The Fundamental Unit of Life
Introduction to Cells
Definition of a Cell: The basic structural and functional unit of life.
Discovery of the Cell: Robert Hooke discovered cells in 1665 using a microscope.
Cell Theory:
All living organisms are composed of one or more cells.
The cell is the basic unit of structure and organization in organisms.
All cells arise from pre-existing cells.
Types of Cells
Prokaryotic Cells: Simple, smaller cells without a nucleus. Example: Bacteria.
Lack membrane-bound organelles.
DNA is circular and found in the nucleoid region.
Eukaryotic Cells: Complex, larger cells with a nucleus. Example: Plant and Animal cells.
Contain membrane-bound organelles.
DNA is linear and enclosed within the nucleus.
Cell Structure and Functions
Cell Membrane
Semi-permeable membrane that controls the movement of substances in and out of the cell.
Composed of a lipid bilayer with embedded proteins.
Cytoplasm
Jelly-like substance within the cell membrane that contains all organelles and cell parts.
Site for most cellular activities.
Nucleus
Control center of the cell containing DNA.
Surrounded by a nuclear membrane with pores that control the movement of materials in and out.
Contains the nucleolus, which is involved in ribosome synthesis.
Mitochondria
Powerhouse of the cell, where cellular respiration occurs to produce energy (ATP).
Have their own DNA and double membrane.
Endoplasmic Reticulum (ER)
Network of membranes involved in protein and lipid synthesis.
Rough ER has ribosomes on its surface and synthesizes proteins.
Smooth ER lacks ribosomes and synthesizes lipids.
Golgi Apparatus
Stacks of flattened membranes involved in modifying, sorting, and packaging proteins and lipids for storage or transport out of the cell.
Lysosomes
Contain digestive enzymes to break down waste materials and cellular debris.
Known as the cell's "clean-up crew."
Ribosomes
Sites of protein synthesis.
Can be free-floating in the cytoplasm or attached to the Rough ER.
Chloroplasts (Plant Cells Only)
Sites of photosynthesis, where light energy is converted into chemical energy.
Contain the green pigment chlorophyll and have their own DNA.
Vacuoles
Storage sacs within the cell.
Plant cells have a large central vacuole that maintains cell rigidity and stores nutrients and waste products.
Cell Wall (Plant Cells Only)
Rigid outer layer that provides support and protection.
Made of cellulose.
Cellular Functions
Metabolism: All chemical reactions within the cell, including catabolism (breaking down molecules) and anabolism (building up molecules).
Growth and Reproduction: Cells grow and reproduce through processes like mitosis (for somatic cells) and meiosis (for reproductive cells).
Response to Stimuli: Cells can respond to changes in their environment, which is vital for survival.
Conclusion
Cells are the fundamental building blocks of life, each carrying out essential functions that contribute to the organism's overall health and functionality. Understanding cell structure and function is crucial to comprehending more complex biological processes.