Ecosystem Energy Flow, Nutrient Cycles, and Plant Responses

Posted on Feb 28, 2025 in Biology

Food: Contains energy and nutrients required for maintenance/survival, growth/development, and reproduction.

Carbon:

  • Auto (from CO2, inorganic)
  • Hetero (from organic molecules)

Energy:

  • Photo (from light)
  • Chemo (oxidizing inorganic or organic molecules)

Organisms:

  • Prokaryotes: Have all carbon and energy types.
  • Protists: Photoautotrophs and chemoheterotrophs.
  • Plants: Photoautotrophs and chemoheterotrophs.
  • Fungi and Animals: Chemoheterotrophs.

Food Chains: Show how energy & nutrients move between organisms.

Food Web: Complex network of interconnected food chains.

Laws of Thermodynamics:

  • 1st Law: Energy is neither created nor destroyed, just converted from one form to another.
  • 2nd Law: When energy is converted, some useful energy is degraded to less useful energy (heat). There is always a loss of energy; less energy is available at higher trophic levels.

Energy and Nutrients in an Ecosystem: Usually flow in the same direction. Nutrients are ultimately recycled, while energy is lost. Energy flows, while nutrients cycle.

Ecological Efficiency: Efficiency at which energy is transferred from one trophic level to the next, averaging 10%.

Pyramid of Energy: Rate at which energy or mass is transferred from one trophic level to the next.

Autotrophs: All food chains begin with them (1st trophic level).

Chemoautotrophs: Some prokaryotes (deep-sea vents).

Photoautotrophs: Most plants, some protists (algae), some bacteria.

Photosynthesis: Cells with chlorophyll capture sunlight and turn it into stored chemical energy: 6CO2 + 6H2O + light energy → C6H12O6 + 6O2.

Cellular Respiration: Almost all cells use stored chemical energy to produce ATP: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy.

Phytoplankton: Diverse mix of microscopic, photosynthetic organisms that float in the upper layers of almost all aquatic biomes, performing 40% of all photosynthesis on Earth.

Vascular Plants: Obtain carbon dioxide through stomata in leaves, water enters through roots, light is absorbed by chlorophyll in leaves, glucose is used by the plant or stored as starch, and oxygen exits through stomata.

Guard Cells: Regulate gas exchange and transpiration by opening and closing stomata. When stomata open, CO2 enters the leaf, and oxygen and water vapor exit the leaf.

Absorption of Visible Light: Photosynthesis takes place in mesophyll cells of leaves, using chlorophylls a & b.

Solar Radiation:

  • Infrared (heat, 53%, not enough energy for photosynthesis)
  • Visible light (45%, red and blue absorbed for photosynthesis, green is reflected)
  • Ultraviolet (2%, can destroy organic molecules)

Plant Excess Food: Stored as glucose, used in cellular respiration, or converted to structural material (wood, fiber). Stored as sucrose (short term) & starch (long term). Food storage roots store starch and other carbohydrates.

Heterotrophs: All food chains end with them (2nd, 3rd, 4th trophic levels).

Chemoheterotrophs: All animals, fungi, some protists, some prokaryotes, and a few plants.

Photoautotrophs: Some bacteria, very rare.

Prokaryotes, Fungi, Protists: Secrete enzymes into the environment. Enzymes break down food (digestion), and they absorb smaller molecules (ingestion). Some engulf food particles (phagocytosis). Their food sources are: dead organic matter (saprobes), other unicellular organisms, living hosts (parasitic and mutualistic symbionts).

Mixotrophs: Some prokaryotes and protists can be autotrophic and/or heterotrophic depending on the environment.

Feeding Mechanisms:

  • Fluid Feeder: Feeds on the fluid of other organisms.
  • Suspension Feeder: Feeds on particles of organic matter suspended in water.
  • Deposit Feeder: Feeds on small pieces of organic matter that have drifted down through the water and settled on the bottom.
  • Bulk Feeder: Eats pieces of other organisms or swallows them whole.

Digestion Types:

  • Intracellular Digestion: Takes place inside the cell, limited to small food particles.
  • Extracellular Digestion: Takes place outside the cell, for larger food items.

Digestive Systems:

  • Gastrovascular Cavity: Cnidarians & flatworms, 1 opening.
  • Digestive Tube: Animals, 2 openings, food moves in 1 direction.

5 Stages of Digestion:

  1. Mechanical processing (chewing)
  2. Secretion of enzymes and other digestive aids
  3. Enzymatic hydrolysis
  4. Absorption
  5. Elimination

Stomach Chambers:

  • Segmented Worm: No chamber stomach.
  • Human: 1 chamber stomach.
  • Ruminant: 4 chamber stomachs.

Mutualistic Microbes: Produce cellulase to break down cellulose, carry out fermentation, and ruminants digest some microbes to supplement their diet.

Plant Tropisms:

  • Phototropism: Auxin migrates away from light – cells elongate on the dark side – stem bends towards light.
  • Gravitropism: Growth response to gravity. Stem placed on its side (auxin migrates to the lower side – cells elongate – stem bends up) important in seed germination.
  • Thigmotropism: Growth response to touch (auxin migrates away from contact – cells elongate – tendrils coil around the object).

Positive & Negative Tropism: Towards stimulus while others away from stimulus.

Solar Tracking: Change leaf orientation to keep leaves perpendicular to the sun.

Sleep Movements: Plants sense changes in light and temperature; leaves or petals fold up and reopen daily.

Turgor Movements from Touch: Contact changes internal water pressure.

Water Conservation: Dry conditions – bulliform cells lose turgor – blades roll up.

Photoperiodism: Affects flowering by inducing the shoot to produce floral buds instead of leaves.

Receptors:

  • Mechanoreceptors: Stimuli are touch, pressure, stretching, sound waves, and motion.
  • Photoreceptors: Cells in the retina that respond to light.
  • Chemoreceptors: Detect changes in the normal environment, such as an increase in blood levels of carbon dioxide or a decrease in blood levels of oxygen.
  • Thermoreceptors: Receptive portion of a sensory neuron, changes in temperature.
  • Nociceptors: Responds to damaging or potentially damaging stimuli.

Neural Signaling:

  1. Reception (pre-synaptic neuron talks to the post-synaptic neuron at the synapse)
  2. Transduction (an action potential travels down the axon to the axon terminal)
  3. Transmission (action potential causes the vesicle to move toward the membrane and release neurotransmitter into the synaptic cleft)
  4. Integration (neurotransmitter binds to the receptor)
  5. Transmission (neurotransmitter can cause an action potential in the post-synaptic neuron)
  6. Response (neurotransmitter is sucked back into the presynaptic neuron to end the action potential)