• All living organisms composed of cells. Some are made form single cell and some are made from many cells.
  • Unicellular- Those organisms which made form only single cell.
  • Multicellular- Those organisms which made form many cells.

Cell-

  • Those organisms which are unicellular, they are capable form independent existing and performing only essential of life.
  • Cell is the fundamental, structural and functional unit of life.
  • The cell were discovered by Robert Hooke in 1665.
  • The living cell discovered by Anton Van Leeuwenhoek in 1674.
  • The nucleus was discovered by Robert Brown.

The Cell Theory-

  • A German botanist, Matthias Schleiden in 1838, examine many plant and noticed that all plant are made form many different types of cell which made tissue.
  • And a British zoologist, Theodore Schwann in 1839, examine many animal and noticed all animal cell has a thin outer layer called plasma membrane.
  • Schleiden and Schwann combine and propose cell theory.
  • In 1855, Rudolf Virchow first explain that cell divided and new cell form form pre-existing cell. After modification of this explanation, both 2 botanist and zoologist proposed cell theory.
  • Cell Theory-
    • All living living things composed of cells and product of cells.
    • All cell arise form pre-existing cells.

About Cell-

  • Nucleus-
    • Inside the cell (both plant and animal or human cell), have dense membrane bound structure.
    • It contain chromosome, which have genetic material like DNA.
  • Cell have may be eukaryotic or prokaryotic-
    • Eukaryotic cell- Well define and membrane bound organelle nucleus.
    • Prokaryotic cell- Not well define and lack of membrane bound organelle nucleus.
  • Both eukaryotic and prokaryotic cell contain semi-fluid which occupy most of volume is called cytoplasm.
  • Organelle- Other constituent like endoplasmic reticulum(ER), golgi apparatus, lysosomes, mitochondria, other microbodies, vacuoles.
  • In animal cell, centrosome present which is another non-membrane bound organelle help in cell division.
  • Cell also have different sizes-
    • Mycoplasma are smallest cell which only 0.3 μm in length.
    • Bacteria are 3-5 μm in legth.
    • The ostrich egg is largest isolated single cell.
    • In humans, red blood cells have 7μm diameter.
    • Nervous cell has some longest cell.
  • Cell also have different shapes-
    • disk-like shaped, polygonal, columnar, cuboid, thread like etc.
    • Different shapes also have different functions

The Prokaryotic Cells-

Prokaryotic Cells

  • Examples: Bacteria, blue-green algae, mycoplasma, and PPLO (Pleuro Pneumonia-Like Organisms).
  • Size & Multiplication: Smaller than eukaryotic cells; reproduce rapidly.
  • Shapes of Bacteria:
    • Bacillus: Rod-like.
    • Coccus: Spherical.
    • Vibrio: Comma-shaped.
    • Spirillum: Spiral.

Key Features

  1. Cell Wall: Surrounds the plasma membrane; absent in mycoplasma.
  2. Cytoplasm: Fluid inside the cell, lacks membrane-bound organelles.
  3. Nucleus: Not well-defined; DNA is naked and circular.
  4. Plasmids: Extra circular DNA; carry genes like antibiotic resistance.
    • Competitive Insight: Plasmids are used in biotechnology for gene cloning.
  5. Ribosomes: Site of protein synthesis; 70S ribosomes composed of 50S and 30S subunits.
    • Multiple ribosomes form polysomes for efficient protein synthesis.
  6. Mesosomes: Plasma membrane infoldings for respiration, DNA replication, and increasing surface area.

Cell Envelope Structure

  • Glycocalyx: Outermost layer; can be:
    • Slime layer: Loose and thin.
    • Capsule: Thick and tough.
  • Cell Wall: Provides shape and protection against bursting or collapsing.
  • Plasma Membrane: Selectively permeable, similar to eukaryotic cells.

