Movement of membrane across plasma membrane



    greater than it inside.
Filtration Hydrostatic       pressure     forces     small

molecules            across            selectively
permeable membranes from areas of

higher    pressure     to   areas    of    lower

A frog’s blood         pressure

forces           water          and
dissolved wastes into the

kidney        tubules      during
urine formation.

Active transport Specific carrier proteins in the plasma membrane bind with molecules or ions

to help them cross the membrane against concentration gradient. Energy is required

Sodium ions move from inside the neurons of the

sciatic    nerve    of   a    frog

(the          sodium-potassium
pump) to the outside of the neurons.

Endocytosis The bulk movement of material into

the   cell    by   formation    of   vesicle     is
called endocytosis.

Pinocytosis The plasma membrane encloses small amounts of fluid droplets (in a vesicle) and takes the n into the cell. The kidney cells of frog



take   in   fluid   to   maintain
fluid balance.

Phagocytosis The plasma membrane forms a vesicle around a solid particle or other cell and draws it into the phagocytic cell. The white blood cells of a frog engulf and digest – harmful bacteria.
Receptor- mediated • endocytosis Extracellular      molecules       bind      with

specific receptor proteins on a plasma membrane, causing the membrane to

invaginate     and   draw    molecules    into

the cell.    .

The   intestinal        cells of a

frog       take       up      large
molecules from the inside of the gut

Exocytosis The movement of material out of a

  1. A    vesicle   (with   particles)   fuses
    with the plasma membrane and expels particles or fluids from the cell across the plasma membrane.
The   sciatic    nerve    of a

frog releases a chemical (neurotransmitter)


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