science 4th

• Gentle giants of the ocean

  Largest animals on Earth
• Amphibians


  Group of animals including frogs, toads, and salamanders, known for their moist skin and ability to live both on land and in water
• Extinction


  Environmental issue that poses a significant threat to biodiversity, referring to the permanent disappearance of species from the Earth
• Biodiversity


  The variety of life on Earth, including all living organisms and their interactions
• Biodiversity changes over time as extinction occurs and new species evolve
• Levels of biodiversity


  • Species
  • Genetic
  • Ecosystem
• Ecosystem


  Interconnected community where living things (plants, animals, and microbes) and non-living things (like soil, water, and sunlight) all work together
• Ecosystem


  • Pond
• Species


  Group of living organisms that are similar to each other and can reproduce offspring that are also able to reproduce
• Biodiversity hotspots


  Regions that contain a high level of species diversity, many endemic species, and a significant number of threatened or endangered species
• Genetic diversity


  Variety of genes within a single species
• Species diversity


  Variety of different types of organisms, or species, in a particular area
• Endemic


  A species that is uniquely found in one part of the world, and that part only
• Ecosystem diversity


  Variety of different ecosystems, or habitats, in a larger region
• Biodiversity is the variety of species and ecosystems on Earth
• Species with high biodiversity


  • A pond with many different kinds of fish, frogs, and plants
• Importance of biodiversity


  It provides humans with resources such as food, medicine, and clean air and water
• Levels of biodiversity


  • Genetic diversity
  • Species diversity
  • Ecosystem diversity
• Species diversity


  Variety of different species in a given area
• Biodiversity hotspots


  Areas with high levels of species richness and endemism
• Endemic species


  Species found only in one specific habitat
• Threats to biodiversity


  • Habitat restoration
  • Conservation efforts
  • Climate change
  • Captive breeding programs
• Loss of biodiversity


  Decreased ecosystem services
• Genetic diversity


  Variety of genes present within a population or species
• Cell


  Tiny units of life
• Robert Hooke


  British scientist who first used the word 'cell' to refer to these tiny units of life in 1665
• Hooke was one of the earliest scientists to study living things under a microscope
• When Hooke looked at a thin slice of cork under his microscope, he saw what looked like a honeycomb
• Antonie van Leeuwenhoek


  Made his own microscope lenses, was the first to observe human cells and bacteria
• Matthias Schleiden


  Proposed in 1838 that the basic unit of plant structure is the cell, and that every part of a plant is composed of cells or their derivatives
• Schleiden's work laid the groundwork for the first tenet of cell theory
• Theodor Schwann


  Proposed in 1839 that all animal tissues are composed of cells, completing the second tenet of cell theory
• Rudolf Virchow


  Proposed in 1855 that cells arise only from pre-existing cells through cell division, completing the third tenet of cell theory
• Cell theory states that:

  • All organisms are made of one or more cells
  • A cell is the smallest unit of structure and function in a living thing
  • All cells come from pre-existing cells
• Reduction division

  The chromosome number is halved. This is essential because it ensures that when gametes (sperm and egg cells) fuse during fertilization, the resulting zygote will have the correct number of chromosomes for the species.
• Prophase I

  1. Chromosomes condense and become visible.

  2. Homologous chromosomes pair up and exchange genetic material in a process called crossing over.
• Crossing over

  • Chromosomes are approximately the same size and they contain the same types of genes in the same locations.
• Metaphase I

  1. Paired homologous chromosomes line up along the metaphase plate.

  2. Each chromosome attaches to spindle fibers from opposite poles.
• Anaphase I

  1. Homologous chromosomes separate and move to opposite poles of the cell.

  2. Sister chromatids remain attached.
• Telophase I

  1. Chromosomes reach the poles and the nuclear envelope reforms.

  2. The cell divides into two daughter cells, each with half the original number of chromosomes (haploid).