Aquatic ecosystems – lakes MCQs With Answer

Aquatic ecosystems – lakes MCQs With Answer

Understanding lake ecology is essential for B.Pharm students studying environmental pharmacology, ecotoxicology, and water quality. This introduction covers limnology basics, lake stratification, trophic states, nutrient cycling, eutrophication, and the fate of pharmaceuticals and personal care products (PPCPs) in freshwater systems. Emphasis is on water quality parameters, bioaccumulation, algal blooms, microbial processes, and monitoring methods relevant to drug residues and antibiotic resistance in aquatic organisms. Clear, keyword-rich content helps you connect pharmacology with environmental impacts, mitigation strategies, and regulatory concerns. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which layer of a stratified lake is warmest and most oxygenated during summer?

• Epilimnion
• Metalimnion
• Hypolimnion
• Benthic zone

Correct Answer: Epilimnion

Q2. The steep temperature gradient separating epilimnion and hypolimnion is called the:

• Thermocline (metalimnion)
• Halocline
• Pycnocline
• Oxiccline

Correct Answer: Thermocline (metalimnion)

Q3. Oligotrophic lakes are best described as:

• High nutrient, high productivity
• Low nutrient, clear water, low productivity
• Moderate nutrient, moderate productivity
• Highly polluted, anoxic

Correct Answer: Low nutrient, clear water, low productivity

Q4. Eutrophication in lakes is primarily driven by increased inputs of:

• Heavy metals
• Nutrients like nitrogen and phosphorus
• Suspended sediments only
• Salinity

Correct Answer: Nutrients like nitrogen and phosphorus

Q5. Secchi depth is a field measure used to assess:

• Water temperature
• Light penetration/turbidity
• Dissolved oxygen concentration
• pH

Correct Answer: Light penetration/turbidity

Q6. Which group forms the base of most lake food webs through photosynthesis?

• Benthic macroinvertebrates
• Planktonic algae and phytoplankton
• Nektonic fish
• Zooplankton predators

Correct Answer: Planktonic algae and phytoplankton

Q7. Hypolimnetic anoxia during summer can lead to release of which nutrient from sediments?

• Silicon
• Phosphorus
• Potassium
• Magnesium

Correct Answer: Phosphorus

Q8. The primary cause of harmful algal blooms (HABs) is:

• Introduction of exotic fish species
• Nutrient enrichment and warm, stable conditions
• Decreased sunlight
• Increased dissolved oxygen

Correct Answer: Nutrient enrichment and warm, stable conditions

Q9. Dissolved oxygen (DO) in a lake is lowest typically in the:

• Epilimnion during daytime
• Hypolimnion during summer stratification
• Surface at noon
• Immediately after turnover

Correct Answer: Hypolimnion during summer stratification

Q10. Biochemical oxygen demand (BOD) measures:

• Oxygen produced by photosynthesis
• Oxygen required by microbes to decompose organic matter
• Maximum possible oxygen solubility
• Amount of dissolved inorganic carbon

Correct Answer: Oxygen required by microbes to decompose organic matter

Q11. Which process converts ammonium to nitrate in oxygenated lake waters?

• Denitrification
• Nitrification
• Ammonification
• Nitrogen fixation

Correct Answer: Nitrification

Q12. Denitrification is important because it:

• Produces oxygen
• Converts nitrate to gaseous nitrogen, removing bioavailable N
• Fixes atmospheric nitrogen into ammonia
• Converts phosphate to organic P

Correct Answer: Converts nitrate to gaseous nitrogen, removing bioavailable N

Q13. The partitioning behavior of a pharmaceutical between water and organic phases is commonly predicted by:

• Biochemical oxygen demand (BOD)
• Octanol–water partition coefficient (Kow)
• pH only
• Secchi depth

Correct Answer: Octanol–water partition coefficient (Kow)

Q14. A high Kow value for a drug suggests it is likely to:

• Remain dissolved in water
• Bioaccumulate in biota and sorb to sediments
• Be rapidly biodegraded
• Be highly volatile

Correct Answer: Bioaccumulate in biota and sorb to sediments

Q15. Photolysis as a removal process in surface waters involves:

• Microbial breakdown in sediments
• Chemical transformation by sunlight
• Sorption to organic matter
• Volatilization to groundwater

Correct Answer: Chemical transformation by sunlight

Q16. Pharmaceuticals that ionize at environmental pH will have their fate influenced strongly by:

• pH and ionic strength
• Water color only
• Salinity alone
• Secchi depth

Correct Answer: pH and ionic strength

Q17. Bioaccumulation factor (BAF) differs from bioconcentration factor (BCF) because BAF:

• Only considers uptake from water
• Includes uptake from both water and diet
• Is always lower than BCF
• Measures sediment accumulation exclusively

Correct Answer: Includes uptake from both water and diet

Q18. Which monitoring parameter is most useful for estimating primary productivity in lakes?

