CHAPTER 7(a) - GASEOUS EXCHANGE

RESPIRATORY SURFACE-ALVEOLUS

1. LARGE SURFACE AREA-human lungs consists of million of alveolus.
2. THIN-wall of alveolus consists of one layer of thin squamous epithelial cells to facilitate diffusion of gaseous such as o2 and co2.
3. MOIST-inner surface of alveolus is lined with fluid and its surface tension is lowered by secretion of surfactant from special septal cells in the alveolus . This fluid dissolve respiratory gaseous for diffusion and speed up gas exchange.
4. Each alveolus is covered by a dense of network capillaries which carries away the oxygen and keep the partial pressure low.

THE RESPIRATORY PIGMENT- HAEMOGLOBIN

-The haemoglobin in red blood cells is responsible in transporting oxygen and carbon dioxide.
-Breathing allows the inspired air to come in contact with the blood vessel that cover the alveoli.

HAEMOGLOBIN

HAEMOGLOBIN

-Haemoglobin is  a complex conjugated protein
-Quaternary in nature
-Protein consists of four polypeptide chains , two alpha and two beta
-These polypeptide chains are globular in nature and called globin
-Each haem group can associate with one molecule of oxygen that gives blood its bright red colour
-Process of associating oxygen with the haem group is called oxygenation
-Its a loose combination which allows dissociation occurs easily

TRANSPORT OF OXYGEN AND CARBON DIOXIDE IN BLOOD

-RBC are round disc , concave on each side(biconcave) and do not contain nucleus. Gives it an extremely high surface area to volume ratio for more efficient gaseous exchange.
-In the blood , only small portion of oxygen can dissolve in plasma as the solubility of o2 to plasma is  very low.
-Haemoglobin in RBC increase the ability of blood to transport o2 by about 65 to 70 times.
-The main function of haemoglobin is to carry oxygen but it can help to transport c02.
-It can do so efficiently because it can bind with oxygen at very low partial pressure of oxygen.
-COOPERATIVITY@When the first o2 bind with the first haem group, the haemoglobin molecule  changes shape slightly. This facilitates the binding of the next oxygen.
-When there is a drop in partial pressure of oxygen, haemoglobin will release oxygen.
-In the tissue, the partial pressure of oxygen is lower that at the alveoli , the tissues are continuously  supplied with oxygen.
-CARBON DIOXIDE is more soluble in blood than oxygen.

SIMPLE ILLUSTRATION

TRANSPORTATION OF CO2 BY BLOOD TO LUNGS

-Either in RBC or BLOOD PLASMA

-Can be done in three different ways

1. Transport by RBC in the form of HYDROGEN CARBONATE IONS(HCO3) 85%

-About 85% of the CO2 produced during respiration diffuse into RBC and combine with water to form carbonic  acid (H2CO3) catalysed by carbonic anhydrase.

H20 + CO2 = H2CO3

-The carbonic acid the dissociate to HCO3 and H+ with the presence of same enzyme carbonic anhydrase

H2CO3 = HCO3 + H+

-Then , the HCO3 diffuse out from the RBC into the plasma. 

-This occur because RBC is very permeable to HCO3 

-Later on, CL(CHLORIDE IONS) diffuse into the RBC to maintain electrical neutrality. This process  is called chloride shift.  

-The hydrogen carbonate ions are then carried to lungs and converted to CO2.

-Dont forget that the H+ is still in the RBC , 

-The presence of H+ ions in the RBC decrease the pH of the blood. 

-This proton are quickly mopped by free haemoglobin to form HAEMOGLOBINIC ACID (HHb)

-The free haemogloobin which acts as a pH buffer is made available from the forced dissociation of  oxyhaemoglobin.

-And oxygen is released to the cell , this phenomenon is called BOHR SHIFT. 

-When blood reaches the lungs , the whole process is repeated.

2. CO2 combines with haemoglobin in the RBC to form CARBAMINO COMPOUND 10%

R as Hb(haemoglobin)

-CO2 produced combine in a reversible reaction with the amino group of haemoglobin and form  carbaminohaemoglobin.
-The carbaminohaemoglobin then transported to the lung where it dissociates to CO2.
-The binding of CO2 to haemoglobin lowers the affinity of haemoglobin  for oxygen.
-Which forces to haemoglobin to release its oxygen load. 

