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Syll1bu1 :
Respiration in plants :outline of the process, gaseous exchange.
Abrief outline
of
the
process
mentioning the terms
Glycolysls and Krebs cycle and
their significance.
~
reference
to
be made
to aerobic and anaerobic respiration with chemical equations in each case Experiments on gaseous exchange and on heat
production.
Like all other organisms, plants too requi_re energy for carrying out bodily activities. In this chapter, you will learn about the two kinds of respiration (aerobic and anaerobic), the manner in which diffusion of respirat~ry gases occurs, as well as a number of interesting experiments to demonstrate respiration in plants.
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-single step, but in a series of
h
C
elh:
These steps occur in two "" .q uiaJor
glycolysis (glucose
pyruvate)
P
cytoplasm and
(ii}
Krebs cycle
(~
+6H
20 +
ATP) occurring in Illit0c ate 2. Each breakdown step is due to aenzyme. p3. The energy liberated in the break.~ glucose molecule is not all
in
the fonn but alarge part of it is converted into energy in the form of.
ATP _ a
substance called adenosine triphosp_ When energy in the form of ATP ;, the ATP is converted to ADP (a diphosphate) and again when more __ available by further breakdown of glucose, is reconverted to ATP and so it goes on (Fig. 7.1). One mole of glucose on c
7.1 WHAT IS RESPIRATION?
oxidation yields 38 molecules of ATP. All living cells in aplant, as well as those in ..
BREAKDOWN OF FOOD (GLUCOSE) IN RESPIM
animals, require energy for various activities of the body.
For example,
building up proteins from amino acids, making starch from glucose, absorbing minerals from the soil, or laying down cell walls by plant cells, are all such activities that require energy. This energy is made available by the breakdown of glucose, a simple carbohydrate. The chemical breakdown of glucose occurs by utilizing oxygen and is represented by the following overall reaction: CJ:f uO, + 60 2enzyme >6C0 2 +
6H 20 +
A'fP
+ Hft
(t:f
enJrgy There are three important characteristics of respiration in this equation. I. The breakdown of glucose (C 6H12 O6)to carbon dioxide and water vapour does not occur in a
~CO2 ENERGY H20
HEAT PHOSPHATE ADP ATP
ENERGY USED IN WORK
Fig. 7.1 Diagrammatic representation to shOW the of energy liberated in respiration CONCISE BJOI.O' \ F~ ' !' I1, The energy currency of the cell IATP - d1 11 d h' hi .
'ties insi e a 1vmg ce nee energy w 1c All acuv1 . .j 1ble in the form of ATP as the 1mmed1ate is ava1 ai Hence, this chemical compound ATP is source. f h II" ,'bed as the energy currency o t e ce .descr1 L' g organisms show two types of metabolic , 1vin activities : Q
~
bolic (constructive or biosynthetic processes), (i) ana .. .it consumes energy. (.. ),atabolic (destructive or breaking down processes), uit gives out energy for use by the organism. Respiration is a breaking down process by which aliving cell oxidises organic substances (glucose) and releases carbon dioxide, water vapour and energy. R~spiration is acatabolic J?rocess of releasing energy from glucose for carrying (?Ut life processes.
~
7.2 RESPIRATION vs. BURNING (Combustion)
Sometimes, respiration is compared with burning such as the burning of coal. Both liberate energy, and both give the end products CO 2 and .water vapour. But this comparison is only superficial. The differences between the two are as follows :
Respiration Burning/Combustion
1. Cellular process
Non-cellular
process 2. Occurs
at body Occurs at high temperature temperature
(at ignition point) 3. Occurs in aseries
Occurs in a single step of chemical steps
4. Carried out
by enzymes
Carried out by
heat
5. Biochemical
process
Physico-chemical process 6. Energy is liberated as All the energy is liberated as
ATP and some heat heat and light.
