Notes: The Evolution of a Cell (From Simple to Complex)

Evolution of Life: the order of their suspected appearance on Earth Fossil evidence of the oldest known life forms supports the theory that the first life forms were prokaryotes. Remember PRO = NO NO what? No nucleus No membrane bound organelles.

First Life Forms The first life forms had to be ANAEROBIC Prokaryotes, since there was little OXYGEN gas (or free O2 ) present in the atmosphere. ANAEROBIC organisms DO NOT need oxygen to survive. In fact – some anaerobic organisms cannot live around oxygen, it is poisonous to them.

First Life Forms The first organisms had to get their organic compounds from other living things or the environment, which meant that they were HETEROTROPHS. HETEROTROPHS = organisms that eat for food or energy.

First Life Forms Eventually AUTOTROPHIC Prokaryotes, which could make their own organic compounds evolved. Two types are: Chemosynthetic – making organic compounds using energy trapped in other chemicals to drive the reaction. Uncommon bacteria… these tend to be found in remote locations, like at the bottom of the ocean near sulfur vents. Photosynthetic – making organic compounds from CO2 and water using sunlight to drive the reaction

First Life Forms AEROBIC Prokaryotes could finally appear due to the rise in oxygen in the atmosphere. As the numbers of photosynthetic prokaryotes grew, so did the concentration of oxygen in the atmosphere. AEROBIC organisms NEED to have oxygen to survive.

Eukaryotic Cells & their Organelles ENDOSYMBIONT THEORY was proposed by Lynn Margulis. She stated that what may have started as an invasion by smaller cells or entrapment by a larger cell, became a mutually BENEFICIAL relationship. Doesn’t make sense yet? Let’s try to make it more clear.

Endosymbiosis Smaller PROKARYOTES entered and began to live & reproduce inside larger prokaryotes. Overtime the two cells began to rely upon the presence of the other for FOOD or SHELTER. This smaller cell was really good at producing ATP and came to be known as the MITOCHONDRIA.

Support for Endosymbiosis Large cells can take in small amounts of food and liquid by forming a pocket in their cell membrane

Primitive Photosynthetic Eukaryote Endosymbiosis Eventually a 2nd small prokaryotic cell was engulfed by the larger cell… This cell was really good at absorbing solar energy and using it to make food for itself and came to be known as the CHLOROPLAST. Primitive Photosynthetic Eukaryote

Support for Endosymbiosis Unlike other organelles, mitochondria & chloroplasts both REPRODUCE independently of the cell. Translated … that means that the cell doesn’t make more chloroplasts and mitochondria – they make make themselves.

Support for Endosymbiosis Both mitochondria & chloroplasts contain their own DNA, which is different from DNA found within the nucleus. It is much simpler and circular in shape, like DNA (CALLED PLASMIDS) found in prokaryotic cells.

Support for Endosymbiosis Both have their own prokaryotic-like RIBOSOMES inside. The ribosomes are simpler than the ribosomes found in the cytoplasm of a eukaryotic cell. Ribosomes

Support for Endosymbiosis Both have two MEMBRANES around them (due to phagocytosis).

What does that mean? That simple prokaryotic cells merged together to form more complex eukaryotic cells. More recently, researchers in Japan found a heterotrophic protist Hatena that behaves like a predator until it ingests a green algae, then it switches to photosynthetic nutrition (and loses its feeding apparatus).