Parts of microscope

Eyepiece:

The lens the viewer looks through to see the specimen.

The eyepiece usually contains a 10X or 15X power lens.

Diopter Adjustment:

Useful as a means to change focus on one eyepiece so as to correct for any difference in vision between your two eyes.

Body tube (Head):

The body tube connects the eyepiece to the objective lenses.

Arm:

The arm connects the body tube to the base of the microscope.

Coarse adjustment:

Brings the specimen into general focus.

Fine adjustment:

Fine tunes the focus and increases the detail of the specimen.

Nosepiece:

A rotating turret that houses the objective lenses.

The viewer spins the nosepiece to select different objective lenses.

Objective lenses:

One of the most important parts of a compound microscope, as they are the lenses closest to the specimen.

A standard microscope has three, four, or five objective lenses that range in power from 4X to 100X.

When focusing the microscope, be careful that the objective lens doesn’t touch the slide, as it could break the slide and destroy the specimen.

Specimen or slide:

The specimen is the object being examined.

Most specimens are mounted on slides, flat rectangles of thin glass.

The specimen is placed on the glass and a cover slip is placed over the specimen.

This allows the slide to be easily inserted or removed from the microscope.

It also allows the specimen to be labeled, transported, and stored without

damage Stage:

The flat platform where the slide is placed.

Stage clips:

Metal clips that hold the slide in place.

Stage height adjustment (Stage Control):

These knobs move the stage left and right or up and down.

Aperture:

The hole in the middle of the stage that allows light from the illuminator to reach the specimen.

On/off switch:

This switch on the base of the microscope turns the illuminator off and on.

Illumination:

The light source for a microscope.

Older microscopes used mirrors to reflect light from an external source up through the bottom of the stage; however, most microscopes now use a low-voltage bulb.

Iris diaphragm:

Adjusts the amount of light that reaches the specimen.

Condenser:

Gathers and focuses light from the illuminator onto the specimen being viewed.

Base:

The base supports the microscope and it’s where illuminator is located.

The parts of a microscope work together in hospitals and in forensic labs, for scientists and students, bacteriologists and biologists so that they may view bacteria, plant and animal cells and tissues, and various microorganisms the world over.

Compound microscopes have furthered medical research, helped to solve crimes, and they have repeatedly proven invaluable in unlocking the secrets of the microscopic world.

Biome

 A biome is a community of plants and animals that have common characteristics for the environment they exist in.

 Biomes are distinct biological communities that have formed in response to a shared physical climate.

 The Earth’s biomes are categorized into two major groups: terrestrial and aquatic.

 Terrestrial biomes are based on land, while aquatic biomes include both ocean and freshwater biomes.

Structure of DNA

 Considering the complex functions of DNA, its structure is simple.

 The two DNA strands run in opposite directions and twist together to form a stable double helix.

During replication or gene transcription, the 2 strands unwind and unzip. 

Preparing genetic finger print

 Genetic fingerprinting is a forensic technique that is used to try to solve crimes by matching DNA found at crime scenes with the DNA of the suspect.

 The main stages in preparing a genic fingerprint are DNA is isolated from the cells

 The DNA is cut into fragments using one or more restriction enzymes.

 The fragments are separated by gel electrophoresis

 The invisible patterns of the separated DNA fragments is transferred from th gel to a nylon membrane. The DNA remains in the membrane in the same relative position as it was in th gel.

 A radioactive gene probe is applied to the membrane. This is made of single Stranded DNA (called c-DNA) and binds with base sequences in the mini-satellite region.

 The membrane is place over a pices of X-ray film to reveal the positions of those fragments that have bound to the probe. 

Protein synthesis

 Protein synthesis is the process whereby biological cells generate new proteins.

 In this process first the DNA code for the protein is rewritten in a molecule of messenger RNA(mRNA); this rewriting of the code is called transcription

 Then the mRNA travels from the nucleus through pores in the nuclear envelop to ribosome

 Free amino acids are carried from the cytoplasm to the ribosome by a molecules transfer RNA(tRNA)

 The ribosome reads the mRNA code and assembles the amino acids carried by t RNA into protein this is called translation. 

