C4.2.1 – Ecosystems as open systems in which both energy and matter can enter and exit

Ecosystem: An ecosystem refers to a community of living organisms interacting with each other and their physical environment. This interaction includes the flow of energy and nutrients, which sustains life within the ecosystem.

• Open Systems: An open system is one where both matter and energy are exchanged with the surroundings. Ecosystems are open systems because they receive energy (mainly in the form of sunlight) from the environment and exchange matter (like water, carbon, and nutrients) with the surroundings through processes like respiration and decomposition.
• Closed Systems: A closed system exchanges only energy with its surroundings, but not matter. For example, a sealed jar with plants and animals inside may be considered a closed system, as it doesn’t exchange material with the outside (except for light or energy).
• Ecosystem as an Open System: Ecosystems allow energy to enter (e.g., sunlight) and exit (e.g., heat), and they allow matter (e.g., nutrients) to cycle between biotic and abiotic components. Matter is not created or destroyed but is recycled through the system, while energy flows through the system in a linear fashion.

C4.1.2 – Sunlight as the principal source of energy that sustains most ecosystems

• Sunlight as the Primary Energy Source: Most ecosystems depend on sunlight as their primary source of energy. This energy is used by plants, algae, and photosynthetic bacteria to produce glucose and other organic compounds via photosynthesis, which in turn supports other organisms.
• Exception – Chemosynthetic Ecosystems: Some ecosystems, such as those found around hydrothermal vents on the ocean floor, do not rely on sunlight. Instead, they rely on chemosynthesis, where energy from the oxidation of inorganic compounds (e.g., hydrogen sulfide) is used to produce food.

C4.2.3 – Flow of chemical energy through food chains

• Food Chain: A food chain is a linear sequence of organisms through which energy and nutrients are transferred from one organism to the next. Each organism in a food chain occupies a specific trophic level.
• Producers and Consumers:
  • Producers: Organisms like plants, algae, and some bacteria that use sunlight or inorganic compounds to produce their own food (via photosynthesis or chemosynthesis).
  • Consumers: Organisms that obtain energy by consuming other organisms.
    • Primary Consumers: Herbivores that feed directly on producers.
    • Secondary Consumers: Carnivores that feed on primary consumers.
    • Tertiary Consumers: Apex predators that feed on secondary consumers.
• Apex Predator: The apex predator is the top predator in a food chain that has no natural predators.
• Arrow in Food Chain: The arrow in a food chain represents the direction of energy flow, indicating the organism that is being consumed.

C4.2.4 – Construction of food chains and food webs to represent feeding relationships in a community

• Food Web: A food web is a more complex and realistic representation of feeding relationships in an ecosystem. Unlike a food chain, which is linear, a food web shows how multiple organisms are interconnected through various food sources.
• Food Chain Construction:
  • Producer: Start with a plant or algae.
  • Primary Consumer: An herbivore that eats the producer.
  • Secondary Consumer: A carnivore that eats the primary consumer.
  • Tertiary Consumer: An apex predator that eats the secondary consumer.
• Why Food Webs Are Better: Food webs are more accurate because organisms in an ecosystem typically feed on multiple species and occupy different trophic levels. Food webs better reflect the complex nature of real ecosystems.