The Fundamental Unit of Life

Introduction

• The fundamental unit of life is the cell.
• Discovered by Robert Hooke in 1665 using a microscope.
• Cells are the building blocks of all living things.

Types of Organisms

• Unicellular organisms: Made up of one cell (e.g., Amoeba, Chlamydomonas, Paramecium, Bacteria).
• Multicellular organisms: Made up of many cells; develop from a single cell.

Cell Variety and Function

• Different cells perform different functions and have different shapes and sizes due to this.
• Examples: Muscle cells, Blood cells, Nerve cells, Bone cells, Ovum, Sperm cells, Fat cells.
• This organization is known as division of labor.

Basic Cell Structure

• Cells contain cell organelles that perform specific functions.
• Common organelles and their functions:
  • Rough Endoplasmic Reticulum (RER): Protein factory.
  • Smooth Endoplasmic Reticulum (SER): Fat factory.
  • Golgi Apparatus: Packaging and distribution center.
  • Mitochondria: Powerhouse of the cell, produces energy.
  • Vacuoles: Storage compartments.
  • Lysosomes: Digest harmful materials, known as suicide bags.
• Plant cells contain exclusive organelles plastids which assist in photosynthesis.

Internal Cell Structure

Plasma Membrane

• Protects cell components; selectively permeable.
• Performs exchange of gases and other materials via diffusion and osmosis.
• Made up of lipids and proteins.
• Processes like endocytosis are used by organisms like Amoeba to ingest food.

Nucleus

• Enclosed by a nuclear membrane with pores.
• Contains chromatin which forms chromosomes during cell division.
• Chromosomes contain DNA and proteins with functional units called genes.
• Prokaryotic cells lack a nuclear membrane (e.g., Bacteria); Eukaryotic cells have an enclosed nucleus.

Organelle Specific Functions

Endoplasmic Reticulum (ER)

• RER has ribosomes, synthesizes proteins.
• SER synthesizes fats, detoxifies toxins, and drugs.
• Facilitates transport within cell.

Golgi Apparatus

• Modifies, stores, and dispatches materials produced in ER.
• Creates lysosomes.

Lysosomes

• Eliminate waste materials, damaged cell parts, and sometimes the cell itself.

Mitochondria

• Double membrane; inner membrane folded to increase surface area for energy production (ATP).
• Own DNA and ribosomes; can manufacture some of their own proteins.

Special Plant Cell Organelles

Plastids

• Chromoplasts (colored, especially chloroplasts for photosynthesis).
• Leukoplasts (colorless, storage of starch, oils, proteins).

Vacuoles

• Storage of materials; larger in plant cells, providing rigidity and storing important substances.
• Perform vital functions in unicellular organisms.

Cell Division

Mitosis

• Produces two identical daughter cells for growth and repair.
• Ensures each daughter cell receives a full set of chromosomes.

Meiosis

• Produces reproductive cells (gametes) with half the number of chromosomes.
• Involves a two-step division resulting in four cells with half the chromosomes.
• Essential for sexual reproduction (sperm and eggs).

Key Processes and Definitions

• Diffusion: Movement of gas molecules from high to low concentration.
• Osmosis: Movement of water molecules through a selectively permeable membrane from high to low concentration.
• Active Transport: Movement of materials into the cell with energy.
• Endocytosis: Process where a cell engulfs material through its membrane.
• Plasmolysis: Loss of water in plant cells causing shrinkage of the cell contents.