Chapter 37: Communities and Ecosystems – Study Guide

Chapter 37: Communities and Ecosystems

Major Themes and Learning Objectives

This chapter explores the structure and dynamics of biological communities and ecosystems, focusing on interspecific interactions, trophic relationships, and the carbon cycle. Understanding these concepts is essential for grasping how organisms interact and how energy and matter flow through ecosystems.

Photosynthesis and Cellular Respiration in the Carbon Cycle

Photosynthesis and cellular respiration are fundamental, complementary processes in the carbon cycle, carried out by different members of an ecosystem.

• Photosynthesis: The process by which plants, algae, and some bacteria convert carbon dioxide and water into glucose and oxygen using sunlight. This stores energy in organic molecules.

• Cellular Respiration: The process by which organisms (including plants and animals) break down glucose to release energy, producing carbon dioxide and water as byproducts.

• Complementarity: Photosynthesis removes CO2 from the atmosphere and stores it in organic molecules; cellular respiration releases CO2 back into the atmosphere.

• Equation for Photosynthesis: $6\ \mathrm{CO}_2 + 6\ \mathrm{H}_2\mathrm{O} + \text{light energy} \rightarrow \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\ \mathrm{O}_2$

• Equation for Cellular Respiration: $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\ \mathrm{O}_2 \rightarrow 6\ \mathrm{CO}_2 + 6\ \mathrm{H}_2\mathrm{O} + \text{ATP}$

• Example: Plants perform both photosynthesis and cellular respiration; animals perform only cellular respiration.

Five Types of Interspecific Interactions

Interspecific interactions are relationships between members of different species within a community. These interactions influence population dynamics and community structure.

• Competition: Both species are negatively affected as they vie for the same resources (e.g., food, space).

• Predation: One species (predator) benefits by eating another (prey), which is harmed.

• Herbivory: An animal consumes plant parts, benefiting the animal and potentially harming the plant.

• Parasitism: One species (parasite) benefits by living on or in another species (host), which is harmed.

• Mutualism: Both species benefit from the interaction (e.g., bees pollinating flowers).

• Example: Cleaner fish remove parasites from larger fish (mutualism); wolves hunt deer (predation).

Trophic Structure and Predator-Prey Relationships

The trophic structure of a community describes the feeding relationships among organisms, forming a food web or food chain.

• Trophic Levels: Include producers (autotrophs), primary consumers (herbivores), secondary consumers (carnivores), tertiary consumers, and decomposers.

• Predator-Prey Relationships: Predators feed on prey, influencing population sizes and community dynamics.

• Diagram: Food webs illustrate complex feeding relationships; food chains show linear energy flow.

• Example: Grass (producer) → rabbit (primary consumer) → fox (secondary consumer).

Relationship Between Cellular Respiration and Photosynthesis in the Carbon Cycle

These processes are interconnected, cycling carbon through the ecosystem.

• Photosynthesis: Captures atmospheric CO2 and incorporates it into organic molecules.

• Cellular Respiration: Releases CO2 from organic molecules back into the atmosphere.

• Cycle: Carbon moves from the atmosphere to organisms and back, maintaining ecosystem balance.

• Example: A carbon atom in CO2 is fixed by a plant, eaten by an animal, and released via respiration.

Organisms Performing Photosynthesis and Cellular Respiration

Different organisms contribute to the carbon cycle through these processes.

• Photosynthesis: Performed by plants, algae, and some bacteria.

• Cellular Respiration: Performed by all living organisms, including plants, animals, fungi, and many bacteria.

• Glucose Source: Plants synthesize glucose via photosynthesis; animals obtain glucose by consuming plants or other animals.

• Example: Plants use sunlight to make glucose; animals eat plants to obtain glucose for respiration.

Tracking a Carbon Atom Through the Carbon Cycle

The carbon cycle describes the movement of carbon atoms through the biosphere, atmosphere, hydrosphere, and geosphere.

• Step 1: Carbon is released as CO2 by organisms during cellular respiration.

• Step 2: Plants absorb CO2 during photosynthesis, converting it into glucose.

• Step 3: Glucose is used by plants or consumed by animals, entering their bodies.

• Step 4: Through cellular respiration, carbon is released again as CO2.

• Step 5: Decomposers break down dead organisms, releasing carbon back into the environment.

• Example: A carbon atom released by a fox during respiration is absorbed by a tree, incorporated into a leaf, eaten by a caterpillar, and released again.

Additional info:

• In ecosystems, energy flows in one direction (from sun to producers to consumers), but matter (such as carbon) cycles repeatedly.

• Decomposers (fungi, bacteria) play a crucial role in recycling carbon and other nutrients.