Shape, Size and Function in Microalgae

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• Shape, Size and Function in Micro-algae
• Micro-algae - huge diversity
• Challenges of life in the aquatic
  environment
• Adaptations to those challenges
• A laboratory exercise

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1 / 100 mm 10 µm
1 / 10 mm
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1 / 100 mm
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1 / 100 mm
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1 / 100 mm
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Very dilute nutrients nitrate, phosphate
arrrrgghhh!
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Extremely low concentrations of nutrients
Warm
More highly concentrated nutrients
Cold
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Which alga is best at supplying itself with
mineral nutrients?
Spheres of increasing size
Cylinder the same volume as the middle sphere
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Diameter Surface area Volume S / V
µm µm2
µm3
1 3.1
0.5 6 10 310
520 0.6 100
31,400 524,000 0.06
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Diameter Surface area Volume S / V
µm µm2
µm3
1 3.1
0.5 6 10 310
520 0.6 100
31,400 524,000 0.06
50 long 595 520
1.1
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Which alga is best at reducing the speed of
sinking?
arrrrgghhh!
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V
Diameter 1 10
100
Sinking rate 1 100
10,000
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All the same volume
Increasing Form resistance
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Extremely low concentrations of nutrients
Ease of movement through the water an advantage.
Warm
More highly concentrated nutrients
Cold
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Daily vertical migration of Volvox
Time4 pm
4 am
Light
0
Temp.
Depthm
Nutrients
50
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Which alga is best at avoiding being eaten?
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0.5 mm
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Chlorella - small and spherical

• Absorbs nutrients efficiently
• Sinks very slowly
• Is easily eaten by Daphnia

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Scenedesmus - intermediate size and
non-spherical

• Absorbs nutrients quite efficiently
• Sinks quite slowly
• Is eaten with some difficulty by Daphnia

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Volvox very large, spherical and able to move
itself using flagella

• Slow growth, inefficient nutrient absorption
• In summer when water is stratified it can
  move up to the light and down to nutrients
• Cannot be eaten by Daphnia

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