NCERT Solutions For Class 9 Science Chapter 5 The Fundamental Unit of Life
5.
THE
FUNDAMENTAL UNIT OF LIFE
6.
TISSUES
7.
MOTION
9.
GRAVITATION
10.
WORK
AND ENERGY
11.
SOUND
12.
IMPROVEMENT
IN FOOD RESOURCES
1. Who
discovered cells, and how?
Answer:
In 1665,
Robert Hooke discovered cells while examining a thin slice of cork through a
self-designed microscope. He observed that the cork resembled the structure of
a honeycomb consisting of numerous tiny compartments. The minuscule boxes are
referred to as cells.
2. Why is
the cell called the structural and functional unit of life?
Answer:
Cells form
the structure of an entity. A group of cells form a tissue, further an organ
and ultimately an organ system. They perform fundamental functions and life
processes such as respiration, digestion, excretion etc., in both unicellular
and multicellular entities. They perform all the activities independently.
Hence, cells are referred to as structural and fundamental units of life.
3. How do
substances like CO2 and water move in and out of the cell?
Discuss.
Answer:
CO2 moves
by diffusion. The cellular waste accumulates in high concentrations in the
cell, whereas the concentration of CO2 in the external
surroundings is comparatively lower. This difference in the concentration level
inside and outside of the cell causes the CO2 to diffuse from a
region of higher (within the cell) to a lower concentration.
H2O
diffuses by osmosis through the cell membrane. It moves from a region of higher
concentration to a lower concentrated region through a selectively permeable
membrane until equilibrium is reached.
4. Why is
the plasma membrane called a selectively permeable membrane?
Answer:
The plasma
membrane is called as a selectively permeable membrane as it permits the
movement of only certain molecules in and out of the cells. Not all molecules
are free to diffuse.
NCERT
Solutions for Class 9 Science Chapter 5 Exercise 5.2
5. Fill
in the gaps in the following table, illustrating the differences between
prokaryotic and eukaryotic cells.
|
Prokaryotic Cell |
Eukaryotic Cell |
|
1. Size: Generally
small (1-10 μm) 1 μm = 10-6m 2. Nuclear region: ______________________________ ______________________________ and known as ___________________ 3. Chromosome: single 4. Membrane-bound cell
organelles absent. |
1. Size: Generally large
(5-100 μm) 2. Nuclear region:
well-defined and surrounded by a nuclear membrane. 3. More than one chromosome. 4. ______________________________ ______________________________ ______________________________ |
Answer:
|
Prokaryotic Cell |
Eukaryotic Cell |
|
1. Size: Generally small
(1-10 μm) 1 μm = 10-6m 2. The nuclear region is
poorly defined due to the absence of a nuclear membrane and is known as the
nucleoid. 3. There is a single chromosome. 4. Membrane-bound cell organelles
absent. |
1. Size: Generally large (5-100 μm) 2. Nuclear region: well-defined and
surrounded by a nuclear membrane. 3. There is more than one
chromosome. 4. Membrane-bound cell organelles
present. |
NCERT
Solutions for Class 9 Science Chapter 5 Exercise 5.3
6. Can
you name the two organelles we have studied that contain their own genetic
material?
Answer:
The two
organelles which have their own genetic material are
1.
Mitochondria
2. Plastids
7. If the
organisation of a cell is destroyed due to some physical or chemical influence,
what will happen?
Answer:
In the event
of any damage to cells and when the revival of cells is not possible, Lysosomes
burst, and enzymes digest such cells. This is why lysosomes are often referred
to as ‘suicide bags’.
8. Why
are lysosomes known as suicide bags?
Answer:
When there
is damage to the cell and when revival is not possible, lysosomes may burst,
and the enzymes digest their own cell. Consequently, lysosomes are known as
suicide bags.
9. Where
are proteins synthesised inside the cell?
Answer:
Protein
synthesis in cells takes place in ribosomes. Hence, ribosomes are also referred
to as protein factories. Ribosomes are particles that are found attached to the
rough endoplasmic reticulum.
NCERT
Solutions for Class 9 Science Chapter 5 Exercise 5.4
1. Make a
comparison and write down ways in which plant cells are different from animal
cells.
