1. Compare the 3 ways in which water and smaller solutes can be transported across the cell membrane. How is this different from bulk transport? 2. Describe how hypotonic, isotonic, and hypertonic solutions affect water balance in cells. 3. What are the two forces directing movement of ions across a membrane? 4. Explain how an electrochemical gradient can facilitate coupled transport. 5. Explain how large particles and molecules such as proteins and polysaccharides cross the plasma membrane. Solution The three ways in which water and smaller molecules can be transported across the cell membrane are, 1). Simple diffusion is a process of passive transport in which molecules diffuse down their concentration gradient. Diffusion of molecules mainly depends on the lipid solubility and their size and polarity. Small molecules such as water, gases such as oxygen, carbon dioxide, ions such as hydrogen ions, etc. can pass through the cell membranes and membranes of cellular organelles by means of simple diffusion. 2). Facilitated diffusion: Facilitated diffusion involves the transport of transport of molecules using the membrane bound proteins. For example, ion channels allow the transport of ions into and out of the cell, which are otherwise, cannot pass through cell membrane. Glucose binds to the carrier molecule present on the cell membrane, and enter into the cell; this process is facilitated by insulin. 3). Active transport: Active transport needs energy, and it help to move ions against their concentration gradients. The concentration of some of the ions is more inside the cell and some is more outside the cell. For example, the concentration of sodium ions is more outside the cell. Still, the sodium ions move from the inside of cell to outside through ion channels, by means of active transport. Bulk transport: It is the transport of macromolecules into and out of the cell by to processes known as Exocytosis or endocytosis. It involves the action of transport vesicles. Eg: Bulk transport of proteins..

1. 1. Compare the 3 ways in which water and smaller solutes can be transported across the cell
membrane. How is this different from bulk transport?
2. Describe how hypotonic, isotonic, and hypertonic solutions affect water balance in cells.
3. What are the two forces directing movement of ions across a membrane?
4. Explain how an electrochemical gradient can facilitate coupled transport.
5. Explain how large particles and molecules such as proteins and polysaccharides cross the
plasma membrane.
Solution
The three ways in which water and smaller molecules can be transported across the cell
membrane are,
1). Simple diffusion is a process of passive transport in which molecules diffuse down their
concentration gradient. Diffusion of molecules mainly depends on the lipid solubility and their
size and polarity.
Small molecules such as water, gases such as oxygen, carbon dioxide, ions such as hydrogen
ions, etc. can pass through the cell membranes and membranes of cellular organelles by means of
simple diffusion.
2). Facilitated diffusion: Facilitated diffusion involves the transport of transport of molecules
using the membrane bound proteins. For example, ion channels allow the transport of ions into
and out of the cell, which are otherwise, cannot pass through cell membrane. Glucose binds to
the carrier molecule present on the cell membrane, and enter into the cell; this process is
facilitated by insulin.
3). Active transport: Active transport needs energy, and it help to move ions against their
concentration gradients. The concentration of some of the ions is more inside the cell and some
is more outside the cell. For example, the concentration of sodium ions is more outside the cell.
Still, the sodium ions move from the inside of cell to outside through ion channels, by means of
active transport.
Bulk transport:
It is the transport of macromolecules into and out of the cell by to processes known as
Exocytosis or endocytosis. It involves the action of transport vesicles. Eg: Bulk transport of
proteins.