Transport in Cells

Question 1

What is the importance of cell transport

Answer 1

In order to survive, cell must be supplied with all substances it needs and waste substances, or substances for export, leave the cell through cell membrane. All functions maintain homeostasis of the cell

Question 2

Define passive transport

Answer 2

During passive transport, substances move according to their own natural tendency without input of energy from the cell

Question 3

Define simple diffusion

Answer 3

Simple diffusion is the net movement of a substance from an area of higher concentration to an area of lower concentration (i.e. down a concentration gradient), until equilibrium is reached

Question 4

What causes simple diffusion

Answer 4

Caused by the constant random motion of all atoms and molecules, caused by kinetic energy of molecules. Diffusion results in equilibrium

Question 5

What are the factors affecting rate of diffusion

Answer 5

Concentration gradient, distance over which diffusion occurs, surface area to volume ratio over which diffusion occurs

Question 6

Define facilitated diffusion

Answer 6

Facilitated diffusion is the diffusion of ions and water-soluble molecules across the cell membrane using two types of transport proteins, channel proteins or carrier proteins, down a concentration gradient

Question 7

What are the characteristics of facilitated diffusion

Answer 7

Its a passive process with no energy required, once all transport proteins are in use, rate of diffusion cannot be increased further

Question 8

Describe function of channel proteins

Answer 8

Provides hydrophilic channel across membrane for ions or hydrophilic molecules to enter or leave the cell. Specific for molecules that can move across membrane.

Question 9

Describe function of carrier proteins

Answer 9

Diffusing substances bind temporarily to the carrier protein, causing it to change shape to transport the substances across the membrane, change in shape may be trigger by binding and release of the particles

Question 10

Define osmosis

Answer 10

Osmosis is the net movement of water molecules from a solution of higher water potential to a solution of lower water potential, through a partially permeable membrane

Question 11

What is water potential

Answer 11

A measure of tendency of water to move from one region to another

Question 12

Describe what happens when plant cells are placed in a diluted solution

Answer 12

Diluted solution has higher water potential than cell sap, water enters plant cells by osmosis. Vacuole swells, pushes cytoplasm and cell membrane against cell wall. Cells become turgid. Cells do not lyse because of rigid cell wall. Pressure exerted by vacuole on cell wall is turgor pressure. Important for plant as it keeps the plant firm and upright, leaves can spread out more. Helps in opening of stomata

Question 13

Describe what happens when plant cells are placed in a concentrated solution

Answer 13

Concentrated solution has lower water potential than cell sap, water leaves cells by osmosis. Vacuole decreases in volume and size and cytoplasm and cell membrane pull away from cell wall. Cell becomes plasmolysed, withdrawal of cell membrane from cell wall is called plasmolysis and reversible if full plasmolysis is not reached. Space between cell wall and cell membrane filled with surrounding solution. Plant starts to wilt as turgor pressure in plant cells decreases

Question 14

What is the condition of animal cells when placed in dilute/concentrated solution

Answer 14

Water enters, cell swells and may burst(dilute–>lysis)
Water leaves, cell shrinks, crenates (concentrated)

Question 15

What are some ways organisms deal with problem of osmosis

Answer 15

Unicellular organisms constantly expel water using contractile vacuoles
Organisms in marine environment must actively pump ions into cells to reduce water potential to reduce water loss by osmosis
Young non-woody plants require cell turgor for support and must actively pump ions into root hair cells to lower water potential so water does not leave by osmosis

Question 16

Define active transport

Answer 16

Active transport is the movement of ions or molecules across cell membrane from region of lower concentration to region of higher concentration(i.e. against concentration gradient) with expenditure of energy from ATP molecule by cell

Question 17

What is the importance of active transport

Answer 17

Allows cells to take up nutrients when concentrations outside cells are lower than inside of cells
Allows cells to get rid of waste products when concentrations outside cell are higher than those inside of cells

Question 18

Describe how the sodium-potassium pump works

Answer 18

An animal cell needs to maintain much higher concentration of potassium ions and much lower concentration of sodium ions compared to surroundings. Cell maintains this using active transport, pumping sodium ions out and potassium ions into cell. Carrier protein used is sodium-potassium pump, ATP is required for carrier protein to change shape. Three sodium ions exchanged for two potassium ions

Question 19

Define bulk transport and uses

Answer 19

Bulk transport is transport of materials in or out of cell by enclosing it within a vesicle
Allows large molecules or large quantities of molecules to enter or leave cell without passing through membrane
Active process as requires expenditure of energy by the cell

Question 20

Describe endocytosis

Answer 20

Endocytosis occurs when substances taken into cells by inward folding of cell membrane to form vesicles that separate from membrane with ATP used to provide energy during the process.

Question 21

Describe phagocytosis

Answer 21

The process of engulfing or ingesting foreign particles by phagocytes. Key feature is formation of pseudopodia, temporary protrusions of cell membrane. Vesicles formed after phagocytosis fuse with lysosomes. Hydrolytic enzymes in lysosomes digest engulfed foreign particles

Question 22

Describe exocytosis

Answer 22

Exocytosis occurs when substances in secretory vesicles move towards and fuse with the cell membrane and releases the contents of the vesicle into fluid around the cell. ATP is used to provide energy during the process