Category: Class 12 Biology Objective Questions

250+ TOP MCQs on Microbes in Household Products-1 and Answers

Biology Multiple Choice Questions on “Microbes in Household Products-1”.

1. Which of the following is also known as baker’s yeast?
a) Saccharomyces cerevisiae
b) Streptococcus pneumonia
c) Leuconostoc mesenteroides
d) Streptococcus faecalis
Answer: a
Clarification: Saccharomyces cerevisiae is also known as baker’s yeast. This yeast is used for fermenting wheat flour after it is kneaded. Similarly, the dough which is used for making bread is also fermented using baker’s yeast.

2. Which of the following gas is responsible for the puffed-up appearance of the dough?
a) NH3
b) CO2
c) O2
d) CH4
Answer: b
Clarification: The dough which is used for making foods such as dosa and idli is fermented by using bacteria like Streptococcus. The puffed-up appearance of this dough is due to the production of CO2 gas.

3. Which of the following enzymes is not produced by baker’s yeast?
a) Amylase
b) Maltase
c) Zymase
d) Lactase
Answer: d
Clarification: Baker’s yeast produces 3 enzymes namely-amylase, maltase and zymase. Amylase changes a small amount of starch into maltose. Maltase changes maltose to glucose and zymase acts on glucose to form bubbles of ethyl alcohol and carbon dioxide.

4. Which of the following bacteria are used for fermenting idli and dosa?
a) Leuconostoc mesenteroides
b) Streptococcus thermophiles
c) Lactobacillus bulgaricus
d) Lactobacillus acidophilus
Answer: a
Clarification: Rice and black gram are soaked overnight, washed, mixed and ground. The mixture is allowed to undergo fermentation with the help of Leuconostoc mesenteroides and Streptococcus faecalis.

5. Which of the following household product is not made from Soybean?
a) Tempeh
b) Yoghurt
c) Sofu
d) Soy sauce
Answer: b
Clarification: Soybean products include Tempeh, Sofu, Tofu and soy sauce. Sofu and Tofu are cheese-like products of soybean obtained after fermentation with Mucor species. While tempeh is an Indonesian food formed by fermenting, drying, salting and frying of soybean.

6. What is the full form of the LAB?
a) Lactic acid Biuret
b) Lactobacillus
c) Lactose basidia
d) Lactic Acid Bacteria
Answer: d
Clarification: LAB stands for Lactic acid bacteria. Indian curd is prepared from both skimmed and cream milk by inoculating the milk with lactic acid bacteria.

7. Milk is a better product than curd.
a) True
b) False
Answer: b
Clarification: Curd is a better product than milk as it removes lactose which some people are allergic. It contains B12 and other vitamins. Curd also possesses antimutagenic and anti-cancerous properties.

8. Which of the following statement is incorrect regarding Yoghurt?
a) It is a fermented milk
b) Mixed with an inoculum containing Streptococcus faecalis
c) Preparation takes approximately 4-5 hours
d) The original flavour of yoghurt is of acetaldehyde
Answer: b
Clarification: Yoghurt is fermented milk. The milk is heated to 80-90°C for half an hour and then it is cooled to 40-43°C and mixed with an inoculum containing Streptococcus thermophilus and Lactobacillus bulgaricus. Preparation of yoghurt takes approximately 4-5 hours. The original flavour of yoghurt and other fermented kinds of milk is of acetaldehyde.

9. Koumiss is fermented milk where a mixture of lactic acid bacteria and yeast are used.
a) True
b) False
Answer: b
Clarification: Koumiss is fermented greyish white milk of east European countries which uses a mixture of Lactobacillus bulgaricus and Lactose fermenting yeast. Kefir is fermented milk where a mixture of lactic acid bacteria and yeast are used as kefir grains.

10. Which of the following viruses is depicted in the diagram below?

a) Tobacco Mosaic Virus
b) Potato spindle virus
c) Influenza virus
d) Coronavirus
Answer: a
Clarification: The given diagram represents the Tobacco mosaic virus which is magnified about 1,00,000-1,50,000 times. D.J. Ivanowsky recognised certain microbes as causal organisms of mosaic disease of tobacco. They were smaller than bacteria because they passed through the bacteria-proof filters.

11. Which of the following parts of a bacteriophage is labelled incorrectly?

a) Head
b) Neck
c) Pins
d) Plate
Answer: c
Clarification: The correct labelling of the diagram of bacteriophage is given as follows:

Bacterial viruses or bacteriophages-viruses that usually infect the bacteria, are usually double-stranded viruses.

