Eukaryotic Organism

Edexcel GCSE Biology: Combined Science 1.1 Cell Structure

1.1.1 Eukaryotic Organisms

• Common Features of Eukaryotic Organisms:

  • All living organisms classified into five kingdoms:

    1. Animals

    2. Plants

    3. Fungi

    4. Protoctists

    5. Prokaryotes (such as: some bacterias & most viruses)

  • First four kingdoms are eukaryotic organisms (eukaryotes).

  • Eukaryotic organisms can be multicellular or single-celled.

  • Cells contain a nucleus with a distinct membrane.

1.1.2 Eukaryotic Organisms: Animals & Plants

• Animals:

  • Multicellular, nucleus present with membrane.

  • No cellulose cell walls or chloroplasts.

  • Feed on organic substances made by other living things.

  • Store carbohydrates as glycogen.

  • Exhibit nervous coordination and movement.

• Plants:

  • Multicellular, nucleus present with membrane.

  • Have cellulose cell walls and chloroplasts.

  • Carry out photosynthesis for feeding.

  • Store carbohydrates as starch or sucrose.

  • No nervous coordination.

1.1.3 Eukaryotic Organisms: Fungi & Protoctists

• Fungi:

  • Usually multicellular (some are unicellular like yeast).

  • Composed of hyphae, which form a mycelium.

  • Cell walls made of chitin, no chloroplasts.

  • Feed by secreting digestive enzymes onto food (saprotrophic nutrition).

  • Examples include moulds, mushrooms, and yeasts.

• Protoctists:

  • Diverse group, mostly microscopic and unicellular.

  • Some share features with animals or plants.

  • Examples include amoeba, Paramecium, Plasmodium, and Chlorella.

1.1.4 Prokaryotic Organisms

• Prokaryotes:

  • Always unicellular, no nucleus (nuclear material in cytoplasm).

  • Much smaller than eukaryotic cells.

  • Lack chloroplasts and mitochondria.

  • Bacteria are key examples:

    • Lactobacillus (used in yoghurt production)

    • Pneumococcus (causes pneumonia).

1.1.5 Specialised Cells

• Specialised Cells:

  • Develop adaptations for specific functions through differentiation.

  • Examples include:

    • Sperm cells: carry male DNA to egg.

    • Egg cells: fertilised by a sperm to develop into an embryo.

    • Ciliated epithelial cells: waft particles and bacteria through mucus.

1.1.6 Microscopy

• History and Techniques:

  • First light microscopes by early scientists (e.g., Hooke, Leeuwenhoek).

  • Light microscopes use light to magnify specimens; modern ones can magnify up to 2,000x.

  • Electron microscopes provide much higher magnification (up to 2,000,000x) using electrons for resolution.

1.1.7 Practical: Microscopy

• Using Optical Microscopes:

  • Light directed through thin biological layers on slides.

  • Common materials observed include cheek and onion cells.

  • Important components: eyepiece lens, objective lenses, stage, light source.

  • Stain specimens to enhance visibility (e.g., methylene blue, iodine).

1.1.8 Using Units

• Converting Units:

  • Unit conversions necessary for magnification calculations (e.g., mm to µm).

  • Examples of conversions:

    • 1 mm = 1000 µm

    • 1 µm = 0.001 mm

  • Worked example: convert 2000 µm to mm.

  • Understand and use standard form for large or small numbers in calculations.