form 4 biology chapter 7 - respiration

7/27/2019 Form 4 Biology Chapter 7 - Respiration

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Chapter 7 : Respiration

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7.1 Respiratory process7.1.1 Energy for living processes

1. All living processes require energy.a) Movements (muscle contractions, movement of chromosomes, cell movements)

b) Catalytic processes (break up complex molecules release energy)c) Anabolic processes (build up complex molecules ; build new cells)d) Maintaining constant body temperature

(generate heat energy to maintain optimum internal environment)

e) Active transport (across plasma membrane against concentration gradient)f) Secretions (enzymes and mucussecreted, packaged, transported)

2. Energy isa) locked up as chemical bonds (as chemical energy)in organic food

molecules (mainly carbohydrates)

b) released during oxidation of food substances in mitochondria of cellsc) supplied in the form that can be used by body cells (ATP)

3. Respiration = oxidation of food substances in the mitochondria of cells torelease energy

7.1.2 Main substrate (reactants) for energy production1. Main substrate (primary energy source)>> glucose

In plants,i. glucose molecules are synthesised from H2O and CO2

during

photosynthesis (in chlorophyll with the presence of sunlight)

ii. some glucose molecules >>oxidised by plant to produceenergy

iii. extra glucose molecules>>converted tostartch/a.a (foodreserves)

In other heterotrophs(cannot synthesise food, only feed on others),i. glucose molecules are obtained from the digestion of

complex

carbohydrates in their food

2. Other substrate (secondary energy sources)>> proteins, fats Must be converted to glucose in liver to produce energy

7.1.3 Types of respiration

Respiration

Aerobic respiration Anaerobic respiration

Cell respiration Gaseous exchange


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Aerobic respiration(respiration that uses oxygen)

Breakdown of glucose to produce energy in the presence of oxygen

i. Breakdown of glucose is complete (release useful ATP+body heat)ii. Release more energy than anaerobic resp. >> more efficient

(A) Gaseous exchange (external respiration / breathing)i. Involve mechanical process of inhalationand exhalationof air into

and out of our lungs

ii. Transfer oxygen from surrounding medium (air & H2O)to cellsiii. Eliminate products of respiration (CO2& H2O) to surrounding

medium

(B) Cell respiration (internal respiration / tissue respiration)i. Involve oxidation of glucose molecules to produce E, CO2, H2Oii. Site : mitochondria of living cells (plants and animals)

Energy production from glucose

1. Glucose is gradually oxidised in a series of enzyme-catalysedreactions.

2. Some energy is lost as body heatSome energy is used to synthesise ATP molecules (energy store)

3. Synthesis of ATP(store energy in A-P-P~P chemical bond) Add 3rdP to ADP using energy from oxidation of glucose 1 glucose molecule2898kJ energy 38ATP + body heat

4. Breaking up of ATP (releases energy stored in A-P-P~P bond) Separated ADP and P is recycled back to an ATP using energy

from oxidation of glucose.

Anaerobic respiration(respiration that takes place in the absence of oxygen)

Breakdown of glucose to produce energy in the absence of oxygen

i. Breakdown of glucose is incompleteii. Only release a small amount of energy >> inefficient

(A) In animals (human muscle cell)produce lactic acid and energyVigorous activity

Muscle cells contract repeatedly and rapidly Demand for oxygen increases Oxygen consumption exceeds oxygen supply

Anaerobic respiration takes place

In the absence of oxygen, glucose is broken down into lacticacid and energy (150kJ)

Energy is used to synthesise 2ATP (from 2ADP + 2P)

Oxygen debt (build-up of lactic acid in muscles)

Lactic acid : toxic, cause muscle fatigue, pain & crampsLungs

Continuous deep & rapid breathing : repay oxygen debt Lactic acid is transported from muscles to liver

Liver

lactic acid is oxidised to produce energy (2ATP)

Energy converts lactic acid back to glucose

Muscles Glucose returns to muscles Excess glucose is converted to glycogen for storage


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(B) In yeast(fungi)and plantsproduce ethanol, CO2and energya) Anaerobic respiration in yeast = alcohol fermentation

