Aquatic ecosystems – rivers MCQs With Answer

Aquatic ecosystems – rivers MCQs With Answer

Rivers are dynamic aquatic ecosystems essential for water supply, biodiversity, and pollutant transport. This SEO-friendly introduction covers riverine ecology, water quality parameters (dissolved oxygen, BOD, COD), nutrient cycling, pharmaceutical contaminants, bioaccumulation, eutrophication, and aquatic toxicology—topics crucial for B. Pharm students studying environmental pharmacology and public health. Understanding how drugs, antibiotics, and heavy metals affect river chemistry, microbial communities, and aquatic organisms helps pharmacists appreciate environmental risks, antibiotic resistance development, and safe disposal practices. Key terms: aquatic ecosystems, rivers, riverine ecology, water quality, pharmaceutical contaminants, bioaccumulation, eutrophication, aquatic toxicology, B. Pharm. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the most direct indicator of the amount of biodegradable organic matter in river water?

• Chemical Oxygen Demand (COD)
• Biological Oxygen Demand (BOD)
• Total Dissolved Solids (TDS)
• pH

Correct Answer: Biological Oxygen Demand (BOD)

Q2. Which parameter measures the total oxygen required to chemically oxidize organic and inorganic matter in water?

• Biological Oxygen Demand (BOD)
• pH
• Chemical Oxygen Demand (COD)
• Dissolved Oxygen (DO)

Correct Answer: Chemical Oxygen Demand (COD)

Q3. Which pharmaceutical property predicts sorption of drugs to river sediments?

• Log P (octanol-water partition coefficient)
• pKa
• Half-life in humans
• Therapeutic dose

Correct Answer: Log P (octanol-water partition coefficient)

Q4. Which process converts ammonium (NH4+) to nitrate (NO3-) in oxygenated river zones?

• Denitrification
• Nitrification
• Ammonification
• Photosynthesis

Correct Answer: Nitrification

Q5. Which is a common ecological consequence of excessive phosphorus input to rivers?

• Increased dissolved oxygen
• Eutrophication and algal blooms
• Lowered turbidity
• Reduced primary productivity

Correct Answer: Eutrophication and algal blooms

Q6. What does LC50 represent in aquatic toxicology studies?

• Lowest concentration causing any effect
• Concentration lethal to 50% of test organisms
• Concentration safe for all organisms
• Level at which fish growth is maximized

Correct Answer: Concentration lethal to 50% of test organisms

Q7. Which river zone is typically cold, fast-flowing and rich in dissolved oxygen?

• Floodplain zone
• Source (headwater) zone
• Estuarine zone
• Transition zone

Correct Answer: Source (headwater) zone

Q8. Which group of organisms is most important as primary producers in many rivers?

• Benthic macroinvertebrates
• Phytoplankton and periphyton
• Fish
• Terrestrial plants

Correct Answer: Phytoplankton and periphyton

Q9. Which measurement indicates the amount of suspended particles that scatter light in river water?

• Turbidity
• Conductivity
• pH
• Dissolved oxygen

Correct Answer: Turbidity

Q10. Which antibiotic-related risk increases in rivers receiving untreated hospital effluent?

• Reduced turbidity
• Selection for antibiotic-resistant bacteria
• Decrease in nitrate concentrations
• Higher dissolved oxygen

Correct Answer: Selection for antibiotic-resistant bacteria

Q11. Bioaccumulation refers to which process in aquatic organisms?

• Loss of pollutants during migration
• Accumulation of substances in an organism over time
• Immediate lethal effect of toxins
• Rapid degradation of pharmaceuticals

Correct Answer: Accumulation of substances in an organism over time

Q12. Biomagnification differs from bioaccumulation because it describes:

• Decrease in pollutant concentration at higher trophic levels
• Increase in pollutant concentration at higher trophic levels
• Absence of pollutants in sediments
• Pollutant removal by microbes

Correct Answer: Increase in pollutant concentration at higher trophic levels

Q13. Which water quality parameter is most affected by thermal pollution?

• pH
• Dissolved oxygen (DO)
• Conductivity
• Hardness

Correct Answer: Dissolved oxygen (DO)

Q14. Which compound class is most likely to persist in river sediments due to hydrophobicity?

• Highly polar antibiotics
• Hydrophobic persistent organic pollutants (POPs)
• Ionized inorganic salts
• Simple sugars

Correct Answer: Hydrophobic persistent organic pollutants (POPs)

Q15. The river continuum concept describes:

• Static conditions along a river
• Changes in physical and biological characteristics from headwaters to mouth
• Only chemical gradients in estuaries
• Human impacts on coastal waters

Correct Answer: Changes in physical and biological characteristics from headwaters to mouth

Q16. Which practice most effectively reduces pharmaceutical entry into rivers?

