Definition

The process by which living organisms obtain food and use it for growth, metabolism, and repair. The stages of nutrition include ingestion, digestion, absorption, transport, assimilation, and excretion.

Types of Nutrition

There are two types.

1) Autotrophic Nutrition

Autotrophic nutrition involves the use of an external energy source to make the complex organic molecules that we call food.

Plants use light energy from the sun as their external energy source, this type of autotrophic nutrition is photosynthesis.

During photosynthesis carbon dioxide and water are used to manufacture carbohydrates. Light energy is trapped by chlorophyll and used to fix carbon dioxide, firstly to reduce it to carbohydrates. Plant manufacture all the other organic molecules that they need from these carbohydrates and very small quantities of mineral ions obtained from the soil.

2) Heterotrophic Nutrition

Heterotrophic nutrition is the nutrition of organisms which need ready made complex organic molecules, they obtain these wither directly from plants, or from organisms which have fed on plants. Thus heterotrophic organisms are the consumers in an ecosystem.

There are various types of heterotrophic nutrition:-

Saprobionts('saprophytes'/'saprotrophs')

1. Feed on the dead remains of other organisms(dead organic material).
2. Secrete enzymes onto the food, then soluble products are absorbed
3. Extracellular digestion.
4. Responsible for decay.
5. The decomposers in an ecosystem.
6. Fungi such as Rhizopus are saprobionts

Parasites

1. Obtain food from another living organism, the host
2. There is a close association between the host and the parasite
3. The host suffers some degree of harm.

Taenia, the pork tapeworm, is a parasite, the adult is an endoparasite of human beings, thus we are the primary host, and it is found attached to the wall of the small intestine of an infected individual, where it absorbs the soluble products of digestion.

Adaptations

1. Large surface area for absorption
2. No alimentary canal
3. Thick outer covering (tergument)
4. Suckers and hooks for attachment to gut wall, to resist peristalsis
5. Large numbers of offspring produced
6. Reduced nervous system

Mutualism ('Symbiosis') is a close association between individuals of two different species, both partners benefit from the association.

Nitrogen fixing bacteria such as Rhizobium can be found in root nodules of leguminous plants (Papilionaceae) such as peas and beans, they provide the plant with a supply of nitrogen in the form of ammonia and receive carbohydrates from the plant.

The bacteria combine nitrogen with hydrogen ions (from carbohydrates) to form ammonia (this needs the enzyme nitrogenase) which can then combine with glutamate to form glutamine.

Holozoic nutrition is the nutrition of 'higher' animals such as human beings.

Nutrition in Plants

Most plants are photoautotrophs, which means that they are able to synthesize food directly from inorganic compounds using light energy - for example from the sun, instead of eating other organisms or relying on nutrients derived from them. This is distinct from chemoautotrophs that do not depend on light energy, but use energy from inorganic compounds.

6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O

The energy for photosynthesis ultimately comes from absorbed photons and involves a reducing agent, which is water in the case of plants, releasing oxygen as product. The light energy is converted to chemical energy (known as light-dependent reactions), in the form of ATP and NADPH, which are used for synthetic reactions in photoautotrophs. The overall equation for the light-dependent reactions under the conditions of non-cyclic electron flow in green plants is:

2H₂O + 2NADP+ + 2ADP + 2Pi + light → 2NADPH + 2H⁺ + 2ATP + O₂

Most notably, plants use the chemical energy to fix carbon dioxide into carbohydrates and other organic compounds through light-independent reactions. The overall equation for carbon fixation (sometimes referred to as carbon reduction) in green plants is:

3CO₂ + 9ATP + 6NADPH + 6H⁺ → C₃H₆O₃-phosphate + 9ADP + 8Pi + 6 NADP+ + 3H₂O

To be more specific, carbon fixation produces an intermediate product, which is then converted to the final carbohydrate products. The carbon skeletons produced by photosynthesis are then variously used to form other organic compounds, such as the building material cellulose, as precursors for lipid and amino acid biosynthesis, or as a fuel in cellular respiration. The latter occurs not only in plants but also in animals when the energy from plants gets passed through a food chain. Organisms dependent on photosynthetic and chemosynthetic organisms are called heterotrophs. In general outline, cellular respiration is the opposite of photosynthesis: Glucose and other compounds are oxidized to produce carbon dioxide, water, and chemical energy. However, the two processes take place through a different sequence of chemical reactions and in different cellular compartments.

