Cell Theory and Cell Size

The Cell Theory

1. All living organisms are composed of cells: Whether it's a single-celled organism, like bacteria or protists, or a complex multicellular organism, such as plants, animals, and humans, all living things are made up of cells.

2. The cell is the basic unit of structure and function in living organisms: Cells are the smallest units of life and carry out all the processes necessary for life, such as metabolism, growth, reproduction, and responding to stimuli. Each cell is capable of performing its functions independently or as part of a larger organism.

3. All cells arise from pre-existing cells: Cells do not spontaneously generate but come from division and reproduction of existing cells. This concept was articulated by Rudolf Virchow in the mid-19th century with his famous phrase "omnis cellula e cellula," which means "every cell stems from another cell."

The cell theory, developed over several centuries by scientists like Robert Hooke, Theodor Schwann, Matthias Schleiden, and others, revolutionized our understanding of life and formed the basis for modern biology. It provides a framework for studying the structure, function, and behavior of living organisms at the cellular level.

Cell Size

Why must cells remain small?

1. Surface area to volume ratio: As a cell grows larger, its volume increases more rapidly than its surface area. This ratio is crucial because the cell membrane (surface area) needs to effectively manage the exchange of nutrients, gases, and waste. A smaller cell has a higher surface area to volume ratio, allowing for more efficient exchange across the cell membrane.

2. Nutrient absorption: Smaller cells have an advantage in absorbing nutrients. Their smaller size allows for quicker and more efficient diffusion of substances across the cell membrane, ensuring that essential nutrients reach the interior of the cell rapidly.

3. Metabolic efficiency: Cells need to maintain a balance between their metabolic activities and the resources available. Smaller cells have a higher metabolic efficiency as they require fewer resources to sustain themselves. Nutrients and energy can be utilized more effectively in smaller cells compared to larger ones.

4. Transportation within the cell: Smaller cells facilitate faster transportation of molecules and organelles within the cell. Substances can move more swiftly across shorter distances, enhancing the overall efficiency of cellular processes.

5. Cellular communication: Cells need to communicate with each other efficiently. Smaller cell size aids in faster intercellular communication, allowing cells to respond more rapidly to signals and changes in their environment.

All Cells Have Three Basic Features:

1. Plasma Membrane (cell Membrane, phospholipid bilayer)
2. Genetic Material (DNA)
3. Cytoplasm (cytosol)
4. Ribosomes (protein synthesis)
5. Cytoskeleton (support, movement,shape)

Endosymbiosis Theory

Eukaryotic cells arose from prokaryotic cells. The mitochondria found in today's eukaryotes evolved from aerobic bacteria and that the chloroplasts found in today's plant cells arose from cyanobacteria

Prokaryotes

• no membrane bound nucleus, chromosomes grouped together in an area called the "nucleoid"
• no membrane bound organelles
• smaller than eukaryotes

Eukaryotes

• has a membrane bound nucleus
• organelles (mitochondria, endoplasmic reticulum, golgi body)
• plants, animals, fungi, protista