1.1.2
Cell Size & Surface Area
Cell Size
Cell Size
Small size, in general, is necessary for all cells, whether prokaryotic or eukaryotic.
Cell size
Cell size
- At 0.1 to 5.0 μm in diameter, prokaryotic cells are significantly smaller than eukaryotic cells, which have diameters ranging from 10 to 100 μm.
- The small size of prokaryotes allows ions and organic molecules that enter them to quickly diffuse to other parts of the cell.
- Similarly, any wastes produced within a prokaryotic cell can quickly diffuse out.
- This is not the case in eukaryotic cells, which have developed different structural adaptations to enhance intracellular transport.
Importance of size
Importance of size
- Small size, in general, is necessary for all cells, whether prokaryotic or eukaryotic.
- Let’s examine why that is so.
- Not all cells are spherical in shape, but most tend to approximate a sphere.
- You may remember from geometry that the formula for the surface area of a sphere is 4πr2, while the formula for its volume is 4πr3/3.
- Thus, as the radius of a cell increases, its surface area increases as the square of its radius, but its volume increases as the cube of its radius (ie much more rapidly).
Importance of size - 2
Importance of size - 2
- So, as a cell increases in size, its surface area-to-volume ratio decreases.
- This same principle would apply if the cell had the shape of a cube.
- If the cell grows too large, the plasma membrane will not have sufficient surface area to support the rate of diffusion required for the increased volume.
- In other words, as a cell grows, it becomes less efficient.
- One way to become more efficient is to divide; another way is to develop organelles that perform specific tasks.
- These adaptations lead to the development of more sophisticated cells called eukaryotic cells.
Importance of size - example
Importance of size - example
- Notice that as a cell increases in size, its surface area-to-volume ratio decreases.
- When there is insufficient surface area to support a cell’s increasing volume, a cell will either divide or die.
- The cell on the left has a volume of 1 mm3 and a surface area of 6 mm2, with a surface area-to-volume ratio of 6 to 1, whereas the cell on the right has a volume of 8 mm3 and a surface area of 24 mm2, with a surface area-to-volume ratio of 3 to 1.
Size & survival
Size & survival
- As mentioned before, most cells are approximately spherical in shape.
- A sphere is the shape with the largest surface area-to-volume ratio.
- As nutrients diffuse into the cell, a sphere is the shape where nutrients would have to travel the least distance to reach the center.
- This is important because nutrients and wastes are always exchanged at the periphery of the cell.
- The shorter the distance these nutrients and wastes have to travel, the faster the exchange of these molecules are.
1Cell Biology
1.1Introduction to Cells
1.2Ultrastructure of Cells
1.3Membrane Structure
1.4Membrane Transport
1.5The Origin of Cells
2Molecular Biology
2.1Water
2.2Carbohydrates & Lipids
2.3Proteins
2.4Enzymes
2.5Structure of DNA & RNA
2.6DNA Replication, Transcription & Translation
2.7Cell Respiration
2.8Photosynthesis
3Genetics
3.1Genes
3.2Chromosomes
3.3Meiosis
3.4Inheritance
3.5Genetic Modification & Biotechnology
4Ecology
4.1Species, Communities & Ecosytems
4.3Carbon Cycle
5Evolution & Biodiversity
5.1Evidence for Evolution
5.2Natural Selection
5.3Classification of Biodiversity
6Human Physiology
6.1Digestion & Absorption
6.2The Blood System
6.3Defence Against Infectious Disease
6.5Neurons & Synapses
7AHL: Nucleic Acids
7.1DNA Structure & Replication
7.2Transcription & Gene Expression
8AHL: Metabolism, Cell Respiration & Photosynthesis
8.1Metabolism
8.2Cell Respiration
9AHL: Plant Biology
9.1Transport in the Xylem of Plants
9.2Transport in the Phloem of Plants
9.3Growth in Plants
10AHL: Genetics & Evolution
10.1Meiosis
10.2Inheritance
10.2.1Linked Genes
10.2.2Sex-Linked Genes
10.2.3Non-Nuclear Inheritance
10.2.4Chi-Squared Test
10.2.5End of Topic Quiz - Inheritance
10.2.6IB Multiple Choice - Non-Mendelian Genetics
10.2.7Introduction to Non-Mendelian Inheritance
10.2.8Extended Response - Inheritance
10.2.9Grade 4-5 (Scientific Practices) - Inheritance
11AHL: Animal Physiology
11.1Antibody Production & Vaccination
11.3The Kidney & Osmoregulation
Jump to other topics
1Cell Biology
1.1Introduction to Cells
1.2Ultrastructure of Cells
1.3Membrane Structure
1.4Membrane Transport
1.5The Origin of Cells
2Molecular Biology
2.1Water
2.2Carbohydrates & Lipids
2.3Proteins
2.4Enzymes
2.5Structure of DNA & RNA
2.6DNA Replication, Transcription & Translation
2.7Cell Respiration
2.8Photosynthesis
3Genetics
3.1Genes
3.2Chromosomes
3.3Meiosis
3.4Inheritance
3.5Genetic Modification & Biotechnology
4Ecology
4.1Species, Communities & Ecosytems
4.3Carbon Cycle
5Evolution & Biodiversity
5.1Evidence for Evolution
5.2Natural Selection
5.3Classification of Biodiversity
6Human Physiology
6.1Digestion & Absorption
6.2The Blood System
6.3Defence Against Infectious Disease
6.5Neurons & Synapses
7AHL: Nucleic Acids
7.1DNA Structure & Replication
7.2Transcription & Gene Expression
8AHL: Metabolism, Cell Respiration & Photosynthesis
8.1Metabolism
8.2Cell Respiration
9AHL: Plant Biology
9.1Transport in the Xylem of Plants
9.2Transport in the Phloem of Plants
9.3Growth in Plants
10AHL: Genetics & Evolution
10.1Meiosis
10.2Inheritance
10.2.1Linked Genes
10.2.2Sex-Linked Genes
10.2.3Non-Nuclear Inheritance
10.2.4Chi-Squared Test
10.2.5End of Topic Quiz - Inheritance
10.2.6IB Multiple Choice - Non-Mendelian Genetics
10.2.7Introduction to Non-Mendelian Inheritance
10.2.8Extended Response - Inheritance
10.2.9Grade 4-5 (Scientific Practices) - Inheritance
11AHL: Animal Physiology
11.1Antibody Production & Vaccination
11.3The Kidney & Osmoregulation
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