NUTRITION
When we walk or ride a bicycle, we are using up energy. Even when we are not doing
any apparent activity, energy is needed to maintain a state of order in our body. We
also need materials from outside in order to grow, develop, synthesise protein &
other substances needed in the body. This source of energy & materials is the food
we eat.
How do living things get their food?
The general requirement for energy & materials is common in all organisms, but it
is fulfilled in different ways. Some organisms use simple food material obtained
from inorganic sources in the form of CO2 & H2O. These organisms, the autotrophs,
include green plants & some bacteria. Other organisms utilise complex substances.
These complex substances have to be broken down into simpler ones before they
can be used for the upkeep & growth of the body. To achieve this, organisms use
bio-catalysts called enzymes. Thus, the heterotrophs survival depends directly
or indirectly on autotrophs. Heterotrophic organisms include animals
& fungi.
Autotrophic Nutrition
●Autotrophic Nutrition – Carbon & energy requirements of the autotrophic
organism are fulfilled by photosynthesis. It is the process by which autotrophs take
in substances from the outside & convert them into stored forms of energy. This
material is taken in the form of CO2 & water which is converted into carbohydrates
in the presence of sunlight & chlorophyll.
Carbohydrates are utilised for providing energy to the plant. The carbohydrates
which are not used immediately are stored in the form of starch, which serves as
the internal energy reserve to be used as & when required by the plant. A somewhat
similar situation is seen in animals where some of the energy derived from the food
we eat is stored in our body in the form of glycogen.
chlorophyll
6CO2+ 12H2O C6H12O6 (glucose) + 6O2 + 6H20
Sunlight
,Let us now see what actually happens during the process of
photosynthesis. The following events occur during this process –
(i) Absorption of light energy by chlorophyll.
(ii) Conversion of light energy to chemical energy & splitting
of water molecules into hydrogen & O2.
(iii) Reduction of CO2 to carbohydrates.
These steps need not take place one after the other immediately. For example,
desert plants take up CO2 at night & prepare an intermediate which is acted
upon by the energy absorbed by the chlorophyll during the day.
Let us see how each of the components of the above reaction are necessary for photosynthesis.
If you carefully observe a cross-section of a leaf under the microscope (shown in Fig. 5.1), you will notice
that some cells contain green dots. These green dots are cell organelles called chloroplasts which contain
chlorophyll. Let us do an activity which demonstrates that chlorophyll is essential for photosynthesis.
, Now, let us study how the plant obtains CO2. Stomata (Fig. 5.3) which are tiny pores present on the surface
of the leaves. Massive amounts of gaseous exchange takes place in the leaves through these pores
for the purpose of photosynthesis. But it is important to note here that exchange of gases occurs
across the surface of stems, roots & leaves as well. Since large amounts of water can also be lost
The
through these stomata, the plant closes these pores when it does not need CO 2 for photosynthesis.
opening & closing of the pore is a function of the guard cells. The
guard cells swell when water flows into them, causing the
stomatal pore to open. Similarly the pore closes if the guard
cells shrink.
Figure 5.3 (a) Open and (b) closed stomatal pore
So far, we have talked about how autotrophs meet their energy requirements. But they also need other
raw materials for building their body. Water used in photosynthesis is taken up from the soil by the roots
in terrestrial plants. Other
materials like nitrogen, phosphorus, iron & magnesium are
taken up from the soil.
●Nitrogen is an essential element used in the synthesis of proteins & other compounds. This is taken
up in the form of inorganic nitrates or nitrites. Or
it is taken up as organic compounds
which have been prepared by bacteria from atmospheric nitrogen.
When we walk or ride a bicycle, we are using up energy. Even when we are not doing
any apparent activity, energy is needed to maintain a state of order in our body. We
also need materials from outside in order to grow, develop, synthesise protein &
other substances needed in the body. This source of energy & materials is the food
we eat.
How do living things get their food?
The general requirement for energy & materials is common in all organisms, but it
is fulfilled in different ways. Some organisms use simple food material obtained
from inorganic sources in the form of CO2 & H2O. These organisms, the autotrophs,
include green plants & some bacteria. Other organisms utilise complex substances.
These complex substances have to be broken down into simpler ones before they
can be used for the upkeep & growth of the body. To achieve this, organisms use
bio-catalysts called enzymes. Thus, the heterotrophs survival depends directly
or indirectly on autotrophs. Heterotrophic organisms include animals
& fungi.
Autotrophic Nutrition
●Autotrophic Nutrition – Carbon & energy requirements of the autotrophic
organism are fulfilled by photosynthesis. It is the process by which autotrophs take
in substances from the outside & convert them into stored forms of energy. This
material is taken in the form of CO2 & water which is converted into carbohydrates
in the presence of sunlight & chlorophyll.
Carbohydrates are utilised for providing energy to the plant. The carbohydrates
which are not used immediately are stored in the form of starch, which serves as
the internal energy reserve to be used as & when required by the plant. A somewhat
similar situation is seen in animals where some of the energy derived from the food
we eat is stored in our body in the form of glycogen.
chlorophyll
6CO2+ 12H2O C6H12O6 (glucose) + 6O2 + 6H20
Sunlight
,Let us now see what actually happens during the process of
photosynthesis. The following events occur during this process –
(i) Absorption of light energy by chlorophyll.
(ii) Conversion of light energy to chemical energy & splitting
of water molecules into hydrogen & O2.
(iii) Reduction of CO2 to carbohydrates.
These steps need not take place one after the other immediately. For example,
desert plants take up CO2 at night & prepare an intermediate which is acted
upon by the energy absorbed by the chlorophyll during the day.
Let us see how each of the components of the above reaction are necessary for photosynthesis.
If you carefully observe a cross-section of a leaf under the microscope (shown in Fig. 5.1), you will notice
that some cells contain green dots. These green dots are cell organelles called chloroplasts which contain
chlorophyll. Let us do an activity which demonstrates that chlorophyll is essential for photosynthesis.
, Now, let us study how the plant obtains CO2. Stomata (Fig. 5.3) which are tiny pores present on the surface
of the leaves. Massive amounts of gaseous exchange takes place in the leaves through these pores
for the purpose of photosynthesis. But it is important to note here that exchange of gases occurs
across the surface of stems, roots & leaves as well. Since large amounts of water can also be lost
The
through these stomata, the plant closes these pores when it does not need CO 2 for photosynthesis.
opening & closing of the pore is a function of the guard cells. The
guard cells swell when water flows into them, causing the
stomatal pore to open. Similarly the pore closes if the guard
cells shrink.
Figure 5.3 (a) Open and (b) closed stomatal pore
So far, we have talked about how autotrophs meet their energy requirements. But they also need other
raw materials for building their body. Water used in photosynthesis is taken up from the soil by the roots
in terrestrial plants. Other
materials like nitrogen, phosphorus, iron & magnesium are
taken up from the soil.
●Nitrogen is an essential element used in the synthesis of proteins & other compounds. This is taken
up in the form of inorganic nitrates or nitrites. Or
it is taken up as organic compounds
which have been prepared by bacteria from atmospheric nitrogen.
