Cell function

Question 1

Passive transport

Answer 1

Movement of materials across the cell membrane WITHOUT the expenditure of energy across a high to low concentration.

Question 2

Diffusion

Answer 2

process of ANY molecule moving from an area of high concentration to an area of low concentration (down its concentration gradient) to achieve equilibrium. Doesn’t require a semi-permeable membrane.

Question 3

Simple diffusion

Answer 3

diffusion of substances directly through phospholipid bilayer. If the cell membrane is permeable to material it can go straight through however since it is selectively permeable only certain things can pass through. Factors like size and polarity: non-polar and small things get through easily e.g. oxygen, polar and large molecules e.g. sugar get rejected however is problematic as it is still needed in the cell
 Generally used to transport molecules that are small and neutral
 E.g. in Gaseous exchange oxygen will readily diffuse across from the alveoli (high in oxygen from the lungs) to the blood stream (no oxygen).

Question 4

Facilitated diffusion

Answer 4

diffusion of substances through cell membrane via channel and carrier proteins (bind to materials and change shape to allow diffusion). Proteins act as channels to allow these substances that can’t pass through the bilayer. The proteins that allow this are specific.

Question 5

Osmosis

Answer 5

process of the movement of water from an area of high water concentration to an area of low water concentration across a semi-permeable membrane

Question 6

Isotonic solutions

Answer 6

Everything is already balanced and at equal concentrations, the rate at which water leaves the cell = rate at which water enters the cell (no net movement) no net movement
RESULT: stay the same, stable shape

Question 7

Hypotonic solutions

Answer 7

solution with a lower solute concentration (high water concentration) e.g. cell in fresh water: water will move in to the cell to try and achieve balance. net movement; into a cell
RESULT:
- An animal cell absorbs water until it pops – lysed
- A plant cell swells but the cell wall stops it from popping – turgid

Question 8

Hypertonic solutions

Answer 8

solution with high solute concentration e.g. cell in salt water: water will move out of the cell to try and achieve balance, net movement: out of a celll
RESULT:
- An animal cell – ‘shrivelled’
- Plant cell – ‘flaccid’  when completely dry ‘plasmolysis’

Question 9

Concentration gradient

Answer 9

an area of high concentration and an area of low concentration exists. The steeper the concentration gradient is:
- The FASTER material will move to an area of low concentration (PT)
- The SLOWER material will move to an area of high concentration (AT)

Question 10

SA:V ratio

Answer 10

Large SA+ small V = max efficiency Surface area to volume ratio = surface area/volume
- Rate of exchange of substance = depends on SA
- As the size of an object DECREASES its SA:V ratio INCREASES  volume increases at a faster rate than SA
- Cells want a HIGH SA:V ratio  the higher the SA:V ratio faster rate of diffusion = the more efficiently materials can be exchanged across its surface  important: cells get all their nutrients and remove waste via cell membrane  if a cell is too big it cannot transport nutrients and oxygen efficiently nor can it remove waste quickly (may die)
- EVOLUTION: instead of individual cells growing larger  have evolved to become multicellular. This allows cells to maintain a high SA/V ratio, ensuring efficient nutrient uptake and waste removal. Specialised cells can perform diff functions increasing overall efficiency and complexity of organism = survival in diverse environments.

Question 11

To increase SA:V ratio

Answer 11

= flattened shape (flatter the shape/larger its SA:V ratio) e.g. red blood cell, lung epithelial cells (increase rate of transport, Cell membrane extensions (most common), don’t want to squish organelles, cell membrane folds in on itself creating ‘tentacles’ that have HUGE SA:V ratio e.g. used for cells that want to absorb nutrients fast – microvilli in the stomach lining

Question 12

particle size and temp

Answer 12

• Only really affect rate of passive transport
• Particle size: smaller particle = faster rate of diffusion  bigger molecules have harder time getting through
• Temperature: increasing temp increases speed at which molecules move  faster moving particles are able to move across the membrane quicker.