Category: Class 12 Biology Objective Questions

Biology Multiple Choice Questions on “Inheritance and Variation Principles – Sex Determination”.

1. Which of the following animals rely on environmental factors for sex determination?
a) Turtles
b) Humans
c) Grasshopper
d) Firefly
Answer: a
Clarification: Turtles are one of the organisms which rely on environmental factors for sex determination completely. They usually depend upon temperature for this purpose.

2. How is the sex of grasshopper determined?
a) Temperature
b) Pressure
c) Humidity
d) Genetically
Answer: d
Clarification: The sex of a grasshopper is determined genetically. Some experiments were carried out by some of the scientists on insects to study the genetic or chromosomal mechanism of sex determination.

3. The chromosomal basis of sex determination was discovered by which of the following scientists?
a) Stevens
b) Grey
c) Henking
d) Wilson
Answer: c
Clarification: The foundation of the chromosomal basis of sex determination was laid down by Henking in 1891. He studied a specific nuclear structure though spermatogenesis in a few insects.

4. Henking gave the term X chromosome.
a) False
b) True
Answer: a
Clarification: Henking was studying spermatogenesis in insects where he observed that only 50% of the sperms received a structure which he later termed as ‘X body’. But he could not explain the significance of this body.

5. Which of the following scientists discovered the Y-chromosome.
a) Stevens
b) Ernst Haeckel
c) Francis Crick
d) Wilson
Answer: a
Clarification: Stevens was the scientist who first discovered Y-chromosome. Many scientists concluded that the ‘X body’ which was discovered by Henking was a chromosome. Therefore, in 1905, X and Y chromosomes were named as sex chromosomes by Stevens and Wilson.

6. In which of the following organisms, the male heterogametic condition is not observed?
a) Grasshoppers
b) Humans
c) Drosophila
d) Birds
Answer: d
Clarification: Birds do not show male heterogametic conditions. Instead, they show the female heterogametic condition. Male heterogametic condition is characterised by male individuals producing two different types of gametes.

7. Which of the following determines the sex of the offspring in male heterogametic conditions?
a) Egg
b) Sperm
c) Both egg and sperm
d) It cannot be determined
Answer: b
Clarification: When the condition of male heterogamety is present, then sperm determines the sex of the offspring because two kinds of sperms are present, one with X-chromosome and the other with Y-chromosome. Eggs of an individual are the same as both of them contain 22+ X chromosomes.

8. In which of the following animals, there is a difference between the male and female numbers of chromosomes?
a) Humans
b) Drosophila
c) Grasshopper
d) Pigeon
Answer: c
Clarification: In a grasshopper, male and female individuals have a different number of chromosomes because grasshoppers exhibit XO type of male heterogamety where 2 kinds of sperms are formed- one with X-chromosome and the other with no sex chromosome.

9. Which of the following does not show XY type of male heterogametic condition?
a) Drosophila
b) Human beings
c) Elephants
d) Grasshoppers
Answer: d
Clarification: Grasshoppers do not show XY type of male heterogametic condition. XY type of male heterogametic condition is shown by a number of insects like Drosophila and mammals including human beings and elephants, the males in this type bear two types of sex chromosomes- X and Y type.

10. Y chromosome is always larger than the X-chromosome.
a) True
b) False
Answer: b
Clarification: Y-chromosome is not larger than X-chromosome, instead, it is often shorter than X-chromosome. In XY type of male heterogametic condition, both males and females have the same number of chromosomes.

11. What is the probability of having a girl child in sixth pregnancy if the first five progenies are boys?
a) 25%
b) 50%
c) 65%
d) 10%
Answer: b
Clarification: The probability of having a girl child in the sixth pregnancy, where the first five progenies were male is 50%. As humans show XY type of male heterogamety, where 50% sperms carry 22+ X chromosomes and the other 50% carry 22+Y chromosomes, therefore in each pregnancy there is 50% probability of either a male or a female child.