3. CO2 dissolve in blood plasma 5%

-About 5% of CO2  dissolve in blood plasma to form carbonic acid ( H2CO3)
-But at a slower rate compared to  in RBC due to lack of enzyme.
-The carbonic acid the ionises to H+ and hydrogen carbonate(HCO3)
-The presence of H+ ions causes in increase in its acidity
-Quickly buffered by plama proteins to form proteinic acid.

PICTURE REFERENCE 

FIRST- CO2  WITH WATER IN RED BLOOD CELLS
SECOND-CO2 WITH HAEMOGLOBIN
THIRD-CO2 WITH WATER AT BLOOD PLASMA

CO2 AND O2

OXYGENATED AND DEOXYGENATED

OXYGEN DISSOCIATION

CHAPTER 7(b) - DISSOCIATION CURVE

OXYGEN DISSOCIATION CURVE OF HAEMOGLOBIN

-Gaseous diffuse  from high partial pressure to low partial pressure
-In inhaled air, the partial pressure of o2 is high but the partial pressure of co2 is low
-oxygen diffuse into the alveolar blood capillaries and co2 diffuse out into the alveolus

LOADING AND UNLOADING OF GASEOUS

-When haemoglobin associates with o2, it undergoes change in shape
-Helps a faster intake of the next oxygen molecule
-The last one is 700 times faster than the first (cooperativity)
-Reverse happens when oxygen dissociates with haemoglobin at a site where the partial pressure of oxygen is low.
-At first, small decrease of Po2 will lead to a big drop of oxygen saturation of haemoglobin
-It then gets harder and harder to remove the oxygen from haemoglobin

DISSOCIATION CURVE

-The haemoglobin can be 95% saturated with oxygen even at a very low Po2(10kPa)
-This is known as oxygen loading
-The partial pressure of oxygen in the lung is 13kPa
-The affinity of haemoglobin for oxygen also lowered by
 (a)2-3-DIPHOSPHOGLYCERATE-product of RBC
 (b)high temperature
-In the respiring cells, the partial pressure of oxygen is very low and oxygen will dissociate from haemoglobin supplying oxygen to the cells

CHANGES BY Pco2

-when the partial pressure of co2 increase or pH decrease will shift the dissociation curve to the right.
-lowering the affinity of haemoglobin for oxygen
-causes oxygen to dissociate from oxyhaemoglobin
-phenomenon is known as BOHR SHIFT

CHANGES BY HIGH TEMPERATURE

-Same goes when the temperature of body increase
-curve shift to the right
-this result in release of more oxygen particularly in vigorous activity

OXYGEN DISSOCIATION CURVE OF MYOGLOBIN

MYOGLOBIN

-Myoglobin is made up of one polypetide chain with a signle iron containing prosthetic group  attached to it
-each myoglobin binf with single oxygen molecule to form oxymyglobin
-the myoglobin dissociation curve is hyperbolic in shape
-this shows that myglobin has higher affinity for oxygen and combines more readily
-but releases it only when the partial pressure of oxygen is low
-myglobin is an oxygen store in muscle

OXYGEN DISSOCIATION CURVE OF FOETAL HAEMOGLOBIN (HbF) AND ADULT HAEMOGLOBIN (HbA)

-During the foetal development , the foetus in the mother's womb is able to obtain the oxygen
-from the mother through increased maternal blood supply to the placenta
-HbF has higher affinity for oxygen than the HbA

HbF VS HbA

-HbF has higher affinity than HbA
-Means hat HbF can easily saturated with oxygen even at low partial pressure
-ensures a sufficient and efficient oxygen supply to the foetus

DOUBLE BOHR EFFECT

-In the maternal blood, there is a high Pco2 which helps to release oxygen
-in the foetal blood , the partial pressure of co2 is low
-so in the foetal ,increase the binding of haemoglobin to oxygen
-taking up more oxygen easily
-this phenomenon is known as double bohr effect
-this causes the curve shifted in the opposite direction
-HbA to the right
-HbF to the left

CHAPTER 7(c) - BREATHING CYCLE

BREATHING MECHANISM

-Events that bring inhaled air to the alveoli and removes exhaled air in a process called ventilation
-ventilation helps to maintain gaseous exchange and blood pH levels
-inspiratory (inhalation) and expiratory (exhalation)
-lungs rely on the diaphragm and the rib cage during breathing

INHALATION AND EXHALATION

-Lungs are not attached to the rib cage by tissues but are separated from it by a thin film of pleural fluid which holds the pleural membrane