Plants absorb light primarily using the pigment chlorophyll, which is the reason that most plants have a green color. The function of chlorophyll is often supported by other accessory pigments such as carotenes and xanthophylls. Both chlorophyll and accessory pigments are contained in organelles (compartments within the cell) called chloroplasts. Although all cells in the green parts of a plant have chloroplasts, most of the energy is captured in the leaves. The cells in the interior tissues of a leaf, called the mesophyll, can contain between 450,000 and 800,000 chloroplasts for every square millimeter of leaf. The surface of the leaf is uniformly coated with a water-resistant waxy cuticle that protects the leaf from excessive evaporation of water and decreases the absorption of ultraviolet or blue light to reduce heating. The transparent epidermis layer allows light to pass through to the palisade mesophyll cells where most of the photosynthesis takes place.

Plants convert light into chemical energy with a maximum photosynthetic efficiency of approximately 6%. By comparison solar panels convert light into electric energy at a photosynthetic efficiency of approximately 10-20%. Actual plant's photosynthetic efficiency varies with the frequency of the light being converted, light intensity, temperature and proportion of CO2 in atmosphere.

1) The light phase in the process of photosynthesis: The two types of photochemical reactions

Cyclic and acyclic photophosphorylations are both photodependent reactions.

• cyclic photophosphorylation:

This is the simplest pathway taken by excited electrons.

- ATP (the high-energy molecule Adenosine Triphosphate) is produced, but no O₂ or NADPH (the redox potential molecule Nicotinamide adenosine diphosphate).

- The excited electrons leave the chlorophyll in the reaction centre, travel along a short electron transport chain and return to the reaction centre.

- During a series of oxydoreduction (redox) steps, the electron is transported from one protein to another.

- All these processes occur within the inner thylakoid membrane.

ATP is produced indirectly by the proton motor force (via an electrochemical gradient) due to the transfer of the protons from the outside to the inside of the thylakoid membrane.

• acyclic photophosphorylation

This reaction involves the two photosystems (I ET II) and the reaction centres (P700 et P680).

Upon being excited by light energy, an electron leaves the chlorophyll molecule in photosystem II. To compensate for this loss, the molecule in question recovers an electron via the photolysis of the water molecule :

H2O  ---> 2H+ + 1/2 O2 + 2e- (Photolysis of water)

This result in the production of O₂ and ATP (indirectly via the proton motor force) and NADP⁺ is reduced to NADPH and H⁺.

The water is therefore the electron donor and NADP⁺ is the final acceptor; the O₂, released into the atmosphere is used for cell respiration purposes.

The light phases therefore convert the solar energy captured by the pigments into chemical energy, which is stored in the high-energy ATP molecules and the NADPH (redox potential) molecules.  ATP is therefore synthesized as the result of the proton motor force and ATP synthetase, which triggers the reaction ADP + Pi ---> ATP.  
The formation of these two molecules favours the binding of CO₂: this is known as the Calvin cycle.

2) the dark phase in the process of photosynthesis: the Calvin cycle

The Calvin cycle takes place in the stroma of eucaryotic chloroplasts.

This is the final stage in the process of photosynthesis in which the ATP and the NADPH produced during the previous photochemical reactions are used.

This cycle consists of a series of biochemical reactions controlled by various enzymes, which result in the reduction and incorporation of atmospheric CO₂ into the organic molecules.

