NUTRITION :
“Nutrition” is a process of intake as well as the utilization of nutrients by an organism. It is the process of breakdown of nutrients into smaller molecules and their absorption. Food provides us with nutrition and energy. It contains different types of nutrients in varying amounts according to the need of our body.
(a) Nutrients:
These are the substances required by our body for its growth, repair, work and maintenance of the body. Different types of nutrients are carbohydrates, fats, proteins, vitamins, mineral etc. Our daily energy need may vary according to our occupation, age, sex and under some specific conditions.
MODES OR NUTRITION
There are several modes of nutrition on the basis of which organisms are classified as follows
(a) Autotrophic :
(Auto = self, trophic = food) It is a mode of nutrition in which organisms prepare their own food. Inorganic molecules like CO2 and H2O are converted into organic molecules like carbohydrates in the presence of sunlight and chlorophyll. e.g. Green plants. Autotrophs are further categorized. as :
(i) Photoautotroph:
Those which utilize sunlight for preparing their food
(ii) Chemoautotroph :
Those which utilize chemical energy for preparing their food.
(b) Heterotrophic :
(Hetero = different; trophic = food) It is a mode of nutrition in which organisms derive their food fro some other animals or plants. They cannot prepare their own food e.g. human being. Heterotrophs are further categorized depending on the nature of the food they consume :
(i) Herbivores :
Animals which eat only plants, e.g. cow, goat etc.
(ii) Carnivores:
They feed on the flesh of other animals, e.g. Lion, vulture etc.
(iii) Omnivores :
They feed on plants and animals both e.g. Dog, human etc.
(iv) Detritivores:
Feed on detritus or dead organic remains, e.g. Earthworm etc
(v) Sanguivorous:
Feed on blood e.g. Leech, female mosquito etc.
(vi) Frugivorous:
Feed on fruits, e.g. Parrot etc.
(vii) Insectivores:
Feed on insects, e.g. Bats etc.
(c) On the Basis of Mode of Feeding Organisms are Categorised As
(i) Holozoic:
They ingest mostly solid but sometimes liquid food. e.g.,
Amoeba, human etc.
(ii) Saprotrophic:
they absorb organic matter from dead and decaying organisms with the help of their enzymes. e.g., Bacteria, fungi etc.
(iii) Parasitic:
They derive their nutrition from other living plants or animals e.g. Plasmodium roundworms etc.
Nutrition can be divided into two categories on the basis of occurrence
Nutrition in Plants:
• Plants are autotrophic in nature. They prepare their own food hence they are called producers
. • They contain a green pigment called chlorophyll which can entrap solar energy which is then converted into chemical energy in the form of food and the process is called “Photosynthesis”.
a)Photosynthesis :
(i) Definition:
The synthesis of organic compounds like glucose from simple inorganic molecules like CO2 and H2O by the cells of green plants having chlorophyll in the presence of sunlight is called photosynthesis.
(ii) Equitation of photosynthesis:
Photosynthesis is a two-step process.
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
(A) Light reaction:
AT, NADPH2 and O2 are produced.
(B) Dark reaction :
CO2 & H2O are converted into glucose.
• Photosynthesis essentially requires two things:
(b) Sunlight:
• For plants sun the basis source of radiant energy.
• Plants utilize the light in the visible region of solar spectra (electromagnetic spectrum) which comes under the range of 390 nm - 780 nm.
• Visible region consists of white light which is a mixture of 7 lights of different wavelengths.
• Maximum photosynthesis occurs in the red region.
• There is minimum photosynthesis in the green region because green parts of plants reflect the whole of the green light.
(c) Chlorophyll:
These are the green pigments present in chloroplast. They are found in green leaves in a maximum amount as well as in other green aerial parts of the plant. T
here are six different types of chlorophyll, they are chlorophyll a,b,c,d,e and bacteriochlorophyll, amongst them chlorophyll a and chlorophyll b are the most commonly occurring chlorophylls
. • Besides chlorophyll certain other pigments are also present in plants like.
(i) Carotenes:
Orange in colour e.g. Carrot.
(ii) Xanthophylls:
Orange-yellow in colour e.g. Maize.
(iii) Phycobilins:
Different colour like red, violet e.g. Blue-green algae, brown algae etc.
(d) Raw Materials of Photosynthesis :
(i) Carbon dioxide :
Terrestrial plants obtain carbon dioxide from the atmosphere through the small openings present on leaves called stomata. ‘Stomata’ are the small pores present on the surface of leaves. They help in exchange of gases and water. Stomata opening is guarded by the presence of guard cells (kidney-shaped). Aquatic plants obtain CO2 dissolved in water through their general body surface so they perform more photosynthesis than terrestrial plants.
(ii) Water:
Plants absorb water from the soil by the process of osmosis. This water is transported to leaves by a special type of tissue called xylem.
• Plants utilize carbon dioxide during photosynthesis, the intensity of light at which amount of CO2 used during photosynthesis becomes equal to the amount of CO2 released during respiration by plants is called as Compensation point.
