Aquatic ecosystems – streams MCQs With Answer

Aquatic ecosystems – streams MCQs With Answer

Understanding aquatic ecosystems, especially streams, is vital for B. Pharm students studying environmental pharmacology, drug fate, and ecotoxicology. Streams are dynamic lotic systems where flow, dissolved oxygen, temperature, pH, nutrients, and microbial communities influence the transport, transformation, and bioavailability of pharmaceuticals and contaminants. This concise, targeted set of MCQs covers stream ecology, water quality parameters (BOD, COD, turbidity), biochemical cycles, pollutant fate (sorption, biodegradation, photolysis), bioindicators, and regulatory aspects relevant to pharmaceutical contamination. These questions help build applied knowledge for drug safety, environmental risk assessment, and stewardship. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What term best describes a flowing freshwater ecosystem such as a stream?

• Lentic
• Lotic
• Palustrine
• Estuarine

Correct Answer: Lotic

Q2. Which parameter measures the amount of oxygen consumed by microorganisms to decompose organic matter?

• pH
• Biochemical Oxygen Demand (BOD)
• Dissolved solids
• Conductivity

Correct Answer: Biochemical Oxygen Demand (BOD)

Q3. Which process describes the microbial conversion of ammonium (NH4+) to nitrate (NO3-) in streams?

• Denitrification
• Nitrification
• Ammonification
• Assimilation

Correct Answer: Nitrification

Q4. Which is the most important physical factor controlling gas exchange and oxygenation in streams?

• Substrate composition
• Flow velocity and turbulence
• Riparian vegetation color
• Water hardness

Correct Answer: Flow velocity and turbulence

Q5. Which indicator organism group is commonly used as a bioindicator of stream water quality?

• Macroinvertebrates
• Terrestrial mammals
• Planktonic foraminifera
• Coral polyps

Correct Answer: Macroinvertebrates

Q6. What does COD (Chemical Oxygen Demand) measure in stream samples?

• Oxygen produced by photosynthesis
• Oxygen required to chemically oxidize organic and inorganic matter
• Total suspended solids
• Microbial biomass concentration

Correct Answer: Oxygen required to chemically oxidize organic and inorganic matter

Q7. Which process removes nitrate in anaerobic sediments by converting it to nitrogen gas?

• Nitrification
• Denitrification
• Photolysis
• Sorption

Correct Answer: Denitrification

Q8. Which factor increases the rate of photodegradation of some pharmaceuticals in stream water?

• High turbidity
• High dissolved organic matter acting as inner filter
• Clear water with high sunlight penetration
• Low temperature

Correct Answer: Clear water with high sunlight penetration

Q9. What is the term for zones beneath and alongside a stream where surface and groundwater interact?

• Riparian buffer
• Hyporheic zone
• Epilimnion
• Limnetic zone

Correct Answer: Hyporheic zone

Q10. Which property of a pharmaceutical most strongly influences its sorption to stream sediments?

• Vapor pressure
• Octanol-water partition coefficient (Kow) and Koc
• Color
• Molecular weight only

Correct Answer: Octanol-water partition coefficient (Kow) and Koc

Q11. Which process often limits biodegradation of hydrophobic pharmaceuticals in streams?

• High solubility increases biodegradation
• Strong sorption to sediments reducing bioavailability
• Rapid photolysis
• High temperatures reducing microbial activity

Correct Answer: Strong sorption to sediments reducing bioavailability

Q12. Stream order (Strahler) increases when:

• Two streams of different orders join
• Two streams of the same order join
• A tributary enters a lake
• Stream flow decreases

Correct Answer: Two streams of the same order join

Q13. Elevated concentrations of which nutrient commonly cause eutrophication in streams and rivers?

• Selenium
• Phosphorus
• Sodium
• Mercury

Correct Answer: Phosphorus

Q14. Which measure indicates water’s ability to neutralize acids?

• pH
• Alkalinity
• Conductivity
• Turbidity

Correct Answer: Alkalinity

Q15. Which parameter is a quick field measure correlating with ionic strength and dissolved salts in stream water?

• BOD
• Conductivity
• DO saturation
• Chlorophyll-a

Correct Answer: Conductivity

Q16. Which of these increases the risk of pharmaceutical residues reaching streams?

• Advanced tertiary wastewater treatment in all facilities
• Direct disposal of unused medicines into sinks and toilets
• Strict take-back programs for medicines
• High dilution in large rivers only

Correct Answer: Direct disposal of unused medicines into sinks and toilets

Q17. Which community component is primary producer in many streams?