The key enzyme in this cycle is Rubisco, which enables CO₂ to bind to RuBP:  Rubisco, or ribulose-1-5-biphosphate carboxylase, accounts for up to 16 % of all the protein present in the chloroplast; it is one of the most indispensable and abundant proteins on the earth.

This cycle is repeated 6 times (i.e., CO₂ is incorporated 6 times), yielding one glucose molecule, for example. This glucose will subsequently be used to synthesize polysaccharides, fatty acids, amino acids, nucleotides and all the other molecules on which the life of the plant depends.

The factors that affect Photosynthesis.

The factors that affect photosynthesis are: (1) light (2) temperature (3) water (4) carbon dioxide.

LIGHT : Intensity and quality of light affect photosynthesis. Chlorophyll absorbs mostly red and orange regions of visible spectrum. The rate of photosynthesis is more in red and orange light. Rate of photosynthesis increases at low intensity of light and decreases at high intensity.

TEMPERATURE : Photosynthesis takes place in the presence of enzymes. At low temperatures the activity of enzymes is low and the rate of photosynthesis is low. As the temperature increases, the enzymes get activated and the process of photosynthesis accelerates. But at very high temperatures the enzymes become denatured and the rate of photosynthesis decreases.

WATER: The rate of photosynthesis decreases under water-deficient conditions as the stomata remain closed to reduce transpiration. This stops gaseous exchange and hence the photosynthesis as carbon dioxide is not available.

CARBON DIOXIDE: The rate of photosynthesis increases with the increase in the concentration of carbon dioxide up to a certain level. Beyond that level it may have inhibitory effect on the rate of photosynthesis.

Nutrition in Amoeba.

The mode of nutrition in amoeba is holozoic. The process of obtaining food is called phagocytosis. Amoeba feeds on microscopic organisms floating on water. The nutrition involves processes like ingestion, digestion, assimilation and egestion.

Process : Amoeba forms pseudopodia to take food. When the tips of

pseudopodia touch each other, the membrane at that point dissolves and the food is encaptured along with lysosomes into food vacuole. Digestive enzymes present in the lysosome digest the food. The digested food diffuses into the cytoplasm and utilized by the cell. This is called assimilation. The undigested food left in the food vacuole is thrown out of the body. This is called egestion.

Nutrition in grasshopper (locust).

Grasshopper is a hrbivorous insect feeding on leaves of plants. The alimentary canal of the grasshopper is divided into three parts : (1) foregut (2) midgut (3) hindgut.

 
Foregut : It starts from mouth and extends upto gizzard. It consists of a short pharynx, narrow oesophagus and crop. The gizzard has a muscular wall and its lumen is lined with cuticle which forms six chitinous teeth. A pair of salivary glands along the crop opens into the cavity of the mouth through ducts.

Midgut : It is the region between gizzard and hindgut. At its anterior end there are fingerlike projections called hepatic caecae which open into the midgut and secrete digestive enzymes.

Hindgut : It is the region between the midgut and anus. It consists of three parts. An anterior ileum, a middle colon and a posterior rectum. The rectum opens outside through the anus. The junction of midgut and hindgut has many yellow threadlike minute tubules called Malphighian tubules which work as excretory organs.

PROCESS OF DIGESTION :Grasshopper holds the food with fore legs and ingests it inside the mouth where the food mixes with saliva. The saliva lubricates and makes the food soft. Its digestive enzyme digests starch. The food then passes to the crop via oesophagus where it is stored temporarily. Then it passes into the gizzard where it is ground by chitinous teeth and then passes into the midgut. Here the food is digested by enzymes secreted by hepatic caecae. The digested food is absorbed and the indigested food passes into the hindgut from where it is egested out through the anus.

 

Reference:

www.colchsfc.ac.uk
www.thefreedictionary.com
www.caribbeanedu.com
www.com.univ-mrs.fr
manojsirscience4u.blogspot.com
www.arbys.com
nutrition.about.com
en.wikipedia.org
www.nutrition.org

Editorial Team, Mindfiesta