Which of the following plant disease(s) are caused by bacteria? (a) Rust of wheat (b) Citrus canker (c) Yellow vein mosaic of bhindi
- A.Only (c)
- B.(a) and (b)
- C.Only (b)
- D.(b) and (c)
Correct answer
Explanation
The correct answer is C, Only (b). Of the three, only citrus canker is caused by bacteria; rust of wheat is caused by a fungus and yellow vein mosaic of bhindi by a virus. Citrus canker produces raised, corky brown spots on the leaves, twigs and fruits of lemon, orange and other citrus plants, and it spreads through the air. Rust of wheat forms reddish-brown powdery patches on the leaves and stems, which is how it got its name. Yellow vein mosaic turns the veins of bhindi, or okra, leaves yellow, and insects carry the virus from plant to plant. NCERT's Class 8 science book gives exactly these three as its examples of bacterial, fungal and viral diseases of plants. A is wrong because yellow vein mosaic is a viral disease, not a bacterial one. B is wrong because it adds rust of wheat, which is a fungal disease. D is wrong because it adds the viral yellow vein mosaic. Exam tip: citrus canker, bacteria; rust of wheat, fungus; yellow vein mosaic of bhindi, virus.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Liver cells turn the toxic ammonia released from the breakdown of amino acids into urea through the ornithine cycle, also called the urea cycle.
Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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It binds oxygen at its iron-containing haem groups and carries some carbon dioxide on its protein chains. Each haemoglobin molecule has four polypeptide chains and four haem groups, and each haem iron can hold one oxygen molecule, forming oxyhaemoglobin in the lungs.
Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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