MCQs:
- What is the primary role of phytoplankton in the global carbon cycle?
- a) Carbon sequestration in ocean sediments
- b) Photosynthesis and carbon dioxide absorption
- c) Carbon production through respiration
- d) Carbon storage in the atmosphere
Answer: b) Photosynthesis and carbon dioxide absorption
Explanation: Phytoplankton absorb carbon dioxide from the atmosphere and convert it into organic compounds through photosynthesis.
- Which process allows phytoplankton to remove carbon dioxide from the atmosphere?
- a) Respiration
- b) Photosynthesis
- c) Carbonate formation
- d) Nitrogen fixation
Answer: b) Photosynthesis
Explanation: Through photosynthesis, phytoplankton absorb carbon dioxide and convert it into sugars and other organic molecules.
- Phytoplankton contribute to the “biological pump” in the ocean. What is the biological pump?
- a) The transfer of nutrients from deep ocean layers to the surface
- b) The movement of carbon dioxide from the atmosphere to the ocean
- c) The movement of carbon from the atmosphere to the ocean floor
- d) The removal of oxygen from the ocean to the atmosphere
Answer: c) The movement of carbon from the atmosphere to the ocean floor
Explanation: The biological pump describes the process by which phytoplankton take in carbon dioxide and, through sinking or being eaten by other organisms, carbon is transferred to the deep ocean.
- What is the main form of carbon that phytoplankton incorporate during photosynthesis?
- a) Methane
- b) Carbonic acid
- c) Carbon dioxide (CO₂)
- d) Bicarbonate ions
Answer: c) Carbon dioxide (CO₂)
Explanation: Phytoplankton use carbon dioxide from the atmosphere in photosynthesis to produce organic molecules.
- What happens to the carbon absorbed by phytoplankton once they die or are consumed by zooplankton?
- a) It is immediately released back into the atmosphere
- b) It sinks to the ocean floor or is transferred to other organisms
- c) It is stored in the zooplankton’s body for a long period
- d) It is released into the ocean surface layers
Answer: b) It sinks to the ocean floor or is transferred to other organisms
Explanation: Dead phytoplankton or those consumed by zooplankton often sink, transferring carbon to deeper layers of the ocean.
- How do phytoplankton impact the global carbon cycle during phytoplankton blooms?
- a) They increase the carbon in the atmosphere
- b) They contribute to significant carbon absorption and storage
- c) They release large amounts of methane
- d) They produce oxygen that helps balance atmospheric gases
Answer: b) They contribute to significant carbon absorption and storage
Explanation: Phytoplankton blooms lead to an increase in photosynthesis, absorbing large amounts of CO₂ and storing it in oceanic carbon pools.
- What factor most influences the growth of phytoplankton in oceans?
- a) Oxygen availability
- b) Nutrient availability and sunlight
- c) Salinity levels
- d) Temperature alone
Answer: b) Nutrient availability and sunlight
Explanation: Phytoplankton growth is heavily influenced by the availability of nutrients like nitrogen and phosphorus, as well as adequate sunlight for photosynthesis.
- Which type of phytoplankton is responsible for the majority of oceanic primary production?
- a) Dinoflagellates
- b) Diatoms
- c) Cyanobacteria
- d) Green algae
Answer: b) Diatoms
Explanation: Diatoms are the primary producers in many ocean ecosystems and contribute significantly to carbon fixation through photosynthesis.
- What is one of the major impacts of ocean acidification on phytoplankton?
- a) Increased growth due to higher CO₂ levels
- b) Decreased carbon sequestration ability
- c) Enhanced nutrient uptake
- d) Faster sinking rates
Answer: b) Decreased carbon sequestration ability
Explanation: Ocean acidification, resulting from higher CO₂ levels, can impair the ability of some phytoplankton, like coccolithophores, to build calcium carbonate shells, reducing their effectiveness in carbon sequestration.
- In what form do phytoplankton primarily store the carbon they capture?
- a) As sugars and carbohydrates
- b) As methane
- c) As calcium carbonate
- d) As proteins
Answer: a) As sugars and carbohydrates
Explanation: Phytoplankton store carbon mainly in the form of sugars, starches, and other carbohydrates formed through photosynthesis.
- What is the significance of the ocean’s “biological pump” in relation to climate regulation?
