Cell Biology: History, Structure, and Organization
Cell Biology: A Comprehensive Study
History of Cell Biology
Robert Hooke (first to observe cells in cork), Robert Brown (discovered the cell nucleus), Purkinje (coined the term protoplasm), and Schwann and Schleiden (*Cell Theory*).
Cell Structure and Organization
Theme
Cells exhibit diverse shapes: star-shaped, elongated, cylindrical, etc.
Size
Cell size varies greatly; most are microscopic. Measurement units include microns and Angstroms.
Organization
Prokaryotic cells (bacteria): Organelles lack membrane-bound DNA; ribosomes are present.
Eukaryotic cells: Possess membrane-bound organelles and DNA.
§ Unicellular: Protozoa (amoeba, paramecium, plasmodium, Trypanosoma gambiense), algae (Euglena viridis)
§ Multicellular: Plants and animals
Sections
Plasma membrane: Surrounds the cell, regulates substance exchange.
Cell wall: Present in plant cells, absent in animal cells.
Cytoplasm: Contains cytosol and organelles.
Nucleus: Contains chromosomes; involved in mitosis (prophase, metaphase, anaphase, telophase).
Plant Tissues
Growth
Primary growth (apical meristems): Longitudinal growth at root and stem tips.
Secondary growth: Increases thickness. The rest in one hundred adults
Protective tissues: bacteria, fungi, etc.
§ Epidermis: Single cell layer; contains impermeable cutin; stomata for gas exchange.
§ Suber: Multi-layered; found in roots and stems; contains impermeable suberin.
Ground tissue (most abundant):
Parenchyma: Thin-walled cells; functions in air and water storage, and photosynthesis.
Supporting tissues:
Collenchyma: Living cells with thick cellulose walls.
Sclerenchyma: Dead cells with hardened lignin.
Secretory tissues:
§ Latex secretory cells: Produce milky liquid.
§ Resin secretory cells: Prevent wood rot.
Conductive tissues:
§ Xylem: Dead cells; lignin-thickened; transports water.
§ Phloem: Living cells; transports sugars.
Animal tissues are composed of specialized cells with less intercellular substance.
Animal Tissues
Nervous Tissue
Found in the brain, heart, and nerves. Composed of neurons:
Axon: Transmits nerve impulses away from the neuron cell body.
Cell body: Contains the nucleus and most of the cytoplasm.
Dendrites: Receive nerve impulses.
Muscle Tissue
§ Smooth muscle tissue: Uninhibited contractions; found in internal organs (stomach, intestines).
§ Skeletal muscle tissue: Voluntary contractions; attached to bones.
§ Cardiac muscle tissue: Found in the heart; simultaneous contractions.
Epithelial Tissue
Closely packed cells with little intercellular substance; one surface is free, the other rests on a basement membrane.
§ Covering epithelium: Covers external surfaces, lines tubes and cavities.
· Simple (single layer): squamous (blood vessels), cuboidal (glands), columnar (intestines)
· Stratified (multiple layers): squamous (surface), cuboidal (glands)
§ Glandular epithelium: Forms glands.
· Exocrine glands: Secrete substances (sweat, milk) onto a surface.
· Endocrine glands: Secrete hormones into the blood.
Connective Tissue
Most abundant tissue; supports and protects other tissues and organs. Contains many intercellular substances and few cells. Composed of elastic fibers, collagen fibers, and reticular fibers. Includes cartilage and bone.
Bacteria
Shape
Cocci (spherical), diplococci (pairs), staphylococci (clusters), streptococci (chains), bacilli (rod-shaped), vibrio (comma-shaped), spirilla (spiral).
Nutrition
Autotrophs: Photosynthetic (e.g., cyanobacteria); chemosynthetic (obtain energy from chemical substances).
Heterotrophs:
§ Fermenters: Produce fermented foods (yogurt, cheese); examples include Lactobacillus and Streptococcus.
§ Symbionts: Beneficial relationships with other organisms.
§ Parasites: Cause disease (e.g., Clostridium tetani).
§ Saprotrophs/Decomposers: Break down dead organic matter.
Eukaryotic Unicellular Organisms
Algae
Example: Euglena viridis
Protozoa
Rhizopoda: Move using pseudopods (e.g., amoeba).
Ciliates: Move using cilia (e.g., Paramecium).
Flagellates: Move using flagella (e.g., Trypanosoma gambiense, causes sleeping sickness).
Sporozoa: Non-motile; mostly parasitic (e.g., Plasmodium, causes malaria).
Cell Theory
- All living things are composed of cells.
- The cell is the basic unit of life.
- All cells come from pre-existing cells.
Body, Organs, and Systems
Organs are composed of different tissues. Systems are composed of organs with related functions (e.g., digestive system, circulatory system).
Viruses
Viruses are very small; only visible with an electron microscope. They are considered a unique form of life, as they do not meet all the criteria of living organisms. They are parasites that reproduce by infecting living cells. They contain nucleic acids (DNA or RNA) and a protein coat (capsid). They have various shapes (spherical, polyhedral, cylindrical). Examples include bacteriophages (infect bacteria), plant viruses, and animal viruses (e.g., Foot and Mouth Disease).