Bio 2 Practical 2

Includes information on Dichotomous Keys, Mycorrhizal Associations, and Fungi

Binomial nomenclature

universal naming system that includes genus and specific epithet (ex. Uranotaenia sapphirina)

Dichotomous key

a tool used to identify organisms. A series of steps that include descriptions of distinguishing characteristics with two distinct options. The user is directed through the key until the species is identified.

Biological species concept

species are defined as distinct populations whose members are unable to produce viable, fertile offspring; they are reproductively isolated.

Cryptic species:

species that can not be distinguished based only on appearance.

How do dichotomous keys present information?

in pairs or couplets (sometimes called doublets), which guide the user through the key based on observed characteristics.

1st Limitation of Dichotomous Keys

Cryptic Species

What must be used to identify cryptic species?

Additional information, such as DNA analysis

Dichotomous Key may not include

newly discovered species, or species that have been recently introduced to an area.

Dichotomous Keys have to be

Continuously updated, since scientific names of organisms can change as more information regarding evolutionary relationships is made available

How many possible outcomes must couplets have?

2, denotes as 1a and 1b

Dichotomous Key Statements

Must be related and are complementary pairs

Are dichotomous key statements written as yes/no answers?

No, they aren’t. This isn’t an accepted method for constructing dichotomous keys

1st Step to Constructing Dichotomous Keys

Identify characteristics that are unique to each species

1st Thing to Avoid when Constructing Dichotomous Keys

Using traits that can be subjective (can be interpreted differently by different users).

Should you use color in dichotomous keys?

No, because color can vary in memebrs of a species, and may be interpreted differently by different people.

2nd Thing to Avoid when Constructing Dichotomous Keys

Terms such as taller, shorter, wider, longer should not be used because they are relative.

If you want to use height or length,

a ruler must be used to distinguish between the doublets

3rd Thing to Avoid when Constructing Dichotomous Keys

descriptions like warty, bumpy, or cute, which reflect an opinion. Use very specific descriptions of characteristics. For example, 'three horns on head', 'two horns on forehead',

How many couplets do you need?

the fewest number of couplets needed to identify all of the organisms. A good rule of thumb is: n-1. If you are writing a key to 4 species of butterflies, you only need 3 couplets.

Arbuscular mycorrhizae (endomycorrhizae)

a type of mycorrhiza in which the symbiont fungus penetrates the cell walls of the roots of a vascular plant forming structures called arbuscules.

Ectomycorrhizae

a type of mycorrhiza in which the symbiont fungus does not penetrate individual cells within the plant root, but instead wraps around the root and may grow into the root in the space in between cells.

Symbiotic

interaction between two different organisms living in close physical association.

Mutualism

symbiosis that is beneficial to both organisms involved.

Parasitism

symbiotic relationship between species, where one organism, the parasite, lives on or in another organism, the host, causing it some harm.

What does mycorrhizal fungi form relationships with?

the roots of vascular plants.

Is the mycorrhizae relationship always beneficial?

No, in general it is when it enhances the growth of the plants, particularly in nutrient poor soil.

How does the fungus benefit in mycorrhizae relationship?

It receives carbohydrates from the plant, up to 15% of the sugars produced by the plant through photosynthesis.

How does the plant benefit in mycorrhizae relationship?

It receives an enhanced uptake of minerals, such as phosphorus, as well as greater water absorption.

What does the fungus do to benefit the plant?

The hyphae of the mycorrhizal fungi reach out into the soil and bring in the water and minerals that the plant roots can't reach.

Why is the mycorrhizae relationship important?

It may have played an important role in the water-to-land transition in plants. Fossils show this relationship existed in the earliest vascular plants.

What happens in the mycorrhizae relationship when the plant doesn’t need it to obtain nutrients?

the fungus would receive sugars from the plant, but not give the plant any benefits in return. In fact, the mycorrhizae would take sugars from the plant, perhaps decreasing the plant growth due to the loss of carbohydrates.

Degree of the contribution of the mycorrhizal fungus to plants depends on what?

the environment and can fall anywhere on a range from mutualistic to parasitic.

Spores

asexual reproductive cells capable of developing into a new organism without fusion with another cell

Mycorrhizae

mutualistic relationship between fungal hyphae and roots of vascular plants

Decomposer

organisms that acquire nutrients from the dead remains of plants & animals

Decomposition

the biological process that breakdowns organic matter accompanied by the release of CO₂ and other organic compounds; a key process in nutrient recycling.

Saprotrophic

decomposers that acquire nutrition via external enzyme digestion and subsequent absorption of the broken down materials

Hypha (plural hyphae)

one of many filaments making up the body of a fungus

Mycelium (plural mycelia)

the densely branched network of hyphae in a fungus

Dikaryotic

having two haploid nuclei that stem from different parent cells (N + N)

Budding

asexual form of reproduction whereby a new organism develops as an outgrowth of the body of the parent (common in yeasts)

What is the cellularity of most fungi?

Multicellular, but some exceptions include the unicellular chytrids & yeasts.

What is the dominant ploidy lifecycle of fungi?

haploid dominant life cycle

How do fungi reproduce?

Through both asexual and sexual reproduction

Are there any “male” or “female fungi”

No, they have mating types

Fungal reproduction

between individuals of compatible mating types. Allowing for genetic variation

Are fungi motile?

No, they must grow outward to find food.

How are fungal spores dispersed?

By the wind.

When and where are the spores released?

When a mushroom pops up out of the ground, it is actually the fruiting body of a club fungus - the spores are released from the gills and are dispersed by the wind.

Which supergroup does fungi belong to?

supergroup Unikonta