• Discovery of Cell: Robert Hooke (1665) saw in thin slice of cork ,honey comb like structure using primitive microscope.He called them cell.
• Leeuwenhoek [1674] discovered free living cell in pond water .[AnimalCule]
Cell Cell is the Structural,Functional and fundametal unit of Life.
• Cell Theory: Proposed by Schleiden and Schwann (1838-39), later expanded by Virchow (1855):
  1. All living organisms are composed of cells
  2. Cell is the basic unit of life
  3. All cells arise from pre-existing cells[Omni-cellula-e-cellula]

Prokaryotic and Eukaryotic Cells

• Eukaryotic Cells: Cells that have a membrane-bound nucleus.
• Prokaryotic Cells: Cells that lack a membrane-bound nucleus.

Cell Membrane

• Semi-permeable phospholipid bilayer
• Functions: Protection, selective transport, cell recognition

PHOSPHOLIPID BILAYER

CELL STRUCTURE

Plant Cell vs Animal Cell

Feature	Plant Cell	Animal Cell
Cell wall	Present	Absent
Chloroplast	Present	Absent
Vacuole	Large	Small or absent
Lysosome	Absent	Present
Centrosome	Absent	Present

Cell Wall (Plant Cells Only)

• Rigid outer layer made of cellulose
• Functions: Structural support, protection, prevents bursting

Cytoplasm

• Jelly-like substance between nucleus and cell membrane
• Contains organelles and cytoskeleton

Nucleus

• Control center of the cell
• Contains chromatin (DNA + proteins)
• Surrounded by nuclear membrane with pores
• Contains nucleolus (ribosome production)

Mitochondria

• Mitochondria are small, cylindrical organelles present in cytoplasm.
• It is double membranous structure.[Outer/inner]
• The inner membrane is folded into finger-like structures called cristae.
• The space inside cristae is called matrix.
• They are Responsible for cellular respiration which provides energy.
• So mitochondria is also called "Power House Of The Cell."
• It was discovered by Richard Altmann.

Plastids

• It is double membranous structure in plant cell.
• It is Responsible for manufacturing and storage of food.
• It was discovered by Ernst Haeckel.
• It is of three types:
  1. Chloroplast
  2. Chromoplast
  3. Leucoplast
• Chromoplast
  - Responsible for non-green pigments (red, yellow, orange).
  - Found in flowers and fruits (e.g., tomatoes, carrots).
  - Attracts pollinators and seed dispersers.
• Leucoplast ()
  - Colorless plastids for storage.
  - Types include:
    • Amyloplasts (store starch)
    • Elaioplasts (store lipids)
    • Proteinoplasts (store proteins)
  - Found in roots and storage tissues.
• Chloroplast
  
• It is present only in plant cells and algae. It contains chlorophyll, which is responsible for the green color of leaves. Chlorophyll absorbs sunlight and thus helps in photosynthesis. Inside the inner membrane, a fluid substance called stroma is present. Within the stroma, disc-like structures called thylakoids bear chlorophyll. Groups of thylakoids form a structure known as a granum. It is also called the Kitchen of the Cell.

Endoplasmic Reticulum

• It was described by Keith R. Porter.
• It is a network of tubes and sheets made up of cisternae, tubules and vesicles.
• There are two types of ER:
  1. Smooth Endoplasmic Reticulum
  2. Rough Endoplasmic Reticulum
• Smooth Endoplasmic Reticulum:
  • It is smooth because ribosomes aren't attached on its surface.
  • They are sites of fat molecule synthesis.
• Rough Endoplasmic Reticulum:
  • It is rough because ribosomes are attached on its surface.
  • They are sites of protein synthesis.
• Functions:
  1. It serves as channel for transport of molecules between cytoplasm and nucleus.
  2. SER helps in fat molecule synthesis and RER helps in protein synthesis.
  3. It helps in detoxification.

Golgi Apparatus

• It was first discovered by scientist Camillo Golgi.
• It is a membrane bound organelle made up of series of flattened stacked pouches called cisternae.
• It is located in the cytoplasm next to the endoplasmic reticulum.
• Golgi body is also called the "Traffic Police Of Cell".
• Functions:
  1. It helps in storage, modification and release of cell products.
  2. Complex sugars are made from simple sugars in Golgi body.
  3. It helps in formation of lysosome.

Lysosomes

• It was discovered by Christian de Duve.
• Lysosome is a spherical sac-like single membranous structure.
• Lysosomes are filled with about 50 different types of digestive enzymes called acid hydrolases.
• Lysosomes are highly polymorphic cell organelles because they are found in different forms.
• Functions:
  1. It helps in digestion of foreign materials received in cell.
  2. It digests old and dead cell organelles.
  3. It is also known as "suicidal bag," because sometimes all lysosomes of a cell burst completely to dissolve the cell organelles.

Ribosomes

• It was discovered by George Palade.
• Ribosomes are minute particles present in cytoplasm.
• It is non-membranous organelle.
• There are two types of ribosomes based on their sedimentation units:
  1. 70S type:
     • Found in prokaryotic cells
     • Has two subunits: 50S and 30S
  2. 80S type:
     • Found in eukaryotic cells
     • Has two subunits: 60S and 40S
• Function: It synthesizes proteins so it is also called protein factory of the cell.

Vacuoles

• Vacuoles are fluid-filled cavities present in the cytoplasm.
• The fluid inside vacuoles is called cell sap.
• They are surrounded by a single membrane called tonoplast.
• In mature plant cells, there is one large central vacuole.
• In animal cells, vacuoles if present are much smaller.
• The vacuole fluid is viscous and contains various substances.
• Functions:
  1. They help to maintain osmotic pressure in the cell.
  2. They act as storage house of pigments, waste products, useful minerals and salts.