Movement of substances into and out of Cells Flashcards
Define diffusion
The net movement of molecules from an
area of high concentration to an area of
low concentration down their
concentration gradient.
How does temperature affect the rate of
diffusion?
As the temperature increases, so does
the rate of diffusion as the particles have
more kinetic energy and move faster.
How does the concentration gradient
affect the rate of diffusion?
The greater the concentration gradient
(the difference between the two areas),
the faster the rate of diffusion.
How does the surface area of the membrane affect the rate of diffusion?
As the surface area increases so does
the rate of diffusion as there is more
space for the particles to move through.
Define osmosis
The net movement of water molecules from a high water potential to a low water potential down their water potential gradient across a partially permeable
membrane.
Define active transport
The movement of molecules from a low concentration to a high concentration against their concentration gradient
using energy.
Is diffusion an active or passive process?
Passive - no energy is required
What is the general size of molecules that can diffuse across partially permeable membranes?
Small - oxygen, amino acids, glucose + water
but not starch or proteins
Why can single celled organisms rely on diffusion?
- have a relatively large surface to volume ratio
- and low metabolic demands
Why can’t multi celled organisms rely on diffusion?
- surface area to volume ratio too small
- many metabolic demands
Adaptations of diffusion in humans
- alveoli in lungs
- villi in small intestine
- root hair cells in plants
Is osmosis an active or passive process?
Passive - it does not require energy from respiration
Define isotonic
If there is no net movement of a substance the solution can be described as isotonic
Define hypertonic
If the concentration of sugar is higher in the external environment than in the internal, water moves out and the solution is said to be hypertonic to the cell
Define hypotonic
If the concentration of sugar is lower in the external environment than in the internal, water moves into the cell and the solution is said to be hypotonic to the cell
Define shrivelled
If the external solution is more concentrated (lower water potential), excess water will
LEAVE the cell causing it to become shrivelled.
Define turgid
If the external solution is more dilute, water will move INTO the cell and into the vacuole,
causing it to swell, resulting in high pressure. The cell is described as turgid
Define plasmolysed
If the external solution is less dilute, water will move OUT of the cell, and the cell will become soft. Eventually the cell membrane will move away from the cell wall, and the cell will die. This is called plasmolysis
Define flaccid
If a plant cell is surrounded by a solution that contains a lower concentration of water molecules than the solution inside the plant cell, water will LEAVE the cell by osmosis and the plant cell will become flaccid
Does active require energy and if so where does it get its energy from?
Yes - cellular respiration
Active transport examples
- root hair cells take up water and minerals from the soil where they are usually in higher concentration in the plant cells than in the soil. This means that it is travelling against the concentration gradient
Active transport concentration gradient
Low to high
Describe a practical to investigate diffusion in non-living systems
1) Cut a 1cm3 cube of agar made of sodium hydroxide and phenolphthalein indicator
2) Place cube in solution of hydrochloric acid
3) Remove the cube and wash with water to stop further reaction
4) Cut the cube in half and measure the distance that the acid has caused agar to become
colourless from outside inwards
5) Repeat the experiment two more times and calculate the mean
6) Repeat with different concentrations of hydrochloric acid
Describe a practical to investigate osmosis
1) Place different sucrose solutions including 0% for a control, in different boiling tubes
2) Dry potato strips on a paper towel and measure the masses
3) Place each potato strip into each sucrose solution for 20 minutes and record how the mass
changed
4) Repeat tests at each solution several times with potato strips of similar masses
What are the main biologically important groups of inorganic molecule
- water
- oxygen
- nitrogen
- carbon dioxide
