Topics to be learn

  • Introduction
  • The cell theory
  • Difference between Animal cell and Plant cell
  • Diffusion
  • Osmosis
  • Hypotonic or Hypertonic or Isotonic solution
  • Plasma membrane or Cell membrane
  • Cell Wall
  • Plasmolysis
  • Nucleus
  • Nucleoid
  • Cytoplasm
  • Endoplasmic Reticulum (ER)
  • Golgi Apparatus
  • Lysosomes
  •  Mitochondria
  • Plastids
  • Vacuoles

Introduction

  • Cell: Basic unit of life, discovered by Robert Hook in 1831.
  • Microscope: Instrument used for observing cells.
  • Leeuwenhoek: Discovered free-living cells in pond water.
  • Nucleus: Discovered by Robert Brown in 1831.
  • Protoplasm: Term coined by Purkinje in 1839 for cell fluid.

The Cell Theory

  • Schleiden and Schwann: Proposed that all organisms are composed of cells.
  • Virchow: Added that cells arise from pre-existing cells.

Types of Organisms

  • Unicellular Organism: Single-celled, performs all functions (e.g., Amoeba, bacteria).
  • Multicellular Organism: Many cells, specialized functions (e.g., fungi, plants, animals).
  • Cell Shape and Size: Varies based on function, shows division of labor.
  • Cell Organelles: Structures like mitochondria perform specific functions.


Types of Cells

  • Prokaryotes

    • Lack nuclear membrane, nucleolus.
    • Single chromosome, asexual reproduction (e.g., bacteria).
    • No membrane-bound organelles, no centrioles, division by binary fission.

  • Eukaryotes

    • Have nuclear membrane, nucleolus.
    • Single or multiple chromosomes, reproduce sexually and asexually.
    • Membrane-bound organelles like mitochondria, may have centrioles, division by mitosis/meiosis.
    • Examples: Fungi, plant cells, animal cells.

Difference between Animal Cell and Plant Cell


Diffusion

  • Definition: Spontaneous movement of a substance from high to low concentration.
  • Examples: Carbon dioxide, oxygen move across cell membrane.

Osmosis

  • Definition: Movement of water through a selectively permeable membrane.
  • Example: Plant cells absorb water via osmosis.

Hypotonic, Hypertonic, Isotonic Solutions


Plasma Membrane (Cell Membrane)

  • Definition: Outer covering of cell separating internal from external environment.
  • Permeability: Allows selective entry and exit of materials.
  • Composition: Made of lipids and proteins.

Properties of Plasma Membrane

  • Flexibility: Composed of lipids and proteins.
  • Function: Enables endocytosis (e.g., food engulfment in Amoeba).

Functions of Plasma Membrane

  • Regulates material entry and exit.
  • Acts as selectively permeable barrier.

Cell Wall

  • Definition: Rigid outer covering in plant cells, outside plasma membrane.
  • Composition: Mainly cellulose, provides structural strength.

Function of Cell Wall

  • Allows cells to withstand hypotonic environments without bursting.
  • Provides structural support to plants, fungi, bacteria.

Plasmolysis

  • Definition: Shrinkage of cell contents away from cell wall due to water loss via osmosis in plant cells.

 Nucleus

  • Function: Controls all cell activities, known as the brain of the cell.

Composition of Nucleus

  • Nuclear Membrane: Double-layered covering with pores for material transfer.
  • Chromosomes: Rod-shaped structures visible during cell division.

Functions of Chromosomes

  • Contain DNA: Genetic information for inheritance.
  • Genes: Functional segments of DNA.
  • Chromatin: DNA in non-dividing cells, organizes into chromosomes during division.

Functions of Nucleus

  • Cellular Reproduction: Central role in cell division.
  • Cell Development: Guides chemical activities and determines cell form.

Nucleoid

  • Definition: Found in bacteria, lacks nuclear membrane, contains nucleic acids.