Motility Structures in Prokaryotes

  1. Flagella:
    • Made of filament, hook, and basal body; enables movement.
    • Arrangement Varieties: Monotrichous (one flagellum), lophotrichous (cluster), etc.
    • Competitive Point: Flagella movement is driven by a proton gradient.
  2. Pili and Fimbriae:
    • Pili: Tubular protein structures for DNA transfer (conjugation).
    • Fimbriae: Bristle-like; help in attachment to surfaces like rocks or host tissues.

Ribosomes and Inclusion Bodies

  • Ribosomes:
    • 70S type in prokaryotes (50S + 30S).
    • Key site for protein synthesis.
  • Inclusion Bodies:
    • Store nutrients like phosphate granules, glycogen granules, and cyanophycean granules.
    • Gas Vacuoles: Found in photosynthetic bacteria; provide buoyancy.

Competitive Exam Insights & Extra Knowledge

  1. Gram Staining:
    • Bacteria are either Gram-positive (retain crystal violet stain) or Gram-negative (do not).
    • Competitive Tip: Gram-positive bacteria have a thicker peptidoglycan layer.
  2. Mesosomes Role: Key in prokaryotic respiration, similar to mitochondria in eukaryotes.
  3. Cyanobacteria Chromatophores: Contain pigments for photosynthesis.

Comparison with Eukaryotic Cells

  • Differences:
    • Prokaryotes lack organelles like mitochondria, Golgi apparatus, etc.
    • DNA is not enclosed in a nucleus.
  • Applications in Biotechnology: Prokaryotes like E. coli are widely used for recombinant DNA techniques.

For Competitive Questions:

  • Focus on bacterial shapes, Gram staining, and structural components like plasmids, ribosomes, and mesosomes.
  • Understand processes like antibiotic resistance and its link to plasmid DNA.
  • Remember examples like cyanobacteria for photosynthesis and mycoplasma as cell wall-lacking bacteria.

Endomembrane System

  • Definition: A group of organelles in eukaryotic cells that work together for specific functions, such as transport and synthesis.
  • Components: Includes the endoplasmic reticulum (ER), Golgi apparatus, lysosomes, and vacuoles.
  • Exclusions: Mitochondria, chloroplasts, and peroxisomes are not part of this system because their functions are independent.

1. Endoplasmic Reticulum (ER)

  • Structure: A network of tubules and cisternae (flattened sacs) dividing the cell into:
    • Luminal compartment: Inside the ER.
    • Extraluminal compartment: Cytoplasm.
  • Types:
    1. Rough ER (RER):
      • Ribosomes attached to the surface.
      • Involved in protein synthesis.
      • Connected to the nuclear membrane.
    2. Smooth ER (SER):
      • No ribosomes, smooth appearance.
      • Involved in lipid synthesis, including steroidal hormones in animals.

Key Insight: Cells active in protein production (like pancreas cells) have more RER, while those producing lipids (like liver cells) have more SER.

2. Golgi Apparatus

  • Discovery: Identified by Camillo Golgi in 1898.
  • Structure:
    • Flattened, disc-shaped sacs (cisternae) arranged near the nucleus.
    • Two faces:
      • Cis-face: Receives materials from the ER.
      • Trans-face: Releases vesicles with processed materials.
  • Functions:
    • Modifies, sorts, and packages proteins and lipids.
    • Produces glycoproteins and glycolipids.

Key Insight: The Golgi apparatus is like a packaging and distribution center for the cell.

3. Lysosomes

  • Structure: Membrane-bound vesicles formed by the Golgi apparatus.
  • Content: Contain digestive enzymes (hydrolases) that function at acidic pH.
  • Functions:
    • Break down macromolecules (proteins, lipids, carbohydrates, nucleic acids).
    • Known as the “suicidal bags” of the cell because they can digest the cell when necessary.

Extra Knowledge: Lysosomal dysfunction can cause diseases like Tay-Sachs, where certain lipids accumulate in nerve cells.