250+ TOP MCQs on Biotechnology – Processes of Recombinant DNA Technology and Answers

Biology Problems for Schools on “Biotechnology – Processes of Recombinant DNA Technology – 3”.

1. The enzyme which cleaves proteins is ______
a) protease
b) RNase
c) lipase
d) Dnase
Answer: a
Clarification: The enzyme which cleaves proteins is a protease. RNase is the enzyme that cleaves the RNA. Lipases are responsible for the breakdown of lipids while DNase catalyzes the breakdown of DNA.

2. Which protein helps in DNA winding?
a) Helicase
b) Histone
c) Lipase
d) Cellulase
Answer: b
Clarification: The DNA is wound around histone proteins. They are alkaline in nature which helps in packaging and condensation of DNA. DNA wound around histone forms a complex called a nucleosome.

3. Which chemical is used to obtain a precipitate of pure DNA?
a) Methanol
b) Ether
c) HCl
d) Ethanol
Answer: d
Clarification: Ethanol is used to obtain the precipitate of pure DNA. It’s used in concentrating and de-salting of nucleic acids. It makes the nucleic acid less hydrophilic thus easing their extraction.

4. DNA is _____ charged.
a) positively
b) neutral
c) negatively
d) polar
Answer: c
Clarification: DNA is a negatively charged molecule. This negative charge arises due to the presence of negatively charged oxygen present in phosphate groups of DNA backbone.

5. DNA moves towards ______ during agarose gel electrophoresis.
a) negative terminal
b) cathode
c) anode
d) does not move
Answer: c
Clarification: During agarose gel electrophoresis the DNA moves towards the anode. Since DNA is negatively charged it moves toward the positively charged terminal. An anode is a positive terminal while the cathode is the negative terminal.

6. Which enzyme helps in joining of DNA?
a) Lyase
b) Ligase
c) Helicase
d) Lipase
Answer: b
Clarification: Ligases are the enzyme that helps in the joining of two strands of DNA. Lyase is responsible for the breakdown of molecules. Helicase helps in the unwinding of DNA. Lipases are enzymes that breakdown lipids.

7. What does PCR stand for?
a) Polymerase chain radioactivity
b) Polymerase chitin reaction
c) Phenol carbohydrate reaction
d) Polymerase chain reaction
Answer: d
Clarification: PCR stands for Polymerase chain reaction. It is a technique used for DNA amplification. It was developed by Kary Mullis and is a useful technique in genetic engineering.

8. The three steps involved in PCR are ________
a) annealing, extension, and denaturation
b) extension, denaturation, and annealing
c) denaturation, annealing, and extension
d) denaturation, extension, and annealing
Answer: c
Clarification: Denaturation, annealing, and extension are three steps involved in PCR. In denaturation, the DNA is denatured. The primers are added in annealing and in extension, the primers extend giving rise to new DNA strands.

9. Taq polymerase is obtained from _______
a) S.typhi
b) E.coli
c) Thermus aquaticus
d) Thermophilus
Answer: c
Clarification: Taq polymerase is a type of DNA polymerase obtained from the bacteria Thermus aquaticus. It is a thermophilic bacteria and its polymerase remains active at high temperatures (>80°C).

10. The transformants containing ______ gene will grow on plates containing antibiotics.
a) antibiotic-resistance
b) amino acid
c) selectable marker
d) vitamin-resistance
Answer: a
Clarification: The transformants which will be successfully transformed and consisting of an antibiotic-resistance gene will grow on plates containing antibiotics. This gene can act as a selectable marker to differentiate between transformants and non-transformants. The non-transformants will not grow on a plate containing antibiotics and will eventually die.

11. Bioreactors can contain volume up to ______ litres.
a) 20
b) 100-1000
c) 1000000
d) 50
Answer: b
Clarification: Bioreactor is a device or vessel which helps in carrying out various biological reactions providing them optimum conditions. It helps in the proper growth of organisms giving us the desired product with its high yield.

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250+ TOP MCQs on Organisms and Populations – Major Abiotic Factors and Answers

Biology Multiple Choice Questions on “Organisms and Populations – Major Abiotic Factors – 1”.

1. Which of the following is known as an edaphic abiotic factor?
a) Light
b) Soil
c) Air
d) Water
Answer: b
Clarification: The edaphic abiotic factor is soil. Edaphic itself means related to soil. Soil is an important abiotic factor affecting the growth of plants. Soil provides support, minerals, and water to plants.