Used in bread, beer and wine productionb) In the absence of oxygen, yeast produces enzyme zymaseto

catalyse conversion of ethanol, CO2and energy

c) Only small amount of energy from glucose is released.The rest of energy : store in chemical bonds of ethanol

Similarities

Both are cellular respiration Both break up glucose molecules (catabolism) Both produce ATP molecules (anabolism) Both take place in living organisms (animal and plant cells) Both produce heat energy as by-product Involve energy expenditure

Differences

Aerobic respiration Aspect Anaerobic respiration

RequiredOxygen

requirementNot required

CompleteBreakdown of

glucoseIncomplete

CO2+ H2O ProductsYeast : CO2+ ethanol ;

Muscle cells:lactic acid

Large amount (2880 kJ)Energy produced

per glucose

molecule

Small amount(210 kJ in fermentation

150 kJ in muscle cell)

3238 molecules

Number of ATP

produced per

glucose molecule

2 molecules of ATP

In cell mitochondria Location In cell cytoplasm


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7.2 Respiratory structures and breathing mechanisms7.2.1 Respiratory structures and adaptations

1. Breathing Involve pumping movements to ventilate the respiratory surface

i. In humans, chest movementsinflate and deflate lungsii. In fish, mouth movementsallow water to pass over gills To maximise the process of gaseous exchange Only take place in complex organism (amoeba, planarian, earthworm)

2. Respiratory structure organisation and arrangement of different parts of a respiratory

system (to be well adapted for gaseous exchange)

3. Respiratory surface / membrane thin and moist membrane that allows oxygen to diffuses into the

body and carbon dioxide to diffuses out of the body

Adaptations of respiratory surfacesi. Large surface area

o maximise the exchange of gasesii. Moist respiratory surface

o diffuse gases in fluid(before diffusing across resp. surface)iii. Thin respiratory surface (one-cell thick)

o for effective diffusion of gasesiv. Network of blood capillaries (beneath respiratory surface)

o provide a rich blood supply to transport gases to andfrom respiratory surface (except protozoa and insects)

Surface area : Volume Ratio (

; SA/V)

1. SA/V ratio = surface area available for gaseous exchange per unitvolume of organisms body

2. For small organisms (planarians ; protozoa amoeba, paramecium) Respiratory surface = body surface Has high SA/V ratio >> high rate of gaseous diffusion (sustain life) Respiratory surface area is large enough for efficient diffusion of

gaseous through its body volume >> to sustain life

3. For large organisms (mammals) Has low SA/V >> low rate of gaseous diffusion (cannot sustain life) Cannot exchange gas by simple diffusion through body surface Has developed specific respiratory structures (trachea, gills, lungs) Contain large respiratory surface areas (for effective gaseous exchange)

i. In fishfilaments and lamellaeii. In amphibians and mammalsair sacs or alveoli in lungs


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Conclusion

a) When the size of an organism increases (x), the value of SA/V ratiodecreases rapidly.

b) Thus, it is impossible for large organisms to sustain life just byexchanging gases through their body surface.

(A) Respiratory structure of protozoa (amoeba and paramecium)

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1. Protozoa = aquatic unicellular animals (inactive)2. Protozoa has no specific respiratory structures

No breathing mechanism is required3. Respiratory surface = plasma membrane

The plasma membrane is fully permeable to gases Diffusion of gases occurs all over the whole plasma membrane in

aqueous solution

4. Diffusion of gases involvei. Oxygen diffuses from surrounding aqueous solution into

cell, down the concentration gradient of O2

ii. Carbon dioxide diffuses from the cell into external aqueoussolution, down the concentration gradient of CO2

5. Has high SA/V ratio diffusion of gases is highly efficient sufficient to sustain life

Length, x(cm) Surface area, SA (cm2) Volume, V (cm3) SA/V (cm-3)

1 6 1 6

2 24 8 3

3 54 27 2

4 96 64 1.55 150 125 1.2

6 216 216 1


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(B) Respiratory structure of fish (multicellular aquatic animal)

