chapter 10

• Life on Earth is solar powered.
• The chloroplasts of plants use a process called photosynthesis to capture light energy from the sun and convert it to chemical energy stored in sugars and other organic molecules.

  Plants and other autotrophs are the producers of the biosphere.

• Photosynthesis nourishes almost all the living world directly or indirectly.
  • All organisms use organic compounds for energy and for carbon skeletons.
  • Organisms obtain organic compounds by one of two major modes: autotrophic nutrition or heterotrophic nutrition.
• Autotrophs produce their organic molecules from CO2 and other inorganic raw materials obtained from the environment.
  • Autotrophs are the ultimate sources of organic compounds for all heterotrophic organisms.
  • Autotrophs are the producers of the biosphere.
• Autotrophs can be separated by the source of energy that drives their metabolism.
  • Photoautotrophs use light as a source of energy to synthesize organic compounds.
    • Photosynthesis occurs in plants, algae, some other protists, and some prokaryotes.
    • Chemoautotrophs harvest energy from oxidizing inorganic substances, such as sulfur and ammonia.
      • Chemoautotrophy is unique to prokaryotes.
• Heterotrophs live on organic compounds produced by other organisms.
  • These organisms are the consumers of the biosphere.
  • The most obvious type of heterotrophs feeds on other organisms.
    • Animals feed this way.
  • Other heterotrophs decompose and feed on dead organisms or on organic litter, like feces and fallen leaves.
    • Most fungi and many prokaryotes get their nourishment this way.
  • Almost all heterotrophs are completely dependent on photoautotrophs for food and for oxygen, a by-product of photosynthesis.

Figure 10.1 shows the absorption spectrum for chlorophyll a and the action spectrum for photosynthesis. Why are they different?

A) Green and yellow wavelengths inhibit the absorption of red and blue wavelengths.

B) Bright sunlight destroys photosynthetic pigments.

C) Oxygen given off during photosynthesis interferes with the absorption of light.

D) Other pigments absorb light in addition to chlorophyll a.

E) Aerobic bacteria take up oxygen, which changes the measurement of the rate of photosynthesis.

What wavelength of light in the figure is most effective in driving photosynthesis?

A) 420 mm

B) 475 mm

C) 575 mm

D) 625 mm

E) 730 mm