GCSE Biology: Conservation, Food Security & Decomposition

Biodiversity is the diversity of life including plants, animals, microbes, and ecosystems. It is the foundation of ecological stability that supports planetary balance. A biodiverse system is most stable, adaptive, and resilient with no human disturbance. When biodiversity declines, ecosystems weaken and become less able to recover from disturbance, leading to ecological deficits, disasters, and catastrophes. Biodiversity has three major levels: (1) Genetic diversity - variation within species that allows adaptation to climate change or other situations; (2) Species diversity - the number and variety of species in a habitat, with different species having different functions that control ecosystem stability; (3) Ecosystem diversity - different types of ecosystems such as forests, wetlands, oceans, rivers, and grasslands, each with different animals and plants suited to their environments. Biodiversity plays a direct role in maintaining Earth's life support systems. Forests, oceans, and wetlands regulate climate. Biodiversity purifies air and water, ensuring human health and survival. Biodiversity supports food security through pollinators that enable global food production. Crop diversity strengthens food resilience by ensuring different crops have different strengths - some tolerate drought, others resist pests or diseases. Biodiversity is the foundation of modern and traditional medicines. Over 50% of pharmaceuticals are derived from plants, animals, or microorganisms.

Biodiversity contributes to ecosystem stability through reduced variability in productivity. David Tilman's experiments showed that communities with higher species richness have less variation in annual productivity. A stable community has three characteristics: (1) Low variation in productivity from year to year, (2) Resistance to occasional disturbances, and (3) Resistance to invasion by alien species. The Rivet Popper Hypothesis compares biodiversity loss to removing rivets from an airplane - initially, removing one rivet may not affect flight safety, but cumulative losses can lead to ecosystem collapse. Biodiversity loss ultimately affects human survival by compromising ecosystem services.

Biodiversity is essential for ecosystem stability and human survival. An ideal ecosystem maintains stability without significant annual changes, resists natural and human-induced disturbances, and withstands foreign species invasion. David Tilman's experiments demonstrated that higher species diversity leads to greater ecosystem productivity and less variation in biomass over time. The Rivet Popper Hypothesis, proposed by Paul Ehrlich, uses an airplane analogy to explain ecosystem stability: just as an airplane is held together by thousands of rivets, an ecosystem is maintained by many species working together. Gradual removal of species eventually compromises the entire structure. Currently, over 15,500 species face extinction: 12% of birds, 23% of mammals, 32% of amphibians, and 31% of reptiles. Major causes include habitat loss (tropical rainforests declining from over 14% to less than half), habitat fragmentation, overexploitation, and invasive species. When biodiversity is damaged, consequences include reduced plant productivity, decreased resistance to environmental stresses, and disruption of ecosystem processes. This demonstrates that biodiversity conservation is not merely an environmental concern but a fundamental requirement for human survival and sustainable development.

Biodiversity—the variety of life on Earth—is essential for human survival and prosperity because it provides ecosystem stability, economic value ($33 trillion annually), water purification, soil fertility, food security (100 billion kg from oceans), and medicines (painkillers, cardiac drugs, anti-cancer treatments, diabetes medications); biodiversity loss increases disease spread (SARS, Ebola, malaria) and threatens future food and medical resources.

Biodiversity loss represents the single biggest problem facing humanity. Without biodiversity, the world as we know it cannot function properly. Every species is a component in the global ecological machine, and only when all components are healthy can the planet operate smoothly. A less wild world is less able to provide for human needs, maintain dependable weather patterns, and absorb human impacts. Biodiversity equals stability, which is essential for human survival.

This section explains energy flow in ecosystems: (1) Food chains are linear sequences starting with producers (green plants) followed by primary consumers (herbivores) and secondary consumers (carnivores); (2) Food webs form when multiple food chains interconnect; (3) Green plants are producers that create food through photosynthesis and form the foundation of all food chains; (4) Energy decreases progressively as it transfers between trophic levels due to energy loss through metabolic processes and waste excretion. This explains why food chains typically have limited trophic levels.

Food chains show linear energy flow: producers → primary consumers → secondary consumers → tertiary consumers. Food webs are interconnected chains showing complex feeding relationships. Energy transfer is inefficient: only ~10% passes to next level, 90% lost as heat/respiration. Biomass decreases up the chain. Trophic pyramids show decreasing biomass, energy, and increasing toxin concentration. Changes at any trophic level cascade through the entire system.

