Transcript 17.1 Excretion in Plants and Animals

Excretion in
Plants and Animals
Contents
Homeostasis
Excretion
Excretion in Plants
Control of gaseous
exchange in plants
Secretion
Homeostasis and
Excretion in Humans
The Lungs
Control of gaseous
exchange in humans
The Skin
The Urinary System
The kidneys
Urinary System Parts
& Functions
Nephrons
Formation of Urine
Pathway of Urine
Skin disorders
Urinary disorders
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Homeostasis
Definition: the maintaining of a constant
internal environment of a cell or organism
or the processes involved with this.
It involves controlling temperature, pH,
concentrations of water, salts, glucose,
carbon dioxide, turgidity, the removal of
waste products of cell metabolism, etc.
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Necessity for homeostasis
Organisms may live in external
environments with fluctuating conditions.
These fluctuating conditions may not be
tolerable to the organisms cells.
Animal cells are bathed in tissue fluid.
This produces an internal environment.
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Excretion
Definition: is the elimination of the waste
products of metabolism.
Takes place in all organisms.
Some waste products are poisonous e.g.
urea and carbon dioxide.
Others (e.g. water) if allowed to accumulate
will have damaging effects on the cells.
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Excretion in Plants
Major waste products are gases: O2 from photosynthesis, and
CO2 and water from respiration.
Leaf is the major organ of excretion in
plants – lenticels also contribute.
The O2 from photosynthesis diffuses from
the cells into the air spaces of the spongy
mesophyll.
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Diffusion of oxygen in a leaf
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The structure of a lenticel
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What happens to the oxygen?
Some of it may be taken in by cells and
used in respiration (produces CO2).
The rest will diffuse out through the
stomata and into the atmosphere.
The shedding of leaves by deciduous trees
will also remove some waste products
from plants.
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Control of gaseous exchange
in plants
(1/4)
Takes place through the stomata.
More found on under surface than upper
surface of leaf.
Each stoma is enclosed by two guard cells.
Their cell walls where they touch are much
thicker than the outer cell walls.
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Guard cells
around stoma
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Control of gaseous exchange
in plants
(2/4)
As water enters the guard cells they expand
unevenly and the inner walls bend away
from each other forming the opening
called a stoma.
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K ions in guard cells control the amount of
water entering the cells.
+
Guard cells take in K ions when light is
present and CO2 levels are low and water
then enters by osmosis.
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Control of gaseous exchange
in plants
(3/4)
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CO2 levels affect the uptake of K ions –
may be related to photosynthesis.
This uptake requires energy (ATP).
Provided by the chloroplasts in guard cells.
In darkness – no photosynthesis - CO2
+
levels rise - K ions exit along with water
– stomata close.
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+
The effect of K ions on guard cells
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Control of gaseous exchange
in plants
(4/4)
If water loss during the day becomes too
great, water will leave the guard cells and
the stomata will close.
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Secretion
secretion: is the release of something
‘useful’ from a cell or gland e.g.
hormones, enzymes.
Excretion is an animal function
the loss from plants is more appropriately
called secretion
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Homeostasis and Excretion
in Humans
The Lungs,
Skin and
Kidney have a role in both homeostasis
and excretion.
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The Lungs
Remove waste CO2 – helps maintain the
correct pH in the blood.
Remove water and heat (secondary function
of lungs) – no real control over quantities
of these lost – depends on the temp. and
humidity of the air we breathe in.
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Control of gaseous exchange
in humans
Controlled by the brain.
Sensors (chemoreceptors) in the brain and
in the walls of the aorta and arteries going
to the head, are sensitive to pH and CO2
levels.
When the level of CO2 rises (pH falls)
sensors pick up the change and the brain
will increase the rate of breathing.
O2 levels in the blood have little effect on
the rate of breathing.
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The Skin
Removes water and urea when we sweat.
Body temperature must be kept within
certain limits. Why?
If the temperature goes above or below the
limits permanent damage can be done to
the organism.
A constant temperature will allow faster
metabolism and greater energy release.
Sweating helps maintain a constant body
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temperature.
Ectotherms & Endotherms
Animals that cannot regulate their internal
temperature are called ectotherms e.g.
lizard – moves into and out of sunshine.
Animals that can regulate their internal
temperature are called endotherms.
They use waste heat from cell activity to
warm up and can also reduce their temp.
if they get too hot.
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Skin & temp. regulation
(1/2)
The skin uses Blood vessels, Sweat
glands and Hairs to control body
temperature e.g. if the body is too hot when exercising.
Blood capillaries at the skin surface dilate
(expand) and allow more blood to flow
through them carrying more heat to the
skin surface thus allowing more heat to be
lost by radiation.
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Skin & temp. regulation
(2/2)
Sweat glands releases sweat onto the
surface of the body. It picks up heat from
the body and evaporates with it - leaving
the body cooler. Sweating is a cooling
process.
