Eukaryotic Evolution & Diversity Sections 2.3 – 2.4

Introduction 3.5 billion years ago, prokaryotes were the only organisms on earth – surviving many harsh environments However, for the past 2 billion years, they have co-existed with more evolved eukaryotic cells

Introduction Eukaryotic organisms are more complex than prokaryotes They have more genes, which allows for more cellular diversity in size, shape, movement, and specialized functions But …. How did they evolve exactly?

Endosymbiosis One main theory is that eukaryotic cells resulted from the merger of 2 or more simpler cells Endosymbiosis – one cell engulfs (swallows up) a different type of cell. The engulfed cell survives within the larger cell https://www.youtube.com/watch?v=3ESXvLHceDc

Chloroplasts & Mitochondria The theory of Endosymbiosis suggests that mitochondria and chloroplasts were once small, free-living prokaryotes and then were engulfed by larger cells – and survived inside these cells Where: The organelle (mitochondria / chloroplast) – is called an endosymbiont The larger engulfing cell – is a host cell https://www.youtube.com/watch?v=3ESXvLHceDc

Multicellularity While this theory help give us some info on the evolution of eukaryotes It DOES NOT account for all the Multicellularity seen in eukaryotes So, scientists have hypothesized that the first multicellular organisms arose from colonies created by dividing individual cells Genes within these cells now contained instructions for cells to become specialized in certain areas For example – some cells specialized in absorbing nutrients (bacteria in soil), while others gathered energy from the sun (cyanobacteria)

Life Cycles and Reproduction Reproduction of eukaryotic cells is much different (based on their more complex nature) than prokaryotes Because of they exist within a wide range of organisms, they reproduce more complex and differently from one organisms to another

Life Cycles and Reproduction For example, in humans eukaryotic cells undergo sexual reproduction – where gamete (sex) cells fertilize into a zygote and undergo further cell division While in other smaller organelles they are able to reproduce asexually via multiple fusion and further cell division Essentially, regardless of the form of reproduction, we see the sexual life cycles alternate between meiosis – producing haploid cells and fertilization – which produces diploid cells

Protists: Unicellular Eukaryotes Section 2.4

Introduction Protists – are large unicellular eukaryotes, that are diversely shaped and are NOT a fungus, plant, or animal

Animal-like Protists AKA – Protozanos = heterotrophs Are animal-like because they consume other organisms for food (i.e. prokaryotes) Some protozanos are Parasites, as they benefit from taking nutrients from other organisms around them Are Categorized into 4 groups

Spore-forming Protists Animal-like Protists Amoeba-like Protists Flagellates Ciliates Spore-forming Protists They are found in fresh and salt water, in soil, and in animals They have contractile vacuoles to get rid of excess water They use flagella's (long hair extensions of their cell membrane) to move Some of them live in water Others are parasites that can cause disease. They have hundreds of tiny hair-like structures known as cilia Use the cilia to sweep food through the water toward them Absorb nutrients from their hosts Do not have cilia or flagella, so they cannot move on their own Ex – Malaria

Fungus-like Protists These protists absorb their food from dead organic matter They are grouped into 2 groups, slime molds and water molds Most fungus-like protists use psuepods, (“false feet”) to move around.

Fungus – like Protists Slime Moulds Can be grouped into 2 sub-categories: Plasmodial slime moulds – not see to the naked eye, which are often found on the ground of forests and fields. They feed by engulfing smaller particles into their cytoplasm Cellular slime mounds – feed by ingesting small bacteria or yeast cells Slime molds will continue to grow as long as food and water are available to it

Fungus – like Protists Water Moulds Most of them are small single-celled organisms Most live on dead organic matter = makes them decomposers But others are parasites on fish, insects, and plants Some parasitic water molds cause diseases These protists still endanger crops today

Plant – like Protists Contain pigments in their chloroplast that allow them to carry out photosynthesis They are producers and consumers They mostly use photosynthesis, but some eat other protists or absorb nutrients for food They are known as algae

Plant – like Protists Algae is multicellular and single celled, but the single celled type can’t be seen without a microscope Single celled algae that floats near the surface of the ocean are phytoplankton. Most multicellular algae are seaweed or kelp.

Plant – like Protists Other types of plantlike protists are diatoms, dinoflagellates, and euglenoids Diatoms Dinoflagellates Euglenoids Single cellular Live in salt and fresh water Use photosynthesis Their cell walls have silica and cellulose Reproduce asexually via Mitosis Most live in salt water Have 2 flagella to help spin around Sometimes are red and produce a strong poison which can get into the water and kill aquatic animals Live mostly in fresh water Have plant and animal characteristics Move by using flagella to push them through the water

Review https://www.youtube.com/watch?v=Ln69k7LyTsU

Homework Section 2.3 – pg. 71 # 1, 5, 6, 9, 11 Section 2.4 – pg. 78 # 1, 2, 8, 13