Ecosystem Energy Flow, Classification, and Biodiversity: General Biology Study Notes

Ecosystem Energy Flow

Primary and Secondary Production

Energy flow in ecosystems begins with primary producers and continues through various trophic levels. Primary production refers to the creation of organic compounds from inorganic sources, mainly through photosynthesis. Secondary production is the amount of chemical energy in consumer food that is converted into new biomass during a time period.

• Primary producers (autotrophs) convert solar energy into chemical energy (biomass).

• Secondary production is performed by organisms that consume other organisms and convert that energy into their own biomass.

• Example: A caterpillar eats a leaf, bringing in energy from the plant and transforming it into caterpillar biomass.

Food Chains and Food Webs

A food chain is a sequence of organisms in which each is the food source for the next. Food webs are complex networks of interconnected food chains, showing the multiple feeding relationships in an ecosystem.

• Food chains are typically limited to about 4 levels due to energy loss at each step.

• Food webs illustrate the interconnectedness and cycling of nutrients and energy.

• There are terrestrial and marine food chains.

• Single-cell organisms can play unique roles in food webs.

Trophic Efficiency and Energy Pyramids

Trophic efficiency is the percentage of energy transferred from one trophic level to the next. The pyramid of energy shows that most energy is at the base (primary producers), and only a small fraction is transferred upward.

• On average, about 10% of energy is transferred between trophic levels.

• Trophic efficiency varies from 5% to 20%.

• Energy is lost as heat at each transfer, limiting the number of trophic levels (usually 3-4).

• Predators at higher levels have less energy and biomass available.

Formula:

$\text{Trophic Efficiency} = \frac{\text{Energy at higher trophic level}}{\text{Energy at lower trophic level}} \times 100\%$

Types of Consumers

Consumers are classified based on their feeding habits:

• Primary consumers: Eat primary producers (herbivores).

• Secondary consumers: Eat herbivores (carnivores).

• Tertiary consumers: Eat other carnivores.

• Omnivores: Eat both plants and animals.

• Scavengers: Feed on dead plant or animal material (e.g., vultures).

• Detritivores: Feed on detritus (partially decomposed organic matter).

• Decomposers: Break down organic matter into simpler chemical compounds (e.g., bacteria, fungi).

Primary Production and Productivity

Gross and Net Primary Productivity

Gross primary productivity (GPP) is the total rate at which light energy is captured by producers and converted into chemical energy. Net primary productivity (NPP) is the rate at which energy is stored as new biomass, available to consumers, after producers use some energy for their own needs.

• GPP measures total energy captured.

• NPP = GPP minus energy used by producers for respiration.

Formula:

$\text{NPP} = \text{GPP} - \text{Respiration}$

Global Patterns of Primary Production

• Middle of the ocean: low productivity.

• Highest productivity: tropical rain forests, algae beds, reefs, swamps, and marshes.

• 22% of Earth's NPP comes from tropical rain forests.

• Phytoplankton are major aquatic producers; zooplankton consume them.

Abiotic and Biotic Components of Ecosystems

Sunlight and Climate

Sunlight drives photosynthesis and influences climate and seasons. Earth's rotation and tilt cause seasonal changes, not the distance from the sun.

• 365 days for Earth to orbit the sun; 24 hours for one rotation.

• Major abiotic components: temperature, water, light, wind.

• Biomes are large ecological zones with characteristic flora and fauna.

Energy and Nutrients

Energy flows through ecosystems, while nutrients cycle. Photosynthesis captures solar energy and transforms it into chemical energy.

• Photosynthesis equation:

$6CO_2 + 6H_2O + \text{solar energy} \rightarrow C_6H_{12}O_6 + 6O_2$

• Inputs: carbon dioxide, water, solar energy

• Outputs: glucose, oxygen

• Plants, algae, and some bacteria use chlorophyll to capture sunlight.

Respiration

Aerobic respiration is the process by which energy-rich molecules (e.g., glucose) are combined with oxygen to produce carbon dioxide, water, and energy.

• Occurs in the presence of oxygen.

• Opposite of photosynthesis.

Formula:

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy}$

Classification and Biodiversity

Taxonomic Hierarchy

Organisms are classified into hierarchical categories from broadest to most specific:

• Domain

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

Mnemonic: Did King Phillip Come Over From Germany?

Prokaryotes vs. Eukaryotes

• Prokaryotes: Cells lack a distinct nucleus and internal membrane-bound organelles (e.g., bacteria, archaea).

• Eukaryotes: Cells have a true nucleus and membrane-bound organelles (e.g., plants, animals, fungi, protists).

Three Domains of Life

• Bacteria: Most diverse and widespread prokaryotes; single-celled organisms.

• Archaea: Prokaryotic; often live in extreme environments; single-celled.

• Eukarya: Multi-celled; includes plants, animals, fungi, protists.

Traditionally, life was divided into five kingdoms, but this is no longer considered valid; more kingdoms may exist.

Homologous vs. Analogous Structures

Classification can be based on anatomical similarities:

• Homologous structures: Similar due to shared ancestry (e.g., human, cat, whale, bat limbs).

• Analogous structures: Similar in function but not due to shared ancestry; result from convergent evolution (e.g., bat, bird, butterfly wings).

Convergent evolution: Species from different evolutionary branches develop similar adaptations due to similar ecological roles.

Ecology: Interactions and Species Concepts

Ecology and Components

Ecology studies the relationships between organisms and their environment, including biotic (living) and abiotic (non-living) components.

• Biotic components: Living organisms.

• Abiotic components: Non-living chemical or physical factors (e.g., temperature, water, nutrients).

Example: The ecology of a polar bear includes its diet (seals), how it finds prey, and its interactions with the environment.

Biological Species Concept

A species is a population of individuals that resemble each other, can interbreed in nature, and produce viable, fertile offspring.

• They look alike.

• Can reproduce with each other.

• Have healthy reproductive status.

Biogeochemical Cycles: Nitrogen Cycle

Nitrogen Cycle

The nitrogen cycle describes the movement of nitrogen through the environment and living organisms. Nitrogen is essential for life but must be converted into usable forms.

• Nitrogen fixation: Conversion of atmospheric nitrogen (N2) into ammonium (NH4+) by bacteria.

• Nitrification: Conversion of ammonium to nitrite (NO2-) and then nitrate (NO3-).

• Assimilation: Plants absorb nitrate and use it to make proteins and other organic compounds.

• Ammonification: Decomposition releases ammonium back into the soil.

• Denitrification: Conversion of nitrate back to nitrogen gas (N2) by bacteria, returning it to the atmosphere.

Step	Process	Key Organisms
Nitrogen Fixation	N2 → NH4+	Bacteria (e.g., cyanobacteria)
Nitrification	NH4+ → NO2- → NO3-	Bacteria
Assimilation	NO3- absorbed by plants	Plants
Ammonification	Organic N → NH4+	Decomposers
Denitrification	NO3- → N2	Bacteria

• Nitrogen is a limiting nutrient in many ecosystems.

• Human activities (fertilizers, fossil fuels) can add excess nitrogen, leading to eutrophication (nutrient overload in water bodies, causing algal blooms and oxygen depletion).

• "Dead zones" can result from runaway eutrophication.

Levels of Biological Organization

• Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biosphere

Take-home message: Energy flow, nutrient cycling, classification, and ecological interactions are fundamental concepts in general biology, essential for understanding the structure and function of living systems.