7. No light energy is produced Light energy is produced 7.3 THE ENTIRE PLANT RESPIRES .
## GR,
Every part of a plant such as the leaves, stem, root~, and even the deepest cell placed in any region respires. Oxygen in plants is obtained from the atmosphere through three inlets :
stomata in leaves
lenticels in stem .... ' general surf ace of the roots
R~piration in Planta
Ploughing or tilling of the soil creates tiny air spaces around soil particles and provides the source of oxygen for the roots. Water-logged and c?mpact soil does not have air spaces which affect respiration of the roots. During daytime, due to photosynthesis, the leaves produce oxygen, some of which is used in respiration and the rest is diffused out. The carbon dioxide produced during respiration in the leaves serves as a raw material for photosynthesis. At night, even the leaves obtain oxygen from the atmosphere and give out carbon dioxide.
# ~
# 'lL_J~~~~1~4~:~ :~ '1. Write the important aspects about the overall chemical _equation of respiration, pertaining to the following : (i) number of steps for glucose to break down into CO
> 2
and H 2
0. (ii) involvement of enzymes. (iii) forms of energy liberated. 2.. List three ways in which respiration is different from burning. 3. Name the three inlets of oxygen for respiration in plants.
7.4 TWO KINDS OF RESPIRATION AEROBIC AND ANAEROBIC A. Aerobic Respiration
Normally, free oxygen is used in respiration and there is complete oxidation of glucose with the formation of carbon dioxide and water as end-products. This is clearly represented by the following chemical equation (however, there are numerous steps in the entire process) :
C6H12 0 6 +60 2 enzyme ) 6C0 2 + 6H 20 + 38 ATP (energy/heat) Respiration proceeds only when oxygen (a constituent of air) is available and is therefore called aerobic (or oxybiotic) respiration. e. Anaerobic Respiration
Sometimes, certain parts of the plants (including
> '
# j'it.
fruits and seeds) may temporarily respire even in the absence of oxygen. In this type of respiration, the glucose molecule is incompletely broken down into ethanol
(ethyl alcohol) and carbon dioxide with the release of a small quantity of energy. This chemical reaction can be represented in the following manner :C6H
> 12
Q6
>
2C
> 2
H50H +2C0
> 2
+ 2ATP Glucose Ethanol This type of respiration is called anaerobic (or
anoxybiotic)
respiration as it proceeds even without oxygen. Anaerobic respiration in any part of aplant cannot continue for more than afew days .and the part ultimately dies. But there are certain microscopic organisms such as certain bacteria and fungi which normally respire only anaerobically. Even the germinating seeds when deprived of air respire anaerobically (described in Experiment No. 5Fig 7.7).
> Table 7.1 Ma)or differences between aerobic and anaerobic respiration
> in
> plants
Aaolric rapindiora
Anaerobic respiration
1. Proceeds in the presence Proceeds without using of
> oxygen.
oxygen.
> ,
2. CAmlplek breakdown of Incomplete breakdown of glucose. glucose. 3. End-products are carbon End-products are ethyl , dioxide and water.
alcohol and carbon dioxide. 4. Energy liberated in large Energy liberated in quantity (38 ATP)
from small quantity (2 ATP)
from one mole of glucose. one mole of glucose. 5. Occurs nonnally Occurs
temporarily for
throughout life.
short periods.
1. Give the overall chemical equation for the
)
two kinds of respiration in plants :(i) Aerobic (ii) Anaerobic 2. Mention any one difference other than those reflected in the two chemical equations given above. 3. Certain organisms respire only anaerobically throughout their lives. Name any two such organisms.
7.s EXPERIMENTS ON RESPIRATIQ~ PLANTS
1. Experiment to prove that oxygen is us9e1 in respiration (Fig. 7.2).
An apparatus is arranged as shown in
Fig.
