What is phenetic classification?
Grouping species that look similar or share similar morphology.
What is phylogenetic classification?
Grouping organisms that share common ancestry, but might not be morphologically similar.
Difference between homologous and analogous structures
Homologous share similar structure and function because they originated from same ancestor.
Analogous are structures with same function but different evolutionary ancestries.
Define paraphyletic group
Group of organisms descended from common evolutionary ancestor, but not including all the descendant groups.
Define polyphyletic group
Group of organisms that are derived from more than one common evolutionary ancestor and is therefore not suitable to be placed in same taxon.
Define monophyletic group
Group of organisms derived from common evolutionary ancestor and not shared with any other group.
*Aim when classifying is recognising groups that are monophyletic.
Origin of eukaryote
Ancestral prokaryote engulfed other prokaryotes, such as mitochondria and chloroplast (endosymbiotic relationship), resulting in heterotrophic and autotrophic eukaryotes.
Evidence for engulfing of prokaryotes
- living species of bacteria (Cyanobacteria) and heterotrophic bacteria resemble chloroplasts and mitochondria
- mitochondria and chloroplasts have their own genome, separate from the nuclear genome
- DNA of mitochondria and chloroplasts are circular, genetically identical in a cell, and haploid like bacteria
- mitochondria and chloroplasts can reproduce by binary fission (similar to prokaryotes)
- nucleus, mitochondria, and chloroplasts all have double membrane
What are Archaeplastida and list types of archaeplastida
Organisms that acquired chloroplasts by engulfing cyanobacteria. Includes glaucophytes (blue-green plants), red algae, chloroplastida (green algae and streptophyta), embryophyta (land plants).
Explain primary endosymbiosis in terms of photosynthesis in Archaeplastida.
The eukaryotic cell engulfs cyanobacteria, wrapping its own wall around it, resulting in double-membraned chloroplast.
Note: This is a single evolutionary event (happened once).
Explain secondary endosymbiosis in terms of photosynthesis in eukaryotes.
Chloroplasts in other lineages have more than 2 membranes and a nucleomorph (secondary endosymbiont’s nucleus).
Secondary endosymbiosis explains this where other cells engulfed an archaeplastida.
How does meiosis occur?
Sexual reproduction that creates haploid gametes. Crossing over occurs (homologous chromatids cross over and exchange material) and four daughter cells are produced.
The union (syngamy) of two gametes to form a zygote.
Benefits and consequences of asexual reproduction
- produces lots of offspring
- individuals are well adapted to local conditions
- individuals pass on all of their genome
- don’t have to use resources to find mates
Consequence: can lead to deleterious mutations accumulating
Limitations to sexual reproduction
- fewer offspring produced, lower fragmentation (via recombination) of advantageous combinations of genes
- pass on only half as many genes to each offspring
- spend resources to find mates
- if sexual dimorphism (organisms of same species exhibit different characteristics beyond sexual differences), usually one of the sexes (female) contributes more to survival of offspring
Benefits to sexual reproduction
- populations can evolve more quickly
- potential increases in genetic diversity, can respond more rapidly to shifts in environmental conditions
- changing environments: offspring may be better adapted
- stable environment: offspring might have fewer deleterious mutations
Zygotic meiosis (fungi, some algae)
After fusing (syngamy) of haploid, forms zygote which will undergo meiosis. Haplontic - dominant generation is haploid (organism spends most of life cycle in haploid condition).
Gametic meiosis (animals, some protists and algae)
Haploid gametes are produced by meiosis, which fuse to form a zygote that grows to form a diploid individual.
Diplontic - dominant generation is diploid (organism spends most of life cycle in diploid condition).
Sporic meiosis (plants and many algae)
Diploid sporophyte undergoes meiosis to produce haploid cells (spores). Haploid cells undergo mitosis to produce gametophyte. Gametophyte produces gametes through mitosis, which fuse to form zygote, which then forms the sporophyte.
Haplo-diplontic - equal abundance of haplo and diplo generation (alternation of generations).
*Note: every species of land plants are haplo-diplontic
Difference between isogamy and anisogamy
Isogamy is a reproductive system where all gametes are morphologically similar, esp. in size (eukaryotic supergroups contain isogamous species, usually unicellular).
Anisogamy - sexually different gametes (see small, motile male gametes fuse with larger, immotile female gametes).
Benefits of anisogamy
- more efficient use of resources
- opportunity for sexual differentiation
- localised production of gametes (in multicellular organisms)
- retention of zygote
What are protists?
Anything that is a eukaryote but is not an animal, land plant, or true fungus.
* Not a natural group
What are algae? Name three main lineages of algae.
Group of organisms that are photosynthetic other than land plants. Not necessarily closely related - polyphyletic, protists.
Three main lineages: glaucophytes, red algae (rhodophytes), green algae (chlorophyta)
Which groups are included in the viridiplantae/chloroplastida?
- streptophyta (includes charophytes, which are polyphyletic, and embryophytes, which are a natural group)
- Note: Green algae includes all chlorophytes and most streptophytes, except embryophytes (land plants).
What is the phragmoplast?
When cells divide mitotically, the phragmoplast splits the two daughter cells.
- In animal cells, it is called cleaving in cytokinesis that divides the cells.
Why did the stomata form?
Land plants had waterproof layer so stomata was formed on cuticle, as plants needed to exchange gases.
Challenges for land plants
- avoid desiccation
- temperature fluctuations
- mechanical support for aerial organs
- UV-B radiation
- interact with soil microbes
- transporting water and nutrients
- limiting water loss
- gas exchange in a dry atmosphere
- reproduction in a dry atmosphere
- defence mechanisms against pathogens
Solutions of land plants to live on land
- sturdy cell wall, but stay small
- sporopollenin (tough thing that surrounds pollen grain, good protection)
- zygote retained and embryo becomes multicellular
- embryo nourished by parent
- cuticle (prevent water loss)
- specialised gas exchange (stomata)
- gametangia with protective layer
- polyphenolics (lignin/tannins/strong polymer formed in internal structure to reduce UV-B)
- live in damp habitat
Features of land plants that were inherited from their green algal progenitors
- cellulosic cell wall
- zygote retention (delayed meiosis)
Define apoplast and symplast
Apoplast: areas outside the plasma membrane
Symplast: areas inside the plasma membrane (i.e. the protoplasts interconnected via plasmodesmata)