1. Structuresa) Impermeable scalescover the skin of bony fish

b) Gillsresp. structure (allow gaseous exchange to occur) Four pairs of gills in the pharynxtwo pairs on each side

c) Gill arch / bony arch Support each gill Has 2 rows of gill filaments (arranged in V-shape)

d) Gill filaments (thin flaps that lie on top of each other, like book pages) Has vertical folds called gill lamellae

e) Gill lamella (resp. surface) Allow gaseous exchange to occur

2. Has small SA/V rationeeds a breathing mechanism to sustain life

3. Breathing mechanismventilation of gillsTo take in water To force water out

Mouth Opens Closes

Operculum (gill cover)Closes against body

wall-

Floor of mouth Lowers down Rises upwardsVolume of buccal cavity Increases Decreases

Pressure of buccal cavity Decreases Increases

Movement of water Forced into the mouth

Forced back over gills ;

Operculum is forced

open by flowing water,

water flows out

4. Gas exchange at respiratory surface

a) Blood vessels bring deoxygenated blood to gill filaments, andthrough tiny capillaries in gill lamellae.

b) In capillaries, blood flows in opposite direction to the flow of waterover lamellae. This helps in absorption of oxygen.


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(C)Respiratory structure of amphibian (frogs and toads)

1. Amphibian : spend its life partly in water and partly on land Its respiratory structure is adapted for both water & land respiration

2. Cutaneous respiration (supply most of the oxygen required by amphibian) Thin and moist skin (has mucous glands in skin) Skin has network of blood capillaries (well supplied with blood) Atmospheric oxygen dissolves in the mucus and diffuses into blood

capillaries

3. Buccal respiration Buccal cavity and pharynx

o Covered by thin epitheliumo Has underlying blood capillaries network

Ventilation of buccal cavityi. Mouth closes, buccal floor lowers, volume of air in buccal

cavity increases, air pressure decreases in the buccal cavity.

ii. Atmospheric air is sucked through nostrils.iii. Oxygen from buccal air dissolves in the epithelial moisture,

4. Pulmonary respiration (when need for oxygen is great swimming, jumping) Has a pair of lungs connected to a short bronchus, which opens to

the pharynx through glottis

o Each lung is moisto Has several hundreds of tiny alveoli (air sacs)o

Each alveolus has a network of blood capillariesunderneath a thin layer of epithelium

In the lungs, oxygen dissolves in the moisture on the epitheliumbefore diffusing across the thin epithelium into blood capillaries

Carbon dioxide diffuses out of the blood capillaries into the lungs5. Breathing mechanismventilation of buccal cavity and lung

(A)Inspirationa) Fill buccal cavity with air

Glottis closes, floor of mouth lowers, nostrils open

Air is sucked into buccal cavityb) Force air into lungs

Nostrils close, glottis opens, floor of mouth rises Air is forced into lungs

c) Both steps repeat to take in more air, pumping frogs toconsiderable size

(B)Expirationa) Nostrils and glottis open, air flows out of its lungs


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(D) Respiratory structure of insects (active animal, need lots of oxygen)

1. Respiratory system of insects = tracheal system Has network of small tubes that channel oxygen directly from

atmosphere outside to every cell of body

Gases are not transported by blood2. Spiracles

Spiracle = valve-like opening (allow air to enter the body of insect) Located on both sides of the thorax and abdomen of most insects One pair of spiracles (one spiracle on each side)per body segment Most adult insects have 2 pairs in thorax and 8 pairs in abdomen

3. Trachea (a system of large tubes)and tracheoles (branch of trachea) Are kept open by stiff rings of chitin(proteinmade exoskeleton) Trachea branch in a tree-like network of smaller tracheoles Tracheoles end on plasma membrane of every cell in body cells of

insects

4. Gas exchange at respiratory surfacea) Tracheolesno chitin lining, have thin, moist& permeablewall

i. Oxygen dissolves in fluid-filled tips of tracheoles in restingmuscles

ii. When muscles contract, the fluid with dissolved oxygen isdrawn deep into muscle cells, making diffusion of oxygen into

the cells faster

iii. Carbon dioxide diffuses from the cells into the tracheoles andtrachea down the concentration gradient of CO2

b) Atmospheric air moves through spiracle into tracheal systemi. Mainly by diffusionii. Oxygen diffuses from atmosphere into tracheal systemiii. Carbon dioxide diffuses from tracheal system into atmosphere

