Movement Through Cell Membrane

Question 1

diffusion

Answer 1

Movement of substances from an area of high concentration to an area of low concentration
along a concentration gradient
slow process
works quickly over short distance

EXAMPLES

1. oxygen passing from alveoli into blood
2. CO2 passing from blood into alveoli

Question 2

passive process

Answer 2

does not require energy to occur

Question 3

Active Transport:

Answer 3

opposite of diffusion
•The substance goes from an area of low concentration to an area of high concentration. i.e. against the concentration gradient
•It requires energy (ATP) produced by mitochondria
•Cells that do a lot of active transport have many mitochondria

Question 4

osmosis

Answer 4

Movement of water / from an area of high water concentration / to an area of low water concentration / across a selectively permeable membrane

Question 5

Cell membranes

Answer 5

• Selectively permeable
• Controls what enters and leaves the cell
• Water can pass through freely in both directions

Question 6

selectively permeable

Answer 6

only allows certain substances to pass through

Question 7

To Demonstrate Osmosis

Answer 7

1. Take 2 pieces of Visking Tubing (selectively permeable membrane)
2. Put some distilled water into one and tie both ends.
3. Put glucose solution into the other and tie both ends
4. Weigh both tubes and note how full each is.
5. Place both tubes in a beaker of distilled water and leave for 1 hour.
6. Remove both tubes,
   a. Dry with tissue
   b. Weigh
   c. Note how full each is

Question 8

results

Answer 8

• The tube with deionised water weighs the same and is just as full as it was at the start
• The tube with the glucose solution is heavier and is swollen (turgid)

Question 9

conclusion

Answer 9

• Osmosis has occurred.
• Water has passed through the Visking tubing from an area where it (water) is in high concentration to an area where it is in low concentration.

Question 10

Turgor Pressure

Answer 10

the pressure of the cytoplasm and vacuole against the cell wall in plant cells

. Cell contents are more concentrated
. cell placed in a solution with high water concentration water enters the cytoplasm and vacuole
. causes them to swell and push the cell membrane against cell wall
. cell wall prevents cell from bursting
. cell in this state is called turgid pressure produced is called turgor pressure
. animal cell the cell will burst causing lysis

Question 11

Plasmolysis

Answer 11

• If a plant is placed in a solution with a lower water concentration than the cell contents (higher salt concentration).
• Water will move out through the cell membrane by osmosis
• This will cause the cell contents to shrink and the cell membrane will move away from the cell wall
• A plant cell in this condition is said to be plasmolysed

Question 12

Crenation

Answer 12

• If an animal cell (e.g. a red blood cell) is placed in a solution with a lower water concentration than the cell contents (a higher salt concentration)
• Water will move out of the cell by osmosis and the cell will shrink (and become irregular in shape)
• An animal cell in this condition is said to be crenated

Question 13

Wilting

Answer 13

a plant that has drooped due to its cells having lost turgidity due to lack of water is described as wilted

Question 14

Locations of Selectively Permeable Membranes within Cells

Answer 14

1. Around Nucleus
2. Around Chloroplasts
3. Around Mitochondria
4. Around Vacuoles:
5. In plant cells the large permanent vacuole is surrounded by a membrane called the Tonoplast

Question 15

Effects of Osmosis

1. Stomatal opening

Answer 15

• Stomata are the pores in the lower epidermis of leaf
• Allow gases and water vapour to enter and leave the leaf
• Surrounded by 2 cells called guard cells which contain chloroplasts
• When the chloroplasts photosynthesise they produce glucose so the concentration of water decreases
• This causes water to move into them by osmosis causing them to swell and the stomata to open
• At night glucose is used in respiration so the concentration of water increases causing water to move out, so the cells become flaccid and the stomata close

Question 16

2. Root pressure

Answer 16

• Water enters root hair by osmosis as cell contents are more concentrated than soil water
• This water dilutes the cell contents, so it is less concentrated than the cell inside it (water concentration is higher)
• Water therefore moves into the next cell inside and so on till it reaches the xylem
• There is now more water in the xylem, so water is forced up the xylem
• Tis is called root pressure

Question 17

3. In kidneys

Answer 17

• Water and substances dissolved in it are forced through the pores in capillaries into Bowman’s capsule.
• From here it passes into the proximal Convoluted tubule
• As it passes through the tubule dissolved substances pass back into capillaris by diffusion (high conc. To low conc.) with the concentration gradient
• Until concentratios are the same
• From this point on active transport is needed to push the dissolved substance against the concentration gradient
• Energy is needed for this so the cells on the PCT have many mitochondria to provide the energy required for this.
• Water passes through the wall into nearby capillaries by osmosis.

Question 18

Applications of Osmosis: Food Preservation

Answer 18

salting

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