12. What is the full form of TDF?
a) Testis determining factor
b) Testes development factor
c) Thyroxine determining factor
d) Thyroid developing factor
Answer: a
Clarification: TDF stands for testis determining factor. TDF is essential for the development of male sex organs and if it is not produced in the body then it leads to the formation of the female sex organ.

13. The given figures show which of the following species of organisms?

a) Grasshopper
b) Butterfly
c) Moth
d) Drosophila
Answer: d
Clarification: The 1^st figure represents a male fruit fly and 2^nd figure represents a female fruit fly. Drosophila melanogaster which is used as a material for experimental genetics because it could be easily grown on a simple synthetic medium in the laboratory and a single mating produces a large number of offspring. Also, females are easily distinguishable from the males by the larger body size and the presence of an egg-laying structure.

14. Which of the following organisms does not show female heterogametic conditions?
a) Butterflies
b) Grasshopper
c) Moth
d) Birds
Answer: b
Clarification: Grasshoppers do not show female heterogametic conditions. Butterflies, moths, and birds show female heterogametic conditions where female individuals produce two different kinds of gametes.

15. In which of the following organisms, male has half the number of chromosomes than female?
a) Moths
b) Grasshoppers
c) Honey bees
d) Butterflies
Answer: c
Clarification: The female progeny of a honey bee develops from the union of a sperm and an egg whereas a male progeny develops from an unfertilised egg by the means of parthenogenesis. This means that the males have half the number of chromosomes than that of a female.

16. What kind of sex-determination system is present in honey bees?
a) Haplodiploid
b) Haploid
c) Diploid
d) XY type
Answer: a
Clarification: Honey bees exhibit a haplodiploid type of sex-determination system. This type of system has special characteristic features like the males produce sperms by mitosis. The male individuals do not have a father and thus cannot have sons, but can have a grandfather and a grandson.

Biology Multiple Choice Questions on “Evolution – Adaptive Radiation”.

1. _______ was the island where Darwin visited and discovered adaptive radiation?
a) Archipelago
b) Galapagos
c) Port Blair
d) Lakshadweep
Answer: b
Clarification: During the voyage of Darwin, he visited the Galapagos island. There, he came across different varieties of species. He saw the variations in the modification of beaks of finches.

2. Which food habit of Darwin’s finches lead to the development of many other varieties?
a) Fruiteater
b) Cactus eater
c) Insect eater
d) Seedeater
Answer: d
Clarification: It was from the seed-eating finches, many other altered forms of beak arose enabling them to be insect, cactus or fruit eaters. This led to the discovery of Adaptive radiation. Darwin’s finches are one of the best examples of this process.

3. Species which have diverged after origin from common ancestor giving rise to new species adapted to new habitats and ways of life is called as _______
a) Adaptive radiation
b) Divergent evolution
c) Convergent evolution
d) Mutation
Answer: a
Clarification: Adaptive radiation is a process that gave rise to a variety of species that originated from its original species. Darwin’s finches show adaptive radiation. They developed different beak varieties from the seed-eating variety.

4. _______ marsupials were taken as examples of adaptive radiation.
a) American
b) Australian
c) Indian
d) African
Answer: b
Clarification: Australian marsupials were taken as examples of adaptive radiation. These were the marsupials which were each different from each other but had a common ancestral stock. They were all within the Australian island continent.

5. What do we call the process when more than one adaptive radiation occurs in a single geological place?
a) Divergent evolution
b) Convergent evolution
c) Saltation
d) Overproduction
Answer: b
Clarification: Convergent evolution is the process when more than one adaptive radiation occurs in a single geological isolated area. It gives rise to analogous organs. They do not show common ancestry but they show evolution.

6. Placental mammals in Australia had similarity with the marsupials.
a) True
b) False
Answer: a
Clarification: Due to the process called adaptive radiation, placental mammals in Australia had similarity with the marsupials. It also indicates convergent evolution without common ancestry. One belongs to placental, whereas the other belongs to marsupials.