5. Breathinga) Smaller or less active insects : entirely by simple diffusion

b) Larger or more active insects : breathe to ventilate tracheal systemi. Muscles in abdomen contract and compress inwards

force air out of the tracheaii. Muscles relax to spring abdomen back to its normal volume

suck in fresh air


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(E) Respiratory structure of humans

1. Structures of human respiratory systema) Nose and nasal cavity

b) Pharynxc) Larynxd) Tracheae) Bronchi and bronchiolesf) Lungs (left and right)

2. Passage of air : nostrilsnasal cavity pharynxglottislarynxtracheabronchusbronchiolealveoli


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3. Mechanism of respirationa) Breathing mechanism : replenish supply of oxygen in lungs and

expel excess carbon dioxide from it

b) Lungs are covered by a double layer of pleural membrane contains pleural fluid

pleural fluid : lubricant between lungs and thorax duringbreathing

c) Lungs do not have any musclesThe expansion and contraction of lungs are caused by

i. Movement of rib cagea. external intercostal muscle running downward toward sternum pull ribs together raise rib cage during respiration

b. internal intercostal muscle running at right angle to external intercostal muscle lower rib cage during expiration

ii. Movement of diaphragm


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4. Manipulating models to explain breathing mechanism in human(A)Bell Jar Lung Model

a) To demonstrate movement of diaphragms during respirationb) Assembling the model

i. Bell jar = thoraxii. Y-glass tube = trachea and bronchiiii. Balloons attached to open ends of Y-glass tube = lungsiv. Balloon rubber membrane = diaphragm

c) Mechanisms of bell jar lung modeli. Inspiration

Pull down diaphragm Volume of cavity ( ) Pressure of cavity ( ) Outside air rushes in to equalize the pressure

balloons inflate

ii. Expiration Push up diaphragm Volume of cavity ( ) Pressure of cavity ( ) Air in balloons is being forced outdeflate

(B)Rib cage Model

a) To demonstrate the rib cage movements caused by intercostalmuscles during respiration

b) Assembling the modeli. Plywood of suitable sizes & shapesRib cage model

= sternum, ribs, vertebrae column

ii. Rubber band that slants forwards and downwards =external intercostal muscles

iii. Rubber band that slants backwards and upwards =internal intercostal muscles

c) Mechanisms of rib cage modeli. Inspiration

External intercostal muscles contract Internal intercostal muscle relax Rib cage is raised upwards and outwards

ii. Expiration Internal intercostal muscles contract External intercostal muscles relax Rib cage is pulled downwards and inwards


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7.3 Gaseous exchange across respiratory surfaces andtransport of gases in humans

7.3.1 Process of gaseous exchange (alveolus & capillaries)1. Characteristics of respiratory surface in alveoli

Large surface area (about 70m2) Thin one-cell thick epithelial surface Moist and permeable epithelial surface Has underlying capillary network (one-cell thick)

2. Partial pressure of a gas = pressure exerted by a particular gas can be said as concentration of the gas (higher conc, high p.pressure) diffusion at respiratory surface (to exchange respiratory gases)

o from high partial pressure region to low partial pressureregion (down the partial pressure gradient)

Gas

Partial pressure in

EffectsAlveolar

air

Alveolar

capillaries

O2 High Low O2diffuses from alveolar air into capillaries

CO2 Low High CO2diffuses from capillaries into alveolar air

Gas

Partial pressure in

EffectsTissue

capillariesBody cells

O2 High Low O2diffuses from tissue capillaries into body cells

CO2 Low High CO2diffuses from body cells into tissue capillaries

Exchange of O2and CO2between alveolus and blood capillaries in lungs

Deoxygenated blood:

a) enters the capillaries around alveolusb) has less O2(low PO2)and more CO2(high PCO2)than alveolar airc) oxygen diffuses from alveolar air into blood capillaries down thepartial pressure of oxygen

o oxygen combines with haemoglobin (respiratory pigment thathas strong affinity for oxygen)to form oxyhaemoglobin

o oxyhaemoglobin is transported away from lungs to otherbody parts

d) carbon dioxide diffuses from blood capillaries into alveolar airdown the partial pressure of carbon dioxide


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7.3.2 Transport of respiratory gases

