Eukaryotes and their Origins

Question 1

Eukaryotic Origin

Answer 1

Evidence suggests that Eukaryotes evolved mid-Proterozoic eon. Before this, all life on Earth was prokaryotes (lacking nucleus and membrane-bound organelles:
- Endosymbiotic Theory

Question 2

Endosymbiotic Theory

Answer 2

leading hypothesis for the origin of eukaryotes; eukaryotes arose as a result of the fusion of archaea cells with bacteria after the archaea cell engulfed an ancient, AEROBIC bacterial cell
- the endosymbiotic bacterial cell remained in the archaea cell in a mutualistic relationship
- the bacterium allowed the host Archaean cell to USE OXYGEN to release energy stored in nutrients and the host cell protected the bacterium from predators
- the descendants are present in all eukaryotic cells today as MITOCHONDRIA

Question 3

Second Endosymbiosis Event

Answer 3

a secondary endosymbiosis event occurred in a group of green algae that engulfed photosynthetic cyanobacterium, leading to the origin of CHLOROPLASTS. it happened at least TWICE with different endosymbionts
1. common ancestor of supergroup Archaeplastida
2. Ancestor of small amoeboid rhizobia taxon

Question 4

Evidence for Endosymbiotic Theory

Answer 4

1. Size
2. DNA
3. Binary Fission
4. Replacement of mitochondria + chloroplast
5. Membranes

Question 5

Evidence: Size

Answer 5

Mito + Chloro are approximately the SAME SIZE as prokaryotic cells, but are located inside larger eukaryotic cells instead of free-living

Question 6

Evidence: DNA

Answer 6

Mito + Chloro each have their own DNA, organized in a circular chromosome like typical prokaryotic genomes, and their genomes contain genes similar to genes found in prokaryotic genomes

Question 7

Evidence: Binary Fission

Answer 7

Mito + Chloro reproduce by BINARY FISSION, a process prokaryotes use to reproduce.
- Eukaryotic cells reproduce by mitosis

Question 8

Evidence: Replacing Mito and Chloro

Answer 8

If mito + chloro are removed from a eukaryotic cell THE CELL HAS NO WAY TO PRODUCE NEW ONES
- genetic instructions to make new mito and chloro are not present in the eukaryotic nuclear genome as they are present in mito and chloro genomes

Question 9

Evidence: Membrane

Answer 9

The membrane composition of mito + chloro are similar in composition to prokaryotic membranes than to eukaryotic membranes

Question 10

Parsimony + The Theory

Answer 10

Since all eukaryotes have mitochondria but only photosynthetic eukaryotes have chloroplasts:
- FIRST, an ancestral eukaryote engulfed the bacteria
- SECOND, only in the plant/algae lineage a later descendant of this ancestral eukaryote then engulfed a cyanobacteria-like species

Question 11

Unique Eukaryote Adaptations/Traits

Answer 11

1. Cells with nuclei surrounded by a nuclear envelope with nuclear pores
2. Mitochondria
3. Mitosis
4. Meiosis + Sex

Question 12

Eukaryotes: Nuclei

Answer 12

This trait is necessary and sufficient to define an organism as eukaryotic. All extant eukaryotes have cells with a nucleus.

Question 13

Eukaryotes: Mitochondria

Answer 13

Some extant eukaryotes have very reduced remnants of mitochondria in their cells, whereas other members of their lineages have mitochondria

Question 14

Eukaryotes: Mitosis

Answer 14

a process of nuclear division wherein replicated chromosomes are divided and separated using elements of the cytoskeleton.
- Universally present in eukaryotes

Question 15

Eukaryotes: Meiosis and Sex

Answer 15

Process of genetic recombination unique to eukaryotes in which diploid nuclei undergo meiosis to yield haploid nuclei and subsequent karyogamy, a stage where 2 haploid nuclei fuse together to create a diploid zygote nucleus

Question 16

Sexual Reproduction

Answer 16

• sexual reproduction with meiosis is a defining feature in eukaryotes
• offspring get half of their DNA from 2 different parents
• always involved 2 changes in ploidy (# of copies of each chromosome

Question 17

Sexual Reproduction: First Ploidy Change

Answer 17

• occurs via meiosis
• a cell division reduces ploidy by 1/2 from diploid to haploid (2n -> 1n)
• n: number of copies of each chromosome

Question 18

Sexual Reproduction: Second Ploidy Change

Answer 18

doubling from 1n -> 2n by fertilization, or the joining of gametes (sperm and egg)

Question 19

Haplontic Life Cycle

Answer 19

sexual life cycle where organisms have a multicellular haploid stage and the diploid stage only exists as a single cell (the fertilized egg)
- EX: fungi

Question 20

Diplontic Life Cycle

Answer 20

sexual life cycle where organisms have a multicellular diploid stage and the haploid stage exists only as a single cell (the gametes)
- EX: animals

Question 21

Haplodiplontic Life Cycle

Answer 21

• AKA alternation of generations
• organisms have both multicellular diploid and haploid stages
• EX: plants

Question 22

Protist

Answer 22

any eukaryote that is not a plant, fungus, or animal (any eukaryote that falls outside these 3 monophyletic groups)
- they do not refer to a monophyletic group

Question 23

Single-Celled Eukaryotes: Humans + Environment

Answer 23

• Human pathogens + parasites
• Plant pathogens and parasites
• Photosynthesis
• Decomposition

Question 24

Single-Celled Eukaryotes: Photosynthesis

Answer 24

phytoplankton, single-celled photosynthetic organisms, are the primary producers of aquatic food webs:
1. Diatoms
2. Dinoflagellates

Question 25

Diatoms

Answer 25

single-celled photosynthetic algae that generate ~20% of O2 produced on the planet and half the organic material in the ocean

Question 26

Dinoflagellates

Answer 26

single-celled species like algae that are endosymbionts of corals and other animals
- play an essential part in coral reefs

Question 27

Single-Celled Eukaryotes: Decomposition

Answer 27

organisms need to be broken down after they die to make inaccessible nutrients into simpler organic molecules
- Oomycetes (fungus-like protists) play an essential role in returning inorganic nutrients to soil and water to foster new plant growth