The Fundamental Unit Of Life - Class 9 Science - Chapter 5 - Notes, NCERT Solutions & Extra Questions
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Extra Questions - The Fundamental Unit Of Life | NCERT | Science | Class 9
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What are genes? Where are they located in the cell?
Genes are the functional units of chromosomes, responsible for transmitting hereditary information from parents to offspring. They are located on chromosomes within the cell.
The round-shaped bacteria are called
A. coccus
B. bacillus
C. vibrio
D. spirillum
The correct answer to the question of what round-shaped bacteria are called is:
Option A: coccus
Bacteria with a round shape are identified as coccus (plural: cocci).
What is the basic structural unit of life?
A) Tissues
B) Nucleus
C) Chlorophyll
D) Cell
The correct option is D) Cell.
A cell represents the basic structural and functional unit of all living organisms. Often termed as the "building blocks of life," cells are the smallest units that can replicate independently and carry out essential life functions.
Is RBC eukaryotic or prokaryotic?
Red Blood Cells (RBCs) are classified as eukaryotic cells. Although in adult human bodies, RBCs lack a nucleus, they initially contain a nucleus during the early fetal stage. This nucleus degenerates as the cells mature. In contrast, prokaryotic cells never possess a nucleus at any stage of their life cycle.
Which one single organism or pair of organisms is correctly assigned to its or their named taxonomic group?
A Paramecium and plasmodium belong to the same kingdom as that of Penicillium.
B Lichen is a composite organism formed by the symbiotic association of an alga and a fungus.
C Yeast used in making bread and beer is a fungus.
D Nostoc and Anabaena are examples of Protista.
The correct answer is Option C: Yeast used in making bread and beer is a fungus.
Yeast is classified as an unicellular fungus. It plays a crucial role in the fermentation process, which is essential for producing bread and beer.
Enumerate functions of the plasma membrane.
Functions of the Plasma Membrane:
The plasma membrane primarily serves to contain the cellular contents, ensuring that the intracellular environment is maintained distinct from the external environment. Additionally, it regulates the passage of materials into and out of the cell, which is crucial for maintaining cellular homeostasis.
Meristematic tissues have prominent nuclei and dense cytoplasm, but they lack a vacuole. Why?
Meristematic cells are characterized by prominent nuclei and dense cytoplasm but notably lack vacuoles. This distinctive feature relates closely to their primary function, which is the ability to divide and generate new cells.
Vacuoles in plant cells typically serve as storage areas for nutrients and substances necessary for cell survival and operation under normal conditions. However, in the case of meristematic cells, their main priority is not storing nutrients but rather rapidly dividing. This process requires an immediate and continuous supply of energy primarily derived from glucose.
Since these cells are constantly dividing and utilizing immediate energy sources, storing nutrients in vacuoles becomes unnecessary. Instead, energy is directly consumed as it is generated, illustrating why these cells feature large nuclei (to manage cell division) and lack vacuoles (as storage is not a priority). This configuration ensures meristematic cells fulfill their role in plant growth effectively.
Function of cell membrane
Function of the Cell Membrane
The cell membrane, also known as the plasma membrane, is a critical biological barrier that encloses the interior of all cells, effectively separating it from the external environment. Its functions include:
Protection: The cell membrane acts as a protective barrier that shields the cell from its surroundings, ensuring the cell's integrity and sustainability.
Selective Permeability: It regulates the entry and exit of substances, ensuring that only specific substances can move in and out at proper rates. This functionality is crucial for maintaining the internal balance of nutrients, ions, and water, which is essential for cell survival.
Boundary and Interaction: By constituting the boundary of the cell, the membrane also plays a vital role in cell communication and signalling with its environment. This interaction can influence cellular activities such as metabolism, growth, and division.
Understanding the role of the cell membrane is fundamental in cell biology as it is central to maintaining the life processes of the cell. Enjoy your learning journey exploring more about how cells function!
Why are cells the fundamental units of life, and why are they important?
