NCERT Textbook - Transport in Plants NEET Notes | EduRev

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 Page 1


UNIT 4
The description of structure and variation of living organisms over a
period of time, ended up as two, apparently irreconcilable perspectives
on biology. The two perspectives essentially rested on two levels of
organisation of life forms and phenomena. One described at organismic
and above level of organisation while the second described at cellular
and molecular level of organisation. The first resulted in ecology and
related disciplines. The second resulted in physiology and biochemistry.
Description of physiological processes, in flowering plants as an
example, is what is given in the chapters in this unit. The processes of
mineral nutrition of plants, photosynthesis, transport, respiration and
ultimately plant growth and development are described in molecular
terms but in the context of cellular activities and even at organism
level. Wherever appropriate, the relation of the physiological processes
to environment is also discussed.
PLANT PHYSIOLOGY
Chapter 11
Transport in Plants
Chapter 12
Mineral Nutrition
Chapter 13
Photosynthesis in Higher
Plants
Chapter 14
Respiration in Plants
Chapter 15
Plant Growth and
Development
2015-16(19/01/2015)
Page 2


UNIT 4
The description of structure and variation of living organisms over a
period of time, ended up as two, apparently irreconcilable perspectives
on biology. The two perspectives essentially rested on two levels of
organisation of life forms and phenomena. One described at organismic
and above level of organisation while the second described at cellular
and molecular level of organisation. The first resulted in ecology and
related disciplines. The second resulted in physiology and biochemistry.
Description of physiological processes, in flowering plants as an
example, is what is given in the chapters in this unit. The processes of
mineral nutrition of plants, photosynthesis, transport, respiration and
ultimately plant growth and development are described in molecular
terms but in the context of cellular activities and even at organism
level. Wherever appropriate, the relation of the physiological processes
to environment is also discussed.
PLANT PHYSIOLOGY
Chapter 11
Transport in Plants
Chapter 12
Mineral Nutrition
Chapter 13
Photosynthesis in Higher
Plants
Chapter 14
Respiration in Plants
Chapter 15
Plant Growth and
Development
2015-16(19/01/2015)
MELVIN CALVIN born in Minnesota in April, 1911, received his
Ph.D. in Chemistry from the University of Minnesota. He served
as Professor of Chemistry at the University of California,
Berkeley.
Just after world war II, when the world was under shock
after the Hiroshima-Nagasaki bombings, and seeing the ill-
effects of radio-activity, Calvin and co-workers put radio-
activity to beneficial use. He along with J.A. Bassham studied
reactions in green plants forming sugar and other substances
from raw materials like carbon dioxide, water and minerals
by labelling the carbon dioxide with C
14
. Calvin proposed that
plants change light energy to chemical energy by transferring
an electron in an organised array of pigment molecules and
other substances. The mapping of the pathway of carbon
assimilation in photosynthesis earned him Nobel Prize in 1961.
The principles of photosynthesis as established by Calvin
are, at present, being used in studies on renewable resource
for energy and materials and basic studies in solar energy
research. Melvin Calvin
2015-16(19/01/2015)
Page 3


UNIT 4
The description of structure and variation of living organisms over a
period of time, ended up as two, apparently irreconcilable perspectives
on biology. The two perspectives essentially rested on two levels of
organisation of life forms and phenomena. One described at organismic
and above level of organisation while the second described at cellular
and molecular level of organisation. The first resulted in ecology and
related disciplines. The second resulted in physiology and biochemistry.
Description of physiological processes, in flowering plants as an
example, is what is given in the chapters in this unit. The processes of
mineral nutrition of plants, photosynthesis, transport, respiration and
ultimately plant growth and development are described in molecular
terms but in the context of cellular activities and even at organism
level. Wherever appropriate, the relation of the physiological processes
to environment is also discussed.
PLANT PHYSIOLOGY
Chapter 11
Transport in Plants
Chapter 12
Mineral Nutrition
Chapter 13
Photosynthesis in Higher
Plants
Chapter 14
Respiration in Plants
Chapter 15
Plant Growth and
Development
2015-16(19/01/2015)
MELVIN CALVIN born in Minnesota in April, 1911, received his
Ph.D. in Chemistry from the University of Minnesota. He served
as Professor of Chemistry at the University of California,
Berkeley.