Cytoplasm

  • Definition: Fluid inside plasma membrane containing organelles.
  • Organelles: Specialized structures performing specific cell functions.

Function of Cytoplasm

  • Facilitates material exchange between organelles.
  • Stores vital chemicals like amino acids, glucose, vitamins, and iron.
  • Site of metabolic pathways such as glycolysis.

Endoplasmic Reticulum (ER)
  • Description: Network of membrane-bound tubes and sheets.
  • Structure: Similar to plasma membrane, composed of lipids and proteins.

Types of Endoplasmic Reticulum

  • Rough Endoplasmic Reticulum (RER)
  • Smooth Endoplasmic Reticulum (SER)

Functions of Endoplasmic Reticulum

  • Rough ER: Has ribosomes for protein synthesis, transports proteins to various cell locations.
  • Smooth ER: Manufactures lipids, aids in membrane biogenesis.
  • Produces enzymes, hormones crucial for cell function.
  • Forms a network system aiding material transport within cytoplasm and between cytoplasm and nucleus.
  • Acts as a framework for biochemical activities.
  • In vertebrate liver cells, crucial for detoxification of poisons and drugs.

Golgi Apparatus
  • Description: System of membrane-bound vesicles in stacks called cisterns.
  • Connection: Often linked with ER, part of complex cellular membrane system.

Function of Golgi Apparatus

  • Packages and dispatches materials synthesized near ER to various targets inside and outside the cell.
  • Stores, modifies, and packages products in vesicles, including formation of complex sugars.
  • Involved in the formation of lysosomes.

Lysosomes
  • Description: Membrane-bound sacs filled with digestive enzymes.
  • Function: Serve as waste disposal system of the cell.

Functions of Lysosomes

  • Digest foreign materials like bacteria and worn-out cell organelles.
  • Contain powerful digestive enzymes produced in the RER.
  • Can break down all organic materials.
  • During cellular disturbances or damage, lysosomes may burst, causing enzymes to digest the cell contents—referred to as 'suicide bags' of the cell.

Mitochondria
  • Description: Powerhouses of the cell.

Structure of Mitochondria

  • Two membrane coverings: outer membrane (porous) and inner membrane (deeply folded).
  • Inner membrane folds create large surface area for ATP generation.

Functions of Mitochondria

  • Release energy as ATP molecules for cell's chemical activities.
  • ATP serves as energy currency for making new compounds and mechanical work.
  • Contains own DNA and ribosomes for protein synthesis.

Plastids
  • Description: Present only in plant cells.

Types of Plastids

  • Chromoplasts (colored plastids), Leucoplasts (white or colorless plastids), Chloroplasts (contain chlorophyll).

Structure of Plastids

  • Internal organization: Membrane layers in stroma, containing own DNA and ribosomes.

Function of Plastids

  • Chloroplasts: Essential for photosynthesis, contain chlorophyll and other pigments.
  • Leucoplasts: Store materials like starch, oils, and proteins.

Vacuoles

  • Description: Storage sacs for solid or liquid contents.

Function of Vacuoles

  • Central in plant cells, occupying 50-90% of cell volume, filled with cell sap for turgidity and rigidity.
  • Store amino acids, sugars, organic acids, proteins.
  • In single-celled organisms like Amoeba, food vacuole holds consumed food.
  • Specialized vacuoles expel excess water and waste in some unicellular organisms.

Cell Division

  • Purpose: Forms new cells for growth, replacing old/dead/injured cells, and producing gametes for reproduction.

  • Types of Cell Division:

    • Mitosis: Cells divide for growth and tissue repair; produces two identical daughter cells with the same number of chromosomes as the mother cell.

    • Meiosis: Cells in reproductive organs divide to form gametes (sperm and egg); involves two consecutive divisions, resulting in four daughter cells with half the number of chromosomes compared to the mother cell.

  • Chromosome Reduction in Meiosis:

    • Ensures offspring receive the correct number of chromosomes (half from each parent).
    • Promotes genetic diversity through mixing of genetic material during fertilization.