Cell and Tissues of Organisms
1. Cells: The Fundamental Units of Life
Cells are the smallest units capable of performing all the processes necessary for life. They are classified
into prokaryotic and eukaryotic cells based on their complexity and organization.
A. Prokaryotic Cells
Structure:
o Cell Wall: Provides structural support and protection. In bacteria, it is made of peptidoglycan,
while in archaea, it is composed of other polysaccharides.
o Cell Membrane: A phospholipid bilayer that regulates the movement of substances in and out of
the cell.
o Cytoplasm: A gel-like substance containing enzymes, ribosomes, and other cellular components.
o Nucleoid: A region where the circular DNA molecule is located. Unlike eukaryotic cells,
prokaryotes lack a membrane-bound nucleus.
o Ribosomes: Smaller than eukaryotic ribosomes (70S), they synthesize proteins.
o Flagella: Whip-like structures used for movement.
o Pili: Hair-like structures that assist in attachment and DNA transfer (conjugation).
o Plasmids: Small, circular DNA molecules that carry additional genes, often for antibiotic
resistance.
Examples: Bacteria (e.g., Escherichia coli) and archaea (e.g., methanogens).
Reproduction: Prokaryotes reproduce asexually through binary fission, where the cell divides into two
identical daughter cells.
B. Eukaryotic Cells
Structure:
o Nucleus: Contains the cell’s DNA and controls cellular activities. It is surrounded by a double
membrane called the nuclear envelope.
o Mitochondria: The "powerhouse of the cell," mitochondria produce ATP through cellular
respiration. They have their own DNA and ribosomes, suggesting an evolutionary origin from
symbiotic bacteria.
o Endoplasmic Reticulum (ER):
Rough ER: Studded with ribosomes, it synthesizes proteins.
Smooth ER: Lacks ribosomes and is involved in lipid synthesis and detoxification.
, o Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or transport to
other organelles.
o Lysosomes: Contain digestive enzymes that break down waste materials, cellular debris, and
foreign invaders.
o Peroxisomes: Break down fatty acids and detoxify harmful substances, producing hydrogen
peroxide as a byproduct.
o Cytoskeleton: A network of protein filaments (microtubules, microfilaments, and intermediate
filaments) that provides structural support, facilitates cell movement, and aids in intracellular
transport.
o Vacuoles: Membrane-bound sacs that store water, nutrients, and waste products.
Central Vacuole (in plants): Maintains turgor pressure, stores nutrients, and helps in
growth.
o Chloroplasts (in plants): Conduct photosynthesis, converting light energy into glucose. Like
mitochondria, they have their own DNA and ribosomes.
o Cell Wall (in plants and fungi): Provides structural support and protection. In plants, it is made
of cellulose, while in fungi, it is composed of chitin.
Examples: Found in plants, animals, fungi, and protists.
Reproduction:
o Mitosis: Produces two genetically identical daughter cells for growth, repair, and asexual
reproduction.
o Meiosis: Produces four genetically diverse gametes (sex cells) for sexual reproduction.
2. Cell Theory
The cell theory is a foundational concept in biology, formulated by Matthias Schleiden, Theodor Schwann,
and Rudolf Virchow:
1. All living organisms are composed of one or more cells.
2. The cell is the basic unit of life.
3. All cells arise from pre-existing cells.
3. Tissues: Groups of Specialized Cells
Tissues are collections of similar cells that work together to perform specific functions. They are organized
into four primary types in animals and several types in plants.
A. Animal Tissues
1. Epithelial Tissue:
o Function: Covers body surfaces, lines cavities, and forms glands.
1. Cells: The Fundamental Units of Life
Cells are the smallest units capable of performing all the processes necessary for life. They are classified
into prokaryotic and eukaryotic cells based on their complexity and organization.
A. Prokaryotic Cells
Structure:
o Cell Wall: Provides structural support and protection. In bacteria, it is made of peptidoglycan,
while in archaea, it is composed of other polysaccharides.
o Cell Membrane: A phospholipid bilayer that regulates the movement of substances in and out of
the cell.
o Cytoplasm: A gel-like substance containing enzymes, ribosomes, and other cellular components.
o Nucleoid: A region where the circular DNA molecule is located. Unlike eukaryotic cells,
prokaryotes lack a membrane-bound nucleus.
o Ribosomes: Smaller than eukaryotic ribosomes (70S), they synthesize proteins.
o Flagella: Whip-like structures used for movement.
o Pili: Hair-like structures that assist in attachment and DNA transfer (conjugation).
o Plasmids: Small, circular DNA molecules that carry additional genes, often for antibiotic
resistance.
Examples: Bacteria (e.g., Escherichia coli) and archaea (e.g., methanogens).
Reproduction: Prokaryotes reproduce asexually through binary fission, where the cell divides into two
identical daughter cells.
B. Eukaryotic Cells
Structure:
o Nucleus: Contains the cell’s DNA and controls cellular activities. It is surrounded by a double
membrane called the nuclear envelope.
o Mitochondria: The "powerhouse of the cell," mitochondria produce ATP through cellular
respiration. They have their own DNA and ribosomes, suggesting an evolutionary origin from
symbiotic bacteria.
o Endoplasmic Reticulum (ER):
Rough ER: Studded with ribosomes, it synthesizes proteins.
Smooth ER: Lacks ribosomes and is involved in lipid synthesis and detoxification.
, o Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or transport to
other organelles.
o Lysosomes: Contain digestive enzymes that break down waste materials, cellular debris, and
foreign invaders.
o Peroxisomes: Break down fatty acids and detoxify harmful substances, producing hydrogen
peroxide as a byproduct.
o Cytoskeleton: A network of protein filaments (microtubules, microfilaments, and intermediate
filaments) that provides structural support, facilitates cell movement, and aids in intracellular
transport.
o Vacuoles: Membrane-bound sacs that store water, nutrients, and waste products.
Central Vacuole (in plants): Maintains turgor pressure, stores nutrients, and helps in
growth.
o Chloroplasts (in plants): Conduct photosynthesis, converting light energy into glucose. Like
mitochondria, they have their own DNA and ribosomes.
o Cell Wall (in plants and fungi): Provides structural support and protection. In plants, it is made
of cellulose, while in fungi, it is composed of chitin.
Examples: Found in plants, animals, fungi, and protists.
Reproduction:
o Mitosis: Produces two genetically identical daughter cells for growth, repair, and asexual
reproduction.
o Meiosis: Produces four genetically diverse gametes (sex cells) for sexual reproduction.
2. Cell Theory
The cell theory is a foundational concept in biology, formulated by Matthias Schleiden, Theodor Schwann,
and Rudolf Virchow:
1. All living organisms are composed of one or more cells.
2. The cell is the basic unit of life.
3. All cells arise from pre-existing cells.
3. Tissues: Groups of Specialized Cells
Tissues are collections of similar cells that work together to perform specific functions. They are organized
into four primary types in animals and several types in plants.
A. Animal Tissues
1. Epithelial Tissue:
o Function: Covers body surfaces, lines cavities, and forms glands.
