Lecture on Cells: The Fundamental Units of Life

Common Features of All Cells

• All cells, regardless of type, have three common components:
  1. Cell Membrane: Separates the inside of the cell from its environment.
  2. Cytoplasm: Jelly-like fluid inside the cell.
  3. DNA: Genetic material of the cell.

Types of Cells

Eukaryotic Cells

• Have organelles, including a nucleus.
• Found in plants and animals.
• More advanced and complex.

Prokaryotic Cells

• Do not have a nucleus or membrane-enclosed organelles.
• Genetic material is not contained within a nucleus.
• Always unicellular organisms, such as bacteria.

Organelles and Their Functions

Nucleus

• Control center of the cell.
• Contains DNA, which dictates cell functions.
• DNA exists as chromatin inside the nuclear membrane and condenses into chromosomes when the cell is ready to divide.
• Contains the nucleolus, where ribosomes are made.

Ribosomes

• Synthesize proteins.
• Can be free in the cytoplasm or attached to the Endoplasmic Reticulum (ER).

Endoplasmic Reticulum (ER)

• Rough ER: Has ribosomes attached; involved in protein transport.
• Smooth ER: No ribosomes attached; involved in lipid synthesis and detoxification.

Golgi Apparatus (Golgi Body)

• Modifies and packages proteins into usable forms.
• Proteins are transported in vesicles.

Vacuoles

• Sac-like structures for storage (e.g., central vacuole in plant cells stores water).

Lysosomes

• Contain enzymes to break down damaged or worn-out cell parts.
• Act as the cell's garbage collectors.

Mitochondria

• Powerhouse of the cell.
• Site of cellular respiration, producing ATP for energy.
• Found in both plant and animal cells.

Cytoskeleton

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

Chloroplasts

• Found in photoautotrophic organisms (e.g., plants).
• Site of photosynthesis, containing green pigment chlorophyll.

Cell Wall

• Found in plant cells.
• Provides shape, support, and protection.
• Absent in animal cells.

Unique Cellular Structures

• Cilia: Hair-like projections that trap particles and expel them (e.g., respiratory tract cells).
• Flagella: Tail-like structures that aid in movement (e.g., sperm cells in humans, certain bacteria).

Summary

• Eukaryotic Cells: Found in plants and animals; have a nucleus and membrane-enclosed organelles.
• Prokaryotic Cells: Unicellular organisms without a nucleus or membrane-enclosed organelles.
• Common to all cells: cell membrane, cytoplasm, and DNA.
• Plant cells have chloroplasts; both plant and animal cells have mitochondria.