Cells are considered the fundamental units of life because they are the smallest units that can carry out all essential life processes independently. This includes nutrition, respiration, excretion, transportation, and reproduction, mirroring the functions of an entire organism. Especially in unicellular organisms, a single cell performs all the functions necessary for life, demonstrating that each cell has the capacity for independent existence. Due to these capabilities, cells are not only the building blocks but also the functional units of life, which makes them vitally important in the study and understanding of biology.
"As the liver has regenerative power, why can't it use this power when it fails to function properly?"
Liver indeed has regenerative powers, allowing it to often heal itself even after significant damage. It is capable of regenerating up to 25% of its mass, which is a critical factor used in therapeutic approaches.
In many situations, healthcare professionals use medications to support the liver and provide it with the necessary time to repair itself. This typically works well when the issue is related to the loss of liver mass, as the liver can often recover from such damage.
However, in the case of acute liver failure, the scenario can be drastically different. Acute liver failure can lead to severe complications such as massive blood loss and increased pressure due to the accumulation of fluids released by the liver. This pressure can impact other organs, including the brain, and could potentially lead to life-threatening conditions. In such severe instances, the last resort might be a liver transplant, as the liver's regenerative capacity is overwhelmed and unable to cope with the rapid progression of failure.
Which is the universal cell organelle?
The term "universal cell organelle" refers to the organelle that is ubiquitous across all cell types. Proteins are crucial for the growth and various functions of a cell, and they are synthesized by ribosomes. Ribosomes are found in every cell, regardless of whether the cell is classified as prokaryotic or eukaryotic. Thus, the organelle considered to be universal due to its presence in all cells is the ribosome.
How will you identify cardiac muscle cells under a microscope? [2 MARK]
Solution
Each feature identified correctly is worth $\frac{1}{2}$ mark.
To identify cardiac muscle cells under a microscope, look for cells that exhibit these distinctive characteristics:
Cylindrical shape
Branched structure
Striated (appear striped)
Uni-nucleated (containing a single nucleus)
Where do cell organelles lie in the cell?
Nucleus
Plasma membrane
Cytoplasm
Mitochondria
The correct option is C: Cytoplasm.
Cytoplasm is the jelly-like substance within the cell where all the cell organelles are embedded. It is the space in the cell that allows these organelles to carry out their specific functions effectively.
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Make a comparison and write down ways in which plant cells are different from animal cells.
Plant cells and animal cells, while both are eukaryotic, exhibit several distinct differences:
- Cell Wall: Plant cells have a rigid cell wall made of cellulose that provides structural support. Animal cells lack a cell wall.
- Plastids: Plant cells contain plastids, including chloroplasts necessary for photosynthesis. Animal cells do not have plastids.
- Vacuoles: Plant cells have a large central vacuole that maintains turgidity and stores nutrients; vacuoles in animal cells are smaller and less common.
- Shape: The presence of a cell wall gives plant cells a fixed, rectangular shape; animal cells have a more flexible and varied shape.
- Centrioles: Animal cells contain centrioles involved in cell division, which are typically absent in plant cells.
How is a prokaryotic cell different from a eukaryotic cell?
Prokaryotic cells and eukaryotic cells differ in several key ways. Prokaryotic cells are generally smaller (**1-10 µm**) and lack a defined nuclear region or nuclear membrane, whereas eukaryotic cells are larger (**5-100 µm**) with a well-defined nucleus enclosed by a nuclear membrane. Prokaryotic cells' genetic material is in a single chromosome and located in a nucleoid, whereas eukaryotic cells have multiple chromosomes within the nucleus. Additionally, prokaryotic cells lack membrane-bound organelles found in eukaryotic cells, such as the endoplasmic reticulum and mitochondria. Eukaryotic cells also have a complex cellular organization, including a cytoskeleton, for maintaining cell shape and structure, which is absent in prokaryotes.
What would happen if the plasma membrane ruptures or breaks down?
