Latest Biological Science Reviewer 7 - LET EXAM - Questions & Answers

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Latest Biological Science Reviewer 7


1. Which of the following is the primary basis for classifying viruses?

A. Chemical composition
B. Host preference
C. Mode replication
D. Morphology

Ans: B. Host preference
- Classification of viruses is defined by host preference, viral morphology, genome type auxiliary structures such as tails or envelopes. Viral particles outside a host cell (so called virions) are inert entities with a genome surrounded by a protective coat.

2. Which fungal groups does NOT reproduce sexually at all; instead it has large distinctive asexual spores?

A. Ascomycetes
B. Basidiomycetes
C. Chytridiomycetes
D. Glomeromycetes

Ans: Glomeromyetes are an important group of fungi that live in close symbiotic  association with with the roots of trees and plants. They reproduce asexually y producing glomerospores and cannot survive without the presence of plant  roots.

3. What is the basis of classifying cocci and bacilli together  in one group?

A. Cell Wall
B. Number of flagella
C. Nutrition
D. Shape

Ans: D. Shape
- In 1872, German biologist Ferdinand Julius Cohn classified bacteria into four major types depending on their shapes (spherical, short rods, threads and spiral). Cocci are types of bacteria are unicellular, spherical or ellipitical shape. Bacilli are rod shaped or cyclindrical bacteria which either remain singly or in pairs

4. Which of the following bacteria has no flagella?

A. Amphitrichous
B. Atrichous
C. Lophotrichous
D. Peritrichous

Ans: B. Atrichous
- Bacteria may be classified according to the presence and absence of flagella. Bacteria without flagella are called atrichous. Monotrichous are bacteria with flagellum attached to one and the bacteria cell. Lophotrichous are bacteria with flagella attached to one end of the bacteria cell. Amphitrichous are bacteria will bunch of flagella arising from both end of the bacteria cell. Peritrichous are bacteria with flagella that are evenly distributed surrounding the entire bacterial cell.

5. A bacterium retained the Gram stain when washed with absolute alcohol and acetone. How will you classify the bacterium?

A. Gram positive
B. Gram negative
C. Miscellaneous staining
D. Not enough information given


Ans: A. Gram positive
- In 1884, Danish scientist Hans Christian Gram devised a method to differentiate two types of bacteria based on the structural differential in their cell wall. In his test, bacteria that retain the crystal violet dye do so because of a thick layer of peptidoglycan and are called Gram-positive bacteria. In contrast, Gram-negative bacteria do not retain the violet dye and are colored red or pink. Chemically, Gram stain is a weak alkaline solution of crystal solution of crystal violet. Compared with Gram-positive bacteria, Gram-negative bacteria are more resistant against antibodies because of their impenetrable cell wall
  
6. Which of the following disease is caused by virus?

A. Cholera
B. Rabies
C. Tetanus
D. Tubercolosis

Ans: B. Rabies
-Rabies infection is caused by the rabies virusis required is spread through the saliva of infected animals. Infected animals can spread the virus by biting another animal or a person. Tetanus, also called lockjaw is a serious infection caused by Clostridium tetani ; this bacteria producers a toxin that afftects the brain and nervous system. A bacterium called Mycobacterium tuberculosis.

7. Which is the causative agent of mad cow disease

A. Bacterium
B. Prion
C. Virus
D. Worm

Ans: B. Prion
- Mad cow disease is an infectious disease caused by prions that the brains of cattle. It is a fatal disease that slowly destroy the brains and spinal cord (central nervous system) in cattle. The actual name of the disease is bovine  spongiform encephalopathy (BSE) a name refers to the changes seen in brain tissue affected cows, Prions are protein molecules that do not contain DNA or RNA and can cause disease in animals.

8. Which prevent/s the stomach from being evaded by most microbes?

A. Acids
B. Bile
C. Digestive enzymes
D. Peristalsis

Ans: A. Acids
- Parietal cells in the stomach secrete  roughly two liters of acid a day in the form of hydrochloric acid. In the stomach functions to kill bacteria. Gastric juice consists of HCI and pepsin and can kill bacteria within 15 minutes when the pH is less than 3.0.

9. Which is a sign of infection?

A. Cough
B. Fatigue
C. Nausea
D. Sore throat

Ans: A. Cough
- Most coughs are caused viral infectious. Although coughing can be a sign of a serious illness more often, it will clear up on its will clear up on its own without the need for medical attention.

10. Which bacteria multiply in the blood?

A. Fungemia
B. Protistemia
C. Speticemia
D. Viremia

Ans: C. Speticemia
- Septicemia is a serious bloodstream infection. It’s also known as bacteremia or blood poisoning. Septicema occurs when a bacterial infection occurs elsewhere in the body, such as in lungs or skin enter the blood stream

11. All are indirect transmission modes of disease spread EXCEPT _____________ .

A. placental transfer
B. droplet in the air
C. eating contaminated food
D. bites from biological vectors

Ans: A. placental transfer
- Direct contact infections spread when disease-causing microorganisms pas from the infected person to the healthy person via direct physical contact with blood or body fluids VERTICAL TRANSMISSION happens when micro organism pass from a mother to her unborn baby, through the placenta. German measles and HIV can pass this way HORIZONTAL TRANSMISSION happens when microorganism pass from one person to another by touching, kissing or sexual intercourse. Indirect contact happens when microorganism are carried to a person in some way , instead. Indirect contact happens when microorganism BORNE TRANSMISSION involves an object carrying the disease-causing microorganism VECTOR-BORNE TRASMISSION involves an animals such as an  insect. For example malaria transmitted by mosquitoes and plague by fleas.

