FULL NOTES - Topic 1 Cell biology

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Topic 1: Cell Biology


1.1 & 1.5 Introduction to cells and origins of cells


Cell Theory

§  All living things are composed of cells, which are the basic unit structure of all living organisms. Organisms consisting of only one cell carry out all functions of life in that cell.

§  Exceptions

o   Multinucleated cells: single plasma membrane + multiple nuclei (e.g. Muscle fibers)

o   Giant algae cells: contradicts cell size theory (e.g. Acetabularia algae, 7 cm long)

o   Virus: protein coat with RNA/DNA, can't reproduce without host, not made of cells

§  Cell theory evidence

o   1662 - Robert Hooke, observed cork cells under a microscope

o   1881 - Robert Brown observed cell nuclei in plant cells

o   1856 - Rudolf Virchow, proposed that cells only arise from pre-existing cells


Limitations of cell size

§  Surface area to volume ratio essential for cells

o   Rate of material exchange: Large surface area for diffusion of waste + molecules

o   Rate of metabolism: increased volume requires increased energy

o   Rate of transportation: increased size increases distance materials must travel

§  Limits the size of cells and creates long, thin cells (nerve cells)


Endosymbiotic theory:

§  The theory that organelles (Mitochondria and chloroplasts) originated a large host cell and ingesting the single celled bacterium and formed a symbiotic relationship.

§  Endosymbiotic theory Evidence

o   Mitochondria and chloroplasts have their own DNA

o   Organelles divide independently to the host cell

o   Organelles have their own ribosomes to produce proteins


First cells

o   Arose from self replicating RNA becoming enclosed within a phospholipid membrane

o   Phospholipid bilayer divided inside and outside aqueous environment

o   Food directly obtain from environment of organic molecules

o   Later photosynthetic organisms developed

o   Diversified

o   Cytoplasm and plasma membrane

o   Presence of genetic material

o   Ability to obtain and process energy


Multicellular organisms

o   A group of cells to form tissues

o   A group of tissues form organs

o   Organs interact to form an organ systems (carrying out specific body functions)

o   Organ systems support a complete organism


Cell differentiation

o   Differentiation: the expression of some genes and not others in a

o   cell’s genome.

o   Leads to the formation of specialist cells and tissues in a multicellular organism

o   Stem cells:undifferentiated cell of a multicellular organism

o   Self renewal: can continuously divide indefinitely

o   Pluripotent: can differentiate into different types of cells

o   Therapeutic uses - E.g. Stargardt Disease, Leukemia

o   Genetic disease causing progressive vision loss

o   Most frequent form of inherited juvenile macular degeneration

o   Stem cells used to replace the dead photo receptors in the eye

o   Leukemia: bone marrow stem cells to replace lost blood cells


Light Microscopes

o   Use lenses


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