Unveiling Life's Microscopic World and Our Solar System

The Microscopic World of Cells

The Universe Hidden from Our View

The seventeenth-century (17th) invention of the microscope revolutionized our understanding of life.

• In 1674, Anton van Leeuwenhoek invented a powerful microscope.
• He observed a drop of water and what he saw were tiny living creatures, which he called animalcules.

Living Cells: The Building Blocks of Life

We are all formed by living cells.

The Discovery of Cells

• In 1665, Robert Hooke discovered cells while observing cork.

Types of Organisms

• Single-celled organisms:
  • Their size is very variable but they are always microscopic.
  • A single cell is able to perform all the functions of a living organism.
• Multicellular organisms:
  • Can often be seen with the naked eye; they are macroscopic.
  • Their cells do not all perform the same activities, specializing in shape and structure to perform specific functions.

Parts of an Animal Cell

• Vacuoles
• Ribosomes
• Cytoplasm
• Mitochondria
• Nucleus
• Nuclear membrane
• Plasma membrane

Parts of a Plant Cell

• Nucleus
• Mitochondria
• Cell wall
• Vacuoles
• Plasma membrane
• Chloroplasts

Types of Cellular Movements

• Amoeboid movement: (e.g., Amoeba)
• Contractile movement: (e.g., Vorticella)
• Resonant motion by means of flagella: (e.g., Euglenas)
• Vibratile movement by cilia: (e.g., Paramecium)

Our Place in the Universe: The Solar System

Components of the Solar System

• The Sun is a huge gas sphere. The most abundant elements are hydrogen and helium. Nuclear reactions take place inside its core.
• There are 8 planets in our solar system:
  • Mercury
  • Venus
  • Earth
  • Mars
  • Jupiter
  • Saturn
  • Uranus
  • Neptune
• Dwarf planets:
  • Ceres
  • Pluto
  • Eris

Planetary Classifications

• Inner or Terrestrial Planets:
  • The four planets nearest the Sun (Mercury, Venus, Earth, Mars).
  • They have a small, rocky surface.
• Outer or Giant Planets:
  • The remaining planets (Jupiter, Saturn, Uranus, Neptune) are the most distant from the Sun.
  • They are larger, gaseous, and liquid, and are often surrounded by rings.

Solar System Vocabulary

• Satellites: Celestial bodies orbiting planets.
• Minor bodies: Asteroids and comets within the solar system.

Planet Earth: A Unique World

Earth's Orbital Characteristics

• Aphelion: The point in Earth's orbit most distant from the Sun.
• Perihelion: The point in Earth's orbit closest to the Sun.

Earth's Movements

• Rotation: Movement around its own axis.
• Revolution (Translational Motion): Movement around the Sun.

Celestial Phenomena

• Solar Eclipse: Occurs when the Moon passes between the Sun and Earth, casting a shadow on Earth.
• Lunar Eclipse: Occurs when the Earth passes between the Sun and Moon, casting a shadow on the Moon.

Layers of the Earth

• Atmosphere
• Hydrosphere
• Geosphere