• Fish
• Benthic algae and periphyton
• Macroinvertebrates
• Detritivorous bacteria only

Correct Answer: Benthic algae and periphyton

Q18. What effect does increased temperature generally have on dissolved oxygen in stream water?

• Increases DO solubility
• Decreases DO solubility
• No effect
• Converts DO to BOD

Correct Answer: Decreases DO solubility

Q19. Which analytical parameter quantifies the toxicity of a contaminant to aquatic species over a concentration range?

• Koc
• LC50
• pKa
• Henry’s law constant

Correct Answer: LC50

Q20. Which process can lead to bioaccumulation and biomagnification of hydrophobic contaminants in stream food webs?

• Rapid photodegradation
• Persistence and lipophilicity leading to accumulation in fatty tissues
• High water solubility causing rapid excretion
• Strong sorption to dissolved organic carbon only

Correct Answer: Persistence and lipophilicity leading to accumulation in fatty tissues

Q21. Which chemical property increases the likelihood that a drug will partition into sediments rather than remain dissolved?

• Low Kow
• High Kow
• High aqueous solubility
• Low molecular polarity

Correct Answer: High Kow

Q22. Which microbial process in sediments can produce hydrogen sulfide under anoxic conditions?

• Sulfate reduction
• Nitrogen fixation
• Nitrification
• Photoautotrophy

Correct Answer: Sulfate reduction

Q23. What is the environmental significance of the hyporheic zone for pharmaceutical fate?

• It has no effect on contaminant processing
• It provides a site for exchange, sorption, microbial degradation, and transformation
• It accelerates volatilization only
• It prevents all contaminant transport

Correct Answer: It provides a site for exchange, sorption, microbial degradation, and transformation

Q24. Which test organism is commonly used to assess acute toxicity in freshwater environments?

• Escherichia coli only
• Daphnia magna
• Arabidopsis thaliana
• Caenorhabditis elegans only

Correct Answer: Daphnia magna

Q25. Which parameter is most directly affected by algal blooms in streams?

• Increased dissolved oxygen at night
• Diurnal oxygen fluctuations and potential hypoxia at night
• Decreased nutrient levels permanently
• Reduced turbidity always

Correct Answer: Diurnal oxygen fluctuations and potential hypoxia at night

Q26. Which removal mechanism is often used in wastewater plants to reduce pharmaceuticals before discharge to streams?

• Chloride addition only
• Advanced oxidation processes, activated carbon adsorption, and biological treatment
• Simple sedimentation alone
• Freezing

Correct Answer: Advanced oxidation processes, activated carbon adsorption, and biological treatment

Q27. Which term describes the gradual dilution and downstream transport of pollutants in a stream?

• Hydraulic retention
• Advection and dispersion
• Sorption only
• Photoionization

Correct Answer: Advection and dispersion

Q28. Which ionic condition often increases the mobility of some heavy metals in stream water?

• High pH promoting precipitation
• Low pH increasing solubility
• High alkalinity immobilizing metals
• High hardness causing permanent binding

Correct Answer: Low pH increasing solubility

Q29. Which process is least important for removal of volatile organic contaminants from stream water?

• Air–water exchange (volatilization)
• Adsorption to fine sediments
• Biodegradation in water column
• Photolytic degradation at surface

Correct Answer: Adsorption to fine sediments

Q30. Which parameter describes the fraction of a pharmaceutical that is ionized at a given pH?

• Henry’s law constant
• pKa and environmental pH
• Koc only
• BOD

Correct Answer: pKa and environmental pH

Q31. Which of these best explains why antibiotics in streams can promote antibiotic resistance?

• They always undergo rapid photodegradation
• Sublethal concentrations exert selective pressure on microbial communities
• Antibiotics increase DO, preventing resistance
• They bind irreversibly to sediment and are inactive

Correct Answer: Sublethal concentrations exert selective pressure on microbial communities

Q32. Which stream habitat feature provides refuge and food for juvenile fish and influences contaminant exposure?

• Riparian canopy and woody debris
• Open sandbars only
• Deep groundwater wells
• Atmospheric layer above stream

Correct Answer: Riparian canopy and woody debris

Q33. What is the likely effect of increased suspended sediments on photolytic degradation of pharmaceuticals?

• Enhances photolysis by scattering light
• Reduces photolysis by decreasing light penetration
• No effect
• Always increases biodegradation instead

Correct Answer: Reduces photolysis by decreasing light penetration

Q34. Which measurement helps estimate the organic matter available for microbial metabolism in stream sediments?

• Chloride concentration
• Total organic carbon (TOC)
• pH alone
• Hardness

Correct Answer: Total organic carbon (TOC)

Q35. Which process can transform pharmaceuticals into potentially more toxic metabolites in streams?

