Biology Notes Form 2
Biology Notes Form 2
Biology Notes Form 2
Form Two
Transport in plants
Simple plants such as mosses and liverworts lack specialized transport system.
Higher plants have specialized transport systems known as the vascular bundle.
Xylem transports water and mineral salts .
Phloem transports dissolved food substances like sugars.
The Stem
The main functions of the stem are;
support and exposure of leaves and flowers to the environment,
conducting water and mineral salts
conducting manufactured food from leaves to other parts of the plant.
In monocotyledonous stems, vascular bundles are scattered all over the stem, while
in dicotyledonous stems vascular bundles are arranged in a ring.
Vascular bundles are continuous from root to stems and leaves.
The epidermis forms a single layer of cells enclosing other tissues.
The outer walls of the cells have waxy cuticle to prevent excessive loss of water.
The cortex is a layer next to the epidermis.
It has collenchyma, parenchyma and schlerenchyma cells.
Collenchyma
Is next to the epidermis and has thickened walls at the corners which strengthen the
stem.
Parenchyma
Cells are irregular in shape, thin walled and loosely arranged hence creating
intercellular spaces filled with air.
They are packing tissues and food storage areas.
Sclerenchyma
Cells are closely connected to vascular bundles.
These cells are thickened by deposition oflignin and they provide support to plants.
Pith
Is the central region having parenchyma cells.
Absorption of Water and Mineral Salts Absorption of Water
Root hair cell has solutes in the vacuole and hence a higher osmotic pressure than
the surrounding soil water solution.
Water moves into the root hair cells by osmosis along a concentration gradient.
This makes the sap in the root hair cell to have a lower osmotic pressure than the
surrounding cells.
Therefore water moves from root hair cells into the surrounding cortex cells by
osmosis.
The process continues until the water gets into the xylem vessels .
Transpiration
Transpiration is the process by which plants lose water in the form of water vapour into
the atmosphere.
Water is lost through stomata, cuticle and lenticels.
Stomatal transpiration:
This accounts for 80-90% of the total transpiration in plants.
Stomata are found on the leaves.
Cuticular transpiration:
The cuticle is found on the leaves, and a little water is lost through it.
Plants with thick cuticles do not lose water through the cuticle.
Lenticular transpiration
Is loss' of water through lenticels.
These are found on stems of woody plants.
Water lost through the stomata and cuticle by evaporation leads to evaporation
of water from surfaces of mesophyll cells .
The mesophyll cells draw water from the xylem vessels by osmosis.
The xylem in the leaf is continuous with xy lem in the stem and root.
Xylem Vessels
Xylem vessels are formed from cells that are elongated along the vertical axis and
arranged end to end.
During development, the cross walls and organelles disappear and a continuous
tube is formed.
The cells are dead and their walls are strengthened by deposition of lignin.
The lignin has been deposited in various ways.
This results in different types of thickening
Annular.
Simple spiral.
Double spiral.
Reticulate.
The bordered pits are areas without lignin on xylem vessels and allow passage of
water in and out of the lumen to neighbouring cells.
Tracheids
Tracheids have cross-walls that are perforated.
Their walls are deposited with lignin.
Unlike the xylem vessels, their end walls are tapering or chisel-shaped.
Their lumen is narrower.
Besides transport of water, xylem has another function of strengthening the plant
which is provided by xylem fibres and xylem parenchyma.
Xylem fibres;
Are cells that are strengthened with lignin.
They form wood.
Xylem parenchyma:
These are cells found between vessels.
They form the packing tissue.
Capillarity:
Is the ability of water to rise in fine capillary tubes due to surface tension.
Xylem vessels are narrow, so water moves through them by capillarity.
Root Pressure:
If the stem of a plant is cut above the ground level, it is observed that cell sap
continues to come out of the cut surface.
This shows that there is a force in the roots that pushes water up to the stem.
This force is known as root pressure.
Importance of Transpiration
Transpiration leads to excessive loss of water if unchecked.
Some beneficial effects are:
Replacement of water lost during the process.
Movement of water up the plant is by continuous absorption of water from the soil.
Mineral salts are transported up the plant.
Transpiration ensures cooling of the plant in hot weather.
Excessive loss of water leads to wilting' and eventually death if water is not available
in the soil.
Wind
Wind carries away water vapour as fast as it diffuses out of the leaves.
This prevents the air around the leaves from becoming saturated with vapour.
On a windy day, the rate of transpiration is high.
Light Intensity
When light intensity is high; more stomata open hence high rate of transpiration.
Atmospheric Pressure
The lower the atmospheric pressure the higher the kinetic energy of water molecules
hence more evaporation.
