Photosynthesis, Respiration, and Net Primary Production Notes

Oxygenic Photosynthesis

• Requires chlorophyll and sunlight to split water, producing oxygen.

• Converts carbon dioxide into organic matter using energy stored in ATP and NADPH.

• Performed by plants, algae, and cyanobacteria, leading to carbon fixation.

Significance of Oxygenic Photosynthesis

• Carbon-based life relies on carbon from photosynthesis ($CO_2$).

• Photosynthesis removes $CO_2$, a greenhouse gas, from the atmosphere.

• Converts solar energy into stored chemical bond energy.

• Produces oxygen for aerobic respiration.

Respiration

• Opposite of photosynthesis.

• Combines sugars and oxygen to produce carbon dioxide, water, and energy.

• Releases energy for maintenance, growth, and reproduction.

• Similar to combustion and decomposition.

Photosynthesis and Respiration Summary

• Rates are approximately equal globally over a year but vary seasonally.

Requirements for Growth

• Plants, algae, and cyanobacteria need: $CO<em>2$, $H</em>2O$, sunlight, suitable temperature, and nutrients.

• Plants require an atmosphere for gas exchange.

Autotrophy vs. Heterotrophy

• Autotrophy: Uses carbon dioxide as the sole carbon source (primary production).

  • Photoautotrophy (using light) or chemoautotrophy (using chemicals).

• Heterotrophy: Consumes other organisms.

• Trophic Level: An organism’s level in a food chain/web.

Net Primary Production (NPP)

• NPP: Organic carbon remaining with autotrophs after respiration.

• Available for trophic transfer.

• Gross Primary Production (GPP): Total carbon fixed by autotrophs.

Estimating Photosynthetic Biomass from Space

• Estimated via chlorophyll detection, a visible pigment in photosynthesizers.

Spatial and Temporal Variation in Primary Producer Biomass

• Varies by region due to nutrients, temperature, and rainfall.

• Seasonal variations exist.

Primary Production in the Ocean: Depth

• Photosynthesis limited to surface layers due to light requirements.

• Respiration occurs as organic matter sinks.

• Seasonal variations occur at high latitudes due to light availability.

Primary Production in the Ocean: Nutrients

• High near coasts due to nutrient runoff and in upwelling zones.

• Examples: end of ocean conveyor belt, Eastern Boundary currents, the Equator.

Primary Production in the Ocean: Trophic Energy vs. Biomass Pyramids

• Differ in aquatic ecosystems due to turnover rates and size differences.

Primary Production on Land Factors

• Solar Energy: Seasonal at high latitudes.

• Temperature: Warmer is preferred.

• Moisture Level: High rainfall supports rain forests.

• Nutrient Availability: Nutrients in soil.

• $CO_2$: Usually not limiting.

• Community Interactions: Herbivores can reduce plant biomass.

Practice Questions (NPP)

• Factors affecting NPP in the ocean vs. on land.

• Impact of global change on NPP.

Main Points

• Photosynthesizers use $CO_2$, water, and solar energy to produce organic matter and oxygen.

• Respiration is the opposite of photosynthesis.

• Autotrophs produce their own food; heterotrophs consume other organisms.

• Biosphere consists of ecosystems with trophic levels and interactions.

Main Points Continued

• Trophic pyramid represents biomass and energy transfer (10% efficiency).

• NPP is organic carbon remaining after autotroph respiration, visible to satellites.

• Ocean primary production influenced by light, nutrients, and consumers.

• Land primary production influenced by light, temperature, moisture, nutrients, and community interactions.