Effect of Density on Populations Practice Test

In a greenhouse experiment, researchers grow the same species of annual plant in identical pots with the same soil and water schedule. Pot Group 1 contains 2 seedlings per pot, and Pot Group 2 contains 20 seedlings per pot. After 5 weeks, Group 1 plants average 18 cm tall with 90% survival, while Group 2 plants average 6 cm tall with 40% survival. Light intensity and temperature are constant across groups. Which factor is most likely responsible for the lower survival in Group 2?

In a laboratory, two identical cultures of yeast were grown with the same initial sugar concentration. Culture L started with $10^5$ cells, and Culture H started with $10^7$ cells. After 24 hours at the same temperature, Culture H had a lower per-cell division rate and higher cell death than Culture L. No antibiotics or toxins were added. Which factor most likely explains the reduced growth in Culture H as density dependent?​​