Most of the plants at higher altitudes where atmospheric pressure is very low have
adaptations to prevent excessive water-loss.
Availability of Water
The more water there is in the soil, the more is absorbed by the plant and hence a lot
of water is lost by transpiration.
Structural Factors
Cuticle
Plants growing in arid or semi-arid areas have leaves covered with a thick waxy
cuticle.
Stomata
The more the stomata, the higher the rate of transpiration.
Xerophytes have few stomata which reduce water-loss.
Some have sunken stomata which reduces the rate of transpiration as the water
vapour accumulates in the pits.
Others have stomata on the lower leaf surface hence reducing the rate of water-loss.
Some plants have reversed stomatal rhythm whereby stomata close during the day
and open at night.
This helps to reduce water-loss.
Phloem
phloem is made up of;
sieve tubes,
companion cells
parenchyma, a packing tissue
schlerenchyma, a strengthening tissue
Sieve Tubes
These are elongated cells arranged end to end along the vertical axis.
The cross walls are perforated by many pores to make a sieve plate.
Most organelles disappear and those that remain are pushed to the sides of the sieve
tube.
Cytoplasmic strands pass through the pores in the plate into adjacent cells.
Food substances are translocated through cytoplasmic strands.
Companion Cells
Companion cells are small cells with large nuclei and many mitochondria.
They are found alongside each sieve element.
The companion cell is connected to the tube through plasmodesmata.
The mitochondria generate energy required for translocation.
Phloem Parenchyma
These are parenchyma cells between sieve elements.
They act as packing tissue.
Transport in Animals
The Circulatory System
Large and complex animals have circulatory systems that consist of tubes, a
transport fluid and a means of pumping the fluid.
Blood is the transport fluid which contains dissolved substances and cells.
The tubes are blood vessels through which dissolved substances are circulated
around the body.
The heart is the pumping organ which keeps the blood in circulation.
Diastole
When ventricular muscles relax, the volume of each ventricle increases while
pressure decreases.
Contractions of atria force the bicuspid and tricuspid valves to open allowing
deoxygenated blood from right atrium into right ventricle which oxygenated blood
flows from left atrium into the left ventricle.
Semi-lunar valves close preventing the backflow of blood into ventricles.
The slight contractions of atria force the , blood flow into ventricles.
The Heartbeat
The heart is capable of contracting and relaxing rhythmically without fatigue due to
its special muscles called cardiac muscles.
The rhythmic contraction of the heart arise from within the heart muscles without
nervous stimulation.
The contraction is said to be myogenic.
The heartbeat is initiated by the pacemaker or sino-artrio-node (SAN) which is
located in the right atrium.
The wave of excitation spreads over the walls of atria.
It is picked by the artrio-ventricular node which is located at the junction:
Of the atria and ventricles, from where the purkinje tissue spreads the wave to the
walls of the ventricles.
The heart contracts and relaxes rhythmically at an average rate of 72 times per
minute.
The rate of the heartbeat is increased by the sympathetic nerve, while it is slowed
down by the vagus nerve.
Heartbeat is also affected by hormones e.g. adrenaline raises the heartbeat.
Structure and Function of Arteries,Capillaries and Veins
Arteries
Arteries carry blood away from the heart.
They carry oxygenated blood except pulmonary artery which carries deoxygenated
blood to the lungs.
Arteries have a thick, muscular wall, which has elastic and collagen fibres that resist
the pressure of the blood flowing in them.
The high pressure is due to the pumping action of the heart.
The pressure in the arteries originate from the pumping action of the heart.
The pulse or number of times the heart beats per minute can be detected by applying
pressure on an artery next to the bone.
e.g. by placing the finger/thumb on the wrist.
The innermost layer of the artery is called endothelium which is smooth.
It offers least possible resistance to blood flow.
Have a narrow lumen .
The aorta forms branches which supply blood to all parts of the body.
These arteries divide into arterioles which further divide to form capillaries.
Capillaries
Capillaries are small vessels whose walls are made of endothelium which is one cell
thick.
This provides a short distance for exchange of substances.
Capillaries penetrate tissues,
The lumen is narrow therefore blood flowing in capillaries is under high pressure.
Pressure forces water and dissolved substances out of the blood to form tissue fluid.
Part of the tissue fluid pass back into capillaries at the venule end.
Excess fluid drains into small channels called lymph capillaries which empty their
contents into lymphatic vessels.
Capillaries join to form larger vessels called venules which in turn join to form veins
which transport blood back to the heart.
