شرح علوم متكاملة لغات الصف الاول الثانوي لغات - الفصل الدراسي الأول
شرح علوم متكاملة اولي ثانوي لغات - ترم أول
Integrated Sciences for Grade 10 (First Year of Secondary School) - First Semester

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In This Lesson :
The physical properties of water and their role in the distribution of living organisms.
Water has unique physical properties that distinguish it from other fluids (liquids and gases), such as the decrease in its density when it reaches the freezing point and its high specific heat capacity. These characteristics influence many natural phenomena and the distribution of living organisms in different environments.

Density
It is the mass per unit volume of a substance at a certain temperature.

Since matter is made up of molecules, the density of a substance depends on the mass of the molecules and the spaces between them. In the case of pure water, the mass of 1 cm³ of it at a temperature of 4°C is equal to 1 gram.
-The density of water at 4°C is 1 g/cm³, which is equivalent to the international unit of density, 1000 kg/m³.

As the temperature of water decreases below 4°C, approaching its freezing point, its density decreases.

The ratio of the density of a given substance to the density of pure water at the same temperature is known as the relative density of the substance.

The density or relative density of liquids is measured using a hydrometer, which is a sealed, hollow glass vessel with a wider lower part for buoyancy.
 
Density of water in polar regions
The density of water changes with temperature. Generally, as the temperature of a substance increases, its volume increases and its density decreases. However, water is an exception to this rule. As pure water is heated from 0°C to 4°C, it contracts and its density increases, reaching its maximum value of 1000 kg/m³ at 4°C. Above 4°C, water expands and its density decreases.
 
Oxygen and carbon dioxide in aquatic environments
Oxygen enters aquatic environments primarily through diffusion from the atmosphere and through photosynthesis by aquatic plants. The process of diffusion is enhanced by factors such as wave action and turbulence, which increase the surface area of water exposed to air. Oxygen is essential for the respiration of aquatic organisms, and its availability can influence the distribution and abundance of marine life.

Solubility of the two gases in water
• The concentration of oxygen gas in the air is about 500 times higher than that of carbon dioxide gas, but oxygen gas is about 50 times less soluble in water.
• Solubility of both gases decreases at higher temperatures. As temperature increases, the proportion of carbon dioxide gas dissolved in water decreases at a faster rate than the decrease in the proportion of oxygen in water.

Effects of Increased Dissolved Oxygen in Water:
1. Enhanced Respiration: Aquatic organisms rely on dissolved oxygen for respiration. Increased levels of dissolved oxygen improve their respiratory efficiency.
2. Improved Metabolism: Higher levels of dissolved oxygen can support the metabolic processes of aquatic organisms and promote growth.
3. Increased Activity: The high levels of dissolved oxygen stimulate aquatic organisms to be more active in swimming, foraging, and reproduction.
4. Maintenance of Ecosystem Balance: A healthy balance of dissolved oxygen in water is crucial for maintaining a stable aquatic ecosystem by supporting diverse populations of fish, invertebrates, and plants.


 ffects of Increased Carbon Dioxide Levels in Water on Aquatic Organisms:
The atmosphere is the primary source of carbon dioxide (CO2) in water.
Increased levels of carbon dioxide (CO2) in water can have several negative impacts on aquatic organisms, including:
1. Acidification: When atmospheric CO2 levels are high, more of it can dissolve in water, leading to increased carbonic acid and a decrease in pH. This acidification can be harmful to many aquatic species, especially those in sensitive life stages such as eggs and larvae.
2. Impaired Respiration: High levels of CO2 can lead to decreased dissolved oxygen levels in water, which is essential for aquatic respiration.
3. Reduced Calcification: Many marine organisms, such as corals, mollusks, and some types of plankton, rely on calcium carbonate to build their shells or skeletons. Calcium carbonate is a solid, sparingly soluble substance in water. Increased CO2 levels can convert it to calcium bicarbonate, which is soluble in water, hindering the ability of these organisms to build or maintain their structures.


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