7 th Grade Biology

Obtaining Food  Bacteria must have a source of food and a way of breaking down the food to release energy.  Some bacteria are autotrophs and make their own food.  They make food in one of two ways.  Some capture the sun’s energy like plants.  Others use the energy from chemical substances in their environment.

Obtaining food  Some bacteria are heterotrophs and cannot make their own food.  They must consume other organisms or the food that other organisms make.  Heterotrophic bacteria may consume a variety of foods- from milk and meat, to decaying leaves on a forest floor.

Respiration  Like all organisms, bacteria need a constant supply of energy to carry out their functions.  This energy comes from food.  The process of breaking down food to release energy is called respiration.  Like many other organisms, most bacteria need oxygen to break down their food.  Some bacteria do not need oxygen, in fact, for them oxygen is a poison.

Reproduction  When bacteria have plenty of food, the right temperature, and other suitable conditions, they thrive and reproduce frequently.  Some can reproduce every 20 min.

Brain Check  What is an autotroph?  Makes it own food- similar to a plant.  What is a heterotroph?  Must consume other organisms  The process of breaking down food to release energy is called __________.  respiration

Asexual Reproduction  Bacteria reproduce by a process called binary fission, in which one cell divides to form two identical cells.  Binary fission is a form of asexual reproduction.  Asexual reproduction is a process that involves only one parent and produces offspring that are identical to the parent.  During this process, a cell duplicates its genetic material and then divides into two separate cells.  Each new cell gets its own complete copy of the parent cell’s genetic material as well as some of the parent’s ribosomes and cytoplasm.

Sexual Reproduction  Sexual reproduction involves two parents who combine their genetic material to produce a new organism, which differs from both parents.  During a process called conjugation, one bacterium transfers some of its genetic material into another.  Using a thin, threadlike bridge that joins the two cells.  When these bacterium divide by binary fission, the new genetic material passes to a the new cells.  Conjugation does not increase the number of bacteria.  It does result in new bacteria that are genetically different from the parent cells.

Endospore Formation  Sometimes, conditions in the environment become unfavorable for the growth of bacteria.  Some bacteria can survive harsh conditions by forming endospores.  An endospore is a small, rounded, thick-walled, resting cell that forms inside a bacterial cell.  It contains the cell’s genetic material and some of its cytoplasm.  Because endospores can resist freezing, heating, and drying, they can survive for many years.  The bacteria that causes botulism, produce heat resistant endospores that can survive improperly canned food.  They are very light, and can be carried off by a breeze, moving it to a better place to open up and multiply.

Words  Pasteurization-the food is heated to a temperature high enough to kill most harmful bacteria without changing the taste of the food.  Louis Pasteur, is its inventor.  Decomposers- organisms that break down large chemicals in dead organisms into small chemicals.  They are nature’s recyclers.