Obtaining and Utilizing Food

All living organisms need food to survive. It also provides the building blocks for the body of a living organism. The essential components of food are carbohydrates, proteins, fats, vitamins and minerals. The components of food are necessary for our body and are called nutrients. Both plants and animals require these nutrients. Depending on the processes involved in obtaining and utilizing food, different organisms follow different types of nutrition. Different types of nutrition

There are two types of nutrition, based on the nature of the raw materials that organisms take from their environment and the way they process it thereafter.

 Holophytic Nutrition Green plants show holophytic nutrition. They take simple inorganic substances like carbon dioxide and water and prepare their food.

 Holozoic nutrition Most animals show holozoic nutrition. They take complex organic food from the environment and then break it down in the body to assimilate and use it.

Modes of nutrition

Depending on the mode of obtaining their food, organisms are categorized as:

 Autotrophs- organisms which are capable of preparing their own food are known as autotrophs. E.g. - green plants.  Heterotrophs- Organisms which cannot prepare their own food and are dependent on other organisms for their food requirements are called heterotrophs. E.g. - animals, non green plants, bacteria, fungi etc.

Autotrophic Nutrition

(Auto= self, trophos= nourishment)

Green plants take in carbon dioxide from the air and water from the soil. Carbon dioxide from air is taken in through the tiny pores present on the surface of the leaves. These pores are called stomata and are surrounded by guard cells.

This process by which plants prepare their food is called photosynthesis (photo= light, synthesis= to combine).

The requirement for photosynthesis is as follows:

 Carbon dioxide taken through stomata from the atmosphere.  Water from the soil by the roots  Sunlight, the energy of the sun required for photosynthesis.  Chlorophyll, the green pigment, present on the leaves and they help to trap the energy of sun. The overall equation for photosynthesis can be demonstrated as follows:

6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O

Glucose and oxygen is formed in the process. The glucose formed is converted to starch and stored in leaves and other parts. Plants which have leaves of other colours also contain chlorophyll. The green colour is masked by these pigments. They also photosynthesise. Small organisms called algae can also photosynthesise. They are found in stagnant water bodies. They also have chlorophyll.

Fig: Section of leaf

Synthesis of food other than carbohydrates

Plants also need nitrogen for synthesizing proteins. They obtain this from soil through the help of bacteria who can fix nitrogen and also from fertilizers added to the soil.

Heterotrophic Nutrition

This is of the following types:

Saprophytic Nutrition- organisms which grow on and derive nourishment from dead and decaying matter are called saprophytes or saprotrophs. This mode of nutrition is known as saprophytic nutrition. E.g. - bacteria, fungi, some non green plants like snow orchid, Indian pine etc. They secrete digestive juices to convert solid dead and decaying matter into liquid and derive nutrition from it.

Parasitic nutrition – organisms which depend on other organisms for food and shelter are called parasites. The organisms which provides food and shelter to the parasites is called host.

The parasites grow on or in the body of the host and derive nutrition from them.

E.g. - Some plants like Cuscuta/ dodder, tapeworms, hookworms, pinworms, head louse etc.

There are some plants which depend on host for some nutrients, these are called partial parasites.

E.g. - Mistletoe depends on host for minerals and water.

Special types of nutrition Insectivorous plants – some plants consume insects as s part of their regular diet. They have special body parts that help them catch insects.

E.g. - Pitcher plant, bladderwort, Venus fly trap, sundew etc. They are green plants capable of photosynthesis but grows in soil poor of nutrients especially nitrogen and hence depend on insects for nutrition.

Symbiotic nutrition – The interaction between two different organisms which lives close physically and benefit from each other is called symbiosis. A symbiotic relationship is a mutually beneficial relationship. E.g. - lichens. They have one fungal and one algal partner. Algae are autotrophs; they synthesize organic food for themselves and their fungal partner. Fungi are saprophytes. They are capable of absorbing water and minerals from the material they are growing on. They supply the algae with water and minerals and also shelter.

How are nutrients replenished in the soil?

 Decomposers play an important role in returning the nutrients to the soil.  Addition of fertilizers also replenishes the soil. Holozoic Nutrition

Holozoic nutrition involves the following processes.

1. Ingestion – intake of food. 2. Digestion – breakdown of complex food to simpler forms. 3. Absorption – food broken down to smaller and simpler nutrients is absorbed by the body. 4. Assimilation – The simpler nutrients are utilized by the body for various functions. 5. Egestion- Undigested food is thrown out of the body. Nutrition in Amoeba

Nutrition in an Amoeba occurs through a process called phagocytosis where the entire organism pretty much engulfs the food it plans on eating up. As amoeba is a unicellular organism, it does not have any specialized organ for the mechanism of nutrition. Its entire process is carried through the body surface with the help of pseudopodia. When the Amoeba senses a suitable food it extends its pseudopodia and encircles the food drawing it inside the body. Here a food vacuole is created and the food is digested and absorbed. The undigested portion is thrown out of the body.