-and lubricates it when the lungs expand during inspiration

-medulla oblongata and pons in the hindbrain control this automatic action

RECEPTORS OF BREATHING MECHANISM

1. CENTRAL CHEMORECEPTOR

-In the medulla region of the hind-brain

-sensitive to the pH of the cerebrospinal fluid (indicator of blood Co2)

-the higher the blood CO2 concentration, the lower the pH of cerebrospinal fluid

2. PERIPHERAL CHEMORECEPTOR 

-located in carotid and the aortic bodies

-both bodies are also sensitive to blood pH

-indicates the changes in arterial CO2 concentration

3. MECHANORECEPTOR (STRETCH RECEPTOR)

-In the bronchial tree 

-help maintain any expansion in the lungs and size of airways

-they send impulses to the expiratory centres to shorten inspiration

**respiratory muscles will react to increase or decrease alveolar ventilation as required by regulating amplitude and depth of each breath**

BREATHING RECEPTORS

DURING VIGOROUS EXERCISE

1.Increase in the partial pressure of co2 in the body

2.Drop in the pH of blood

3.Rise in the carbon dioxide partial pressure is detected by chemoreceptors in the carotid artery

4.Impulse are send to stimulate the inspiratory and the cardiovascular center in the brain

5.Inspiratory cente then sends out impulse through

6.Intercostal nerve to stimulate the contraction of the external intercostal muscle of the rib cage

7.Phrenic nerve to stimulate the contraction of the radial muscle of the diaphragm

8.Both contractions bring the rib cage outwards and upwards

9.Air inhaled to the lungs

10.Inhalation and Exhalation are carried out more frequently to increase the rate of alveolar ventilation for faster gaseous exchange in the body.

11.Too much oxygen can cause an increase in the metabolic rate of carbohydrate, fats and protein which will result in accumulation of co2 causing an increase in the rate of ventilation as well as cardiac frequency

CHAPTER 7(d) - GASEOUS EXCHANGE IN PLANTS

THE STRUCTURE AND FUNCTION OF STOMATA

-Stoma is an opening on the epidermis of leaves
-Stoma is actually an opening of two specialised photosynthetic epidermal cells, called guard cells
-the guard cells plays an important role in the opening and closing of stomata
-the guard cell is bean -shaped and its unique as its inner cellulose wall thicker than outer

OPENING AND CLOSING OF STOMATA

-Stoma plays an important role in the exchange of respiratory gaseous
-absorption of co2 for photosynthesis and regulation of water in plants

-Oxygen produced diffuse out through the stomatal pores
-carbon dioxide diffuse in from the atmosphere into the leaves
-under severe water deficit , stomata close automatically
-this is due to the release of ABSCISIC ACID by plant during the water stress condition
-the closure of stomata helps to prevent water loss
-opening and closing of stomata is a response of increse or decrease in water potential

POTASSIUM ION ACCUMULATION HYPOTHESIS

-Opening of the stomata is associated with the influx of potassium ions into the guard cells from the epidermal cells

OPENING

1. During the day, blue light increase the activity of the proton pumps found in the membrane of             guard cells
2. The proton pumps use ATP produced during photosynthesis light reaction to transport H+ ions out
3. When H+ ions are pumped out , K+ ions diffuse into the guard cells through channel protein to           maintain the electrical potential
4. Accumulation of K+ ions in the sap of the guard cells causes its water potential to decrease
5. Water moves into the guard cells by osmosis
6. Guard cells becomes turgid and curve inwards more and causes stomata to open

CLOSING

1. In the dark or night, when the proton pumps are inactive , K+ ions diffuse out of the guard cells
2. Increase the water potential and water moves out of guard cells by osmosis
3. The guard cells lose turgidity and the stomatal aperture closes

WATER STRESS

-During peak transpiration, the tissues of roots, stem and leaves may come under some degree of water shortage
-plant may release abscisic acid
-will trigger the closure of stomatal aperture
-by activating the metabolic ion pump mechanism on the membrane
-K+ will moves out of the guard cells
-resulting in decrease of K+ concentration
-water potential inside the guard cell increase, water flows out
-lose turgidity and stomatal aperture closes

FACTORS AFFECTING THE OPENING AND CLOSING OF STOMATA


1.Water balance@shortage of water, stomata will close
2.Concentration of CO2@low concentration of co2 in the atmosphere will cause stomata open
3.Light@hight light intensity but not very high will cause the stomata to open, guard cells are more sensitive to blue light than red light
4.Circadian rhythm@some plants havea biological clock whereby stomata will open during the day and close at night. In the case of CAM, plants like cactus , the stomata open during the night, and close during the day to avoid excessive loss of water

