Cells Why are cells small?. Surface area to volume ratio and cell size Cell size is limited by the...
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Transcript of Cells Why are cells small?. Surface area to volume ratio and cell size Cell size is limited by the...
CellsWhy are cells small?
Surface area to volume Surface area to volume ratio and cell sizeratio and cell size
Cell size is limited by the surface area to volume ratio
As an object increases in volume, so does it’s surface area but not at the same rate.
Biological significanceBiological significance
Cell volume determines amount of activity in a given amount of time.
The surface area determines the amount of material that can be moved into and out of a cell
Cells must maintain a large surface area to volume ratio to function
This explains why large animals have many small cells rather than a few large ones
How Cells Get How Cells Get Around the SA/V Around the SA/V
ProblemProblem
Avoidance - stay small Small size maximizes surface area to
volume Allows most efficient import/export
possible. Small cells can gather nutrients and
reproduce extremely rapidly Examples - bacteria, yeasts
Geometric SolutionsGeometric Solutions
Increase surface area
1.Elongate or flatten out A sphere has a low SA/V ratio. Cells
that are drawn out (e.g. cylinder), or flattened have much more membrane per unit of cytoplasm.
Examples - Eubacteria, red blood cells
2. Fold the surface membrane
Extending the outer surface of a cell into folds, fingers or indentations increases the total surface area by a factor of several times
Examples – amoeba, intestinal cells (microvilli)
Decrease effective Decrease effective volumevolume
Hollow out centre of cell
A cell with a large water-filled vacuole in the center has much less active cytoplasm than its measurements would suggest. Its metabolic demands are therefore not as great.
Example - Mature plant cells
Increasing rate of Increasing rate of supplysupply
1. Seek out areas where nutrient concentration is high
Mobile cells can avoid areas with sparse nutrients and actively seek areas where nutrient concentration is high
2. Actively acquire bulk nutrients
By taking in food in vacuoles, cells increase their total imports and provide themselves with small, extremely rich bubbles of nutrients.
Examples – amoeba, paramecium, intestinal villi
3. Improve transportation of nutrients within cell
By moving nutrients rapidly away from the membrane, concentrations gradients across the membrane can be maintained.
Improving efficiency to Improving efficiency to reduce demandreduce demand
1. Division of labour within cell
The complex organelles of Eukaryotic cells allow them to have specialized areas in the cytoplasm to. The cell is much more efficient.
2 Division of labour between cells
Form tissues – by joining together cells can form an organism that can have a large size. Each cell can specialize and maintain mutual dependent relationship with the other cells of the organism (homeostasis)
Example - Plants, animals, fungi, some algae