Cell: The Unit of Life – CBSE NCERT Study Resources

The fluid mosaic model describes the plasma membrane as a dynamic structure composed of lipids, proteins, and carbohydrates. Our textbook shows that phospholipids form a bilayer, with hydrophobic tails inward and hydrophilic heads outward.

• Proteins are embedded (integral) or attached (peripheral), aiding transport and signaling.
• Cholesterol maintains fluidity across temperatures.

This model explains membrane flexibility and selective permeability, critical for cell homeostasis. For example, glucose transporters (integral proteins) facilitate nutrient uptake.

Research on membrane rafts could reveal new drug delivery mechanisms.

Prokaryotes lack membrane-bound organelles, while eukaryotes have a defined nucleus and compartments. Our textbook highlights 70S ribosomes in prokaryotes vs. 80S in eukaryotes.

• Prokaryotic DNA is circular and naked; eukaryotic DNA is linear and histone-bound.
• Examples: E. coli (prokaryote) vs. human liver cells (eukaryote).

This distinction underpins antibiotic targeting (e.g., streptomycin inhibits prokaryotic ribosomes).

Studying extremophiles (prokaryotes) may yield industrial enzymes.

The endosymbiotic theory proposes that mitochondria and chloroplasts evolved from engulfed prokaryotes. We studied their double membranes and independent DNA as key evidence.

• Both organelles have 70S ribosomes and replicate via binary fission.
• Example: cyanobacteria resemble chloroplasts in photosynthesis.

This theory explains eukaryotic cell complexity. Horizontal gene transfer supports this (e.g., mitochondrial genes in nuclear DNA).

Research may clarify organelle-host coevolution in diseases.

Lysosomes contain hydrolytic enzymes that break down cellular waste. Our textbook terms them suicidal bags due to their role in autolysis during apoptosis.

• Autophagy recycles damaged organelles (e.g., mitochondria) via lysosomal degradation.
• Example: Tadpole tail resorption involves lysosomal activity.

Dysfunctional lysosomes cause storage disorders like Tay-Sachs disease.

Targeting autophagy could treat neurodegenerative diseases.

The Golgi apparatus modifies, sorts, and packages proteins. We studied its cis-trans face organization for sequential processing.

• It adds carbohydrate tags (glycosylation) for cellular recognition.
• Example: Insulin maturation involves Golgi-mediated cleavage.

Defects disrupt secretion (e.g., I-cell disease due to missing Golgi enzymes).

Engineering Golgi function could enhance biopharmaceutical production.

The fluid mosaic model describes the plasma membrane as a dynamic structure with phospholipids, proteins, and carbohydrates. Our textbook shows it resembles a 'sea' where lipids and proteins float.

• Phospholipid bilayer forms the matrix.
• Proteins are embedded (integral) or attached (peripheral).
• Cholesterol maintains fluidity.

Unlike the static sandwich model, this model explains membrane flexibility and selective permeability. For example, transport proteins facilitate molecule movement.

Understanding this aids in drug delivery research, like liposome-based therapies.

Prokaryotic cells lack membrane-bound organelles, while eukaryotic cells have them. We studied examples like bacteria (prokaryotic) and plant cells (eukaryotic).

• Prokaryotes: No nucleus; DNA in nucleoid.
• Eukaryotes: True nucleus with nuclear envelope.
• Mitochondria have their own DNA and ribosomes, enabling partial independence.

Mitochondria’s semi-autonomy supports the endosymbiotic theory. For instance, they divide independently via binary fission.

Studying these differences helps in antibiotic development targeting prokaryotic ribosomes.

Lysosomes digest cellular waste, while peroxisomes detoxify harmful substances. Our textbook shows they are both vesicular organelles.

• Lysosomes contain hydrolytic enzymes (e.g., breaking down pathogens).
• Peroxisomes oxidize toxins, producing H₂O₂.
• Example: Liver cells use peroxisomes to detoxify alcohol.

Their malfunction causes diseases like Tay-Sachs (lysosomes) or Zellweger syndrome (peroxisomes).

Research on enzyme replacement therapy could treat such disorders.

The cytoskeleton is a network of microtubules, microfilaments, and intermediate filaments. We studied its role in structural support and movement.

• Microtubules form cilia/flagella (e.g., sperm motility).
• Microfilaments enable muscle contraction (actin-myosin interaction).