CHAPTER 8(a) - TRANSPORT SYSTEM IN MAMMALS

MAMMALIAN HEART

-a pump which is the heart
-transporting vessel , arteries , veins , capillaries , lymphatic vessel
-transporting fluid which is the blood and lymph
-heart is actually a muscular pump
-heart wall consists of cardiac muscle
-very specialized muscle which is myogenic
-cardiac muscle consists of striated muscle fibre, joined one another by intercalated discs

CARDIAC MUSCLE

CORONARY ARTERIES- transport oxygenated blood
CORONARY VEINS-transport deoxygenated blood

PERICARDIUM SAC

-the heart is tightly contained in a fluid filled, double membranous pericardium sac
-this fluid reduce friction between the heart and the surrounding tissues
-elastic nature of pericardium prevents the heart from being overstretched
-due to overfill of blood
-attached to diaphragm , firmly anchoring the heart in position

HUMAN HEART

1.Right atrium collects deoxygenated blood from superior and inferior vena cava
2.Left atrium collects oxygenated blood from the pulmonary vein
3.Right ventricles pumps deoxygenated blood into the pumonary arteries
4.Left ventricles pumps oxygenated blood into the aorta at high pressure


CONFUSED? CHECK THIS OUT..

VALVES

-There are 4 chambers in heart
-right and left atrium & right and left ventricles
-Atriums are seperated by interatrial septum
-ventricles are seperated by interventricular septum
-outer part of ventricles are thicker , transport blood to lungs and body


SA NODE AND AVN

-SA NODE (sinoatrial node) located close to entry of vena cava
-responsible for initiation and excitation of the heartbeat
-known as heartbeat pacemaker
-AVN (atrioventricular node) located in the centre of the heart
-is responsible in spreading electrical impulses from the atria to ventricles

AVN (ATRIOVENTRICULAR NODE)

-Connected with two bundle of His
-and their network of conducting fibres called purkinje tissue
-conducting fibres help to spread the electrical impulses from the AVN to the apex of the heart to initiate ventricles to contract

SA NODE (SINOATRIAL NODE)

-supplied with two nerve sets of the autonomic nervous system
-vagus nerve (parasympathetic) and the sympathetic
-they do not trigger the heartbeat
-but affect the pacemaker so as to influence the rate of heartbeat
-sympathetic nerve speed up the heartbeat
-parasympathetic slows it down


CARDIAC CYCLE

-SYSTOLE@CONTRACTION OF THE CARDIAC MUSCLE
-DIASTOLE@RELAXATION OF THE CARDIAC MUSCLE
-When the atria are at their systolic stage, the ventricles are in diastole stage and vice versa
-Each cycle of contraction and relaxation of the heart is called one beat of the heart
-Average of heartbeats in one minutes is 70

WATCH THESE 2 VIDEOS FOR BETTER UNDERSTANDING 

1.ATRIAL SYSTOLE
-begins with the contraction of left and fight atrium
-causes the atrial pressure to increase
-force the tricuspid and bicuspid valves to open
-allowing blood to flow from atria to ventricle
-contraction of atrial walls also seals off the vena cava and pulmonary veins
-due from previous cycle, the ventricles are at lower pressure
-thus allowing blood to flow in from the atria to the ventricle

2.VENTRICULAR SYSTOLE
-right and left ventricles contract
-pressure begin to build up
-blood is forced to be pumped into the pulmonary artery and aorta
-forcing the semilunar valves to open
-increase in ventricular pressure and decrease in atrial pressure pressure forces the tricuspid and bicuspid valve to close
-the recoil of blood against the bicuspid and tricuspid valve makes the first lub sound
-at the same time, relaxing of the atrial wall and the contraction of ventricles wall
-allow the refilling of the atria under relatively low pressure
-deoxygenated blood flows into the right atrium
-oxygenated blood flows from pulmonary vein to left atrium

3.VENTRICULAR AND ATRIAL DIASTOLE
-when the ventricular systole ends, followed by short period where both are relaxed
-in ventricular diastole, the pressure of aorta and the pulmonary artery become higher
-forces the semilunar valves to shut
-recoil of the blood against the valve makes the second DUP sound
-closing of the semilunar valves also prevent backflow blood from aorta and pulmonary arteries
-fall in the ventricular pressure allows the increasing blood of atrium
-from here the sequence returns to atrial sytole

