# Module B Quiz — Question Bank **Source:** Canvas quiz, submitted Jun 10 at 11:25 a.m. (attempt took 13 minutes) **Score:** 1.9 / 2.0 — Question 8 answered incorrectly; all others correct. **Note:** Correct answers are marked with ✅. For multiple-choice questions the student's selection was not captured in the paste; correct answers are identified from course content. --- ## Question 1 — Shark lift (True/False) ✅ Correct > In most cases, sharks need to produce lift by moving water over their pectoral fins. - **True** ✅ - False *Rationale: Cartilage and high liver oil are not buoyant enough, so most sharks sink if they stop swimming. Stiff pectoral fins generate lift in motion, like airplane wings.* --- ## Question 2 — Diatom asexual division (True/False) ✅ Correct > During asexual reproduction, diatoms only produce new epithecas in daughter cells. - True - **False** ✅ *Rationale: Each daughter cell keeps one old valve (epitheca or hypotheca) as its new epitheca and builds a NEW **hypotheca**. The daughter that inherits the smaller hypotheca ends up smaller — this is why average cell size shrinks each generation.* --- ## Question 3 — Salps and the biological pump ✅ Correct > Salps (Family Salpidae) possess a notable combination of traits that make them exceptional drivers of the biological carbon pump. Which of the following describes this capability? - They remain anchored to the subtidal rocks via strong holdfast arrays to bury carbon under sand. - They dissolve the skeletal matrices of passing fish to absorb pure dissolved organic carbon. - They completely eliminate heterotrophic bacteria to prevent the breakdown of particulate matter. - **They are the fastest-growing multicellular animals, capable of rapid asexual cloning, and produce some of the largest, fast-sinking fecal pellets of any zooplankton.** ✅ - They build glass frustules that lock away carbon monoxide in deep benthic trenches. *Rationale: During a bloom, salps clone fast, filter feed efficiently, and their large fecal pellets sink quickly, exporting carbon to the deep ocean.* --- ## Question 4 — Characteristics of bony fish ✅ Correct > Which of the following is a characteristic of most bony fish (class Osteichthyes)? - **They have a swim bladder for buoyancy control.** ✅ - They need to swim continuously to maintain oxygen flow across their gills. - Their skeletons are made of cartilage. - They rely on a high oil content in their bodies for buoyancy. *Rationale: Most (not all) bony fish use a gas-filled swim bladder. Cartilage skeletons, oil-based buoyancy, and obligatory swimming describe cartilaginous fish (sharks and rays).* --- ## Question 5 — Mitochondrial DNA location (True/False) ✅ Correct > Mitochondrial DNA is primarily contained in the nucleus of a eukaryotic cell. - True - **False** ✅ *Rationale: Mitochondria contain their own small circular DNA (evidence for endosymbiosis). Many ancestral organelle genes moved to the nucleus over time, but the mitochondrial DNA molecule itself sits inside the mitochondrion.* --- ## Question 6 — Seagrass vs. macroalgae nutrient uptake ✅ Correct > How does the nutrient acquisition mechanism of Seagrasses fundamentally differ from that of marine Macroalgae? - **Seagrasses have true root systems that actively absorb nutrients directly from the soft sediments, whereas macroalgae must absorb nutrients from the water column across their thallus.** ✅ - Seagrasses utilize mixotrophy to capture nanoflagellates, while macroalgae are strictly chemosynthetic. - Macroalgae use their holdfasts to drain nutrients from host fish, while seagrasses rely entirely on solar cosmic rays. - Seagrasses filter feed on particulate organic matter (POM) using fine hair-like blades. - There is no difference; both groups absorb nutrients exclusively through complex silica valves. *Rationale: Seagrasses are true plants with roots. Macroalgae are not plants — the holdfast is only an anchor and does not absorb nutrients.* --- ## Question 7 — Importance of dimethyl sulfide (DMS) ✅ Correct > Why is dimethyl sulfide (DMS) an important molecule (choose the best answer)? - It is a dinoflagellate toxin that has the potential to disrupt food webs. - It increases light absorption of different wavelengths that increases photosynthetic efficiency. - It is a deterrent to macroalgae grazing. - It is a primary energy source for archaea organisms in the sediment. - **It will increase cloud coverage during a dinoflagellate bloom, potentially cooling the surface.** ✅ *Rationale: Many mixotrophic dinoflagellates produce DMSP, which breaks down into DMS. DMS acts as a cloud-forming nucleus, so it plays a role in climate regulation.