A food chain shows which organism eats which other organism in a linear sequence. Trophic levels represent the position of organisms in the food chain: producers at level 1, primary consumers at level 2, secondary at level 3, tertiary at level 4, and quaternary at level 5. The 10% law states that only 10% of energy transfers between trophic levels, with 90% lost as heat. This explains why food chains rarely exceed 4-5 levels. Energy flows unidirectionally from the sun through producers to consumers.

Trophic levels represent functional positions in food chains based on feeding habits: T1 (producers), T2 (primary consumers/herbivores), T3 (secondary consumers/carnivores), T4 (top carnivores). Food chains show linear energy flow pathways, while food webs represent interconnected networks of feeding relationships. Two main types exist: grazing food chains (starting with living producers) and detritus food chains (starting with dead organic matter). In aquatic ecosystems, grazing food chains dominate due to limited decomposition at depth. In terrestrial ecosystems, detritus food chains are more important. The 10% rule states only 10% of energy transfers between trophic levels, limiting ecosystems to about 4-5 trophic levels.

A food chain consists of producers (plants), primary consumers (herbivores), and secondary consumers (carnivores). A key rule states that consuming 10kg of food produces 1kg of biomass. When calculating biomass transfer: divide producer biomass by 10 for the first consumer, then divide again by 10 for the second consumer. Biomass decreases at each trophic level because organisms use energy for vital functions like movement, respiration, and temperature regulation, with some lost as heat and waste.

Decomposers (bacteria and fungi) play a crucial role in the carbon cycle by breaking down dead organic matter. During decomposition, decomposers release carbon dioxide through cellular respiration, returning carbon to the atmosphere and completing the cycle.

Decomposers, including bacteria and fungi, play a crucial role in the carbon cycle by breaking down organic matter from dead organisms. This decomposition process releases carbon back to the atmosphere in the form of carbon dioxide, completing the cycle and making carbon available for reuse by living organisms.

Decomposers (bacteria and fungi) break down dead organic matter from plants and animals. During decomposition, they break down organic compounds and release carbon dioxide back into the atmosphere through respiration. This process returns carbon to the atmosphere, making it available again for photosynthesis by producers.

Decomposers (bacteria and fungi) play a crucial role in nutrient cycling by breaking down complex organic matter from dead organisms and waste products into simple inorganic compounds. This decomposition process releases locked-up nutrients (carbon, nitrogen, phosphorus) back into the soil in forms that producers can absorb. Without decomposers, organic matter would remain locked in dead bodies and waste, making nutrients unavailable for ecosystem recycling.

Decomposers (bacteria and fungi) play a crucial role in the carbon cycle by breaking down dead organic matter. During respiration, they release carbon dioxide back into the atmosphere. This process recycles carbon from dead organisms back into the ecosystem, making it available for photosynthesis by plants.

A rate of change describes how one quantity changes in relation to another. To calculate it, find the change in the quantity (final minus initial) and divide by the change in time (final time minus initial time). For example, if email entries increased from 10 to 62 over 3 years, the rate is (62-10)÷3 = 17 entries per year. Positive rates show increases, while negative rates show decreases. Graphically, positive rates appear as upward-slanting lines, negative rates as downward-slanting lines, and zero rates as horizontal lines.

Rate of change is the ratio of two quantities, describing how one quantity changes in relation to another. The formula is: Rate of Change = (Change in Quantity 1) / (Change in Quantity 2). To calculate: (1) Identify the two quantities, (2) Determine which comes first in the question, (3) Place the change in that quantity in the numerator, (4) Place the change in the other quantity in the denominator, (5) Always subtract the first value from the second value. A positive result indicates an increase in the quantity, while a negative result indicates a decrease.

When rate of change is not specified with respect to any variable, use time as the reference. To calculate rate of change: (1) Identify initial and final values, (2) Calculate the change (final - initial), (3) Identify the reference variable (usually time), (4) Divide the change by the change in the reference variable. For example, if a quantity increases from 5 to 10 over 5 seconds, the rate of change is (10-5)/5 = 1 unit per second.

To calculate a rate of change, first determine the total change by finding the difference between initial and final values. Then divide this total change by the time period to find the rate per unit time. For example, if 4,650 bushes were removed in 5 hours, the rate is 4,650 ÷ 5 = 930 bushes per hour.

To find the rate of change, divide the total change by the time period. If a piece of ice decreases from 35.6 to 35.4 in one second, the change is 0.2 per second. To find the change after 8 seconds, multiply the rate by time: 0.2 × 8 = 1.6. The final amount = initial amount - total change = 35.6 - 1.6 = 34.