2. Which of the following is known as a topographic abiotic factor?
a) Earth’s surface
b) Wind
c) Temperature
d) Humidity
Answer: a
Clarification: The topographic abiotic factor is the Earth’s surface. It tells about the physical features of a surface or region. It contains geographic positions and elevations for both natural and man-made features.

3. What is the temperature at hydrothermal sea vents?
a) 50°C
b) 110°C
c) 25°C
d) 0°C
Answer: b
Clarification: The hydrothermal sea vents are present at sea-floor. It includes geysers or hot springs present on the ocean floor which contains geothermally heated water. It has a temperature above 100°C which may rise up to 400°C.

4. Which animal is not found in the forests of Kerala?
a) Cow
b) Bats
c) Cat
d) Snow leopard
Answer: d
Clarification: Snow leopards are not found in the forests of Kerala. They are native to mountain ranges of central and north Asia. They require low temperatures for survival while Kerala has high temperatures and no snowfall.

5. Which one of the following is an abiotic factor?
a) Animals
b) Plants
c) Humidity
d) Fungi
Answer: c
Clarification: Among the following humidity is an abiotic factor. Humidity is invisible to vapors in the atmosphere. It directly affects the vegetation by affecting the rate of transpiration in plants. The rate of transpiration increases with a decrease in humidity.

6. What are plants growing at high temperatures alternatively called?
a) Mesotherms
b) Megatherms
c) Microtherms
d) Conifers
Answer: b
Clarification: The plants growing at high temperatures are termed as megatherms. These plants usually grow near the equator in tropical rainforests. They need abundant moisture along with high temperatures.

7. What are plants growing in high-low temperature called?
a) Microaerophils
b) Megatherms
c) Microtherms
d) Mesotherms
Answer: d
Clarification: Mesotherms are plants that survive at a high temperature of summer along with a low temperature of winter. They are found deciduous forests of tropical and subtropical regions.

8. What are plants growing at low temperatures called?
a) Mesotherms
b) Megatherms
c) Microtherms
d) Shrubs
Answer: c
Clarification: Plants growing at low temperatures are called microtherms. They are found in temperate regions with high altitudes. Mostly consists of coniferous plants.

9. What are plants growing at very low temperatures called?
a) Mesotherms
b) Microtherms
c) Megatherms
d) Hekistotherms
Answer: d
Clarification: Hekistotherms are the plants growing at very low temperatures. They are found in tropic regions (Arctic and Alpine). Alpine plants grow maximally at low temperatures.

10. What are warm-blooded animals called?
a) Tropical
b) Mesotherms
c) Homeotherms
d) Euryhaline
Answer: c
Clarification: The warm-blooded animals are called homeotherms. They have the ability to maintain their body temperature at a constant level despite the change in temperature of the surrounding environment. Examples are mammals, birds.

11. What are cold-blooded animals called?
a) Homeotherms
b) Poikilotherms
c) Littoral
d) Stenohaline
Answer: b
Clarification: Poikilotherms are cold-blooded animals. They cannot regulate their body temperature and take on the temperature of their surrounding environment. An example is reptiles.

12. Which is a universal solvent?
a) Alcohol
b) Ether
c) Water
d) Benzene
Answer: c
Clarification: Water is a universal solvent. It can dissolve almost any solute that is solid, liquid or gas. It is polar in nature and can form various types of bonds and interactions with other molecules.

13. What are plants growing in an aquatic environment called?
a) Mesotherms
b) Hydrophytes
c) Tropical
d) Microtherms
Answer: b
Clarification: Plants growing in or on the water are called hydrophytes. They survive in water for such a long time with the help of osmosis. They have a large number of stomata on the upper surface which helps in more loss of water and helps in survival.

14. Which one of the following is a problem for aquatic animals?
a) Wind
b) Precipitation
c) Humidity
d) Endo osmosis
Answer: d
Clarification: Endo-osmosis is a problem for aquatic animals. It leads to an increase in body fluid concentration which may lead to cell lysis. Also, exo-osmosis may also harm these animals as this leads to water loss from the body leading to shrinkage and dehydration.

15. Organisms that can tolerate a wide range of salinities are called?
a) Euryhaline
b) Mesotherms
c) Temperate
d) Stenohaline
Answer: a
Clarification: Organisms that can tolerate a wide range of salinities are called euryhaline. These organisms can live in fresh, brackish or salty water. An example is a salmon.

250+ TOP MCQs on Population Interactions-4 and Answers

Biology Assessment Questions for Class 12 on “Population Interactions-4”.