Veins
Veins carry deoxygenated blood from the tissues to the heart (except pulmonary
vein which carries oxygenated blood from the lungs to the heart).
Veins have a wider lumen than arteries.
Their walls are thinner than those of arteries.
Blood pressure in the veins is low.
Forward flow of blood in veins is assisted by contraction of skeletal muscles, hence
the need for exercise.
Veins have valves along their length to prevent backflow of blood.
This ensures that blood flows towards the heart.
The way the valves work can be demonstrated on the arm.
By pressing on one vein with two fingers, leaving one and pushing blood toward the
heart then releasing the latter finger, it can be observed that the part in between is
left with the vein not being visible.
This is because bleed does not flow back towards the first finger.
Antibodies include:
Antitoxins which neutralise toxins.
Agglutinins cause bacteria to clump together and they die.
Lysins digest cell membranes of microorganisms.
Opsonins adhere to outer walls of microorganisms making it easier for phagocytes to
ingest them.
Lymphocytes' are made in the thymus gland and lymph nodes.
There are about 7,000 leucocytes per cubic millimetre of blood.
Platelets (Thrombocytes)
Platelets are small irregularly shaped cells formed from large bone marrow cells
called megakaryocytes.
There are about 250,000 platelets per cubic millimetre of blood.
They initiate the process of blood clotting.
The process of clotting involves a series of complex reactions whereby fibrinogen is
converted into a fibrin clot.
When blood vessels are injured platelets are exposed to air and they release
thromboplastin (thrombokinasewhich initiates the blood clotting process.
Thromboplastin neutralises heparin the anti-clotting factor in blood and activates
prothrombin to thrombin.
The process requires calcium ions and vitamin K.
Thrombin activates the conversion of fibrinogen to fibrin which forms a meshwork of
fibres on the cut surface to trap red blood cells to form a clot.
The clot forms a scab that stops bleeding and protects the damaged tissues from
entry of micro-organisms.
Blood clotting reduces loss of blood when blood vessels are injured.
Excessive loss of blood leads to anaemia and dehydration.
Mineral salts lost in blood leads to osmotic imbalance in the body.
This can be corrected through blood transfusion and intravenous fluid.
Blood Transfusion
Blood transfusion is the transfer of blood from a donor to the circulatory system of the
recipient.
A recipient will receive blood from a donor if the recipient has no corresponding
antibodies to the donor's antigens.
If the donor's blood and the recipient's blood are not compatible, agglutination occurs
whereby red blood cells clump together.
Blood typing
A person of blood group 0 can donate blood to a person of any other blood group.
A person of blood group 0 is called a universal donor.
A person of blood group AB can receive blood from any other group.
A person with blood group AB is called a universal recipient.
A person of blood group A can only donate blood to another person with blood
group A or a person with blood group AB.
A person of blood group B can only donate blood to somebody with blood group B
or a person with blood group AB.
A person with blood group AB can only donate blood to a person with blood
groupAB.
Blood screening has become a very important step in controlling HIV/AIDS.
It is therefore important to properly screen blood before any transfusion is done.
Rhesus Factor
The Rhesus factor is present in individuals with the Rhesus antigen in their red blood
cells.
Such individuals are said to be Rhesus positive (Rh+), while those without the antigen
are Rhesus negative (Rh-).
If blood from an Rh+ individual is introduced into a person who is Rh- , the latter
develops antibodies against the Rhesus factor.
There may not be any reaction after this transfusion.
However a subsequent transfusion with Rh+ blood causes a severe reaction, and
agglutination occurs i.e. clumping of red blood cells.
The clump can block the flow of blood, and cause death.
Erythroblastosis foetalis (haemolytic disease of the newborn) results when an Rh-
mother carries an Rh+ foetus.
This arises when the father is Rh+.
During the latter stage of pregnancy, fragments of Rhesus positive red blood cells of
the foetus may enter mother's circulation.
These cause the mother to produce Rhesus antibodies which can pass across the.
placenta to the foetus and destroy foetal red blood cells.
During the first pregnancy, enough antibodies are not formed to affect the foetus.
Subsequent pregnancies result in rapid production of Rhesus antibodies by the
mother.
These destroy the red blood cells of the foetus, the condition called haemolytic
disease of the newborn.
The baby is born anaemic and with yellow eyes (jaundiced).
The condition can be corrected by a complete replacement of baby's blood with safe
healthy blood.
Lymphatic System
The lymphatic system consists of lymph vessels.
Lymph vessels have valves to ensure unidirectional movement of lymph.
Lymph is excess tissue fluid i.e. blood minus blood cells and plasma proteins.
Flow of lymph is assisted by breathing and muscular contractions.
