Biology Class on Onion Cells

Study Notes

Cell Structures and Discoveries

Onion bulbs and other organisms consist of cells, which serve as their fundamental building blocks.
Cells were first identified by Robert Hooke in 1665 using a primitive microscope with cork slices.
Leeuwenhoek observed free-living cells in pond water in 1674 with an improved microscope.
Robert Brown discovered the nucleus in 1831.
Protoplasm, the cell's fluid, was named by Purkinje in 1839.
Cell theory was proposed by Schleiden (plants) and Schwann (animals) in 1838-1839, stating that all living things are composed of cells.
Virchow expanded the cell theory in 1855, asserting that all cells arise from pre-existing cells.
The electron microscope, invented in 1940, allowed detailed study of cell structures and organelles.

Unicellular vs. Multicellular Organisms

Unicellular organisms, such as Amoeba and bacteria, consist of a single cell.
Multicellular organisms are composed of many cells, which specialize to perform different functions.

Cell Functionality and Organization

Cells perform basic life functions through specific structures known as organelles.
Major components visible in almost every cell include the plasma membrane, nucleus, and cytoplasm.
The plasma membrane is selectively permeable, regulating entry and exit of materials.

Membrane Transport Mechanisms

Diffusion allows substances to move from high to low concentration, essential for gas exchange (e.g., oxygen and carbon dioxide).
Osmosis is the diffusion of water across a selectively permeable membrane, vital in both unicellular organisms and plant cells.
Cells can actively transport nutrients and other substances, which may require energy.

Plasma Membrane and Cell Wall

The plasma membrane is flexible, composed of lipids and proteins, allowing food intake through endocytosis.
Plant cells also possess a cell wall made of cellulose, providing structural strength.
Plasmolysis occurs when plant cells lose water, causing contraction away from the cell wall.

Nucleus and Genetic Material

The nucleus contains chromosomes, which hold DNA—the genetic material crucial for inheritance.
Chromatin exists in non-dividing cells as tangled threads; it organizes into chromosomes during cell division.
Prokaryotic cells, like bacteria, have undefined nuclear regions (nucleoid) and lack a nuclear membrane, while eukaryotic cells have well-defined nuclei.

General Cell Properties

Basic functions of living cells include growth, reproduction, and response to stimuli.
Organelles perform specific roles, allowing division of labor not only within multicellular organisms but also within individual cells.

Description

Explore the fascinating world of onion cells through this quiz. Delve into the similarities and structures visible under the microscope, revealing how all onion bulbs share basic cellular characteristics. Test your knowledge on cell structures and their significance in biology.