4.1 Cell Transport Mechanisms

Question 1

why are transport systems needed in cells

Answer 1

-cells require a supply of chemicals like glucose or oxygen for cellular respiration
-respiration is what supplies us with energy for the other reactions of life, and produces waste product carbon dioxide
-waste products need to be removed

Question 2

what is the role of the cell surface membrane

Answer 2

acts as a gatekeeper for the cell and controls the transport of materials into and out of the membrane
also control transport within the cells, e.g ER and golgi apparatus are membrane bound organelles that control the movement of substances within the cell

Question 3

what are the roles of the following structures within the cell
-glycoproteins
-peripheral proteins
-membrane bilayer
-integral proteins

Answer 3

• Gly. often act as antigens, important for cell recognition or hormone receptors
• Per. may be enzymes, involved in regulating transport
• Bil. fluid bilayer of phospholipids, the polar heads face the inside and outside of the cell, with a hydrophobic lipid core
• Int. main transport system of the membranes, forming permanent

Question 4

what is the difference between active and passive transport

Answer 4

Passive transport takes place as a result of concentration or pressure gradients and involves no energy whilst active transport requires (ATP) adenosine trio phosphate

Question 5

name and define the three modes of passive transport

Answer 5

Diffusion- movement of particles in a liquid or gas from an area of relatively high concentration to an area of relatively low concentration
Facilitated diffusion- Diffusion that takes place through carrier proteins or the protein lined pores in the cell membrane
Osmosis- the movement of solvent molecules down a concentration gradient through a partially permeable membrane

Question 6

name and define the three modes of active transport

Answer 6

Endocytosis- the movement of large molecules into cells through vesicle formation
Exocytosis- The movement of large molecules out of cells through vesicle formation
Active transport- the direct movement of substances across a cell membrane using ATP produced in cellular respiration

Question 7

name the factors that affect how a molecule would be transported across a membrane

Answer 7

• the size of the molecule
• its solubility in lipids and water
• the presence of absence of charge

Question 8

give examples of small molecules, a large molecule and a charged particle

Answer 8

Small - oxygen and carbon dioxide (pass freely)
Large - steroid hormones
Charged - sodium ions

Question 9

Define diffusion and state WHY it happens

Answer 9

The movement of molecules from an area of high concentration to an area of low concentration

This is due to the random movement that occurs because of the energy they have, which is dependent on the temperature

Question 10

which molecules can and can’t move across a membrane by simple diffusion

Answer 10

Can - oxygen and carbon dioxide because they’re small
Can’t - anything larger than carbon dioxide, and ions

Question 11

Which molecules move by facilitated diffusion

Answer 11

anything with a strong positive or negative charge or large molecules

Question 12

How does facilitated diffusion work by gated channels

Answer 12

Large or charged molecules e.g. amino acids move across the cell membrane down a concentration gradient
using the specific proteins in the membrane (that form pores) that only allow specific substances to move through passively by changing shape

Question 13

what is a gated channel

Answer 13

Channels that only open only when specific molecules are present or when there’s an electrical charge across the membrane e.g. passing of nerve impulses

Question 14

describe the form of facilitated diffusion that occurs with carrier proteins found floating around the surface of the membrane

Answer 14

the carrier proteins are found on the outside of the cell when there is a higher conc. pf the molecule on the outside (and visa versa)
the carrier proteins are specific to each molecule or group of molecules
the proteins pick up the molecule, change shape, transport it through the membrane an release it
it does not require energy

Question 15

define osmosis

Answer 15

the net movement of molecules from a region of high concentration to a region of low concentration through a partially permeable membrane

Question 16

what is considered when finding the osmotic concentration

Answer 16

the osmotic concentrations concerns only the solutes that have an osmotic effect. Many large, insoluble molecules found in the cytoplasm, (starch and lipids) don’t affect the movement of water

Question 17

describe how to model osmosis in cells

Answer 17

using an artificial membrane that is permeable to some molecules but not others e.g water and sucrose

Question 18

define an isotonic solution

Answer 18

osmotic concentration of the solutes in the solution is the same as the those in the cells

Question 19

define a hypotonic solution

Answer 19

the osmotic concentration of the solutes in the solution us lower than that in the cytoplasm of the cells

Question 20

define a hypertonic solution

Answer 20

The external solution has a high solute concentration and low water concentration in comparison to the cells

Question 21

why does osmosis in animals need to be kept to a minimum

Answer 21

because animal cells are fragile, they shrivel and burst easily and cytoplasm looses is structure

Question 22

how is hydrostatic pressure induced

Answer 22

when cytoplasm swells and presses against cell walls

Question 23

what is pressure potential

Answer 23

the inward pressure of cell wall on the cytoplasm

Question 24

when is the cell in turgor

Answer 24

when the osmotic force of water moving into the plant is equal to the pressure potential

Question 25

incipient plasmolysis

Answer 25

when a cell is put in a slightly hypertonic solution, the membrane begins to pull away from the cell wall and the protoplasm shrinks.

Question 26

what is water potential

Answer 26

• a measure of the potential of water to move OUT of a solution by osmosis
• the maximum value is given as 0, and it would be the value of pure water, so anything else is negative

Question 27

if the turgor pressure is equal to the osmotic potential, what is happening?

Answer 27

water moves into cell by osmosis, cell swells, cell wall stops further swelling, hydrostatic pressure induced, turgor pressure induced (inwards pressure), turgor pressure rises until its equal to osmotic force pulling water into cell

Question 28

what is osmotic potential

Answer 28

the potential of water to move out of a solution across a partially permeable membrane from a hypotonic to hypertonic solution

Question 29

define osmosis

Answer 29

the net movement of water from an area of higher osmotic potential to an area of lower osmotic potential through a partially permeable membrane

Question 30

define osmosis (water potential)

Answer 30

the net movement of water molecules from an area of higher water potential to an area of lower water potential

Question 31

equation for water potential

Answer 31

turgor pressure + osmotic potential
turgor pressure- usually +ive
osmotic potential - always -ive

Question 32

what is active transport

Answer 32

is the movement of substances across a membrane with a carrier protein against the concentration gradient using energy in the form of ATP supplied by the cell

Question 33

describe the use of ATP

Answer 33

the enzyme ATPase catalyses hydrolysis of ATP which breaks a bond and forms two more, releasing the energy used by the cell

Question 34

describe the process of endocytosis

Answer 34

large molecule of a certain shape will be transported by a protein in the cell membrane that changes shape to transport the molecule onto the other side of the cell. The change in shape requires energy from ATP hydrolysis. The carrier protein then reverts back to original shape to allow for transportation of more molecules

Question 35

what are the points of evidence for active transport

Answer 35

1. it only takes place in living things
2. rate of active transport depends on temp. and oxygen conc. which affect respiration rate and ATP production rate
3. cells that are known to carry out a lot of active transport have a lot of mitochondria to respire and produce ATP
4. poisons that prevent ATPase working also prevent active transport