THE INITIATION OF HEARTBEAT

-heartbeat starts from SA NODE found in the cardiac muscle
-contraction of cardiac muscle is stimulated by electrical impulse
-cardiac muscle can contract by itself and is characterized as myogenic
-this rhythm of contraction can be made to go slower or faster by nervous impulses or hormone
-SA NODE is sometimes known as pace maker

SEQUENCE OF HEARTBEAT INITIATION 

1.Electrical impulse initiated by the pacemaker SA node spread out of the wall of atrium
2.But are prevented to spread in the walls of ventricles
3.By artrioventricular septum
4.Instead, the impulse will travel to ventricles via the AV node
5.The impulse reach the AV node after 0.3 seconds after being emitted by SA NODE
6.When the AV node receive the impulse, it pauses for 0.9 seconds
7.This delay of impulses give time for the impulses to spread all over the atrium
8.From the AV node, the impulses are reemitted along the bundle of His and the purkinje fibres
9.Spread all the impulses to the ventricular wall
10.Causes simultaneous contraction through the ventricles


ELECTROCARDIOGRAM (ECG)

ECG

Depolarization in the context of biology refers to the sudden change within a cell during which the cell undergoes a dramatic electrical change

1. P-wave@ depolarisation of the cardiac muscle at the atria arises from the electrical impulse emitted from the SA node, depolarisation spread as a wave of impulse in both atria
2. P-Q interval@ time required for the impulse to spread to the ventricles
3. QRS complex@ depolarisation of ventricles that leads to ventricular contraction. This wave is large because the ventricles are thicker 
4. ST ridge@occurs as the ventricles slowly repolarise leading to ventricular diastole
5.The heart rate can be calculated from the time taken between one P wave to next

CONTROL OF HEART RATE 

-The heart rate means number of heartbeats per minute
-heart muscle has its own inherent rhythm
-however , can still be controlled by hormones and autonomic nervous system
-although the pacemaker trigger the heartbeat,its also supplied with specific nerve
-SA node is supplied with two nerve sets of autonomic nervous system
-vagus nerve(parasympathetic) and sympathetic
-both these originate from medulla oblongata of the brain

SYMPATHETIC NERVE

1. Stimulating impulse are transported to the SA node
2. Causing in increase of depolarisation(voltage increased)
3. Result in  an increase in the rate of contraction of the cardiac muscle
4. Thus increase the heart rate increase

PARASYMPATHETIC NERVE

1. Inhibitory impulses are transmitted to the SA node
2. Causing  a decreased depolarisation
3. Activity of the heart is retarded, resulting in a decrease of rate of heartbeat

HORMONAL CONTROL OF HEART RATE 

-Stimulation of the adrenal gland by the sympathetic nerve triggers the release of two hormones
-Noradrenline and Adrenaline
-Noradrenaline hormone increase both heart rate and ventricular contraction
-Adrenaline triggers a (flight and fight) response  by speeding up the heart rate
-thus preparing the body for extreme exertion
-blood pressure increase and deliver the blood to where it needs such as muscle cells
-increase of thyroxine, a hormone secreted by thyroid gland also increase the heart rate
-heart rate also influenced by body size , gender , age , stress , state of health ,body temperature , drugs , smoking habits and alcoholic drinks


CARDIOVASCULAR DISEASE 

-most of the disease are caused by atheroma
-atheroma@deposit of cholestrol, fibrous tissue, dead muscle cells , blood platelets inside lining of arteries
-atheroma is also known as arteriosclerosis or hardening of the arteries
-patches of atheroma are called plaque

1. HYPERTENSION ( HIGH BLOOD PRESSURE)

-when arteies become narro due to atheroma
-heart has to pump blood more forcefully to maintain blood flow
-consequently , blood pressure exerted on the artery walls build up
-if this continue , result in hypertension
-hardening of the artery wall due to atheroma will cause the wall to loose its elasticity
-this loss in elasticity will result in higher blood pressure
-hypertension can also cause tiny arteries to rupture
-blood capillaries in the brain rupture , the person suffers a stroke
-resulting in brain damage and paralysis of the body

2. CORONARY HEART DISEASE, ANGINA PECTORIS, MYOCARDIAL INFARCTION

 -If an  embolus , atheroma , thrombus(blood clot) occurs in the coronary arteries
-a region of the heart muscle will be deprived of oxygenated blood
-will lead to a gripping , acute chest pain known as angina pectoris
-which sometimes extends down the left arm
-in a severe coronary thrombosis, the heart muscle supplied by the blocked coronary arteries may be suffocated
-due to inadequate supply of oxygen
-commonly called heart attack or myocardial infarction
-the heart beat muscle becomes increasingly fast and irregular
-this condition called ventricular fibrillation

