The Bio Brief

 What are Cell Organelles?

• Cells have small structures inside them called organelles
• Each organelle has a specific function
• Eukaryotic cells (plant & animal cells) have membrane-bound organelles
• Prokaryotic cells do not

 Think of a cell like a factory, and organelles are different departments doing different jobs.

 ENDOPLASMIC RETICULUM (ER)

 What is ER?

• A network of membranes
• Looks like tubes and flattened sacs
• Helps in transport and production

 Types of ER

Endoplasmic Reticulum

        |

 ———————

 |                   |

Rough ER (RER)   Smooth ER (SER)

 Rough ER (RER)

• Has ribosomes attached
• Makes proteins
• Proteins are sent to different parts of the cell

 Smooth ER (SER)

• No ribosomes
• Makes fats (lipids)
• Helps in detoxification (especially in liver cells)

 Functions of ER

• Protein & lipid synthesis
• Transport inside cell
• Helps in membrane formation (membrane biogenesis)

 GOLGI APPARATUS (POST OFFICE OF CELL)

 Structure

• Stack of flattened membrane sacs called cisterns

ER → Golgi Apparatus → Vesicles → Destination

 Functions

• Modifies proteins & lipids
• Packages them into vesicles
• Sends them inside or outside the cell
• Helps in lysosome formation

 Analogy: ER = factory → Golgi = post office → vesicles = parcels

 LYSOSOMES (SUICIDE BAGS)

 Structure

• Small membrane-bound sacs
• Filled with digestive enzymes

 Functions

• Digests:
  • Waste material
  • Old organelles
  • Bacteria & foreign particles

Waste / Bacteria

        ↓

     Lysosome

        ↓

 Broken into simple substances

 If cell is damaged → lysosome bursts → cell digests itself Hence called “suicide bags”

 MITOCHONDRIA (POWERHOUSE)

 Structure

• Double membrane
• Inner membrane has folds called cristae

Outer Membrane

   Inner    

  Folded → Cristae

 Functions

• Produces ATP (energy)
• ATP = energy currency of the cell

Special Features

• Has its own DNA
• Has ribosomes
• Can make some of its own proteins

 PLASTIDS (ONLY IN PLANT CELLS)

 Types of Plastids

Plastids

   |

———————

|                   |

Chloroplasts     Leucoplasts

 Chloroplasts

• Green plastids
• Contain chlorophyll
• Site of photosynthesis

Sunlight + CO₂ + Water

        ↓

   Chloroplast

        ↓

     Food + O₂

 Leucoplasts

• Colourless
• Storage of:
  • Starch
  • Oils
  • Proteins

Special Point: Plastids have their own DNA & ribosomes (like mitochondria)

VACUOLES (STORAGE TANK)

 Structure

• Membrane-bound sacs
• Size varies

 In Plant Cells

• Very large central vacuole
• Filled with cell sap
• Maintains:
  • Turgidity
  • Rigidity

 In Animal Cells

• Small vacuoles

 In Amoeba

• Food vacuole stores food
• Contractile vacuole removes excess water

 QUICK REVISION TABLE

Organelle	Main Function
ER	Protein & lipid synthesis
Golgi	Packaging & transport
Lysosome	Digestion & waste removal
Mitochondria	Energy (ATP) production
Plastids	Photosynthesis & storage
Vacuole	Storage & rigidity

FINAL POINT:  

Cell = basic structural & functional unit of life.  Organelles work together to:

• Respire
• Get nutrition
• Remove waste
• Make proteins

Differences Between Plant Cell and Animal Cell

Feature	Plant Cell	Animal Cell
Cell wall	Present (made of cellulose)	Absent
Shape	Usually rectangular / fixed	Usually round or irregular
Chloroplast	Present (photosynthesis)	Absent
Plastids	Present	Absent
Vacuole	Large central vacuole	Small or temporary vacuoles
Mode of nutrition	Autotrophic (makes its own food)	Heterotrophic
Mitochondria	Present	Present
Lysosomes	Rare	Common
Centrosome	Absent	Present
Storage material	Starch	Glycogen