7Flask (A) contains germinating bean seeds and (B) has dead (boiled) seeds tog.et.~er with antiseptic (such as carbolic acid) to avoid bact decay. Wet cotton provides water to both sarnp Asmall tube containing soda lime (a mixture sodium hydroxide and calcium oxide) is suspen in each flask for absorbing any carbon dioXi released by the seeds. After afew days, the deliv tube connected with flask (A) will show agreat rise in water level. When a burning paper introduced into each flask after removing th corks, the flame is immediately put off in flask (A but it:-continues for ashort while in flask (B). proves that oxygen was absent in flask (A) ther showing that it was used up by the germinatin seeds and the volume of oxygen so used up
w
indicated by the rise of water level in the delivery tube. There are two simple questions which you can surely answer. Why is there aslight increase in the level of water in the delivery tube of flask
(B)?
Which of the two flasks, (A) or (B), is acontrol?
> FLASK A
> GERMINATING.......,---,...
> BEANS
> ~~~
> WET COTTON WOOl.
# .,.
> FLASK B
> Fig. 7.2 Experiment to show the utilisation of oxygen in respiration. '
## . ..
f;ONCISE BIOLOGY -IX \ !
> f
> i.
A proper Experiment Must Have : Two Components :
> '
f.XPERIMENTAL and CONTROL SET-UPS
## ! An experiment consists of two set-ups - an : . erimental set-up and a control set-up. Both exp h. h dt hidentical 1n w 1c every con 1 10n 1s t e same
:eptone. ~he ~et-up in which the condition under siudy is missing 1s called the control. -
'. Experiment to prove that carbon dioxide is
2; produced during respiration in germinating
~ seeds (Fig. 7 3).
: Take two flasks~ and B. Place some wet cotton-wool at the bottom of each flask. Soaked seeds (such
> BOILED BEANS WET COTTON WOOL TESTING FOR CO 2l'-'---LIMEWATER
> Fig. 7.3 Experiment to show the production of carbon dioxide in germinating seeds. TWO-H RUBB
s
B
> KOH SOLUTION LIMEWATER (Dissolves any CO 2present in air)
as pea or bean) are placed in flask (A) and an equal number of boiled (dead) seeds are placed in flask (B) (Fig. 7.3). J
A little antiseptic (such as carbolic acid) is added to flask (B) to prevent bacterial growth on dead seeds, which would otherwise respire and release carbon dioxide. The flasks are securely corked and left in similar conditions of light and temperature. A few days later, the seeds in flask (A) will be found to have clearly germinated and those in flask (B) show no signs of any germination (as they are dead). The gases in each flask are then tested by removing the cork and tilting the flask over a test tube containing limewater (a dilute aqueous solution of calcium hydroxide) and then shaking up the test tube. The expected gas carbon dioxide being heavier than air would "flow down" into the test tube. The gas from flask (A) would turn the lime-water milky, showing the presence of carbon dioxide in it, while the gas in flask (B) will show no effect. Therefore, the conclusion is that the germinating (respiring) seeds give out carbon dixoide. . . ' ~ ~ ..
An alternative meihod for the same
experiment
A similar more directly observable experiment to. show that carbon dioxide is prod~ced during respiration in germinating seeds (pea or gram seeds) is arranged as shown in Fig. 7.4. The air drawn in conical flask A is cleared of any CO 2 present in it The clear limewater in flask B confirms that the air entering flask C is CO 2 free. The limewater in flask D turning milky proves that the source of CO was only the germinating seeds. 2
>
> TOAIR SUCTION PUMP LIMEWATER TURNS MILKY Fig. 7.4 To show that carbon dioxide is given out during respiration of germinating seeds.
llespfraUon ha Plants .. IJ 3. Experiment to prove that carbon dioxide is produced by green plants during respiration (Fig. 7.5).