Just after world war II, when the world was under shock
after the Hiroshima-Nagasaki bombings, and seeing the ill-
effects of radio-activity, Calvin and co-workers put radio-
activity to beneficial use. He along with J.A. Bassham studied
reactions in green plants forming sugar and other substances
from raw materials like carbon dioxide, water and minerals
by labelling the carbon dioxide with C
14
. Calvin proposed that
plants change light energy to chemical energy by transferring
an electron in an organised array of pigment molecules and
other substances. The mapping of the pathway of carbon
assimilation in photosynthesis earned him Nobel Prize in 1961.
The principles of photosynthesis as established by Calvin
are, at present, being used in studies on renewable resource
for energy and materials and basic studies in solar energy
research. Melvin Calvin
2015-16(19/01/2015)
Have you ever wondered how water reaches the top of tall trees, or for that
matter how and why substances move from one cell to the other, whether
all substances move in a similar way, in the same direction and whether
metabolic energy is required for moving substances.  Plants need to move
molecules over very long distances, much more than animals do; they also
do not have a circulatory system in place.  Water taken up by the roots has
to reach all parts of the plant, up to the very tip of the growing stem.  The
photosynthates or food synthesised by the leaves have also to be moved to
all parts including the root tips embedded deep inside the soil.  Movement
across short distances, say within the cell, across the membranes and from
cell to cell within the tissue has also to take place. To understand some of
the transport processes that take place in plants, one would have to recollect
one’s basic knowledge about the structure of the cell and the anatomy of
the plant body.  We also need to revisit our understanding of diffusion,
besides gaining some knowledge about chemical potential and ions.
When we talk of the movement of substances we need first to define
what kind of movement we are talking about, and also what substances
we are looking at. In a flowering plant the substances that would need to
be transported are water, mineral nutrients, organic nutrients and plant
growth regulators. Over small distances substances move by diffusion
and by cytoplasmic streaming supplemented by active transport.
Transport over longer distances proceeds through the vascular system
(the xylem and the phloem) and is called translocation.
An important aspect that needs to be considered is the direction of
transport. In rooted plants, transport in xylem (of water and minerals) is
essentially unidirectional, from roots to the stems. Organic and mineral
nutrients however, undergo multidirectional transport. Organic
TRANSPORT IN PLANTS
CHAPTER  11
11.1 Means of
Transport
11.2 Plant-Water
Relations
11.3 Long Distance
Transport of
Water
11.4 Transpiration
11.5 Uptake and
Transport of
Mineral
Nutrients
11.6   Phloem
Transport: Flow
from Source to
Sink
2015-16(19/01/2015)
Page 4


UNIT 4
The description of structure and variation of living organisms over a
period of time, ended up as two, apparently irreconcilable perspectives
on biology. The two perspectives essentially rested on two levels of
organisation of life forms and phenomena. One described at organismic
and above level of organisation while the second described at cellular
and molecular level of organisation. The first resulted in ecology and
related disciplines. The second resulted in physiology and biochemistry.
Description of physiological processes, in flowering plants as an
example, is what is given in the chapters in this unit. The processes of
mineral nutrition of plants, photosynthesis, transport, respiration and
ultimately plant growth and development are described in molecular
terms but in the context of cellular activities and even at organism
level. Wherever appropriate, the relation of the physiological processes
to environment is also discussed.
PLANT PHYSIOLOGY
Chapter 11
Transport in Plants
Chapter 12
Mineral Nutrition
Chapter 13
Photosynthesis in Higher
Plants
Chapter 14
Respiration in Plants
Chapter 15
Plant Growth and
Development
2015-16(19/01/2015)
MELVIN CALVIN born in Minnesota in April, 1911, received his
Ph.D. in Chemistry from the University of Minnesota. He served
as Professor of Chemistry at the University of California,
Berkeley.
