NCERT Notes for Class 8 | NCERT Quiz | NCERT Standard 8 - Science

All questions are based on chapter 2 : Nutrition in Plants
1. Plants collect nitrogen from
A. Air
B. Soil
C. Soil and Air
D. Plants dont need nitrogen

2. We know that oxygen is released as a by product of photosynthesis. But plants do photosynthesis for the production of?
A. Carbohydrates
B. Fats
C. Protiens
D. All the above

3. Saprotrophic nutrition is most common in?
A. Bacteria
B. Alge
C. Fungi
D. Bryophytes

4.Lichens posses which mode of nutrition?
A. Autotropic
B. Heterotropic
C. Symbiotic
D. None of these

5. Rhizobium helps plants in the production of
A. Hydrogen
B. Nitrogen
C. Potassium
D. CO2

6. Cuscuta (Amarbel) posses which mode of nutrition?
A. Autotropic
B. Heterotropic
C. Symbiotic
D. None of these

7. Below given are some of the sheep breeds found in India. Among these,which one produces the best quality wool
A. Lohi
B. Nali
C. Marwar
D. Patanwadi

Know more about Answers
1.Nitrogen is present in abundance in gaseous form in the air.However, plants cannot absorb nitrogen in this form. Soil has certain bacteria that convert gaseous nitrogen into a usable form and release it into the soil. These soluble forms are absorbed by the plants along with water.Proteins are nitrogenous substances which contain nitrogen.
2. Leaves are the food factories of plants. The synthesis of food in plants occurs in leaves . Therefore, all the raw materials must reach there. Water and minerals present in the soil are absorbed by the roots and transported to the leaves. Carbon dioxide from air is taken in through the tiny pores present on the surface of the leaves. Such pores are called stomata.The leaves have a green pigment called  chlorophyll.  It helps leaves to capture the energy of the sunlight. This energy is used to synthesise (prepare) food from carbon dioxide and water. Since the synthesis of food occurs in the presence of sunlight, it is called photosynthesis. So chlorophyll,sunlight, carbon dioxide (CO2) and water (H2O)are necessary to carry out the process of photosynthesis. During this process carbohydrates (CH2O) are produced and oxygen (O2) are released.
3. Fungi secrete digestive juices on the dead and decaying matter and convert it into a solution. Then they absorb the  nutrients from it. This mode of nutrition in which organisms take in nutrients in solution form from dead and decaying matter is called saprotrophic nutrition. Plants which use saprotrophic mode of nutrition are called saprotrophs.
Fungi also grow on pickles, leather, clothes and other articles that are left in hot and humid weather for long time. The fungal spores are generally present in the air. When they land on wet and warm things they germinate and grow. eg :  mushroom
4. Lichens are composite organisms consisting of a symbiotic association of a fungus (the mycobiont) with a photosynthetic partner (the photobiont or phycobiont), usually either a green alga or cyanobacterium.  Lichens are widespread and may be long-lived;however, many are also vulnerable to environmental disturbance, and may be useful to scientists in assessing the effects of air pollution,ozone depletion, and metal contamination.
5. Though nitrogen gas is available in plenty in the air, plants cannot use it in the manner they can use carbon dioxide. They need nitrogen in a soluble form.The bacterium called  Rhizobium can take atmospheric nitrogen and convert it into a soluble form. But  Rhizobium cannot make its own food. So it lives in the roots of gram, peas, moong beans and other legumes and provides them
with nitrogen. Most of the pulses (dals) are obtained from leguminous plants. In return, the plants provide food and shelter to the bacteria.