• Direct disposal into storm drains
• Proper drug take-back programs and safe disposal
• Flushing unused medicines down toilets
• Increasing patient doses to reduce leftover pills

Correct Answer: Proper drug take-back programs and safe disposal

Q17. Which microbial test indicates fecal contamination in river water?

• Alkalinity test
• Total coliform or fecal coliform count
• Biochemical oxygen demand

Correct Answer: Total coliform or fecal coliform count

Q18. Which redox condition favors denitrification in river sediments?

• Strongly aerobic
• Anoxic or low oxygen
• High light intensity
• Low organic matter

Correct Answer: Anoxic or low oxygen

Q19. Which river management strategy helps maintain riparian buffer function?

• Clearing riparian vegetation for development
• Preserving or restoring native riparian vegetation
• Channelizing the river with concrete
• Allowing unlimited livestock access to banks

Correct Answer: Preserving or restoring native riparian vegetation

Q20. In adsorption to sediments, which factor increases pollutant sorption?

• Lower organic carbon content of sediment
• Higher organic carbon content of sediment
• Higher dissolved oxygen
• Lower temperature

Correct Answer: Higher organic carbon content of sediment

Q21. Which analytical parameter indicates ionic strength and total dissolved ions in river water?

• Turbidity
• Conductivity
• BOD
• pH

Correct Answer: Conductivity

Q22. Which effect is a likely outcome of chronic low-level pharmaceutical exposure in aquatic organisms?

• Immediate mass mortality only
• Sublethal effects like endocrine disruption and behavioral changes
• Instant degradation of compounds
• Increased water hardness

Correct Answer: Sublethal effects like endocrine disruption and behavioral changes

Q23. Which nutrient removal process commonly occurs in wastewater treatment plants to prevent river eutrophication?

• Chlorination only
• Biological nitrogen and phosphorus removal
• Adding heavy metals
• Increasing pH to 12

Correct Answer: Biological nitrogen and phosphorus removal

Q24. Which term describes the concentration of a pollutant at which no observed adverse effect occurs?

• LC50
• NOEC (No Observed Effect Concentration)
• EC50
• LC0

Correct Answer: NOEC (No Observed Effect Concentration)

Q25. Which of the following increases the risk of hypoxic zones in rivers?

• Decreased nutrient loading
• Increased organic loading leading to high BOD
• Enhanced aeration
• Restoration of wetlands

Correct Answer: Increased organic loading leading to high BOD

Q26. Which river compartment often acts as a long-term sink for hydrophobic pharmaceuticals?

• Surface water only
• Suspended solids and sediments
• Dissolved oxygen layer
• Open air above river

Correct Answer: Suspended solids and sediments

Q27. Which process can reduce the concentration of certain pharmaceuticals via microbial action?

• Photolysis only in the dark
• Biodegradation by river microbes
• Adsorption to plastic debris
• Evaporation at ambient temperature

Correct Answer: Biodegradation by river microbes

Q28. What is the primary cause of increased turbidity after heavy rainfall?

• Decrease in suspended sediments
• Increased runoff carrying soil and sediments
• Rapid increase in dissolved oxygen
• Lowered river flow

Correct Answer: Increased runoff carrying soil and sediments

Q29. Which heavy metal is notorious for bioaccumulating and causing neurological effects in fish and humans?

• Sodium
• Lead
• Mercury
• Calcium

Correct Answer: Mercury

Q30. Which pH range generally favors survival of most freshwater aquatic organisms?

• pH 2–3
• pH 4–5
• pH 6.5–8.5
• pH 10–12

Correct Answer: pH 6.5–8.5

Q31. Which process increases nitrate removal in riparian zones before water enters rivers?

• Nitrification under oxic conditions
• Denitrification in anaerobic sediments
• Photosynthesis by algae
• Ionization of pharmaceuticals

Correct Answer: Denitrification in anaerobic sediments

Q32. Which aquatic indicator species is commonly used to assess river health and pollution?

• Salmon and mayfly nymphs
• House sparrows
• Desert lizards
• Cactus plants

Correct Answer: Salmon and mayfly nymphs

Q33. What effect does hard water (high Ca2+ and Mg2+) have on some pharmaceuticals?

• No interaction expected
• Can affect ionization and reduce bioavailability through complexation
• Always increases toxicity
• Instantly degrades the drug

Correct Answer: Can affect ionization and reduce bioavailability through complexation

Q34. Which measurement technique is commonly used for dissolved oxygen in rivers?