Transport of O2(lun gs to respir ing body cells)and gaseous exchange

1. In the form ofa) Dissolved gas molecules in blood plasma (1%)

b) Oxyhaemoglobin in red blood cells (99%)

o Oxygen is constantly being used up by body cellso Partial pressure of oxygen in body cells >> lowo Oxyhaemoglobin gives upoxygen to body cells

(that has low PO2)

Transport of CO2(respir ing body cells to lungs)and gaseous exchange

1. In the form ofa) Dissolved gas molecules in blood plasma (5%)

b) Carbamino-haemoglobin in red blood cells (10%)

c) Bicarbonate/Hydrogen carbonate ions in blood plasma (85%)

2. When blood carrying CO2reaches the lungs,a) Bicarbonate ions : convert back to CO2 and diffuse into alveolar air

b) Carbamino-haemoglobin : breaks down to release CO2and diffuseinto alveolar air

c) Dissolved CO2in blood plasma : diffuses from capillaries intoalveolar air down the partial pressure gradient of CO2


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Composition of inhaled and exhaled air

1. Inhaled air = air we breathe in Has normal percentage composition of different atmospheric gases

2. Alveolar air = air inside alveolus Contains atmospheric air + residual air (air already in the lungs) Oxygen : lowest % composition

o O2diffuse into blood capillaries Carbon dioxide : highest % composition

o CO2diffuse directly from blood capillaries into alveolar air Water vapour : saturated

o the by-product of cellular respiration is excreted Nitrogen : similar % composition

o not used up by body cells3. Exhaled air = air we breathe out

Oxygen : lower % than inhaled air, higher than alveolar air Carbon dioxide : lower % than alveolar air

o diluted by residual air in trachea and bronchi Water vapour : saturated Nitrogen : similar % composition


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7.4 Regulatory mechanism in respiration7.4.1 Changein the rateofrespiration after vigorous exerciseRate of respiration = number of breaths (inhalation + exhalation)per min.

determined by counting no. of times the chest rises or falls per min. increase during exercise, excitement, pain, fever decline during relaxation and sleep normal rate = 1420 times per minutes

Correlation between rate of respiration with O 2and CO2 contents in body

1. Vigorous physical activities increase metabolic rate causing:a) an increase in oxygen consumption for cell respiration to release

more energy

b) an increase in carbon dioxide production2. When oxygen is low and carbon dioxide is high, the body reacts by:

a) raising rate of respiration bring in more O2 eliminate excess CO2

b) increasing rate of heart beat transport more O2to respiring body cells transport excess CO2to lungs

c) dilating the arteries of body cells increase O

2supply

speed up removal of CO2


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Regulatory mechanism of oxygen and carbon dioxide contents in body

1. Regulation of breathing (or ventilation) is automatic Can still exercise voluntary control over breathing muscles (esp.

during singing, shouting, blowing, stop breathing)

2. Respiratory centre is a group of cells situated in the medulla oblongata (hind brain) consists of inspiratory centre and expiratory centre regulates basic rhythm of breathing (breathing rate)

o by controlling the intensity & frequency of contractions of: intercostal muscles diaphragm (muscles)

3. Chemoreceptors = sensory receptors in the body that responds tochemical stimuli (conc. of CO2main stimuli ; conc. of oxygen)

a) Central chemoreceptorsi. Located in the medulla oblongataii. Detect the increase of CO2in blood indirectly

Sensitive to the formation of H+that enters thecerebrospinal fluid (fluid flowing around brain &

spinal cordprotect brain & spinal cord)

b) Peripheral chemoreceptorsi. Consist of carotid bodies on carotid arteries and aortic

bodies on aorta

ii. Sensitive to pH values greatly reduced amount of oxygen

4. General respiratory regulatory systema) When the body exercises vigorously, it usesup O2and releases CO2.

b) Chemoreceptors detect the high conc. of CO2and low conc. of O2.c) Nerve impulses are sent to the respiratory centre.d) The respiratory centre will send nerve impulses for body to react.

o by adjusting the contractions of intercostal muscles anddiaphragmcausing more rapid and deeper breathing


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Regulation of respiration by central chemoreceptors(detect CO2through H+)

1. Central chemoreceptors are sensitive to H+in cerebrospinal fluid.2. Increased physical activity increases production of carbon dioxide.3. Carbon dioxide dissolves in blood plasma to form carbonic acid.

