Question 1

How does energy flow through a food chain from producers to consumers?

Accepted Answer

Energy begins when plants capture sunlight and convert it into chemical energy stored in carbohydrates. When animals consume plants or other animals, they break down these molecules, releasing energy as heat or storing it in their tissues. This energy transfer continues through each trophic level—from producers to primary consumers to secondary consumers—with each stage representing a step in the food chain where biomass and energy are passed along.

Question 2

What is the difference between gross primary productivity and net primary productivity?

Accepted Answer

Gross primary productivity (GPP) is the total light energy plants capture from the sun through photosynthesis. Net primary productivity (NPP) is the energy remaining after plants use some for cellular respiration and release it as heat and carbon dioxide. NPP represents the actual energy available for storage as biomass and for consumption by primary consumers in the ecosystem.

Question 3

Why does biomass decrease at each trophic level in a food chain?

Accepted Answer

Biomass decreases at each level because organisms use energy for metabolism, releasing heat and carbon dioxide during cellular respiration. Additionally, not all consumed biomass is converted into consumer tissue—some is lost as waste. These energy losses mean that only a fraction of biomass from one trophic level transfers to the next, creating a pyramid structure with the largest biomass at the producer level.

Question 4

What is biomass and how is it measured in an ecosystem?

Accepted Answer

Biomass is the total organic matter stored in an organism, excluding water content. It is typically measured in energy units such as calories or kilocalories. To calculate biomass accurately, the weight of water is subtracted from an organism's total weight, providing a measure of the actual energy-storing material available for transfer between trophic levels in a food chain.

Question 5

How can the removal of a keystone predator disrupt ecosystem balance?

Accepted Answer

Keystone predators control prey populations and maintain ecosystem diversity. When removed, prey species can overpopulate, consuming excessive resources and reducing available space for other organisms. This imbalance demonstrates how understanding energy transfer and population growth exponential logistic growth patterns helps scientists identify which species are critical for maintaining ecosystem stability and preventing secondary extinctions.

Question 6

What is biomagnification and why is it a concern in aquatic food chains?

Accepted Answer

Biomagnification occurs when toxins like mercury are absorbed by organisms at the base of a food chain and then accumulate at higher concentrations as they move up through trophic levels. Large predatory fish at the top of aquatic food chains may contain dangerously high mercury levels, posing health risks to consumers. This demonstrates how energy transfer mechanisms can also transfer harmful substances through ecosystems.

Question 7

How do autotrophic and heterotrophic organisms differ in energy acquisition?

Accepted Answer

Autotrophic organisms, or primary producers, synthesize organic molecules from inorganic material using energy from sunlight or chemical sources. Heterotrophic organisms cannot create their own organic materials and must obtain energy by consuming other organisms. This fundamental difference establishes the foundation of food chains, where producers capture initial energy and consumers depend on that energy flowing through trophic levels.

Dynamique de l’énergie

La chaîne alimentaire

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