Organisms and Their Environment Study Guide
Energy Flow in Biological Systems
The Principal Source of Energy: The sun is the principal source of energy input to biological systems.
The Flow of Energy Through Living Organisms:
* Energy begins with the sun.
* Plants: Plants use light energy from the sun to create their own food. This energy is stored within their cells as chemical energy.
* Animals: Animals obtain energy by eating plants.
* Predation: Energy is subsequently passed on when animals are consumed by other animals.
* Decomposition: Eventually, energy is returned to the environment through the process of decomposition.Importance: This continuous flow of energy is vital for the survival and functional processes of all living organisms.
Essential Definitions in Ecology
Producer: An organism that makes its own organic nutrients, usually using energy from sunlight through the process of photosynthesis.
Consumer: An organism that gets its energy by feeding on other organisms.
Herbivore: An animal that gets its energy by eating plants.
Carnivore: An animal that gets its energy by eating other animals.
Decomposer: An organism that gets its energy from dead or waste organic material.
Food Chains and Food Webs
Food Chain Definition: A food chain shows the transfer of energy from one organism to the next, beginning with a producer.
Energy Flow Direction: In a food chain, arrows are used between each organism. These arrows always point in the direction of energy flow, moving from the food source to the consumer.
Classification of Consumers: Consumers are classified based on their position in the food chain:
* Primary consumers.
* Secondary consumers.
* Tertiary consumers.
* Caternary (Quaternary) consumers.Example: Grassland Ecosystem Food Chain:
* Grass: Acts as the producer, obtaining energy from the sun.
* Rabbit: Consumes the grass, and the energy stored in the grass is transferred to the rabbit.
* Fox: Acts as the predator, obtaining energy by preying on the rabbit.Food Web Definition: A food web is a network of interconnected food chains.
Example: Interconnected Food Web:
* Chain 1: Grass $\rightarrow$ Rabbit $\rightarrow$ Fox.
* Chain 2: Grass $\rightarrow$ Snail $\rightarrow$ Thrush $\rightarrow$ Fox.
* In this web, different chains share the same producer (grass) and the same top predator (fox), allowing them to be joined together.
Trophic Levels
Definition: A trophic level is the position of an organism in a food chain, food web, or ecological pyramid.
Feeding Levels: Each step in a food chain represents a different feeding level.
Specific Trophic Level Breakdown:
* Producers: Organisms that make their own organic nutrients (e.g., through photosynthesis using sunlight).
* Primary Consumers: Herbivores that feed directly on producers or plants.
* Secondary Consumers: Predators that feed on primary consumers.
* Tertiary Consumers: Predators that feed on secondary consumers.
* Cotternary Consumers: Predators that feed on tertiary consumers.Hypothetical Example of Trophic Levels:
* Producer: Plant.
* Primary Consumer: Grasshopper.
* Secondary Consumer: Mouse.
* Tertiary Consumer: Snake.
* Coternary Consumer: Hawk.
Human Impact on Food Chains and Ecosystems
System Interconnectivity: Food webs are highly interconnected; changes in the population of a single species can cause ripple effects throughout the entire web.
Anthropogenic Drivers of Change: Many fluctuations in plant and animal populations are the result of human activities.
Over-harvesting of Food Species:
* This disrupts food chains because organisms that rely on these species for food will lack the resources to survive.
* Consequence: Leading to population declines in dependent species.Introduction of Foreign Species:
* The introduction of non-native species creates competition for resources (food, space, etc.).
* Consequence: This harms existing species and disrupts the balance of the ecosystem.Case Study: Introduction of Owls to Control Grasshoppers:
* Scenario: Humans introduce owls to a habitat to reduce the population of grasshoppers (considered pests).
* Impact on Primary Producers: The population of grass would increase because there are fewer grasshoppers feeding on them.
* Significant Impact on Consumers: Populations of frogs and mice would decrease significantly because grasshoppers are their only food source.
* Slight Impact on Consumers: The population of thrushes would decrease slightly; while they eat grasshoppers, they have snails as an alternative food source.
* Conclusion: When one trophic level is damaged or altered, all subsequent levels are impacted as the available food supply decreases.
Ecological Pyramids
Definition: Graphical representations that illustrate the feeding relationships of organisms at each trophic level.
Pyramid of Numbers
Function: Shows the number of individual organisms at each trophic level of a food chain.
Structure: Producers are placed at the bottom, with consecutive levels of consumers stacked on top.
General Shape: Usually, as the size of an individual organism increases at higher levels, the number of individuals decreases, resulting in a narrow top and wide base.
Exceptions (Non-Pyramidal Shapes): A pyramid of numbers is not always pyramid-shaped.
* Example: One single large tree (producer) can support many smaller caterpillars (primary consumers), which in turn are eaten by birds.Limitations: This model can be misleading as it does not depict the true amount of energy present at each level. In the tree example, it may incorrectly appear as though there are not enough producers to support the chain.
Pyramid of Biomass
Biomass Definition: The total dry mass of one animal or plant species in a food chain or food web.
Function: Shows the total mass of organisms at each trophic level rather than the count of individuals.
Advantages: It provides a clearer picture of the actual amount of animal or plant material available. It usually maintains a true pyramid shape because biomass is lost at each successive level.
Comparative Example (Oak Tree, Aphids, Ladybirds):
* Pyramid of Numbers: Might show a very small base (one tree) and a huge middle (many aphids), appearing unstable.
* Pyramid of Biomass: Shows the oak tree having significantly more mass than the aphids, demonstrating it has more than enough energy to support the chain.
Pyramid of Energy
Function: Shows the flow of energy at each trophic level in an ecosystem.
Energy Transfer Efficiency:
* Energy decreases as it moves through trophic levels.
* The Rule: At each trophic level, approximately of the original energy is lost.
* Only of the energy is available to the organism at the next trophic level.Reasons for Energy Loss:
* Respiration.
* Movement.
* Maintaining body temperature.
* Undigested parts of food that cannot be processed.Consequences of Energy Loss:
* Energy transfer is often inefficient.
* Food chains are generally limited to fewer than trophic levels because there is insufficient energy to sustain higher levels.Human Food Consumption Efficiency:
* It is more energy-efficient for humans to eat crop plants directly than to eat livestock that were fed on crops.
* Consuming crops directly utilizes the stored energy of plants more efficiently.
* Consuming livestock involves an extra transfer step where significant energy is lost.Analytical Advantage: The pyramid of energy is the most advantageous representation because it accounts for energy loss and provides an accurate depiction of energy availability at higher levels.