Integrated Science First Term 1st Secondary Grade

Aquatic Ecosystem: Chemical Reactions and Water Quality

• Water's unique properties support life, including the ability to dissolve many chemicals.
• Water exists in three states: solid (ice), liquid, and gas (vapor) within Earth's temperature range.
• Essential for life; all living organisms possess a cell membrane that regulates interaction with the environment.
• Cell membranes allow water and nutrients to enter cells and facilitate waste removal.

Earth's Water Spheres

• Water covers approximately 70% of Earth’s surface, with about 97% of this as salt water in oceans, seas, and salt lakes.
• Freshwater sources, crucial for life, are found in rivers, lakes, and underground aquifers.
• Water vapor is a key component of the atmosphere.
• The cryosphere includes frozen water in polar regions, mountain peaks, and glaciers.
• Egypt's aquatic diversity includes the Nile River, Gulf of Suez, Gulf of Aqaba, Red Sea, Mediterranean Sea, and various lakes.

Water Cycle and Its Processes

• The water cycle, or hydrological cycle, is a closed system where water constantly moves in different forms.
• Major processes include:
  • Evaporation: Conversion of water to vapor, contributing to cloud formation.
  • Precipitation: Rain or snow falling back to the ground.
  • Transpiration and Respiration: Biological processes that release water vapor.
  • Infiltration: Water moving through soil and rocks to form groundwater.
• Water vapor can chemically react and contribute to acid rain, which affects rock dissolution.

Chemical Structure and Properties of Water

• Water (H2O) consists of two hydrogen atoms and one oxygen atom in a 2:1 ratio.
• Oxygen comprises 88.89% of the water molecule's mass, while hydrogen constitutes 11.11%.
• The molecular structure includes two covalent bonds at a bond angle of about 104.5 degrees.

Chemical Properties of Water

• Water is not found in a pure form; it contains various ions and chemical substances.
• Polarity: The oxygen atom's higher electronegativity creates partial negative and positive charges within the water molecule.
• The polarity leads to unique properties, enabling water to dissolve a variety of substances and participate in chemical reactions.