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Unit 5 - Biodiversity

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Phylogeny

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  • A phylum is a biological level of classification between Kingdom and Class

  • Phylogeny demonstrates the history of the evolution of a species or group. It is mainly about lines of descent and their relationships among other groups of organisms

  • Phylogenetic trees are used to show these lines. They also represent hypotheses about the evolutionary road.  A phylogenetic tree may be built using morphological, biochemical, behavioral, or even molecular attributes of species or other groups

  • In the phylogenetic tree, species are organized and classified into groups based on shared attributes. These attributes or traits are different from the group's ancestor

  • DNA sequences of genes or proteins can be used for comparing species and building phylogenetic trees

 

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Bacteria and Archaea

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Bacteria and Archaea are unicellular prokaryotes (no nucleus). Pro means “before”, karyote means “kernel”, referring to the nucleus. They are single-celled microorganisms

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Archaea and bacterial cells lack membrane-bound organelles, including the nucleus.  They also generally have a single circular chromosome, located in an area of the cell called the nucleoid

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The Oxygen Revolution

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The Oxygen Revolution refers to the rise of oxygen levels in Earth’s atmosphere. The evolution of oxygen-generating photosynthesis by bacteria, more specifically cyanobacteria, led to the first free molecular oxygen approximately 2.6 billion years ago.

  • Phototrophs (or phototrophic organisms) gain their energy from sunlight.  Chemotrophs (or chemosynthetic organisms) obtain their energy from chemical compounds

  • Prokaryotes not only can use various sources of energy but also different sources of carbon compounds. Organisms that can fix inorganic carbon (e.g. carbon dioxide) into organic carbon (e.g. glucose) are called autotrophs. Heterotrophs must obtain carbon from organic compounds

Plants

Plant diversity

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Classification of plants:

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  1. Bryophytes (mosses) and are nonvascular (no vascular tissue to transport water/nutrients)

  2. Vascular Plants - have xylem and phloem, which transport water and nutrients, respectively.  Vascular plants include:

A. Seedless plants reproduce via spores, such as ferns

B. Seed plants

  • Gymnosperms are cone bearing. E.g. cedars, sequoias, redwoods, pines, yews, and junipers

  • Angiosperms (Anthophyta) are flowering plants. E.g., roses, daisies, apples, and lemons. There are 2 classes of angiosperms: monocots, like grasses (corn, wheat, rye, oats), and dicots, e.g. peanuts

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Plant life on land:

Land plants have:

● a cell wall that

  • is made of cellulose

  • lends support to cells to maintain shape
     

● Roots and root hairs

  • absorb water and nutrients from the soil
     

● Stomates

  • open to allow gas exchange; they release O2 and absorb CO2

  • close to minimize excessive water loss
     

● Cuticle

  • the waxy coating on leaves

  • helps prevent excessive water loss from leaves
     

● Gametangia

  • protective jacket of cells

  • forms around gametes and zygotes

  • prevents drying out
     

● Sporopollenin

  • a tough polymer

  • resistant to almost all kinds of environmental damage

  • protects plants in the harsh terrestrial environment

  • found in walls of spores and pollen
     

● Seeds and pollen

  • Seeds help disperse offspring; they have a safeguarding coat that prevents desiccation

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Plant Tissue:
 

There are three types of plant tissue:

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  • dermal tissue (external)

  • vascular tissue (internal)

  • ground tissue (in the ground, roots)

Image by Jesse Dodds

Fungi

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  • Fungi can be single-celled or very complex multicellular organisms. The multicellular ones often have a stage in the life cycle when they are dikaryotic (have two nuclei per cell) before karyogamy (fusion of nuclei) occurs

  • Some are decomposers, which means they grow in the ground or on dead plants and break down the organic matter. That's why they play an essential role in the cycling of carbon and other elements

  • Some of them are parasites of plants causing diseases. For example, mildews, rusts, scabs, or canker

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Key points to remember about fungi:

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  • Fungi have more in common with animals than plants

  • They are heterotrophic

  • they use complex organic compounds as sources of energy and carbon, and not photosynthesis

  • Fungi can reproduce either asexually, sexually, or both

  • The majority of fungi produce spores, which are haploid cells that can undergo mitosis in order to form multicellular, haploid individuals

Animal Diversity

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  • All animals are eukaryotes and they are multicellular heterotrophs

  • In contrast to Prokarya, most eukaryotes have multiple, linear chromosomes

  • There are more than 1.3 million living species of animals identified

 

Five things that define an animal:

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  • Most animals reproduce sexually. The diploid stage usually dominates the life cycle


Key points of animal phylogeny:

  • All animals share a common ancestor

  • The animal kingdom is monophyletic, which is a clade called Metazoa

  • Eumetazoa is a clade of animals with actual tissues

  • All animals except sponges belong to a clade of eumetazoans

  • Most animal phyla belong to the clade Bilateria

  • Bilateria is a clade of those with bilateral symmetry 

 

Animals can be characterized by morphology:

  • Animals can be categorized according to the symmetry of their bodies

    • Sponges lack symmetry and have NO true tissue.  They are also excluded from the clade Eumetazoa ("true animals")

    • Some animals, such as sea anemones, have radial symmetry

    • Many animals have bilateral symmetry

  • The animal body also vary based on the organization of the animal’s tissues

    • Actual tissues are populations of special cells separated from other tissues

    • Animals with only two germ layers, such as cnidarians, are diploblastic

    • Other animals are triploblastic, which means they have three germ layers.  In these animals, a third germ layer, the mesoderm, lies between the endoderm and ectoderm

  • Bilateria can be divided by the presence or absence of a body cavity (coelom vs. pseudocoelom vs. acoelom).  A coelom is a fluid-filled cavity.

  • Most animals can also be categorized by developmental modes: it either has a protostome development (mouth side develops first) or a deuterostome development (anus side develops first)

  • In gastrulation, the developing digestive tube of an embryo initially forms as a little pouch, the archenteron

In addition to knowing the concepts and terminology, it's also crucial to apply them by doing plenty of practice problems.  If you're struggling to find good problems to work through, check out our popular Practice Portal!  

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