4. Vacuoles

  • Structure: Membrane-bound spaces enclosed by a tonoplast (single membrane).
  • Functions:
    • Stores water, nutrients, and waste.
    • In plant cells, it can occupy up to 90% of the cell volume.
  • Special Cases:
    • In Amoeba, the contractile vacuole helps in osmoregulation.
    • In some protists, food vacuoles digest ingested food.

5. Mitochondria

  • Structure:
    • Double-membrane-bound organelle.
    • Inner membrane has folds called cristae, increasing surface area for energy production.
    • Matrix contains DNA, RNA, ribosomes, and enzymes.
  • Function: Site of aerobic respiration, producing ATP (energy currency of the cell).
  • Nickname: Powerhouse of the cell.

Extra Knowledge: Mitochondria have their own DNA, inherited maternally in most species.

6. Plastids (Plant Cells)

  • Types:
    1. Chloroplasts: Contain chlorophyll for photosynthesis.
    2. Chromoplasts: Store pigments (carotene, xanthophylls) giving yellow, orange, or red color.
    3. Leucoplasts: Store non-pigmented substances:
      • Amyloplasts: Starch (e.g., potato).
      • Elaioplasts: Oils and fats.
      • Aleuroplasts: Proteins.
  • Structure of Chloroplasts:
    • Double membrane with internal grana (stacks of thylakoids).
    • Stroma: Fluid containing enzymes, DNA, and 70S ribosomes.

Key Insight: Chloroplasts are the site of the light (grana) and dark (stroma) reactions of photosynthesis.

7. Ribosomes

  • Structure: Non-membranous, made of RNA and proteins.
  • Types:
    • Eukaryotic Ribosomes: 80S (60S + 40S).
    • Prokaryotic Ribosomes: 70S (50S + 30S).
  • Function: Synthesize proteins, free in cytoplasm or attached to RER.

Extra Knowledge: The “S” (Svedberg unit) indicates size and density.

8. Cytoskeleton

  • Structure: Network of microtubules, microfilaments, and intermediate filaments.
  • Functions:
    • Provides shape.
    • Aids in cell movement.
    • Facilitates organelle positioning.

9. Cilia and Flagella

  • Structure: Hair-like extensions with a 9+2 microtubule arrangement.
  • Functions:
    • Cilia: Move fluids or substances across the cell surface.
    • Flagella: Propel the cell forward (e.g., sperm cells).

10. Nucleus

  • Structure:
    • Enclosed by a double membrane with nuclear pores for molecule exchange.
    • Contains nucleoplasm, nucleolus, and chromatin.
  • Functions:
    • Controls cell activities.
    • Stores genetic material (DNA).

Extra Knowledge: Variations include multinucleated cells (e.g., muscle fibers) and anucleated cells (e.g., red blood cells in mammals).

Summary

The cell is a complex and dynamic structure, with each organelle performing specific roles essential for life. Understanding these components is crucial for both academic studies and competitive exams, as these concepts form the basis of cellular biology.

These all are the notes of chapter 8 biology. And important questions are below HERE. *#THANKS FOR VISITING, VISIT AGAIN#* 😊

1. What is a cell?

Answer: A cell is the fundamental, structural, and functional unit of life. It is the smallest unit capable of independent existence and performing essential life processes.

2. What are unicellular and multicellular organisms?

Answer:

  • Unicellular organisms: Made of a single cell, e.g., bacteria and amoeba.
  • Multicellular organisms: Made of many cells, e.g., humans and plants.

3. Who discovered the cell and when?

Answer:

  • Robert Hooke discovered the cell in 1665.
  • Anton Van Leeuwenhoek discovered living cells in 1674.