Swellings called lymph glands occur at certain points along the lymph vessels.
Lymph glands are oval bodies consisting of connective tissues and lymph spaces.
The lymph spaces contain lymphocytes which are phagocytic.
Lymph has the same composition as blood except that it does not contain red blood
cells and plasma proteins.
Lymph is excess tissue fluid.
Excess tissue fluid is drained into lymph vessels by hydrostatic pressure.
The lymph vessels unite to form major lymphatic system.
The main lymph vessels empty the contents into sub-clavian veins which take it to the
heart.
Immune Responses
Immune response is the production of antibodies in response to antigens.
An antigen is any foreign material or organism that is introduced into the body and
causes the production of antibodies.
Antigens are protein in nature.
An antibody is a protein whose structure is complementary to the antigen.
This means that a specific antibody deals with a specific antigen to make it harmless.
When harmful organisms or proteins invade the body, lymphocytes produce
complementary antibodies, while bone marrow and thymus gland produce more
phagocytes and lymphocytes respectively.
Types of Immunity
END OF NOTES
Respiration
Aerobic Respiration
This involves breakdown of organic substances in tissue cells in the presence of
oxygen .
All multicellular organisms and most unicellular organisms e.g. some bactena respire
aerobically.
In the process, glucose is fully broken down to carbon (IV) oxide and hydrogen which
forms water when it combines with the oxygen.
Energy produced is used to make an energy rich compound known as adenosine
triphosphate (ATP).
It consists of adenine, an organic base, five carbon ribose-sugar and three phosphate
groups.
ATP is synthesised from adenosine diphosphate (ADP) and inorganic phosphate.
The last bond connecting the phosphate group is a high-energy bond.
Cellular activities depend directly onATP as an energy source.
When an ATP molecule is broken down, it yields energy.
Process of Respiration
The breakdown of glucose takes place in many steps.
Each step is catalysed by a specific enzyme.
Energy is released in some of these steps and as a result molecules of ATP are
synthesised.
All the steps can be grouped into three main stages:
Glycolysis.
The initial steps in the breakdown of glucose are referred to as glycolysis and they
take place in the cytoplasm.
Glycolysis consists of reactions in which glucose is gradually broken down into
molecules of a carbon compound called pyruvic acid or pyruvate.
Before glucose can be broken, it is first activated through addition of energy from
ATP and phosphate groups.
This is referred to as phosphorylation.
The phosphorylated sugar is broken down into two molecules of a 3-carbon sugar
(triose sugar) each of which is then converted into pyruvic acid.
If oxygen is present, pyruvic acid is converted into a 2-carbon compound called acetyl
coenzyme A (acetyl Co A).
Glycolysis results in the net production of two molecules of ATP.
The next series of reactions involve decarboxylation i.e. removal of carbon as carbon
(IV) oxide and dehydrogenation, removal of hydrogen as hydrogen ions and
electrons.
These reactions occur in the mitochondria and constitute the Tri-carboxylic Acid Cycle
(T.C.A.) or Kreb's citric acid cycle.
The acetyl Co A combines with 4-carbon compound with oxalo-acetic acid to form
citric acid - a 6 carbon compound.
The citric acid is incorporated into a cyclical series of reactions that result in removal
of carbon (IV) oxide molecules, four pairs of hydrogen, ions and electrons.
Hydrogen ions and electrons are taken to the inner mitochondria membrane where
enzymes and electron carriers effect release of a lot of energy.
Hydrogen finally combines with oxygen to form water, and 36 molecules of ATP are
synthesised.
Anaerobic Respiration
Anaerobic respiration involves breakdown of organic substances in the absence of
oxygen.
It takes place in some bacteria and some fungi.
Organisms which obtain energy by anaerobic respiration are referred to as
anaerobes.
Obligate anaerobes are those organisms which do not require oxygen at all and may
even die if oxygen is present.
Facultative anaerobes are those organisms which survive either in the absence or in
the presence of oxygen.
Such organisms tend to thrive better when oxygen is present e.g. yeast.
Practical Activities
To Show the Gas Produced When the Food is burned
A little food substance e.g., maize flour or meat is placed inside a boiling tube.
The boiling tube is stoppered using a rubber bung connected to a delivery tube
inserted into a test-tube with limewater.
The food is heated strongly to bum.
Observations are made on the changes in lime water (calcium hydroxide) as gas is
produced.
The clear lime water turns white due to formation of calcium carbonate precipitate
proving that carbon (Iv) oxide is produced.