Disruptions cause diseases like muscular dystrophy. Drugs like colchicine target microtubules to treat gout.

Understanding cytoskeleton dynamics aids in cancer research (e.g., inhibiting cell division).

The ER is a membranous network with two types: rough ER (ribosome-studded) and smooth ER (lacks ribosomes). Our textbook shows it’s involved in protein/lipid synthesis.

• Rough ER: Synthesizes secretory proteins (e.g., insulin).
• Smooth ER: Detoxifies drugs (e.g., liver cells) and stores Ca²⁺.

Alcohol abuse damages smooth ER, reducing detox efficiency. Ribophorins in rough ER ensure protein folding.

ER stress studies may lead to treatments for diabetes (protein misfolding).

The fluid mosaic model, proposed by Singer and Nicolson, describes the plasma membrane as a dynamic bilayer of phospholipids with embedded proteins. Our textbook shows it includes cholesterol for stability and glycoproteins for cell recognition.

• Phospholipids form a semi-permeable barrier.
• Integral proteins act as channels (e.g., aquaporins for water).
• Cholesterol prevents solidification at low temperatures.

This model explains membrane flexibility and selective transport, verified by freeze-fracture electron microscopy. For example, carrier proteins enable glucose uptake.

Prokaryotes (e.g., bacteria) lack a nucleus, while eukaryotes (e.g., plant cells) have defined organelles. We studied that prokaryotic DNA is circular and naked, whereas eukaryotes have linear DNA with histones.

• Prokaryotes: Mesosomes replace mitochondria.
• Eukaryotes: Endoplasmic reticulum aids protein synthesis.

This divergence supports the endosymbiotic theory, as mitochondria resemble prokaryotes. Current data shows 70S ribosomes in prokaryotes vs. 80S in eukaryotes.

Mitochondria are double-membraned organelles with cristae (inner folds) and matrix. Our textbook highlights their role in aerobic respiration via the Krebs cycle and ETC.

• Cristae increase surface area for ATP synthesis.
• Matrix contains enzymes for oxidative phosphorylation.

They’re called 'powerhouses' as they generate ~30 ATP/glucose molecule. For example, muscle cells have abundant mitochondria for energy.

Lysosomes are acidic, enzyme-filled vesicles that digest cellular waste. We studied their pH-dependent enzyme activation, preventing self-digestion.

• Hydrolases break down pathogens (e.g., macrophages).
• Autolysis during apoptosis earns the 'suicidal' tag.

Their malfunction causes diseases like Tay-Sachs. Current research shows lysosomal storage disorders affect 1 in 5,000 births.

Cell division ensures growth (mitosis) and genetic diversity (meiosis). Our textbook shows mitosis produces diploid cells, while meiosis yields haploid gametes.

• Mitosis: Equational division (e.g., skin cell renewal).
• Meiosis: Reductional division (e.g., sperm formation).

Errors in meiosis cause Down syndrome (trisomy 21). Advanced studies link unchecked mitosis to cancer.

The plasma membrane is a selectively permeable barrier that surrounds the cell, composed of a phospholipid bilayer, proteins, carbohydrates, and cholesterol. Its structure is best explained by the fluid mosaic model proposed by Singer and Nicolson.

Structure:
1. Phospholipid bilayer: Forms the basic framework with hydrophilic heads facing outward and hydrophobic tails inward.
2. Proteins: Embedded (integral) or attached (peripheral) for transport, signaling, and enzymatic functions.
3. Carbohydrates: Attached to lipids (glycolipids) or proteins (glycoproteins) for cell recognition.
4. Cholesterol: Provides stability and fluidity.

Functions:

• Regulates material exchange (selective permeability).
• Maintains cell shape and protects internal components.
• Facilitates cell-cell communication and signaling.

Fluid Mosaic Model: The membrane is dynamic, with lipids and proteins able to move laterally, giving it a 'fluid' property. The 'mosaic' aspect refers to the scattered arrangement of proteins within the bilayer.

Diagram: (Draw a labeled diagram showing phospholipid bilayer, integral & peripheral proteins, glycoproteins, glycolipids, and cholesterol.)

Prokaryotic and eukaryotic cells differ significantly in their structural complexity and organization:

1. Nucleus:
Prokaryotic: Lacks a true nucleus; genetic material is in the nucleoid region.
Eukaryotic: Has a well-defined nucleus enclosed by a nuclear membrane.

