2.2C Second law of thermodynamics Notes

1. The Second Law of Thermodynamics states that energy transformations are inefficient and that in every transformation, some energy is degraded into a less useful form, typically heat.
2. This law relates to the quality of energy, not its quantity.
3. Although the total energy in a system remains constant (as per the First Law), the amount of usable energy decreases after each transformation.
4. In ecosystems, the largest energy losses occur during cellular respiration, when chemical energy from food is transformed into heat.

Energy Degradation in Ecosystems

1. Energy enters ecosystems as concentrated light from the Sun (a high-quality energy form).
2. Through photosynthesis, this is converted into chemical energy in biomass.
3. As organisms use this energy (through respiration, growth, movement, etc.), much is released as heat.
4. Thus, with each transformation, energy disperses, increasing entropy (disorder) in the system.

Energy Transformations and Inefficiency in Ecosystems

1. Energy enters ecosystems in a concentrated form (solar radiation) and gradually becomes dispersed as it moves through trophic levels.
2. At each stage:
   1. Producers absorb only a small portion of incoming solar energy due to reflection, transmission, and inefficiency of photosynthesis.
   2. Consumers and decomposers lose energy through respiration, excretion, and movement.
   3. Heat is the most significant form of energy degradation.
3. In ecosystems, the largest energy losses occur during cellular respiration, where chemical energy is converted into work and heat.

Ecological Efficiency and Energy Availability

1. Ecological efficiency measures how much energy is transferred from one trophic level to the next.
2. Formula:
   $$\text{Ecological efficiency} = \frac{\text{Energy used for growth (new biomass)}}{\text{Energy supplied}} \times 100$$
3. Typically, this value ranges between 5%-20%, with an average of 10% in most ecosystems.
4. This inefficiency limits biomass production at higher trophic levels and determines ecosystem carrying capacity.

Consumers Obtain Energy from Producers or Other Organisms

1. Consumers are organisms that obtain energy and matter by feeding on other organisms.
2. They are heterotrophs, unable to produce their own food because they lack photosynthetic pigments like chlorophyll.
3. Consumers depend on carbon-containing organic compounds (e.g., carbohydrates, fats, proteins) synthesized by autotrophs.
4. They play a crucial role in transferring chemical energy and matter through food chains and webs.

Types of Consumers and Their Energy Strategies

1. Herbivores

1. Feed directly on producers (plants or algae).
2. Represent primary consumers in food chains.
3. Possess specialized teeth, digestive tracts, or symbiotic bacteria to break down cellulose.

2. Detritivores

1. Feed on dead organic matter (detritus) such as fallen leaves, feces, and carcass fragments.
2. Have internal digestion systems that allow them to process decomposing material.
3. Help fragment organic matter, increasing surface area for decomposers.

3. Predators

1. Hunt, capture, and kill other animals (prey) for food.
2. Usually occupy higher trophic levels and maintain ecosystem balance by controlling population size.
3. Rely on acute sensory adaptations, speed, or stealth to capture prey.

4. Parasites

1. Derive nutrients from a host organism, often harming but not immediately killing it.
2. Exhibit specialized adaptations for attachment and nutrient absorption.
3. Can live internally (endoparasites, e.g., tapeworms) or externally (ectoparasites, e.g., ticks).

5. Saprotrophs

1. Include fungi and bacteria that secrete digestive enzymes onto dead organic matter.
2. Digest food externally and absorb nutrients.
3. This process is called saprotrophic digestion.
4. Play a vital role in nutrient recycling, breaking complex organic molecules into simpler inorganic forms.

6. Scavengers

1. Feed on dead animals they did not kill themselves.
2. Often consume carrion left behind by predators or natural deaths.
3. Help prevent the spread of disease by removing carcasses from ecosystems.

7. Decomposers

1. Break down dead organic material and return nutrients to the soil and atmosphere.
2. Include bacteria, fungi, and some protists.
3. Enable nutrient recycling by converting complex organic compounds into inorganic substances (e.g., nitrates, carbon dioxide).
4. Their activity contributes to humus formation in soil, enhancing fertility and structure.

Interconnected Roles of Consumers

1. Each consumer type contributes differently to energy transfer and matter cycling.
2. Together, they maintain ecosystem stability, nutrient availability, and biomass flow.
3. Consumers and decomposers close the loop between energy degradation and matter recycling.

Integration of Thermodynamics and Consumer Roles

1. The Second Law of Thermodynamics explains why consumers and decomposers experience significant energy losses during respiration.
2. Heat generated during these processes cannot be recovered, which limits the total energy available for higher trophic levels.
3. Thus, both energy degradation (entropy increase) and trophic inefficiency shape the structure and productivity of ecosystems.