4. EXCRETION AND HOMEOSTASIS
Definition of terms. 3. Secretion is the production and release
1. Excretion is the process by which of useful substances produced by the
living organisms separate and cells e.g. hormones, enzymes, sebum,
remove/eliminate metabolic waste oxalates and mucus.
products from the body cells. 4. Homeostasis is the maintenance of
These waste products include: carbon (IV) internal environment constant despite
oxide, nitrogenous wastes, excess water, the changes in the external
mineral salts, tannins, excess quinine and environment.
resins. 5. Osmoregulation is the process by
Need/significance/ importance of which the osmotic pressure of
blood and tissue fluids is kept
excretion. constant.
It prevents accumulation of metabolic 6. Thermoregulation refers to
wastes which may become poisonous/ maintenance or keeping the body
toxic to the cells. This would alter the temperature constant.
conditions under which cells function
efficiently leading to death.
2. Egestion/excreation is the removal
of indigestible and undigested food
materials from the gut/ alimentary
canal.
1 © Sam obare Mar-21
, EXCRETION IN PLANTS.
Reasons why plants lack complex 4. Most products are converted into
excretory organs. non-toxic/ harmless form/
1. Plant metabolic activities are few and products.
produce/ release metabolic wastes 5. Plants wastes are stored in
slowly. temporary structures in less toxic
form which then fall off e.g.
2. Plants produce less toxic wastes leaves, flowers, fruits and the
because they mainly break down bark.
carbohydrates to produce carbon (IV) Reasons why plants are able to
oxide and water. accumulate their wastes for long.
3. Some excretory products are reutilized 1. Most of the products are
within the plant body e.g. carbon (IV) harmless/less toxic.
oxide and water are used for 2. Most products are converted into
photosynthesis and some oxygen used non-toxic/ harmless form/
for respiration. products.
2 © Sam obare Mar-21
,METHODS OF EXCRETION IN PLANTS/PROCESS OF EXCRETION IN
PLANTS/ HOW DOES EXCRETION OCCUR IN PLANTS?
1. Transpiration -excess water is 4. Tissue/organ fall- plants store
excreted in form of water some of their wastes in flowers,
vapour through the fruits, seeds, old leaves and the
stomata/lenticels. bark and when these organs fall
2. Diffusion- carbon (IV) oxide off from the plants, the wastes
(from respiration) and oxygen are eliminated.
(from photosynthesis) are 5. Exudation- some wastes (e.g.
eliminated through diffusion latex, salts, gum, calcium
through lenticels, cuticle and pectate, resins) are excreted in
stomata. semi-solid form.
3. Deposition/storage in non 6. Guttation- excess water is
toxic form- some wastes (e.g. excreted in form of droplets
calcium oxalate, caffeine, through hydathodes.
nicotine and quinine) are stored
in tissues (e.g. leaves, fruits,
flowers, bark) in non-toxic
form.
3 © Sam obare Mar-21
, Economic importance of plant excretory
products.
1) Tannin- it is deposited in dead tissues 5) Cannabis- it is stored in fruits, flowers
of wood and barks of acacia, wattle and and leaves of bhang (Cannabis sativa)
mangrove trees. Used to treat cancer.
It is used in leather treatment/ tanning It is a pain killer.
/softening of leather.
6) Nicotine- it is found in leaves of
Also used in making ink. tobacco plants.
2) Caffeine- it is stored in coffee berries It is used to manufacture insecticides and
and tea leaves. narcotic drugs.
It is used as a mild stimulant (to increase 7) Rubber- it is made from latex of rubber
mental activity and reduces fatigue). plant.
3) Quinine- it is stored in the bark of It is used in shoe industry.
cinchoma tree and aloe leaves.
It is used to manufacture chewing gums.
It is used for treatment of malaria.
8) Colchicine-
4) Cocaine- it is obtained from the
leaves of cocoa plant. Used to treat gout disease.
It is used as a local anaesthesia/ pain killer. It is used in cancer therapy.
Induces polyploidy in plants/hinders cell
division/used in genetic engineering/
animal and plant breeding research.
