predicting the growth of microorganisms. objectives students will use sterile techniques to collect...
TRANSCRIPT
PREDICTING THE GROWTH OF
MICROORGANISMS
Objectives
Students will • Use sterile techniques to collect a sample • Observe the growth of microorganisms on a
nutrient agar plate • Create nutrient jelly ideal for growing microbes
for observation. • Understand the environment for culturing
microbial growth.
SUMMARY
This lab is designed to give students a “hands-on” experience to help answer the question: How can you determine where in
your environment you might find microorganisms?
KEY CONCEPTS
• Microbes are very small and have been around a long time
• Microbes are everywhere; they are extremely abundant and diverse
Growth is in a general manner a process where an individual organism is becoming larger.
Bacteria, however, are so small that it is almost impossible to measure the growth of an individual. Therefore, the growth of bacteria is described through the size of their colonies. In relevant conditions, bacteria are growing so well that the number of bacteria increases twice in an hour or even with a shorter time.
• Bacteria are very small, one celled, microscopic organisms that are found in air, water, soil, and the bodies of other living organisms. If provided with the right conditions they will multiply into a visible colony of bacteria cells.
• The nutrient jelly provides a nutritious environment where the bacteria and fungi can grow into a visible group of cells (colony).
PRECAUTIONS
Most bacteria and fungi collected in the environment will not be
harmful. However, once they multiply into millions of colonies in a
petri dish they become more of a hazard. Be sure to protect open cuts
with rubber gloves and never ingest or breathe in growing bacteria.
Keep growing petri dishes taped closed. When the experiment is
finished, a teacher or demonstrator should safely destroy the fuzzy
bacteria colonies.
BACTERIAL COLONY MORPHOLOGY
Bacteria grow on solid media as colonies. A
colony is defined as a visible mass of
microorganisms all originating from a single
mother cell, therefore a colony constitutes a
clone of bacteria all genetically alike.
Edges (also called margin)
BACTERIAL SHAPES
PETRI DISH
Is a shallow cylindrical
glass or plastic lidded
dish that biologists use
to culture cells – such
as bacteria
AGAR
Is a jelly-like substance, obtained from algae
Where can we find bacteria?
How can you find bacteria? You can’t see it, so how do you find it?• Under the right conditions, bacteria grows very fast,
exponentially• Some bacteria populations can double every 10
minutes• Bacteria grow in colonies – a colony is a visible mass of
bacterial growth on solid medium that developed from 1 or a few cells
• A colony can contain millions of cells• We can find bacteria by growing it in the right
conditions until it is visible to the human eye
How to Sample Bacteria• Get a sterile swab – don’t touch the cotton end• Swab the area to be tested• Open your Petri dish carefully and swab the
cotton in the specified area on the agar• Close the Petri dish quickly• Get a new swab for each sample• When done, close the Petri dish and use scotch
tape to seal the sides• Put the Petri dish upside down in a dark, warm
place