This document discusses the four main classes of infectious agents: bacteria, fungi, viruses, and parasites. It provides details about each type, including their characteristics, examples of diseases they cause, and how they are transmitted. Bacteria are single-celled organisms that can spread through various fluids or surfaces. Fungi are multi-cellular organisms like yeast and mushrooms that typically cause skin or lung infections. Viruses are the smallest and can only replicate inside host cells, spreading through various fluids, aerosols, or vectors. Parasites live in or on another organism and reproduce at their host's expense, with examples including roundworms, protozoa, tapeworms and flukes.

1. Biology Project
DONE BY;
M.MOHANA PRIYAA (914)
IX
CAUVERY GLOBAL SCHOOL

2. Topic;
Infectious Agents

3. What are Infectious Agents?
o An Infectious Agent is
something that infiltrates
another living thing, like you.
When an infectious agent
hitches a ride, you have
officially become an infected
host.
o There are four main classes of
Infectious Agents. These fab
four can infect all sorts of
living things.
Infectious agents
are tricky little
invaders. They
sneak in, use our
body, and often
make us sick in the
process.

4. The infectious agents no.1)Bacteria
The infectious agents no.2)Fungi
The infectious agents no.3)Viruses
The infectious agents no.4)Parasites
These causes
infectious disease.
They are
collectively known
as Pathogens.

5. Infectious Agent
No. 1
BACTERIA

6. o Bacteria are single-celled simple critters, but bacteria
have tons of characteristics, and they are very diverse.
o They are even on us and in organisms without a nucleus.
o It may seem like they are de of us at all times.
o In fact, our intestine has a permanent infection. But,
these gut bacteria are actually very helpful for digestion.
o Many people take probiotic supplements to encourage the
growth of this group of healthy bacteria.
o They come in many shapes including ball-, rod- and spiral-
shaped.
o Most bacteria are not harmful and some are actually
beneficial. Less than one per cent of bacteria will actually
make us ill.
o Infectious bacteria can grow, divide and spread in the
body, leading to infectious disease.
 Bacteria are spread in many ways
including:
o Spread by aerosols (through coughing and
sneezing). For example, Streptococcus.
o Spread by surface and skin contact. For
example, Staphylococcus aureus,
including MRSA
o Spread through body fluids, such as blood
and saliva. For example, meningococcal
disease (meningitis).
o A pro-biotic is meant to be pro-bacteria,
an antibiotic is harmful to bacteria.
o Antibiotics are usually given to treat
severe bacterial infections.

7. Infectious Agent
No. 2
FUNGI

8. o The third type of infectious agents is fungi.
o Fungi are multi-cellular or single celled organisms with a
nucleus and organelles, but they are unique from plants or
animals.
o Fungi like to feed by absorbing nutrients from their
surroundings.
o Yeast and mushrooms are types of fungi. Most types of fungi
are not dangerous, but there are some that can infect
humans and cause trouble.
o Often a fungal infection affects the skin and causes a minor
rash, but other fungi can also cause more serious problems,
like a lung infection or a blood infection.
o There are about 300 fungi that are known to make people
sick
o Fungi are microorganisms characterised by cell walls made
from a substance called chitin.
o Most fungi are harmless to humans and some are
edible.
o Other fungi can be infectious and may lead to life-
threatening diseases.
o Fungi reproduce by releasing spores that can be
picked up by direct contact or even inhaled.
o Fungal infections often affect the lungs, skin or
nails. Some infections may also penetrate the body
to affect organs and cause whole-body infections.
Examples of fungal infections include:
• Athlete’s foot: itching, scaling or cracking of the
skin
• Ringworm: reddish, itchy, scaly rash usually on the
skin and scalp
• Thrush: caused by the fungus Candida
albicans which can infect the mouth, vagina,
stomach and urinary tract.

9. Infectious Agent
No. 3
VIRUS

10. o Viruses are tiny infectious agents that replicate only in the living cells of
other organisms.
o They are even tinier than bacteria.
o A virus isn't technically alive because it cannot function unless it has a
host.
o Viruses have a very simple structure consisting of genetic material in the
form of DNA or RNA Within a protein Capsule.
o They can infect all types of life forms, from animals to plants
and bacteria to amoebae
o Their favourite and only activity is to hang around in an 'off' position and
wait.
o If they get inside a host, they will whir into action.
o Their only goal is to hijack the host cell's machinery and replicate
themselves.
o This can occur right away or they might lay dormant for a bit before they
replicate.
o After new viruses have been made, they go out into the world and the
cycle starts over.
• Viruses can be spread in many ways including:
• From plant to plant by insects that feed on
plant sap. For example, Potato virus which is
spread by aphids.
• From animal to animal by blood-sucking insects.
For example, Dengue virus which is spread by
mosquitos.
• Spread by aerosols (through coughing and
sneezing). For example, influenza virus.
• Spread by not washing hands after going to the
toilet. For example, norovirus or rotavirus.
• Spread by sexual contact. For
example, HIV And Human Papillomavirus (HPV)
• Spread by exposure to infected blood. For
example, Hepatitis B.
• Viruses can often be prevented
through vaccines

11. Infectious Agent
No.4
PARASITES

12. o Parasites are organisms that live in/on another organism
and benefit by getting nutrients at the expense of their
host.
o Parasites can be found in many different body sites, for
example in the blood, liver, digestive system, brain and even
the eyes.
o There are several groups of parasites that infect
humans:
o Roundworms: these are nematode worms that can get into
humans by ingestion, directly penetrating the skin or
through insect bites. Examples: Hookworms, Wuchereria
Bancroft , Whipworm
o Protozoa: These are single-celled parasites. Many are
delivered by biting insects or are ingested with
contaminated water or food. They invade or eat host
cells, or swim around the bloodstream and quickly
reproduce by copying themselves. Examples: Giardia,
Plasmodium falciparum, Trichomonas
o Tapeworms (Helminth): These are flatworms whose heads
hook on to the intestinal wall of their host.
Their larvae Migrate to other parts of the body. They can
live in the host for decades. Example: Pork tapeworm
o Flukes: Blood flukes are flatworms that are caught
through contact with contaminated water. Blood fluke
larvae are released from infected snails into
freshwater. Liver flukes can be found in raw or
undercooked fish or water plants and can live in the body
of the host for decades. Example: Schistosomes