If the plasma membrane ruptures or breaks down, the cell will lose its selectively permeable nature. This would disrupt the balance of materials moving in and out of the cell, leading to an inability to regulate the entry and exit of substances. Consequently, harmful substances could enter the cell and essential substances could leak out, leading to a disturbance in the cell’s internal environment. Ultimately, this could result in the loss of cellular homeostasis, leading to cellular damage or death. The plasma membrane’s integrity is crucial for the survival and proper functioning of the cell.
What would happen to the life of a cell if there was no Golgi apparatus?
If a cell lacked a Golgi apparatus, it would face significant challenges in storing, modifying, and packaging biological molecules. The absence of the Golgi apparatus would disrupt the delivery of proteins and lipids needed for cell membrane formation and the export of materials essential for various cellular functions. This disruption could affect the production of lysosomes, crucial for waste disposal. Consequently, without the Golgi apparatus, a cell would struggle to maintain its structural integrity, process and transport biological molecules efficiently, ultimately impairing its survival and functionality.
Which organelle is known as the powerhouse of the cell? Why?
The organelle known as the powerhouse of the cell is the mitochondria. This designation is due to its crucial role in producing energy required for various cellular activities. Mitochondria convert energy from food molecules into ATP (Adenosine Triphosphate), which acts as a direct energy source for the cell, facilitating its functions. This energy conversion process, known as cellular respiration, highlights the mitochondria's unique ability to generate the majority of the cell's supply of ATP. Additionally, mitochondria possess their own DNA and ribosomes, allowing them to synthesize some of their own proteins, further underlining their importance in cellular energy production.
Where do the lipids and proteins constituting the cell membrane get synthesised?
The lipids and proteins constituting the cell membrane are synthesised in two key organelles of the cell, namely, the Endoplasmic Reticulum (ER) and the Golgi apparatus. The ER is classified into two types: Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER). The RER, with its ribosomes, is primarily involved in the synthesis of proteins. These proteins are then transported and processed through the Golgi apparatus, which also plays a crucial role in the synthesis and packing of lipids. Additionally, the SER aids in the manufacture of fat molecules or lipids important for various cellular functions, including the composition of the cell membrane.
How does an Amoeba obtain its food?
An Amoeba obtains its food through a process known as endocytosis. This method involves the flexibility of the cell membrane, allowing the Amoeba to engulf food and other materials from its external environment. The plasma membrane of the Amoeba extends outward to encircle the food item, forming a food vacuole. The materials inside this vacuole are then digested internally. The flexibility of the Amoeba's cell membrane is crucial for this process, enabling it to adapt its shape to surround and ingest the food.
What is osmosis?
Osmosis is the net diffusion of water across a selectively permeable membrane toward a higher solute concentration. It occurs when there is a difference in water concentration on the two sides of a membrane. Water moves from an area of higher water concentration to one of lower water concentration, playing a crucial role in gaseous exchange and absorption of water by plant roots.
Carry out the following osmosis experiment:
- Take four peeled potato halves and scoos 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 $\mathrm{C}$
(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 $\mathrm{B}$ and $\mathrm{C}$.
(ii) Why is potato A necessary for this experiment?
(iii) Explain why water does not gather in the hollowed out portions of $\mathrm{A}$ and $\mathrm{D}$.
(i) Water gathers in the hollowed portions of B and C due to osmosis. In osmosis, water moves from a region of lower solute concentration (outside the potato) to a region of higher solute concentration (inside the potato cups B and C), leading to water accumulation in these cups.
(ii) Potato A is necessary as a control to show what happens when no solute is added, demonstrating the effects are due to osmosis in the presence of solute.
(iii) Water does not gather in the hollowed portions of A and D because cup A lacks solute to draw water in by osmosis, and the cells in the boiled potato cup D are dead, preventing osmosis.
Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?
