Midterm

Question 1

1. What is the relationship between snails and Hydrilla?

Answer 1

Mutualistic relationship. Snails get food and shelter from Hydrilla, while eating extra plant material and keeping the environment healthy for Hydrilla.

Question 2

2. Why did the color of the indicator solution change?

Answer 2

The color change from blue to yellow indicates increased acidity due to carbon dioxide released by snails and Hydrilla during respiration.

Question 3

3. What was the importance of control in your experiment? What would you conclude if the color of the solution in the control changed?

Answer 3

The control group is used for comparison. If its color changed, it would invalidate the experiment’s results.

Question 4

4. When you began the experiment, was there CO₂ in the water? In the test tubes that contained Hydrilla, where did the CO₂ go?

Answer 4

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).

Question 5

5. What gas did the snails release? What observation supports this inference?

Answer 5

Snails release carbon dioxide during respiration, as observed by the yellow indicator color.

Question 6

6. In your own words, explain how balance in the ecosystem is maintained in the carbon-oxygen cycle

Answer 6

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.

Question 7

1. Outline and briefly discuss the cellular and physiological effects of temperature change on living organisms.

Answer 7

Temperature affects organisms at the cellular level (enzymes, protein folding) and whole-organism level (sweating, shivering).

Question 8

2. What is meant by van’t Hoff’s rule? Is it true for both terrestrial & aquatic ecosystems? Explain.

Answer 8

This rule states that reaction rates, like metabolism, roughly double with every 10°C temperature increase. It applies to both land and water ecosystems.

Question 9

3. Differentiate the following terms: ectotherms, endotherms, poikilotherms, homeotherms, osmoconformers, osmoregulators, eurytopic, and stenotopic.

Answer 9

• 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.

Question 10

4. 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?

Answer 10

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.

Question 11

5. Discuss the relationship between salinity and mortality among freshwater snails. Outline the cellular mechanism that could possibly explain the observed effects.

Answer 11

Salt kills freshwater snails through osmosis, causing water loss and disrupting functions.

Question 12

6. Provide a feasible explanation for the observed effect of salinity on % germination and growth rate in corn seeds.

Answer 12

Salinity affects corn seed germination and growth by:
* Reducing water uptake
* Accumulating harmful ions
* Suppressing growth

Question 13

Explain the mathematical models for the exponential and logistic growth patterns.

Answer 13

• 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)

Question 14

What is meant by doubling time? How is it computed?

Answer 14

• 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”).

Question 15

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?

Answer 15

r = In (a(t)/N0) / t

Question 16

What would be some advantages of having a high intrinsic growth rate value? Why don’t all organisms have a high r value?

Answer 16

• 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).

Question 17

How is the concept of life history i.e., r- and K-selection related to the concept of population growth?

Answer 17

• r-selected: Reproduce rapidly in unpredictable environments, invest less in each offspring.
• K-selected: Reproduce slowly in stable environments, invest more in fewer offspring.

Question 18

What are the factors that limit population growth rate? Differentiate density-dependent factors with density-independent factors.

Answer 18

• Density-dependent: Affected by population density (predation, competition, disease).
• Density-independent: Not affected by population density (weather, natural disasters, pollution).

Question 19

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?

Answer 19

• 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.

Question 20

What are the assumptions in the light and dark bottle method of measuring aquatic productivity?

Answer 20

• 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.

Question 21

What physical factors make an ecosystem highly productive?

Answer 21

• 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.

Question 22

Name and describe very briefly some other methods used by ecologists to estimate productivity in aquatic ecosystems.

Answer 22

• 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.

Question 23

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.

Answer 23

• Depends on the ecosystem, research question, and limitations of each method.

Question 24

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?

Answer 24

• Selective eaters: Choose specific leaf parts based on nutrition, toxicity, and accessibility.
• Species-specific preferences: Adaptations and habitat specialization influence food choices.

Question 25

What would be the ultimate fate of the energy contained in the uneaten part of the leaf? Does any of it ever flow again through larger animals such as carnivores?

Answer 25

• Decomposers break down uneaten leaves, releasing nutrients back into the ecosystem.
• Some energy is lost as heat, while the rest is recycled.
• Uneaten leaves indirectly support the ecosystem through nutrient cycling.

Question 26

Do herbivores prefer young leaves to old ones? How might time of the year affect your calculations? What about time emergence of various species of leaf-eating animals? Do insects eat leaves as larvae or adults, or both? How does your data compare with that of other groups?

Answer 26

• Young leaves: Preferred by many herbivores due to softness and higher nutrients.
• Seasonality: Herbivore activity and damage may vary depending on the season.
• Herbivore emergence: Timing of herbivore appearance may be linked to leaf emergence.
• Insect feeding stages: Some insects feed only as larvae, while others feed throughout their life cycle.
• Our group: Irregularly torn notches
• Other groups: Different patterns (linear, circular holes)
• Similar overall leaf area consumed despite different feeding patterns.
• Variations may be due to different leaf types consumed by each group.

Question 27

Eco problem: Anaerobic soil condition

Answer 27

Pneumatophores: Mangroves have special structures called pneumatophores that help them breathe. These structures allow them to take in oxygen from the air and bring it down to their roots, even when underwater or in wet soil.

Prop roots: Some mangroves also have prop roots that help deliver air to their roots when underwater. These roots have many tiny openings that allow them to exchange gases with the soil, even when oxygen levels are low.

Question 28

Eco problem: High salinity

Answer 28

Succulent leaves: Mangroves have special adaptations to survive in salty and dry environments. They store water in their leaves, have a waxy coating to minimize evaporation, and some even have salt glands to get rid of excess salt.

Salt-exclusion: Some mangrove species have a special wall that blocks most of the salt from entering their system, protecting them from dehydration.

Question 29

Eco problem: Unstable substrate

Answer 29

Stilt roots: Stilt roots in some mangroves help them breathe during low tide and provide support in unstable soil.

Prop roots: Prop roots help mangrove trees stay balanced and anchored in areas with loose soil. They also help stabilize the surrounding soil.

Question 30

Eco problem: Desiccation (due to high salinity)

Answer 30

Stomatal regulation: Mangroves can control their water loss by closing their stomata and adjusting their leaves’ position.

Vivipary: Mangrove seeds can germinate even in salty and oxygen-depleted water. They start growing while still attached to the parent tree, which provides them with nutrients.