2.2.2
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.
1Unity & Diversity - Molecules
1.1Water
1.2DNA Structure & Replication
1.3Transcription & Gene Expression
2Unity & Diversity - Cells
2.1The Origin of Cells
2.2Introduction to Cells
2.3Ultrastructure of Cells
2.4Cell Division
2.5Structure of DNA & RNA
2.6DNA Replication, Transcription & Translation
2.7Cell Respiration
2.8Photosynthesis
2.9Viruses
3Unity & Diversity - Organisms
3.1Diversity of Organisms
3.2Evidence for Evolution
4Unity & Diversity - Ecosystems
4.1Classification
4.3Evolution & Speciation
4.3.1Evidence for Evolution - Fossils & DNA
4.3.2Evidence for Evolution - Anatomy & Geography
4.3.3IB Multiple Choice - Evidence for Evolution
4.3.4Extended Response - DNA & Evolution
4.3.5Populations
4.3.6Mutations, Genetic Drift, & Gene Flow
4.3.7Speciation
4.3.8Rate of Speciation
4.3.9Allopatric & Sympatric Speciation
4.4Conservation of Biodiversity
5Form & Function - Molecules
6Form & Function - Cells
6.1Membranes & Membrane Transport
6.2Organelles & Compartmentalization
6.3Cell Specialization
7Form & Function - Organisms
7.2Transport
7.3Muscle & Motility
8Form & Function - Ecosystems
8.1Species, Communities & Ecosytems
8.3Carbon Cycle
9Interaction & Interdependence - Molecules
9.1Enzymes
9.2Metabolism
9.3Cell Respiration
10Interaction & Interdependence - Cells
10.1Chemical Signalling
10.2Neural Signalling
10.3Adaptation to Environment
10.4Ecological Niches
11Interaction & Interdependence - Organisms
11.1Integration of Body Systems
12Interaction & Interdependence - Ecosystems
12.1Populations & Communities
12.2Transfers of Energy & Matter
13Continuity & Change - Molecules
13.1DNA Replication
13.2Protein Synthesis
14Continuity & Change - Cells
15Continuity & Change - Organisms
15.1Inheritance
15.1.1Non-Nuclear Inheritance
15.1.2Linked Genes
15.1.3IB Multiple Choice - Non-Mendelian Genetics
15.1.4Extended Response - Inheritance
15.1.5Introduction to Non-Mendelian Inheritance
15.1.6Chi-Squared Test
15.1.7End of Topic Quiz - Inheritance
15.1.8Sex-Linked Genes
15.1.9Grade 4-5 (Scientific Practices) - Inheritance
16Continuity & Change - Ecosystems
16.1Natural Selection
16.2Stability & Change
Jump to other topics
1Unity & Diversity - Molecules
1.1Water
1.2DNA Structure & Replication
1.3Transcription & Gene Expression
2Unity & Diversity - Cells
2.1The Origin of Cells
2.2Introduction to Cells
2.3Ultrastructure of Cells
2.4Cell Division
2.5Structure of DNA & RNA
2.6DNA Replication, Transcription & Translation
2.7Cell Respiration
2.8Photosynthesis
2.9Viruses
3Unity & Diversity - Organisms
3.1Diversity of Organisms
3.2Evidence for Evolution
4Unity & Diversity - Ecosystems
4.1Classification
4.3Evolution & Speciation
4.3.1Evidence for Evolution - Fossils & DNA
4.3.2Evidence for Evolution - Anatomy & Geography
4.3.3IB Multiple Choice - Evidence for Evolution
4.3.4Extended Response - DNA & Evolution
4.3.5Populations
4.3.6Mutations, Genetic Drift, & Gene Flow
4.3.7Speciation
4.3.8Rate of Speciation
4.3.9Allopatric & Sympatric Speciation
4.4Conservation of Biodiversity
5Form & Function - Molecules
6Form & Function - Cells
6.1Membranes & Membrane Transport
6.2Organelles & Compartmentalization
6.3Cell Specialization
7Form & Function - Organisms
7.2Transport
7.3Muscle & Motility
8Form & Function - Ecosystems
8.1Species, Communities & Ecosytems
8.3Carbon Cycle
9Interaction & Interdependence - Molecules
9.1Enzymes
9.2Metabolism
9.3Cell Respiration
10Interaction & Interdependence - Cells
10.1Chemical Signalling
10.2Neural Signalling
10.3Adaptation to Environment
10.4Ecological Niches
11Interaction & Interdependence - Organisms
11.1Integration of Body Systems
12Interaction & Interdependence - Ecosystems
12.1Populations & Communities
12.2Transfers of Energy & Matter
13Continuity & Change - Molecules
13.1DNA Replication
13.2Protein Synthesis
14Continuity & Change - Cells
15Continuity & Change - Organisms
15.1Inheritance
15.1.1Non-Nuclear Inheritance
15.1.2Linked Genes
15.1.3IB Multiple Choice - Non-Mendelian Genetics
15.1.4Extended Response - Inheritance
15.1.5Introduction to Non-Mendelian Inheritance
15.1.6Chi-Squared Test
15.1.7End of Topic Quiz - Inheritance
15.1.8Sex-Linked Genes
15.1.9Grade 4-5 (Scientific Practices) - Inheritance
16Continuity & Change - Ecosystems
16.1Natural Selection
16.2Stability & Change
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