Homeostasis: staying within limits
News paper Article…….
What happened?What part of the body does it affect?
Body cells require a relatively stable internal
environment for normal functioningThe external environment is composed of the environment.The internal environment is the liquid. This includes tissue fluid and plasma.
Extra- and intracellular fluids
Tissue fluid and plasma move. 3 examples include:•Nutrients & gas that pass from tissue fluid to blood•Waste products from tissue to blood•Oxygen from tissue to cells
Homeostasis: keeping within
limitsDespite changes in the external environment, the internal environment of living things remains fairly constant.
The maintenance of a constant internal environment is known as homeostasis.
Systems involved in homeostasisThe systems involved include:
1. Circulatory system2. Respiratory system3. Urinary system4. Nervous system5. Hormonal6. Digestive7. Skin
Variables associated with
homeostasisNutrientsIons (Na+, Ca+, Cl-)WaterBlood volumeRed blood cellsTemperatureOxygen levels
TaskExplain why each of the above variables is
important in maintaining stability.
Detecting and Responding
In order to maintain stable conditions, organisms need to:
•Detect changes•Counteracting change
This type of control is known as negative feedback.
Negative Feedback
What variables are controlled by
negative feedback?Blood glucose levelsTemperatureWater balanceOxygen concentrationpH levelsetc
Hormones in actionControlling blood glucose
levelsThe hormones involved in controlling this variable are insulin and glucagon.
These hormones are produced in the pancreas.
Blood glucose levelsInsulin – controls how much glucose is absorbed, from the blood, by the cells
Glucagon – notifies the liver to release glucose into the blood
Blood glucose levelsAlpha cells – increase production of glucagon which acts on the liver to convert glycogen to glucose
Beta cells – decrease production on insulin. Therefore less glucose will be absorbed by the cells
If the blood glucose levels
fall…
Cells involved....Beta cells
Reduces insulin in the blood
Less glucose being absorbed
Blood glucose levels rise
Cells involved....Alpha cells
increases glucagon production which acts on the liver
Liver converts glucagen into glucose
Blood glucose levels rise
If the blood glucose levels
rise…
Cells involved....Beta cells
Increase insulin in the blood
More glucose being absorbed
Blood glucose levels falls
Cells involved....Alpha cells
Decrease glucagon production which acts on the liver
Blood glucose moves into liver and converted to glucogen
Blood glucose levels falls
Example
Positive Feedback
The change is encouraged
Example is child birth
Cell Communication
Multicellular organisms are composed of many cells.
Communication can either beChemical Electrical
They are referred to as signalling molecules
Hormones as cell communicators
This is an example of cell communication
Hormones can travel different distancesAction on the same cellDiffusion through tissue fluid (action on nearby cells)
Transport through the blood stream (action on distant cells
Hormones are diffused through the body
Cells have receptors which are specific to each hormone.
Cells can either have one or many different kinds of receptors for different hormones
Different types of hormones
There are three types of hormones
Amino derivativesSteroid hormonesPeptide hormones
Amino Acid derivativesWhen are they made…
Made in advance by cells and then stored
Life spanShort life span
SolubilityWater soluble
ExampleAlanine
Steroid hormonesWhen are they made…
Made on demandLife span
Long life spanSolubility
Lipid solubleExample
Estrogen
Peptide hormonesWhen are they made…
Made in advance by cells and then stored
Life spanShort life span
SolubilityWater soluble
ExampleAntidiuretic hormone
Steroids have a lipid base, therefore are referred to as hydrophobic (lipophilic) and is insoluble in water
A carrier protein is needed for this hormone to travel through the blood stream.
Amino acid derivatives & peptide hormones are hydrophilic and is soluble in water.
No assistance to travel through the bloodstream
Unable to pass through the membrane without assistance
A G-protein is needed to transmit their message
The difference is how they enter their target cell.
General Pathwaya) Hormone binds to receptor
on cell membrane or within cellb) Signal detected within cellc) Signal transduction a series
of events that changes the signal received by the cell
d) Cell activates response to signal
Hormones in plantsPlant growth and development is influenced by both internal and external factors
Internal factors include: chemicals
External factors include: light, gravity, temperature & day length
TropismsPlants that respond to external factors are known as tropisms.
