Lab Quiz 2

Compare and contrast the exponential and logistic models of population growth.

• Exponential Model: J-shaped curve, assumes unlimited resources, constant growth rate.

• Logistic Model:  S-shaped curve,  accounts for resource limits, growth slows as  population approaches carrying capacity (K ).

• Similarities:  Both model population growth over time.

What is a key assumption of the exponential population growth model?

Unlimited resources

What shape is characteristic of the logistic population growth curve?

S-shaped

What does the logistic growth model account for that the exponential model does not?

Resource limits

What is 'K' in the context of the logistic growth model?

Carrying capacity

What do both exponential and logistic models attempt to model?

Population growth over time

Distinguish between density-dependent and density-independent factors affecting population growth, and provide examples for each.

• Density-Dependent: Effects depend on population density (biotic). Examples: Competition, predation, disease.

• Density-Independent: Effects occur regardless of population density (abiotic). Examples: Natural disasters, weather, climate change.

Are competition and predation density-dependent or density-independent factors?

 Density-dependent 

Are natural disasters and weather density-dependent or density-independent factors?

Density-independent

What type of growth model best fits the entire human population?

Exponential model (specifically J-shaped growth, transitioning toward limits)

Can the current trend of human population growth continue indefinitely?

No

What are the main reasons why the current trend of human population growth cannot continue indefinitely?

Earth has a finite carrying capacity (K) for resources, and resistance factors will eventually slow growth.

What non-biological factors can influence human population growth?

• Technological advancements (medicine, agriculture)

• Economic policies

• Access to clean water/energy

• Government regulations (e.g., family planning policies)

Describe the typical shape of a population pyramid for a growing, shrinking, and stable population.

• Growing: Wide base (high proportion of young), tapering quickly.

• Shrinking: Narrow base, wider middle/older age groups.

• Stable: Relatively even proportions across age groups, tapering gradually (bell-shaped).

What does a wide base in a population pyramid indicate?

A growing population

What does a narrow base in a population pyramid indicate?

A shrinking population

What shape is characteristic of a population that is staying the same in size?

Bell-shaped (relatively even proportions across age groups, tapering gradually)

What are Phytoplankton's?

microscopic, photosynthetic "drifters" in aquatic systems. They are primary producers at the base of aquatic food webs, converting inorganic CO2 and sunlight into organic energy (glucose) while releasing O2

What is the primary importance of phytoplankton in aquatic ecosystems?

They produce over 50% of Earth’s oxygen and form the primary producer base of food webs.

 What specific pigment do all phytoplankton have in common? 

Chlorophyll a

What is the primary role of chlorophyll a in phytoplankton?

It absorbs light energy needed to drive photosynthesis and convert light energy into chemical energy.

What adaptations allow phytoplankton to remain in the photic zone?

High surface-area-to-volume ratios, flat cellular shapes, forming filaments or colonies, storing low-density molecules (like oils), and using flagella to swim toward light

What type of phytoplankton is characterized by filamentous structures and can include Anabaena or Oscillatoria?

Cyanobacteria (or green algae)

What is a photosynthetic pigment found in cyanobacteria besides chlorophyll  a?

Phycocyanin

What type of phytoplankton is characterized by a silica cell wall called a frustule?

Diatoms

What structure in  diatoms  allows for gas exchange?

Striae

What is the primary function of chlorophyll a in autotrophs like diatoms?

It absorbs light energy to convert carbon dioxide and water into chemical energy (glucose) and oxygen.

Why are chlorophyll a concentrations measured in aquatic ecosystems?

As an indicator of phytoplankton biomass, primary productivity, and aquatic ecosystem health/water quality.

Why should samples for chlorophyll analysis be kept in the dark and cold?

To prevent pigment degradation (photo-oxidation) and slow down enzymatic breakdown of chlorophyll.

Why are glass fiber filters frozen before chlorophyll extraction?

Freezing forms ice crystals that rupture phytoplankton cell walls, facilitating chlorophyll extraction.

Why is acetone used as a solvent for chlorophyll extraction instead of water?

Chlorophyll pigments are non-polar lipids and insoluble in water, so an organic solvent like 90% acetone is required to dissolve and extract them

What is the purpose of centrifuging samples in chlorophyll analysis?

To separate cell debris and filter fibers from the liquid extract for clear spectrophotometer readings.

Chlorophyll a has absorption peaks at 664 nm and 432 nm, with the peak at 432 nm being greater. Why is 664 nm often used for measurement?

664 nm is specific to chlorophyll a, while 432 nm overlaps with other pigments like carotenoids and chlorophyll b/c, reducing background interference.

Why are measurements at 630 nm and 647 nm sometimes taken in addition to 664 nm when calculating chlorophyll a concentration? 

To correct for spectral overlap from chlorophyll c (at 630 nm) and chlorophyll b (at 647 nm) using trichromatic equations.

What is the peak absorption wavelength for chlorophyll b?

 647 nm 

What is the peak absorption wavelength for chlorophyll c?

630 nm