📚 Unit 2: Cells
🔖 1. Introduction to Cells
⦁ Definition: Cells are the basic structural and functional units of life. They are the smallest units that can carry out all the processes necessary for life.
⦁ Cell Theory:
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 through the process of cell division.
🔖 2. Types of Cells
⦁ Prokaryotic Cells:
⦁ Characteristics:
⦁ Lack a defined nucleus; their genetic material is located in a nucleoid region.
⦁ Generally smaller and simpler than eukaryotic cells.
⦁ Have a cell wall, plasma membrane, ribosomes, and may contain plasmids (small circular DNA).
⦁ Examples:
⦁ Bacteria (e.g., Escherichia coli) and Archaea (extremophiles).
⦁ Reproduction: Primarily asexual reproduction through binary fission.
⦁ Eukaryotic Cells:
⦁ Characteristics:
⦁ Contain a true nucleus enclosed by a nuclear membrane.
⦁ Possess membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum).
⦁ Can be unicellular (e.g., amoeba) or multicellular (e.g., humans).
⦁ Examples:
⦁ Animals, plants, fungi, and protists.
⦁ Complexity: More complex than prokaryotic cells, allowing for specialized functions and activities.
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🔖 3. Cell Structure and Organelles
⦁ Cell Membrane:
⦁ Composed of a phospholipid bilayer with embedded proteins.
⦁ Functions:
⦁ Selectively permeable barrier regulating the entry and exit of substances.
⦁ Involved in cell communication through receptor proteins.
⦁ Nucleus:
⦁ Contains most of the cell's genetic material (DNA).
⦁ Surrounded by a nuclear envelope with pores facilitating the transport of materials.
⦁ Nucleolus: Site of ribosomal RNA (rRNA) synthesis and ribosome assembly.
⦁ Cytoplasm:
⦁ Gel-like substance, composed mostly of water, where organelles are suspended.
⦁ Site of numerous metabolic reactions.
⦁ Mitochondria:
⦁ Known as the "powerhouse of the cell," they generate ATP through cellular respiration.
⦁ Contain their own DNA (mtDNA) and double membrane structure.
⦁ Endoplasmic Reticulum (ER):
⦁ Rough ER: Studded with ribosomes for protein synthesis; involved in the modification and transport of proteins.
⦁ Smooth ER: Lacks ribosomes; involved in lipid synthesis, detoxification, and calcium storage.
⦁ Golgi Apparatus:
⦁ Stack of membrane-bound vesicles that modify, sort, and package proteins and lipids for secretion or delivery to other organelles.
⦁ Function: Acts like a processing and shipping center, ensuring proteins reach their destination.
⦁ Lysosomes:
⦁ Organelles containing digestive enzymes; involved in the breakdown of waste materials and cellular debris.
⦁ Play roles in apoptosis (programmed cell death) and recycling of cellular components.
⦁ Peroxisomes:
⦁ Contain enzymes for fatty acid oxidation and detoxification of harmful substances (e.g., hydrogen peroxide).
⦁ Cytoskeleton:
⦁ Network of protein filaments and tubules (microfilaments, intermediate filaments, and microtubules).
⦁ Provides structural support, aids in cell movement, and facilitates intracellular transport.
⦁ Centrioles:
⦁ Cylindrical structures involved in cell division (mitosis and meiosis) by organizing the mitotic spindle.
⦁ Chloroplasts (in plant cells):
⦁ Site of photosynthesis, converting light energy into chemical energy (glucose).
⦁ Contain green pigment (chlorophyll) and also have their own DNA.
⦁ Cell Wall (in plant cells):
⦁ Rigid outer layer made primarily of cellulose; provides structure, support, and protecti🔖 4. Cellular Processes
⦁ Diffusion:
⦁ Passive movement of molecules from an area of higher concentration to lower concentration.
⦁ Examples: Movement of oxygen and carbon dioxide in and out of cells.
