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Area of Study 2: EXPECTED LEARNING To revise homeostasis and immunity. Quiz. What are two differences between the endocrine and nervous systems? What are the 5 plant hormones and what do they do?

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  • What are two differences between the endocrine and nervous systems?
  • What are the 5 plant hormones and what do they do?
  • What is the main difference in the signal transduction pathway between amine/polypeptide and steroid hormones?
  • Describe the three lines of defence and the major parts/cells of the immune system involved in each
  • What is an autoimmune disease? What is an immunodeficiency disease? (definition and eg)
  • What is involved in an allergic response?

The maintenance of a constant internal environment despite changes in external environment

NB. Internal environment = The medium in which the body cells of multicellular organisms are bathed (i.e. extracellular fluid, interstitial fluid, plasma, lymph)

what needs to be kept within narrow limits
What needs to be kept within narrow limits?

M.I.T.G.O.W.B + pH + wastes

  • Metabolites (eg blood glucose concentration)
  • Ions (eg salts)
  • Temperature
  • Gases (eg CO2 and O2)
  • Osmolarity (ie water balance)
  • Wastes (e.g. urea)
  • Blood Pressure
  • pH
detecting signals from external environment
Detecting signals from external environment

Mechanoreceptorsrespond to mechanicalenergy (e.g. ear drum)

Thermoreceptorsrespond to heat or cold (e.g. nerve endings in skin)

Electromagnetic receptors respond to electromagnetic energy (e.g. ampullae of Lorenzini in sharks)

Photoreceptorsrespond to visible light and UV radiation (e.g. eyes).

Chemoreceptors respond to chemical

stimuli (e.g. olfactory)

stimulus response model
Stimulus-response model



Transmission - nerves

Control centre

Transmission – nerves or hormones



stimulus response model example negative feedback
Stimulus-response model exampleNegative Feedback

Transmission - nerves

Negative feedback – response counteracts the stimulus

Transmission - nerves

two types of feedback
Positive Feedback

Negative Feedback

Two Types of Feedback

Organ or Gland

Organ or Gland

Promotes or encourages more of the original substanceto be released

Inhibits (stops) further release of the original substance

Releases a substance to act on a system

Releases a substance to act on a system

System Acted


System Acted


Releases a secondary substance which acts on the gland or organ

Releases a secondary substance which acts on the gland or organ

endocrine system
Endocrine System
  • Uses chemical signals for cell to cell communication
  • Coordinates the function of cells
  • Response to an endocrine signal occurs within minutes to hours
endocrine system1
Endocrine System

Endocrine glands

Release hormones into the bloodstream.


Chemicals released in one part of the body that travel through the bloodstream and affect the activities of cells inother parts. body.

  • Cell to cell communication molecules
    • Made in gland(s) or cells
    • Transported by blood
    • Distant or local target tissue receptors – can only communicate message to cell with the corresponding receptor (on cell membrane or within cytosol)
    • Activate physiological response
    • Negative feedback prevents hormone overproduction
long distance communication endocrine hormones
Long Distance Communication: Endocrine Hormones
  • Made in endocrine cells
  • Transported via blood to act at a site distant from the secreting cell or gland
  • Receptors on target cells
local communication paracrine and autocrine hormones
Local communication: Paracrine and Autocrine Hormones
  • Act locally, either on the secreting cell or a neighbouring cell
  • Diffuse to target
      • Autocrine – receptor on same cell
      • Paracrine – neighbouring cells
  • e.g. cytokines in immune system
  • Chemicals released by animals to communicate with other members of their own species
  • Can be used for:
    • Attracting mates
    • Inducing mating activity
    • Marking territory
    • Signalling alarm
    • Marking food trails
plant tropisms
Plant tropisms
  • A plant growth response to an external stimulus
    • Light = phototropism
    • Gravity = geotropism
    • Thigmotropism = touch
  • Growth towards the stimulus is a positive tropism
  • Growth away from the stimulus is a negative tropism
  • Responses rely upon chemical signals that initiate a signal transduction pathway in plant cells to produce a growth response.
  • Indole acetic acid and related molecules
  • Photo-and gravitropism
  • Stimulates cell elongation
  • Made in the shoot apex
  • Travels down the stem
  • Apical dominance
  • Prevents leaf abscission (ie leaf shedding)
  • Enhances fruit growth

