Biology 20 Unit A: Matter and Energy in the Biosphere & Biogeochemical Cycles

Flashcards covering ecosystem energy dynamics, thermodynamics, persistent pollutants, hydrologic and biogeochemical cycles, atmospheric evolution, ozone layer depletion, and eutrophication.

What defines a closed system like Earth in terms of matter and energy?

In a closed system, energy can be added or lost, but matter does not enter or leave.

What is the key difference between how matter and energy behave in the biosphere?

Matter cycles through decomposers and recycled nutrients, whereas energy flows in one direction and cannot change back once transformed.

What percentage of incoming solar radiation is absorbed by the Earth's land and oceans?

$$51\%$$

What are the three distinct zones that comprise the biosphere?

The lithosphere (land), hydrosphere (water), and atmosphere (air).

What is dynamic equilibrium in an ecosystem?

A condition in which a system continuously adjusts to changes in order to maintain a steady state within fluctuating limits.

How does biodiversity affect the stability of an ecosystem?

Greater biodiversity (a higher number of different species) increases stability, allowing the ecosystem to better adjust to changes and maintain dynamic equilibrium.

What does the First Law of Thermodynamics state?

Energy cannot be created or destroyed, only converted from one form to another.

What is entropy as defined by the Second Law of Thermodynamics?

Entropy is a measurement of non-usable or waste energy in a system, which is lost primarily as heat during energy transfers.

What is the balanced chemical equation for photosynthesis?

$$6\text{CO}_2 + 12\text{H}_2\text{O} + \text{energy from sun} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 + 6\text{H}_2\text{O}$$

What is the definition of a trophic level?

The number of energy transfers an organism is from the original source of energy entering the ecosystem.

How do photoautotrophs and chemoautotrophs differ in how they synthesize glucose?

Photoautotrophs use light energy in photosynthesis, whereas chemoautotrophs use chemical energy from compounds like sulfur and ammonia in chemosynthesis.

Why are terrestrial food webs rarely longer than five trophic links?

Because approximately $90\%$ of an organism's ingested energy is used for its own metabolic processes, leaving only about $10\%$ available for the next consumer.

Which ecological pyramid is the only type capable of having a narrow base?

A pyramid of numbers, which occurs when the primary producers are very large individual organisms, such as trees.

What does a pyramid of biomass measure at each trophic level?

It measures the total dry mass of living material per unit area ($g/m^2$), reflecting the stored energy content.

What is the difference between bioaccumulation and biomagnification?

Bioaccumulation is the buildup of a toxin in an individual organism over time, while biomagnification is the increasing concentration of persistent chemicals at higher trophic levels.

What detrimental developmental effect does DDT cause in bird populations?

It causes eggshell thinning, leading to reproductive failure.

What qualifies matter as organic, and what is a common exception containing carbon?

Organic compounds contain carbon usually bonded to hydrogen; carbon dioxide ($\text{CO}_2$) is a common inorganic exception.

What are the relative proportions of Nitrogen, Oxygen, and Carbon Dioxide in Earth's atmosphere?

Nitrogen accounts for $78\%$, Oxygen accounts for $21\%$, and Carbon Dioxide accounts for $0.04\%$.

What chemical structure makes water a polar molecule?

Water has covalent bonds where charge separation creates a positive end near the hydrogen atoms and a negative end near the oxygen atom.

What pH threshold defines acid rain?

A pH level of less than $5.6$.

Which industrial pollutants combine with water vapor in the atmosphere to produce acid rain?

Sulfur dioxide ($\text{SO}_2$) and nitrogen oxides ($\text{NO}_x$).

Where is the vast majority of Earth's carbon reservoir stored?

In rock.

What is carbon fixation?

The process by which plants absorb inorganic carbon ($\text{CO}_2$) from the atmosphere and incorporate it into organic molecules like glucose.

What would Earth's average global temperature be without the natural greenhouse effect?

Without the natural greenhouse effect, the average global temperature would be $-19\,^\circ\text{C}$, compared to its actual average of $14\,^\circ\text{C}$.

What causes the seasonal zigzag pattern in atmospheric $\text{CO}_2$ levels recorded at Mauna Loa?

High rates of photosynthesis by coniferous trees in the taiga during snow-free periods, which significantly lower global $\text{CO}_2$ levels.

What is albedo and what is its formula?

Albedo is the measurement of light reflection off a surface, calculated as $\text{Albedo} = \frac{\text{Reflected Light}}{\text{Incoming Light}}$.

How do light/shiny surfaces differ from dark/dull surfaces in terms of albedo and thermal absorption?

Light and shiny surfaces have a high albedo and reflect most heat, while dark and dull surfaces have a low albedo and absorb most heat.

What are stromatolites?

Stromatolites are layered, rock-like fossilized structures formed by slime-secreting colonies of cyanobacteria.

Why is stratospheric ozone beneficial, whereas tropospheric ozone is harmful?

Stratospheric ozone forms a protective layer absorbing harmful UV radiation, while tropospheric ozone near ground level acts as a toxic pollutant damaging respiratory tissue and plant life.

How do chlorofluorocarbons (CFCs) destroy stratospheric ozone?

UV radiation breaks CFCs apart to release free chlorine atoms, which bond to ozone ($\text{O}_3$) molecules and strip away oxygen atoms.

What was the purpose of the 1987 Montreal Protocol?

It was an international treaty designed to protect the stratospheric ozone layer by phasing out ozone-depleting substances like CFCs.

What is biological nitrogen fixation, and which plant family famously participates in it?

Nitrogen fixation is the process of converting atmospheric $\text{N}_2$ gas into ammonia ($\text{NH}_3$) or ammonium ($\text{NH}_4^+$); legumes (e.g., clover, beans, peas, peanuts) participate via root nodules.

What is nitrification in the nitrogen cycle?

The biological conversion of ammonia ($\text{NH}_3$) or ammonium ($\text{NH}_4^+$) into nitrites ($\text{NO}_2^-$) and then usable nitrates ($\text{NO}_3^-$) by nitrifying soil bacteria.

What process returns fixed nitrogen back to the atmosphere as $\text{N}_2$ gas?

Denitrification, carried out by anaerobic denitrifying bacteria in low-oxygen environments.

Why is the phosphorus cycle considered one of the slowest biogeochemical cycles?

Phosphorus is stored mainly in rocks and ocean sediments, relying on extremely slow geological processes like weathering, erosion, and uplifting.

How does fertilizer run-off cause fish mortality during eutrophication?

Fertilizer causes algal blooms that block sunlight and kill submerged plants; as decomposers break down the dead organic matter, they consume oxygen, deoxygenating the water and suffocating fish.