- What is the relationship between snails and Hydrilla?
Mutualistic relationship. Snails get food and shelter from Hydrilla, while eating extra plant material and keeping the environment healthy for Hydrilla.
- Why did the color of the indicator solution change?
The color change from blue to yellow indicates increased acidity due to carbon dioxide released by snails and Hydrilla during respiration.
- What was the importance of control in your experiment? What would you conclude if the color of the solution in the control changed?
The control group is used for comparison. If its color changed, it would invalidate the experiment’s results.
- When you began the experiment, was there CO₂ in the water? In the test tubes that contained Hydrilla, where did the CO₂ go?
The initial water had some CO2, but not enough to change the indicator color. In the Hydrilla tubes, the plant used the CO2 for photosynthesis, making the water slightly alkaline (light blue indicator). In the snail tubes, snails produced more CO2 than the Hydrilla could use, making the water more acidic (yellow indicator).
- What gas did the snails release? What observation supports this inference?
Snails release carbon dioxide during respiration, as observed by the yellow indicator color.
- In your own words, explain how balance in the ecosystem is maintained in the carbon-oxygen cycle
Plants take in CO2 for photosynthesis and release oxygen. Animals take in oxygen and release CO2 for respiration. This cycle maintains a balance of these gases essential for life.
- Outline and briefly discuss the cellular and physiological effects of temperature change on living organisms.
Temperature affects organisms at the cellular level (enzymes, protein folding) and whole-organism level (sweating, shivering).
- What is meant by van’t Hoff’s rule? Is it true for both terrestrial & aquatic ecosystems? Explain.
This rule states that reaction rates, like metabolism, roughly double with every 10°C temperature increase. It applies to both land and water ecosystems.
- Differentiate the following terms: ectotherms, endotherms, poikilotherms, homeotherms, osmoconformers, osmoregulators, eurytopic, and stenotopic.
- Endotherms/homeotherms: Maintain constant body temperature (e.g., humans, birds).
- Poikilotherms/ectotherms: Body temperature changes with the environment (e.g., reptiles, fish).
- Osmoregulators: Control salt concentration in their bodies (e.g., most fish).
- Osmoconformers: Body fluids adjust to the environment (e.g., jellyfish).
- Eurytopic: Thrive in diverse environments.
- Stenotopic: Thrive in narrow environmental ranges.
- Provide an explanation for the observed behavioral responses of fish to pH changes. In general, what are the physiological effects of pH changes on living organisms? Would you say that your observations typify the conditions in acidic lakes?
Fish show various responses (behavioral, physiological) to pH changes. Varying pH levels can harm living things. Observed effects may not represent typical conditions in acidic lakes.
- Discuss the relationship between salinity and mortality among freshwater snails. Outline the cellular mechanism that could possibly explain the observed effects.
Salt kills freshwater snails through osmosis, causing water loss and disrupting functions.
- Provide a feasible explanation for the observed effect of salinity on % germination and growth rate in corn seeds.
Salinity affects corn seed germination and growth by:
* Reducing water uptake
* Accumulating harmful ions
* Suppressing growth
Explain the mathematical models for the exponential and logistic growth patterns.
- Exponential growth: N(t) = N0 * e^(rt) (fast, uncontrolled growth)
- Logistic growth: N(t) = K / (1 + (K - N0) / N0 * e^(-rt)) (slows down as population reaches carrying capacity, K)
What is meant by doubling time? How is it computed?
- The time it takes for a population to double in size.
- Calculated as t = 0.69 / r (using growth rate, r) or t ≈ 70 / r (using “Rule of 70”).
Would you be able to compute the value of r from your obtained data? If yes, what is the computed value of r for the two selected populations?
r = In (a(t)/N0) / t
What would be some advantages of having a high intrinsic growth rate value? Why don’t all organisms have a high r value?
- High r: organisms reproduce quickly with many offspring, requiring minimal resources per offspring (r-selected).
- Not all organisms have high r due to environmental limitations (carrying capacity).
How is the concept of life history i.e., r- and K-selection related to the concept of population growth?
- r-selected: Reproduce rapidly in unpredictable environments, invest less in each offspring.
- K-selected: Reproduce slowly in stable environments, invest more in fewer offspring.
What are the factors that limit population growth rate? Differentiate density-dependent factors with density-independent factors.
- Density-dependent: Affected by population density (predation, competition, disease).
- Density-independent: Not affected by population density (weather, natural disasters, pollution).
Why is oxygen produced over a given time used as an index of productivity? Why do limnologists generally express production as carbon fixed rather than oxygen liberated?
- Oxygen production: Used as an index, but not preferred by limnologists.
- Carbon fixation: Preferred method as it reflects biomass accumulation.
- Light & dark bottle method: Compares light and dark bottles to estimate photosynthesis and respiration.
What are the assumptions in the light and dark bottle method of measuring aquatic productivity?
- Light: Energy source for producers.
- Temperature: Affects organism function.
- Humidity: Affects water loss and distribution.
- Nutrients: Essential for growth.
- pH: Affects plant and animal distribution.
What physical factors make an ecosystem highly productive?
- Chlorophyll fluorescence: Measures photosynthetic activity.
- Biomass change: Increased biomass indicates higher productivity.
- Modeling: Predicts productivity under different conditions.
- Chlorophyll a content: Indicator of primary productivity.
- Carbon dioxide uptake/oxygen output: Measures ecosystem function and carbon cycling.
Name and describe very briefly some other methods used by ecologists to estimate productivity in aquatic ecosystems.
- Biomass accumulation ratio: Compares standing crop to net primary productivity.
- Allometry: Estimates biomass and productivity based on organism size.
- Gas exchange: Measures oxygen and carbon dioxide exchange.
- Ground observations: Estimates gross primary productivity through field observations.
- Harvest method: Calculates production from planting/seeding to harvest.
- Enclosure studies: Measures carbon dioxide exchange in controlled environments.
- Flux techniques: Measures carbon dioxide levels to estimate productivity.
- Model simulations: Simulate various factors to estimate productivity.
List down and describe very briefly the harvest method or other methods used by ecologists to estimate productivity in terrestrial ecosystems, e.g., forest ecosystems.
- Depends on the ecosystem, research question, and limitations of each method.
Do herbivores eat only specific portions of the leaves? Can this be used to classify herbivores? Are herbivores species-specific in their choices of food?
- Selective eaters: Choose specific leaf parts based on nutrition, toxicity, and accessibility.
- Species-specific preferences: Adaptations and habitat specialization influence food choices.
