natural science

1. Cells: The Basic Units of Life

Cells are the smallest functional units of living organisms and are fundamental to understanding biology.

1.1 The Cell Theory

  • All living organisms are made of one or more cells.

  • The cell is the basic unit of life.

  • All cells arise from pre-existing cells.

1.2 Plant vs. Animal Cells

  • Plant Cells: Contain a cell wall for structural support, chloroplasts for photosynthesis, and a large central vacuole.

  • Animal Cells: Do not have a cell wall or chloroplasts; they have smaller, temporary vacuoles.

  • Common Organelles:

    • Nucleus: The control center containing genetic material ($DNA$).

    • Mitochondria: The site of cellular respiration where energy is produced ($ATP$).

    • Cell Membrane: A semi-permeable barrier controlling the entry and exit of substances.

2. Matter and Materials

2.1 The Atom

  • Atoms are the building blocks of all matter.

  • Structure:

    • Protons: Positively charged particles ($+1$) located in the nucleus.

    • Neutrons: Neutral particles ($0$) located in the nucleus.

    • Electrons: Negatively charged particles ($-1$) orbiting the nucleus in shells.

  • Atomic Notation:

    • Atomic Number ($Z$): The number of protons in the nucleus.

    • Mass Number ($A$): The total number of protons and neutrons.

    • Formula for neutrons ($N$): A = Z + N

2.2 The Periodic Table

  • Elements are arranged by increasing atomic number.

  • Groups: Vertical columns showing elements with similar chemical properties.

  • Periods: Horizontal rows showing the number of energy levels (shells).

3. Chemical Reactions

  • A process where reactants are transformed into products through the breaking and forming of chemical bonds.

  • Law of Conservation of Mass: Mass cannot be created or destroyed. Therefore, equations must be balanced.

  • Example: Phosphorus reacting with oxygen: 4P + 5O{2} \rightarrow 2P{2}O_{5}

4. Forces and Energy

4.1 Forces and Weight

  • Force ($F$): A push or pull on an object, measured in Newtons ($N$).

  • Weight ($W$): The gravitational force acting on an object's mass ($m$).

    • Formula: W = m \times g, where $g$ is gravitational acceleration ($g \approx 9.8 m/s^{2}$ on Earth).

4.2 Work and Power

  • Work ($W_{work}$): Done when a force moves an object over a distance ($d$).

    • Formula: W_{work} = F \times d

  • Power ($P$): The rate at which work is done.

    • Formula: P = \frac{W_{work}}{t}, where $t$ is time.