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Figure shows the two crop fields [Plots A and B] have been treated by manures and chemical fertilizers respectively, keeping other environmental factors same. Observe the graph and answer the following questions. (i) Why does plot B show sudden increase and then gradual decrease in yield? (ii) Why is the highest peak in plot A graph slightly delayed? (iii) What is the reason for the different pattern of the two graphs?

i) With addition of chemical fertilizer there is sudden increase in yield due to release of nutrients N,P,K etc in high quantity. The gradual... View Article

Read the following pairs of examples of organisms: (a) moss and sponge (b) yeast and Amoeba (c) bacteria and a blue-green alga (d) penicillium and Spirogyra The pair that belongs to the group prokaryotes is_____

(c) bacteria and a blue-green alga Blue-Green Algae are a type of photosynthetic bacteria consisting either of single cells or colonies, which is... View Article

Weeds affect the crop plants by (a) killing of plants in field before they grow (b) dominating the plants to grow c) competing for various resources of crops (plants) causing low availability of nutrients (d) all of the above

c) Competing for various resources of crops causing low availability of nutrients Weeds are defined as the unwanted plants in crop fields which... View Article

Choose the wrong statement (a) High blood pressure is caused by excessive weight and lack of exercise. (b) Cancers can be caused by genetic abnormalities (c) Peptic ulcers are caused by eating acidic food (d) Acne is not caused by staphylococci

c) Peptic ulcers are caused by eating acidic food. Peptic ulcer is caused by bacterium Helicobacter pylori.Peptic ulcers are open sores that... View Article

We eat food composed of all the nutrients like carbohydrates, proteins, fats, vitamins, minerals and water. After digestion, these are absorbed in the form of glucose, amino acids, fatty acids, glycerol etc. What mechanisms are involved in the absorption of digested food and water?

Diffusion is a process in which the molecules intermingle due to their kinetic energy and movement of molecules is from higher concentration to... View Article

Suggest a suitable word for each of the following statements. (a) Chemicals added to food to prevent the growth of microorganisms. (b) Nitrogen-fixing microorganism present in the root nodules of legumes. (c) The agent spreads pathogens from one place to another. (d) Chemicals which kill or stop the growth of pathogens.

(a) Preservatives are the chemicals added in food. They prevent microbial infection without altering the taste or appearance.(b) Rhizobium are... View Article

John and Radha were classmates since childhood. When Radha became eleven years old, she developed a little swelling on her neck. She visited the doctor who started medication for her. After a few years, John also developed a slight protrusion on his throat. He got worried and went to the doctor. But, the doctor assured him that it was a normal feature in boys while they are growing up. Can you think of any reasons for the difference in diagnoses?

The swelling on the neck of Radha may have been because of goiter, a condition of the thyroid gland during which the gland produces insufficient... View Article

If you are provided with some vegetables to cook, you generally add salt to the vegetables during the cooking process. After adding salt, vegetables release water. What mechanism is responsible for this?

Exosmosis is the process of movement of water molecules from inside to the outside of the cell, where the solution is hypertonic due to the... View Article

Anu wants to boil water quickly in a test tube. On observing the different zones of the flame, she is not able to decide which zone of the flame will be best for boiling water quickly. Help her in this activity.

Anu should boil the water in the hottest zone of the flame, which is non-luminous zone or the outermost zone of the flame A candle flame consists... View Article

The property to flow is unique to fluids. Which one of the following statements is correct? (a) Only gases behave like fluids (b) Gases and solids behave like fluids (c) Gases and liquids behave like fluids (d) Only liquids are fluids

(c) Gases and liquids behave like fluids Gases and liquids behave like fluids. Both gases and liquids tend to flow due to less force of... View Article

It is believed that the height of a child depends upon the genes inherited from parents. However, it is often seen that tall parents may have short children and vice-versa. Are there factors other than genes, that can cause these variations?

Yes, though the height of a child depends upon genes inherited from a parent there are various factors which affect the height of a child. These... View Article

Generally, metallic oxides are basic and non-metallic oxides are acidic in nature. The solution of which of the following oxides in water will change the colour of blue litmus to red? (a) Sulphur dioxide (b) Magnesium oxide (c) Iron oxide (d) Copper oxide

Sulphur dioxide The oxides of a metal are basic in nature or in other words they react with acids to form salt and water. Metal oxides react to... View Article

Find out incorrect sentence (a) Parenchymatous tissues have intercellular spaces (b) Collenchymatous tissues are irregularly thickened at corners (c) Apical and intercalary meristems are permanent tissues (d) Meristematic tissues, in its early stage, lack vacuoles

c) Apical and intercalary meristems are permanent tissues Apical and intercalary meristems are not themselves permanent tissue instead they... View Article

Choose the correct statement with respect to unicellular organisms: (a) in unicellular organisms, tissues work in co-ordination to perform different functions. (b) unicellular organisms do not require food. (c) unicellular organisms respire and reproduce. (d) all unicellular organisms move by cilia.

c) Unicellular organisms respire and reproduce The unicellular organisms respire aerobically or anaerobically. They do not have any respiratory... View Article

Read the following statements and write the appropriate term against each statement. A. I control the functions of a cell. Who am I? ………………. B. I am like a policeman. I do not allow anything and everything to get in and out of the cell. Who am I? ………………. C. I transfer characters from parents to offsprings. Who am I? ……………….

A. I control the function of a cell. I am the nucleus The nucleus is a double-membraned organelle that contains the genetic material and other... View Article

The nitrogen molecules present in air can be converted into nitrates and nitrites by (a) a biological process of nitrogen-fixing bacteria present in soil (b) a biological process of carbon fixing factor present in soil (c) any of the industries manufacturing nitrogenous compounds (d) the plants used as cereal crops in field

a) A biological process of nitrogen fixing bacteria present in soil Nitrogen fixation is a biological process in which nitrogen molecules... View Article

Which of the following statement(s) is (are) true about respiration? (i) During inhalation, ribs move inward and diaphragm is raised (ii) In the alveoli, exchange of gases takes place i.e., oxygen from alveolar air diffuses into blood and carbon dioxide from the blood into the alveolar air (iii) Haemoglobin has a greater affinity for carbon dioxide than oxygen (iv) Alveoli increase surface area for exchange of gases (a) (i) and (iv) (b) (ii) and (iii) (c) (i) and (iii) (d) (ii) and (iv)

(d) (ii) and (iv) Gas exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them. Inhaled oxygen moves... View Article

Two glass jars A and B are filled with carbon dioxide and oxygen gases, respectively. In each jar, a lighted candle is placed simultaneously. In which jar will the candle remain lighted for a longer time and why?

In jar B, because oxygen is a supporter of combustion. In glass jar B the candle remains lighted for a longer time as it contains oxygen gas... View Article

Explain giving reasons (a) Balanced diet is necessary for maintaining healthy body. (b) Health of an organism depends upon the surrounding environmental conditions. (c) Our surrounding area should be free of stagnant water. (d) Social harmony and good economic conditions are necessary for good health.

A balanced diet can not only help you physically but also helps in improving the mental health. Food is necessary for the growth and development... View Article

Meena and Hari observed an animal in their garden. Hari called it an insect while Meena said it was an earthworm. Choose the character from the following which confirms that it is an insect. (a) Bilateral symmetrical body (b) Body with jointed legs (c) Cylindrical body (d) Body with little segmentation

b) Body with jointed legs The term “arthropod” means “jointed legs”. The phylum included invertebrates with an... View Article

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