AICE MARINE SCIENCE | Chap 3: Interactions in Marine Ecosystem

Describe what is meant by the term productivity.

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Answer explanation

Productivity is the amount of new biomass which is produced/created by bacteria and plants through the processes of photosynthesis and chemosynthesis over a given amount of time in an area.

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Three factors that affect productivity. Both Must apply to be correct. (Select all that apply)

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Answer explanation

Factors that affect the productivity in an ecosystem are the temperature, light intensity, nutrient, respiration rate, and carbon dioxide concentration.

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Explain the difference between gross primary production and net primary production.

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Answer explanation

Gross primary production is the amount of energy that is fixed by producers within a specified area over a given amount of time. Net primary production is similar with the difference being that it accounts for respiration.

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The gross primary production in an ecosystem is 78,935 kJ m^-2 year^-1 and the energy lost in respiration is 23,675 kJ m^-2 year^-1. Calculate the net primary production.

• 55259

• 55261

• 53259

• 5.53

Answer explanation

The next primary production for the given problem is 55261 kJ m^-1y^r-1.

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Describe the process of photosynthesis

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Photosynthesis is the process by which energy is captured from the sun and converted to usable energy which can be consumed by organisms in trophic levels above the primary producers. Light photons are captured by chlorophyll in producers such as phytoplankton and algae. Carbon dioxide and water combine and yield to the production of glucose and oxygen gas. 

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Explain why photosynthesis does not occur at hydrothermal vents on the ocean floor.

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Answer explanation

Photosynthesis does not occur at hydrothermal vents located on the ocean floor, because they are located outside the photic zone and therefore no light photons are able to penetrate to the depth of hydrothermal vents. Producers such as marine grass, and algae are not present at this depth making it impossible for photosynthesis to occur.

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The solar energy falling on the ocean is 1.7 x 10⁶ kJ m^-2 year^-1 and the phytoplankton are able to use 18,754 kJ m^-2 year^-1 of this.

 I. Calculate the percentage of the Sun’s energy that is used by phytoplankton. Show your working.

Ii. Explain why 100% of the energy is not used.

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Answer explanation

i) 1.10% (or 1.11%) of the sun's energy is used by phytoplankton.

ii) 100% of the energy is not used because some of the energy is reflected off the waters surface, some misses the chlorophyll and therefore cant be absorbed. Lastly chlorophyll pigments can only absorb some wavelengths of light, so any alternating wavelengths will not be transmitted.

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Study the graph in figure 3.30, which shows the approximate chlorophyll concentrations off the coast of California over the course of the year. 

a. Describe the trend or patterns shown 

b. Explain why the amount of chlorophyll increase in march

c. Suggest and explain what will happen to the population of zooplankton, in march and April. 

d. Within this ecosystem, herring feed on the zooplankton and mackerel. Draw the pyramid of numbers for this food change.

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Answer explanation

Describe the trend or patterns shown

Looking at Figure 3.30, we can see an initial gradual increase in the chlorophyll until March. At this point a rapid increase in seen between March and April. Fluctuations are seen after this point until June when a decreasing trend can be noticed from July to December. The concentration begins at around 2 (units) and goes up to a high in March of 7 (units). In December the ending chlorophyll level measured is about 2 (units).

Explain why the amount of chlorophyll increase in March.

Due to the warmer temperatures of March and the higher levels of sunlight, and day-length needed to cause this increase in temperature, chlorophyll and algae are able to be more productive and have a higher growth rate. A overall greater rate of photosynthesis can be seen.

Suggest and explain what will happen to the population of zooplankton, in March and april. 

In March and April, the populations of Zooplankton will increase as there will be more food for them to consume, therefore there will be enough nutrients to allow for their population to expand.

Within this ecosystem, herring feed on the zooplankton and mackerel.

Pyramid is attached.

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 Describe how nutrient-rich water from deep in the ocean enters the reservoir of nutrients at the surface.

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Answer explanation

Nutrient-rich water enters the reservoir by upwelling, where cold water is pushed to the surface. This fertilizes the surface layers and increases productivity. These waters are higher in concentration and nutrients because the remains of living things sinks down.

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Describe two other ways in which nutrients enter surface layers 

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Answer explanation

Tectonic processes are another way by which nutrients enter the surface layer. At Hydrothermal vents, nutrients dissolve in the water that is near the magma chamber. When the water is released from the vents it meets the cold water. Minerals remain dissolved in the water available for organisms that live near there. Nutrients that are added will eventually reach the surface. Run-Off could also be used to answer the question as water moves into rivers and streams and from there go to the ocean. As it makes its way to the sea, it picks up nutrients from the soil that are carried away.

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