4 © Sam obare Mar-21
Definition of terms. 3. Secretion is the production and release
1. Excretion is the process by which of useful substances produced by the
living organisms separate and cells e.g. hormones, enzymes, sebum,
remove/eliminate metabolic waste oxalates and mucus.
products from the body cells. 4. Homeostasis is the maintenance of
These waste products include: carbon (IV) internal environment constant despite
oxide, nitrogenous wastes, excess water, the changes in the external
mineral salts, tannins, excess quinine and environment.
resins. 5. Osmoregulation is the process by
Need/significance/ importance of which the osmotic pressure of
blood and tissue fluids is kept
excretion. constant.
It prevents accumulation of metabolic 6. Thermoregulation refers to
wastes which may become poisonous/ maintenance or keeping the body
toxic to the cells. This would alter the temperature constant.
conditions under which cells function
efficiently leading to death.
2. Egestion/excreation is the removal
of indigestible and undigested food
materials from the gut/ alimentary
canal.
1 © Sam obare Mar-21
, EXCRETION IN PLANTS.
Reasons why plants lack complex 4. Most products are converted into
excretory organs. non-toxic/ harmless form/
1. Plant metabolic activities are few and products.
produce/ release metabolic wastes 5. Plants wastes are stored in
slowly. temporary structures in less toxic
form which then fall off e.g.
2. Plants produce less toxic wastes leaves, flowers, fruits and the
because they mainly break down bark.
carbohydrates to produce carbon (IV) Reasons why plants are able to
oxide and water. accumulate their wastes for long.
3. Some excretory products are reutilized 1. Most of the products are
within the plant body e.g. carbon (IV) harmless/less toxic.
oxide and water are used for 2. Most products are converted into
photosynthesis and some oxygen used non-toxic/ harmless form/
for respiration. products.
2 © Sam obare Mar-21
,METHODS OF EXCRETION IN PLANTS/PROCESS OF EXCRETION IN
PLANTS/ HOW DOES EXCRETION OCCUR IN PLANTS?
1. Transpiration -excess water is 4. Tissue/organ fall- plants store
excreted in form of water some of their wastes in flowers,
vapour through the fruits, seeds, old leaves and the
stomata/lenticels. bark and when these organs fall
2. Diffusion- carbon (IV) oxide off from the plants, the wastes
(from respiration) and oxygen are eliminated.
(from photosynthesis) are 5. Exudation- some wastes (e.g.
eliminated through diffusion latex, salts, gum, calcium
through lenticels, cuticle and pectate, resins) are excreted in
stomata. semi-solid form.
3. Deposition/storage in non 6. Guttation- excess water is
toxic form- some wastes (e.g. excreted in form of droplets
calcium oxalate, caffeine, through hydathodes.
nicotine and quinine) are stored
in tissues (e.g. leaves, fruits,
flowers, bark) in non-toxic
form.
3 © Sam obare Mar-21
, Economic importance of plant excretory
products.
1) Tannin- it is deposited in dead tissues 5) Cannabis- it is stored in fruits, flowers
of wood and barks of acacia, wattle and and leaves of bhang (Cannabis sativa)
mangrove trees. Used to treat cancer.
It is used in leather treatment/ tanning It is a pain killer.
/softening of leather.
6) Nicotine- it is found in leaves of
Also used in making ink. tobacco plants.
2) Caffeine- it is stored in coffee berries It is used to manufacture insecticides and
and tea leaves. narcotic drugs.
It is used as a mild stimulant (to increase 7) Rubber- it is made from latex of rubber
mental activity and reduces fatigue). plant.
3) Quinine- it is stored in the bark of It is used in shoe industry.
cinchoma tree and aloe leaves.
It is used to manufacture chewing gums.
It is used for treatment of malaria.
8) Colchicine-
4) Cocaine- it is obtained from the
leaves of cocoa plant. Used to treat gout disease.
It is used as a local anaesthesia/ pain killer. It is used in cancer therapy.
Induces polyploidy in plants/hinders cell
division/used in genetic engineering/
animal and plant breeding research.
4 © Sam obare Mar-21