The type of cell division required for the growth and repair of the body is known as mitosis. In this process, a mother cell divides to form two identical daughter cells, helping in tissue growth and repair by maintaining the same number of chromosomes as the mother cell. On the other hand, the type of cell division involved in the formation of gametes (reproductive cells) is called meiosis. During meiosis, a cell divides to produce four new cells, each with half the number of chromosomes, which is crucial for sexual reproduction.
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Comprehensive Notes on "The Fundamental Unit of Life"
Introduction to Cells
Discovery of Cells:The journey into understanding cells began in 1665 when Robert Hooke examined a thin slice of cork through a self-designed microscope. He observed that the cork resembled a honeycomb structure consisting of many small compartments, which he termed 'cells'—a Latin word for 'little rooms.' This was a pivotal moment in biological history, as it marked the discovery that living organisms are composed of individual units called cells. Later, Antonie van Leeuwenhoek (1674) observed free-living cells in pond water, furthering our knowledge of the microscopic world.
The Cell - Structural Unit of Life
Cells are the fundamental structural and functional units of life. This means that they perform all the essential functions necessary for an organism's survival. The term 'cell' encompasses various types, shapes, and sizes, each suited to its function in the body.
Structure of a Cell
Under a microscope, typical cells display several key features:
Plasma Membrane: The outermost boundary.
Nucleus: The control center.
Cytoplasm: The jelly-like substance hosting various organelles.
Plasma Membrane or Cell Membrane
The plasma membrane is a selectively permeable barrier that regulates the entry and exit of substances. It permits the passage of essential nutrients and gases via diffusion and osmosis, processes critical for cell survival.
Diffusion and Osmosis:
Diffusion: Movement of molecules from high to low concentration.
Osmosis: Movement of water through a selectively permeable membrane.
Osmotic Conditions:
Hypotonic Solution: Higher water concentration outside the cell leads to water influx.
Isotonic Solution: Balanced water concentration.
Hypertonic Solution: Lower water concentration outside causes water to exit the cell.
Cell Wall
Plant cells possess an additional rigid layer called the cell wall, made primarily of cellulose. It offers structural strength and helps in withstanding osmotic changes. Plasmolysis is the shrinkage of the cell's contents due to water loss and can be observed in plant cells.
Nucleus
The nucleus, enclosed by a nuclear membrane, houses chromosomes composed of DNA and proteins. It orchestrates cellular activities and plays a crucial role in inheritance and cell division.
Types of Cells
Prokaryotic Cells:
Lack a defined nucleus and organelles.
Examples: Bacteria.
Eukaryotic Cells:
Possess a well-defined nucleus and membrane-bound organelles.
Examples: Plant and Animal cells.
Cytoplasm
The cytoplasm is the jelly-like substance within the cell membrane, containing various organelles that perform distinct functions necessary for the cell's operation.
Cell Organelles and Functions
Endoplasmic Reticulum (ER):
Rough ER (RER): Studded with ribosomes, synthesizes proteins.
Smooth ER (SER): Synthesizes lipids and detoxifies chemicals.
Golgi Apparatus:
Packages and dispatches materials synthesized in the ER.
Modifies and stores substances.
Lysosomes:
Contain digestive enzymes to break down waste and cellular debris.
Known as 'suicide bags' for their role in cell autolysis.
Mitochondria:
The powerhouse of the cell, generating energy in the form of ATP.
Contains its own DNA and ribosomes.
Plastids:
Chloroplasts: Conduct photosynthesis in plants.
Leucoplasts: Store starch, oils, and proteins.
Vacuoles:
Storage sacs larger in plant cells, containing cell sap to maintain turgidity and store essential substances.
Cell Division
New cells are formed for growth, repair, and reproduction through processes called mitosis and meiosis.
Mitosis: Produces two identical daughter cells.
Meiosis: Produces four genetically distinct cells with half the chromosome number, essential for sexual reproduction.
Conclusion
Cells are the fundamental units that make up all living organisms. Their intricate structure, composed of the plasma membrane, nucleus, cytoplasm, and various organelles, allows them to perform vital life processes. Understanding cell biology is foundational for exploring more complex biological systems and processes.
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