CHAPTER 8(b) - TRANSPORT SYSTEM IN VASCULAR PLANTS

XYLEM AND PHLOEM 

-Xylem tissues transport water and dissolved minerals
-phloem tissue transport organic compound and dissolved  food substance
-transportation of water  substances by phloem is called translocation

UPTAKE OF WATER BY THE ROOT

-Water is absorbed into root hairs by osmosis as a result of water potential

-water potential exist because higher concentration of dissolved substance in the cell sap of the vacuoles

-the water potential of the soil solution is higher than the cell sap of the root hair

-water molecules will move to the root hair from the soil by osmosis

-via the fully permeable cellulose wall and semi permeable cell membrane

-At times , water is actively taken into the root and require energy

MOVEMENT OF WATER ACROSS THE CORTEX OF THE ROOT 

-From ROOT HAIR , water is passed through the cortical region of the root

-comprising mostly of parenchyma cells

-water movement across the root cortex may occur in three ways

1. APOPLAST PATHWAY

-water diffuse through the pores of cellulose cell wall

-pathway works only when there is a water potential gradient

-water potential gradient of the root cells is always negative than the soil solution

-water is also drawn is this pathway by effect of transpirational stream

-however, upon reaching the endodermis cells, water is forced to move from the apoplast pathway into the cytoplasm of the cells

-as movement of water is prevented by the waterproof suberin of the casparian strip

-in this way water does not leak easily

2. SYMPLAST PATHWAY

-water is able to move quickly across the root through pores called plasmodemata

-which link the cytoplasm of adjacent  cortical cells

-water moves down the water potential gradient

- water potential gradient is always maintained to the xylem through the cortex  from the root hairs

3. VACUOLAR PATHWAY

-water is transported by osmosis from the vacuole of one cell to the vacuole of another 

-through the cell wall

-in this pathway water is transported is a slower rate

-dependent on water potential gradient too

UPTAKE OF INORGANIC IONS BY ROOTS

-Inorganic ions are essential for the healthy growth of a plant

-typically , inorganic ions are taken up by roots by two ways

1. PASSIVE UPTAKE

-Inorganic ions are absorbed into root hairs from the soil by diffusion

-the concentration of the inorganic ions in the soil are higher than the cell sap of the root hairs

-no energy is required

2. ACTIVE UPTAKE

-Inorganic ions are actively transported into the root hair against the concentration gradient

-this is done with the help of channel protein, carrier protein and tonoplast found in root hair

-the ions that released from the complex into the cytoplasm of the root cells cannot move out

-will accumulate in the cytoplasm of the cell

-this causes concentration of ions in the root cells is higher than the soil ions 

-the carrier molecule that are released will return to carry new ions from outside cell membrane

-most of the inorganic ions are taken up using this method

-once absorbed by the root hairs ,the inorganic ions will move together with water as a solution across the root cortex either with that three ways

-like water, the movement of inorganic ions may be slowed down by the casparian strip when being transported through the endodermal cells

-inorganic ions will then actively transported  into the xylem from the endodermis

-this will be followed by an influx of water into the xylem which form the basic of root pressure

MOVEMENT OF WATER AND INORGANIC IONS UP THE XYLEM

-Water and inorganic ions move up the stem of a plant through the xylem

-three theories are used to explain the movement of xylem sap up the plant sap against gravity

-root pressure, cohsion tension and transpirational pull

1. ROOT PRESSURE THEORY

-the active transport of inorganic ions into the xylem from endodermal cells

-causes the water potential of the xylem sap to lower drastically

-draws the water  from surrounding root cells to enter the xylem by osmosis

-the hydrostatic pressure generated by this method helps to push water to stem

-but not strong enough to reach the top of tall trees

-root pressure is created by active process which requires energy

-this can be demonstrated when roots subjected to high temperature or poison

-wont show any water being forced out of the stem

-root pressure is believed to cause guttaiton 

-guttation is a process which water oozes out at the tips of the leaves

-normally occurs night or humid day

-guttation ensures water  and dissolved inorganic ions continue to move up a plant when transpiration rate are low

-root pressure alone are too weak to move water up to leaves

2. COHESION  TENSION  THEORY

-transportation of water up the stem was discovered to be pulled from the top of the plant