• Compensation point occurs at the low light intensity that is during the morning and during evening hours.
(e) Site Photosynthesis:
Site of photosynthesis is different in prokaryotes and eukaryotes.
• In prokaryotes: Photosynthesis occurs in lamellar chromatophores.
• In eukaryotes: Photosynthesis occurs in chloroplast.
• Exception: Fungi ( It lacks chlorophyll so no photosynthesis occurs here).
• In higher plants chloroplast in the main site of photosynthesis.
• Chloroplast is also called as a green plastid. • Plastid was first observed by Haeckel. • Plastids are of 3 different types on the basis of pigments present in
them.
(i) Leucoplast:
White in colour, found in underground parts, lacks and coloured pigment. Helps in the storage of protein (Aleuroplst), oil (Elaioplast), starch (Amyloplst)
(ii) Chloroplast:
Colour other than green found in aerial parts on the plants
(iii) Chloroplast:
Contain green pigment, called chlorophyll.
• Chloroplast was discovered by Schimper.
• Number of chloroplasts is variable in different species of plants.
• In lower plants like algae they are 1 or 2 number.
• In higher plants their number varies from 40 -100 per palisade cell or more.
• Chloroplast also have variable shapes, for example, cup-shaped, ribbon-shaped etc. in algae while it is discoidal in higher plants.
TS of leaf
Structure of Chloroplast
• A typical structure of chloroplast is a double membranous structure having two parts.
(i) Grana:
It is a lamellar system consisting of stacks of granum lamella each bounded by a membranous box called as thylakoid. They
are 40 - 60 per cell. A number of thylakoids per grana are 50 or more Chlorophyll molecules are found inside the thylakoid membrane where they trap solar energy in the form of small energy packets called ‘photon’ or ‘quanta’. Grana are interconnected to each other by a channel called stroma lamellae or Fret’s channel.
(ii) Stroma:
It is a non pigmented proteinaceous matrix in which grana remain embedded. It contains enzymes for a dark reaction.
(f) Mechanism of Photosynthesis :
(i) Light reaction:
• It is also called a photochemical process.
• It was discovered by ‘Robert Hill’ therefore it is also called as Hill’s reaction
•Site: Grana of the chloroplast.
• Raw materials: Light and water.
• Regulation: This process is regulated by chlorophyll molecules.
• It consists of 3 steps :
(A) Photoexcitation of chlorophyll molecule:
During this process, the chlorophyll molecule receives sunlight in the form of small energy bundles called photons and become excited to higher energy level.
(B) Photolysis:
It is also called as photooxidation of water, this takes place in the presence of Mn+2 and Cl- ions.
O2 is liberated as a by-product and H+ ions are used for the reduction of NADP 2NADP + 4H+ 2NADPH2
C) Photophosphorylation:
During this process, ATP is produced. It takes place in quantasomes. Mg+2 ions and inorganic phosphate are required to convert ADP ATP, ADP + IP ATP.
(ii) Dark reaction
: • It is also called a thermochemical reaction
. • It was discovered by Melvin calving and Benson, therefore, it is also called a Calving cycle Site = Stroma of chloroplast.
• Raw materials : They require CO2, NADPH2, ATP and Enzymes.
• Regulated by : Light reaction and enzymes.
• It involves three basic steps :
(A) Carboxylation : In this step CO2 is captured by CO2 acceptors like RUBP (C3 Plants) PET (C4Plants) with the help of carboxylase enzyme i.e. RUBISCO & PEPCO respectively.
(B) Synthesis: This phase cap true CO2 is assimilated into glucose in the presence of phosphatase and isomerase enzymes and RUBP is regenerated back.
(C) Regeneration of RUBP
1.4 FACTORS AFFECTING PHOTOSYNTHESIS
(a) Light ;
Normally plants utilize sunlight but marine algae can perform photosynthesis even in the moonlight. Plants can also perform photosynthesis in the artificial lights.
• Highest rate of photosynthesis: Red light
• Minimum photosynthesis: Greenlight
• Very high light intensity can cause a reduction in the rate of photosynthesis by causing
(i) A decrease in transpiration rate
(ii) Denaturation of a chlorophyll molecule
(b) Temperature:
Optimum range = 250 C to 300 C It ranges from 100 - 400 C In some forms like algae of hot spring 600 - 700 is normal
(c) Carbon dioxide:
It is the first limiting factor of 0.03 - 0.1% is present in the atmospheric concentration of CO2 rate of photosynthesis.
above 0.9% between 0.1 to 0.9%, it is constant and it is called a saturation point.
(d) Oxygen:
O2 acts as a competitive inhibitor of CO2. Over concentration of O2 stops photosynthesis.
(e) Chlorophyll:
The chlorophyll content is directly proportional to the rate of photosynthesis. No photosynthesis occurs in etiolated cells, In variegated leaves, it occurs only at places where chlorophyll is present.
SIGNIFICANCE OF PHOTOSYNTHESIS: Photosynthesis is a boon to nature and to human beings. It has
the following significance :
(i) Production of food material
(ii) Atmospheric control and purification of air.
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