7. Lemur is a placental mammal that resembles _______ of Australian marsupials.
a) Bobcat
b) Numbat
c) Spotted cuscus
d) Flying phalanger
Answer: c
Clarification: Lemur resembles spotted cuscus. They appear to be similar because of the phenomenon called adaptive radiation. They have similar looks and appearance but does not have a common ancestral line.

8. Tasmanian wolf is an example of ________
a) Australian marsupial
b) Placental mammal
c) American marsupial
d) Placental wolves
Answer: a
Clarification: Tasmanian wolf belongs to Australian marsupial. Adaptive radiation was the process that gave rise to a variety of marsupials in Australia. They exhibit a large number of homologous organs.

9. Adaptive radiation does not confirm _______
a) Divergent evolution
b) Homology
c) Convergent evolution
d) Evolution of new forms
Answer: c
Clarification: It is not adaptive radiation that confirms convergent evolution. It is an adaptive convergence that confirms convergent evolution. The remaining options are applicable to adaptive radiation.

10. Which of the following is not an example of placental mammals?
a) Mole
b) Anteater
c) Mouse
d) Tasmanian tiger cat
Answer: d
Clarification: Tasmanian tiger cat belongs to Australian marsupials. The remaining options belong to placental mammals. The Tasmanian tiger cat resembles bobcat of placental mammals. They show convergent evolution.

11. Which of the following is a vestigial organ in animals?
a) Nictitating membrane
b) Scrotum
c) Tail
d) Eyelashes
Answer: a
Clarification: Vestigial organs are the organs which are present in reduced form and do not perform any function in the body. Here, the nictitating membrane is an example of a vestigial organ. It is a translucent membrane that forms an inner eyelid in birds, reptiles, and mammals.

Biology Interview Questions and Answers on “Bacterial Diseases in Humans-2”.

1. Which of the following is the carrier of Plague bacteria?
a) Anopheles mosquito
b) Aedes aegypti
c) Xenopsylla
d) Rhinovirus
Answer: c
Clarification: Plague spreads from rat through rat flea-Xenopsylla. They carry the pathogen Yersinia pestis. When the infected rats die, the fleas leave their body and can even bite the man and inject plague germs into his/her blood.

2. Which of the following is not a type of plague?
a) Bubonic plague
b) Septicemic plague
c) Pneumonic plague
d) Typhi plague
Answer: d
Clarification: Plague is of three basic forms- Bubonic plague is the most common type in which formation of buboes or swelling of lymph nodes occur in the neck and armpit regions. Septicemic plague causes the rupturing of blood vessels causing black patches on the skin and pneumonic plague is the only form of plague that can be transmitted from person to person.

3. What is the full form of BCG vaccine?
a) Bacteria Cold Gene
b) Bacillus Coded Gene
c) Bacillus Calmette–Guérin
d) Bacteria Coded-Guerin
Answer: c
Clarification: The full form of BCG vaccine is Bacillus Calmette–Guérin. It is an attenuated vaccine. It is commonly used for the prevention of tuberculosis disease. It is generally given between birth to six months of the baby.

4. Leprosy disease was discovered by _________
a) Hansen
b) Karl Joseph Eberth
c) Robert Koch
d) Dr Jay Levy
Answer: a
Clarification: Leprosy was first discovered by Hansen and that’s why it is commonly known as Hansen’s disease. Karl Joseph Eberth was the first person to discover typhoid, Robert Koch was the first person to discover tuberculosis and Dr Jay Levy’s group played an important role in the discovery of HIV.

5. Which medication is commonly given to treat Leprosy?
a) Ibuprofen
b) DDS (diamino-diphenyl sulphone)
c) Ciprofloxacin
d) Isotretinoin
Answer: b
Clarification: DDS (diamino-diphenyl sulphone) is commonly given to patients suffering from Leprosy. Ibuprofen is used to treat inflammation, pain and fever. Ciprofloxacin is given to patients suffering from typhoid fever and Isotretinoin is an antibiotic used to treat severe form of acne.