-this force is caused by the evaporation

-as we know , water will move from high water potential to low water potential

-evaporation occur because the water potential of the atmosphere is lower that in the leaves                 -this will create  a tension which pull water molecules through the xylem vessels

-As water molecules leave the xylem to replace those lost by evaporation, they pull other water molecules with them

-the strong cohesion or stickiness of water allow this to happen

-continuous column of water moving through the xylem vessels forms the transpiration stream

-when water is pulled out of the xylem vessel, a low pressure is created inside the xylem 

-called transpirational pull

-the pull generated this way is sufficient to move water up to the leaves

                                             

CHAPTER 9(a) - NERVOUS SYSTEM

NERVOUS SYSTEM

1. CENTRAL NERVOUS SYSTEM

-brain which receives and process sensory information

-stores memory and generates thoughts and emotions

-spinal cord which conducts to and from brain and control reflex action

2. PERIPHERAL NERVOUS SYSTEM

-include spinal nerve from the spinal cord

-cranial nerve from the brain

-it connects the brain and spinal cord (CNS) to the rest of the body

-it contains two system

(a) SENSORY ( AFFERENT ) NEURONES

-which carry signals to the CNS from sensory organs

(b) MOTOR ( EFFERENT ) NEURONES

-which carry signals from CNS to organs and muscles

-this part of the PNS can be divided into two

SOMATIC NERVOUS SYSTEM

-controls voluntary movements by activating skeletal muscle

AUTONOMIC NERVOUS SYSTEM

-controls involuntary responses by influencing the heart and glands

-this is controlled by medulla oblongata  and hypothalamus of the brain

-it consist of sympathetic nervous system ( FIGHT AND FLIGHT )

-and parasympathetic nervous system ( RELAXATION ) 

NERVOUS SYSTEM

CONTROLS

1. DETECTING CHANGES ( STIMULI )

2. PROCESSING THE INFORMATION

3. INITIATING THE RESPONSES ( TO EFFECTOR )

-The changes within the body or in the outside can be detected by organism is called stimuli

-The collecting of information is carried out by receptor 

-The response to the stimuli depends on activities  of network of nerve cells & neurones

-These cells are specialised for transmitting neural signal which are electrical signal and chemical messages

-These signals are transmitted by from the receptor to the CENTRAL NERVOUS SYSTEM

-By sensory or afferent neurones

-The processing or integration of this information is performed by CNS

-The action by effector are the response to the stimuli

NEURONE 

-functional unit of the nervous system

-specialised for transmitting neural signal from one location to another

-neurone has a large cells body containing the nucleus

-sensory neurone (afferent ) sensory organs to CNS

-motor neurone (efferent) CNS to organ

-interneurones are located in the CNS, they integrate sensory output and motor output

1. DENDRITES 

-short and highly branched 

-specialised to receive to receive stimuli and send signals to the cell body

2. AXON

-extend from the cell body , may be one meter or more in length 

-it conducts nerve impulse away from the cell body

-the axon divides at its end forming many terminal branches at the synaptic terminals

3. SYNAPTIC TERMINALS

-release neurotransmitter chemical that transmit signals from one neurone to another

-the junction between  a synaptic terminals and another neurones is called SYNAPSE

4. MYELIN SHEATH 

-is formed when schwann cells wrap themselves around the axon

5. NODES OF RANVIER

-gaps in the myelin sheath

-at this point the axon is not insulated with myelin sheath

-the axon is described as myelinated

FORMATION OF RESTING POTENTIAL AND ACTION POTENTIAL 

RESTING POTENTIAL

EXCITABLE CELLS - able to generate large changes in their membrane potential

-resting potential is the difference in electrical charge across the cell membrane of a resting neurone

-the potential difference across the cell surface membrane of a resting neurone  or nerve cells is called  its resting potential

-resting potential s about -70mV , negative because  the inside of the cell is more negative

-the resting potential arises from the differences in the concentration inside n outside

-the concentration of K+ inside the cells is high, NA+ is low

-fluid outside the cells,  NA+ is high while K+ is low

RESTING POTENTIAL

UNEQUAL DISTRIBUTION OF IONS IS DUE TO THE FOLLOWING

1. ACTIVE TRANSPORT OF IONS

-pumps found in the cells actively transport sodium ions out of the cell and potassium ion in

-these pumps are driven by the energy supplied by ATP

-for every three NA+ pumped out, two K+ are pumped in

-hence there are greater NA ions outside, and K+ inside

2. PASSIVE DIFFUSION OF IONS ( FACILITATED DIFFUSION )

-not controlled by gates

-allow movement of specific ions down the concentration gradient

-the membrane is more permeable to potassium ion than sodium because there are many potassium ion channel

