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
functioning
The 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 limits
Despite 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
homeostasis
The systems involved include:
1.
2.
3.
4.
5.
6.
7.
Circulatory system
Respiratory system
Urinary system
Nervous system
Hormonal
Digestive
Skin
Variables associated
with homeostasis
Nutrients
Ions (Na+, Ca+, Cl-)
Water
Blood volume
Red blood cells
Temperature
Oxygen levels
Task
Explain 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
Negative Feedback
What variables are
controlled by negative
feedback?
Blood glucose levels
Temperature
Water balance
Oxygen concentration
pH levels
Hormones in action
Controlling blood glucose
levels
The hormones involved in
controlling this variable are
insulin and glucagon.
These hormones are produced
in the pancreas.
Blood glucose levels
Insulin – controls how
much glucose is absorbed,
from the blood, by the cells
Glucagon – notifies the
liver to release glucose into
the blood
Blood glucose levels
Alpha 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
If the blood
glucose levels
fall…
Cells involved....
Beta cells
 Reduces insulin in the
blood
Less glucose being
absorbed
Blood glucose levels
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
Cells involved....
Alpha cells
 Decrease glucagon
production which acts on the
liver
Blood glucose moves into
liver and converted to
glucogen
Example
Positive Feedback
The change is
encouraged
Example is child birth
Cell
Communication
Multicellular organisms are
composed of many cells.
Communication can either be
Chemical
Electrical
They are referred to as signalling
molecules
Hormones as cell
communicators
This is an example of cell
communication
Hormones can travel different
distances
Action on the same cell
Diffusion through tissue fluid (action
on nearby cells)
Transport through the blood stream
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 derivatives
Steroid hormones
Peptide hormones
Amino Acid derivatives
When are they made…
Made in advance by cells and then
stored
Life span
Short life span
Solubility
Water soluble
Example
Steroid hormones
When are they made…
Made on demand
Life span
Long life span
Solubility
Lipid soluble
Example
Estrogen
Peptide hormones
When are they made…
Made in advance by cells and then
stored
Life span
Short life span
Solubility
Water soluble
Example
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
General Pathway
a) Hormone binds to receptor on
cell membrane or within cell
b) Signal detected within cell
c) Signal transduction a series of
events that changes the signal
received by the cell
d) Cell activates response to signal
Hormones in plants
Plant growth and
development is influenced
by both internal and
external factors
Internal factors include:
chemicals
External factors include: light,
Tropisms
Plants that respond to external
factors are known as tropisms.
Some include
Phototropism
Geotropism
Thigmatropism
Photoperiodism
Phototropism
External Factor
Light
Hormone involved
Auxin
Response
Plant moves towards the light
Geotropism
External Factor
gravity
Hormone involved
Auxin
Response
Roots grow towards the earth
Shoots grow towards the sky
Thigmotropism
External Factor
touch
Hormone involved
Auxin
Response
Plant grows along like a vine
Photoperiodism
External Factor
Amount of day light
Hormone involved
florigen
Response
Flowers open and close to
increase pollination
Plant hormones
Plant 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.Auxin
2.Cytokinins
3.Gibberellins
4.Ethylene
Auxin
Produced in…
The tip of the coleoptile
Evidence…
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
Auxin
Function at low
concentration
Enlarges and elongates
cells
Stimulates elongation of
young developing shoots
and roots
Auxin
Function at high
concentration
Inhibits growth in roots
IAA…
Indoleacetic acid
Influences growth and
development in plants
(enlargement and elongation of
plant cells)
Apical Dominance
Lateral 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
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?
Phototropism
Plants 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
Positive
phototropism
 moves towards the light
Negative
phototropism
Worksheet…
Investigating phototropism
page 19
Hormonal plants – plant
growth regulators page 28 - 29
Geotropism
Roots 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 growth
Upper side grows fast causing it to turn
Shoots
Auxin accumulation in the shoots on the lower
side
Increases cell growth and elongation
Positive geotropism
 moves towards the gravity
Negative geotropism
moves away from the
gravity
Worksheet…
Investigating geotropism page
21
Cytokinins
Produced 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
Gibberellins
Produced in
The seed
Its 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 Acid
Produced in
The leaves
Its 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.
Ethylene
Produced in
A variety of tissue type
Its 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 System
Is composed of the brain, spine
and nerves around the body
They are categorised into the
following groups
Central nervous system
Peripheral nervous system