1. In which of the following a free-living organism catches kills and eats individuals of other species?
a) Commensalism
b) Parasitism
c) Mutualism
d) Predation
Answer: d
Clarification: Predation is an interaction in which an organism (predator) is benefited by killing another organism (prey). It is the ecological process of energy transfer and best-known examples involve carnivorous interactions.

2. Which is an important predator in the rocky intertidal communities of the American Pacific Coast?
a) Pisaster
b) Labeo
c) Camel
d) Shark
Answer: a
Clarification: Pisater is an important predator in the rocky intertidal communities of the American Pacific Coast that feeds on barnacles, planktons, echinoids, etc. Predation is an interaction in which an organism (predator) is benefited by killing another organism (prey).

3. In which condition the prey might become extinct?
a) When the predator is less
b) When the prey is overexploited
c) When the prey is less
d) When the predator is overexploited
Answer: b
Clarification: The prey might become extinct when the prey itself is overexploited or killed by the predators. Predation is an interaction in which an organism (predator) is benefited by killing another organism (prey).

4. What are insects living on plant sap called?
a) Photophagous
b) Cynophagous
c) Autophagous
d) Phytophagous
Answer: d
Clarification: Phytophagous are insects living on plant sap. These insects attack fruits, flowers, leaves, stems, and roots. These are herbivores feeding on herbs (plants).

5. Which one of the following are a morphological means of defense?
a) Leaves
b) Petals
c) Thorns
d) Stem
Answer: c
Clarification: Thorns of plants are morphological means of defense. They are pointy branches or stems. They protect plants against herbivores. They are the first line of defense in plants.

6. Which one of the following is a chemical produced by plants against grazers and browsers?
a) Sap
b) Opium
c) Water
d) Agar
Answer: b
Clarification: Opium is the chemical produced by plants against grazers and browsers. These are secondary metabolites. Along with this plants also produce alkaloids, benzoxazinoids, cyanogenic glycosides, glucosinolates, terpenoids, and phenolics for chemical defense.

7. What do South American lakes visiting flamingoes and resident fishes compete for?
a) Phytoplankton
b) Small fishes
c) Water
d) Zooplankton
Answer: d
Clarification: The visiting flamingoes and resident fishes of the South American lakes compete for zooplankton. It is an example of competition. In competition interaction, the fitness of one organism overpowers the presence and fitness of another.

8. Which organism has become extinct in the Galapagos Islands?
a) Goats
b) Birds
c) Abingdon tortoise
d) Herbs
Answer: c
Clarification: Abingdon tortoise has become extinct in the Galapagos Islands due to the introduction of goats in that area. This was due to the greater browsing capacity of goats. It is an example of a competition in which the presence of goats lowered the fitness of tortoise.

9. What is the phenomenon called in which two species competing for the same resources can avoid competition by choosing?
a) Resource structuring
b) Competition
c) Predation
d) Resource partitioning
Answer: d
Clarification: Resource partitioning in which two species competing for the same resources can avoid competition by choosing. In this, the resources are divided by the species within an ecological niche. It is an adaptation of interspecific competition.

10. Who dominates on the rocky sea coasts of Scotland?
a) Shark
b) Aquatic plants
c) Larger and competitively superior barnacle Balanus
d) Smaller barnacle Chathamalus
Answer: c
Clarification: The larger and competitively superior barnacle BalanusI dominates the rocky coasts of Scotland. Due to this the smaller barnacle Chathamalus is excluded from that zone. It is an example of ‘competitive release’ which was shown by Connell’s elegant field experiments.

11. What is a mutualistic relationship between a fungus and photosynthesizing algae called?
a) Mycorrhiza
b) Lichens
c) Cyanobacteria
d) Sponges
Answer: b
Clarification: The mutualistic relationship between a fungus and photosynthesizing algae is called lichens. It is a composite organism and has many colors, forms, and sizes. They are used in the food industry, making dyes and have medicinal use.

12. For what purpose does the female wasp use the fruit?
a) Prey
b) Predation
c) Oviposition
d) Playing
Answer: c
Clarification: The female wasp uses fruit to lay its eggs i.e. oviposition. It also uses the developing seeds of fruits for nourishing its larvae. In return, the wasp helps in the pollination of fig inflorescence.

