解题
### **Section A: Ecosystem Ecology Worked Solution**
**2 (a) (i)**
* A valid 4-trophic level marine food chain:
\[\text{Seagrass} \longrightarrow \text{Green sea turtle} \longrightarrow \text{Tiger shark} \longrightarrow \text{Decomposer/Parasitic roundworm}\]
* Or using algal epiphytes/consumers:
\[\text{Marine algae} \longrightarrow \text{Herbivorous fish} \longrightarrow \text{Green sea turtle} \longrightarrow \text{Tiger shark}\]
* *Note: Arrows must point from the food resource to the consumer to show energy flow direction.*
**2 (a) (ii)**
* Chlorophyll is a green pigment found in the chloroplasts of primary producers (algae, seagrasses).
* It absorbs light energy (specifically blue and red wavelengths) from the Sun.
* This light energy is used to power the chemical reaction of photosynthesis, which converts carbon dioxide and water into glucose (chemical energy) and oxygen.
**2 (a) (iii)**
* **Community:** All the populations of different species (fish, turtles, sharks, corals, seagrasses) living and interacting in the same sanctuary area at the same time.
* **Niche:** The specific ecological role or function of an organism within its habitat, such as the green sea turtle acting as a major marine herbivore that grazes seagrass beds, preventing them from becoming overgrown.
---
### **Section B: Pollution and Bioaccumulation Worked Solution**
**2 (b) (i)**
* **Bioaccumulation:** Soluble heavy metals (like mercury) are absorbed by individual organisms (e.g., phytoplankton/algae) from the water but cannot be easily excreted or broken down, so they accumulate inside the organism's body tissues over its lifespan.
* **Biomagnification:** When herbivores eat these producers, they consume the accumulated toxins. Because a predator eats many prey organisms over its life, the concentration of the toxin increases significantly at each successive trophic level.
* **Impact on Apex Predators:** Tiger sharks sit at the top of the food chain, meaning they consume large quantities of highly contaminated prey. Consequently, they suffer from the highest toxic concentrations, leading to reproductive failure, brain damage, or death.
**2 (b) (ii)**
* **Ingestion:** Floating plastic bags resemble jellyfish (which some turtles eat). Ingestion blocks the digestive tract, leading to a false sense of fullness, starvation, and death.
* **Entanglement:** Turtles get caught in discarded plastic fishing lines/nets ("ghost nets"), restricting their movement, causing physical injury/amputations, and preventing them from reaching the surface to breathe, leading to drowning.
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### **Section C: Biodiversity and Conservation Worked Solution**
**2 (c) (i)**
* \[\text{Initial population (2010)} = 1200\]
* \[\text{Final population (2025)} = 380\]
* \[\text{Decrease} = 1200 - 380 = 820\]
* \[\text{Percentage Decrease} = \frac{820}{1200} \times 100 = 68.33\%\]
* Accept: \(68.3\%\) or \(68\%\).
**2 (c) (ii)**
* Poaching of turtle eggs from nests and harvesting adult females for meat/shells.
* Coastal development and artificial lighting on nesting beaches, which disorients hatchlings (causing them to crawl inland toward city lights instead of the sea) and deters females from nesting.
**2 (c) (iii)**
* Establish beach patrols by community rangers during nesting season to deter poachers.
* Enact local laws banning artificial lights or vehicle access on nesting beaches during nighttime hours.
* Install protective mesh cages over identified nests to keep out natural and introduced predators (e.g., feral dogs, crabs).
**2 (c) (iv)**
* Provides alternative employment (as guides, boat captains, hotel staff) for local fishers and poachers, reducing the economic incentive to harvest turtles.
* Guided tours generate direct revenue through national park entrance fees, which can fund turtle research and beach protection patrols.
* Raises environmental awareness and educates both tourists and local communities about turtle ecology.
---
### **Section D: Conservation Priorities Worked Solution**
**2 (d)**
* **Evaluation (Disagree / To a small extent agree):**
* While protecting sea turtles (a keystone species) is highly important, focusing *only* on them is a flawed approach because species cannot survive without their habitats.
* Mangrove forests serve as crucial coastal buffers, trapping sediments and filtering agricultural run-off before it reaches offshore coral reefs and seagrass meadows where turtles feed.
