Final Exam Question Themes 9-11, 19-22

The fossil record (two related questions, T9)

• The fossil record provides evidence of the extinction of species, the origin and diversification of new groups, and transitional fossils

• The geologic record is divided into the: Archaean, Proterozoic, and the Phanerozoic Eons. (Precambrian = Hadean + Archaean + Proterozoic)

• The limits of the fossil record is that it is biased and incomplete because fossilization requires burial in sediment → probability of fossilization and discovery of fossils is very low

• Relative dating → Sedimentary strata reveal the relative ages of fossils (limits: gaps in sedimentary sequence and sediments can be moved by major land movement)

• Absolute dating → Radiometric dating

Origin of life (three questions, T9)

• Life likely originate on earth from a series of chemical reactions that ultimately led to the formation of the first living organisms

  • Conditions on early earth made the chemical processes needed for life possible

  • It is not yet possible to definitively describe the steps that led to the mergence of life

• Hypothesized multi-step process for the formation of simple cells:

  1. Abiotic synthesis of small organic molecules

     • Terrestrial origins (deep-sea hydrothermal vents, volcanoes, Miller-Urey)

     • Extraterrestrial/Panspermia (have been detected in comets and meteorites)

  2. Polymerization of small organic molecules into organic polymers

     • Monomers to polymers

  3. Formation of protocells

     • cell-like structures that form when organic molecules become enclosed within vesicles

  4. Emergence of self-replicating molecules

     • RNA world hypothesis, suggests that RNA was the first self-replicated molecule bc its much simpler than DNA

• GOE → Great Oxygenation Event (2.7-2.3 b.y.a.)

  • when O2 became accumulating in the atmospheres and oceans which dramatically altered Earth’s environment

  • Caused the extinction of many prokaryotic groups, marking the end of the Archaean Eon

Prokaryote metabolic diversity (T10)

• Prokaryotic metabolic diversity:

  • Phototrophs

  • Chemotrophs

  • Autotrophs

  • Heterotrophs

  • O2 and Nitrogen Metabolism

Endosymbiotic theory (two questions, T11)

• Endosymbiosis is a symbiosis between two species in which one organism lives inside another organism’s cells or tissue

• The endosymbiont theory (endosymbiotic origin of eukaryotic cells)

  • Endosymbionts → proteobacteria (mitochondria) and cyanobacteria (chloroplasts/plastids)

  • Primary endosymbiosis (1°) → Prokaryotic cells are engulfed as endosymbionts by either prokaryotic or eukaryotic cells

  • Secondary endosymbiosis (2°) → Eukaryotic cells themselves become endosymbionts being taken up by other eukaryotic cells

Animal phylogeny (T19)

• Key features of the phylogeny of extant animals:

  • All animals share a single common ancestor → an ancestral colonial flagellated protist

    • Ancestral colonial flagellated protist → single-celled organism that formed a colony and had a flagella (whip like structures used for movement)

    • Kindom Animalia constitutes clade Metazoa, (all multicellular animals)

  • Sponges are basal (primitive) animals in the phylogeny

  • Eumatazoa (“true animals”) is a clade of animals with true tissues (excludes sponges)

  • Most animal phyla belong to the clade Bilateria animals with bilateral symmetry (bilaterians) (mirror halves)

  • Bilaterians split into 3 major clades—all are invertebrates, except Chordata, which includes vertebrates (like us with backbones)

Origin of animals (T19-20)

• The common ancestor of animals evolved 800-650 mya and was a flagellated eukaryote.

• The earliest multicellular eukaryotes

  • Multicellular eukaryotes evolved in multiple lineages, giving rise to algae, plants, fungi, and animals.

  • Whole-body animal fossils date from the Ediacaran Period: the Ediacaran biota (635-540 mya) are diverse soft-bodied, mostly sessile marine organisms that disappeared by the Cambrian.

  • Cambrian explosion (535-525 mya): the origin of most major phyla of living bilaterian animals.
    Hypotheses for Cambrian explosion: evolution of predation; incr. in oceanic O₂; evolution of the Hox genes.

Animal development (two questions, T19)

• Embryonic development sequence:

  • Diploid zygote undergoes a series of rapis mitotic cell divisions call cleavage, transforming the zygote into a solid ball of cells

  • Cleave transforms morula into hollow blastula (hallow ball)

  • Gastrulation → ‘C’ fold inwards, producing two layers of embryonic tissues (ectoderm/outer layer and endoderm/inner layer)

• Embryonic development is conserved by Hox genes

  • crucial becasue they play a fundamental role in determining the body plan and segment identity during embryonic development

  • Hox genes proteins coordinates the development of various structures along the anterior-posterior axis, e.g. legs, antennae, and wings in fruit flies or the different types of vertebrae in humans

• Animals exhibit two primary modes of development:

  • Direct development → animal after birth or emergence from an egg is a small version of its adult form, eg. humans

  • Indirect development → has ‘larvae’ stages morphological behavioural differences from the sexually mature adult stages, eg. butterfly

Animal groupings (T19-20)

• Invertebrates: Typically exhibit indirect development, with stages such as larval forms that differ significantly from adult morphology.

• Vertebrates: Generally display direct development, although some exceptions exist with species like amphibians, which undergo metamorphosis before reaching adulthood.

• Body plan:

  • Symmetry, Asymetrical, Radial, Bilateral, Cephalization

  • Tissues → diploblastic (ecto and endo) are radial, triploblastic (ecto, endo, and meso (muscle)

  • Triploblastic body cavity: coelom, hemocoel, no body cavity)

    • coelom is a fluid-filled body cavity completely lined with mesoderm, found in animals like humans and worms to cushion and support organs.

    • hemocoel is a blood-filled cavity found in insects and arthropods, where blood flows freely around organs in an open circulatory system.

Characteristics of eukaryotic life cycles (6 questions, all relevant topics)

• Alternation between haploid and diploid stages

  • Haploid = 1 set of chromosomes (n)

  • Diploid = 2 sets (2n)

• Meiosis creates haploid cells from diploid ones

  • Important for sexual reproduction

  • Reduces chromosome number

• Fertilization restores diploid state

  • Two haploid gametes fuse to form a zygote

• Mitosis helps with growth and development

  • Happens in both haploid or diploid stages, depending on the species

• Three types of cycles:

  • Animal-like → diploid-dominant (humans)

  • Fungi-like → haploid-dominant

  • Plant-like → alternation of generations (both stages are multicellular)

Porifera/Sponges (T21)

Cnidaria (T21)

Differentiating between invertebrates using characteristics (T21-25)

Parasitic invertebrates (T22)