• Secchi depth
• Chlorophyll-a concentration
• Conductivity
• Alkalinity

Correct Answer: Chlorophyll-a concentration

Q19. Antibiotic residues in lakes can promote:

• Reduced primary production only
• Development and spread of antibiotic resistance genes
• Immediate depletion of dissolved oxygen
• Increase in salinity

Correct Answer: Development and spread of antibiotic resistance genes

Q20. The term ‘residence time’ of a lake refers to:

• The time it takes for a lake to freeze
• The average time water remains in the lake before outflow
• Duration of algal blooms
• Time for sediments to settle

Correct Answer: The average time water remains in the lake before outflow

Q21. A meromictic lake is characterized by:

• Complete annual mixing from surface to bottom
• Permanent stratification with a deep layer that does not mix
• Always being oligotrophic
• Being saltwater

Correct Answer: Permanent stratification with a deep layer that does not mix

Q22. Which organism group is primarily responsible for secondary production by grazing on phytoplankton?

• Benthic algae
• Zooplankton
• Phytoplankton
• Macrophytes

Correct Answer: Zooplankton

Q23. The benthic zone of a lake refers to the:

• Open water surface area
• Bottom substrate and associated sediments
• Thermocline layer
• Floating macrophyte zone only

Correct Answer: Bottom substrate and associated sediments

Q24. Sorption of pharmaceuticals to sediments is enhanced by:

• Low organic carbon content
• High organic carbon and fine particle size
• High turbulence only
• Low pH exclusively

Correct Answer: High organic carbon and fine particle size

Q25. Which parameter is most directly impacted by algal respiration and bacterial decomposition at night?

• pH remains constant
• Dissolved oxygen decreases
• Conductivity sharply drops
• Secchi depth increases

Correct Answer: Dissolved oxygen decreases

Q26. Which compound class in lakes is commonly resistant to biodegradation and may persist as trace contaminants?

• Simple sugars
• Highly chlorinated organics and some pharmaceuticals
• Ammonium salts
• Low molecular weight alcohols

Correct Answer: Highly chlorinated organics and some pharmaceuticals

Q27. In lake management, ‘biomanipulation’ typically refers to:

• Adding chemical coagulants
• Altering food webs, e.g., fish removal to increase grazing on algae
• Dredging sediments exclusively
• Introducing nutrient load

Correct Answer: Altering food webs, e.g., fish removal to increase grazing on algae

Q28. Which test organism is commonly used for acute toxicity tests of water samples?

• Escherichia coli only
• Daphnia magna
• Saccharomyces cerevisiae
• Human cell cultures exclusively

Correct Answer: Daphnia magna

Q29. The redox potential (Eh) of sediments controls the speciation of which element critical to nutrient cycles?

• Carbon
• Iron and manganese
• Sodium only
• Chlorine exclusively

Correct Answer: Iron and manganese

Q30. Which microbial process can generate methane in anoxic lake sediments?

• Denitrification
• Methanogenesis
• Photolysis
• Nitrification

Correct Answer: Methanogenesis

Q31. Pharmaceuticals entering lakes primarily from sewage are termed:

• Natural organic matter
• Emerging contaminants or PPCPs (pharmaceuticals and personal care products)
• Inorganic nutrients
• Primary producers

Correct Answer: Emerging contaminants or PPCPs (pharmaceuticals and personal care products)

Q32. Which statement about lake turnover in temperate lakes is correct?

• Turnover never affects oxygen distribution
• Spring and autumn turnover mix the water column, re-oxygenating deep waters
• Turnover only occurs in tropical lakes
• Turnover permanently stratifies the lake

Correct Answer: Spring and autumn turnover mix the water column, re-oxygenating deep waters

Q33. Harmful cyanobacterial toxins often produced during blooms include:

• Microcystins and cylindrospermopsin
• Penicillin
• Simple sugars
• Sodium chloride

Correct Answer: Microcystins and cylindrospermopsin

Q34. Macrophytes influence lake ecosystems by:

• Stabilizing sediments and providing habitat
• Always causing toxic blooms
• Eliminating all nutrient inputs
• Preventing light penetration entirely

Correct Answer: Stabilizing sediments and providing habitat

Q35. Which method is commonly used to estimate chlorophyll-a in water samples?