* Mangroves are also nursery habitats for the fish species that support the entire marine food web. If mangroves are destroyed, coral reefs and seagrass beds degrade, which directly harms turtle populations.
* Therefore, an ecosystem-based management approach that protects habitats like mangroves is far more effective and sustainable than focusing solely on single endangered species.
评分标准
**Section A: Ecosystem Ecology**
* **2(a)(i)**:
* M1: All four organisms in the correct logical trophic order starting with a primary producer (e.g., Seagrass/Algae) and including the green sea turtle **[1]**
* M2: Arrows drawn pointing in the correct direction (from producer to consumer/predator) **[1]**
* **2(a)(ii)**:
* M1: Chlorophyll is a green light-absorbing pigment found in chloroplasts **[1]**
* M2: Absorbs solar energy (light) and converts it to chemical energy **[1]**
* M3: Powers photosynthesis to convert carbon dioxide and water into glucose/organic nutrients and oxygen **[1]**
* **2(a)(iii)**:
* M1: Community = All the interacting populations of different species in a given area/habitat **[1]**
* M2: Niche = The unique functional role/job of an organism within its ecosystem **[1]**
**Section B: Pollution and Bioaccumulation**
* **2(b)(i)**:
* M1: Toxins/heavy metals are absorbed by producers and cannot be easily excreted/metabolized (bioaccumulation) **[1]**
* M2: The concentration of toxins increases at each successive trophic level (biomagnification) **[1]**
* M3: Because organisms eat many individuals of the trophic level below them **[1]**
* M4: Top predators (tiger sharks) suffer the highest concentrations, causing severe neurological or reproductive damage **[1]**
* **2(b)(ii)**: Any two from:
* M1: Ingestion of plastics (mistaken for jellyfish) blocks the gut, leading to starvation **[1]**
* M2: Entanglement in ghost nets restricts movement, causing drowning or severe physical lacerations **[1]**
* M3: Toxic chemicals (additives) from swallowed plastics leach into body tissues **[1]**
**Section C: Biodiversity and Conservation**
* **2(c)(i)**:
* M1: Correct calculation of decline (\(1200 - 380 = 820\)) OR setup: \(\frac{1200 - 380}{1200} \times 100\) **[1]**
* M2: Correct percentage: \(68.3\%\) (accept \(68\%\) or \(68.33\%\)) **[1]**
* **2(c)(ii)**: Any two from:
* M1: Poaching of eggs/meat by humans **[1]**
* M2: Coastal development/infrastructure taking up beach space **[1]**
* M3: Light pollution on beaches disorienting hatchlings/nesting females **[1]**
* M4: Accidental capture in commercial fishing gear/trawls (bycatch) **[1]**
* **2(c)(iii)**: Any three from:
* M1: Employment of beach rangers to patrol nesting areas to deter egg thieves/poachers **[1]**
* M2: Installation of protective cages or wire mesh over nests to deter predators **[1]**
* M3: Banning vehicles and artificial lighting on nesting beaches during the nesting/hatching seasons **[1]**
* M4: Beach restoration to clear beach obstacles (debris, coastal sea walls) **[1]**
* **2(c)(iv)**: Any three from:
* M1: Generates ecotourism revenue which can fund nesting beach patrol operations **[1]**
* M2: Provides alternative livelihoods (guides, captains, accommodation) so locals do not resort to poaching **[1]**
* M3: Increases educational awareness among visitors and local communities **[1]**
* M4: Incentivizes governments to strengthen marine environmental laws **[1]**
**Section D: Conservation Priorities**
* **2(d)**: Level of response marked question.
* *Level 3 (3-4 marks):* Balanced evaluation of the statement. Student clearly understands ecosystem interconnectedness. Candidate details how single-species protection fails if feeding/nursery habitats (like mangroves) are degraded. Precise vocabulary (keystone species, ecological services, trophic levels) is used accurately.
* *Level 2 (1-2 marks):* Suggests agreement or disagreement but lacks detailed ecological reasoning. Focuses only on sea turtles or only on mangroves without explaining their connection.
* *Level 1 (0 marks):* No creditable response.