Coping with Environmental Variation: Energy


Toolmaking Crows: A Case Study


CONCEPT 5.1 Organisms obtain energy from sunlight, from inorganic chemical compounds, or through the consumption of organic compounds.

Learning Objective:

5.1.1 Differentiate autotrophy from heterotrophy in the context of building energy compounds using external sources of energy versus consuming them from organic matter.

Sources of Energy

CONCEPT 5.2 Radiant and chemical energy captured by autotrophs is converted into stored energy in carbon–carbon bonds.

Learning Objectives:

5.2.1 Summarize chemosynthesis, which results in the synthesis of energy-rich carbon–carbon bonds.

5.2.2 Outline the steps in the light-driven reactions and carbon reactions of photosynthesis, describing their outcomes and how they produce energy-rich compounds in photoautotrophs.

5.2.3 Illustrate how photosynthetic organisms acclimatize and adapt to variations in the intensity of light.

5.2.4 Evaluate the trade-offs that result when a plant controls water loss.

5.2.5 Describe how temperature influences photosynthetic rates through its effect on enzymes and chloroplast membranes.


  • Chemosynthesis harvests energy from inorganic compounds
  • Photosynthesis is the powerhouse for life on Earth

Analyzing Data 5.1: How Does Acclimatization Affect Plant Energy Balance?

CONCEPT 5.3 Environmental constraints have resulted in the evolution of biochemical pathways that improve the efficiency of photosynthesis.

Learning Objectives:

5.3.1 Explain the difference between photosynthesis and photorespiration and evaluate conditions where photorespiration is detrimental to plant growth.

5.3.2 Summarize how biochemical and anatomical adaptations associated with the C4 photosynthetic pathway minimize photorespiration, thereby enhancing photosynthesis rates.

5.3.3 Describe how crassulacean acid metabolism reduces water loss relative to the C3 or C4 photosynthetic pathways.

Photosynthetic Pathways

  • Photorespiration lowers the efficiency of photosynthesis
  • C4 photosynthesis lowers photorespiratory energy loss
  • CAM photosynthesis enhances water conservation

Ecological Toolkit: 5.1 Stable Isotopes

CONCEPT 5.4 Heterotrophs have adaptations for acquiring and assimilating energy efficiently from a variety of organic sources.

Learning Objectives:

5.4.1 Illustrate how the chemical makeup of a food item determines the benefit it provides to the consumer eating it.

5.4.2 Explain how morphological and behavioral adaptations enable heterotrophs to obtain food more efficiently.

5.4.3 Describe how increasing complexity in the digestive systems of heterotrophs makes the assimilation of energy and nutrients more efficient.


  • Food sources differ in their chemistry and availability
  • Heterotrophs obtain food using diverse strategies
  • Heterotrophs vary in the complexity of their digestion and assimilation

A Case Study Revisited: Toolmaking Crows

Connections in Nature: Tool Use: Adaptation or Learned Behavior?