🔖 1. Introduction to Cells
⦁ Definition: Cells are the basic structural and functional units of life. They are the smallest units that can carry out all the processes necessary for life.
⦁ Cell Theory:
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 through the process of cell division.
🔖 2. Types of Cells
⦁ Prokaryotic Cells:
⦁ Characteristics:
⦁ Lack a defined nucleus; their genetic material is located in a nucleoid region.
⦁ Generally smaller and simpler than eukaryotic cells.
⦁ Have a cell wall, plasma membrane, ribosomes, and may contain plasmids (small circular DNA).
⦁ Examples:
⦁ Bacteria (e.g., Escherichia coli) and Archaea (extremophiles).
⦁ Reproduction: Primarily asexual reproduction through binary fission.
⦁ Eukaryotic Cells:
⦁ Characteristics:
⦁ Contain a true nucleus enclosed by a nuclear membrane.
⦁ Possess membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum).
⦁ Can be unicellular (e.g., amoeba) or multicellular (e.g., humans).
⦁ Examples:
⦁ Animals, plants, fungi, and protists.
⦁ Complexity: More complex than prokaryotic cells, allowing for specialized functions and activities.
————————
🔖 3. Cell Structure and Organelles
⦁ Cell Membrane:
⦁ Composed of a phospholipid bilayer with embedded proteins.
⦁ Functions:
⦁ Selectively permeable barrier regulating the entry and exit of substances.
⦁ Involved in cell communication through receptor proteins.
⦁ Nucleus:
⦁ Contains most of the cell's genetic material (DNA).
⦁ Surrounded by a nuclear envelope with pores facilitating the transport of materials.
⦁ Nucleolus: Site of ribosomal RNA (rRNA) synthesis and ribosome assembly.
⦁ Cytoplasm:
⦁ Gel-like substance, composed mostly of water, where organelles are suspended.
⦁ Site of numerous metabolic reactions.
⦁ Mitochondria:
⦁ Known as the "powerhouse of the cell," they generate ATP through cellular respiration.
⦁ Contain their own DNA (mtDNA) and double membrane structure.
⦁ Endoplasmic Reticulum (ER):
⦁ Rough ER: Studded with ribosomes for protein synthesis; involved in the modification and transport of proteins.
⦁ Smooth ER: Lacks ribosomes; involved in lipid synthesis, detoxification, and calcium storage.
⦁ Golgi Apparatus:
⦁ Stack of membrane-bound vesicles that modify, sort, and package proteins and lipids for secretion or delivery to other organelles.
⦁ Function: Acts like a processing and shipping center, ensuring proteins reach their destination.
⦁ Lysosomes:
⦁ Organelles containing digestive enzymes; involved in the breakdown of waste materials and cellular debris.
⦁ Play roles in apoptosis (programmed cell death) and recycling of cellular components.
⦁ Peroxisomes:
⦁ Contain enzymes for fatty acid oxidation and detoxification of harmful substances (e.g., hydrogen peroxide).
⦁ Cytoskeleton:
⦁ Network of protein filaments and tubules (microfilaments, intermediate filaments, and microtubules).
⦁ Provides structural support, aids in cell movement, and facilitates intracellular transport.
⦁ Centrioles:
⦁ Cylindrical structures involved in cell division (mitosis and meiosis) by organizing the mitotic spindle.
⦁ Chloroplasts (in plant cells):
⦁ Site of photosynthesis, converting light energy into chemical energy (glucose).
⦁ Contain green pigment (chlorophyll) and also have their own DNA.
⦁ Cell Wall (in plant cells):
⦁ Rigid outer layer made primarily of cellulose; provides structure, support, and protecti🔖 4. Cellular Processes
⦁ Diffusion:
⦁ Passive movement of molecules from an area of higher concentration to lower concentration.
⦁ Examples: Movement of oxygen and carbon dioxide in and out of cells.