Question

1. a student read that liquid extracted from an aloe vera plant promotes the healing of burned tissue. she decided to investigate the effect of different concentrations of aloe vera extract on the regeneration (regrowth of lost or damaged tissue) rate in planaria. planaria are small flatworms known for their ability to regenerate.

planaria regeneration
image: cut planaria worm in two, grows new tail, grows new head
source: adapted from https://goo.gl/images/4wtovv

the student used a sterile scalpel to cut each of 30 planaria in half. this gave her 10 heads and 10 tails for each of three experimental groups. the planaria were kept in separate petri dishes in the same amount of water and at the same temperature. group 1 received 0% aloe vera extract, group 2 received a 20% concentration of the extract, and group 3 received a 40% concentration. on days 7, 10, and 14, she recorded the amount of tissue regeneration in all three groups. she observed that the group with 20% aloe vera added regenerated more slowly than the group with 40% added.

a reasonable inference based on these results would be that

1. the application of aloe vera to earthworms would have no effect on tissue regeneration
2. if she applied 30% aloe vera to a group, it would regenerate tissue more rapidly than the 40% group
3. aloe vera affected the rate of cell division, resulting in an increased rate of regeneration
4. the control group, which received no aloe vera, did not regenerate

Explanation:

1. Option 1: The experiment is on planaria, not earthworms, so we can't infer about earthworms. Eliminate.
2. Option 2: The data shows 40% has faster regeneration than 20%, but we can't assume 30% is faster than 40% (no info on the trend between 20 - 40%). Eliminate.
3. Option 3: The experimental groups (20% and 40% Aloe vera) had different regeneration rates than the control (0%), and higher concentration (40%) had faster regeneration than 20%. This suggests Aloe vera affects cell division (which drives regeneration) to increase the rate. This is a reasonable inference.
4. Option 4: Planaria are known to regenerate, and the control group (0% Aloe vera) would still regenerate (just maybe slower), so this is incorrect. Eliminate.

Answer:

1. Aloe vera affected the rate of cell division, resulting in an increased rate of regeneration