- a) It helps to cool the ocean’s surface temperature
- b) It decreases atmospheric CO₂, thereby mitigating global warming
- c) It contributes to increased global temperatures
- d) It eliminates ocean pollution
Answer: b) It decreases atmospheric CO₂, thereby mitigating global warming
Explanation: The biological pump helps mitigate climate change by removing CO₂ from the atmosphere and sequestering it in the ocean.
- What is the relationship between phytoplankton and the marine food web?
- a) They are primary consumers
- b) They are secondary producers
- c) They are primary producers and form the base of the food web
- d) They consume organic carbon from other marine organisms
Answer: c) They are primary producers and form the base of the food web
Explanation: Phytoplankton serve as primary producers in the marine ecosystem, forming the base of the food web and providing energy for higher trophic levels.
- What happens to the carbon fixed by phytoplankton in the deep ocean?
- a) It is released back into the atmosphere
- b) It stays there indefinitely, trapped in deep-sea sediments
- c) It is reabsorbed by phytoplankton
- d) It is utilized by deep-sea bacteria for respiration
Answer: b) It stays there indefinitely, trapped in deep-sea sediments
Explanation: Some of the carbon fixed by phytoplankton is transferred to the deep ocean through the biological pump, where it can be stored in sediments for long periods.
- Which of the following marine organisms consumes phytoplankton as its primary food source?
- a) Whales
- b) Sharks
- c) Zooplankton
- d) Sea turtles
Answer: c) Zooplankton
Explanation: Zooplankton are the primary consumers of phytoplankton, forming an important link between primary producers and higher trophic levels.
- What impact do increased levels of atmospheric CO₂ have on phytoplankton productivity?
- a) It has no effect on their productivity
- b) It can stimulate increased growth under certain conditions
- c) It reduces their growth significantly
- d) It causes them to migrate to different areas
Answer: b) It can stimulate increased growth under certain conditions
Explanation: Elevated CO₂ levels may enhance phytoplankton growth, particularly in nutrient-rich regions, but may not have a uniform effect across all marine environments.
- What is the role of cyanobacteria in the carbon cycle?
- a) They only contribute to nitrogen fixation
- b) They sequester carbon by converting it to methane
- c) They fix carbon dioxide and contribute to global carbon cycling
- d) They are decomposers that release carbon into the atmosphere
Answer: c) They fix carbon dioxide and contribute to global carbon cycling
Explanation: Cyanobacteria, like phytoplankton, fix CO₂ through photosynthesis, contributing significantly to global carbon cycling.
- What is one of the effects of reduced phytoplankton populations on carbon cycling?
- a) Increased carbon sequestration in the deep ocean
- b) Higher atmospheric CO₂ levels
- c) Increased carbon storage in ocean sediments
- d) Reduced global temperatures
Answer: b) Higher atmospheric CO₂ levels
Explanation: Reduced phytoplankton populations limit carbon absorption from the atmosphere, leading to higher CO₂ levels.
- What is the impact of nutrient pollution on phytoplankton growth?
- a) It always results in a decrease in phytoplankton
- b) It can cause phytoplankton blooms and hypoxia
- c) It reduces phytoplankton populations significantly
- d) It has no significant effect
Answer: b) It can cause phytoplankton blooms and hypoxia
Explanation: Excessive nutrients, especially nitrogen and phosphorus, can cause phytoplankton blooms, leading to oxygen depletion and hypoxia.
- Which of the following is an example of a phytoplankton species that contributes to significant carbon fixation?
- a) Aurelia aurita (moon jellyfish)
- b) Trichodesmium (a cyanobacterium)
- c) Carcharodon carcharias (great white shark)
- d) Crassostrea virginica (Eastern oyster)
Answer: b) Trichodesmium (a cyanobacterium)
Explanation: Trichodesmium, a type of cyanobacterium, is a significant contributor to nitrogen fixation and carbon cycling in marine ecosystems.
- Which of the following processes allows carbon to be stored in deep ocean sediments?
- a) Phytoplankton grazing
- b) Ocean currents
- c) Phytoplankton sinking or consumption by zooplankton
- d) Evaporation
Answer: c) Phytoplankton sinking or consumption by zooplankton
Explanation: As phytoplankton die or are consumed by zooplankton, their carbon-rich remains sink to the ocean floor, where it can be stored in deep-sea sediments.
- Which is a major factor influencing phytoplankton’s ability to fix carbon efficiently?
