Chapter 3 Mvt of Substances Flashcards
Define ‘concentration gradient’. Explain why.
Definition: Difference in
concentration between two
regions.
Movement of fluid particles is
random. Particles diffuse down
their concentration gradient.
The steeper the conc. grad.,
the faster the rate of diffusion.
(Addn: Smaller structures have
a higher SA2V ratio.)
How should you answer questions?
In answers
1. What process has taken place? (Diffusion/Osmosis/Active transport)
2. Where is the area of higher concentration/water potential of named molecules involved?
3. Where is the area of lower concentration/water potential of named molecules involved?
4. In what direction do the named molecules move? (From [region] to [region])
5. What are my final observations/results?
Define diffusion
Diffusion refers to the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient, with or without a partially
permeable membrane.
Explain diffusion of gases in root hair cells.
● Only respiration occurs in root hair cells as there are no chloroplasts present for photosynthesis.
When gaseous exchange occurs, the cell takes in oxygen and produces carbon dioxide.
● There is a higher concentration of carbon dioxide in the RHC than in the soil → carbon dioxide
diffuses out of the RHC into the soil.
● There is therefore a lower concentration of oxygen in the RHC than in the soil → oxygen
diffuses into the RHC from the soil.
Explain diffusion of gases in lungs.
(ppm: wall of alveolus and blood capillary)
● There is a higher concentration of oxygen in the alveoli (air sucs) in the lungs than in the blood in the capillaries surrounding the alveoli.
● Oxygen dissolves in a thin film of moisture on the inner wall of alveoli and diffuses from the alveoli into the blood capillaries and into the red blood cells.
● There is a higher concentration of carbon dioxide in the blood in capillaries surrounding the alveoli, than in the alveoli in the lungs. → Carbon dioxide diffuses out of the blood capillaries and into the alveoli, dissolving in the thin film of moisture on the inner wall of the alveoli
Define ‘osmosis’.
Definition: net movement of water molecules from a solution of higher water potential to a solution of lower water potential through a ppm.
What is a ‘hypertonic solution’?
Concentrated solution with a lower water potential compared to hypotonic
solution.
What is an isotonic solution?
Similar water potential between the two solutions
What is hypotonic solution?
Dilute solution with a higher water potential compared to hypertonic
solution.
What is the effect of hypertonic solution on RBC?
RBC crenates (shrinks) due to higher
water potential in the RBC than in
the hypertonic solution. Water
molecules move out by osmosis from
the RBC into the hypertonic solution.
What is the effect of isotonic solutioon on RBC?
RBC retains the same shape and size
as the water potential of the cell and
solution is similar. No net mvt of
water molecules in or out of the cell.
What is the efefect of hypotonic solution on RBC?
RBC expands and eventually bursts
as there is higher water potential in
the hypotonic solution than in the
RBC. Water molecules move by
osmosis from the hypotonic solution
into the RBC. RBC lacks a cell wall to
provide structural support.
What is the effect of hypertonic solution on plant cell?
Plant cell (PC) is plasmolysed
(shrinks) due to it having higher
water potential than in the
hypertonic solution. Water moves out
by osmosis from the PC into the
hypertonic solution.
What is the effect of hypotonic solution on plant cell?
PC becomes turgid (bloated) as there
is higher water potential in the
hypotonic solution than in the PC.
Water moves by osmosis from the
solution into the cell. PC does not
burst as the plant tissue is firm
(presence of cell wall)
Define turgor pressure in plants an explain its importance.
Definition: pressure exerted by the water in the vacuole on the cell wall.
Importance:
1. Turgor maintains the shape of soft tissues in plants.
2. Turgor provides mechanical support for herbaceous plants to remain firm and upright to get maximum sunlight for photosynthesis.
3. Loss of turgidity → plant wilts. Turgor pressure in guard cells allow stomata to be opened, enabling transpiration and exchange of gases.