Carbonic acid dissociates into bicarbonate ions and hydrogen ions.

4. The H+ions in blood plasma enter into the cerebrospinal fluid.5. The central chemoreceptors in the medulla oblongata detects the

increase of H+ions. Nerve impulses are sent to the respiratory centre.

6.

The respiratory centre then send nerve impulses to the intercostalmuscles and the diaphragm muscles.

Stronger and more rapid contraction is produced7. Breathing becomes faster & deeper CO2levels return to normal.

Regulation of respiration by the peripheral chemoreceptors (detect O2level)

1. Peripheral chemoreceptors are sensitive to oxygen level in blood. Only activated when oxygen level drops to very low value

o E.g. at high altitudes where atmospheric oxygen is very thin2. At high altitudes (4000m above sea level, 40% less oxygen than at sea level)

May experience mountain sicknesshypoxia (shortage of O2)o Breathlessness, headache, nausea, vomiting, heart

palpitations

Chemoreceptors in carotic and aortic bodieso detect stimulus ( PO2)send nerve impulse to medulla

oblongata

o medulla oblongata is stimulated to increaserate of respiration and rate of heartbeat

o unpleasant symptoms wear off acclimatized3. Oxygen levels are secondary stimuli (normally not important to increase

respiration)

For healthy people, oxygen level rarely decrease to the point ofstimulating respiration


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Human respiration in different situations

RelaxingVigorous

activitiesFear

Rate of

respiration(breathing)

At optimal

level

(1420 times

per minute)

Increase

increase supply of oxygen eliminate carbon dioxide

Rate of

heart beat

At optimal

level

(6070 times

per minute)

Increase

pump more blood around the body transport more oxygen to muscle cells remove carbon dioxide and water to lungs

to be exhaled

Rate of cell

respiration

At optimal

level

Increase

produce energy for the body to react

Explanation

To maintain

all normal

body

functions

Body

require lots

of energy

for

muscular

contractions

Brain stimulates adrenalglands to release adrenalin

into bloodstream.

Adrenaline is carried throughbody and reaches lungs, heart

and muscles.

Prepare the body for flight orfight response

7.5 Waysofmaintaining a healthy respiratory systemGood habits

1. Eat a healthy diet to maintain good general health

2. Exercise daily to stay fit and strong

3. Breathe in through the nose, instead of mouth hairs in the nose can filter off airborne particles mucus in the nose can trap the airborne particles

4. Practice breathing exercises Breathe from the diaphragm, breathe in slowly and deeply

Harmful habits

1. Avoid breathing in polluted air(wear proper protective device:facial masks) Has airborne particle (dust, pollen, mould, dirt, soil, ash, soot)

o easily inhaled deep into lungs and absorbed into bodyo may cause lung problems

2. Do not smoke and avoid breathing in secondary cigarette smoke Cigarette smoke enters lungs and poisons the cells

o Tar : collects in lungs when tobacco smokes cool

carcinogenic, bronchitis, damage lung tissue, breakdown alveoli, decrease TSA for gaseous exchange

o Nicotine : cause addiction, high b.p. (narrow arteries)andheart rate, sticky blood (easy to clot stroke)

o Carbon monoxide : limit ability to transport O2(breathless) combines irreversibly with haemoglobin to form

carboxyhaemoglobin

o may cause asthma, bronchitis, emphysema, lung cancer


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7.6 Respiration in plants7.6.1 Energy requirement in plants

1. Need energy for all their living processes Photosynthesis Growth and development Active transport Reproduction

2. Carry out cell respiration to produce energy Need less energy compared to animals Animals need to :

o move from place to placeo keep their bodies warm (esp. homeotherm)o maintain their metabolic rate

7.6.2 Intake of oxygen by plants for respiration1. For unicellular plants (diatomsalgae)

absorb oxygen by diffusion throughout cell surface >> large SA/V2. For green plants (mesophytes and xerophytes)

Has thick cuticle(wax)on epidermiso prevent excessive water loss through evaporationo but make simple diffusion= impossible

need special structures to allow diffusion of oxygena) stomata (tiny pores on leaves and young stems)

o 90% of total intake of oxygen & carbon dioxide takes placeo each stoma is surrounded by 2 guard cellso stoma allows exchange of gases between atmospheric air

and internal tissues of leaf

b) lenticels (on old woody tree trunks and roots)c) roots

o oxygen diffuses from air spaces between soil particles intoroot tissues by diffusion