• Secchi disk transparency only
• Spectrophotometric or fluorometric analysis after extraction
• pH titration
• Measuring conductivity

Correct Answer: Spectrophotometric or fluorometric analysis after extraction

Q36. The primary sink for hydrophobic pharmaceuticals in lakes is:

• Evaporation to the atmosphere
• Sorption to sediments and particulate organic matter
• Immediate photodegradation at depth
• Conversion to inorganic salts

Correct Answer: Sorption to sediments and particulate organic matter

Q37. Which factor increases the bioavailability of ionizable pharmaceuticals to aquatic organisms?

• Strong sorption to sediment only
• Presence of dissolved organic matter that increases dissolved fraction
• Extreme cold temperatures only
• Complete degradation

Correct Answer: Presence of dissolved organic matter that increases dissolved fraction

Q38. Which lake trophic state is most associated with frequent algal blooms and high nutrient loads?

• Oligotrophic
• Mesotrophic
• Eutrophic
• Ultra-oligotrophic

Correct Answer: Eutrophic

Q39. The term ‘allochthonous’ organic matter in lakes refers to:

• Organic matter produced within the lake
• Organic matter imported from the watershed or terrestrial sources
• Only inorganic nutrients
• Dead fish exclusively

Correct Answer: Organic matter imported from the watershed or terrestrial sources

Q40. In risk assessment of pharmaceuticals in lakes, PEC stands for:

• Predicted Environmental Concentration
• Primary Ecological Carbon
• Pollutant Emission Coefficient
• Photolysis Expected Constant

Correct Answer: Predicted Environmental Concentration

Q41. Which process can transform dissolved organic nitrogen into ammonium in lake sediments?

• Nitrification
• Ammonification (mineralization)
• Photodegradation
• Volatilization

Correct Answer: Ammonification (mineralization)

Q42. Which management practice reduces external phosphorus loading to lakes?

• Applying more fertilizer to nearby fields
• Constructed wetlands and buffer strips in the watershed
• Increasing fish stocking density
• Removing macrophytes only

Correct Answer: Constructed wetlands and buffer strips in the watershed

Q43. The term ‘pelagic zone’ in a lake means the:

• Bottom sediment region
• Open water column away from the shore
• Shallow littoral area only
• Vegetated shoreline exclusively

Correct Answer: Open water column away from the shore

Q44. Which analytical technique is widely used to detect trace pharmaceuticals in lake water?

• Microscopy only
• Liquid chromatography coupled with mass spectrometry (LC-MS/MS)
• Simple pH strips
• Secchi disk

Correct Answer: Liquid chromatography coupled with mass spectrometry (LC-MS/MS)

Q45. Biofilm communities on surfaces in lakes are important because they:

• Increase turbidity only
• Mediate biodegradation and nutrient cycling
• Prevent all microbial activity
• Only consist of dead cells

Correct Answer: Mediate biodegradation and nutrient cycling

Q46. Which parameter often correlates inversely with Secchi depth?

• Water clarity
• Turbidity and chlorophyll-a concentration
• pH stability
• Depth of thermocline only

Correct Answer: Turbidity and chlorophyll-a concentration

Q47. Which of the following is a common consequence of hypoxia for fish in lakes?

• Increased growth rates
• Stress, reduced growth, and possible fish kills
• Immediate increase in reproduction
• Increased oxygen uptake efficiency permanently

Correct Answer: Stress, reduced growth, and possible fish kills

Q48. Which lake sampling strategy helps capture vertical gradients in temperature, oxygen, and pollutants?

• Single surface grab sample only
• Depth-profile sampling at multiple depths
• Sampling at the outflow only
• Collecting sediment core only

Correct Answer: Depth-profile sampling at multiple depths

Q49. Which factor increases the risk of antibiotic resistance gene proliferation in lake microbial communities?

• Low nutrient levels and no contaminants
• Chronic low concentrations of antibiotics and horizontal gene transfer
• Frequent lake turnover only
• High Secchi depth exclusively

Correct Answer: Chronic low concentrations of antibiotics and horizontal gene transfer

Q50. Restoration of a eutrophic lake may include which in-lake technique to reduce phosphorus availability?

• Adding iron salts (phosphate inactivation) to the water column
• Increasing external nutrient loads
• Removing macrophytes to increase erosion
• Raising water temperature artificially

Correct Answer: Adding iron salts (phosphate inactivation) to the water column

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com