Biological Membrane

Question 1

List the stages of active transport:

Answer 1

1) The molecule or ion to be transported binds to the receptors in the channel of the carrier protein on the outside of the cell.
2) On the inside of the cell ATP binds to the carrier protein and is hydrolysed into ADP and phosphate.
3) Binding of the phosphate molecule to carrier proteins causes the protein to change shape- opening up to the inside of the cell.
4) The molecule/ ion is released to the inside of the cell.
5) The phosphate molecule is released from the carrier protein and recombines with ADP to form ATP.
6) The carrier protein returns to its original shape.

Question 2

What effects the rate of diffusion?

Answer 2

SA, and the thickness of membrane.

Question 3

What effects the rate of facilitated diffusion?

Answer 3

The rate is dependent on temperature, conc gradient, membrane surface area and thickness, and the number of channel proteins present (the more, the higher the rate of diffusion).

Question 4

What does diffusion across a membrane involve?

Answer 4

Involves particles passing through the phospholipid bilayer. It can only happen if the membrane is permeable to the particles- non-polar molecules such as O2 diffuse through freely down a concentration gradient. The hydrophobic interior of the membrane repels substances with positive or negative charge.

Question 5

Facilitated diffusion

Answer 5

Diffusion across a membrane through protein channels is called facilitated diffusion. Membranes with protein channels are selectively permeable as most proteins channels are specific to one molecule or ion. Facilitated diffusion can also involve carrier protein (active transport) change shape when specific molecule binds. In facilitated diffusion molecules move down a concentration gradient and doesn’t require external energy.

Question 6

Active Transport

Answer 6

The movement of molecule ions into or out of a cell from a region of lower concentration to a region of higher concentration. This process requires energy and carrier proteins. Metabolic energy is supplied by ATP. Carrier proteins span the membrane and act as pumps:

Question 7

Why and when is bulk transport used?

Answer 7

Large molecules such as enzymes, hormones, and whole cells like bacteria are too large to move through channel or carrier proteins (so uses bulk transport instead).

Question 8

Endocytosis

Answer 8

bulk transport of materials into cells. Two types, phagocytosis for solids and pinocytosis for liquids (both have the same process). The cell surface membrane first invaginate (bends inwards) when it comes into contact with the materials to be transported. The membrane enfolds the material until eventually the membrane fuses, forming vesicle. The vesicle pinches off and moves into the cytoplasm to transfer the materials for further processing within the cell.

Question 9

Exocytosis

Answer 9

The reverse of endocytosis.

Vesicles move towards and fuse with the cell surface membrane. The contents of the vesicles are then released outside the cell.

Question 10

Water potential

Units

Answer 10

The tendency of water to move from one place to another, the values are always negative and 0 is the highest possible value
Water potential is measured in (kPa)

Question 11

Osmosis

Answer 11

It is the diffusion of water through a partially permeable membrane from a more dilute solution to a more concentrated solution – down the water potential gradient).

Question 12

What sort of process is osmosis and diffusion

Answer 12

They’re both passive (I.e energy from ATP is not used)

Question 13

Osmoregulation

Answer 13

Is keeping the contraction of cell cytoplasm or blood at a suitable concentration

Question 14

Turgor

Answer 14

is the pressure of the swollen cell contents against the cell wall when the external solution more dilute than the cell sap of the vacuole.

Question 15

What’s the role of turgor in plants

Answer 15

• Mechanical support for soft non-woody tissue, e.g., leaves.
• Change in shape of guard cells forming the stomatal opening between them.
• Enlargement of young immature plant cells to mature size.

Question 16

What’s a partially permeable membrane

Answer 16

barrier that permits the passage of some substances but not others; it allows the passage of the solvent molecules but not some of the larger solute molecules.

Question 17

Why are cell membrane are described as selectively permeable?

Answer 17

because not only do they allow the passage of water but also allow the passage of certain solutes. The presence of particular solutes stimulates the membrane to open specific channels or trigger active transport mechanisms to allow the passage of those chemicals across the membrane.

Question 18

Plants Cells in a hypotonic solution

Answer 18

cells have lower water potential

• the plant cells gain water by osmosis.
• the vacuole and cytoplasm increase in volume.
• the cell membrane is pushed harder against the cell wall causing it to stretch a little.
• the plant tissue becomes stiffer (= turgid)

Question 19

Plant cells in a hypertonic solution

Answer 19

cells have higher water potential

• the plant cells lose water by osmosis.
• the vacuole and cytoplasm decrease in volume.
• the cell shrinks away from the cell wall.
• shrinkage stops when the cell sap is at the same concentration as the external solution.
• the plant tissue becomes flaccid, it has shrunk slightly
• may go on to become plasmolysed.

Question 20

Isotonic

Answer 20

Same water potential

Question 21

Osmosis in animals

Placed with higher water potential than cytoplasm

Answer 21

water molecules move into the cell by osmosis, increasing the hydrostatic pressure inside the cell. All cells have a thin cell surface membrane, cannot stretch much and withstand increased pressure. It will break and the cell will burst (cytolysis).

Question 22

Osmosis in animals

Placed in water potential lower than cytoplasm

Answer 22

it will lose water to the solution by osmosis, down the water potential gradient (causing a reduction in the volume of the cell, and the cell membrane to “pucker”, crenation).

Question 23

Why do multicellular organisms usually have control mechanisms

Answer 23

to make sure cells continuously surrounded by aqueous solution (with equal water potential). Isotonic- same water potential