topic 2 the ecosystem

this segment is concerned solely with

topic two point three point one

which is to construct simple keys and use

published keys

for the identification

of organisms

so lets find an organism that needs identifying

suppose you are out doing a

study of a

polluted pond or lake

and found you this

floating

as a result of maybe runoff

from a farm

and your job was to identify

the species

that you're looking at

so that you can go ahead and write

a report of what's going on

your first step

is likely to be

take a sample of it to the lab and look at it

with a microscope

when you look in there

your likely to find

this

this should tell you that you are looking at algae

provided that you've got some

basic knowledge of

what you're doing

and algae have

chloroplasts in their cells

lots of the green stuff

used in photosynthesis

and this

particular algae that we have

is made up of long

unbranched filaments

with this

basic information in mind

our next step

in identification

is this

key..and

see if you could figure out how it works just by looking at it

this of course is a very simple

version of

a dichotomous key and

the content of this

is adapted from this URL here

at the bottom

so if you have had a look

maybe you've figured out how it works

but this is how it works if you have any trouble

the key the dichotomous key is made up of

a series of statements

and each set of statements

is aimed at dividing

the big group

into

smaller groups

so that you can eventually zero in on the identity of the unknown species that

you're trying to

identify

for instance what we found in the pond is

microscopic

it's not macroscopic we needed a microscope to see details of it

so the first statement

or pair statements

which is why we get the name

dichotomous branching into two

the first pair of statements

says microscopic or macroscopic and

our response should be that it's a microscopic

so that

means that we are directed

to go to

number two

which then asks

does it contain chloroplasts or not and it does contain chloroplasts

so we go to three

and in three

are the cells solitary which means just by themselves

or are they in

colonies

or are they filamentous

well.. we might not be sure about what a colony is

but if it's grouped with solitary we've already identified that

the algae is filamentous so

that takes us to five

long thin

unbranched

filaments

unbrached filaments

so that takes us from five

over to seven

and at seven

we're asked are the chloroplasts in a

spiral like a spring or are they not in a spiral

and we don't have any evidence that they are in a spiral

so that leads us to eight

do we have a single chloroplasts or many small chloroplasts

and you can see here

that our specimen has many small chloroplasts

and that leads us

to identify our specimen

as

microspora

and this is how you use

a simple dichotomous key

having used it though you

are likely to be asking

why a key

why do you need to

go through this system when maybe you could just look through the pages of the

book or

go online and search for kinds of algae

and that could very well work

if you just had maybe fifty types of algae to pick from

that could certainly work

or maybe even a hundred

but if you had eight thousand

species

and more

of algae

it could be the bit time consuming

think about looking for somebody in a town with

eight thousand homes

it would take some time to carry out your search

but if you

had some important information about who we were looking for

and each time you asked a question

of somebody

it narrowed your search down

then it will be a whole lot easier

so this is what

a dichotomous key does

it takes

information that you know simple information that you can observe

and it very quickly allows you

to move

toward identifying the

name

of what you have in front of you

trying to

figure out

the keys

are usually made by biologists

for biologists

so in the real world of biology in trying to identify things

its definitely and asset if you have a

basic knowledge of some of the terms

like the terms

we've used here to understand the key like

microscopic and microscopic

to know what chloroplasts are

to know what

filamentous means and

what solitary and colonial mean

that would also be helpful

so a basic understanding

of the structure

of what you're looking at

certainly is helpful

because

ultimately to identify we have to work with things that are easy to observe

it is no point talking about things that are

really complicated and hard to see

we would like to..quickly identify what we are looking at

so let's stop here now and have

a look at your activity

your activity requires you to make a key for

eight organisms that..you are

hopefully very familiar with a beetle

scorpion

centipede and

dragonfly ladybug spider and butterfy

so go ahead and

look back at

our sample key

look at how it's made up

pairs of statements

and try to organize

our eight

specimens here

in a key of your own

and a hint

is to look for features like

body segments

wings and legs

things that are easy to observe and would be very useful

in separating

the members of this group

your answer doesn't have to

exactly match this to be right

so you could have a very good answer that

does not match this and if you have it

totally wrong and you think you need to another shot at this

go to your refrigerator

and take out

vegetables or some food items

and try making a key to identify the names

of what you have in the refrigerator

for maybe for the purpose of some

alien being that you have staying with you

who won't know the names of what's in the refrigerator

but they might be able to identify

some of the features