Auxin 

  • Cytokinins delay and even reverse senescence
  • Release buds from apical dominance
  • Stimulate cell division

Cytokinins 

  • Essential for stem elongation
  • Found as the toxin produced by some fungi that caused rice to grow too tall
  • Dwarf plant varieties often lack gibberellins
  • Gibberellins are involved in bolting of rosette plants
  • Promote cell division and elongation
  • Gibberellins are used to improve grapes
  • Gibberellins are involved in seed germination
    • gibberellins will induce genes to make enzymes that break down starch
ethylene gas
Ethylene gas
  • The smallest hormone
  • Important in seed germination, fruit ripening, epinasty (i.e. downward bending of leaves), abscission of leaves
  • Sex expression in cucurbits (i.e. pumpkins, zuccini)
abscisic acid aba
Abscisic acid (ABA)
  • Generally acts as an inhibitor
  • Important in water stress and other stresses
  • Causes stomatal closure
  • Prevents premature germination of seeds
  • Changes gene expression patterns
responding to light
Responding to light
  • Plants possess light-sensitive enzymes – phytochromes
  • Exist in two forms that interchange according to the light they are exposed to.
    • active form (Pfr) at sunrise (i.e. red light)
    • inactive form (Pr) at sunset (ie far-red light)
  • when exposed to red light the enzyme is able to catalyse a number of reactions within the cell, leading to altered transcription of genes in the nucleus, or activation of proteins already in the cell
  • influences responses such as seed germination, stem elongation, and formation of leaves, flowers, fruits, and seeds
  • Photoperiodism is a biological response to a change in relative length of daylight and darkness as it changes throughout the year.
  • Phytochrome, and other chemicals not yet identified, probably influence flowering and other growth processes.
  • "Long-day plants" flower in the spring as daylength becomes longer (e.g. spinach).
  • "Short-day plants" flower in late summer or early autumn when daylength becomes shorter (e.g. broad beans).
  • "Day-neutral plants" flower when they are mature.
signal transduction pathway
Signal transduction pathway

A mechanism linking a mechanical or chemical stimulus to a specific cellular response.

  • Communicating cells may be close together or far apart
cell communication
Cell communication
  • Production of extracellular signalling molecule (called a ligand) by a cell
  • Detection of this ligand by a receptor protein on or in target cell
  • Transduction of ligand through cell
  • Cellular response
  • Control or regulation of ligand or response
2 detecting the signal
2. Detecting the signal

To stimulate a response, hormones bind to specific receptor on OR in the target cell to form hormone-receptor complex

  • The cell targeted by a particular signal has a receptor molecule complementary to the signal molecule, or ligand.
  • Most amine and polypeptide-based hormones are not able to move through cell membrane – receptor proteins are on the cell membrane
  • Steroid hormones move through membrane and bind with receptors in cytoplasm
receptor locations
Receptor locations
  • Cytosolic or Nuclear
    • Lipophilic ligand enters cell
    • Often activates gene
    • Slower response
  • Cell membrane
    • Lipophobic ligand can't enter cell
    • Outer surface receptor
    • Fast response

Figure 6-4: Target cell receptors

3 transduction
3. Transduction
  • Converts the change in the receptor to a form that can bring about a cellular response.
  • This might involve a series of steps - a signal transduction pathway - that alters and amplifies the change.
  • Small amounts of signalling molecule can produce a significant response or even multiple responses due to amplification.
3 transduction1
3. Transduction
  • Once a hormone-receptor complex is formed, the way the signal is transferred depends on the type of hormone:
    • Amine and polypeptide hormones: Second messenger is produced that stimulates cell response.
    • Steroid hormones: hormone can enter the cell easily, binding to receptor and initiating response. Tends to be slower, but longer lasting than second messenger response.
non steroidal lipophobic hormones
Non-steroidal, lipophobic hormones
  • Usually involves the binding of extracellular signalling molecules, like hormones and neurotransmitters, to receptors that face outwards from the membrane and trigger events inside the cell.
  • The binding of a hormone with a receptor often stimulates the action of a second protein (e.g. G protein), or an enzyme, within the cytoplasm.
  • This enzyme can then stimulate the activity of other enzymes to bring about a response.
steroidal lipophillic hormones
Steroidal, lipophillic hormones
  • Lipid soluble hormone travels in bloodstream via a carrier protein( insoluble in water) and passes through the cell membrane.
  • Binds to receptor protein found only in target cells.
  • Hormone-receptor complex then enters the nucleus.
  • Binds to specific regulator site for the targeted gene.
  • Stimulates the gene to produce mRNA.
  • mRNA is read by ribosomes to produce a specific protein.
4 response
4. Response
  • the transduction process brings about a cellular response.
  • can be one of many different cellular activities, such as:
    • activation/inhibition of a certain enzyme
    • rearrangement of the cytoskeleton
    • regulate protein expression through activation of specific genes.
    • Open or close protein channels, etc
  • Once the cellular response is initiated, the ligand is degraded by cell enzymes
the nervous system
The nervous system
  • This communication system controls and coordinates functions throughout the body and responds to internal and external stimuli.
  • Maintains homeostasis by detecting change and coordinating action of effector organs
  • Responsible for unidirectional, fast communication




