Ch 7 - Energy + Nutrients

Which photosynthetic pathway is used by most plants and all algae?

C3 photosynthesis.

Why must stomata open in C3 plants?

To allow CO2 to enter for carbon fixation.

What is a major disadvantage of opening stomata in C3 plants?

Water may escape down its gradient.

What process produces CO2 and consumes energy in C3 plants?

Photorespiration.

When is photorespiration most significant in C3 plants?

When CO2 levels are reduced, such as when stomata are closed.

Which photosynthetic pathway is generally most prone to water loss?

C3 photosynthesis.

What is the main advantage of C4 photosynthesis over C3 photosynthesis?

It concentrates CO2 and reduces water loss.

Why do C4 plants need to open fewer stomata?

Because the initial reaction concentrates CO2, improving inward diffusion and conserving water.

In C4 photosynthesis, where are carbon-fixation acids metabolized to release CO2?

In bundle sheath cells.

Which photosynthetic pathway spatially separates initial carbon fixation from the Calvin cycle?

C4 photosynthesis.

How does C4 photosynthesis help reduce photorespiration?

By concentrating CO2 around the Calvin cycle.

Which photosynthetic pathway fixes carbon at night?

CAM photosynthesis.

In what kinds of plants is CAM photosynthesis most common?

Succulent plants in arid or semiarid environments and tropical epiphytes.

Why does CAM photosynthesis reduce water loss?

Because carbon fixation occurs at night when vapor pressure deficit is lower.

What is the major tradeoff of CAM photosynthesis?

Low photosynthetic rate but very high water-use efficiency.

Which photosynthetic pathway has the highest water-use efficiency?

CAM photosynthesis.

Which photosynthetic pathway temporally separates carbon fixation from the Calvin cycle?

CAM photosynthesis.

What does water-use efficiency measure?

Units of carbon fixed per unit of water lost.

Which pathway is best adapted for extreme water conservation?

CAM photosynthesis.

What is photosynthetically active radiation (PAR)?

Visible light between infrared and ultraviolet wavelengths.

How is PAR quantified?

As photon flux density.

What is photon flux density?

The number of photons striking a square meter each second.

Why is PAR measured as photon flux density instead of energy alone?

Because chlorophyll absorbs discrete photons.

How does wavelength relate to energy in light?

Shorter wavelengths have more energy, and longer wavelengths have less energy.

What environmental factors can affect light amount and quality?

Season, weather, time of day, topography, and refraction.

Light behaves as what two things in physics and biology?

A wave and a particle.

Autotrophs use what kinds of carbon and energy sources?

Inorganic sources.

Photosynthetic organisms use what as their carbon source?

CO2.

Heterotrophs use what as sources of both carbon and energy?

Organic molecules.

Which trophic group feeds on plants?

Herbivores.

Which trophic group mainly feeds on animals?

Carnivores.

Which trophic group feeds on non-living organic matter, usually plant remains?

Detritivores.

What is chemosynthesis?

The synthesis of organic molecules using energy from chemical reactions rather than light.

Which terrestrial organisms commonly perform chemosynthesis?

Microbes, bacteria, and fungi.

Which five elements make up most of the biomass of plants, animals, fungi, and bacteria?

Carbon, oxygen, hydrogen, nitrogen, and phosphorus.

What is ecological stoichiometry concerned with?

The balance of multiple chemical elements in ecological interactions.

How does the C:N ratio of plants compare with that of herbivores?

Plants have a higher C:N ratio than herbivores.

Why must herbivores often eat large amounts of plant material?

Because plant tissue is relatively poor in essential nutrients such as nitrogen.

What do herbivores generally prefer in food quality?

Plant tissue with relatively higher nutrient content and lower structural defenses.

How does carnivore food quality generally compare with herbivore food quality?

Animal tissue is usually closer to carnivore nutrient requirements than plant tissue is to herbivore requirements.

What is one major nutritional problem faced by herbivores?

Their food nutrient content differs greatly from their growth requirements.

What plant defenses make herbivory more difficult?

Thorns, silica, cellulose, lignin, and toxic compounds.

Why are cellulose and lignin difficult for herbivores to use?

They are hard to digest.

How can plant toxins affect herbivores?

They reduce feeding efficiency or reduce nutrient availability.

Compared with temperate species, tropical plant species tend to have what toxin pattern?

A higher proportion contain toxic alkaloids, and those alkaloids are more toxic.

Why are detritivores important in ecosystems?

They play key roles in nutrient cycling.

What type of material do detritivores feed on?

Dead plant material rich in carbon and energy but poor in nitrogen.

How does the nitrogen content of dead leaves compare with that of living leaves?

Dead leaves may have about half the nitrogen content of living leaves.

Why is dead plant material a poor-quality food source?

It has high carbon but relatively low nitrogen.

How do the C:N and C:P ratios of carnivores compare with those of their prey?

Both carnivores and their prey tend to have relatively low C:N and C:P ratios.

Why can carnivores not always choose the most nutritionally rich prey?

Because diet varies geographically and prey availability is limited.

What does energy limitation mean in ecology?

The rate at which organisms can take in energy is limited.

As photon flux density increases, what happens to photosynthetic rate?

It increases and then levels off at a maximum rate.

What is Pmax?

The maximum rate of photosynthesis.

What does Isat represent?

The photon flux density at which photosynthesis becomes saturated.

Why does photosynthesis level off at high light intensity?

Because the photosynthetic system becomes saturated.

What is an animal functional response?

The feeding rate increases with food availability and then levels off.

What does optimal foraging theory predict?

What, when, and where organisms will feed to acquire energy effectively.

Why can organisms not maximize all life functions at the same time when energy is limited?

Because limited energy creates tradeoffs among functions.

How did actual bluegill sunfish diets compare with optimal foraging predictions?

They matched the predicted optimal diets fairly well.

What kind of prey did bluegill sunfish tend to select?

Prey that were less common and larger than average.

What plant trait reflects allocation to belowground versus aboveground structures?

Root:shoot ratio.

How does infertile soil affect root:shoot ratio?

Plants in infertile soil have higher root:shoot ratios.

Why do plants increase root:shoot ratio in infertile soil?

To allocate more biomass to roots for nutrient acquisition.

What does a higher root:shoot ratio indicate about plant investment?

Relatively greater investment in roots than shoots.