Cells & Viruses


Eukaryotic Cells


  • complex & large cells (compared to prokaryotic)
  • singular or multicellular organsisms
  • always have a nucleus
  • all other organisms but bacteria and archea


  • Nucleus - nuclear envelope & nucleolus
  • Ribosomes
  • Cell surface membrane
  • Rough endoplastic reticulum (RER) & smooth endplastic reticulum (SER)
  • Mitochondria
  • Golgi body & golgi vesicles
  • Lysosomes
  • Cytoplasm
  • Cytosol
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Mitochondria & Chloroplasts


They carry out aerobic respiration by releasing energy from food molecules to produce ATP, which powers the cell's metabolic reactions.

The inner membrane folds into cristae, enclosing the matirix. This increases surface area meaning more ATP synthase can fit and so more aerobic respiration takes place.

C6H12O6 + 6O2 -> 6CO2 + 6H2O


They are the site of photosynthesis, which makes ATP meaning they also contain ATP synthase.

It is surrounded by a double membrane, also containing thylakoid membranes which are stacked to create grana.

6CO2 + 6H2O -(light)-> C6H12O6 + 6O2

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Prokaryotic Cells


  • no nucleus
  • no membrane-bound organelles
  • the cell is much smaller than eukaryotic cells
  • ribosomes are smaller than in eukaryotic cells
  • sometimes has a capsule (slimy outer layer)
  • one or more flagellum may be present (rare in eukaryotic cells)
  • DNA is short, circular and isn't wrapped around histone proteins
  • one or more plasmids may be present
  • cell wall is made from murein
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Cells, tissues, organs & systems

Cell = There are many different types of cell in an organism, each with a different function - e.g. sperm, pollen, macrophage.

Tissue = a group of similar cells with a common origin, often performing the same function - e.g. epithilium, muscle, xylem.

Organ = 2 or more tissues working together to perform a specific function - e.g. flower, root, skin.

System = 2 or more organs working together to perfom a specific function - e.g. immune system, respiratory system, endocrine system.

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Structure of Viruses

They are non-living as they don't perform the basic funtions of living organisms, meaning they can't be killed. They are also acellular, meaning they aren't a cell and can't reproduce through cell division.


  • Attachment Proteins = to attach and gain entry to host cells. Identified as the antigen by the immune system
  • Genetic Material = DNA/RNA which codes for the virus' proteins
  • Caspid = a container for genetic material made from protein subunits
  • Envelope (only some viruses have this) = a membrane enclosing the caspid, but isn't a cell surface membrane.

All viruses have the main 3 componants, no matter how they look.

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Viral Replication & Treatment


  • Virus attaches to a cell
  • Virus penetrates the cell membrane and injects nucleic acid (DNA/RNA) into the cell
  • Viral nucleic acid replicates using the host cell's machinary - the cell's enzymes copy the viral genetic material and the cell's ribosomes make the viral proteins
  • New viral nucleic acid are packaged into viral particles and released from the cell. The host cell may be destroyed in the process.


Antibiotics are chemicals that specifically kill bacteria by targetting vital molecules specific to bacterial cells (e.g enzymes and ribosomes).

They can't kill viruses as they mainly use the enzymes of the host cell to replicate. Also, viruses inhabit the host cells so it's hard to make effective drugs that can enter cells.

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Cell Fractionation

  • Tissue is cut into smaller pieces & placed in a chilled, isotonic, buffered solution:
    • Chilled = slows down/stops the rate of reaction of lysozymes. It prevents the enzymes from hydrolysing the cells organelles
    • Isotonic = same water potential as the organelles so osmosis doesn't occur. It prevents the organelles from bursting or shrivelling up.
    • Buffered = pH is controlled, allowing enzymes to function properly. It prevents them from denaturing so organelle function can be studied
  • Tissue is homogenised to break open cells, releasing the organelles
  • Filter it through muslin cloth. It prevents contamination from unbroken cells.
  • Spin in a centrifuge at high speeds to seperate the organelles by densities. Larger organelles collect at the bottom (called pellet) and smaller organelles collected above (called supernatant).
  • Remove the supernatant and respin it at higher speeds to seperate the smaller densities.

1st spin = nuclei

2nd spin = chloroplasts & mitochondria

3rd spin = ribosomes & others

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