1. What do substances move across to get into and out of cells ?
Answer
The cell membrane.
2. Define the term "osmosis".
Answer
Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
3. Define the term "active transport".
Answer
Active transport moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient) using energy from respiration.
4. Which molecules are absorbed into the blood by active transport and used for cell respiration ?
Answer
Sugar (or glucose).
5. Insects do not have lungs or blood. Suggest how insects obtain the oxygen they need for aerobic respiration.
Answer
Insects are small and so have a relatively large surface area to volume ratio and can obtain their oxygen by diffusion.
6. How does a change in the concentration gradient influence the rate at which substances diffuse into or out of cells ?
Answer
A steeper concentration gradient (bigger difference in concentration) will cause a faster rate of diffusion because the particles will move more readily from higher to lower concentration.
7. Why do we use a partially permeable membrane to study osmosis with sugar solutions ?
Answer
So that only water could move into and out of the bag.
8. A student investigates osmosis by observing how different concentrations of salt solution affect the mass of carrot cylinders. He places dried equal-sized carrot pieces into solutions with varying concentrations for one hour, measuring their mass before and after to assess water movement. Give the variables that the student controlled in this investigation. Why the carrot pieces must be dry ?
Answer
The variables are: the volume of each solution, the diameter and length of the carrot cylinders, and the duration the cylinders remained in the solution. The carrot pieces must be dry to ensure that surface water does not artificially increase their mass.
9. Root hair cells absorb water and mineral ions from the soil. The figure below shows a root hair cell. Describe how the shape of the root hair cell increases the rate of water uptake.
Answer
Cell has a large surface area for diffusion (or osmosis).