- a) Ocean temperature
- b) Depth of the ocean
- c) Nutrient availability and light intensity
- d) Ocean salinity
Answer: c) Nutrient availability and light intensity
Explanation: Phytoplankton require sufficient nutrients (like nitrogen and phosphorus) and light to perform photosynthesis and fix carbon.
- What is the effect of climate change on phytoplankton productivity?
- a) It has no significant impact
- b) It may reduce productivity in certain regions due to temperature rise and nutrient limitation
- c) It enhances phytoplankton growth everywhere
- d) It leads to an increase in carbon sequestration
Answer: b) It may reduce productivity in certain regions due to temperature rise and nutrient limitation
Explanation: Climate change can alter ocean temperatures, nutrient availability, and stratification, potentially reducing phytoplankton productivity in some areas.
- How does phytoplankton affect the global carbon cycle when they undergo photosynthesis?
- a) They release carbon into the atmosphere
- b) They fix carbon into organic molecules, which can be transferred to the deep ocean
- c) They increase atmospheric oxygen
- d) They produce carbon dioxide in the water
Answer: b) They fix carbon into organic molecules, which can be transferred to the deep ocean
Explanation: Phytoplankton convert carbon dioxide into organic carbon during photosynthesis, and this carbon can eventually be transferred to deep ocean sediments.
- What role do phytoplankton play in the ocean’s role as a carbon sink?
- a) They increase ocean temperatures
- b) They contribute to the ocean absorbing large amounts of atmospheric CO₂
- c) They prevent carbon from entering the ocean
- d) They create toxic environments for marine life
Answer: b) They contribute to the ocean absorbing large amounts of atmospheric CO₂
Explanation: Phytoplankton are essential for the ocean’s role as a carbon sink by absorbing atmospheric CO₂ and fixing it into organic carbon during photosynthesis.
- How does the decline of phytoplankton affect the global carbon cycle?
- a) It leads to increased atmospheric CO₂
- b) It accelerates the biological pump
- c) It stabilizes the carbon cycle
- d) It increases carbon sequestration
Answer: a) It leads to increased atmospheric CO₂
Explanation: A decline in phytoplankton reduces the ocean’s ability to absorb CO₂, leading to higher levels of carbon in the atmosphere.
- Which of the following actions could increase phytoplankton growth in a particular area of the ocean?
- a) Reduced sunlight
- b) Increased nutrient runoff from land
- c) Higher ocean salinity
- d) Higher ocean temperatures
Answer: b) Increased nutrient runoff from land
Explanation: Increased nutrient availability, particularly nitrogen and phosphorus from agricultural runoff, can stimulate phytoplankton blooms.
- What does the carbon fixed by phytoplankton primarily contribute to in the food web?
- a) Oxygen production
- b) Energy for higher trophic levels
- c) Phytoplankton respiration
- d) Water purification
Answer: b) Energy for higher trophic levels
Explanation: The carbon fixed by phytoplankton provides the energy source for a wide range of marine organisms, including zooplankton, fish, and marine mammals.
- What is the consequence of reducing the phytoplankton population in marine ecosystems?
- a) Increased atmospheric oxygen
- b) Reduced primary production and a decline in marine food webs
- c) Increased carbon sequestration in the ocean
- d) Greater carbon fixation and lower CO₂ levels
Answer: b) Reduced primary production and a decline in marine food webs
Explanation: Phytoplankton form the base of marine food webs, and their decline would lead to reduced primary production and impact higher trophic levels.
- What is the relationship between phytoplankton and atmospheric CO₂?
- a) Phytoplankton release CO₂ into the atmosphere
- b) Phytoplankton absorb and fix CO₂ during photosynthesis
- c) Phytoplankton store CO₂ in the atmosphere
- d) Phytoplankton cause increased CO₂ emissions
Answer: b) Phytoplankton absorb and fix CO₂ during photosynthesis
Explanation: During photosynthesis, phytoplankton absorb atmospheric CO₂, converting it into organic carbon and helping regulate global CO₂ levels.
- Which of the following factors could lead to a decrease in phytoplankton populations?
- a) Increased nutrient availability
- b) Decreased ocean temperatures
- c) Ocean acidification and warming
- d) Increased sunlight
Answer: c) Ocean acidification and warming
Explanation: Ocean acidification and warming can negatively affect phytoplankton, especially those that rely on calcium carbonate for shell formation.