6. Food poisoning is commonly caused by which species of Clostridium?
a) Clostridium butyricum
b) Clostridium tetani
c) Clostridium perfringes
d) Clostridium botulinum
Answer: d
Clarification: Clostridium botulinum commonly causes food poisoning in human beings. Clostridium tetani and Clostridium perfringes cause tetanus and gangrene respectively. Clostridium butyricum is a great prebiotic for our gut and maintains the health of our brain.

7. Exotoxins are toxins released by bacteria in the medium or into the surroundings
a) True
b) False
Answer: a
Clarification: Exotoxins are toxins which are released by bacteria into the surrounding medium while Endotoxins are the toxins released by the bacteria into its own body and when it bursts, then toxins enter into the medium.

8. How many of the following diseases are caused by bacteria?

Cholera, AIDS, pneumonia, Mumps, Measles, Whooping Cough, 
typhoid, gangrene, gonorrhoea, influenza, plague, Diphtheria, 
Syphilis, Elephantiasis 

a) Five
b) Six
c) Seven
d) Eight
Answer: c
Clarification: There are seven diseases from the box caused by bacteria-Cholera is caused by Vibrio cholerae, Pneumonia is caused by Haemophilus influenzae, whooping cough is caused by Bordetella pertussis, Typhoid is caused by Salmonella typhi, Gangrene is caused by Clostridium perfringes, Plague is caused by Yersinia pestis, Diphtheria is caused by Corynebacterium diphtheria.

9. What is the first sign or symptom of tetanus?
a) Stiffness of neck
b) Swelling in neck
c) Paralysis
d) Numbness in fingers
Answer: a
Clarification: Stiffness of neck is the first symptom of Tetanus. Then there is difficulty in swallowing and chewing. Subsequently, spasms of muscles of the jaw and face take place. There is severe pain. It is often fatal disease.

10. What is the full form of ATS injection?
a) Anti Tuberculosis Serum
b) Artificial Typhoid Serum
c) Anti Tetanus Serum
d) Alpha Typhoid Sebum
Answer: c
Clarification: ATS stands for Anti Tetanus Serum injection. It should be administered within 48 hours of injury if the person has not had a tetanus shot in the past five years because Clostridium tetani enter in the blood through any wound or cut.

11. Which of the following diseases is caused by the species of Mycobacterium bacteria?
a) Typhoid and Tetanus
b) Leprosy and Tuberculosis
c) Gonorrhoea and Syphilis
d) Influenza and Leprosy
Answer: b
Clarification: Leprosy is caused by Mycobacterium leprae bacterium and tuberculosis is caused by Mycobacterium tuberculosis bacterium.

Biology for Interviews,

Biology Multiple Choice Questions on “Human Health and Disease – Autoimmunity”.

1. Which of the following is the cause of autoimmune diseases?
a) Immune System begins to attack its cells and tissues
b) Immune System starts producing cells and tissues
c) Immune System fails completely
d) Immune System produces WBCs in a huge number
Answer: a
Clarification: Autoimmune diseases are caused when the immune system starts attacking its cells and tissues. It is an abnormal immune reaction in which the body begins to reject substances and tissues of the body.

2. Which of the following is not an autoantigen?
a) RBCs
b) Liver Cells
c) Acetylcholine receptors
d) Brain
Answer: d
Clarification: Amongst the following options, Brain is not an autoantigen. RBCs, Liver cells and Acetylcholine receptors are autoantigens of Chronic anaemia, Chronic Hepatitis and Myasthenia gravis respectively.

3. Which of the following is not an autoimmune disorder?
a) Rheumatoid Arthritis
b) Multiple sclerosis
c) Influenza
d) Chronic Hepatitis
Answer: c
Clarification: Influenza is not an autoimmune disorder as it is caused by a virus, Myxovirus Influenzae. Rheumatoid arthritis, Multiple Sclerosis and Chronic hepatitis are some of the autoimmune diseases.