Set up an apparatus as shown in Fig. 7.5 using asmall potted plant such as Geranium. The bell jar should be placed on aglass sheet and its rim as well as all other connections should be vaselined to make them air-tight. The outside air is drawn int? ~e apparatus with the help of an air pump. This air passes through the soda lime which absorbs any carbon dioxide present in the incoming air, and the limewater (Flask A) through which it passes
will
not tum milky. As the air leaves the bell jar, and passes through another sample of limewater (Flask B), the carbon dioxide present in it would turn the limewater milky. It is necessary that this experiment is carried out in the dark, or the bell jar is completely covered by apiece of
black
cloth to prevent photosynthesis (so that the carbon dioxide liberated in respiration is not used up in the synthesis of starch). AIR ~==~
> SODA LIME CO 2FREE
> AIR
> FLASK A
> -AIRl I,
> AIR
> SUCTION PUMP LIMEWATER LIMEWATER (Clear) (Tums milky)
> Fig.
> 7.5 Experiment to show that carbon dioxide is given out by agreen plant during respiration.
4. Experiment to show that heat Is evolved during respiration (Fig. 7.6). Take two thermoflasks and mark them (A) and (B). Take about 30 g of pea or bean seeds and soak them in water for more than
24
hours. 'Divide the seeds into two equal groups. Kill one group of
seeds by boiling them, and then wash them with dilute formalin or carbolic acid to prevent bacterial decay. Put the live germinating seeds in 11 ... ~THERMOMETER
A.
(Experiment) WET COTTONWOOL
> en
> Cww
> en
> C, z
~
> .z
# -
> ~
> a: wC,
..
B
(Control)
> Fig. 7.6 Experiment to show liberation of \heat during germination. ,
flask (A) and the killed ones in flask (B): Insert thermometer in each flask and plug their mo with cotton wool. After afew hours, thermometer in flask A will
show ahigher rea thus indicating that the germinating (live
an
respiring) seeds give out heat. The thermometer flask
(B) will
not show any rise in temperature.
5. Experiment to demonstrate anaerobi respiration (Fig. 7 .7).
Take eight to ten soaked and peeled pea se in atest tube. Fill the test tube with mercury
an
invert the test tube in abeaker filled with mercurf -.The .. see_ds will be_ completely surrounded
by
mercury. After about two dayS: the level of mercury
in
the test tube will fall (Fig. 7.7) and the liberated gas will be found to be carbon dioxide. Carbon dioxide can be tested by. introducing a stick of potassium hydroxide into the test tube, which will
float up through mercury and on coming into contact
with
the gas, will absorb the carbon dioxide ~d the level of mercury will again rise. Asimilar control experiment could be set up in which the seeds may be kept after killing them by heating and sterilizing them with some antiseptic. No gas will be
# Jiu39Mia th(Will GERMINATING __,,___,,, SEEDS
> i
.. .l +\II
> ~-MERCURY--
# 11
~n~
> .-I
# ..
> AFTER 2-3 DAYS
> Fig. 7.7
> Experiment to demonstrate anaerobic respiration.
liberated in the control.
[Note
:
Peeling off the seed coat of the germinating seeds before introducing them into the test-tube may hasten the outward diffusion of CO)
# I
1. In experiments on respiration, the seeds taken 1as control are boiled. Why ? :
2. What is the use of the following in the experiments on res pi ration ?
Respiration
-
the opposite of photosynthesis.
In the differences mentioned in Table 7.2 below, there are at least five points in which photosynthesis and respiration are exactly opposite to each other. Can you make out these points?
1.
2. 3. 4. 5. 6. 7.
Table 7.2 Photosynthesis and Respiration Contrasted PHOTOSYNTHESIS RESPIRATION
Occurs only in the Occurs in all living cells. presence of chlorophyll .Occurs only in the Occurs at all
times.
presence of light. Uses carbon dioxide Uses oxygen and and water. glucose. Oxygen is released Carbon dioxide is as an end product. released as end product. Light energy is -Chemical energy
> is
partly converted into converted into heat and chemical energy which partly into useful energy is stored.
> -
for various activities. ~ Results in gain in weight. Results in loss in weight
> .
