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From Maria. Please Read - Bot 3/ MCB1 Lab

Monday, July 7, 2008

11:41 AM

Hey there classmates!

Galing to kay Maria.. pa compare nalang ng mga answers sa Bot3/MCB1 Lab

(Both Exercise/Experiment Number 2)

Hehehe. I-comment niyo nalang ang mga answers or kung meron lang kayong i-clarify. :)

So, here goes nothing.

---

Maria Brigida C. Mabras MCB 1 lab


Exercise 2. Isolation of Microorganism into Pure Culture


1. Explain the principle behind isolation by streak plating.

Purpose: To obtain isolated colonies of a pure or mixed culture.

Principle: By spreading a large amount of bacteria over the large surface area of a plate, the amount of bacteria is diluted until individual cells are spread on the surface of the plate. From these individual cells a single colony arises. All of the cells in this colony are genetically identical.


2. Why do we normally incubate plate in an inverted position?


3. Why should the media be cooled to around 45 degree Celsius before pouring in spread plating?in pour plating?

Media should be cooled to around 45 degree Celsius because at this temperature the media is still liquid; hence, it can be poured in spread and pour plating. Furthermore, the media above 45 degree Celsius is still hot and might not kill the microorganisms in the inoculum which will be placed on the plates. Also, the media below the said temperature is solid; hence, it cannot be poured in any of the plating techniques.


4. What are the advantages and disadvantages of spread and pour plating? Can you consider them as reliable methods of determining cell concentration?


Spread Plating:

advantages:

• With spread plating you get more individual, isolated colonies, making it much easier to count.
• spread plate is generally used when calculating CFUs/ml
• with spread plates, you can pour your media in advance and then test several dilutions
  

disadvantages: _____________. (pakisupply nalang).
Pour Plating:

advantages:

• you can see if your bacteria is an anaerobe, aerobe or a facultative aerobe
• pour plate can be used as an alternative

disadvantages:

• One of the disadvantage of the pour plate is that there might be difficulty when colonies are required to be picked for further screening and analyses.
• One potential problem when doing a pour plate is that you can add your bacteria to the media before it has cooled sufficiently, therefore killing some of the bacteria and affecting your CFUs/ml
• if you don't swirl the media enough after you add the dilution of bacteria, you won't get even distribution of colonies on a plate, making it pretty hard to count accurate CFUs
  

________________________________________________________________________________

Maria Brigida C. Mabras BOT 3


1.List down the protozoan and fungus-like characteristics of slime molds.

Fungus-like characteristics of slime molds:

• composed of threadlike filaments of eukaryotic cells called hyphae, collectively referred to as a mycelium
• found in damp, shady areas with abundant organic matter
• not plant parasites, but they may injure plants by covering and shading them
  

Protozoan-like characteristics of slime molds:

• slime molds warrant their own classification within Protista because of their unusual morphology
• At some stages in their life cycle, they show clearly protozoan characteristics
  

2.Why are myxomycetes of special interest to biologists?

Slime molds like Physarum polycephalum are useful for studying cytoplasmic streaming. They have also been used to study the biochemical events that surround mitosis, since all the nuclei in a medium-sized plasmodium divide in synchrony. It has been observed that they can find their way through mazes by spreading out and choosing the shortest path, an interesting example of information processing without a nervous system. Myxomycete plasmodia have also been used to study the genetics of asexual cell fusion. The giant size of the plasmodial cells allows for easy evaluation of complete or partial cell fusion.

In 2006, researchers at the University of Southampton and the University of Kobe reported that they had built a six-legged robot whose movement was remotely controlled by a Physarum slime mold. The mold directed the robot into a dark corner most similar to its natural habitat.

Slime molds are sometimes studied in advanced mathematics courses.


3.What are the possible roles of myxomycetes in the biosphere?

Their activities are as necessary to the continued functioning of the biosphere as are those of the primary producers. Decomposition releases carbon dioxide into the atmosphere and returns nitrogenous compounds and other materials to the soil where they can be used again by the green plants and eventually the animals


4.Why are slime molds usually found in moist habitats?s

Number one.

Slime molds were once placed in the kingdom Fungi, although some authorities now place them in the kingdom Protoctista (Protista). Most fungi are composed of threadlike filaments of eukaryotic cells called hyphae, collectively referred to as a mycelium. Slime molds are composed of an acellular mass of naked protoplasm with no cell walls in its vegetative state. They are typically found in damp, shady areas with abundant organic matter, although they may move to bright areas to "fruit."

The myxomycetes (plasmodial slime molds) are a group of fungus-like organisms usually present and sometimes abundant in terrestrial ecosystems. The myxomycete life cycle involves two very different trophic (feeding) stages, one consisting of uninucleate amoebae, with or without flagella, and the other consisting of a distinctive multinucleate structure, the plasmodium. Myxomycete plasmodia typically occur in cool, moist, shady places such as within crevices of decaying wood, beneath the partially decayed bark of logs and stumps, and in leaf litter on the forest floor. Under favorable conditions, the plasmodium gives rise to one or more fruiting bodies containing spores. The spores of myxomycetes are for most species apparently wind-dispersed and complete the life cycle by germinating to produce the uninucleate amoeboflagellate cells.

The fruiting bodies produced by myxomycetes are somewhat suggestive of those produced by higher fungi, although they are considerably smaller (usually no more than 1-2 mm tall). Although large enough to be seen with the naked eye, they are best observed with a hand lens or under a stereomicroscope. Only then can their intricate nature be fully appreciated. Fruiting bodies may take the shape of tiny goblets, globes, plumes, or other shapes more difficult to describe. Some occur in tightly packed clusters, while others are scattered or even solitary. Many of the more intricate forms have a spore case held aloft on a delicate stalk, but others are attached directly to the substrate by their bases.
Slime molds belong to a class of fungi, the Myxomycetes, that is characterized by the production of relatively large, single-celled, multinucleate bodies called plasmodia (singular = plasmodium). Plasmodia are the feeding stages of slime molds, and they are frequently seen on lawns, small plants, mulch, and decaying wood in late summer. Slime molds are not plant parasites, but they may injure plants by covering and shading them.

2. Utility in research

Slime mold on lawn, USA. Trail of movement can be seen.

Dictyostelids are used as examples of cellular communication and differentiation, and may provide insights into how multicellular organisms develop.

Slime molds like Physarum polycephalum are useful for studying cytoplasmic streaming. They have also been used to study the biochemical events that surround mitosis, since all the nuclei in a medium-sized plasmodium divide in synchrony. It has been observed that they can find their way through mazes by spreading out and choosing the shortest path, an interesting example of information processing without a nervous system. Myxomycete plasmodia have also been used to study the genetics of asexual cell fusion. The giant size of the plasmodial cells allows for easy evaluation of complete or partial cell fusion.

In 2006, researchers at the University of Southampton and the University of Kobe reported that they had built a six-legged robot whose movement was remotely controlled by a Physarum slime mold. The mold directed the robot into a dark corner most similar to its natural habitat.

Slime molds are sometimes studied in advanced mathematics courses.

posted by The Biologist and the Scientist @ 11:41 AM

 

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