Nutrients in Plants

Summary

Nutrition
Nutrition is the mode of intake of food by the organism and its utilisation by the body. All organisms need food to perform their life processes. Food comprises of different nutrients which include carbohydrates, proteins, fats, vitamins and minerals. Food provides us energy to grow, repair the damaged parts in our body. Living organisms include microorganisms, plants and animals.

Plants obtain their nutrition by various modes. The mode of nutrition in plants can be autotrophic mode or heterotrophic mode. Plants can be classified into autotrophs and heterotrophs.

  • Autotrophic plants can synthesise their own food by the process of photosynthesis. 
  • Heterotrophic plants cannot synthesise food on their own but depend on other organisms for their nutrition. Heterotrophic plants can be further classified into parasites, saprophytes and symbiotic plants. 


Autotrophic mode of nutrition - Photosynthesis
It is an autotrophic mode of nutrition. Photosynthesis is a process by which green plants can synthesise glucose from raw materials like carbon dioxide and water in the presence of sunlight and chlorophyll. Photosynthesis involves the conversion of solar energy into chemical energy to synthesise starch.
 



Requirements for photosynthesis


 

Facts about photosynthesis
All chlorophyll-containing plants, including algae, and some plants with red, brown or other dominant pigments, make their food by photosynthesis.

  • Leaves are considered as food factories of a plant.
  • Roots absorb water and minerals from the soil and are transported to different parts of the plant.
  • Stomata present in the lower epidermis of the leaf take in carbon dioxide from the air.
  • Leaves have special structures called as chloroplasts. Chloroplasts possess chlorophyll, a green colour pigment present in the leaf captures energy from sunlight. Sun is the ultimate source of sunlight for all the living organisms on earth.
  • Plants synthesise glucose using carbon dioxide and water in the presence of sunlight.
  • Oxygen and water are released as by-products through the stomata during daytime.
  • The food synthesised is transported to other parts of the plant for utilisation and storage.
  • Glucose is a carbohydrate. Glucose synthesised by the process of photosynthesis is converted into complex compounds like starch and cellulose. Starch is stored in different parts of the plant.
  • Plants also prepare proteins with the help of nitrogen which is obtained from the soil.  
  • Thus, the minerals dissolved in water are used to convert sugar synthesised into carbohydrates, proteins and fats.
  • These food components stored are the source of energy for other heterotrophic plants and animals.


Activity 1
Aim: To prove the essentiality of  green colour pigment chlorophyll for photosynthesis.
Procedure: Following steps are performed in a sequential order.
Step-1: Take a beaker with boiling water and drop a leaf into it. Let it boil for 2 minutes.
Step-2: Take the leaf out of the beaker and place it in a test tube with alcohol. Place this test tube in a hot water bath for 10 minutes. Alcohol decolourises the leaf by removing chlorophyll from it by the process of bleaching.
Step-3: Remove the leaf from alcohol and wash it with warm water. Place it on a tile for further test.
Step-4: Add 2 drops of iodine on to the leaf. The portions which contained chlorophyll turn into bluish-black colour. The portions which did not contain chlorophyll and did not participate in photosynthesis remain the same.
Inference: From the experiment we can infer that green parts of the leaves synthesised starch and non-green parts did not perform photosynthesis to form starch.

Activity 2
Aim:  To explain the essentiality of light in photosynthesis
Procedure: Following steps are performed in a sequential order.
Step-1: A leaf is selected on a plant and is covered with black paper.
Step-2: Plant is destarched by keeping it in atmost darkness for 3 days. Pick a leaf and test it to confirm that the plant is starch free. i.e. It did not perform photosynthesis in the darkness.
Step-3: Expose the same plant to sunlight for a day.  
Step-4: Test the leaf covered with black paper using iodine. It does not turn blue-black as it has not synthesised starch. Starch synthesis did not happen as it is not exposed to sunlight.    
Inference: Photosynthesis did not occur in the leaf covered with black paper confirming the essentiality of light for the synthesis of starch.