• Mass spectrometry
• Winkler titration or electrochemical probe
• Fluorescence microscopy
• pH meter

Correct Answer: Winkler titration or electrochemical probe

Q35. Which class of contaminants from pharmaceuticals is especially concerning for endocrine disruption in fish?

• Analgesics
• Synthetic hormones and endocrine active compounds
• Simple carbohydrates
• Salts of sodium chloride

Correct Answer: Synthetic hormones and endocrine active compounds

Q36. Which river management action can reduce downstream transport of pollutants during storms?

• Removal of wetlands
• Constructing retention ponds and restoring wetlands
• Channel widening with impermeable surfaces
• Allowing unchecked urban runoff

Correct Answer: Constructing retention ponds and restoring wetlands

Q37. Which phenomenon describes oxygen depletion driven by microbial decomposition of algal blooms?

• Eutrophication leading to hypoxia
• Oligotrophication
• Photosynthetic oxygenation
• Increased conductivity

Correct Answer: Eutrophication leading to hypoxia

Q38. Which parameter directly influences the ionization state of weakly acidic or basic drugs in river water?

• Temperature only
• pH of the water
• Turbidity
• Conductivity

Correct Answer: pH of the water

Q39. Which is a common source of pharmaceutical residues entering rivers?

• Industrial effluent only
• Municipal wastewater treatment plant effluent and improper disposal
• Natural plant exudates exclusively
• Atmospheric nitrogen fixation

Correct Answer: Municipal wastewater treatment plant effluent and improper disposal

Q40. Which community in rivers forms a key interface for nutrient cycling and pollutant transformation?

• Terrestrial mammals
• Benthic microbial biofilms
• Airborne plankton
• Forest canopy

Correct Answer: Benthic microbial biofilms

Q41. Which process is most responsible for rapid short-term oxygen depletion after a sewage spill?

• Photosynthesis by algae
• Microbial decomposition increasing BOD
• Evaporation of oxygen
• Sorption of oxygen to sediments

Correct Answer: Microbial decomposition increasing BOD

Q42. Which factor commonly increases the mobility of heavy metals in river systems?

• Higher pH leading to precipitation
• Lower pH and higher dissolved organic carbon
• Freezing temperatures
• Dry riverbed with no water flow

Correct Answer: Lower pH and higher dissolved organic carbon

Q43. Which monitoring approach helps detect long-term trends of pharmaceuticals in a river?

• Single grab sample once per year
• Regular integrated sampling and targeted chemical analysis
• Visual inspection only
• Measuring only pH monthly

Correct Answer: Regular integrated sampling and targeted chemical analysis

Q44. Which ecological role do macroinvertebrates often serve in biomonitoring rivers?

• Primary producers that fix nitrogen
• Indicator species reflecting water quality and habitat integrity
• Main source of pharmaceutical contamination
• Agents that increase river temperature

Correct Answer: Indicator species reflecting water quality and habitat integrity

Q45. Which chemical used in agriculture is a major nonpoint source pollutant in rivers?

• Fertilizers and pesticides
• Table salt
• Vitamin supplements
• Household soap only

Correct Answer: Fertilizers and pesticides

Q46. Which is the best immediate action to limit pharmaceutical pollution after a hospital wastewater leak?

• Ignore and continue discharge
• Containment, source control and notification of authorities
• Increase patient dispensing rates
• Dilute volume by adding untreated water

Correct Answer: Containment, source control and notification of authorities

Q47. Which characteristic of a drug increases its potential to bioaccumulate in aquatic organisms?

• Very low log Kow
• High lipophilicity and slow biotransformation
• Rapid biodegradability
• High water solubility and rapid excretion

Correct Answer: High lipophilicity and slow biotransformation

Q48. Which river feature enhances habitat complexity and supports diverse aquatic life?

• Monotonous straightened channel
• Presence of riffles, pools and varied substrates
• Complete removal of large woody debris
• Excessive bank armoring with concrete

Correct Answer: Presence of riffles, pools and varied substrates

Q49. Which regulatory metric often guides safe discharge limits for point-source pollutants into rivers?

• Ambient air quality index
• Maximum allowable concentrations and effluent standards
• Soil pH only
• Noise pollution limits

Correct Answer: Maximum allowable concentrations and effluent standards

Q50. Which integrated approach best reduces pharmaceutical contamination and protects river ecosystems?

• Only upgrading wastewater treatment plants
• Combining source reduction, improved treatment, take-back programs, and monitoring
• Stopping all agricultural activities near rivers
• Allowing uncontrolled discharge and relying on dilution

Correct Answer: Combining source reduction, improved treatment, take-back programs, and monitoring

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