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Unit 8: Ecology

AP Biology


Nutrient Cycles & Succession

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.
Mar 21 2019

Community Ecology

Live Stream Notes: In this live stream, we discuss community ecology. We learn that community ecology is the relationship among different species in the same environment. We start by discussing energy and how it flows through the trophic levels. Trophic levels consist of the producers (like plants and algae), primary consumers (like deer and rabbits), secondary consumers (like snakes), and tertiary consumers (like hawks and sharks). As we move up the trophic levels, we see that 90% energy is “lost” as heat per a level so the next level up only gets 10% of the previous trophic level’s energy. This is why tertiary consumers eat so much than secondary consumers. On the other hand, producers make up the largest portion of the food web and the energy pyramid. When a secondary consumer species is removed from an environment, the food source may be decreased for the tertiary consumers leading to a decrease in population while there would be overpopulation of the primary consumers and maybe even depletion of the producers. This species, usually near the top of the food web, would be a keystone species because it has a drastic impact on the food chain. We also learned that there are 3 relationships species can have other than predator and prey, parasitism (one benefits, one hurts), commensalism (one benefits, one does not have effects), and mutualism (both benefit). After doing 2 FRQ questions, we end the session by discussing the difference between commensalism and mutualism.
Mar 14 2019

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