Answer:
The
following table depicts the differences between plant cells and animal cells.
|
Characteristic |
Plant Cell |
Animal Cell |
|
Cell Wall |
Present |
Absent |
|
Shape of Cell |
With distinct edges, the shape is
either rectangular or square-shaped. |
Round and irregular
shape |
|
Nucleus |
Present. It lies on one side of the
cell |
Present. It lies in
the centre of the cell |
|
Lysosomes |
Rarely present |
Always present |
|
Plastids |
Present |
Absent |
|
Structure of Vacuoles |
Single or a few large vacuoles that
are centrally located |
Presence of numerous
and small vacuoles |
2. How is
a prokaryotic cell different from a eukaryotic cell?
Answer:
The
following are the differences between prokaryotic and eukaryotic cells.
|
Feature |
Prokaryotic Cell |
Eukaryotic Cell |
|
Size |
Generally small (1-10 μm) |
Generally large (5-100 μm) |
|
Nuclear Region |
Not well defined; nucleoid instead
of nucleus |
Well-defined; surrounded by a
nuclear membrane |
|
Chromosomes |
Single chromosome |
More than one chromosome |
|
Membrane-bound Organelles |
Absent |
Present |
3. What
would happen if the plasma membrane ruptures or breaks down?
Answer:
If the
plasma membrane ruptures or breaks down, molecules of some substances will
freely move in and out of the cell. Normally, the plasma membrane acts as a
barrier that controls the exchange of materials through processes like osmosis
and diffusion. If this barrier is compromised, the cell can’t maintain its
internal environment properly.
As a result,
essential protoplasmic material can leak out or harmful substances can enter
unchecked. This disruption can lead to the death of the cell due to the loss of
its vital components and inability to function properly.
4. What
would happen to the life of a cell if there was no Golgi apparatus?
Answer:
The Golgi
apparatus consists of stacks of membrane-bound vesicles with several key
functions:
- Storage of Substances: It stores and accumulates
various molecules and substances synthesized by the cell.
- Packaging of Substances: It modifies, sorts, and
packages proteins and other molecules into vesicles for transport to
different parts of the cell or for secretion outside the cell.
- Manufacture of Substances: While the Golgi apparatus
primarily processes and modifies substances rather than directly
manufacturing them, it plays a crucial role in modifying proteins and
lipids synthesized in the endoplasmic reticulum.
Without the
Golgi apparatus, cells would be unable to properly package and transport
materials essential for their functioning. This would impair processes such as
secretion, cell signaling, and the maintenance of cellular structure. The Golgi
apparatus is involved in the formation of lysosomes, which are essential for
cellular digestion and recycling. Therefore, the absence of a functional Golgi
apparatus would severely compromise the cell’s ability to function and survive.
5. Which
organelle is known as the powerhouse of the cell? Why?
Answer:
Mitochondria
are referred to as the powerhouse of the cell because they generate energy
required for various life activities. They achieve this by releasing energy in
the form of ATP (Adenosine triphosphate) molecules. ATP is essential for
numerous chemical processes that sustain life, including muscle contraction,
protein synthesis, and cellular metabolism. This ability to produce ATP makes
mitochondria crucial for providing the energy necessary for cells to function
effectively, earning ATP the nickname ‘energy currency of the cell’.
6. Where
do the lipids and proteins constituting the cell membrane get synthesised?
Answer:
Lipids and
proteins are synthesised in the ER (Endoplasmic Reticulum).
7. How
does an Amoeba obtain its food?
Answer:
Through the
process of endocytosis, an Amoeba obtains its food. The Amoeba’s flexible cell
membrane allows it to engulf food particles, forming a food vacuole around them
with the help of pseudopodia, which are extensions of its cell membrane. Once
the food is trapped inside the food vacuole, Amoeba secretes digestive enzymes
into the vacuole.
These
enzymes break down the engulfed food particles through digestion, allowing the
Amoeba to absorb nutrients and sustain itself. This process of endocytosis and
digestion is essential for the Amoeba’s nutrition and survival.
8. What
is osmosis?
Answer:
Osmosis is
the process where water molecules move across a semipermeable membrane from an
area of higher water concentration to an area of lower water concentration.
This movement occurs until equilibrium is reached, balancing the concentration
of water on both sides of the membrane. Osmosis plays a crucial role in
biological systems, helping regulate the balance of water and solutes inside
cells and organisms.
