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Chapter 1 Aquatic ecosystem 1-3 Oxygen and carbon dioxide in the aquatic environment Rivers and seas naturally contain sufficient levels of oxygen and carbon dioxide to keep aquatic life of plants, fish, and microorganisms such as bacteria and algae. The main...

Chapter 1 Aquatic ecosystem 1-3 Oxygen and carbon dioxide in the aquatic environment Rivers and seas naturally contain sufficient levels of oxygen and carbon dioxide to keep aquatic life of plants, fish, and microorganisms such as bacteria and algae. The main source of oxygen in water is atmospheric air, where oxygen is slightly soluble in water. In addition, phytoplankton, algae, and aquatic plants produce oxygen in water in the process of photosynthesis. In seas and oceans, more oxygen dissolves in water as a result of waves and water currents in the ocean, which increase the rate of gas exchange between the atmosphere and water. Overall, these natural processes provide marine creatures with the oxygen necessary for their survival Solubility of the two gases O2 and CO2 in water The concentration of oxygen gas in the air is about 500 times higher than that of carbon dioxide, but oxygen gas is about 50 times less soluble in water. The solubility of the two gases in salty ocean water is about 20-30% lower than their solubility in fresh water. In general, the solubility of the two gases decreases at higher temperatures. As the temperature increases, the percentage of CO2 dissolved in water decreases, but at a greater rate than the percentage of oxygen in water. The graph shows the relationship between the solubility of oxygen and carbon dioxide in fresh water at different temperatures under normal atmospheric composition. The effect of increasing the percentage of dissolved oxygen in water: a. Enhancement (improving) of respiration: Aquatic organisms depend on dissolved oxygen in water for respiration. Increasing the amount of oxygen in water improves their ability to breathe. b. Improved metabolism: High levels of dissolved oxygen can support the metabolism of aquatic organisms and improve growth. c. Increased activity: Adequate levels of dissolved oxygen stimulate aquatic organisms to be more active in swimming, hunting, and reproduction. d. Maintain balance of the ecosystem: A healthy level of dissolved oxygen in water is critical in maintaining a stable aquatic ecosystem by supporting diverse populations of fish, invertebrates, and plants. 16 Chemical reactions and their impact on water quality 1−1 Lesson Research activity Search about the factors that lead to the lack of oxygen gas in water and the effects of the lack of this gas. Sources of carbon dioxide in the aquatic environment: 1- The atmosphere is the main source of carbon dioxide (CO2) in water. Carbon dioxide is exchanged between the atmosphere and water. 2- Marine organisms produce carbon dioxide gas that dissolves in the surrounding water as a waste product of their metabolism. 3- Human activities such as industrial pollution, and the decomposition of organic matter carried by agricultural wastewater. The effect of increased CO2 in water on aquatic organisms: Increased CO2 in water can have several negative effects on aquatic organisms, including: 1. Acidification: When CO2 levels are high in the atmosphere, it can dissolve in greater amounts in water, leading to an increase in carbonic acid and a decrease in the pH value of the water. This acidification can be harmful to many species of aquatic organisms, especially those in sensitive life stages such as the egg and larval stages. 2. Weak respiration: High levels of carbon dioxide can reduce the amount of dissolved oxygen in the water necessary for aquatic organisms to breathe. 3. Reduced calcification: Many marine organisms such as corals, mollusks, and some species of plankton depend on calcium carbonate to form their shells or skeletons. Increased CO2 converts it into calcium bicarbonate, which dissolves in water, disrupting the ability of these organisms to build or maintain their skeletons. The effect of CO2 deficiency in water on aquatic organisms: 1. Reduced photosynthesis: Aquatic plants and algae need carbon dioxide for photosynthesis. Decreasing the availability of CO2 in water may limit their ability to produce energy, affecting the overall productivity of the ecosystem. 2. Effects on food chains: A change in the level of CO2 in the water can affect productive organisms such as phytoplankton and algae, thereby affecting organisms at higher levels of the food chain. 3. Disruption of pH balance: Low concentrations of CO2 may lead to an increase in the pH of water, negatively affecting sensitive species that are adapted to a certain pH range 17 Chapter 1 Aquatic ecosystem 1-4 Biological adaptations of living organisms in the aquatic environment Get ready In the world of aquatic creatures, every organism has a set of adaptations that help it to survive in its environment, whether it is a deep ocean or a shallow lake. In this lesson, we will explore these physiological, behavioral, and structural adaptations that allow aquatic organisms to survive under different environmental conditions. Learn:Learn Physiological (functional) adaptation: Organisms in the aquatic environment develop special physiological adaptations that enable them to survive in their environments. That is, adaptations or modifications in the way they perform their biological/vital functions. For example, some deep- ocean fish have special abilities to regulate respiration under the state of oxygen deficiency. To adapt to the high-water pressure at great depths, deep-sea fish have Electric Eel strong and durable arteries and veins that can withstand the high pressure. They also have the ability to effectively adjust their blood pressure to equalize the external pressure. A famous example is the Electric Eel, which lives at depths of thousands of meters, where oxygen levels are extremely low. These fish have developed very large gills, with very fine capillaries that maximize the efficiency of extracting the little oxygen found in water. In addition, they can slow down their metabolism to minimize their oxygen needs. Osmosis and osmotic pressure: Osmosis is the phenomenon of water transfer from a dilute solution to a concentrated solution through a semi-permeable membrane separating the two solutions as shown in the figure. Osmotic pressure is the pressure created in a solution due to the difference in solute concentration in the solution and leads to the diffusion of water from the less concentrated solution (low osmotic pressure) towards the more concentrated solution (higher osmotic pressure). 