Integrated Science First Term 1st Secondary Grade

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.

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.

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.

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.

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.