Transcript Symbiosis - Glow Blogs

Higher Biology
Unit 3
3.5- Symbiosis
Symbiosis
• Symbiosis refers to the relationship
between 2 organisms of different
species that live in direct contact with
one another
• They are relationships that have
evolved over millions of years
• This coevolution is essential as a change
in one would affect the other
Types of symbiosis
• Parasitism- one organism (the parasite)
benefits at the expense of the other
(the host)
Parasitism
• A parasite gains its nutrition from the host
organism
• The host is harmed or at least loses some
energy/materials to the parasite
• In many cases a balance has evolved between
the parasite and host
• Parasites often require a limited metabolism
and must maintain contact with their host
• Effective parasites do not cause their host to
die (at least until completion of its life cycle)
Parasitic feeding
The liver fluke is a parasite that
lives and feeds inside its host.
Mosquitos are parasites
that live and feed outside
their host.
Parasite Transmission
• Transmission of a parasite to a new host
can occur in 3 main ways
• Direct contact
• Release of resistant stages
• Use of a vector
Direct contact
• Direct contact involved transmission of
a parasite form one host to another
through direct physical contact
• Examples include head and body lice
Release of resistant stages
• Different stages of the parasites
development area able to withstand
adverse conditions until they come into
contact with a suitable host
• Examples include cat fleas
Use of a vector
• A vector is a carrier of a pathogen such
as bacteria or viruses
• An example is mosquitoes carrying
Plasmodium the unicellular organisms
that causes malaria from human to
human
Parasitic Life Cycles
• In a direct life cycle eggs are shed and
pass to a new member of the host
species
• This involves one species of host only
and is common in parasites that feed
outside of their host
Parasitic Life Cycles
• Indirect life cycles are more highly
evolved
• In addition to a primary host species used
as the site of sexual reproduction the
parasite uses a secondary host species
• A new primary host becomes infected
when it is invaded by or consumes the
infected secondary host
• This type of life cycle is more common in
parasites that live and feed inside their
hosts
Tapeworm Life Cycle
Types of symbiosis
• Mutualism- both organisms benefit from
the relationship
Origin of mitochondria and
chloroplasts
• Mitochondria and chloroplasts are
believed to have evolved from 2 types
of prokaryote that had become resident
in larger cells
• Mitochondria were aerobic, nonphotosynthetic prokaryotes
• Chloroplasts were photosynthetic
prokaryotes
Evidence to support this theory
• Mitochondria and chloroplast have their
own circular DNA
• Both organelles features ribosomes more
similar to those found in prokaryotes than
eukaryotes
• A strong similatiry exists in structure and
size between prokaryotes and these
organelles
• Molecular studies of ribosomal RNA
indicate these organelles originated in
bacteria