18 Chemical reactions and their impact on water quality 1−4 Lesson Practical activity: Tools: Sugar solution - Thistle funnel - Cellophane paper - Glass beaker half-filled with tap water - Rubber band – Stand Steps: Tightly fix the cellophane paper to the opening of the funnel with the rubber band. Fill the funnel with the sugar solution, submerge it in the water-filled beaker and hold it vertically. Mark the solution level in the stem of the funnel Leave the device for a sufficient period of time and observe what happens, and record your observations. We can observe that the solution level in the funnel stem increases as it draws water from the beaker by osmosis, since the sugar concentration in the funnel is higher than its concentration in the beaker. Physiological adaptations of freshwater organisms to low osmotic pressure The previous experiment showed what could happen to an organism living in freshwater when the osmotic pressure of the water is lower than the osmotic pressure of their bodies. In this case, the bodies of these organisms will draw large amounts of water, causing them to burst and die. So, how do these organisms adapt to the characteristics of the freshwater environment? Unicellular organisms, such as amoeba, paramecium, and euglena, have a structure or an organelle called a contractile vacuole that collects excess water in the cell and when it is filled with water, it moves towards the cell membrane where it discharges its water content to the outside of the cell. 19 Chapter 1 Aquatic ecosystem Multicellular organisms, such as fish, eliminate excess water that enters the body through the skin, mouth, and gills by the kidneys in the form of dilute urine. In fish, the kidneys are located in the abdominal cavity on either side of the spine. While fish that live in saltwater need to swallow large amounts of sea water to compensate for the osmotic loss of water from their body, and then they excrete excess salts through their kidneys and specialized cells in their gills. As a physiological adaptation to the high salinity of the ocean and sea water, sharks maintain the balance of water and salts within their bodies through controlling the level of urea in their blood. Urea is a nitrogenous compound that is excreted in the urine of many animals to get rid of it. Sharks keep a high concentration of urea in their blood, which increases their osmotic pressure, bringing it close to the osmotic pressure of the surrounding water. This helps minimize the loss of water from their body to the surrounding environment of high salinity. Behavioral adaptations: Behavioral adaptations include certain actions or behaviors that organisms use to avoid extreme conditions or to better utilize available resources. For example, some fish migrate between fresh and salt water to reproduce and survive. Salmon are born in freshwater, then move to the sea where they spend most of their adult life, before returning to rivers again to reproduce. When salmon eggs hatch, their young spend the first period of their Salmon migration lives in freshwater. During this stage, the youngsters adapt to the freshwater environment. Upon reaching a certain size, the fish undergo a biological process known as “Smoltification” which allows them to move to the saltwater of the sea. When salmon reach sexual maturity, they begin to return to the rivers where they were born to reproduce. The ability of salmon to move between different environments is due to their ability to make complex physiological adaptations. For example, their circulatory and respiratory systems adapt to changes in salinity and different amounts of oxygen in fresh and salt water. 20 Chemical reactions and their impact on water quality 1−4 Lesson Structural adaptations Structural adaptations include changes in the physical structure of organisms that help them survive in their environments. For example, fish that live in the deep ocean have very large eyes to be able to see in the dark, and their bodies are compressed to withstand the very high pressure in deep water. An example of a Ice fish compressed deep-sea fish is the icefish, which lives in the cold southern oceans, at depths of about 2000 meters. Among the general structural adaptations of fish are a streamlined body that reduces water resistance to the fish's movement, gills that enable it to extract dissolved oxygen in water, and its body is covered with scales and mucus to be waterproof and to reduce water resistance to its movement, fins are movement organs, and bony fish have an air bladder or swim bladder that helps them float in the water. Gas exchange and cellular respiration: Gas exchange is when an organism obtains oxygen from atmospheric air or the surrounding environment and removes carbon dioxide. Cellular respiration is a vital process in which the organism breaks down the bonds in food molecules, especially glucose, to obtain stored energy. Unicellular organisms, such as amoeba obtain oxygen and eliminate carbon dioxide through the cell membrane by diffusion. activity Analyze the relationship between biological adaptations and the aquatic environment: Search the Internet to find biological adaptations found in both the lionfish and the colorful octopus Colored Octopus Lionfish 21