Just after world war II, when the world was under shock
after the Hiroshima-Nagasaki bombings, and seeing the ill-
effects of radio-activity, Calvin and co-workers put radio-
activity to beneficial use. He along with J.A. Bassham studied
reactions in green plants forming sugar and other substances
from raw materials like carbon dioxide, water and minerals
by labelling the carbon dioxide with C
14
. Calvin proposed that
plants change light energy to chemical energy by transferring
an electron in an organised array of pigment molecules and
other substances. The mapping of the pathway of carbon
assimilation in photosynthesis earned him Nobel Prize in 1961.
The principles of photosynthesis as established by Calvin
are, at present, being used in studies on renewable resource
for energy and materials and basic studies in solar energy
research. Melvin Calvin
2015-16(19/01/2015)
Have you ever wondered how water reaches the top of tall trees, or for that
matter how and why substances move from one cell to the other, whether
all substances move in a similar way, in the same direction and whether
metabolic energy is required for moving substances.  Plants need to move
molecules over very long distances, much more than animals do; they also
do not have a circulatory system in place.  Water taken up by the roots has
to reach all parts of the plant, up to the very tip of the growing stem.  The
photosynthates or food synthesised by the leaves have also to be moved to
all parts including the root tips embedded deep inside the soil.  Movement
across short distances, say within the cell, across the membranes and from
cell to cell within the tissue has also to take place. To understand some of
the transport processes that take place in plants, one would have to recollect
one’s basic knowledge about the structure of the cell and the anatomy of
the plant body.  We also need to revisit our understanding of diffusion,
besides gaining some knowledge about chemical potential and ions.
When we talk of the movement of substances we need first to define
what kind of movement we are talking about, and also what substances
we are looking at. In a flowering plant the substances that would need to
be transported are water, mineral nutrients, organic nutrients and plant
growth regulators. Over small distances substances move by diffusion
and by cytoplasmic streaming supplemented by active transport.
Transport over longer distances proceeds through the vascular system
(the xylem and the phloem) and is called translocation.
An important aspect that needs to be considered is the direction of
transport. In rooted plants, transport in xylem (of water and minerals) is
essentially unidirectional, from roots to the stems. Organic and mineral
nutrients however, undergo multidirectional transport. Organic
TRANSPORT IN PLANTS
CHAPTER  11
11.1 Means of
Transport
11.2 Plant-Water
Relations
11.3 Long Distance
Transport of
Water
11.4 Transpiration
11.5 Uptake and
Transport of
Mineral
Nutrients
11.6   Phloem
Transport: Flow
from Source to
Sink
2015-16(19/01/2015)
176 BIOLOGY
compounds synthesised in the photosynthetic leaves are exported to all
other parts of the plant including storage organs.  From the storage organs
they are later re-exported.  The mineral nutrients are taken up by the
roots and transported upwards into the stem, leaves and the growing
regions.  When any plant part undergoes senescence, nutrients may be
withdrawn from such regions and moved to the growing parts.  Hormones
or plant growth regulators and other chemical stimuli are also transported,
though in very small amounts, sometimes in a strictly polarised or
unidirectional manner from where they are synthesised to other parts.
Hence, in a flowering plant there is a complex traffic of compounds (but
probably very orderly) moving in different directions, each organ receiving
some substances and giving out some others.
11.1 MEANS OF TRANSPORT
11.1.1 Diffusion
Movement by diffusion is passive, and may be from one part of the cell to
the other, or from cell to cell, or over short distances, say, from the inter-
cellular spaces of the leaf to the outside.  No energy expenditure takes place.
In diffusion, molecules move in a random fashion, the net result being
substances moving from regions of higher concentration to regions of lower
concentration.  Diffusion is a slow process and is not dependent on a ‘living
system’. Diffusion is obvious in gases and liquids, but diffusion in solids
rather than of solids is more likely.  Diffusion is very important to plants
since it is the only means for gaseous movement within the plant body.
Diffusion rates are affected by the gradient of concentration, the
permeability of the membrane separating them, temperature and pressure.
