Laboratory Skills-Skills

Indicators
Indicators are substances which are used to provide information about the classification of a particular ubstance. Some commonly used indicators in the living environment/biology lab include Litmus (pH) paper, Lugol's (iodine) solution, and Benedict's solution.

Dichotomous Keys
Making sense of observations is important in science. Classification provides a means of describing objects or organisms by their common characteristics. A dichotomous key is used to provide a method of sorting categories of organisms and specifically identifying particular organisms.

Dissection
The dissection of representative plant and animal specimens is a required skill for the living environment/biology course. Dissection provides information about the internal and external characteristics of a specimen in a direct manner which other techniques can not as directly provide. Flowers, frogs, and fetal pigs are commonly dissected specimens.

Indicators
An indicator is any substance used to assist in the classification of another substance. There are many different kinds of indicators. Some common kinds of indicators used in Living Environment/Biology will be indicated below.

Some Common Indicators

1. Litmus paper turns red or a shade of red in acids. Litmus turns blue or a shade of blue in bases. It is important to place a few drops or a small amount of the substance to be tested on the litmus paper when testing it. Do not dip the litmus paper in the substance to be tested. A paper which provides a more specific indication of the pH level of a substance is pH paper. This paper turns different shades of various colors which may be compared to a scale to determine the pH value.

2. Bromthymol blue is an indicator used to show the presence of either carbon dioxide in solution or an acidic solution. Low levels of carbon dioxide or acid will result in the bromthymol blue solution remaining blue, while higher levels of carbon dioxide or acid will result in the bromthymol solution taking on a yellow tint. Frequently this indicator is used in biology labs to indicate photosynthetic activity (solution turns blue as CO2 is used) or respiratory activity (solution turns yellow as CO2 is added to the solution).

3. Lugol's iodine solution (which is actually IKI) is a brown solution which turns black in the presence of starches. The test tube at the right shows Lugol's (iodine) solution mixed with a starch suspension.

4. Benedict's solution is used to detect the presence of simple sugars such as glucose. When a simple sugar is mixed in Benedict's solution and heated for a short period of time in a test tube, it goes through a variety of color changes, eventually ending as an orange-red or brick red color. The use of Benedict's solution before and after to detect the presence of the simple sugar glucose is shown in the pictures on the right.

Stains
Very frequently it is helpful to dye certain cell structures so that they can be seen more clearly. Chemicals that dye parts of cells for this purpose are called stains. Two commonly used stains in the biology laboratory are Lugol's iodine solution and methylene blue. Lugol's iodine solution is a good stain to make the nuclei of plant cells stand out more prominently. It has the unfortunate drawback of killing the cells it is used on however. Methylene blue is often used to stain animal cells, such as human cheek cells, to make their nuclei more observable. It is a vital dye which does not immediately kill the specimen.

Correctly Staining Specimens

A specimen is obtained and placed on the slide with forceps. A cover slip is then lowered on to the specimen from an approximately 45 degree angle gently. This reduces the number of air bubbles the specimen will have. The student then places a drop or two of water on the specimen.
The student places a drop of stain beside and under one corner of the cover slip.
The student places a towel on the opposite side of the cover slip in the water beside the cover slip. This will draw the stain through the entire specimen in a few seconds without removing the cover slip. This technique will also remove any air bubbles which have formed. The stained specimen may now be observed. Note that this technique can be used to draw salt water or distilled water into a specimen having a cover slip over it without removing the cover slip as well.

Dichotomous Keys
A dichotomous key is a sequence of steps that allows the identification of a living thing. The key will consist of a series of choices that lead the user to the correct name of a given item. The term dichotomous means that there will always be two choices in each step of the key until the organism is correctly identified.

Using a Dichotomous Key to Identify an Organism

The example below will illustrate the use of a dichotomous key to identify the unknown creature above.

Steps in the Dichotomous Key	Identification Process
Taxonomic Key to Stream Water Animals 1. A. With a shell go to 2 B. Without a shell go to 3	** The creature clearly does not have a shell, so go to #3.
2. A. Shell made of two parts held together by a hinge Clam B. Shell made of only one part Snail
3. A. Body flat, oval and brown Water Penny B. Body not exactly like a water penny go to 4	** This creature does not have an oval body it is long, so go to #4.
4. A. With six jointed legs go to 5 B. With more than six jointed legs go to 12 C. With less than six jointed legs; body often wormlike go to 14	** The creature has 6 jointed legs, so go to #5.
5. A. With two or three thin, hair-like tails go to 6 B. Without thin, hair-like tails go to 7	** The creature has three thin tails, so go to #6.
6. A. With one hook at the end of each leg; usually with three tails, sometimes only two Mayfly B. With two hooks at the end of each leg; two tails Stonefly	** This organism clearly has three tails and only a single hook at the end of each leg which makes it a Mayfly larva.
7 A. Body with many long, pointed parts go to 8 B. Body not exactly like this go to 9 8. A. Body brown or black, often very large Hellgrammite B. Body white, yellow or tan; not so large Beetle larva 9. A. Body with hook-like claws at tail end; animal sometimes protected with bits of sand, pebbles or twigs Caddisfly B. Body without hook-like claws go to 10 10 A. Body small, dark, hard and beetle-like Riffle beetle B. Body not exactly like this go to 11 11 A. With 3 wide tails Damselfly B. Without tails, but with three short points Dragonfly 12 A. With two large claws and eight legs; large Crayfish B. Without large claws; smaller go to 13 13. A. Body flattened side to side; usually white Scud B. Body flattened top to bottom; usually gray Sowbug 14. A. Body with very small legs; usually with a head go to 15 B. Body without any legs or head go to 16 15 A. Tail-end of body wider than the other Black fly larva B. Tail-end of body not wider Midge 16. A Body brown, plump, and caterpillar-like Crane fly larva B. Body not exactly like this go to 17 17. A. Body with suckers at each end Leech B. Body without suckers; small, thin and worm-like Aquatic worm	We didn't need to go beyond step 6 with the organism we classified above, but some organisms might require the use of many more steps before its proper identification.

