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A rocky shore is a dynamic zone - NSC Marine Sciences - Question 5 - 2022 - Paper 2
Question 5
A rocky shore is a dynamic zone. It is ever changing and the organisms living in this area have to be adapted to these environmental changes. During a large storm, ... show full transcript
Worked Solution & Example Answer:A rocky shore is a dynamic zone - NSC Marine Sciences - Question 5 - 2022 - Paper 2
Step 1
Compare the circulatory mechanism in marine Osteichthyes and Echinoderms.
Answer
Marine Osteichthyes (bony fish) possess a closed circulatory system, characterized by a two-chambered heart. Their heart consists of an atrium, which receives blood returning from the body, and a ventricle that pumps it to the gills for oxygenation, and then out to the body. This process is referred to as single circulation. The blood in Osteichthyes is oxygenated in the gills and is rich in hemoglobin, which facilitates efficient oxygen transport.
In contrast, Echinoderms utilize a unique water-vascular system instead of blood. This system comprises fluid-filled coelomic chambers and papulae, which assist in locomotion and feeding. They do not have a closed circulatory system; instead, their water-vascular system circulates fluid, facilitating the transport of nutrients and waste. Cilia lining the water-vascular system help to move the fluid, thus distributing substances throughout their body.
Step 2
Discuss osmoregulation and excretion in both organisms.
Answer
Osmoregulation in Osteichthyes is managed primarily through their kidneys, which help to regulate the balance of salt and water in their bodies. They excrete excess salts and reabsorb water to maintain homeostasis, especially when transitioning between saline and freshwater environments. Their gills also assist in this process by expelling excess CO₂ and taking in oxygen.
Echinoderms lack specialized excretory organs; they rely on their coelomocytes to manage waste. They can absorb nutrients through their tube feet and eliminate waste through the same passage. Since Echinoderms are typically marine organisms, they are stenohaline, meaning they cannot tolerate significant changes to salinity. This affects their osmoregulation as they can only survive in stable saline conditions.
Step 3
Critique why the Echinoderms numbers were reduced and the fishes were not.
Answer
The decrease in the population of Echinoderms following the storm can be linked to their inability to cope with rapid changes in their environment, particularly concerning salinity. After heavy rain, the influx of freshwater can dilute the salinity of their habitat, resulting in osmotic stress. Echinoderms, being stenohaline, cannot withstand significant fluctuations in salinity, which may cause physiological stress leading to death.
Conversely, Osteichthyes have adapted systems that allow them to regulate their internal environment better. Their kidneys can excrete excess water and manage salt levels more efficiently, providing them with a better resilience to the transient changes in salinity caused by rainwater dilution. As a result, the fish population remained stable, as they could survive the immediate post-storm conditions more effectively than the Echinoderms.