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 in 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 two 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?
(iii)
Explain why water does not gather in the hollowed-out portions of A and D.
Answer:
(i) Water
accumulates in the hollowed portions of B and C as a difference in the water
concentration
is observed.
Thereby, endosmosis occurs as the cells act as a semipermeable membrane.
(ii) Potato
A is essential in this experiment as it is significant to compare different
scenarios seen in
potato cups
B, C and D. Potato A in this experiment clearly shows that the potato cavity on
its
own cannot
bring about water movement.
(iii) Cup in
A does not show any change in the water flow concentration for osmosis to
occur, which
requires
concentration to be higher than the other. Cells in cup D are dead; thus, there
is no
existence of
a semipermeable membrane for water flow. Consequently, osmosis does not occur.
10. Which
type of cell division is required for the growth and repair of the body, and
which type is involved in the formation of gametes?
Answer:
Mitosis: Mitosis is a type of cell
division involved in the growth, development, and repair of the body. It
produces two identical daughter cells, each with the same number of chromosomes
as the parent cell. This process ensures that the body’s cells can replace
damaged or worn-out cells and maintain proper function.
Meiosis: Meiosis is a type of cell
division that occurs in specialized cells called germ cells, which are involved
in sexual reproduction. It results in the formation of gametes (sperm and egg
cells) with half the number of chromosomes as the parent cell. During
fertilization, these gametes combine to form a new organism with a full set of
chromosomes.
What you have learnt
• The
fundamental organisational unit of life is the cell.
• Cells are
enclosed by a plasma membrane composed of lipids and proteins.
• The cell
membrane is an active part of the cell. It regulates the movement of materials
between the ordered interior of the cell and the outer environment.
• In plant
cells, a cell wall composed mainly of cellulose is located outside the cell
membrane.
• The
presence of the cell wall enables the cells of plants, fungi and bacteria to
exist in hypotonic media without bursting.
• The
nucleus in eukaryotes is separated from the cytoplasm by double-layered
membrane and it directs the life processes of the cell.
• The ER
functions both as a passageway for intracellular transport and as a
manufacturing surface.
• The Golgi
apparatus consists of stacks of membrane-bound vesicles that function in the
storage, modification and packaging of substances manufactured in the cell.
• Most plant
cells have large membranous organelles called plastids, which are of two
types—chromoplasts and leucoplasts.
•
Chromoplasts that contain chlorophyll are called chloroplasts and they perform
photosynthesis.
• The
primary function of leucoplasts is storage.
• Most
mature plant cells have a large central vacuole that helps to maintain the
turgidity of the cell and stores important substances including wastes.
•
Prokaryotic cells have no membrane-bound organelles, their chromosomes are
composed of only nucleic acid, and they have only very small ribosomes as
organelles.
• Cells in
organisms divide for growth of body, for replacing dead cells, and for forming
gametes for reproduction.
Keywords
|
1. Cell 2. Cell theory 3. Prokaryotic cell 4. Eukaryotic cell 5. Cell membrane (plasma
membrane) 6. Cytoplasm 7. Nucleus 8. Nucleolus 9. Nuclear membrane 10. Chromosomes 11. Genes 12. Mitochondria 13. Endoplasmic reticulum
(ER) 14. Golgi apparatus
|
15. Lysosomes 16. Ribosomes 17. Chloroplasts 18. Cell wall 19. Vacuoles 20. Osmosis 21. Diffusion 22. Plasmolysis 23. Active transport 24. Tissues 25. Organelles 26. Multicellular 27. Unicellular 28. Cell division (Mitosis, Meiosis) |
Here are some frequently asked questions (FAQ) on
"The
Fundamental Unit of Life":
Here are some frequently asked questions (FAQ) on
"The
Fundamental Unit of Life":
1. Who discovered the
cell?
Robert Hooke is the
scientist credited with discovering the cell.
2. What is not a role of
the cell membrane?
While the cell membrane
protects the cell and regulates what enters and exits, it does not control cell
division.
3. Which organelle
generates energy for the cell?
Mitochondria, often
called the "powerhouse," produces energy in the form of ATP.
4. What is exclusive to
plant cells?
Plant cells have a cell
wall, a structure that animal cells lack.
