Introduction to Cells

Cells are the fundamental units of life, forming the basis of all living organisms. Despite the diversity of cell types, they share three common components:

• Cell Membrane: Separates the interior from the external environment.
• Cytoplasm: A jelly-like fluid inside the cell.
• DNA: The genetic material of the cell.

Categories of Cells

Cells are divided into two broad categories:

Eukaryotic Cells

• Characteristics:
  • Contain organelles, including a nucleus.
  • Considered more advanced and complex.
• Examples: Found in plants and animals.

Prokaryotic Cells

• Characteristics:
  • Lack a nucleus and membrane-enclosed organelles.
  • Genetic material is not contained within a nucleus.
• Examples: Always unicellular organisms, such as bacteria.

Organelles in Cells

Nucleus

• Function: Control center of the cell containing DNA.
• DNA Forms:
  • Chromatin: Spread out form of DNA inside the nuclear membrane.
  • Chromosomes: Condensed structures of DNA when the cell is ready to divide.
• Nucleolus: Site where ribosomes are made.

Ribosomes

• Function: Synthesize proteins.
• Location: Float in cytoplasm or attach to Endoplasmic Reticulum (ER).

Endoplasmic Reticulum (ER)

• Types:
  • Rough ER: Has ribosomes attached.
  • Smooth ER: Lacks ribosomes.
• Function: Transports materials like proteins.

Golgi Apparatus (Golgi Body)

• Function: Modifies and customizes proteins by folding or adding lipids/carbohydrates.

Vacuoles

• Function: Storage of materials.
• Example: Central vacuole in plant cells stores water.

Lysosomes

• Function: Break down damaged or worn-out cell parts using enzymes.

Mitochondria

• Function: Powerhouse of the cell, produces ATP through cellular respiration.
• Energy Demand: Cells needing more energy have more mitochondria.

Cytoskeleton

• Components:
  • Microfilaments: Thread-like structures made of protein.
  • Microtubules: Thin hollow tubes.
• Function: Maintains cell shape.

Chloroplasts

• Function: Site of photosynthesis in photoautotrophic organisms.
• Appearance: Green due to chlorophyll.

Unique Cell Structures

Plant Cells

• Cell Wall: Provides shape, support, and protection.
• Chloroplasts: Present for photosynthesis.

Animal Cells

• Lack cell walls.

Cilia

• Function: Traps and expels particles in the respiratory tract.
• Appearance: Microscopic hair-like projections.

Flagella

• Function: Movement or propulsion of certain cells.
• Example: Sperm cells in humans.

Summary

• Eukaryotic Cells: Have a nucleus and organelles; found in plants and animals.
• Prokaryotic Cells: Unicellular, lack a nucleus and membrane-enclosed organelles.
• Common Features: All cells have a cell membrane, cytoplasm, and genetic material.
• Plant vs. Animal Cells: Only plant cells have chloroplasts, but both have mitochondria.