Fig: Mechanism of feeding in Amoeba Digestion in Human

The basic components of the human digestive system are a long tube called alimentary canal and the associated glands.

The process of digestion starts in the mouth and ends in the anus.

1. Mouth – Ingestion occurs through the mouth. The mouth consists of the teeth, tongue, buccal cavity and three pairs of salivary glands. The salivary glands produce saliva which helps in softening the food. The saliva also contain the enzyme (digestive juice) called salivary amylase which breaks down starch into glucose. The food is broken down with the help of teeth and mixed with saliva. This process is called mastication and the food forms a bolus (pulpy mass) There are two sets of teeth in Human called temporary or milk teeth which is 20 in number. This set is gradually replaced by the permanent set consisting of 32 teeth. Each jaw contains: Incisors or cutting teeth-2 in number. Canines or tearing teeth-2 in number. Premolars or grinding teeth-4 in number. Molars or crushing and chewing teeth-6 in number. Tongue is a muscular organ that helps in tasting food. The tongue can sense four major types of taste viz sweet, sour, salty and bitter. This is possible due to the presence of mucous membrane and taste buds on the surface of the tongue.

Fig: Different types of teeth

2. Oesophagus/ Food pipe – The mouth has two openings, one for the windpipe and other for the food pipe. Each time we swallow a flap like structure called epiglottis closes the windpipe and prevents food from entering it. In the oesophagus the food travels in a wave like contra called peristalsis and is pushed into the stomach 3. Stomach – It is a muscular J-shaped bag where partial digestion takes place. The muscles of the stomach churn the food and convert it to a semi-formal solid paste called chyme. The walls of the stomach contain millions of gastric glands, which release gastric juice that help break down proteins. The gastric juice contains HCl (hydrochloric acid) and the enzyme pepsin in an inactive form. The HCl kills germs in the food and activates inactive pepsinogen to pepsin for protein digestion. 4. Small Intestine – It is a long, narrow, coiled tube where the digestion is completed. It received juices from liver, pancreas and other intestinal glands which contains various enzymes for digestion. Liver secretes bile, which helps to breakdown large fat globules into droplets (emulsification of fat) which makes it easier for digestion. Pancreatic juice from pancreas contains all the enzymes for digestion.

Intestinal glands secrete intestinal juice which helps in digestion of carbohydrates, fats and protein into their units.

The inner wall of the small intestine contains millions of finger like projections called villi (sing. Villus), which are supplied with a network of capillaries. The villi increase the surface area for absorption.

5. Large Intestine – The undigested portion of food is passed to large intestine where most water gets reabsorbed. The waste now almost solid, is moved to the last part of the large intestine called rectum. The rectum terminates into any through which the faecal matter is removed.

Fig: Human Digestive system

Digestion in grass eating animals

You must have noticed the grass eating animals continuously chewing their food even when they are not eating. They have a special part in their stomach called the rumen. Here, they store the food that they eat, where digestion takes place to form “cud”. This cud returns as small lumps to the mouth from time to time on which the animal chews on. This entire process is called rumination and such animals are known as ruminants.

Digestive System of Ruminants

Ruminants have a very special type of digestive system. A four-chambered stomach is a peculiar characteristic of these animals. Let’s know more about it. The main components of their digestive system include:

Fig: Ruminant Stomach

 Mouth: The mouth lacks any enzymes and just chews as well as softens the food.

 Oesophagus: It directs the movement from mouth to the rumen.

 Rumen: This is the part that distinguishes the ruminants from others. It is a large sac-like structure that is present in between the oesophagus and the small intestine. Food is stored here temporarily after which it returns to the mouth for chewing. It returns to the mouth by a process called antiperistalsis.You can see the ruminant lying down quietly and chewing on the cud. The food then passes down to the reticulum after getting chewed

 Reticulum: The bacteria present here ferment the food. They help in digesting the cellulose present in plants. It separates finely ground material from coarse ones as well as retains the hard pieces of wood.

 Omasum: It has parallel leaf-like components with rough surfaces. It is mainly responsible for absorption of water. Food gets ground more finely

 Abomasum: Breakdown of proteins takes place here with the help of enzymes. It passes on to the small intestine where rest of the digestion takes place just like humans.

Let’s Revise:

1. Differentiate between autotrophs and heterotrophs.

Ans-

Autotrophs Heterotrophs Organisms which can prepare their own food. Organisms which cannot prepare their own food. They can make food from simple raw materials They depend directly or indirectly on autotrophs. like carbon dioxide, water in presence of chlorophyll and sunlight. E.g.: Some bacteria, green plants etc. E.g.: Non- green plants, fungi, animals etc.

