Science textbook solutions for Class 7 Science Chapter 4 Nutrition in Living Organisms


Important points to remember :
  1. The process  of  taking in and using food, which takes place  in living  organisms is called  nutrition. 
  2. Autotrophic nutrition Some organisms can produce their own  food and thus nourish themselves. This is called  autotrophic nutrition. 
  3. Heterotrophic nutrition Some organisms  depend on  other organisms, plants or animals, for their  food. This is called heterotrophic  nutrition. 
  4. Nutrients can be classified into two types, namely, macro-nutrients  and micronutrients. 
  5. The transport system of plants consists of the  xylem  and the  phloem. 
  6. two or more  than  two different  types of plants live together  to fulfill  their  needs of nutrition, protection,  support, etc.  with each  others’ help. This type of nutrition  is called  symbiotic nutrition. 
  7. Food gets spoiled due to some fungi. Some fungi cause diseases or illness while some fungi have medicinal  properties. 
  8. Yeast and some mushrooms are useful. Yeast is used in fermentation processes and for making bread. Mushrooms  are a rich source of  iron and vitamins. 


Question 1: Classify according to food-type.
tiger, cow, vulture, bacteria, deer, goat, human, fungus, lion, sparrow, buffalo, frog, cockroach, tick.
Answer :
tiger- carnivore
cow- herbivore
vulture- scavenger
bacteria- decomposers
deer- herbivore
goat- herbivore
human- omnivore
fungus- decopmosers
lion- carnivores
sparrow- herbivore
buffalo- herbivore
frog- carnivore
cockroach- carnivore
tick- parasite


Question 2: Match the pairs.
Group 'A'.                             Group 'B'
1) Parasitic plant.               a) Mushroom

2) Insectivorous plant.      b) Lichen

3) Saprophytic plant.        c) Drosera

4) Symbiotic plant.            d) Cuscuta

Answer : 
1) Parasitic plant - d) Cuscuta
2) Insectivorous plant - c) Drosera
3) Saprophytic plant - a) Mushroom
4) Symbiotic plant -b) Lichen


Question 3: Answer the following questions in your own words.

a) Why do living organisms need nutrition ?
Answer : because most of the life-processes like metabolism, respiration, excretion are go on continuously  in living organisms. Substances which are  digested  and assimilated  for obtaining energy and for the growth and health that's why nutrient are required.
Need for nutrition 
1. To supply the energy required for doing  work.
2. Growth and development  of the body.
3. To replace  the damaged cells  and repair tissues.
4. To fight diseases.

b) Explain the process of production of food in plants.
Answer : Plants also need  food for their growth.

  1. They can produce  their  own food.  With the help of  sunlight and chlorophyll, plants make their food in their leaves, using water and nutrients from the soil  and carbon dioxide  from the air. This process is called  as photosynthesis. 
  2. Plants  convert light energy into chemical energy and  store  it in the form of food. Water, minerals and salts are absorbed by roots from the  soil. 
  3. The stem transports them  up to the leaves. The leaves have microscopic  openings called stomata through which they take in  the CO2  from the  air. 
  4. The  chloroplasts present in  the leaves contain chlorophyll, which absorbs sunlight,  helping  to convert carbon dioxide and  water into food. 
  5. Oxygen is given out in this process. Besides  leaves,  photosynthesis  takes place  in some other  parts like  green stems, too, as they contain  chlorophyll.


c) What is meant by parasitic plants ? Name their different types with examples of each.
Answer : Cuscuta is known as a parasite as it depends on another plant for its survival. The plant on which it grows is known as the host. Cuscuta can be seen around in the form of yellow tubular structures growing on the stems of other plants. It is devoid of leaves. Another such example of parasitic plants is Loranthus.

d) Explain the various steps of nutrition in animals.
Answer : Steps in nutrition
1.  Ingestion  - Food is taken into the body. 2.  Digestion  - Conversion of food into simple soluble forms.
3.  Absorption  - Transfer of soluble food to the blood.
4.  Assimilation  - Utilization of absorbed food by cells and tissues for energy production, growth and repair.
5.  Egestion  - Removal of waste products and undigested food from body.

e) Name some unicellular organisms in which all life-processes take place within their unicellular body.
Answer : Many prokaryotic or unicellular organisms in which all life processes take place within their body are- Amoeba, Paramoecium, BGA and Euglena.


