Topic 4.2 Energy Flow

Essential idea:

Ecosystems require a continuous supply of energy to fuel life processes and to replace energy lost as heat.

Nature of science:

Use theories to explain natural phenomena—the concept of energy flow explains the limited length of food chains.

Understandings:

U1• Most ecosystems rely on a supply of energy from sunlight.

U2• Light energy is converted to chemical energy in carbon compounds by

photosynthesis.

U3• Chemical energy in carbon compounds flows through food chains by means of feeding.

U4• Energy released from carbon compounds by respiration is used in living organisms and converted to heat.

U5• Living organisms cannot convert heat to other forms of energy.

U6• Heat is lost from ecosystems.

U7• Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.

Applications and skills:

S1• Skill: Quantitative representations of energy flow using pyramids of energy.

Guidance:

• Pyramids of number and biomass are not required. Students should be clear that biomass in terrestrial ecosystems diminishes with energy along food

chains due to loss of carbon dioxide, water and other waste products, such as urea.

International-mindedness:

• The energetics of food chains is a factor in the efficiency of food production for the alleviation of world hunger.

Utilization: Links to other sections of the course

Syllabus and cross-curricular links:

Biology

Topic 2.8 Cell respiration

Topic 2.9 Photosynthesis

Physics

Topic 2.3 Work, energy and power

Topic B.2 Thermodynamics

Environmental systems and societies

Topic 2.3 Flows of energy and matter

Flipped Notes: 4.2 IB Biology Notes By Cheryl Haus

Understandings:

U1• Most ecosystems rely on a supply of energy from sunlight.

Where does the energy in a food chain start from?

What are some examples of ecosystems that do not use sunlight as their initial energy source?

Ecosystem / Initial Energy Source / Example Food Chain

Producers like plants and algae, rely on sunlight ______(they need it for photosynthesis)

Consumers rely on sunlight ______, because their food sources needed light for photosynthesis

U2• Light energy is converted to chemical energy in carbon compounds by photosynthesis.

Review: Topic 2.9 Photosynthesis

Formula and Energy Conversion for Photosynthesis:

Formula and Energy Conversion for Cellular Respiration

Energy in food is measured in calories (kilocalories)

What is on food labels? ______why?______

Photosynthesis is the process by which cells synthesize organic compounds (e.g. glucose) from inorganic molecules (CO2and H2O) in the presence of sunlight.This process requires a photosynthetic pigment (chlorophyll) and can only occur in certain organisms (plants, some protists and certain bacteria)

Photosynthetic organisms use the light energy from the sun to create chemical energy (ATP)

  • This chemical energy can either be used directly by the organism or used to synthesize organic compounds (e.g. glucose)


Animals then consume these organic compounds as food and release the stored energy via cell respiration

  • Photosynthesis (anabolic synthesis of organic compounds) is essentially the reverse of cell respiration (catabolic breakdown)

U3• Chemical energy in carbon compounds flows through food chains by means of feeding.

Energy flow: ______

In a food chain, what do the arrows represent?______

Food Chain = ______AND ______

Trophic Level = ______

*** Notes that the Primary consumer is at the second trophic level

DO WORKBOOK ACTIVITY 122 & 123

U4• Energy released from carbon compounds by respiration is used in living organisms and converted to heat.

Energy stored in organic molecules (e.g. sugars and lipids) can be released by cell respiration to produce ATP

Cell Respiration:

  • This ATP is then used to fuel metabolic reactions required for growth and homeostasis
  • A by-product of these chemical reactions isheat(thermal energy), which is released from the organism

Not all energy stored in organic molecules is transferred via heterotrophic feeding – some of the chemical energy is lost by:

  • Being excreted as part of the organism’s feces
  • Remaining unconsumed as the uneaten portions of the food

U5• Living organisms cannot convert heat to other forms of energy.

What happens to the nutrients in an ecosystem?

What happens to the energy in an ecosystem?

Organisms can convert many types of energy:

• Light energy to chemical energy in photosynthesis.

• Chemical energy to kinetic energy in muscle contraction.

• Chemical energy to electric energy in neurons.

• Chemical energy to heat energy in heat generating adipose tissue (for homeostasis)

But once the energy becomes heat, organisms cannot convert it to any other form of energy.

U6• Heat is lost from ecosystems.

  • Only ______(in food) can be transferred from one ______to the next
  • Unfortunately only ______of the energy in one trophic level is transferred to the next

Where does the heat Go? Reasons for energy loss

  1. .______
  2. .______
  3. .______
  4. ***______

You are weird if you eat shrimp shells

Applications and skills:

S1• Skill: Quantitative representations of energy flow using pyramids of energy.

Pyramids of energy: ______

Why can they not be a triangular shape?

Units: ______

Why? What is this a measure of? ______

DO WORKBOOK ACTIVITY 125 & 126

Are pyramids of population and energy interchangeable?

Explain:

Construct a Pyramid of energy in which producers make 100,000 kJ/m2/yr

U7• Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.

Although there are exceptions, most food chains only have ____ trophic levels

Why is this?

What is the difference between a food chain and a food web?

Can an organism be in more that one trophic level within a food web? ______Explain

DO WORKBOOK ACTIVITY 124 (optional)