2. Products Carbon dioxide and water. Ethanol in plants and lactic acid in
animals-
38 molecules of A TP (2880 KJ)
2 molecules of ATP 210KJ from each
from
3. Energy yield
each molecule of glucose. molecule of glucose.
Fermentation of grains is used to produce all kinds of beverages e.g., traditional beer
and sour porridge.
Fermentation of milk.
End of Topic
GASEOUS EXCHANGE IN PLANTS AND ANIMALS
Necessity for Gaseous Exchange in Living Organisms
Living organisms require energy to perform cellular activities.
The energy comes from breakdown of food in respiration.
Carbon (IV) oxide is a by product of respiration and its accumulation in cells is harmful
which has to be removed.
Most organisms use oxygen for respiration which is obtained from the environment.
Photosynthetic cells of green plants use carbon (Iv) oxide as a raw material for
photosynthesis and produce oxygen as a byproduct.
The movement of these gases between the cells of organisms and the environment
comprises gaseous exchange.
The process of moving oxygen into the body and carbon (Iv) oxide out of the body is
called breathing or ventilation.
Gaseous exchange involves the passage of oxygen and carbon (IV) oxide through a
respiratory surface.
Diffusion is the main process involved in gaseous exchange.
Gaseous Exchange in Plants
Oxygen is required by plants for the production of energy for cellular activities.
Carbon (IV) oxide is required as a raw material for the synthesis of complex organic
substances.
Oxygen and carbon (IV) oxide are obtained from the atmosphere in the case of
terrestrial plants and from the surrounding water in the case of aquatic plants.
Gaseous exchange takes place mainly through the stomata.
Process of Gaseous Exchange in Root Stem and Leaves of Aquatic and Terrestrial
Plants
Gaseous Exchange in leaves of Terrestrial Plants
Gaseous exchange takes place by diffusion.
The structure of the leaf is adapted for gaseous exchange by having intercellular
spaces that are filled.
These are many and large in the spongy mesophyll.
When stomata are open,carbon(IV)oxide from the atmosphere diffuses into the
substomatal air chambers.
From here, it moves into the intercellular space in the spongy mesophyll layer.
The CO2 goes into solution when it comes into contact with the cell surface and
diffuses into the cytoplasm.
A concentration gradient is maintained between the cytoplasm of the cells and the
intercellular spaces.
CO2 therefore continues to diffuse into the cells.
The oxygen produced during photosynthesis moves out of the cells and into the
intercellular spaces.
From here it moves to the substomatal air chambers and eventually diffuses out of
the leaf through the stomata.
At night oxygen enters the cells while CO2 moves out.
Two pairs on the thoracic segments and eight pairs on the sides of abdominal
segments.
Each spiracle lies in a cavity from which the trachea arises.
Spiracles are guarded with valves that close and thus prevent excessive loss of water
vapour.
A filtering apparatus i.e. hairs also traps dust and parasites which would clog the
trachea if they gained entry.
The valves are operated by action of paired muscles.
Ventilation in Insects
Ventilation in insects is brought about by the contraction and relaxation of the
abdominal muscles.
In locusts, air is drawn into the body through the thoracic spiracles and expelled
through the abdominal spiracles.
Air enters and leaves the tracheae as abdominal muscles contract and relax.
The muscles contract laterally so the abdomen becomes wider and when they relax
it becomes narrow.
Relaxation of muscles results in low pressure hence inspiration occurs while
contraction of muscles results in higher air pressure and expiration occurs.
In locusts, air enters through spiracles in the thorax during inspiration and leaves
through the abdominal spiracles during expiration.
This results in efficient ventilation.
Maximum extraction of oxygen from the air occurs sometimes when all spiracles
close and hence contraction of abdominal muscles results in air circulating within the
tracheoles.
The valves in the spiracles regulate the opening and closing of spiracles.
Observation of Spiracle in Locust
Some fresh grass is placed in a gas jar.
A locust is introduced into the jar.
A wire mesh is placed on top or muslin cloth tied around the mouth of the beaker
with rubber band.
The insect is left to settle.
Students can approach and observe in silence the spiracles and the abdominal
movements during breathing.
Alternatively the locust is held by the legs and observation of spiracles is made by the
aid of hand lens.
Ventilation
As the fish opens the mouth, the floor of the mouth is lowered.
This increases the volume of the buccal cavity.
Pressure inside the mouth is lowered causing water to be drawn into the buccal
cavity.
Meanwhile, the operculum is closed, preventing water from entering or leaving
through the opening.
As the mouth closes and the floor of the mouth is raised, the volume of buccal cavity
decreases while pressure in the opercular cavity increases due to contraction of
opercular muscles.
