The cells, tissues and organs in plants and animals are adapted to take up and get rid of dissolved substances.
a) Dissolved substances move by diffusion and by active transport.
Remember diffusion happens from high to low concentrations ( down the gradient). Active transport is when substances are moved against the gradient ( low to high).
b) Water often moves across boundaries by osmosis.
Osmosis is the diffusion of water from a dilute to a more concentrated solution through a partially permeable membrane that allows the passage of water molecules.
c) Differences in the concentrations of the solutions inside and outside a cell will cause water to move into or out of the cell by osmosis.
Remember we did the potato experiment?
- How could this graph be improved? What do think of the line of best fit?
- Why have they used % change in mass?
- What’s the significance of where the line crosses the x axis?
d) Most soft drinks contain water, sugar and ions.
e) Sports drinks contain sugars to replace the sugar used in energy release during the activity. They also contain water and ions to replace the water and ions lost during sweating.
■ evaluate the claims of manufacturers about sports drinks
f) If water and ions are not replaced, the ion / water balance of the body is disturbed and the cells do not work as efficiently.
Active transport enables cells to absorb ions from very dilute solutions.
g) Substances are sometimes absorbed against a concentration gradient. This requires the use of energy from respiration ( happens in mitochondria rem?) . The process is called active transport.
This animation shows more detail than you need but look at the active transport and osmosis parts : transport animation
Be sure to have done all the questions in the textbook and then try these :