2. How water is transported to the leaves?

Ans- Water is transported to the leaves by a tissue called the phloem.

3. Give reasons for the following:

a) Pitcher plant is green and carries out photosynthesis, still it feeds on insects.

Ans- Pitcher plants live in areas where the soil lacks nitrogen. So, to get the supply of nitrogen they trap insects although they can photosynthesise.

b) Algae and fungi lives in close association with each other.

Ans- Algae provides the fungi with food and the fungi provide water and shelter to the algae. This is a symbiotic association called lichen.

c) Mistletoe is called a partial parasite.

Ans- Mistletoe takes its supply of water and nutrients from the host plants. It then photosynthesises to prepare its food. Hence, it is called a partial parasite.

d) Plants cannot photosynthesise in a dark room.

Ans- Light is required for photosynthesis for splitting water. Hence, plants cannot photosynthesise in a dark room.

e) Rice tastes sweet after being chewed in mouth.

Ans- The amylase in saliva acts on rice and roti and breaks down the starch to sugar. Hence, rice and roti tastes sweet in the mouth.

f) Projections are present in small intestine.

Ans- Finger like projections called villi are present in the small intestine as they increase the surface area available for absorption.

4. State the significance of photosynthesis.

Ans- Photosynthesis has the following significance:

 The food produced during photosynthesis is not totally utilised by the plants but is stored. This stored food is utilised by all living organisms.  Oxygen released as a by-product during photosynthesis is an important respiratory gas which is essential for life. 5. What is meant by peristalsis? What is its role in our body?

Ans- The wave like movement which occurs due to contraction and relaxation of muscles along the alimentary canal is called peristalsis.

Peristalsis helps in pushing the food down the alimentary canal, mixing juices during digestion and helps in egestion.

6. How do bile and hydrochloric acid help in the process of digestion? Ans- Bile helps in breaking down large fat molecules in droplets and increases the surface area for the enzymes to act on it.

Hydrochloric acid converts inactive pepsin into its active form which is essential for protein digestion and also kills the germs present in food.

7. Differentiate between absorption and assimilation.

Ans- Absorption is the process by which the digested food is taken up by the body and transported to different parts whereas assimilation is the process in which the digested components of food is utilized for different activities in the body.

8. Write short notes on molars and premolars.

Ans- Molars- are the largest of all teeth. They are situated at the last behind the premolars. They have broader and larger surface. They are designed to grind food. There are twelve molars in total.

Premolars- There are eight premolars present in the mouth, situated between the molars and canines. They are flat and used for crushing food.

9. State the functions of tongue and teeth in digestion.

Ans- The teeth help in chewing the food thus breaking them into small pieces for easy digestion. The tongue helps in mixing the saliva with the food. It also helps in pushing the small food bolus towards the oesophagus.

10. What are ruminants? How are they able to digest cellulose?

Ans- Herbivores who has a four chambered stomach specially designed to digest plant material are called ruminants. Ruminants can digest cellulose as they have microorganisms living in symbiotic association in the first chamber of their stomach. These help in breaking down the cellulose.

HOTS

11. What would happen if the leaves did not possess chlorophyll?

Ans- If the leaves did not possess chlorophyll then the energy of the Sun could not be trapped and water molecule could not be split. Hence, there will be no photosynthesis.

12. The stomach wall is not digested by its own enzyme. Why?

Ans- The stomach wall is not digested by its own enzyme because; stomach wall has glands which secretes mucous which protects the stomach from being digested.

Questions to be done in CW notebook

1. What are the two types of nutrition shown by living organisms? 2. Why are green plants called autotrophs? 3. Define photosynthesis. 4. Write the word equation of photosynthesis. 5. What is the role played by chlorophyll in the process of photosynthesis? 6. Define the following terms giving examples for each:

(a) Saprophytes (b) Parasites (c) Symbionts (d) Herbivore (e) Carnivore (f) Omnivore

7. What is holozoic nutrition? Name its steps.

8. Give reasons for the following:

(a) Mistletoe is a partial parasite.

(b) Carnivorous plants trap insects.

(c) Rice and Roti taste sweet after being chewed in mouth.

(d) Digestion of fat becomes difficult if gall bladder is removed.

(e) Inner wall of small intestine is thrown into finger like villi.

9. State the functions of different parts of the alimentary canal:

(a) Tongue (b) Teeth (c) Large intestine

10. Name the secretions of the following glands and give their significance in digestion:

(a) Glands of Stomach (b) Liver (c) Pancreas

11. Differentiate between:

(a) Mastication and Peristalsis

(b) Milk teeth and Permanent teeth

12. Draw and label the human digestive system.