The plasma membrane is both a barrier and gateway between the cytoplasm and ECF.

It is selectively permeable—it allows some things through, such as nutrients and wastes, but usually prevents other things, such as proteins and phosphates, from entering or leaving the cell.

The methods of moving substances through the membrane can be classified in two overlapping ways:

as passive or active mechanisms and as carrier-mediated or not.

Passive mechanisms require no energy (ATP) expenditure by the cell.

In most cases, the random molecular motion of the particles themselves provides the necessary energy.

include filtration, diffusion, and osmosis.

, however, consume ATP. These include active transport and vesicular transport.

Carrier-mediated mechanisms use a membrane protein to transport substances from one side of the membrane to the other

but some transport processes, such as osmosis, do not involve carriers.

Filtration is a process in which a physical pressure forces fluid through a selectively permeable membrane. A coffee filter is an everyday example.

The weight of the water drives water and dissolved matter through the filter, while the filter holds back larger particles (the coffee grounds).

In physiology, the most important case of filtration is seen in the blood capillaries, where blood pressure forces fluid through gaps in the capillary wall (Fig. 3.13).

This is how water, salts, nutrients, and other solutes are transferred from the bloodstream to the tissue fluid and how the kidneys filter wastes from the blood.

Capillaries hold back larger particles such as blood cells and proteins. In most cases, water and solutes filter through narrow gaps between the capillary cells.

In some capillaries, however, the cells have large filtration pores through them, like the holes in a slice of Swiss cheese, allowing for more rapid filtration of large solutes such as protein hormones.

in capillary forces water and small solutes such as salts through narrow clefts between capillary cells.

Filtration Through the Wall of a Blood Capillary.

Water and small solutes pass through gaps between cells, while blood cells and other large particles are held back.

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3.3a

Question	Answer
One of the most important functions of ----- is to control the passage of materials into and out of the organelles and the cell as a whole.	cellular membranes
The plasma membrane is both a barrier and gateway between the cytoplasm and ECF.	It is selectively permeable—it allows some things through, such as nutrients and wastes, but usually prevents other things, such as proteins and phosphates, from entering or leaving the cell.
The methods of moving substances through the membrane can be classified in two overlapping ways:	as passive or active mechanisms and as carrier-mediated or not.
Passive mechanisms require no energy (ATP) expenditure by the cell.	In most cases, the random molecular motion of the particles themselves provides the necessary energy.
Passive mechanisms	include filtration, diffusion, and osmosis.
Active mechanisms	, however, consume ATP. These include active transport and vesicular transport.
Carrier-mediated mechanisms use a membrane protein to transport substances from one side of the membrane to the other	but some transport processes, such as osmosis, do not involve carriers.
Filtration is a process in which a physical pressure forces fluid through a selectively permeable membrane. A coffee filter is an everyday example.	The weight of the water drives water and dissolved matter through the filter, while the filter holds back larger particles (the coffee grounds).
In physiology, the most important case of filtration is seen in the blood capillaries, where blood pressure forces fluid through gaps in the capillary wall (Fig. 3.13).	This is how water, salts, nutrients, and other solutes are transferred from the bloodstream to the tissue fluid and how the kidneys filter wastes from the blood.
Capillaries hold back larger particles such as blood cells and proteins. In most cases, water and solutes filter through narrow gaps between the capillary cells.	In some capillaries, however, the cells have large filtration pores through them, like the holes in a slice of Swiss cheese, allowing for more rapid filtration of large solutes such as protein hormones.
Blood pressure	in capillary forces water and small solutes such as salts through narrow clefts between capillary cells.
Filtration Through the Wall of a Blood Capillary.	Water and small solutes pass through gaps between cells, while blood cells and other large particles are held back.

Created by: Russells3709

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