4. Muscular dystrophy is an autoimmune disease while Myasthenia gravis is a genetic disorder.
a) True
b) False
Answer: b
Clarification: Muscular dystrophy is a genetic disorder that leads to the degeneration of muscles. Myasthenia gravis is an autoimmune disease which is caused by an autoantigen i.e. acetylcholine receptors of muscle cells.

5. In which of the following diseases the autoantigens are β-cells?
a) Myasthenia gravis
b) Insulin-dependent diabetes
c) Multiple sclerosis
d) Chronic anaemia
Answer: b
Clarification: In Insulin-dependent diabetes, the autoantigens are β-cells. Autoantigens are substances of the patient’s body that develop antigenic activity and hence destroy the patient’s body cells and tissues.

6. In Multiple sclerosis, the antibodies attack the ‘Node of Ranvier’ of the nerve cells.
a) True
b) False
Answer: b
Clarification: Multiple sclerosis is an autoimmune disease in which antibodies attack the myelin sheath of nerve cells. The symptoms involve loss of vision, pain, fatigue and impaired coordination of the mind and the body.

7. Which of the following is not an immune system disorder?
a) Allergies
b) Immunodeficiency
c) Genetic Disorders
d) Autoimmune Diseases
Answer: c
Clarification: Immune system is a multicomponent interactive system. Any defect in the system results in discomfort, disease or even death. There are three types of defects- Allergies, Immunodeficiency and Autoimmune disorders.

8. Which of the following is an autoimmune disease?
a) Addison’s disease
b) Syphilis
c) Tuberculosis
d) AIDS
Answer: a
Clarification: Addison’s disease is an autoimmune disease. In this disease, antibodies attack the patient’s cells of adrenal glands that results in a deficiency of certain hormones. People with Addison’s disease are more likely than others to have other autoimmune diseases as well.

9. Which of the following statements is incorrect regarding Rheumatoid arthritis?
a) It is an autoimmune disorder
b) It occurs only in old people
c) Inflammation of synovial fluid
d) Diagnosed by the presence of rheumatoid factor
Answer: b
Clarification: Rheumatoid arthritis is an autoimmune disorder that can occur at any age. The primary symptom is inflammation of the synovial membrane. If it is left untreated, then the membrane thickens and synovial fluid increases, exerting pressure that causes pain.

10. In Myasthenia gravis, antibodies start attacking the ______________
a) Proprioceptors
b) Chemoreceptors
c) Acetylcholine receptors
d) Cortisol receptors
Answer: c
Clarification: In Myasthenia gravis, antibodies start attacking the acetylcholine receptors present on the sarcolemma, due to which the neurotransmitter i.e. acetylcholine could not bind to its receptors and hence, could not initiate nerve transmission. The skeletal muscles of the patient become weak and lead to paralysis.

Biology Multiple Choice Questions on “Poultry Farm Management”.

1. Which of the following is not typically included in Poultry farming?
a) Cow
b) Chicken
c) Duck
d) Turkey
Answer: a
Clarification: Poultry is the class of domesticated fowl used for food or for their eggs. They typically include chicken and ducks, and sometimes turkey and geese. The word poultry is often used to refer to the meat of only these birds but in a more general sense, it may refer to the meat of other birds too.

2. Which of the following is not an important component of poultry farm management?
a) Disease-free breed
b) Proper food
c) Dirty conditions
d) Safe farm conditions
Answer: c
Clarification: Selection of disease-free and suitable breeds, proper and safe farm conditions, proper food and water, proper hygiene and health care are important components of poultry farm management.

3. What is a domestic fowl?
a) It lives in a particular region
b) It is a foreign breed
c) A bird kept for obtaining meat and eggs
d) A specific bird kept for breeding purposes only
Answer: c
Clarification: Domestic fowl constitutes a major poultry bird as 90% of poultry farming is connected with rearing, breeding and management of Domestic fowl which is used for obtaining meat and eggs.