Food (glucose) is Food (glucose) is broken manufactured. down oxidised (Constructive or (Destructive or anabolic process )catabolic process)
-j;
> I
(i) Soda lime (ii) Limewater __ 3. Suppose we conduct an experiment to 7 .7 RESPIRATION IN PLANTS COMPARED
demonstrate respiration in a green plant What
WITH RESPIRATION IN ANIMALS
special precaution is required to be taken in It? .. 4. In experiment no. 5, we are using mercury in the test tube and the beaker. Why can't we use water instead ?
7.6 RESPIRATION CONTRASTED WITH PHOTOSYNTHESIS
.In
many respects, respiration and photosynthesis in plants are distinctly opposite processes. The requirements of one are the products of the other and therefore, they are complementary to each other. Th 15 1s the reason why we cannot conduct an :.XPeriment on plant respiration during daytime, in ght The fundamental differences between plant respiration and photosynthesis are given in Table 7.2.
> i
~ir-~ttum In Plants The basic aspects of respiration are same in
all
organisms. However, there are some differences in respiration between plants and animals. For
example:
(i) In plants there is no gaseous transport, the respiratory gases simply diffuse in and out by cell to cell diffusion. In animals, the blood transports respiratory gases. (ii) One of the end products of anaerobic respiration in plants is
ethanol/ethyl alcohol while in animals it is lactic acid.
(iii) In plants the process produces little heat as
compared to animals. ,.. .Fill in the blanks : In anaerobic respiration in plant s, th e e nd 1d t
and ...... pro UC IS . .instead of ............
~
... ... in animals. .
2. The table below is intended to give _certain differences between photosyn th esis and respiration, but a few points are given ~rongly. Strike out the wrong ones and wnte the correct words instead.
PHOTOSYNTHESIS
(i) Results in loss in weight (ii) Sucrose is the product
RESPIRATION
Results in gain in weight Sucrose is broken down Occurs in all . (iii) Occurs in green cells only cells l. (iv) Uses water and oxygen POINTS TO REMEMBER
> l
Uses glucose and . 'oxygen ;
> ~
> - . .:~1
> , - t
## .
# -
Why one should not sleep under a tree at night
I ?
co or something e se .,.
> 2
The carbon dioxide released by trees du t'on at night is too little to cause any hresp1ra 1 (we have much more of this gas~ o~ bedroollls But the droppings of the perchmg birds and night-active insects, spiders, snak~s, etc., are rdangers. But believe it, there are no ghosts or sp resting on the trees! However, sleeping under a tree during hot mid-day is definitely good as one gets both oxygen due to photosynthesis and , coolness due to ... , . .
~. transpiration._
> ~
> ,
Respiration is the breakdown of glucose to yield energy in the form of ATP.
The breakdown of glucose occurs in two major phases : glycolysis and Krebs cycle. '..
Respiration occurs in a series of steps carried out by enzymes.
The plants have three inlets for oxygen from the atmosphere - stomata in leaves, lenticels in stem and the general
surfac
.:
of the
root
There are two kinds of respiration - aerobic (using oxygen and releasing carbon dioxide, water and energy) and anaerob (without using oxygen, releasing ethanol, carbon dioxide and energy). . _ :.
Aerobic respiration occurs normally thoughout life, whereas anaerobic respiration occurs temporarily for short periods.
In plants, respiration is opposite to photosynthesis with respect to several features, e.g. gases used and released.
gain
, loss in weight, etc. . . . . . .
~
.. . . . ,.
A. MULTIPLE CHOICE TYPE
J. Choose the correct answer from the options given
below:
(a) _ Glycolysis is a process (i) in which glycogen is broken down into
glucose
(ii) which occurs in mitochondria
(iii) in which glucose is broken down into ruvate
. , '-. < . ,. . , . -
> .,_ 11 ~ l' . .1t
(b) In plants, a common function is perl'onned b. (i) Stomata and veins (ii) Stomata and lenticels . .
> ..
(iii) Lenticels and sepals (iv) Lenticels and hydathodes (c) Anaerobic respiration no