13. Pseudo-copulation occurs in which of the following flower?
a) Rose
b) The Mediterranean orchid Ophrys
c) Mangifera indica
d) Neem
Answer: b
Clarification: Pseudo-copulation is observed in the Mediterranean orchid Ophrys. It is the process in which the male copulates with the flowers that resemble the female insect of the same species. It is observed in bees, flies, and wasps.

14. Which plant has lost its chlorophyll and leaves in the course of evolution?
a) Mango
b) Cactus
c) Neem
d) Cuscuta
Answer: d
Clarification: Cuscuta a parasitic plant has lost its chlorophyll during the course of evolution. It is an obligate, ectoparasitic dodder plant that completely depends on the host for nutrients. It binds to the host with the help of haustoria.

15. The cattle egret shows commensalism with which organism?
a) Grazing cattle
b) Dog
c) Cat
d) Fish
Answer: a
Clarification: The cattle egret shows commensalism with grazing cattle. It is a white-colored bird that eats insects and flies wandering around cattle. It is a relationship in which the egret is benefited while the cattle are neither harmed nor benefited.

To practice Biology Assessment Questions for Class 12,

250+ TOP MCQs on Ecological Succession and Answers

Biology Assessment Questions for Pharmacy Entrance Exams on “Ecological Succession”.

1. Which of the following community develops during the end of the biotic succession?
a) Pioneering community
b) Climax community
c) Primary community
d) Secondary community

Answer: b
Clarification: The changes in the community are constant, orderly and sequential. These changes lead to the formation of a stable, self-perpetuating and final biotic community that developed during the end of biotic succession known as a climax community.

2. Which of the following is known as the first biotic community to develop on a bare land?
a) Pioneer community
b) Climax community
c) Secondary community
d) Individual community

Answer: a
Clarification: The first biotic community to invade a bare land or area is known as the pioneer community. This community consists of one or fewer species containing small-sized organisms. Mostly mosses, lichens, and lower grass species are the pioneering species.

3. Which community develops in between the pioneering and climax communities?
a) Primary community
b) Transitional community
c) Secondary community
d) Tertiary community

Answer: b
Clarification: The community occupying intermediate place or developing between the pioneering and climax communities is called a transitional community. Seral communities are the individual transitional communities of a sere that develop in that area during the succession.

4. Imagine a barren land where once existed a forest. Due to deforestation and fire in that forest, all the species got extinct. A new species came, colonized and expanded in this forest. What kind of succession pattern did this species follow?
a) Primary succession
b) Climax succession
c) Tertiary succession
d) Secondary succession

Answer: d
Clarification: The species in the above example follow a secondary succession. A biological succession occurring in the barren area where there, once life existed is known as secondary succession.

5. Imagine a newly created barren land made of igneous rocks. Some new species came, colonized and grew in this rocky area. What kind of succession pattern did this species follow?
a) Secondary succession
b) Climax succession
c) Primary succession
d) Tertiary succession

Answer: c
Clarification: The species in the above example follow a primary succession. A biological succession (growth of living organisms) occurring on a previously unoccupied or bare land is known as primary succession.

250+ TOP MCQs on Environmental Issues – Water Pollution and its Control – 1 and Answers

Biology Multiple Choice Questions on “Environmental Issues – Water Pollution and its Control – 1”.

1. When the government of India did pass the Water (Prevention and Control of Pollution) Act?
a) 1999
b) 1974
c) 1896
d) 2010
Answer: b
Clarification: In 1974, the Water (Prevention and Control of Pollution) Act was passed by the government of India. It is comprehensive legislation for maintaining or restoring of wholesomeness of water by prevention and control of the pollution of water.

2. How much percent of impurities are enough to make domestic sewage unfit for humans?
a) 0.1 percent
b) 1 percent
c) 5 percent
d) 10 percent
Answer: a
Clarification: To make domestic sewage unfit for humans 0.1 percent of impurities are enough. These 0.1 percent impurities contain dissolved materials (ammonia, nitrate, sodium, etc.), colloidal materials (bacteria, cloth, fecal matter, etc.) and suspended solids (clay, sand, and silt).

3. Which of the following are the suspended solids in the domestic sewage?
a) Ammonia
b) Sand
c) Calcium
d) Bacteria
Answer: b
Clarification: The suspended solids like sand, clay, and silt are commonly found in domestic sewage. They are the impurities that are visible and do not dissolve in water. They can be removed easily by physical or mechanical means.

4. Which of the following are the colloidal materials present in domestic sewage?
a) Calcium
b) Sand
c) Ammonia
d) Fecal matter
Answer: d
Clarification: The substances that do not readily dissolve in water but also are not settled down are known as colloidal substances. They may be filtered out in a Gooch Crucible and contains fecal matter, bacteria, cloth, and paper fibers.