4. Poultry birds which are exclusively grown for meat are called ___________
a) layers
b) cockerel
c) rooster
d) broilers
Answer: d
Clarification: Poultry birds which are exclusively grown for meat are called broilers. Layers are female fowls raised for egg production. A cockerel is young male fowl. Rooster is the mature male fowl.

5. In pen mating, several males are kept in the company of a large flock of females.
a) True
b) False
Answer: b
Clarification: In pen mating, 10-50 hens and one cock are kept in small enclosures called pens. In flock mating, several males are kept in the company of a large flock of females.

6. Which of the following is not a characteristic feature of a broiler?
a) Generally, they are females
b) Sold in fresh or frozen form
c) Grown for 6-7 weeks
d) Also called as table birds
Answer: a
Clarification: Broilers are also called as Table birds. They are quick growing birds which are generally males but can also be a female. They are grown for 6-7 weeks when they attain a weight of 1.5-2 kg. Broilers are sold in fresh or frozen form after removal of feathers, head and feet.

7. Which of the following is not a characteristic feature of Layers?
a) Females having a high rate of egg production
b) They are never vaccinated
c) Birds are given a fresh balanced diet
d) The best layers belong to White Leghorn
Answer: b
Clarification: Layers are females which have a high rate of egg production. Birds are always vaccinated. They are debeaked twice. Birds are always given fresh balanced diet. Females start laying eggs in about 22 weeks. The best layers belong to White Leghorn.

8. Usually, females of dual-purpose breeds are raised as broilers while the males are raised as layers.
a) True
b) False
Answer: b
Clarification: Dual purpose breeds are the breeds which are raised both as broilers as well as layers. Usually, males of dual-purpose breeds are raised as broilers while the females are raised as layers.

9. Which of the following is not obtained by eating eggs?
a) Protein
b) Lipid
c) Carbohydrate
d) Alcohol
Answer: d
Clarification: Egg contains 12.9% of protein. It contains 11.5% of lipids which is mostly found in the egg yolk. It contains 0.2-0.7% of carbohydrates. Egg contains almost all minerals and vitamins.

10. The following diagram represents which of the following chicken?

a) White Plymouth Rock
b) White leghorn
c) White Cornish
d) Hubbard
Answer: b
Clarification: The given figure represents White leghorn. It is the most common poultry bird with an average egg output of 250 per annum. The best layers belong to white leghorn.

11. Which of the following is an Indian breed of Poultry?
a) Busra
b) White leghorn
c) Australorp
d) Plymouth Rock
Answer: a
Clarification: Busra is an Indian breed of Poultry. Other examples include Ghagus, Aseel, Chittagong, Cochin, Brahma, Kadaknath. White Leghorn, Australorp and Plymouth Rock are Mediterranean, British and American breeds respectively.

12. Which of the following is not an exotic breed reared in India?
a) Rhode Island Red
b) White leghorn
c) Plymouth Rock
d) Ghagus
Answer: d
Clarification: Presently, in India, about 80% of the chicken are reared from three exotic breeds-Rhode Island Red, White leghorn (for eggs) and Plymouth Rock (for broilers). Crosses have been made between exotic and indigenous breeds in order to increase immunity against diseases.

Biology Multiple Choice Questions on “Plant Diseases caused by Viruses and Bacteria”.

1. Which of the following group of viruses generally attack plants?
a) Retroviruses
b) Riboviruses
c) Rheoviruses
d) Enteroviruses
Answer: b
Clarification: Viruses that generally affect plants are riboviruses with ssRNA genome. Viruses are obligate parasites which are nucleoprotein entities consisting of DNA or RNA as the genetic material. 50% of the plants are rod-like.

2. Which of the following is not a method by which viral infection spreads in plants?
a) Exuding sap of infected plants
b) Infected seeds
c) Through meristem
d) Infected pollen
Answer: c
Clarification: Virus infection spreads from either an infected plant or plant residue by agricultural implements, exuding sap of infected plants, vegetative propagules, infected seeds or pollen, Aphids, mites or other insect vectors, Nematodes and Fungal spores.