2. Membrane-bound organelles:
Prokaryotic: Absent (e.g., no mitochondria, Golgi apparatus).
Eukaryotic: Present (e.g., mitochondria, ER, lysosomes).

3. Cell size:
Prokaryotic: Generally smaller (1-10 µm).
Eukaryotic: Larger (10-100 µm).

4. Cell wall:
Prokaryotic: Composed of peptidoglycan (in bacteria).
Eukaryotic: Present in plants (cellulose) and fungi (chitin), absent in animals.

5. Ribosomes:
Prokaryotic: 70S type.
Eukaryotic: 80S type (with larger subunits).

Examples:
Prokaryotic: Bacteria (e.g., E. coli), Archaea.
Eukaryotic: Animal cells (e.g., human cheek cells), plant cells (e.g., onion peel cells).

The plasma membrane is a dynamic, semi-permeable barrier that surrounds the cell, maintaining its integrity and regulating the movement of substances. According to the Fluid Mosaic Model, proposed by Singer and Nicolson, the membrane consists of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

Structure:

• Phospholipid bilayer: Forms the basic framework with hydrophilic heads facing outward and hydrophobic tails inward.
• Proteins: Integral proteins span the membrane, while peripheral proteins attach superficially. They act as channels, carriers, or receptors.
• Cholesterol: Provides stability and fluidity.
• Carbohydrates: Attached to proteins (glycoproteins) or lipids (glycolipids) for cell recognition.

Function:

• Acts as a selective barrier, allowing only specific molecules to pass (e.g., via diffusion, osmosis, or active transport).
• Facilitates cell signaling through receptor proteins.
• Maintains cell shape and protects internal organelles.

Selective Permeability: The membrane's structure ensures only small, non-polar molecules (e.g., O₂, CO₂) diffuse freely, while ions and large molecules require transport proteins. This property is crucial for homeostasis, nutrient uptake, and waste removal.

The endoplasmic reticulum (ER) is a network of membranous tubules and sacs present in eukaryotic cells. It plays a crucial role in protein synthesis, lipid metabolism, and detoxification. The ER is divided into two types based on structure and function: rough ER and smooth ER.

Structure of Rough ER:
The rough ER is studded with ribosomes on its outer surface, giving it a rough appearance under a microscope. These ribosomes are responsible for protein synthesis.

Functions of Rough ER:
1. Synthesizes proteins, which are later transported to the Golgi apparatus for modification.
2. Provides a pathway for the transport of materials within the cell.

Structure of Smooth ER:
The smooth ER lacks ribosomes, making its surface smooth. It is primarily involved in lipid synthesis and detoxification.

Functions of Smooth ER:
1. Synthesizes lipids, including phospholipids and steroids.
2. Detoxifies harmful substances, such as drugs and alcohol, in liver cells.
3. Stores calcium ions, which are essential for muscle contraction.

Key Differences:
1. Rough ER has ribosomes, while smooth ER does not.
2. Rough ER is involved in protein synthesis, whereas smooth ER focuses on lipid synthesis and detoxification.

Understanding these differences helps in appreciating the specialized roles of each ER type in maintaining cellular functions.

The plasma membrane is a selectively permeable barrier that surrounds the cell, maintaining its internal environment. According to the Fluid Mosaic Model, proposed by Singer and Nicolson, the membrane consists of a phospholipid bilayer with embedded proteins, giving it a fluid-like and mosaic appearance.

Structure:
The phospholipid bilayer has hydrophilic (water-loving) heads facing outward and hydrophobic (water-fearing) tails inward. Proteins are scattered throughout, either as integral (embedded) or peripheral (surface-bound) proteins. Cholesterol provides stability, and carbohydrates act as recognition sites.

Functions:

• Selective Permeability: Controls entry and exit of substances.
• Cell Signaling: Receptor proteins detect external signals.
• Transport: Facilitates diffusion, active transport, and osmosis.
• Protection: Shields the cell from mechanical damage.

Maintaining Integrity:
The fluidity allows flexibility, while cholesterol prevents excessive movement, ensuring stability. Proteins and carbohydrates help in cell recognition and adhesion, maintaining cellular organization.

