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Population levels are controlled by:

1.

Quantity and diversity of materials

-

minimum

requirements

2. 3. 4.

A. Solutes and WaterActivity

Critical abiotic factors

B. Temperature

Tolerance limits of organisms

C. Pressure

Biotic factors

D. Radiation

Physical factors affecting distribution of m/os

Physical factors affecting distribution of m/os

A. Solutes

an-d Water

Activity

.

Affected by changes in osmotic concentration

.

Hypotonic solution (lower osmotic conc.):

' .

Water enter cell

Strategy:

)

)

Hypertonic solution (higher osmotic conc.): shrinks the cell (plasmolysis)

- Water leaves

-

cell burst

+fhwlw vacuoles Wn

&

)

Strategy:

F

MJclranosensitive (MS) channels Protozoa: contractile

)

.

Having compatible solutes

to

intracellular concentrations which can metabolism and growth.

F

ubr"ryr*t

increase

be used for

E.g. increase uptake/synthesis of 6;;;,.

betaine, proline, and etc.

hf ,r'tP

Physical factors affecting OistriUution of m/os

it.

Physical factors affecting distribution of m/os

A. Solutes and WaterActlvitv

- Amount

of water available to m/os can be reduced

by

(a) interaction with solute molecules (osmotic effect) (b) adsorption to the surfaces of solids

-

Quantity of water availability = water activity/water potential (a*)

-

High osmotic pressure

)

a,

is low

Pure water, 3w = 1.0 Honey, aw = 0.6

- Difficulty for m/os to grow at low a* - Mostly grow at ?* = 0,9 and above. - Bacteria; 0.9 - 0.91


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