3. Which of the following is not a method by which a virus enters a healthy host?
a) By vectors
b) Meristem
c) Infected fungal spores
d) Through wounds
Answer: b
Clarification: Virus enters the healthy host through wounds made mechanically or by vectors, infected fungal spores and infected pollen. They enter the cells, multiply and reach phloem which helps in spreading the virus throughout the plant.

4. Common symptoms of viral infection in plants are local lesions and ring spots.
a) True
b) False
Answer: a
Clarification: Common symptoms of viral diseases in plants are mosaics, local lesions, necrosis, ring spots, pitting, stunting, proliferation, leaf rolls, etc. Variegation of flowers (flower breaking) produces unique designs.

5. Which of the following is not a common measure of controlling viral infections?
a) Using healthy virus-free seeds
b) Antibiotics
c) Using resistant varieties
d) Protection from insect vectors
Answer: b
Clarification: Pesticides and antibiotics are useless in controlling viral infections. Control is achieved through resistant varieties, using healthy virus-free seeds, protection from insect vectors, sterilisation of agricultural implements and sanitation.

6. Which of the following organism causes Bean Mosaic Disease in plants?
a) Virus
b) Bacteria
c) Fungi
d) Nematode
Answer: a
Clarification: Bean Mosaic Disease is caused by mainly two viruses, Common Mosaic Virus and Yellow Mosaic Virus. It is a common disease of beans of all types like Soya bean, Mung bean, Urd bean, French bean, Broad bean, Winged bean, etc.

7. Which of the following is not a symptom of Bean Mosaic disease?
a) Plants are bunchy
b) Leaves show mottling
c) Mosaic appearance on leaves
d) Blackening of leaflets
Answer: d
Clarification: Bean mosaic infected plants are stunted and bunchy. Their leaves show mottling, yellowing and malformations. Mosaic appears due to the occurrence of light and dark green areas with clearing or yellowing of veins. Seeds are small, malformed or aborted.

8. Which of the following is not a method of overcoming the infection of Bean mosaic disease?
a) Virus-free seeds
b) Cutting leaves
c) Delayed planting
d) Sowing resistant varieties
Answer: b
Clarification: Infection of mosaic virus can be overcome by using virus-free seeds, delayed planting, sowing resistant varieties, by removal of weeds and hosts of the virus, soil treatment with insecticides and foliar spray to restrict vectors.

9. Which of the following is not a bacterial plant pathogen?
a) Pseudomonas
b) Clostridium
c) Puccinia
d) Xanthomonas
Answer: b
Clarification: About 900 species of bacteria are plant pathogens, e.g; species of Acidovorax, Pseudomonas, Rhizobacter, Rhizomonas, Xanthomonas, Bacillus, Clostridium, Clavibacter, etc. Bacterial pathogens of plants may be obligate pathogens, facultative pathogens and facultative saprophytes.

10. Bacteria spread from infected plants to healthy plants only by air currents.
a) True
b) False
Answer: b
Clarification: Bacteria spread from infected plants to healthy plants by air, water, mechanical contact, insects, other animals and human beings. Some insects function as vectors in which bacteria can survive and multiply.

11. Which of the following is not a symptom of bacterial diseases in plants?
a) Blight
b) Mosaic
c) Wilts
d) Rots
Answer: b
Clarification: The symptoms of bacterial disease in plants include local lesions and necrosis, blights, rots, wilts, overgrowths, thickness and galls, stunting, scabs and cankers.

12. Which of the following is not a method of controlling bacterial diseases in plants?
a) Roguing of infected plants
b) Sanitation methods
c) Quarantine
d) Virus-free seeds
Answer: d
Clarification: Bacterial diseases in plants can be controlled by roguing of infected plants, sanitation measures, use of healthy disease-free seeds, chemical sprays, antibiotics, periodic sterilisation of soil and by growing resistant varieties.