11.1.2 Facilitated Diffusion
As pointed out earlier, a gradient must already be present for diffusion to
occur.  The diffusion rate depends on the size of the substances; obviously
smaller substances diffuse faster.  The diffusion of any substance across a
membrane also depends on its solubility in lipids, the major constituent of
the membrane. Substances soluble in lipids diffuse through the membrane
faster.  Substances that have a hydrophilic moiety, find it difficult to pass
through the membrane; their movement has to be facilitated.  Membrane
proteins provide sites at which such molecules cross the membrane.  They
do not set up a concentration gradient: a concentration gradient must
already be present for molecules to diffuse even if facilitated by the proteins.
This process is called facilitated diffusion.
In facilitated diffusion special proteins help move substances across
membranes without expenditure of ATP energy. Facilitated diffusion
cannot cause net transport of molecules from a low to a high concentration
– this would require input of energy.   Transport rate reaches a maximum
when all of the protein transporters are being used (saturation).  Facilitated
2015-16(19/01/2015)
Page 5


UNIT 4
The description of structure and variation of living organisms over a
period of time, ended up as two, apparently irreconcilable perspectives
on biology. The two perspectives essentially rested on two levels of
organisation of life forms and phenomena. One described at organismic
and above level of organisation while the second described at cellular
and molecular level of organisation. The first resulted in ecology and
related disciplines. The second resulted in physiology and biochemistry.
Description of physiological processes, in flowering plants as an
example, is what is given in the chapters in this unit. The processes of
mineral nutrition of plants, photosynthesis, transport, respiration and
ultimately plant growth and development are described in molecular
terms but in the context of cellular activities and even at organism
level. Wherever appropriate, the relation of the physiological processes
to environment is also discussed.
PLANT PHYSIOLOGY
Chapter 11
Transport in Plants
Chapter 12
Mineral Nutrition
Chapter 13
Photosynthesis in Higher
Plants
Chapter 14
Respiration in Plants
Chapter 15
Plant Growth and
Development
2015-16(19/01/2015)
MELVIN CALVIN born in Minnesota in April, 1911, received his
Ph.D. in Chemistry from the University of Minnesota. He served
as Professor of Chemistry at the University of California,
Berkeley.
Just after world war II, when the world was under shock
after the Hiroshima-Nagasaki bombings, and seeing the ill-
effects of radio-activity, Calvin and co-workers put radio-
activity to beneficial use. He along with J.A. Bassham studied
reactions in green plants forming sugar and other substances
from raw materials like carbon dioxide, water and minerals
by labelling the carbon dioxide with C
14
. Calvin proposed that
plants change light energy to chemical energy by transferring
an electron in an organised array of pigment molecules and
other substances. The mapping of the pathway of carbon
assimilation in photosynthesis earned him Nobel Prize in 1961.
The principles of photosynthesis as established by Calvin
are, at present, being used in studies on renewable resource
for energy and materials and basic studies in solar energy
research. Melvin Calvin
2015-16(19/01/2015)
Have you ever wondered how water reaches the top of tall trees, or for that
matter how and why substances move from one cell to the other, whether
all substances move in a similar way, in the same direction and whether
metabolic energy is required for moving substances.  Plants need to move
molecules over very long distances, much more than animals do; they also
do not have a circulatory system in place.  Water taken up by the roots has
to reach all parts of the plant, up to the very tip of the growing stem.  The
photosynthates or food synthesised by the leaves have also to be moved to
all parts including the root tips embedded deep inside the soil.  Movement
across short distances, say within the cell, across the membranes and from
cell to cell within the tissue has also to take place. To understand some of
the transport processes that take place in plants, one would have to recollect
one’s basic knowledge about the structure of the cell and the anatomy of
the plant body.  We also need to revisit our understanding of diffusion,
besides gaining some knowledge about chemical potential and ions.
When we talk of the movement of substances we need first to define
what kind of movement we are talking about, and also what substances
we are looking at. In a flowering plant the substances that would need to
be transported are water, mineral nutrients, organic nutrients and plant
growth regulators. Over small distances substances move by diffusion
and by cytoplasmic streaming supplemented by active transport.
Transport over longer distances proceeds through the vascular system
(the xylem and the phloem) and is called translocation.