5. Which type of cell
lacks a true nucleus?
Prokaryotic cells, like
bacteria, do not have a well-defined nucleus.
6. Which organelle
carries its own DNA?
Mitochondria, the energy
producer of the cell, contains its own genetic material.
7. What do ribosomes do?
Ribosomes are
responsible for making proteins, the building blocks of life.
8. What is osmosis?
Osmosis is the movement
of water from an area of higher concentration to a lower concentration.
9. What forms the cell
wall in plants?
The cell wall of plant
cells is made of cellulose, providing structure and strength.
10. Which part of the
cell directs its activities?
The nucleus is the
control center, regulating the cell's functions and storing genetic material.
11. What does the Golgi
apparatus do?
The Golgi apparatus
packages proteins for transport and distribution.
12. When does
plasmolysis occur?
Plasmolysis happens when
a cell loses water in a hypertonic solution, causing the membrane to pull away
from the cell wall.
13. What sets the rough
and smooth ER apart?
The rough endoplasmic
reticulum has ribosomes attached to it, while the smooth ER does not.
14. What is the role of
chloroplasts?
Chloroplasts are
involved in photosynthesis, the process through which plants produce energy
from sunlight.
15. What is active
transport?
Active transport, like
the sodium-potassium pump, moves molecules against their concentration gradient
using energy.
MCQs:
1. Who discovered cells?
a) Robert Brown
b) Robert Hooke
c) Anton van Leeuwenhoek
d) Theodor Schwann
Answer: b) Robert Hooke
2. Which of the following is not a function of the cell
membrane?
a) Protecting the cell
b) Transporting substances
c) Controlling cell division
d) Allowing selective entry and exit of substances
Answer: c) Controlling cell division
3. Which organelle is known as the powerhouse of the
cell?
a) Nucleus
b) Endoplasmic reticulum
c) Mitochondria
d) Golgi apparatus
Answer: c) Mitochondria
4. Which of the following is present only in plant cells?
a) Mitochondria
b) Cell wall
c) Ribosomes
d) Lysosomes
Answer: b) Cell wall
5. Which of the following is a prokaryotic cell?
a) Plant cell
b) Animal cell
c) Bacterial cell
d) Fungal cell
Answer: c) Bacterial cell
6. Which of the following organelles contains its own
DNA?
a) Ribosomes
b) Mitochondria
c) Golgi apparatus
d) Lysosomes
Answer: b) Mitochondria
7. What is the function of ribosomes?
a) Energy production
b) Protein synthesis
c) Lipid synthesis
d) Waste removal
Answer: b) Protein synthesis
8. Osmosis refers to the movement of:
a) Water from a high to low concentration
b) Solutes from a low to high concentration
c) Water from a low to high concentration
d) Solutes from a high to low concentration
Answer: a) Water from a high to low concentration
9. The cell wall is made up of:
a) Protein
b) Lipids
c) Cellulose
d) Nucleic acid
Answer: c) Cellulose
10. Which structure controls the activities of the cell?
a) Mitochondria
b) Ribosomes
c) Nucleus
d) Golgi apparatus
Answer: c) Nucleus
11. Which of the following is a function of the Golgi
apparatus?
a) Lipid synthesis
b) Protein packaging
c) Photosynthesis
d) Respiration
Answer: b) Protein packaging
12. Plasmolysis occurs in a cell when:
a) It is placed in a hypertonic solution
b) It is placed in a hypotonic solution
c) It is placed in an isotonic solution
d) It absorbs too much water
Answer: a) It is placed in a hypertonic solution
13. What is the main difference between rough and smooth
endoplasmic reticulum?
a) Rough ER has ribosomes, smooth ER does not
b) Smooth ER has ribosomes, rough ER does not
c) Rough ER synthesizes lipids, smooth ER synthesizes proteins
d) Rough ER is involved in photosynthesis
Answer: a) Rough ER has ribosomes, smooth ER does not
14. Chloroplasts are involved in:
a) Cellular respiration
b) Protein synthesis
c) Photosynthesis
d) Osmosis
Answer: c) Photosynthesis
15. Which of the following is an example of active
transport?
a) Osmosis
b) Diffusion
c) Movement of glucose into the cell
d) Sodium-potassium pump
Answer: d) Sodium-potassium pump
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