Cell Theory and Plant Cell Components

Cell Theory

• All living organisms are made up of one or more cells
• All living cells arise from pre-existing cells by division
• The cell is the basic unit of structure and function in all living organisms

Plant Cell Components

• Cell Wall
  • Non-living outer covering of a plant cell
  • Can be tough, rigid, sometimes flexible
  • Made up of cellulose, hemicellulose, pectin
  • May be thin or thick, multilayered
  • Functions
    • Provides definite shape, strength, and rigidity
    • Prevents drying up (desiccation) of cells
    • Helps in controlling cell expansion
    • Protects cell from external pathogens
• Plasma Membrane
  • Extremely delicate, thin, elastic, living, semi-permeable membrane
  • Made up of two layers of lipid molecules in which protein molecules are floating
  • Can be observed only under an electron microscope
  • Functions
    • Maintains the shape and size of the cell
    • Protects the internal contents of the cell
    • Regulates the entry and exit of substances in and out of the cell
    • Maintains homeostasis
• Cytoplasm
  • Jelly-like material formed by 80% of water
  • Present between the plasma membrane and the nucleus
  • Contains a clear liquid portion called cytosol and various particles
  • Particles are proteins, carbohydrates, nucleic acids, lipids, and inorganic ions
  • Also contains many organelles with distinct structure and function
  • Some of these organelles are visible only under an electron microscope
• Chloroplast
  • Double membrane-bound organelles found mainly in plant cells
  • Usually spherical or discoidal in shape
  • Shows two distinct regions: grana and stroma
  • Grana are stacks of thylakoids (membrane-bound, flattened discs)
  • Thylakoids contain chlorophyll molecules which are responsible for photosynthesis
  • Stroma is a colorless dense fluid
  • Functions
    • Convert light energy into chemical energy in the form of food
    • Provide green colour to leaves, stems, and vegetables
• Mitochondria
  • Small, rod-shaped organelles bounded by two membranes: inner and outer
  • The outer membrane is smooth and encloses the contents of mitochondria
  • The inner membrane is folded in the form of shelf-like inward projections called cristae
  • Inner cavity is filled with matrix which contains many enzymes
  • Contains their own DNA, which are responsible for many enzymatic actions
  • Functions
    • Synthesize energy-rich compound ATP
    • ATP molecules provide energy for the vital activities of living cells
• Nucleus
  • Nucleus has a double-layered covering called the nuclear membrane
  • The nuclear membrane has pores of diameter about 80-100 nm
  • Colorless dense sap present inside the nucleus known as nucleoplasm
  • Nucleoplasm contains round shaped nucleolus and a network of chromatin fibers
  • Fibers are composed of deoxyribonucleic acid (DNA) and protein histone
  • These fibers condense to form chromosomes during cell division
  • Chromosomes contain stretches of DNA called genes
  • Genes transfer the hereditary information from one generation to the next
  • Functions
    • Control all the cell activities like metabolism, protein synthesis, growth, and cell division
    • Nucleolus synthesizes ribonucleic acid (RNA) to constitute ribosomes
    • Store hereditary information in genes
• Vacuoles
  • Single membrane sacs filled with liquid or sap (water, sugar, and ions)
  • In animal cells, vacuoles are temporary, small in size, and few in number
  • In plant cells, vacuoles are large and more in number
  • May be contractile or non-contractile
  • Functions
    • Store various substances including waste products
    • Maintain osmotic pressure of the cell
    • Provide turgidity and rigidity to plant cells

Osmosis

• Passage of water from a region of low concentration of solute to a region of high concentration, across a semipermeable membrane
• Isotonic: Same solute concentration
• Hypotonic: Low solute concentration
• Hypertonic: High solute concentration

Plasmolysis

• Loss of water from the cell by osmosis
• This is evident when the cell contents pull away from the rigid cell wall as the water moves out
• Steps of Plasmolysis
  • Initial stage: The cell remains in a turgid state
  • Plasmolysis begins: The protoplasm starts shrinking
  • Continued Plasmolysis: Cytoplasmic contents pull away from the cell wall, causing a space between the cell wall and the protoplasm
  • Complete Plasmolysis: The protoplasm is shrunk to a very small size

Explore the fundamental concepts of cell theory and the essential components of plant cells. This quiz covers the structure, function, and significance of cell walls and plasma membranes in plant biology. Test your knowledge of these critical topics in cellular biology!