• Biotransformation by microbial enzymes
• Complete mineralization only
• Instantaneous volatilization
• Dilution to harmless levels

Correct Answer: Biotransformation by microbial enzymes

Q36. Which factor most strongly affects residence time of water in a stream reach?

• Stream width variability only
• Flow velocity and channel morphology
• Length of riparian plants only
• Ambient air temperature exclusively

Correct Answer: Flow velocity and channel morphology

Q37. In ecotoxicology, which endpoint measures chronic sublethal effects over longer exposures?

• LC50 (acute lethality)
• NOEC (No Observed Effect Concentration)
• Vapor pressure
• Kow only

Correct Answer: NOEC (No Observed Effect Concentration)

Q38. Which human activity commonly increases nutrient loading (nitrogen and phosphorus) to streams?

• Implementing buffer strips
• Agricultural runoff and wastewater discharge
• Reforestation of riparian zones
• Advanced wastewater tertiary treatment

Correct Answer: Agricultural runoff and wastewater discharge

Q39. Which stream sampling approach is best to capture temporal variability of pharmaceutical concentrations?

• Single grab sample at midday
• Composite sampling over time or automated samplers
• Sampling only after storm events always
• Sampling only at headwaters once a year

Correct Answer: Composite sampling over time or automated samplers

Q40. Which chemical behavior does Henry’s law constant predict for a pharmaceutical?

• Degree of ionization
• Potential for volatilization from water to air
• Sorption to organic carbon
• Biodegradation rate directly

Correct Answer: Potential for volatilization from water to air

Q41. Which management practice helps reduce pharmaceutical contamination entering streams?

• Encouraging direct flushing of unused drugs
• Medicine take-back programs and source control
• Removing riparian vegetation
• Increasing impervious surfaces near streams

Correct Answer: Medicine take-back programs and source control

Q42. Which sediment characteristic increases sorption of hydrophobic drugs?

• High organic carbon content
• Very low surface area
• Predominantly coarse sand with low organic matter
• High oxygen concentration only

Correct Answer: High organic carbon content

Q43. Which operational parameter in WWTPs enhances biodegradation of pharmaceuticals?

• Short hydraulic retention time with no biomass
• Longer sludge retention time and active microbial communities
• Complete absence of oxygen always
• Immediate chlorination without biological treatment

Correct Answer: Longer sludge retention time and active microbial communities

Q44. Which compound class is often persistent and found in streams due to resistance to biodegradation?

• Simple sugars
• Fluorinated pharmaceuticals and PFAS
• Aliphatic alcohols
• Readily biodegradable amino acids

Correct Answer: Fluorinated pharmaceuticals and PFAS

Q45. Which method is commonly used to assess microbial water quality in streams?

• Measuring LC50 of fish
• Coliform or E. coli counts
• Kow measurement
• Measuring turbidity only

Correct Answer: Coliform or E. coli counts

Q46. Which physical change commonly results from urbanization and affects stream ecosystem health?

• Decreased flow variability and increased infiltration
• Increased peak flows and flashiness due to impervious surfaces
• Enhanced natural riparian filtration
• Lower pollutant loads always

Correct Answer: Increased peak flows and flashiness due to impervious surfaces

Q47. Which property of pharmaceuticals can change with pH, affecting transport and uptake?

• Half-life inert to pH
• Ionization state (ionized vs. non-ionized)
• Color only
• Vapor pressure immutably

Correct Answer: Ionization state (ionized vs. non-ionized)

Q48. Why are periphyton communities relevant to pharmaceutical fate in streams?

• They only reduce DO and do not interact with contaminants
• They can uptake, transform, and store contaminants and influence local biogeochemistry
• They are absent from most streams
• They only exist in marine environments

Correct Answer: They can uptake, transform, and store contaminants and influence local biogeochemistry

Q49. Which monitoring metric integrates biological, chemical, and physical stream health into assessment?

• BOD only
• Multimetric indices using community structure (e.g., macroinvertebrate-based indices)
• Temperature alone
• Conductivity alone

Correct Answer: Multimetric indices using community structure (e.g., macroinvertebrate-based indices)

Q50. Which regulatory guideline focuses on protecting aquatic life from waterborne contaminants?

• Dietary Reference Intake (DRI)
• Environmental quality standards and water quality criteria (e.g., EPA aquatic life criteria)
• Pharmacopoeial standards only
• Human blood pressure guidelines

Correct Answer: Environmental quality standards and water quality criteria (e.g., EPA aquatic life criteria)

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