All Subjects



AP Bio



Unit 8

Nutrient Cycles & Succession

52 min videomarch 21, 2019

In today’s live stream, we discussed various nutrient cycles and ecological succession. We started by talking about the role and importance of nutrients, specifically carbon, nitrogen, and phosphorus. We then talked about how water transforms within a cycle, reviewing that precipitation occurs when water from the air turns into a liquid on the ground, that evaporation occurs when liquid water evaporates into the air, that condensation occurs when water vapor turns into liquid droplets, and that transpiration occurs when plants lose water through their stomata. Next, we discussed the carbon cycle. The carbon cycle starts with the cellular respiration of plants and animals who release carbon dioxide into the air. Next, through photosynthesis, carbon dioxide is incorporated into the plants’ biochemistry, and when the plants become a food source for consumers, the carbon goes through the food chain. Through cellular respiration of the consumers, the carbon enters the air again. In the nitrogen cycle, bacteria first go through fixation to turn the nitrogen in the air into ammonia in the soil. Through other bacteria, the ammonia is then changed to nitrate through nitrification. Now the plants can absorb the nitrates and ammonia through their roots resulting in the nitrogen becoming a part of their bodily functions. If they get eaten, the nitrogen then gets transferred to the consumer until finally, an animal dies and decomposes, putting the nitrogen back into the soil. The nitrogen can also go back into the air when the denitrifying bacteria turn the nitrates into atmospheric nitrogen. In the phosphorus cycle, plants suck up the phosphorus in the soil. When they get eaten, the phosphorus, like nitrogen, gets transferred to the consumer who uses to make ATP or other macromolecules. When they die, the phosphorus gets returned into the soil and the cycle starts again. Next, we talked about succession, both the primary and the secondary kinds. Primary succession is when there is no soil available in the beginning, but eventually, after the soil is created, life would start occurring. Secondary succession is when soil already exists in the environment and just the life existing before was killed by a natural disaster, like a fire. This means that life can grow easily in the environment because the nutrient-rich soil already exists. After discussing how species diversity, defined in terms of species richness and relative abundance, works for a little bit, we talked about invasive species and how they might have decreased the species diversity of an environment. Finally, we end the session by answering a couple of questions from the chat both relating to nutrient cycles and succession and relating to other topics in biology like DNA replication.