Medulla Oblongata

Spinal Cord

The Central Nervous System (CNS)

  • Consists of the brain and spinal cord
the peripheral nervous system pns
The peripheral nervous system (PNS)
  • Nerves extending out to the rest of the body from the CNS
  • Includes all sensory neurons, motor neurons, and sense organs
nerve cells neurons
Nerve cells: Neurons
  • The basic functional unit of the nervous system.
  • Send impulses to and from the CNS and PNS and the effectors (muscles/glands)
the nervous system1
The nervous system
  • Sensory receptors monitor changes in the environment
  • Afferent or sensory nerve cells transfer messages to the central nervous system (CNS)
  • Efferent or motor nerve cells transfer messages from the CNS to effector organs
  • (See Jacaranda diagram)
nerve impulses
Nerve impulses
  • Information is transferred in the form of an electrical impulse
  • The cell membrane of a nerve cell is polarised
    • i.e. there is a difference in charge between the inside and outside of the cell
neuron at rest resting potential
Neuron at rest: Resting potential
  • A condition where the outside of the membrane is positively (+) charged compared to the inside which is negatively (-) charged.
  • Neuron is said to be polarized.
nerve impulses action potential
Nerve impulses: Action potential
  • As an impulse moves along an axon, the permeability of the membrane changes
    • Positive sodium ions move into the neuron
    • Potassium ions move out of the neuron
    • The inside of the membrane is positively (+) charged compared to the outside which is negatively (-) charged.
    • This is called an ACTION POTENTIAL
nerve impulses1
Nerve impulses

neuron communication synapses
Neuron Communication: Synapses
  • A synapse is the junction between two nerve cells (e.g. axon bulb of one neuron and the dendrite or cell body of a second neuron).
  • A very small gap, called the synaptic cleft, lies between the two neurons.
  • Molecules called neurotransmitters relay messages across the synaptic cleft between the two neurons. The communication between neurons is chemical in nature.
neuron communication synapses2
Neuron Communication: Synapses
  • Communication across the synapse involves:
    • Release of neurotransmitters (e.g. actylcholine)from secretory vesicles of presynaptic neuron
    • Exocytosis of neurotransmitter across the presynaptic membrane and release into the synaptic cleft
    • Attachment of transmitter to protein receptors on the postsynaptic membrane, opening protein channels, leading to stimulation of the neuron or effector cell
    • Deactivation of neurotransmitter by enzymes and reabsorption into presynaptic neuron

reflex arc
Reflex arc
  • An involuntary response that is processed in the spinal cord not the brain.
  • Reflexes protect the body before the brain knows what is going on
  • Immunity
    • The ability of the body to fight infection and/or foreign invaders by producing antibodies or killing infected cells.
  • Immune System
    • The system in the body responsible for maintaining homeostasis by recognizing harmful from non-harmful organisms and produces an appropriate response.
foreign invaders
Foreign Invaders
  • Pathogens
    • Cellular or non-cellular agents that cause disease/immune response.
  • Antigens
    • Compounds, usually proteins, on the outside of pathogens that can trigger the immune system to respond.
major parts of the immune system
Major Parts of the Immune System
  • Blood - White Blood Cells in particular.
  • Lymphatic system - vessels carry a type of fluid named lymph, which bathes the tissue of the body and also is a ‘transport network’ for immune cells.
  • Lymph nodes - the centre of activity where lymphocytes (a type of white blood cell) are continually circulating from tissue in the body, to the lymph nodes and back again by using the bloodstream and lymphatic vessels.
  • Thymus Gland – Produces T Lymphocytes
  • Bone Marrow – Produces B Lymphocytes

What is self and non-self?

