Essential Knowledge 2.D.4:
Plants and animals have a variety of
chemical defenses against infections
that affect dynamic homeostasis.
Plants, invertebrates and
vertebrates have multiple,
nonspecific immune
responses.
Invertebrates
Invertebrate immune systems have nonspecific response
mechanisms, but they lack pathogen-specific defense
responses.
 innate immune system, also known as non-specific
immune system (respond in a generic way)

2 types of invertebrate defenses
 Insects' exoskeleton made mostly of a polysaccharide called
chitin, serves as an effective barrier against microbes
 Phagocytosis is used to engulf bacteria cells
Plants Innate Response
 Plant defenses against pathogens include molecular
recognition systems with systemic responses;
 Infection triggers chemical responses that destroy
infected and adjacent cells, thus localizing the
effects.
• Vertebrate immune systems have nonspecific and
nonheritable defense mechanisms against pathogens.
Vertebrate nonspecific Immunity
 The epithelial surfaces form a physical barrier.
 gastrointestinal and respiratory tract, movement due to
peristalsis or cilia helps remove infectious agents; and mucus
traps infectious agents
 The gut can prevent the colonization of pathogenic bacteria
by secreting toxic substances
 The flushing action of tears and saliva helps prevent infection
of the eyes and mouth.
 Inflammation is one of the first responses of the immune
system to infection or irritation. Ex: histamine
 All white blood cells (WBC) are known as leukocytes. Leukocytes
are different from other cells of the body in that they are not
tightly associated with a particular organ or tissue; thus, they
function similar to independent, single-celled organisms.
Leukocytes are able to move freely and interact with and capture
cellular debris, foreign particles, or invading microorganisms.
Unlike many other cells in the body, most innate immune
leukocytes cannot divide or reproduce on their own, but are the
products of multipotent hematopoietic stem cells present in the
bone marrow.
 The innate leukocytes include: Natural killer cells, mast cells,
eosinophils, basophils; and the phagocytic cells including
macrophagess, neutrophilss and dendritic cells, and function
within the immune system by identifying and eliminating
pathogens that might cause infection.
 All white blood cells (WBC) are known as leukocytes.
Leukocytes are different from other cells of the body in
that they are not tightly associated with a particular organ
or tissue; thus, they function similar to independent,
single-celled organisms. Leukocytes are able to move freely
and interact with and capture cellular debris, foreign parti
es, or invading microorganisms. Unlike many other cells in
the body, most innate immune leukocytes cannot divide or
reproduce on their own, but are the products of
multipotent hematopoietic stem cells present in the bone
marrow.
 The innate leukocytes include: Natural killer cells, mast
cells, eosinophils, basophils; and the phagocytic cells
including macrophagess, neutrophilss and dendritic cells,
and function within the immune system by identifying and
eliminating pathogens that might cause infection.
The mammalian immune system includes two types
of specific responses: cell mediated and humoral
 Cell-mediated immunity is an immune response that
does not involve antibodies but rather involves the activation
of phagocytes, antigen-specific cytotoxic T-lymphocytes(a
type of white blood cell), and the release of various
cytokines in response to an antigen
 Cell-mediated immunity is directed
primarily at microbes that survive
in phagocytes and microbes that infect non-phagocytic cells.
It is most effective in removing virus-infected cells, but also
participates in defending against fungi, protozoans, cancers,
and intracellular bacteria.
Humoral
 In the humoral response, B cells, a type of lymphocytic white
blood cell, produce antibodies against specific antigens.
 Humoral immunity is so named because it involves
substances found in the humours, or body fluids.
 The principal function of B cells is to make antibodies
 Antibodies are proteins produced by B cells, and each
antibody is specific to a particular antigen.
 A second exposure to an antigen results in a more rapid and
enhanced immune response.
 What are memory T-cells?
 Memory T-cells are derived from normal T-cells that have
learned how to overcome an invader by ‘remembering’ the
strategy used to defeat previous infections. (adaptive
immunity)