Question 4: Give reasons.
a) Insectivorous plants are attractively coloured.
Answer : Many Insectivorous plants are attractively coloured so that they can attract insects and feed upon them. Insectivorous plants grow in soil or water which are deficient in nitrogen compounds and in order to meet this deficiency, they feed on insects.

b) Butterflies have a long tube-like proboscis.
Answer : 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.


Question 6: Think and answer.
a) We prepare a variety of foodstuffs and dishes at home. Are we then autotrophic organisms ?
Answer : We prepare a variety of food stuffs and dishes at homes. This does not make us autotrophs. This is because autotrophs prepare food on their own with the help of sunlight, water, minerals and chlorophyll.

b) Which organisms are greater in number - autotrophs or heterotrophs ? Why?
Answer : Heterotrops are greater in number as autotrophs are only organisms with chlorophyll which helps them produce their food. Autotrops are less in number. Such types of organisms are larger in number. Hence Heterotrophs are greater in number.

c) The number of heterotrophs found in desert regions is smaller. However, they are found in greater numbers in the sea. Why is this so ?
Answer : The number of heterotrophs found in desert regions is smaller. This is because in desert regions the number of autotrophs is less and this provides less number of sources of food to the heterotrophs which, in turn, affects the food chain.

d) What damage or harm do ectoparasitic and endoparasitic animals cause ?
Answer : Ectoparasites and endoparasites devoid the host of its nutrition. Some of the parasites are known to cause diseases like Ascaris/roundworm which is an endoparasite of intestine causes ascariasis. Another example is of Wuchereria which causes elephantiasis or filariasis. It is an endoparasite which lives in lymphatic vessels of lower limbs.


e) Why is plant food not produced in any other parts of the plant except the green ones ?
Answer : Plant food is only produced in the green part of the plants as chlorophyll is present in those green parts. The broad hard part of the plants does not possess any chlorophyll and therefore plant food cannot be created in those parts.


# let's recall 
1. What is malnutrition ? 
Answer : Malnutrition means lack of proper nutrition, caused by not having enough to eat, not eating enough of the right things, or being unable to use the food that one does eat.

2. Which are the ways to prevent malnutrition ?
Answer : The best way to prevent malnutrition is to eat a healthy, balanced diet.
Preventing malnutrition

  1. plenty of fruit and vegetables. 
  2. plenty of starchy foods such as bread, rice, potatoes, pasta. 
  3. some milk and dairy foods or non-dairy alternatives. 
  4. some sources of protein, such as meat, fish, eggs and beans.


3. Which  are the different  substances excreted  by plants? Why?.
Answer : The different substances excreted by plants are oxygen, carbon dioxide, and water droplets. Explanation: Plants release oxygen during the day. This oxygen is a by-product of photosynthesis

4. Which are the various  nutrients in food ?  For what purpose are the nutrients used ? Answer : Nutrients necessary for various activities of the  body are obtained from food. They are supplied  to  the  various parts of body through blood. The  food that  we consume does not mix with blood as it  is. It needs  to  convert into soluble  forms that can easily mix in blood. Nutrition  in animals involves various steps from ingestion  to egestion.

# Find out
1. How does photosynthesis occur in dark red or purple coloured  leaves ?
Answer : In photosynthesis, plants convert light energy to chemical energy. Typically, chlorophyll absorbs mostly red and blue light to excite the electrons in the photosystems for photosynthesis. Hence, plants with higher concentrations of carotenoids will appear dark red or purple.

2. What is  chemosynthesis ? Which plants produce their food by chemosynthesis ?
Answer :  Chemosynthesis is the conversion of one or more carbon-containing molecules and nutrients into organic matter using the oxidative inorganic compounds or methane as a energy source as in photosynthesis.


# Use your brain power
1. Which part of  the loranthus plant carries out photosynthesis ?
Answer - Leaves of the loranthus plant carries out photosynthesis.

2. From where do they obtain minerals  and water ? 
Answer : soil

3. Why  is loranthus  known as a  partially  parasitic  plant ?
Answer : Loranthus plants are famous partially parasitic plants as they can absorb nutrient as well as water from other plants , they does not grow on soil instead they have special system known as "Historia" by which it penetrates in to woody tree and grow on aerial parts of tree.


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