-more potassium ions diffuse out than sodium ions move into the nerve cells

-sodium and potassium  voltage gated ions channel are closed during this phase

-this unequal distribution of ions causes inside of an axon is more negative than outside

-during resting potential

-the membrane is said to be polarised

ACTION POTENTIAL

-action potential is nerve impulse

-it is an electrical excitation that travels rapidly along an axon

-this result in the change of potential across the axon

-from negative  -70mV to positive +40mV

-an action potential is initiated when  the voltage reached a certain critical point

-known as the TRESSHOLD LEVEL that is -50mV

-membrane potential is made up of by specific voltage gated channel in the plasma membrane

CHARACTERISTIC OF NERVE IMPULSE 

RESPIRATORY PERIOD

-this is the short period immediately after the generation of action potential

-which the neuron cannot respond to another stimulus

-the neurone is insensitive to depolarisation that is the inward movement of sodium is prevented

GENERATION OF ACTION POTENTIAL

1. RESTING STATE

-voltage gated sodium ions and potassium ions are closed

2. THRESHOLD LEVEL

-stimulus open some sodium ion channels

-sodium ions diffuse into the cell

-the cytoplasm of the axon becomes more positive

-when the threshold potential is reached ( -50mV )

-more voltage gated ion channels open

3. DEPOLARISTAION 

-more voltage gated sodium ions open

-the potassium gated channel remain closed

-sodium ions rush into the cells

-the inside of the cell become positive

-an action potential is triggered

4. REPOLARISATION 

-voltage gated sodium ions channels closed

-the voltage gated potassium ions opens

-potassium ions leave the cell

-the loss of positive ions (K+) causes the inside of the cell to become more negative

5.UNDERSHOOT

-the voltage gated sodium ions are closed

-the slow acting potassium ions gates remain open

-allowing potassium ions to keep moving out of the cells

-the continued flow makes the membrane more negative than the resting state

-this is called hyperpolarisation

6. RETURN TO RESTING STATE

-the volatge gated sodium and poatassium ions are closed

-the resting potential is restored by sodium -potassium pumps and passive diffusion of ions through non gated ions channel

CONFUSED ... CHECK THIS OUT 

REFRACTORY PERIOD

1. ABSOLUTE REFRACTORY PERIOD

-this period is immediately after the repolarisation of an action potential @no.5

-the axon potential cannot transmit any new impulsed

-lasts for one milliseconds

2. RELATIVE REFRACTORY PERIOD 

-this is after  the absolute  refractory period 

-when the axon can transmit new impulses if the stimulus is more intense than normally required

-this lasts for 5 milliseconds 

FREQUENCY OF ACTION POTENTIAL

-the stronger the stimulus , the greater the  frequency of action potential set up

SPEED OF CONDUCTIONS

1. DIAMETER OF AXON

-the larger the diameter, the faster the speed of conduction of the action potential 

2. MYELIN SHEATH 

-neurones of vertebrate have an outer covering of myelin sheath produced by schwann cells

-acts as electrical insulator

-myelin sheath is not continuous

-absents at point called node of ranvier

-axon potential cannot form in the part of the axon covered with myelin sheath 

-hence action potential jumps from one node of ranvier to another

-this type of conduction is called saltatory conduction

STRUCTURE OF SYNAPSE AND ROLE OF NEUROSTRANSMITTER 

-Junction of two neurones , between a neurone and is called synapse
-the swelling of the terminal branches of an axon are called synaptic knobs
-cyotoplasm of syanaptic knob contains numerous mitochondria  and synaptic vesicle
-each vesicle contain a chemical called neurotransmitter
-which is responsible for transmission of nerve impulse across a synapse

-beginning of synapse @ presynaptic membrane
-ending of synapse @ postsynaptic membrane
-seperated by a gap of 20nm called synaptic cleft
-postsynaptic  membrane contains a large number of protein molecules
-which acts as a receptor site for the transmitter substance

1. SPREAD OF IMPULSE ALONG AXON

-its always negative inside , positive outside
-K+ inside , Na+ outside , action potential is created when sodium ions move into the cell
-depolarisation , voltage being positive
-repolarisation , voltage being negative
-the difference in potential between the active site and resting membrane parts causes a localised current to be established

2. SPREAD OF IMPULSE ACROSS SYNAPSE