The operculum is forced to open and water escapes.
As water passes over the gills, oxygen is absorbed and carbon dioxide from the gills
dissolves in the water.
As the water flows over the gill filaments oxygen in the water is at a higher
concentration than that in the blood flowing, in the gill.
Oxygen diffuses through the thin walls of gill filaments/lamellae into the blood.
Carbon (IV) oxide is at a higher concentration in the blood than in the water.
It diffuses out of blood through walls of gill filaments into the water.
Counter Current Flow
In the bony fish direction of flow of water over the gills is opposite that of blood
flow through the gill filaments .
This adaptation ensures that maximum amount of oxygen diffuses from the water
into the blood in the gill filament.
This ensures efficient uptake of oxygen from the water.
Where the flow is along the same direction (parallel flow) less oxygen is extracted
from the water.
Inspiration
The ribs are raised upwards and outwards by the contraction of the external
intercostal muscles, accompanied by the relaxation of internal intercostal muscles.
The diaphragm muscles contract and diaphragm moves downwards.
The volume of thoracic cavity increases, thus reducing the pressure.
Air rushes into the lungs from outside through the nostrils.
Expiration
The internal intercostal muscles contract while external ones relax and the ribs move
downwards and inwards.
The diaphragm muscles relaxes and it is pushed upwards by the abdominal organs. It
thus assumes a dome shape.
The volume of the thoracic cavity decreases, thus increasing the pressure.
Air is forced out of the lungs.
As a result of gaseous exchange in the alveolus, expired air has different volumes of
atmospheric gases as compared to inspired air.
Lung Capacity
The amount of air that human lungs can hold is known as lung capacity.
The lungs of an adult human are capable of holding 5,000 cm3 of air when fully
inflated.
However, during normal breathing only about 500 cm3 of air is exchanged.
This is known as the tidal volume.
A small amount of air always remains in the lungs even after a forced expiration.
This is known as the residual volume.
The volume of air inspired or expired during forced breathing is called vital capacity.
Control of Rate Of Breathing
The rate of breathing is controlled by the respiratory centre in the medulla of the
brain.
This centre sends impulses to the diaphragm through the phrenic nerve.
Impulses are also sent to the intercostal muscles.
The respiratory centre responds to the amount of carbon (IV) oxide in the blood.
If the amount of carbon (IV) oxide rises, the respiratory centre sends impulses to the
diaphragm and the intercostal muscles which respond by contracting in order to
increase the ventilation rate.
Carbon (IV) oxide is therefore removed at a faster rate.
Dissection
of a Small Mammal (Rabbit) to Show Respiratory Organs
The rabbit is placed in a bucket containing cotton wool which has been soakedin
chloroform.
The bucket is covered tightly with a lid.
The dead rabbit is placed on the dissecting board ventral side upwards.
Pin the rabbit to the dissecting board by the legs.
Dissect the rabbit to expose the respiratory organs.
Ensure that you note the following features.
Ribs, intercostal muscles, diaphragm, lungs, bronchi, trachea, pleural membranes,
thoracic cavity.
Diseases of the Respiratory System
Asthma
Asthma is a chronic disease characterised by narrowing of air passages.
Causes:
Allergy
Due to pollen, dust, fur, animal hair, spores among others.
If these substances are inhaled, they trigger release of chemical substances and they
may cause swelling of the bronchioles and bring about an asthma attack.
Heredity
Asthma is usually associated with certain disorders which tend to occur in more than
one member of a given family, thus suggesting' a hereditary tendency.
Emotional or mental stress
Strains the body immune system hence predisposes to asthma attack.
Symptoms
Asthma is characterized by wheezing and difficulty in breathing accompanied by
feeling of tightness in the chest as a result of contraction of the smooth muscles
lining the air passages.
Treatment and Control
There is no definite cure for asthma.
The best way where applicable is to avoid whatever triggers an attack (allergen).
Treatment is usually by administering drugs called bronchodilators.
The drugs are inhaled, taken orally or injected intravenously depending on severity of
attack to relief bronchial spasms.
Bronchitis
This is an inflammation of bronchial tubes.
Causes
This is due to an infection of bronchi and bronchioles by bacteria and viruses.
Symptoms
Difficulty in breathing.
Cough that produces mucus.
Treatment
Antibiotics are administered.
Pulmonary Tuberculosis
Tuberculosis is a contagious disease that results in destruction of the lung tissue.
Causes
Tuberculosis is caused by the bacterium Mycobacterium tuberculosis.
Human tuberculosis is spread through droplet infection i.e., in saliva and sputum.