* --- ## Question 8 — Why silicoflagellate sex was discovered only recently ❌ Incorrect (0 / 0.1) > Which of the following best explains why scientists only recently discovered that silicoflagellates go through sexual reproduction. - **Scientist had not identified the ameboid form of silicoflagellates until recently.** ✅ (correct answer) - Silicoflagellates do not actually go through sexual reproduction. - Silicoflagellates would struggle to find a mate in the open ocean. - The silica spines make sexual reproduction impossible. - Silicoflagellates are too small to be able to see sexual reproduction. *Rationale: Silicoflagellates have two forms. The skeleton-bearing form reproduces asexually by binary fission. The naked amoeboid form — only recently described — is the one that engages in sexual reproduction.* --- ## Question 9 — What is NOT true of tuna ✅ Correct > Which of the following is NOT a characteristic of tuna? - Tuna can average speeds faster than 65 kilometres per day. - Tuna utilize a high caloric diet to feed their activity that can result in a high internal temperatures (compared to ocean temperatures). - As a bony fish, tuna have reduced or eliminated their swim bladders and must use muscular movement to change depths in the water column. - Tuna have evolved less scales than most bony fish due to its fast moving lifestyle. - **Tuna can be highly maneuverable in tight, compact environments.** ✅ *Rationale: Tuna are built for cruising speed and acceleration, not maneuverability. High maneuverability suits fish of reefs and kelp forests. A tuna's stiff body, finlets, and reduced swim bladder all favor efficient long-distance propulsion.* --- ## Question 10 — Largest single-clone autotroph ever recorded ✅ Correct > What is the largest single clone autotrophic organism ever recorded geologically, and where is it located? - A giant thallus of brown kelp off the coast of British Columbia measuring 1.8 kilometers. - A colonial mat of Trichodesmium sp. spanning the entire width of the Red Sea. - A 3,000 mm colony of barrel-shaped gelatinous salps drifting in the Southern Ocean. - An ancient community of Asgard archaea near Loki's Castle hydrothermal vents. - **A single individual of the seagrass Posidonia australis in Shark Bay, Western Australia, covering roughly 200 square kilometers and connected by rhizomes.** ✅ *Rationale: This seagrass clone is the largest plant ever recorded. It may have originated from a single seed ~4,500 years ago.* --- ## Question 11 — Coccolithophores and climate sensitivity ✅ Correct > Why are coccolithophores often considered to be more sensitive to climate change than other phytoplankton? - **Their shells are made of CaCO₃ that becomes harder to form when ocean pH decreases** ✅ - They tend to grow better is warmer water - They can only grow in cold water - The only contain chlorophyll a and do not have other accessory pigments - Their optimum light absorption is in the blue wavelengths *Rationale: Ocean acidification lowers pH, which makes calcium carbonate plates harder to form and easier to dissolve. Coccoliths also become weaker or malformed at low pH, making coccolithophores key indicator organisms.* --- ## Question 12 — Pneumatocysts ✅ Correct > What are 'pneumatocysts' in marine macroalgae, and what gas do they characteristically contain to preserve organism orientation? - They are silica-walled valves containing liquid hydrogen sulfide. - They are root nodules containing nitrogen gas. - They are reproductive vesicles that store linear maternal DNA arrays. - **They are air-filled bladders that provide buoyancy to keep the blades close to the sunlit ocean surface, typically containing carbon monoxide.** ✅ - They are microscopic internal microtubules filled with sulfuric acid. *Rationale: Pneumatocysts lift the photosynthetic blades toward the light. They range from grape- to volleyball-sized and generally contain carbon monoxide.* --- ## Question 13 — Advantage of mixotrophy in dinoflagellates ✅ Correct > Which of the following is an important advantage to mixotrophic dinoflagellates? - Mixotrophy allows photosynthetic dinoflagellate to use nitrogen fixers as a symbiont. - **Mixotrophy allows for nutrient acquisition in low nutrient tropical waters.** ✅ - Mixotrophy allows dinoflagellates to be bigger and thus less likely to be hunted as prey. - Mixotrophy allows dinoflagellates to swim faster to avoid prey. - Mixotrophy allows for better camouflage so they can more successfully avoid predators. *Rationale: Mixotrophs can photosynthesize AND ingest organic carbon (prey or DOM). This dual strategy keeps them growing when light or nutrients run low — a big advantage in stratified, nutrient-poor tropical water.