Activity 3
Aim: To prove the requirement of carbon dioxide for photosynthesis
Procedure: Following steps are performed in a sequential order.
Step-1: A potted plant is taken and placed in complete darkness for few hours.
Step-2: Take potassium hydroxide in a conical flask rubber stoppered with a cork. Insert one leaf ( still attached to parent plant) into through a hole in the rubber cork. Potassium hydroxide absorbs all the left-over carbon dioxide from the flask.
Step-3: Entire arrangement is exposed to sunlightfor 6 hours.
Step-4: The leaf placed in the conical flask with potassium hydroxide solution is tested with iodine solution. This does not turn into bluish-black colour.    
Inference:  The leaf trapped inside the conical flask did not perform photosynthesis as it did not receive any carbon dioxide.

Heterotrophic mode of nutrition
Heterotrophic plants do not possess chlorophyll. Therefore, they cannot produce their own food using the process of photosynthesis. Heterotrophic plants obtain food from other plants by following either a parasitic, saprophytic or symbiotic mode.



a) Parasitic mode:
The organisms which exhibit parasitic mode of nutrition are called as parasites. Parasites obtain their nourishment from other living organisms. In parasitic mode of nutrition, plants depend on other plants or animals for their nourishment. Such plants are called as parasites and the ones on which parasites depend are called as hosts. 

  • e.g.Mistletoe is another parasitic plant which depends on other organisms for its nourishment.
  • e.g.Cuscuta is a parasitic plant which develops special roots called haustoria. Haustoria penetrate deep into host plant tissues and just absorb the nutrients from them.


b) Insectivorous mode:
These are the plants with special leaves that are modified into special structures. These structures have the ability to trap the organisms.

  • e.g. Nepenthes is otherwise called as pitcher plant has its leaves modified into pitchers closed with leaves. These have a network of fibres which entangle the trapped organism and later digest it by secreting some hydrolysing enzymes to digest them.
  • e.g. Venus fly trap feeds on small animals and insects to obtain their nourishment. These plants especially obtain the nitrogen they require from insects and small animals.


c) Saprophytic mode:  
The plants which exhibit saprotrophic mode of nutrition are called as saprotrophs. Saprotrophs are the plants that obtain their nutrition from dead and decaying organic matter. Saprotrophs secrete digestive juices onto dead and decaying matter to dissolve it and then absorb nutrients from it.

  • e.g. Indian pipe which is found on dead and rotting material, inhabits fungus in its roots. These extend their mycelium and secrete enzymes to digest the decaying matter.
  • e.g. Coral roots are another type of plants exhibiting saprophytic nutrition.


d) Symbiotic mode: 
Symbiosis is the phenomenon by which two organisms maintain relationship with each other to be mutually benefitted. In symbiotic mode, organisms develop a special relationship with certain other organisms to obtain nourishment. Organisms involved in this type of relationship are called as symbionts.

  • e.g. Rhizobium bacteria and Leguminous plants are symbionts exhibiting symbiosis. Plants cannot utilise atmospheric nitrogen directly. Hence, leguminous plants establish a symbiotic relationship with bacteria like Rhizobium. Both the organisms of symbiotic relationship are mutually benefited. Leguminous plant provides shelter and nourishment for the bacteria and in turn bacteria fix atmospheric nitrogen to the plant.
  • e.g. Digestion in ruminants is a good example of symbiosis. A large sac-like structure called the caecum lies between the small and large intestines. The symbiotic bacteria present in the caecum help in complete digestion of cellulose. Microorganisms present in the stomach of ruminants help in digesting cellulose and in turn obtain shelter and nourishment form the animal. A symbiotic relationship exists between microorganisms and the ruminants. 
  • e.g. Lichens form a very good example of symbiotic relationship. Lichens are formed by the symbiotic relationship between algae and fungi sharing a single colony. Fungus provides water, nutrients and shelter in the form of network formed by mycelium. Algae synthesises the food for entire colony by the process of photosynthesis.  

Differences between a parasite and a saprotroph
                 PARASITE                   SAPROTROPH
An organism that depends on other organisms for its food and nourishment. An organism that obtains its nourishment from dead and decaying.
It develops special organs like suckers, hooks or haustoria to obtain nourishment from the host. It is capable of secreting some enzymes which can digest complex molecules of into simpler forms.
e.g. Cuscuta, Nephenthes etc. e.g. Fungi, Bacteria.

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