Some includePhototropismGeotropismThigmatropismPhotoperiodism
PhototropismExternal Factor
LightHormone involved
AuxinResponse
Plant moves towards the light
GeotropismExternal Factor
gravityHormone involved
AuxinResponse
Roots grow towards the earthShoots grow towards the sky
ThigmotropismExternal Factor
touchHormone involved
AuxinResponse
Plant grows along like a vine
PhotoperiodismExternal Factor
Amount of day lightHormone involved
florigenResponse
Flowers open and close to increase pollination
Plant hormonesPlant hormones are
produced by plant cells and in relatively small amounts.
They travel via the phloem and xylem and act on other cells in the plants
Plant hormone classification
Plant hormones are grouped into the following five groups
1.Auxin2.Cytokinins3.Gibberellins4.Ethylene5.Abscicic acid
AuxinProduced in…
The tip of the coleoptileEvidence…
Tips were removed and grow no longer occurred
When tip was placed onto agar, which was then placed onto coleoptile without a tip it grew
AuxinFunction at low concentration
Enlarges and elongates cellsStimulates elongation of young developing shoots and roots
Involved in fruit development.
AuxinFunction at high concentration
Inhibits growth in roots
IAA…Indoleacetic acidInfluences growth and
development in plants (enlargement and elongation of plant cells)
Apical DominanceLateral buds do not
grow and the concentration of growth is located at the apex (top/tip) of the plant
If tip removed lateral buds will grow
Tip removed from a growing shoot
If the tip is removed growth will no longer occur
This is because auxin is stored in the tip. When removed no cell development occurs
If tip is removed and placed onto a piece of agar that auxin store in the tip will diffuse into the agar
When agar is placed onto the growing shoot (tip removed) the shoot will continue to grow
What does this experiment illustrate?
PhototropismPlants move
towards the sunlight. Why?
To obtain more light, so that photosynthesis is maximised
Stimulus: Light
How does it work?Coleoptile A
Light is evenly dispersed Therefore auxin is evenly
dispersed Coleoptile grows straight
Coleoptile B Light is concentrated on one side Auxin moves away from light
source (ie dark side) Highly concentrated on the darker
side causes cells to elongate and grow faster than the other side. This causes the shoot to bend towards the light
Positive phototropism moves towards the light
Negative phototropism
moves away from the light
Worksheet…Investigating phototropism page 19
Hormonal plants – plant growth regulators page 28 - 29
GeotropismRoots and shoots
will change direction if a pot is turned on its side. Why?
So that roots will direct itself to water and shoots towards light
Stimulus: Gravity
How does it work?Roots
Gravity is concentrated on the lower side Auxin is concentrated on the lower side which
cause inhibition of cell growthUpper side grows fast causing it to turn
ShootsAuxin accumulation in the shoots on the
lower sideIncreases cell growth and elongationShoot bends upwards
Positive geotropism moves towards the gravity
Negative geotropism moves away from the gravity
Worksheet…Investigating geotropism page 21
CytokininsProduced in
The roots and can be translocated to the shoots
Its function is to…Growth promoting hormone which acts on shoots, roots and fruits
promote cell division and differentiation
GibberellinsProduced in
The seedIts function is to…
Stimulate stem elongation by stimulating cell division and elongation.
Stimulates bolting/flowering in response to long days. Breaks seed dormancy and initiate bud development
Stimulates enzyme production (a-amylase) in germinating cereal grains for mobilization of seed reserves.
Can delay aging in leaves and citrus fruits.
Abscisic AcidProduced in
The leavesIts function is to…
Stimulates the closure of stomata Inhibits shoot growth but will not have as much affect on roots or may even promote growth of roots.
Induces seeds to synthesize storage proteins.
Has some effect on induction and maintenance of dormancy.
EthyleneProduced in
A variety of tissue typeIts function is to…
Stimulates the release of dormancy. Stimulates shoot and root growth and
differentiation (triple response) Stimulates leaf and fruit abscission. Stimulates flower opening. Stimulates flower and aging. Stimulates fruit ripening.
Nervous SystemIs composed of the brain,
spine and nerves around the body
They are categorised into the following groupsCentral nervous systemPeripheral nervous system