Solution-Class 7-General Science-Chapter-4-Nutrition in Living Organisms-Mah-Board

Living organisms need nutrition for the following reasons :

(1) For the continuous supply of energy to perform work.

(2) To help in the growth and development of the body.

(3) To replace the worn out tissue and to repair the damaged tissues.

(4) To have resistance to infections and diseases

(1) The plants prepare the food by the process of photosynthesis. Plants absorb water and minerals present in the soil with the help of roots.

(2) The carbon dioxide is taken from the air and with the help of chlorophyll in the presence of sunlight, plant prepares glucose in the process of photosynthesis.

(3) In the process oxygen is liberated by the plant.

(4) Chemical reaction of the photosynthesis :

(1) The plants that depend on other plants for their nutrition are called parasitic plants.

(2) The parasitic plants are heterotrophic in their mode of nutrition, Some of them lack chlorophyll and thus cannot perform photosynthesis on their own.

(3) Loranthus is partial parasite. It sucks the nutrition from its host but prepares its own food.

(4) Cuscuta or Dedder does not have chlorophyll. It looks yellow, wire like climber, Hence it is complete parasite on the host tree.

There are main five steps of nutrition in animals, viz, ingestion, digestion, absorption, assimilation and egestion.

• Ingestion − The process of taking in of food into the body is called ingestion. Ingestion of food in humans is done with the help of the buccal cavity. 
• Digestion − The process where conversion of food into soluble form occurs.
• Absorption − The nutrients from the digested food are absorbed in the small intestine with the help of finger-like projections called villi.
• Assimilation − The absorbed nutrients are transported via the blood vessels to the different organs, to be utilised for different life processes. 
• Egestion − The process of removal of faecal matter through the anus is called egestion. 

The unicellular organisms in which all life processes take place within their body are- Amoeba, Paramoecium and Euglena.

Insectivorous plants feed on insects. They need to capture the insects. In order to attract these insects towards the plant, they are attractively coloured.

Butterflies have a long tube like proboscis which is a straw-like structure which enables them to drink juices and nectar. It is coiled-up like a garden hose when it is not in use.

By preparing variety of foodstuffs and dishes at home, we do not become autotrophic.

Autotrophic is a term which is used for organisms which can produce their own food.

We humans depend on plants for our food and the products which we get from them are used by us to make a variety of foodstuffs.

Also, autotrophic organisms contain chloroplast which is an absolute necessity to be classified as an autotroph and we do not possess any such structures. So, we cannot be considered autotrophs.

We are Heterotrophs

Autotrophs are the organisms which are greater in number.

It is because heterotrophs are dependant on autotrophs to meet their food requirements.

If heterotrophs exceed the number of autotrophs, then all the autotrophs will vanish and so will be the heterotrophs. However, this is not the case because autotrophs are always more than heterotrophs so that they can help in sustaining the heterotrophs.

(1) In desert region, the autotrophs are lesser in number as well as heterotrophs dependent on them are also less.

(2) The food is scarce, therefore. the number of heterotrophs also reduces.

(3) In oceans and seas there are multitude of zooplankton and phytoplankton, Phytoplankton are very small, microscopic floating plants which we may not see.

(4) The food chain in the seas is dependent on these planktonic species. Therefore, the number of
heterotrophs found in desert regions is smaller but they are found in greater numbers in the sea.

(1) Parasitic organisms depend on the host for its nutrition.

(2) Ectuparasites have specialized mouth parts. With the help of these, they suck the blood. e.g. mosquito and bed bugs. The biting insects cause a lot of discomfort.

(3) Mosquitoes spread many diseases such as malaria, dengue and elephantiasis. (4) Endoparasites live inside the body of host.
e.g., Round worm. hook worm, pin worm etc.

(5) They absorb host's nutrients and cause malnourishment to the host. Both ectoparasites und endoparasites cause damage to our health.

Plant food is produced by a special process known as photosynthesis.

The process of photosynthesis requires specialized structures called chloroplasts and these structures are found only in green regions of plants.

The green colour of specific parts of plants is due to the presence of chlorophyll pigment present in these chloroplasts. Structures in plants which do not contain chloroplast, do not appear green in colour and are not capable of producing food.