Junior Cycle Science Quiz: Constructing a Food Web Activity
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Constructing a Food Web Activity

Ecology is the study of how living things on Earth interact with and rely on other living and non-living things in the environment where they live.

Ecology is the study of ecosystems.
Ecosystems describe the network of relations among organisms. Examples of ecosystems include forest ecosystems, grassland ecosystems and desert ecosystems.

Living organisms need energy to survive.
A food chain shows how each living thing gets its food. Some animals eat plants and some animals eat other animals. 
Arrows in a food chain show the direction of energy flow from one organism to the organism that eats it.
Only 10% of the energy in an organism is passed onto the next, this is why food chains a short.

A food web is similar to a food chain but larger, it is a diagram that combines many food chains into one picture. ​
1. Energy Flow in Ecosystems
The Role of the Sun:
  • The Sun is the primary source of energy for most ecosystems.
  • Solar energy is captured by plants through photosynthesis to produce food (glucose).
Energy Transfer:
  • Producers: Plants (and some algae) convert sunlight into chemical energy stored in glucose.
  • Consumers:
    • Primary Consumers: Herbivores that eat plants (e.g., rabbits, deer).
    • Secondary Consumers: Carnivores that eat herbivores (e.g., foxes, wolves).
    • Tertiary Consumers: Top predators that eat other carnivores (e.g., eagles, lions).
  • Decomposers: Organisms like fungi and bacteria break down dead plants and animals, returning nutrients to the soil.
Energy Loss:
  • At each trophic level, energy is lost as heat due to metabolism, with only about 10% of energy transferred to the next level.

2. Matter Cycles in Ecosystems
Key Cycles:
  1. The Carbon Cycle:
    • Carbon moves between the atmosphere, organisms, and the Earth.
    • Plants absorb carbon dioxide (CO2CO_2CO2​) during photosynthesis and return it during respiration.
    • Decomposers release CO2CO_2CO2​ when breaking down dead material.
  2. The Water Cycle:
    • Involves processes like evaporation, condensation, precipitation, and collection.
    • Essential for transporting nutrients within ecosystems.
  3. The Nitrogen Cycle:
    • Nitrogen in the air is converted by bacteria into forms plants can absorb (e.g., nitrates).
    • Returned to the atmosphere when organisms decompose or through denitrifying bacteria.

3. Food Chains and Food Webs
​Food Chain:
  • A simple linear representation of energy flow.
  • Example: Grass → Rabbit → Fox.
Food Web:
  • A complex network showing all feeding relationships in an ecosystem.
  • Highlights how species are interconnected and dependent on each other.

4. Importance of Decomposers
  • Decomposers recycle nutrients by breaking down organic matter into simpler substances.
  • They release nutrients like nitrogen and carbon back into the soil for plants to use.

5. Key Points to Remember
  1. Energy flows in one direction through ecosystems—from producers to consumers to decomposers.
  2. Matter cycles continuously between organisms and the environment through processes like photosynthesis, respiration, and decomposition.
  3. Energy is constantly lost as heat, making ecosystems dependent on a continuous energy input from the Sun.

Summary
  • Energy flows through ecosystems in a one-way path from the Sun to producers and then to consumers, with energy being lost as heat at each step.
  • Matter, on the other hand, is recycled through ecosystems via the carbon, nitrogen, and water cycles, ensuring nutrients are reused.

Questions: 

Q1: What is the primary source of energy for most ecosystems?
A: The Sun is the primary source of energy for most ecosystems.
Q2: What is the role of producers in an ecosystem?
A: Producers, like plants and algae, convert sunlight into chemical energy through photosynthesis.
Q3: What are primary consumers?
A: Primary consumers are herbivores that feed on producers (e.g., rabbits, deer).
Q4: How much energy is typically transferred between trophic levels?
A: About 10% of energy is transferred from one trophic level to the next, with the rest lost as heat.
Q5: What is a food chain?
A: A food chain is a linear representation of how energy flows through an ecosystem (e.g., Grass → Rabbit → Fox).
Q6: What is the difference between a food chain and a food web?
A:
  • A food chain shows a simple energy flow in a straight line.
  • A food web shows interconnected food chains and complex feeding relationships.
Q7: What is the role of decomposers in an ecosystem?
A: Decomposers break down dead plants and animals, recycling nutrients back into the soil.
Q8: What is the carbon cycle?
A: The carbon cycle describes how carbon moves between the atmosphere, organisms, and Earth through processes like photosynthesis, respiration, and decomposition.
Q9: How does energy flow differ from matter cycling in ecosystems?
A:
  • Energy flows in one direction (from the Sun to producers, consumers, and decomposers).
  • Matter cycles continuously between organisms and the environment.
Q10: Name three key processes in the water cycle.
A: Evaporation, condensation, and precipitation.
Q11: Why are decomposers essential to nutrient cycles?
A: Decomposers recycle nutrients like nitrogen and carbon, making them available for plants to use.
Q12: What is the nitrogen cycle?
A: The nitrogen cycle describes how nitrogen is converted into forms usable by plants and returned to the atmosphere by decomposers and denitrifying bacteria.
Q13: What happens to energy as it moves through trophic levels?
A: Energy is lost as heat at each trophic level due to metabolic processes.
Q14: Why is only 10% of energy transferred between trophic levels?
A: Most energy is used for metabolism, growth, and reproduction, while the rest is lost as heat.
Q15: Give an example of a simple food chain.
A: Grass → Grasshopper → Frog → Snake → Hawk.