Tuberculosis can also spread from cattle to man through contaminated milk.
From a mother suffering from the disease to a baby through breast feeding.
The disease is currently on the rise due to the lowered immunity in persons with HIV
and AIDS (Human Immuno Deficiency Syndrome).
Tuberculosis is common in areas where there is dirt, overcrowding and
malnourishment.
Symptoms
It is characterised by a dry cough, lack of breath and body wasting.
Prevention
Proper nutrition with a diet rich in proteins and vitamins to boost immunity.
Isolation of sick persons reduces its spread.
Utensils used by the sick should be sterilised by boiling.
Avoidance of crowded places and living in well ventilated houses.
Immunisation with B.C.G. vaccine gives protection against tuberculosis.
This is done a few days after birth with subsequent boosters.
Treatment
Treatment is by use of antibiotics.
Pneumonia
Pneumonia is infection resulting in inflammation of lungs.
The alveoli get filled with fluid and bacterial cells decreasing surface are for gaseous
exchange.
Pneumonia is caused by bacteria and virus.
More infections occur during cold weather.
The old and the weak in health are most vulnerable.
Symptoms
Pain in the chest accompanied by a fever, high body temperatures (39-40°C) and
general body weakness.
Prevention
Maintain good health through proper feeding.
Avoid extreme cold.
Treatment
If the condition is caused by pneumococcus bacteria, antibiotics are administered.
If breathing is difficult, oxygen may be given using an oxygen mask.
Whooping Cough
Whooping cough is an acute infection of respiratory tract.
The disease is more common in children under the age of five but adults may also be
affected.
Causes
It is caused by Bordetella pertusisbacteria and is usually spread by droplets produced
when a sick person coughs.
Symptoms:
Severe coughing and frequent vomiting.
Thick sticky mucus is produced.
Severe broncho-pneumonia.
Convulsions in some cases.
Prevention
Children may be immunised against whooping cough by means of a vaccine which is
usually combined with those against diphtheria and tetanus.
It is called "Triple Vaccine" or Diptheria, Pertusisand Tetanus (DPT).
Treatment
Antibiotics are administered.
To reduce the coughing, the patient should be given drugs.
END OF CHAPTER NOTES
Practical Activities
Observation of permanent slides of terrestrial and aquatic leaves and stems
Leaves
Observation of T.S. of bean and water lily are made under low and 'medium power
objectives. Stomata and air space are seen.
Labelled drawings of each are made.
The number and distribution of stomata on the lower and upper leaf surface is noted.
Also the size of air spaces and their distribution.
Stem
Prepared slides (TS) of stems of terrestrial and aquatic plants such as croton and
reeds are obtained.
Observations under low power and medium power of a microscope are made.
Labelled drawings are made and the following are noted:
Lenticels on terrestrial stems.
Large air spaces (aerenchyma) in aquatic stems.
Gum Exudate from acacia Used in food processing and printing industry.
4. Water Osmoregulation.
5. Cholesterol Excess intake of fats. --
.i->:
The main excretory organs in mammals such as human beings include lungs, kidneys,
skin and liver.
The Nephron
A nephron is a coiled tubule at one end of which is a cup-shaped structure called the
Bowman's capsule.
The capsule encloses a bunch of capillaries called the glomerulus.
The glomerulus receives blood from an afferent arteriole a branch of the renal
artery.
Blood is taken away from the glomerulus by efferent arteriole leading to the renal
vein.
The Bowman's capsule leads to the proximal convoluted tubule that is coiled and
extends into a U-shaped part called loop of Henle.
From the loop of Henle is the distal convoluted tubule that is also coiled.
This leads to the collecting duct which receives contents of many nephrons.
Collecting ducts lead to the pelvis of the kidney.
Mechanism of Excretion
Excretion takes place in three steps:
Filtration, reabsorption and removal.
Filtration
The kidneys receive blood from renal artery a branch of the aorta.
This blood is rich in nitrogenous waste e.g. urea.
It contains dissolved food substances, plasma proteins,hormones and oxygen.
Blood flow in capillaries is under pressure due to the narrowness of the capillaries.
The afferent arteriole entering the glomerulus is wider than the efferent arteriole
leaving it.
This creates pressure in the glomerulus.
Due to this pressure, dissolved substances such as urea, uric acid, glucose, mineral
salts and amino acids are forced out of the glomerulus into the Bowman's capsule.
Large sized molecules in the plasma such as proteins and red blood cells are not
filtered out because they are too large.
This process of filtration is called ultra-filtration or pressure filtration and the
filtrate is called glomerular filtrate.