Hairs lie flat against the body allowing free
movement of air over the body surface
thus cooling the body. In cold weather
hairs stand erect (by contraction of the
erector muscles = piloerection) and trap a
layer of air, which acts as an insulator. 23
A diagram of the skin showing some of the
structures used in temperature regulation.
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Diagram of skin structure
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Sweating
May cause a lack of water if the body
overheats.
Various salts also lost.
Water should be drunk during and after
exercise, to replace lost water.
‘Sports’ drinks have various salts added to
them to help replace the ones lost.
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Sweat
sweat: perspiration, or liquid produced
by sweat glands;
contains water
(95%),
salts
(2%),
carbon dioxide (3%),
urea
(%) and
lactic acid
(%).
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Skin & heat retention
Adipose tissue – good insulator.
Blood capillaries constrict (=
vasoconstriction) – what effect will this
have?
Erector muscles contract – hairs stand up what effect will this have?
Brain initiates an increased metabolic rate what effect will this have?
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The Urinary System
The kidneys are the main excretory organs
of the body.
They excrete nitrogen-containing waste
products e.g. urea.
They are brown bean-shaped organs found
in the lower addomen, one each side of
the back bone.
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The human
excretory system
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Human urinary system
Note the following
Thee tubes attached to each kidney – name,
direction of flow & contents of each.
Bladder – muscular bag that stores urine.
Urethra carries urine to the exterior through
the penis in males and exits above the
opening of the vagina in females.
Sphincter muscle at base of bladder.
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The kidneys
Three main areas:
Cortex – outer edge.
Medulla – lying inside cortex made of
pyramids – striped appearance
Pelvis – hollow area connected to ureter.
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L.S. through a kidney 2
Urinary System Parts & Functions
Part
Function
1.
Excretion = remove waste products
from the blood.
Kidney
2.
Osmoregulation = control the
amount of water and salt in the
blood.
Ureter
Carries urine from kidney to the bladder.
Bladder Stores urine (approx 500ml).
Urethra Carries urine from bladder to the exterior
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The structure of a nephron
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The structure of a nephron
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Nephrons
Between one and two million nephrons in
each kidney.
The functional units of the kidney.
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Formation of Urine
Water and dissolved substances (e.g. urea,
uric acid, glucose, amino acids, vitamins,
salts) pass from the blood in the
glomerulus to the space in the Bowman's
Capsule.
This process called PRESSURE-FILTRATION
is aided by
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Pressure-filtration aided by:
(a) The efferent arteriole being narrower
than the afferent causes a build up of
pressure in the glomerulus.
(b) Blood in the afferent arteriole is under
pressure from the heart.
Blood cells and plasma proteins are too big
to pass through the wall of the capillaries
and do not enter the Bowman’s capsule.
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In Proximal Convoluted Tubule
Cells here have micro-villi and numerous
mitochondria.
All the high threshold substances are
reabsorbed here by a combination of
diffusion, osmosis and active transport.
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In the Loop of Henle
DESCENDING LIMB - water is drawn out by
osmosis.
ASCENDING LIMB - salt diffuses out into the
cells of the medulla. Salt concentration of
the medulla is increased.
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In Distal Convoluted Tubule
Some water reabsorbed here by osmosis
and
salts secreted from the blood by active
transport.
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In Collecting Duct
(1/3)
The urine passes down the collecting duct
(through the medulla) into the ureter.
Due to high salt concentration in the
medulla water is drawn from the collecting
ducts by osmosis thus concentrating the
urine and conserving water in the body.
The reabsorption of water here is controlled
by the hormone ADH (Anti Diuretic
Hormone).
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In Collecting Duct
(2/3)
Its action depends on the water content
of the blood.
If the blood contains not enough water
(or too much salt) the pituitary gland
releases ADH - this increases the
permeability of the collecting ducts and
results in more water being reabsorbed
and the production of a concentrated
urine.
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In Collecting Duct
(3/3)
If the blood contains too much water (or
too little salt) then the production of
ADH is reduced, thus reducing the
permeability of the collecting ducts
resulting in the production of copious
amounts of watery urine = DIURESIS.
Note: Alcohol inhibits ADH production –
no ADH leads to diabetes insipidus.
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Pathway of Urine
Urine passes into pelvis of kidney,
flows down the ureters
into the bladder for storage.
When the bladder is approx. 60% full we
get the urge to empty it.
Sphincter muscle relaxes and urine released
through urethra.
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Summary of urine formation
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Skin disorders
Not examinable
for information only
Acne vulgaris
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Boils
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Epidermal cyst
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Warts
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Moles
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Skin cancer
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Urinary disorders
Not examinable
for information only
Incontinence
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Kidney stones
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END
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