y3.1: cell transport 🚦

Question 1

importance of cell transport

Answer 1

• SURVIVE
• maintain homeostasis => constant internal environment (more on homeostasis !! )

Question 2

what is passive transport?

Answer 2

Substances move according to natural tendency without input of energy from the cell (no ATP from mitochondria)

Question 3

modes of passive transport

Answer 3

1) Simple diffusion
2) Facilitated diffusion
3) Osmosis

Question 4

what is simple diffusion?

Answer 4

simple diffusion is the net movement of a substance from an area of higher concentration to an area of lower concentration down its concentration gradient until equilibrium is reached

Question 5

how does simple diffusion work?

Answer 5

• caused by the constant random morion of molecules due to kinetic energy
• diffusion results in equilibrium (no NET movement)

Question 6

factors affecting rate of diffusion

Answer 6

1) concentration gradient
- steeper = greater rate of diffusion
2) distance over which diffusion occurs
- shorter = greater rate of diffusion
3) surface area to volume ratio
- larger = greather rate of diffusion
4) temperature
5) membrane permeability

Question 7

what is facilitated diffusion? (living cells only)

Answer 7

facilitated diffusion is the diffusion of ions and water-soluble molecules through cell membrane using channel proteins or carrier proteins (transport proteins), down a concentration gradient

Question 8

characteristics of facilitated diffusion

Answer 8

1) passive process - no energy required
2) once all transport proteins are in use, the rate of diffusion cannot be increase further (plateau can be reached before equilibrium is reached)

Question 9

what are channel proteins and what substances do they transport?

Answer 9

• hydrophillic channel across the membrane (so that hydrophillic substances dont contact hydrophobic phospholipid tails)
• transport ions or hydrophillic molecules

Question 10

what are carrier proteins? (facilitated diffusion)

Answer 10

• substances bind temporarily to the carrier protein, causing it to change shape to transport the substances across the membrane
  => change in shape triggered by the binding and release of particcles
• more specific in nature (sites)

Question 11

what is osmosis?

Answer 11

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 12

what is water potential?

Answer 12

water potential is a measure of the tendency of water to move from one region to another
- the more concentrated, the lower water potential
- always move from higher to lower down a water potential gradient

Question 13

explain the process of osmosis

Answer 13

1) compare water potential: A has a higher water potential than B
2) direction of movement of water: more water molecules move from the A to B
3) process: by osmosis
4) conclude: hence, the water level at B increases

Question 14

why can water molecules pass through membrane but not sucrose?

Answer 14

• membrane is partially permeable
• sucrose molecules are too big to pass through the pores of the membrane

Question 15

what happens to a cell placed in a diluted solution (high WP)?

Answer 15

water enters, cell swells and..
animal: lyses
plant: becomes turgid

Question 16

what happens when a cell is placed in a concentrated solution (low WP)?

Answer 16

water leaves the cell…
animal: cell shrinks and crenates
plant: cytoplasm shrinks and cell becomes flaccid and then plasmolysed

Question 17

why do plant cells not lyse?

Answer 17

presence of rigid cell wall; creates turgor pressure to keep the plant upright

Question 18

problems caused by osmosis (passive)

Answer 18

• unicellular organisms in fresh water habitats are in high WP environment
  => survive by constantly expelling water using contractile vacuoles to prevent swelling and lysis
• organisms in low WP environment
  => must actively pump ions in their cells to lower WP; reduce water loss by osmosis
• young non-woody plants rely on turgor pressure for support
  => actively pump ions into root hair cells to lower WP; reduce water loss by osmosis

Question 19

what is active transport? (live cells only, not applicable for water)

Answer 19

active transport is the movement of ions or molecules across a cell membrane from a region of lower concentration to region of higher concentration against a concentration gradient with the expenditure of energy from the ATP molecule by the cell

Question 20

what is the importance of active transport?

Answer 20

• allows cells to take up ions or nutrients even when concentration outside > concentration inside
• maintain its internal concentration regardless of surrounding concentration
• enables cells to get rid of waste products

Question 21

how is active transport carried out?

Answer 21

requires the use of specific carrier proteins + ATP
- ATP is required for carrier protein to change its shape

Question 22

what is bulk transport? and why don’t i remember studying this at all?

Answer 22

bulk transport is the tranport of materials into or out of a cell by enclosing it within a vesicle
- active process because it requires energy expenditure by cell

Question 23

what is the importance of bulk transport?

Answer 23

allows large molecules such as proteins and polysaccharides (not glucose and amino acids) or large quantities of molecules to enter or leave the cell without actually passing through the membrane

Question 24

what is endocytosis?

Answer 24

substances are taken into the cells by inward folding of the cell membrane to form vesicles that separate from the membrane
- ATP is used to provide energy during this progress

Question 25

what is phagocytosis?

Answer 25

process of engulfing or ingesting foreign particles (WBC or amoeba food)
- formation of pseudopodia => temporary protrusions of the cell membrane
- vesicles formed after phagocytosis fuse with lysosomes containing hydrolytic enzymes => digest / breaks down engulfed foreign particles

Question 26

what is exocytosis?

Answer 26

substances in vesicles move towards and fuse with the cell membrane, releasing the contents of the vesicle into the fluid around the cell
- ATP used during the process

Question 27

not a card but there’s a pretty slay table of comparison on page 66 so go look at that!

Answer 27

yas