12. Dinoflagellates are known for producing red tides. In what way are they beneficial?

A. They kill off unnecessary fishes
B. They form limestone when they die
C. they glow to guide fishermen t night
D. They form zooxanthellae that provides coral reef with nutrients

Ans: D. They form zooxanthellae that provides coral reef with nutrients
- zooxanthellae  is a term for any dinoflagellate that participates in symbiosis with sponges. Coral, clams, Mollusk, flat worms jelly fish , etc. zooxanthellae are the symbiotic algae that live within the hard or stony corals. The symbionic relation is based on the corals inablilty to generate sufficient amounts of foods and the algae’s ability for photosynthesis and converting chemical elements into energy. The coral in return provides protection as wel as nutrient rich environment for excellent algae growth.

13. Which of the following is/are an important conclusion/s in Gregor Mendel’s experiments ?

I. An individual inherits one such units from each parent for each trait
II. A trait may not show up in an individual but can still be passed to the next generation.
III. The inheritance of each trait is determined by “units” of “factors” that are passed on to go descendents unchanged.

A. I only
B. I and II only
C. II and III only
D. I, II and III

Ans: D. I, II and III
- All the three statements are major points of Gregor Mendel’s expirements.

14. The gene for seed color in pea plants exist in two forms. There is one form or allele for yellow seed color (Y) and another for green seed colors (y). Which law describes this condition?

A. Law of Dominance
B. Law of Inheritance
C. Law of independent Assortment
D. Law of segregation

Ans: D. Law of segregation
- Law of Segregation(Mendel First law) states that during the formation of reproductive cells (gametes) pairs of hereditary factors (genes) for specific trait separate so that chance determines which factor for a particular trait is inherited traits will    be dominant and the other recessive unless both factors are recessive. All these three are parts of Mendel’s Laws of Inheritance.

15. Based on the findings on Mendel’s dihybrid cross experiments, he was able to formulate the Law of Independent Assortment. Which of the following  BEST describes this law?

A. The biological selection of an allele  for one trait has nothing to do with the selection of an  allele for any other trait
B. During gamete formation. The alleles for each gene segregate from each other so that each gamete carries only one for each gene.
C. Paternal and maternal chromosomes get separated in meiosis and the alletes with the traits of a character are separated into two different gametes
D. Some alleles are dominant while others are recessive; an organism with atleast one dominant allele will display the effect of the dominant allele

Ans: A. The biological selection of an allele  for one trait has nothing to do with the selection of an  allele for any other trait
- In Mendel’s monohybrid crosses, an idealized 3:1 ratio between dominant and recessive phenotypes resulted. In dihybrid crosses, however he found at 9:3:3:1 ratios. This shows that each of the word alleles is inherited independently from the other, with a 3:1 phenotypic ratio for each. Choices B and pertain to the Law of segregation while Choice D refers to the Law of Dominance.

16. What is the main function of chromosomes?

A. They house the DNA
B. They carry genetic information
C. They build the right protein for every cell
D. They caralyze the assembly of amino acids into protein chains

Ans: B. They carry genetic information
- Chromosomes are threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes. Genes

17. What are the sex chromosomes of a male mammal?

A. XX
B. XY
C. YY                                   
D. XYY

Ans: B. XY
- For mammals, the sex chromosomes carried by the sperm determines the sex of the offspring. A male offspring is produce if an egg is fertilized by a Y-bearing sperm, and a female offspring is produce if an egg is fertilized by an X-bearing sperm. Male has XY chromosomes while XX chromosomes.

18. The dominance of an allele may imply that is dominant in the population as a whole. Therefore, the most common allele is always dominant.

A. Absolutely true
B. Absolutely false
C. Not always
D. No enough information given

Ans: C. Not always
- The most common allele is not always dominant. In humans  allele that causes a form of dwarfism known as achondroplasia dominant but it very rare just like the dominant allele that causes Hunting disease, progressive brain disorder.

19. When Mendel crossed a plant derived from a green seed with a plant grow from a yellow seed the off spring could be all yellow, or they could be a mix of green and yellow peas. What does this mean ?

A. The yellow seed trait is a recessive trait
B. The green seed trait is a dominant trait
C. Green seed color is dominant over yellow
D. Yellow seed color is dominant over green

Ans: D. Yellow seed color is dominant over green
- Since the offspring could be all yellow or  a mix of green and yellow peas, the yellow seed trait is said to be dominant over green. Although Mendel reffered to traits as dominant or recessive. Modern biologist reserve these terms for alleles. When two different alleles are present in an organism, the dominant allele may ask the expression of the receive allele. The allele, however, is still present.

20. To whom shall a color-blind man (cY) pass his defective allele?

A. Sons
B. Daughters
C. Both sons and daughters
D. Grandsons and granddaughters

Ans: B. Daughters
- A color blind man (cY) will pass his defective allele only to his daughters, because only his daughters because only his daughters inherit his X chromosomes. Usually the daughters will have normal color vision because they will also inherit a normal C allele from their mother who is very likely homozygous normal (CC)

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