Anatomical Direction

Before beginning a dissection, it is important to have an understanding of some of the basic directional terminology associated with the dissection of specimens. Some of these terms include proximal, which means toward the body, and distal, which means to move away from the body. Other important anatomical directions are indicated below.

Dissection Safety
Proper safety procedures when working with dissection tools and specimens is of greatest importance. Some safety rules to engage in when dissecting specimens are as follows.

Dissection Safety Rules

Follow all instructions given by your teacher.
Inform your teacher of any illness as a result of exposure to chemicals used in specimen preparation.
Avoid contact with preservative chemicals. Rinse the specimens completely before dissection.
Know where the eye-wash fountain is if needed.
Wear safety goggles to prevent the splashing of any chemicals into the eyes.
Properly mount dissection specimens to dissecting pan. Do not dissect a specimen while holding it.
Handle scalpel or razor blade (safety edged) with extreme care.
Always cut away from your body and away from others.
Never ingest specimen parts.
Never remove specimens or specimen parts from the classroom -- until the dissection is completed all parts of the dissection must remain within the dissecting pan.
Properly dispose of dissected materials.
Store specimens in as directed by your teacher.
Clean up the work area and return all equipment to the proper place when the dissection is completed.
Wash hands after each dissection.

Plant Dissection
Many kinds of flowering plants, such as lilies, daffodils, or tulips are commonly subjects for dissection in biology. The flower is the plant structure specialized for reproduction in advanced plants. The processes of meiosis and fertilization occur in the flower.

Some Key Flower structures

petals: colored parts inside the sepals which attract insects

sepals: structures which are usually green outside the petals which help to protect the flower

stamen: forms the male reproductive organ and consists of an anther and a filament

anther: pollen box in which pollen grains are formed containing the genetic material which produces sperm

filament: supports the anther

pistil or carpel: female reproductive organ which consists of three parts

stigma: found at the top of the pistil, is often sticky and hairy adapting it to catch and hold pollen

style: tube-like connection between the stigma and the ovary

ovary: enlarged part of the pistil attached to the receptacle (stem tip on which the flower rests) and contains the ovules

ovules: small white structures within the walls of the ovary which produces the plant egg cells

Animal Dissection
The dissection of animals is important for many reasons. It helps in the learning about the internal structures of animals. It also allows students to learn how organs and tissues are interrelated. Another purpose of dissection is to allow the comparison of organisms in terms of their organs and relative complexities. While many good simulations of dissections may be observed, it seldom can replace the benefits of the actual participation in an actual dissection.

Some common vertebrate organisms dissected in the living environment lab include the frog and the fetal pig. Usually the dissection procedure involves tying the organism down firmly on the dissection pan, cutting the organism open on its ventral side (as pictured below), and pinning its tissues and muscles back to observe its internal organs. Different teachers may have their own preferences in terms of their emphasis on the tissues and organs to be observed in a dissection.

Key Internal Organs of the Frog
Organ	Body System	Major Function
brain	nervous	thinking and coordination of body activities
heart	circulatory	pumps blood through the body
stomach	digestive	stores and begins the chemical digestion of food
small intestine	digestive	finishes chemical digestion and absorbs digested nutrients into the blood
liver	digestive (and other systems)	makes bile, detoxifies poisons, many other functions
gall bladder	digestive	stores bile from liver for release into small intestine to aid in fat digestion
lungs	respiratory	exchanges gases with the external environment (aided by the skin in the frog)
kidneys	excretory	filter wastes from the blood
ureter	excretory	carries wastes to the urinary bladder
urinary bladder	excretory	stores urine before its release from the body
pancreas	endocrine/digestive	produces hormones like insulin which regulate blood sugar, produces pancreatic juice which aids in digestion in the small intestine
ovaries	reproductive	makes eggs in female frog
testes	reproductive	makes eggs in male frog