Redi’s expt

 As late as the 17th century, people including some biologists believed that some forms of life were generated by spontaneous generation from non-living matter.

 To test the hypothesis, Francesco Redi did an experiment in 1665.

 In his first trial, he placed fresh meat in open containers and as expected, the rotting meat attracted flies, and the meat was soon swarming with maggots, which hatched into flies.

 In his second trial, he covered the jars so that flies could not get in thus no maggots were produced.

 To answer the objection that the cover cut off fresh air necessary for spontaneous generation, Iin his third trial Redi covered the jars with porous gauze instead of an air-tight cover.

Flies were attracted to the smell of the rotting meat, clustered on the gauze, which was soon swarming with maggots, but the meat itself remained free of maggots.

 Thus from the three trials he proved that flies are necessary to produce flies: they do not arise spontaneously from rotting meat.

 Therefor, Redi's experiment simply but effectively demonstrates that life is necessary to produce life.

Pasture’s Expt

 Pasteur's experiment has all of the hallmarks of modern scientific inquiry.

It begins with a hypothesis and it tests that hypothesis using a carefully controlled experiment.

This same process -- based on the same logical sequence of steps -- has been employed by scientists for nearly 150 years.

 First, Pasteur prepared a nutrient broth

 Next, he placed equal amounts of the broth into two long-necked flasks. He left one flask with a straight neck. The other he bent to form an "S" shape.

 Then he boiled the broth in each flask to kill any living matter in the liquid. The sterile broths were then left to sit, at room temperature and exposed to the air, in their open-mouthed flasks.

 After several weeks, Pasteur observed that the broth in the straight-neck flask was discolored and cloudy, while the broth in the curved-neck flask had not changed.

 He concluded that germs in the air were able to fall unobstructed down the straight-necked flask and contaminate the broth. The other flask, however, trapped germs in its curved neck, preventing them from reaching the broth, which never changed color or became cloudy.

 If spontaneous generation had been a real phenomenon, Pasteur argued, the broth in the curved-neck flask would have eventually become reinjected because the germs would have spontaneously generated. But the curved-neck flask never became infected, indicating that the germs could only come from ot

her germs. 

Miller’s Expt

 In the 1950's, biochemists Stanley Miller and Harold Urey, conducted an experiment which demonstrated that several organic compounds could be formed spontaneously by simulating the conditions of Earth's early atmosphere

 The experiment used water (H2O), methane (CH4), ammonia (NH3) and hydrogen (H2) - materials which were believed to represent the major components of the early Earth's atmosphere.

 The chemicals were all sealed and circulated inside a sterile array of glass tubes and flasks connected together in a loop, with one flask half-full of liquid water and another flask containing a pair of electrodes.

 The liquid water was heated to add water vapor to the chemical mixture and the resulting gases were circulated around the apparatus, simulating the Earth's atmosphere.

 The flask with heated water represents water on the Earth's surface and the recycled water vapor is just as water evaporates from lakes and seas, before going into the atmosphere and forming into rain.

 Sparks were fired between the electrodes to simulate lightning storms (believed to be common on the early earth) through the water vapors, and then the vapors were cooled again so that the water could condense (simulating the oceans) and trickle back into the first water flask in a continuous cycle.

 At the end of one week of continuous operation, Miller and Urey observed, by analyzing the cooled water, that as much as 10-15% of the carbon within the system was now in the form of organic compounds.

Two percent of the carbon had formed amino acids, including 13 of the 22 that are used to make proteins in living cells, with glycine as the most abundant.

 The molecules produced were simple organic molecules, far from a complete living biochemical system, but the experiment established that the hypothetical processes could produce some building blocks of life without requiring life to synthesize them first. 

Investigating the behavior of woodlice

 The purpose of this activity is to investigate how woodlice respond to stimuli, in this case: light.

