APES Notes 1.9 & 1.10 - Trophic Levels & The 10% Rule

Summary

This video covers topics related to trophic levels and the 10% rule in ecosystems. It explains how energy and matter flow through trophic levels, emphasizing that only 10% of energy is transferred between levels, with the rest lost as heat. Key concepts include the conservation of energy and matter, the first law of thermodynamics, and examples like photosynthesis. The video also discusses how the 10% rule applies to biomass and provides calculations to determine energy at different trophic levels, illustrating why larger ecosystems can support only a small number of top predators.

Takeaways

• 🌞 Energy and matter are conserved through ecosystems, never created or destroyed, only transformed.
• 🌿 Photosynthesis demonstrates both the conservation of matter and energy by converting sunlight into chemical energy (glucose).
• 🔥 The first law of thermodynamics states that energy is never destroyed, just transformed into different forms.
• 🐰 As energy moves through trophic levels, a significant portion is lost as heat, limiting the energy available for higher levels.
• 🔋 Only 10% of energy moves up to the next trophic level, while the other 90% is used for processes like movement and metabolism.
• 🌲 Producers form the base of the trophic pyramid, with primary consumers (herbivores) eating plants and secondary consumers (carnivores) eating primary consumers.
• 📉 The 10% rule applies to both energy and biomass, meaning that only 10% of the biomass from one trophic level can support the next.
• 🌳 Large ecosystems, like forests, can only support a small number of top predators (e.g., wolves) due to the limited energy available at higher trophic levels.
• 🔢 Calculating energy across trophic levels is done by dividing by 10 or moving the decimal point one place to the left.
• 📊 Practice questions involve explaining why large ecosystems support few top predators and calculating available energy for tertiary consumers.

Q & A

What are the two main topics covered in this video?

The video covers trophic levels and the 10% rule, which explain how energy flows through ecosystems and how the available energy decreases as we move up the trophic pyramid.

What is the first objective of the lesson?

The first objective is to explain how energy and matter flow through trophic levels.

What is the second objective of the lesson?

The second objective is to determine how energy decreases as it flows through an ecosystem.

What does the first law of thermodynamics state?

The first law of thermodynamics states that energy is never created or destroyed, it is only transformed from one form to another.

What happens to the matter when a tree dies?

When a tree dies, its matter (carbon, nitrogen, water, phosphorus) is conserved and transformed into different forms, such as being returned to the soil or atmosphere, or absorbed by decomposers.

What is the 10% rule in the context of trophic levels?

The 10% rule states that only 10% of the energy from one trophic level is transferred to the next level, while 90% is lost as heat or used by the organism for life processes.

Why is the trophic pyramid shaped the way it is?

The trophic pyramid is wide at the bottom and narrows at the top because energy decreases with each step up the pyramid, meaning fewer organisms can be supported at higher trophic levels.

How does energy transfer from the sun to a rabbit through photosynthesis?

Energy from the sun is converted into chemical energy in the form of glucose by plants through photosynthesis. When a rabbit eats the plant, it absorbs this chemical energy, which it uses for growth and movement.

How is energy lost when it is transferred from one form to another?

Each time energy is transferred from one form to another (e.g., chemical to electrical to light energy), some of it is lost as heat and becomes unusable by organisms.

Why can a large forest only support a small number of wolves?

A large forest can only support a small number of wolves because, according to the 10% rule, only a small fraction of the energy available from plants is passed up to the wolves at the top of the trophic pyramid. Most of the energy is lost as heat or used up by organisms at lower levels.