Value-added: The membrane's dynamic nature enables cells to adapt to environmental changes, crucial for survival.

The plasma membrane is a selectively permeable barrier that surrounds the cell, maintaining its integrity and regulating the movement of substances. It is composed of a phospholipid bilayer, proteins, carbohydrates, and cholesterol.

Structure:
1. Phospholipid Bilayer: Forms the basic framework with hydrophilic heads facing outward and hydrophobic tails inward.
2. Proteins: Embedded (integral) or attached (peripheral) for transport, signaling, and structural support.
3. Carbohydrates: Attached to proteins (glycoproteins) or lipids (glycolipids) for cell recognition.
4. Cholesterol: Provides stability and fluidity.

Functions:

• Regulates entry and exit of materials (selective permeability).
• Provides mechanical strength and shape.
• Facilitates cell communication and signaling.
• Acts as a site for enzymatic reactions.

The fluid mosaic model describes the membrane as a dynamic structure where lipids and proteins move laterally, giving it a fluid-like property. The mosaic aspect refers to the scattered arrangement of proteins.

Diagram: (Draw a labeled diagram showing phospholipid bilayer, integral/peripheral proteins, glycoproteins, glycolipids, and cholesterol.)

Value-added: The membrane's fluidity allows cells to adapt to temperature changes, and its asymmetry (different composition in inner/outer layers) is crucial for functions like apoptosis.

The plasma membrane is a selectively permeable barrier that surrounds the cell, composed of phospholipids, proteins, and carbohydrates. Its structure is described by the fluid mosaic model, which states that the membrane is a dynamic, flexible layer with proteins embedded or attached to the lipid bilayer.

Structure:
1. Phospholipid bilayer: Forms the basic framework, with hydrophilic heads facing outward and hydrophobic tails inward.
2. Proteins: Integral proteins span the membrane, while peripheral proteins are loosely attached.
3. Cholesterol: Provides stability and fluidity.
4. Carbohydrates: Attached to proteins (glycoproteins) or lipids (glycolipids) for cell recognition.

Functions:

• Regulates transport of substances (diffusion, osmosis, active transport).
• Provides mechanical strength and shape.
• Facilitates cell signaling and communication.
• Acts as a site for enzymatic reactions.

The fluid mosaic model emphasizes the membrane's dynamic nature, where lipids and proteins move laterally, enabling flexibility and functionality.

The plasma membrane is a selectively permeable barrier that surrounds the cell, maintaining its integrity and regulating the movement of substances. It is composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

Structure:
1. Phospholipid Bilayer: Forms the basic framework with hydrophilic heads facing outward and hydrophobic tails inward.
2. Proteins: Integral proteins span the membrane, while peripheral proteins attach superficially.
3. Cholesterol: Provides stability and fluidity.
4. Carbohydrates: Attached to lipids (glycolipids) or proteins (glycoproteins) for cell recognition.

Functions:

• Regulates transport (diffusion, osmosis, active transport).
• Provides mechanical support.
• Facilitates cell signaling via receptor proteins.
• Maintains cell homeostasis.

Fluid Mosaic Model: Proposed by Singer and Nicolson, it describes the membrane as a dynamic structure where lipids and proteins move laterally, giving it a fluid nature. The mosaic aspect refers to the scattered arrangement of proteins.

Diagram: (Draw a labeled diagram showing phospholipid bilayer, integral/peripheral proteins, cholesterol, and glycoproteins.)

Value-added: The membrane's fluidity allows cells to adapt to temperature changes, and its selective permeability is crucial for nutrient uptake and waste removal.

Mitochondria are double-membraned, semi-autonomous organelles found in eukaryotic cells, responsible for ATP production through cellular respiration.

Structure:
1. Outer membrane: Smooth and permeable to small molecules.
2. Inner membrane: Folded into cristae to increase surface area for ATP synthesis.
3. Intermembrane space: Contains enzymes for phosphorylation.
4. Matrix: Contains mitochondrial DNA, ribosomes, and enzymes for the Krebs cycle.

Functions:

• Produces ATP via oxidative phosphorylation.
• Stores calcium ions for cell signaling.
• Generates heat through thermogenesis.
• Plays a role in apoptosis (programmed cell death).

Mitochondria are called the powerhouse of the cell because they generate most of the cell's energy (ATP) through aerobic respiration, fueling metabolic activities.