Selective Reabsorption
As the filtrate flows through the renal tubules the useful substances are selectively
reabsorbed back into the blood.
In theproximal convoluted tube all the glucose, all amino acids and some mineral
salts are actively reabsorbed by active transport.
The cells lining this tubule have numerous mitochondria which provide the energy
needed.
Cells of the tubule have microvilli which increases the surface area for re-absorption.
The tubule is coiled, which reduces the speed of flow of the filtrate e.g. giving more
time for efficient re-absorption.
The tubule is well supplied with blood capillaries for transportation of reabsorbed
substances.
The ascending loop has thick wall and is impermeable to water.
Sodium is actively pumped out of it towards the descending loop.
As glomerular filtrate moves down the descending loop, water is reabsorbed into the
blood by osmosis in the distal convoluted tubule and in the collecting duct.
Permeability of the collecting duct and proximal convoluted tubule is increased by
anti-diuretic hormone (ADH) whose secretion is influenced by the osmotic pressure
of the blood.
The remaining fluid consisting of water, urea, uric acid and some mineral salts is
called urine.
The urine is discharged into the collecting d ct and carried to the pelvis.
The loop of Henle is short in semi-aquatic mammals, and long in some mammals like
the desert rat.
Removal
The urine is conveyed from the pelvis to the ureter.
The ureter carries the urine to the bladder where it is stored temporarily and
discharged to the outside through the urethra at intervals.
Common Kidney Diseases
Uraemia
This is a condition in which concentration of urea in the blood.
It may be due to formation of cysts in tubules or reduction in blood supply to the
glomeruli as a result of contraction of renal artery.
Symptoms
Symptoms include yellow colouration of skin, smell of urine in breath, nausea and
vomiting.
Treatment includes dialysis to remove excess urea and a diet low in proteins and salts
especially sodium and potassium.
Kidney Stones
Kidney stones are solid deposits of calcium and other saIts.
They are usually formed in the pelvis of the kidney where they may obstruct the flow
of urine.
Causes: the stones are formed due to crystallisation of salts around pus, blood or
dead tissue.
Symptoms: include blood in urine, frequent urination, pain, chills and fever. Severe
pain when urinating.
Treatment
Use of laser beams to disintegrate the stones.
Pain killing drugs like morphine.
Stones can be removed by surgery.
Taking hot baths and massage.
Nephritis
Nephritis is the inflation of glomerulus of the kidney.
Causes: Bacterial infection, sore throat or tonsillitis, blockage of glomeruli by
antibody-antigen complex.
Signs and Symptoms: include headaches, fever, vomiting, oedema.
Control includes dietary restrictions especially salt and proteins.
Prompt treatment of bacterial infections.
Cirrhosis
Cirrhosis is a condition in which liver cells degenerate and are replaced by scar tissue .
This causes the liver to shrink, harden, become fibrous and fail to carry out its
functions.
Causes
Chronic alcohol abuse, schistosomiasis infection, obstruction of gall-bladder.
Symptoms
Headache, nausea, vomiting of blood and lack of appetite, weight loss, indigestion
and jaundice.
Control and Treatment
Avoid alcohol consumption and fatty diet.
Use drugs to kill the schistosomes if that is the cause.
Jaundice
This is a yellow colouration of the skin and eyes.
Cause:
Presence of excess bile pigments.
This happens due to blockage of bile duct or destruction of liver.
Symptoms:
Yellow pigmentation of skin and eyes, nausea, vomiting and lack of appetite. Itching
of skin.
Treatment
Removal of stones from the gall bladder by surgery.
Give patient fat-free diet, reduced amount of proteins.
Give antihistamines to reduce itching.
Homeostasis
Homeostasis is the maintenance of a constant internal environment.
The internal environment consists of intercellular or tissue fluid.
This fluid is the medium in the space surrounding cells.
Tissue fluid is made by ultra-filtration in the capillaries.
Dissolved substances in the blood are forced out of the capillaries and into
intercellular spaces.
Cells obtain their requirements from tissue fluid while waste products from cells
diffuse out into the tissue fluid.
Some of the fluid gets back into the blood capillaries while excess fluid is drained into
the lymph vessels.
Cells function efficiently if there is little or no fluctuation in the internal environment.
The factors that need to be regulated include temperature, osmotic pressure and
pH.
The body works as a self-regulating system and can detect changes in its working
conditions bringing about corrective responses.
This requires a negative feedback mechanism e.g. when body temperature falls
below normal, mechanisms are set in place that bring about increase in temperature.
And when the increase is above normal, mechanisms that lower the temperature are
set in place.
This is called a negative feedback and it restores the conditions to normal.