4. What is the cell theory, and who proposed it?

Answer:

  • Cell Theory:
    1. All living things are made up of cells and their products.
    2. All cells arise from pre-existing cells.
  • Contributors:
    • Matthias Schleiden (1838): Found plants are made of cells.
    • Theodor Schwann (1839): Found animals have cells with plasma membranes.
    • Rudolf Virchow (1855): Explained that cells arise from pre-existing cells.

5. What is the difference between prokaryotic and eukaryotic cells?

Answer:

  • Prokaryotic Cells:
    • No well-defined nucleus; DNA is circular and naked.
    • No membrane-bound organelles.
    • Example: Bacteria, blue-green algae.
  • Eukaryotic Cells:
    • Well-defined nucleus with a membrane.
    • Have membrane-bound organelles like mitochondria, Golgi apparatus, etc.
    • Example: Plant and animal cells.

6. What is the cytoplasm?

Answer:
The cytoplasm is the semi-fluid substance inside the cell that surrounds organelles. It occupies most of the cell’s volume.

7. What is the function of the nucleus in a cell?

Answer:
The nucleus controls all cell activities and contains chromosomes, which store genetic material like DNA.

8. What are organelles, and can you name a few?

Answer:
Organelles are specialized structures within a cell that perform specific functions. Examples include:

  • Mitochondria: Produces energy.
  • Golgi apparatus: Packages and modifies proteins.
  • Lysosomes: Break down waste and macromolecules.
  • Endoplasmic reticulum (ER): Helps in protein (RER) and lipid (SER) synthesis.

9. What are the smallest and largest cells?

Answer:

  • Smallest cell: Mycoplasma (0.3 μm).
  • Largest cell: Ostrich egg.
  • Longest cell: Nerve cells.

10. What are the shapes of cells, and why do they vary?

Answer:
Cells have different shapes like disc-shaped, columnar, cuboid, or thread-like, depending on their functions. For example:

  • Red blood cells: Disc-shaped for carrying oxygen.
  • Nerve cells: Thread-like for transmitting signals.

11. What are ribosomes, and what do they do?

Answer:
Ribosomes are non-membranous structures made of RNA and proteins. They are the sites of protein synthesis.

12. What is the role of the mitochondria?

Answer:
Mitochondria are known as the powerhouse of the cell. They produce energy in the form of ATP through aerobic respiration.

13. What are vacuoles, and what is their function?

Answer:
Vacuoles are storage sacs in cells. They store water, nutrients, and waste. In plant cells, vacuoles help maintain turgor pressure.

14. What is the difference between rough and smooth endoplasmic reticulum?

Answer:

  • Rough ER (RER): Has ribosomes; helps in protein synthesis.
  • Smooth ER (SER): Lacks ribosomes; helps in lipid synthesis.

15. What are plasmids?

Answer:
Plasmids are extra circular DNA found in prokaryotic cells. They often carry genes for antibiotic resistance and are used in biotechnology.

16. What is Gram staining, and why is it important?

Answer:
Gram staining is a method to classify bacteria as:

  • Gram-positive: Retains crystal violet stain (thick cell wall).
  • Gram-negative: Does not retain the stain (thin cell wall).
    It helps in identifying bacteria and their susceptibility to antibiotics.

17. What is the cytoskeleton, and what is its role?

Answer:
The cytoskeleton is a network of microtubules and filaments that:

  • Provides cell shape.
  • Aids in cell movement.
  • Helps position organelles.

18. What are cilia and flagella?

Answer:
Cilia and flagella are hair-like structures that help in movement.

  • Cilia: Move substances across the cell surface.
  • Flagella: Propel the entire cell (e.g., sperm cells).

19. What is the function of lysosomes?

Answer:
Lysosomes contain digestive enzymes that break down waste, damaged organelles, and macromolecules. They are known as the “suicidal bags” of the cell.

20. Why are mitochondria and chloroplasts unique?

Answer:
Both have their own DNA and ribosomes, enabling them to produce some of their own proteins. Mitochondria are involved in energy production, while chloroplasts are involved in photosynthesis (in plants).