An important aspect that needs to be considered is the direction of
transport. In rooted plants, transport in xylem (of water and minerals) is
essentially unidirectional, from roots to the stems. Organic and mineral
nutrients however, undergo multidirectional transport. Organic
TRANSPORT IN PLANTS
CHAPTER  11
11.1 Means of
Transport
11.2 Plant-Water
Relations
11.3 Long Distance
Transport of
Water
11.4 Transpiration
11.5 Uptake and
Transport of
Mineral
Nutrients
11.6   Phloem
Transport: Flow
from Source to
Sink
2015-16(19/01/2015)
176 BIOLOGY
compounds synthesised in the photosynthetic leaves are exported to all
other parts of the plant including storage organs.  From the storage organs
they are later re-exported.  The mineral nutrients are taken up by the
roots and transported upwards into the stem, leaves and the growing
regions.  When any plant part undergoes senescence, nutrients may be
withdrawn from such regions and moved to the growing parts.  Hormones
or plant growth regulators and other chemical stimuli are also transported,
though in very small amounts, sometimes in a strictly polarised or
unidirectional manner from where they are synthesised to other parts.
Hence, in a flowering plant there is a complex traffic of compounds (but
probably very orderly) moving in different directions, each organ receiving
some substances and giving out some others.
11.1 MEANS OF TRANSPORT
11.1.1 Diffusion
Movement by diffusion is passive, and may be from one part of the cell to
the other, or from cell to cell, or over short distances, say, from the inter-
cellular spaces of the leaf to the outside.  No energy expenditure takes place.
In diffusion, molecules move in a random fashion, the net result being
substances moving from regions of higher concentration to regions of lower
concentration.  Diffusion is a slow process and is not dependent on a ‘living
system’. Diffusion is obvious in gases and liquids, but diffusion in solids
rather than of solids is more likely.  Diffusion is very important to plants
since it is the only means for gaseous movement within the plant body.
Diffusion rates are affected by the gradient of concentration, the
permeability of the membrane separating them, temperature and pressure.
11.1.2 Facilitated Diffusion
As pointed out earlier, a gradient must already be present for diffusion to
occur.  The diffusion rate depends on the size of the substances; obviously
smaller substances diffuse faster.  The diffusion of any substance across a
membrane also depends on its solubility in lipids, the major constituent of
the membrane. Substances soluble in lipids diffuse through the membrane
faster.  Substances that have a hydrophilic moiety, find it difficult to pass
through the membrane; their movement has to be facilitated.  Membrane
proteins provide sites at which such molecules cross the membrane.  They
do not set up a concentration gradient: a concentration gradient must
already be present for molecules to diffuse even if facilitated by the proteins.
This process is called facilitated diffusion.
In facilitated diffusion special proteins help move substances across
membranes without expenditure of ATP energy. Facilitated diffusion
cannot cause net transport of molecules from a low to a high concentration
– this would require input of energy.   Transport rate reaches a maximum
when all of the protein transporters are being used (saturation).  Facilitated
2015-16(19/01/2015)
TRANSPORT IN P LANTS 177
diffusion is very specific: it allows cell to
select substances for uptake.  It is
sensitive to inhibitors which react with
protein side chains.
The proteins form channels in the
membrane for molecules to pass through.
Some channels are always open; others
can be controlled.  Some are large,
allowing a variety of molecules to cross.
The porins are proteins that form huge
pores in the outer membranes of the
plastids, mitochondria and some bacteria
allowing molecules up to the size of small
proteins to pass through.
Figure 11.1 shows an extracellular
molecule bound to the transport protein;
the transport protein then rotates and
releases the molecule inside the cell, e.g.,
water channels – made up of eight
different types of aquaporins.
11.1.2.1 Passive symports and
antiports
Some carrier or transport proteins allow
diffusion only if two types of molecules
move together. In a symport, both
molecules cross the membrane in the same
direction; in an antiport, they move in
opposite directions (Figure 11.2). When a
Figure 11.1 Facilitated diffusion
Uniport
Carrier protein
Membrane
Antiport
Symport
A
A
A
B
B
Figure 11.2 Facilitated diffusion
2015-16(19/01/2015)
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