell wall is thick and rigid. 2. It
is present in both plants and animals. It is present only in plants.
3. It is made up of lipids and proteins. It is made up of cellulose.
Q17. What is
endocytosis? Give one example.
Solution
The flexibility of the
cell membrane enables the cell to engulf food and other materials from its
external environment. This process is called endocytosis. Example: Amoeba
engulfs its food by endocytosis.
Q18. What will happen to
red blood cells if they are placed in i. Hypotonic solution ii. Isotonic
solution iii. Hypertonic solution
Solution
i. RBCs (Red Blood
Corpuscles) will swell if they are placed in a hypotonic solution. The cells
will gain water by osmosis (endosmosis). The cells might burst and rupture if
they are placed in the hypotonic solution for a longer time. ii. RBCs (Red
Blood Corpuscles) will remain the same if they are placed in an isotonic
solution. No change will occur in the shape and size of the cells.
iii. RBCs (Red Blood Corpuscles) will shrink if they are placed in a hypertonic
solution. The cells will lose water by osmosis (exosmosis).
Q19. How do substances
like CO2 and water move in and out of the cell?
Solution
CO2 moves
in and out of the cells by the process of diffusion which involves the movement
of molecules from a region of higher concentration to a region of lower
concentration across the cell membrane. Water moves in and out of the cells by
osmosis which involves the movement of water through a semi-permeable membrane
from a solution of a lower concentration of solutes to a higher concentration
of solutes to which the membrane is relatively impermeable.
Q20. What is a cell? Why
is cell called the structural and functional unit of life?
Solution
A cell is the basic
structural and functional unit of living organisms. The cell is called the
structural and functional unit of life because it maintains the structure of
living organisms and performs all the life functions like intake of food
materials, excretion, metabolism, and respiration.
Q21. What is
plasmolysis? Give an example.
Solution
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 is known as plasmolysis. Example:
Shrinkage of vegetables when kept in a salt solution.
Q22. Explain active transport.
Solution
Active transport is the
pumping of molecules or ions across a membrane against their concentration
gradient. It always involves the expenditure of energy, the source of which is
ATP because materials are pumped against the concentration gradient.
Q23. Name a cell
organelle which contains its own genetic material.
Solution
The cell organelles
plastids and mitochondria have their own genetic material.
Q24. How does a cell
membrane form a barrier and establish a connection with the adjacent cells?
Solution
The cell membrane forms
the outer boundary of the cell and keeps the cell contents intact within the
cell. In this way, it forms a barrier to the outside environment. At the same
time, it allows only certain substances to enter and leave the cell. Thus, it
keeps the cell connected with its environment.
Q25. (a) What is DNA?
Where is it found? (b) Name the functional segment of DNA.
Solution
(a) DNA is Deoxyribo
Nucleic Acid which contains information necessary for constructing
and organizing cells and the inheritance of features from one generation
to another. DNA is found in the chromosomes. (b) The functional segment of
DNA is a gene.
Q26. Differentiate
between plant cells and animal cells on the basis of: a) Plastids b) Vacuoles
c) Position of nucleus in cell
Solution
Criteria Plant
cells Animal cells 1. Plastids They are present in plant cells. They are absent
in animal cells. 2. Vacuoles They are large sized in plant cells. They are
small sized in animal cells. 3. Position of nucleus in cell The nucleus is
towards the periphery of the plant cell. The nucleus is present in the centre
of the animal cell.
Q27. Give four examples
of animal cells showing different structures.
Solution
Examples of animal
cells differing in their structures: Nerve cells Ovum Smooth muscle cells Fat
cells
Q28. Name the plastid
which stores starch, oils and protein granules.
Solution
Leucoplast is a type of plastid
which stores starch, oil and protein granules.
Q29. State the technical
term for a medium which has exactly the same solute concentration as the cell.
Why does the size of the cell remain the same when placed in such a solution?
Solution
Isotonic solution has
exactly the same concentration of solute as the cell. Water crosses the cell
membrane in both the directions but the amount of water entering the cell is
equal to the amount of water leaving the cell. As a result, there is no overall
movement of water.
Q30. (a) List any three
differences between a prokaryotic and eukaryotic cell. (b) Write the
composition of a chromosome. Name the part of the cell where it is formed.
Solution
(a) Differences between a
prokaryotic and eukaryotic cell: Prokaryotic cell Eukaryotic cell (i) It
is small in size. (ii) The nuclear region is not well-defined.
(iii) Single chromosome is found. (i) It is large in size.
(ii) The nuclear region is well-defined and is surrounded by a nuclear membrane.
(iii) More than one chromosome is present. (b) A chromosome is
composed of DNA and proteins. It is formed in the nucleus during cell
division.
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