Questions and Answers
Who discovered cells and how?
Robert Hooke discovered cells by observing a cork slice under a primitive microscope.
Why is the cell called the structural and functional unit of life?
The cell is called the structural and functional unit of life because all organisms are made up of cells, which perform all necessary life functions.
The outermost covering of the cell is called the ______.
plasma membrane
What is the movement of water molecules through a selectively permeable membrane called?
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What happens during plasmolysis in plant cells?
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What are chromosomes made up of?
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All unicellular organisms are multicellular.
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What term did Purkinje coin for the fluid substance of the cell?
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What is the process by which cells divide to produce new cells called?
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Which of the following are eukaryotes?
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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.
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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.