  • Self= cells and other substances that are a part of the organism and carry “self” markers (i.e. MHC markers)
  • Non-self = organisms, cells and other substances that are not part of the organismand carry antigens

Major Histocompatibility Complex

  • Simple terms: Major Histocompatibility complex is a cluster of genes that produce proteins that form the markers on our cells. These markers are known as MHC Class 1 molecules.
  • Each person’s MHC markers
  • are different


Edward Non-Self

T Cell


MHC marker protein recognised

how does the body fight pathogens
How does the body fight pathogens?

The Body’s THREE lines of Defense





Pathogen Invades Tissue

Non-Specific Defences

Specific Defences

Barriers to Entry




Natural Flora

Physiological Mechanisms


Chemical Mechanisms Complement proteins Interferons


Phagocytes (granulocytes,

Macrophages), Natural killer cells (cytotoxic)

Inflammation Mast cells

Release of Histamine

First line of defense

Second line of defense


Pathogen Invades Tissue

Non-Specific Defences

Specific Defences



Cytotoxic t-cells (Tc) kill body cells infected with a pathogen

Helper T-cells (Th) - stimulate B cells

Memory cells – remember antigen

Plasma cells – produce antibodies

Third line of defense


ANTIGENS: Any substance foreign to the body that triggers a response from the immune system, such as producing antibodies in order to neutralise it.- Usually made up of proteins but can be polysaccharides

- All have unique shapes

- A way to remember:antigens = antibody generators

- Antibodies are generated to attack thepathogen behind the antigen being detected

antibodies immunoglobulins

The third line of defense involves the production of antibodies:

  • Y-shaped proteinmolecules
  • Produced by B-cells
  • Made up of variable (recognizes antigen) and constant regions.
  • Function: Recognize antigens, bind to and deactivate them.
antigens and antibodies

immune response summary


Helper T - Cell


Active B - Cell

Kills Infected Cells

Memory T- Cell

Plasma Cell

Memory B-Cell


Deactivates Antigens

Immune Response Summary

Displays copy of antigen on surface of cell


Cellular Immunity

acquiring immunity
Acquiring immunity

Short lasting vaccines

Long lasting vaccines

autoimmune diseases
Autoimmune Diseases
  • Autoimmune diseases cause antibodies in the immune system to act against the body’s tissues!
  • There are 80 different types (e.g. MS, Chrohn’s disease etc)
  • The cause is unknown…

BUT, it is genetic and can pass through your family.

  • An autoimmune disorder may result in:

-The destruction of body tissue

-Abnormal growth of an organ

-Changes in organ function

immunonodeficiency diseases
Immunonodeficiency diseases
  • Immunodeficiency refers to a malfunction or deficiency in one or more components of the immune system.


Disorders where part of the immune system is missing or not functioning properly. Most are genetic disorders.


Same as Primary Immunodeficiency, but is caused by a secondary nature, e.g. caused by another disease, drug treatment or environmental exposure to toxins (e.g. HIV leading to AIDS)

  • Overreaction of immune system to harmless antigens (e.g. dust, pollen etc)
  • Mast cells are immune cells involved in allergic responses. Circulating basophil cells are also involved in allergic responses, but to a much lesser extent. Both kinds of cells contain large granules of histamine.
  • IgE binds to mast cells and, to some extent, to basophils. IgEantibodies are made against antigens such as dust, pollen and plant spores.
  • If a person contains IgE antibodies for a particular antigen, they are said to be sensitised to that antigen.
  • If the person is further exposed to the same antigen, cross links are
  • formed between the antibody on the mast cells and the antigen. These antibody–antigen cross links trigger mast cells to release active agents such as histamine(which causes contraction of smooth muscle.
  • What are two differences between the endocrine and nervous systems?
  • What are the 5 plant hormones and what do they do?
  • What is the main difference in the signal transduction pathway between amine/polypeptide and steroid hormones?
  • Describe the three lines of defence and the major parts/cells of the immune system involved in each
  • What is an autoimmune disease? What is an immunodeficiency disease? (definition and eg)
  • What is involved in an allergic response?