 Materials needed for this experiment Choice chamber

•Paper to black out half of the choice chamber

• Woodlice (At least 10)

• Container to store woodlice with bark/leaf mold

• Lamp

• Stopwatch Method

 Set up the choice chamber so that half of it is dark and half of it is open to the light.

 Taping paper to the lid, base and around the sides may be a good way to do this.

 Position the lamp over the chamber

 Introduce a known number of woodlice, at least ten, to the center of the choice chamber and replace the lid, ensuring the covered halves line up

 Switch on the lamp Start a stopcock and on the minute for ten minutes count the number of woodlice in the exposed half.

 Note down any behavior you notice too, for example how far into the light half do the woodlice tend to go

Result

When brought into the light, the woodlice start to move around much more quickly. This increase rate of movement is a response to the increased intensity of light- it is a kinesis. 

Pavlov’s classical conditioning Expt

 Classical conditioning (also known as Pavlovian conditioning) is learning through association and was discovered by Pavlov, a Russian physiologist.

 Classical conditioning basically involves forming an association between two stimuli resulting in a learned response.

There are three basic phases of this process:

Phase 1: Before Conditioning

 The first part of the classical conditioning process requires a naturally occurring stimulus that will automatically elicit a response.

Salivating in response to the smell of food is a good example of a naturally occurring stimulus.

Phase 2: During Conditioning

 During the second phase of the classical conditioning process, the previously neutral stimulus is repeatedly paired with the unconditioned stimulus.

As a result of this pairing, an association between the previously neutral stimulus and the UCS is formed. At this point, the once neutral stimulus becomes known as the conditioned stimulus (CS).

The subject has now been conditioned to respond to this stimulus.

 In this example, suppose that when the dog smelled its favorite food, it also heard the sound of a bell.

While the bell is unrelated to the smell of the food, if the sound of the bell is paired multiple times with the smell, the sound would eventually trigger the conditioned response.

In this case, the sound of the bell becomes conditioned stimulus.

Phase 3: After Conditioning

 Once the association has been made between the UCS and the CS, presenting the conditioned stimulus alone will come to evoke a response even without the unconditioned stimulus. The resulting response is known as the conditioned response (CR).

 The conditioned response is the learned response to the previously neutral stimulus. In our example, the conditioned response would be feeling hungry when you heard the sound of the whistle.

Skinner’s Expt

 Skinner proposed his theory on operant conditioning by conducting various experiments on animals.

He used a special box known as “Skinner Box” for his experiment on rats.

 As the first step to his experiment, he placed a hungry rat inside the Skinner box.

 The rat was initially inactive inside the box, but gradually as it began to adapt to the environment of the box, it began to explore around.

 Eventually, the rat discovered a lever, upon pressing which; food was released inside the box.

 After it filled its hunger, it started exploring the box again, and after a while it pressed the lever for the second time as it grew hungry again.

 This phenomenon continued for the third, fourth and the fifth time, and after a while, the hungry rat immediately pressed the lever once it was placed in the box.

Then the conditioning was deemed to be complete.

 This experiment also deals with and explains the effects of positive reinforcement. Upon pressing the lever, the hungry rat was served with food, which filled its hunger; hence, it’s a positive reinforcement.

 Skinner also conducted an experiment that explained negative reinforcement. Skinner placed a rat in a chamber in the similar manner, but instead of keeping it hungry, he subjected the chamber to an unpleasant electric current.

 The rat having experienced the discomfort started to desperately move around the box and accidentally knocked the lever.

 Pressing of the lever immediately seized the flow of unpleasant current. After a few times, the rat had smartened enough to go directly to the lever in order to prevent itself from the discomfort.

 The electric current reacted as the negative reinforcement, and the consequence of escaping the electric current made sure that the rat repeated the action again and again.

Here too, the pressing of the lever is an operant response, and the complete stop of the electric current flow is its reward

 Both the experiment clearly explains the working of operant conditioning.

The important part in any operant conditioning learning is to recognize the operant behavior and the consequence resulted in that particular environment.