* --- ## Question 14 — Ecological role of zooxanthellae ✅ Correct > What is the ecological role of zooxanthellae in their symbiotic relationship with coral reefs? - **They provide organic matter and assist in CaCO₃ skeleton formation** ✅ - They provide silica for reef structural integrity - They provide substrate for corals to grow larger - They release toxins as a protection mechanism for the coral - They act as the primary predator of coral polyps *Rationale: Zooxanthellae are photosynthetic dinoflagellates living inside coral tissue. They transfer organic carbon to the host and raise local pH, which promotes calcium carbonate deposition. (See Module D, coral reefs.)* --- ## Question 15 — Prokaryotic vs. eukaryotic cells: NOT true ✅ Correct > When comparing prokaryotic and eukaryotic cells, which statement is NOT true? - **Eukaryotic cells are exclusively multicellular, whereas prokaryotic cells are always unicellular.** ✅ - Both cell types can possess cell walls, though their chemical compositions differ. - Genetic material is found in a circular loop in prokaryotes and in linear chromosomes in eukaryotes. - Prokaryotic cells lack a membrane-bound nucleus, whereas eukaryotic cells have one. - Bacterial DNA can be found inside all eukaryotes. *Rationale: The flagged statement is false — many eukaryotes are single-celled (all eukaryotic phytoplankton, for example). The last option is true by endosymbiosis: organelle DNA and genes transferred to the nucleus are bacterial in origin.* --- ## Question 16 — What is NOT a dinoflagellate characteristic ✅ Correct > Which of the following is NOT a characteristic of Dinoflagellates? - **They can form resting auxospores** ✅ - Most dinoflagellate photoautotrophs can obtain energy from external carbon sources - They are important producers of harmful algal blooms - Some are 'naked' - more likely (but not always) found in warmer waters - They can contain cellulose *Rationale: Auxospores belong to diatoms. Dinoflagellates form a **resting cyst** (with a tough pellicle) after sexual reproduction. The other options are true: mixotrophy, HABs, athecate (naked) forms, warm-water preference, and cellulose thecal plates.* --- ## Question 17 — Viruses and "killing the winner" ✅ Correct > How do marine viruses maintain phytoplankton species diversity in the surface oceans through a mechanism termed 'killing the winner'? - By forming a physical barrier of viral biomass that blocks toxic solar radiation for smaller species. - By consuming the excess fixed nitrogen before larger diatoms can absorb it. - **By multiplying exponentially inside the dominant, blooming phytoplankton species, causing them to burst in mass numbers and preventing them from outcompeting other species.** ✅ - By forcing competing algae to undergo immediate resting cyst formation in the sediments. - By selectively transferring photosynthetic genes into heterotrophic decomposers. *Rationale: Viruses are host-specific and track host density. When one species blooms, its viruses explode, crash the bloom, and release DOM — letting other species coexist.* --- ## Question 18 — Purpose of the vacuole ✅ Correct > Eukaryotic phytoplankton often have a vacuole in their cells. What is a purpose? - it controls chlorophyll production - **it allows for storage** ✅ - it decreases the surface area/volume ratio - it acts a a receptacle for chloroplasts - it helps with respiration *Rationale: The vacuole stores sugars and nutrients so the cell can keep dividing when nutrients or light run low. Adjusting vacuole contents also helps control buoyancy.* --- ## Question 19 — True statement about viruses ✅ Correct > Select the statement that is TRUE from the statements below in terms of viruses. - Viruses are only found in areas of large productivity. - Viruses are triggered by DOM in the ocean. - All statements listed are true, - **Viral infections of phytoplankton can keep any single species of phytoplankton from becoming dominant.** ✅ - Viruses only infect plankton. *Rationale: This is the "killing the winner" effect. The other options are false: viruses are found everywhere (~10⁷ per liter), and they also infect fish, shellfish, seabirds, and marine mammals.* --- ## Question 20 — Multicellular phytoplankton ✅ Correct > Which of the following is an example of multicellular phytoplankton? - copepods - **sargassum** ✅ - diatoms - sea lettuce - fucus *Rationale: Sargassum is the only truly multicellular phytoplankton — a free-floating brown macroalga of the Sargasso Sea. Diatoms are unicellular. Sea lettuce (Ulva) and Fucus are attached macroalgae, not plankton. Copepods are zooplankton.*