Chap 2: Movement of Substances Flashcards
Define diffusion
Net movement of particles from a region of higher to lower concentration down a concentration gradient
State examples of diffusion
Humans:
- Gaseous exchange in lungs
- Absorbing digestive food substances in small intestine
Plants:
= Gaseous exchange in leaves
- Absorbing mineral salts
Describe what happens during gaseous exchange in lungs
- carbon dioxide diffuses out of blood into air space in lungs (higher concentration of CO2 in blood)
- oxygen from air space diffuses into red blood cells (higher concentration of O2 in air space)
Features of gaseous exchange in lungs
- large surface area
- short distance (one cell thick)
- concentration gradient
Describe what happens when absorbing digestive food substances
Also state the features
Glucose molecules from small intestines diffuse into blood capillary/bloodstream
(more digested substances in SI than bloodstream)
Features: large surface area, concentration gradient
Describe what happens during photosynthesis
- CO2 diffuses into leaf from surroundings
- O2 and water vapour diffuses out of leaf
Describe what happens during gaseous exchange when the plant is not photosynthesising
- O2 diffuses into leaf
- CO2 and water vapour diffuses out of leaf
Describe what happens when plants absorb mineral salts
- Mineral salts from soil diffuse into cell sap of root hair cell
- higher concentration of mineral salts in soil than root hair cells
State the factors affecting diffusion and how
- Diffusion distance
[shorter the distance, higher rate of diffusion] - Surface area-to-volume ratio
[greater ratio, higher rate of diffusion] - Concentration gradient
[steeper the gradient, higher rate of diffusion]
Define osmosis
net movement of water molecules down a potential water gradient from a region of higher to lower water potential across a partially permeable membrane
What happens to an animal cell placed in higher water potential?
[CYTOLYSIS]
- cell has lower water potential than solution, osmosis occurs from solution to cell
- more water added, cell expands and bursts
What happens to an animal cell placed in lower water potentials?
[CRENATION]
- cell has higher water potential than solution, osmosis occurs from cell to solution
- water lost, cell shrinks, spikes and becomes dehydrated {crenated}
What happens to a plant cell placed in higher water potential?
[TURGID]
- water molecules enter cell, vacuole increases
- cell expands/swells and becomes turgid
(cell does not burst due to cell wall)
turgor pressure: pressure exerted by water to cell
What happens to a plant cell placed in lower water potential?
[PLASMOLYSIS]
- water molecules leave cell, vacuole shrinks
- cell stops exerting pressure on cell wall
- cell shrinks and becomes flaccid/limps (plasmolysed)
What happens to cells placed in same water potential?
Nothing. No movement of water.