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Intake of oxygen during the night

1. At night (dark condition), photosynthesis does not take place.2. Oxygen cannot enter into the leaf as stomata are closed.3. Aerobic respiration can still occur because respiring cells can use

a) oxygen from air trapped ini. substomatal air spacesii. intercellular air spaces

b) oxygen taken in through lenticels and root hairs of plantso oxygen dissolves in the thin layer of moisture on the walls

of cells

o then dissolves into respiring cells down the oxygen gradientIntake of oxygen during the day

1. During daytime (has sunlight), photosynthesis takes place.2. Atmospheric carbon dioxide diffuses through the stomata into

chloroplasts of leaves.

Carbon dioxide is used in photosynthesis and oxygen is produced.3. As rate of photosynthesis increases, it exceeds the rate of respiration.

More oxygen is produced to be used up by the respiring plant cells Some oxygen diffuses from chloroplasts into the mitochondria Some oxygen diffuses into the intercellular air spaces and

substomatal air spaces

4. Partial pressure of oxygen in substomatal air spaces is higher than theatmospheric airoxygen diffuses out from the substomatal air spaces

through stomata into atmospheric airdown the partial pressure

gradient of oxygen

Net exchange of gases in a leaf

Daytime Night-time

Main reaction Photosynthesis (has sunlight) Respiration (no sunlight)

Net intake CO2 O2

Net output O2 CO2

Compensation point

1. In the dark, green plant cannot undergo photosynthesis. Respiration still continues Taking in oxygen and releasing carbon dioxide.

2. When light intensity increases (sunrise), rate of photosynthesis increases Oxygen is released, amount of oxygen released increases gradually

3. Compensation point (light compensation point // point of light intensity) No net exchange of oxygen and carbon dioxide

o all the released oxygen (by photosynthesis)is used up in cellrespiration

o all the released carbon dioxide (by cell respiration)is used up inphotosynthesis

4. If rate of photosynthesis and rate of respiration remain at this point:a) No growth and development in green plants

o No extra materials (glucose)are synthesised by photosynthesisb) Oxygen-breathing living organisms will die of suffocation

o Oxygen used is not replenished by photosynthesis


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7.6.3 Type of respiration in plantsAerobic respiration

1. Take place in the mitochondria of plant cells in the presence of oxygen2. Glucose is oxidised to release energy, CO2, H2O

3. Most energy is kept as ATP molecules, some is released as heat energy.Anaerobic respiration(certain green plantsrice plants)

1. Take place in the absence of oxygen for a certain period of time When there is a flood, supply of oxygen to roots is cut off Can only undergo anaerobic respiration

2. Glucose is partially broken down into ethanol and CO2

3. Most energy is still locked up in the ethanol molecule.4. When anaerobic situation prolongs, concentration of ethanol increases

ethanol is toxic to cells poison the plants only plants adapted to flooding can survive >> rice plants

5. Rice plants (high tolerance to ethanol) Has large air spaces (hollow aerenchyma along the stem)

o allowO2topenetratethroughtheroot(that submerged in water) Has shallow roots

o allow easy access to oxygen that diffuses into surface layerof waterlogged soil

Similarities

Both take place in living cells. Both involve changes in chemical energy. Both are necessary for continuity of li fe. Both are enzyme-catalysed reactions. Both are metabolic processes.

Differences

Photosynthesis Respiration

Types of metabolism

Anabolism

(synthesis of organic

materials)

Catabolism

(breaking down organic

materials)

Energy change Stores energy in glucose Releases energy fromglucose

Organelles involved Chloroplast Mitochondrion

Chemical equation

Reactants H2O, CO2 Glucose and oxygen

Products Glucose and O2 CO2, H2O, energy

Chlorophyll

requirement

Yes

(happen only in green plant

cells)

No

(happen in all living

organisms that use oxygen)

Light energy

requirement

Yes

(happen only in the presence

of sunlight)

No

(happen all the time)


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form 4 biology chapter 7 - respiration

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