5. Which of the following are the dissolved materials present in domestic sewage?
a) Sand
b) Clay
c) Nutrients
d) Bacteria
Answer: c
Clarification: These are the smaller size particles that can easily pass through all the filters hence said as dissolved materials. They contain various nutrients like ammonia, calcium, nitrate, phosphate, and sodium.

6. Which materials are easily removed from the polluted water?
a) Liquid
b) Solids
c) Dissolved
d) Nutrients
Answer: b
Clarification: The large-sized solid materials can be easily removed from the polluted water by physical or mechanical means. These can be plastics, metals, sand, etc.

7. Which materials are hard to remove from the polluted water?
a) Sand
b) Plastic
c) Solids
d) Dissolved salts
Answer: d
Clarification: The smaller sized dissolved materials are hard to remove from domestic sewage water as they can pass through the filters easily. They contain nutrients such as ammonia, calcium, nitrate, phosphate, and sodium.

8. Which sewage contains biodegradable waste such as organic matter?
a) Medical waste
b) Plastic waste
c) Domestic waste
d) Wild waste
Answer: c
Clarification: The biodegradable organic matter is a component of domestic sewage. The organic compounds present in domestic wastewater are carbohydrates, proteins, and fats (containing carbon, hydrogen, oxygen, nitrogen, sulphur, phosphorus, etc.).

9. Who is responsible for the degradation of biodegradable organic matter present in the domestic sewage?
a) Animals
b) Humans
c) Plastic
d) Bacteria and other microbes
Answer: d
Clarification: The degradation of biodegradable organic matter present in the domestic sewage is done by microbes. They degrade this organic matter and uptake the essential nutrients required for their growth and development.

10. How is the amount of biodegradable organic matter in sewage water estimated?
a) Chemical Oxygen Demand
b) Physical Oxygen Demand
c) Biological Oxygen Demand
d) Mathematical Oxygen Demand
Answer: c
Clarification: The amount of biodegradable organic matter in sewage water estimated with the help of biological oxygen demand. It is used for indicating the organic strength of wastewater. It is designated as BOD.

11. Who utilizes the maximum amount of oxygen in the upstream of sewage discharge?
a) Animals
b) Microorganisms
c) Humans
d) Plants
Answer: b
Clarification: In the upstream of sewage water, the maximum oxygen is used by the microorganisms. Due to this, there is less oxygen availability in the downstream that is rivers, ponds, or the other water bodies where the fully processed wastewater is released.

12. What happens when the maximum amount of oxygen in the upstream of sewage discharge is utilized by microbes?
a) Natality of aquatic plants
b) Natality of aquatic fishes
c) Mortality of aquatic creatures
d) Mortality of bacteria
Answer: c
Clarification: When the maximum amount of oxygen in the upstream of sewage discharge is utilized by microbes, there is less oxygen availability in the downstream that is rivers, ponds, or the other water bodies. Due to this, the aquatic organisms living in that respective ecosystem die due to a deficiency of oxygen.

13. What is the excess growth of plankton in water due to the presence of nutrients called?
a) Fungal bloom
b) Algal bloom
c) Plantae bloom
d) Animal bloom
Answer: b
Clarification: The excessive growth of planktons in any water body due to the presence of nutrients is known as an algal bloom. An algal bloom or marine bloom or water bloom is a rapid increase of algae in an aquatic system (freshwater as well as marine water).

14. Which of the following is the effect of high BOD?
a) More birth of aquatic plants
b) More birth of fishes
c) Higher dissolved oxygen
d) Lower dissolved oxygen
Answer: d
Clarification: The high BOD results in the reduction of dissolved oxygen in the water. This is because the maximum amount of oxygen is utilized by microbes in decomposing the organic wastes of water.

15. What do BOD and COD stand for?
a) Biological Oxygen Demand and Chemical Oxygen Demand respectively
b) Chemical Oxygen Demand and Biological Oxygen Demand respectively
c) Botanical Oxygen Demand and Chemical Oxygen Demand respectively
d) Basic Oxygen Demand and Chemical Oxygen Demand respectively
Answer: a
Clarification: The BOD and COD stand for the Biological Oxygen Demand and Chemical Oxygen Demand respectively. BOD is the dissolved oxygen is utilized by microbes in decomposing the organic wastes of water while COD is the measure of the amount of oxygen necessary to oxidize all the pollutants present in water.