1.5

1.5 Ions and Living Cells

• Ions = positively or negatively charged

particles that are formed when certain

substances dissolve in a solvent.

• Example: Salt dissolving in water

becomes Na+ and Cl - ions

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1.5 Ions and Living Cells

• Water ionizes from H2O into:

H+ and OH - (hydroxide) ions

• Acids have a higher level of H+ ions

than OH - ions

• Bases have a higher level of OH - than

H+ ions

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1.5 Ions and Living Cells

A. Table salt example

• NaCl, in water, dissociates into Na+ and Cl–

• They remain as ions due to water’s polarity

• Sodium ions (Na+) are very important in

water balance in organisms

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B. Ionization Occurs when a non-ionic compound

is converted into ions

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C. pH Scale - converts the amount of H+ ions into

a number from 0 - 14

1. Neutral solutions - have equal numbers of

H+ and OH– ions .

• They have a pH of 7

2. Acidic solutions - have more H+ than OH– ions.

• They have a pH that is less than 7.

3. Alkaline (Basic) solutions - have more OH–

than H+ ions.

• They have a pH that is greater than 7

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C. pH Scale - converts the amount of H+ ions into

4. Logaritmic scale - a change of one pH unit is a

change of 10x the amount of H+

• ex: pH of 3 is 10 times more acidic than pH 4

• ex. pH of 3 is 100 times more acidic than a pH 5

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D. Biological importance of pH

• Cells must carry out chemical

reactions and most reactions

require a specific pH

• all organisms have mechanisms to

regulate pH

• each cell type (and sometimes

organism) has a specific pH in

which to operates.

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Buffers

Take a minute or two & write down a

description of what a buffer is and what

it does IN YOUR OWN WORDS.

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What is a buffer?

• ***A buffer maintains the pH of a system

even when external conditions threaten

to change pH.

• ***In effect, this means that small

additions of acid or base to a buffered

solution DON’T cause pH changes (or

only slight changes in pH).

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***How do buffers work?

• When hydrogen ions (acid) are added

to a buffer, they will be neutralized by

the base (OH- ions) in the buffer.

Hydroxide ions (base added) will be

neutralized by the acid (H+ ions).

• The result is to protect the original

solution from pH changes when small

amounts of acids or bases are added. 12

Why are buffers important?

Stable pH allows chemical reactions to

occur

Cells have natural buffers that help

maintain the cell’s typical pH; this

protects the internal environment.

Different types of buffers are effective

within different ranges. 13

Buffers

Buffers are specific to the type of cell,

tissue, or organ where they are found,

and specific to the role they have in

maintaining pH.

Blood must be kept between a pH of 7.35

to 7.45

CO2 + H2O ---> H2CO3 (carbonic acid

Could cause change in blood pH

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Acidosis and Alkalosis

• Acidosis: blood pH falls below 7.35

– Depression of CNS

– Below 7.0 = coma and/or death

• Alkalosis: blood pH above 7.45

– Results in spasms or convulsions

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Buffers

• Different buffers work better under

specific external and internal conditions.

• Example:

Stomach cells = pH 2

Blood = pH 7.35-7.45

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Limitation of buffers

• Buffers can be used up if too much acid

or base is added

• Once buffers are used up, greater

changes will occur in the pH