Cell Structure and Function

Basic Characteristics of Cells

• Smallest living units of an organism.
• All cells have:
  • Cell Membrane: Separates the inside of the cell from its environment.
  • Cytoplasm: Jelly-like fluid inside the cell.
  • DNA: Genetic material of the cell.

Categories of Cells

Eukaryotic Cells

• Organelles: Specialized structures including the nucleus.
• More advanced and complex.
• Found in plants and animals.

Prokaryotic Cells

• No nucleus or membrane-enclosed organelles.
• Genetic material not contained within a nucleus.
• Always unicellular organisms, e.g., bacteria.

Organelles and Their Functions

Nucleus

• Control Center of the cell.
• Contains DNA.
• Chromatin: Tangled form of DNA inside the nuclear membrane.
• Chromosomes: Condensed DNA structures when a cell is ready to divide.
• Nucleolus: Structure where ribosomes are made.

Ribosomes

• Synthesizing proteins.
• Can be free-floating or attached to the endoplasmic reticulum (ER).

Endoplasmic Reticulum (ER)

• Rough ER: Has ribosomes attached.
• Smooth ER: No ribosomes attached.
• Membrane-enclosed passageway for transporting materials such as proteins.

Golgi Apparatus (Golgi Body)

• Customizes proteins into usable shapes.
• Can add materials such as lipids or carbohydrates.

Vacuoles

• Sac-like structures for storage.
• Plant cells: Central vacuole stores water.

Lysosomes

• Garbage collectors in animal cells.
• Filled with enzymes to break down cellular debris.

Mitochondria

• Powerhouse of the cell.
• Makes ATP molecules during cellular respiration.
• Found in both plant and animal cells.

Cytoskeleton

• Maintains cell shape.
• Includes microfilaments (protein threads) and microtubules (hollow tubes).

Chloroplasts (Plant Cells)

• Where photosynthesis occurs.
• Contains chlorophyll (green pigment).

Cell Wall (Plant Cells)

• Outside the cell membrane.
• Shapes, supports, and protects the cell.
• Absent in animal cells.

Specialized Features in Some Cells

Cilia

• Microscopic hair-like projections.
• Move in waves to trap inhaled particles.
• Found in human respiratory tract cells.

Flagella

• Tail-like structures aiding cell movement.
• Present in some bacteria and human sperm cells.

Summary

• Eukaryotic Cells: Plant and animal cells with nucleus and membrane-enclosed organelles.
• Prokaryotic Cells: Unicellular organisms without these structures.
• All cells have a cell membrane, cytoplasm, and genetic material.
• Both plant and animal cells have mitochondria, but only plant cells have chloroplasts.