All Free Biology MCQs with Answers

91. A transgenic organism is one that

• A. has been cloned from an adult cell
• B. has twice the normal number of chromosomes
• C. has been produced by crossing two closely related species
• D. carries a functional gene deliberately transferred from another species

Explanation: Transgenic animals and plants express a foreign gene, examples being goats that secrete a human clotting factor in their milk and crops given a bacterial gene for pest resistance. The change is heritable because the gene is present in every cell including the gametes. A clone carries no foreign gene at all, which is why cloning and genetic modification are separate ideas.

92. Bt cotton, widely grown in Pakistan, has been given a gene from a bacterium so that the plant can

• A. produce a protein toxic to the insect pests that attack it
• B. fix nitrogen from the air
• C. survive without any water
• D. ripen its bolls faster

Explanation: The gene comes from Bacillus thuringiensis and codes for a crystal protein that kills bollworm larvae feeding on the plant, so far less insecticide has to be sprayed. The benefits are lower cost and less chemical exposure for farm workers, while the main concern is that pest populations may evolve resistance if the crop is grown continuously. Nitrogen fixation by cereals and cotton remains a research goal, not an achievement.

93. The main achievement of the Human Genome Project was

• A. curing all inherited diseases
• B. determining the complete base sequence of human DNA
• C. producing the first cloned human being
• D. creating an artificial human chromosome

Explanation: The project, completed in draft form in 2001, established the order of roughly three billion base pairs and located about twenty thousand protein coding genes. Knowing the sequence is the starting point for identifying disease genes, designing drugs and studying human evolution, but it is not itself a cure for anything. No human has been cloned, and doing so is banned in almost every country.

94. Stem cells are valuable in medicine because they

• A. cannot be rejected by any patient
• B. are found only in bone marrow
• C. are unspecialised and can divide and differentiate into several types of cell
• D. contain twice as many genes as ordinary cells

Explanation: Because they are not yet committed, stem cells can be directed to replace tissue that the body cannot regenerate, such as heart muscle after an infarction or nerve cells after injury, and bone marrow transplants already use them routinely. Embryonic stem cells can form any tissue but raise ethical objections, while adult stem cells are more limited in what they can become. Every cell of a person carries the same genes.

95. The hepatitis B vaccine now in use is made by

• A. killing whole hepatitis B viruses with formalin
• B. growing the virus in chick embryos
• C. collecting antibodies from recovered patients
• D. inserting the gene for a viral surface protein into yeast, which then makes that protein

Explanation: Only the surface antigen is produced, so the vaccine can provoke an immune response with no possibility of causing the disease and with no need to handle live virus. Vaccines of this kind are called subunit or recombinant vaccines. Collecting antibodies from recovered patients would give passive immunity for a few weeks, which is treatment rather than vaccination.

96. Interferon, once extremely expensive because it had to be extracted from human blood, is now obtained by

• A. expressing the human interferon gene in cultured microorganisms
• B. chemical synthesis from simple sugars
• C. purifying it from the milk of cows
• D. growing viruses in the laboratory and collecting their protein

Explanation: Cloning the gene into bacteria or yeast turned a protein that could only be obtained in microgram amounts into one that can be produced by the kilogram, which is what made treatment of hepatitis C and some cancers practical. This cost collapse is the general pattern of recombinant protein manufacture, as it was with insulin and growth hormone. Interferon is a human protein, not a viral one.

97. Which is a genuine concern about growing genetically modified crops?

• A. The modified gene will change the DNA of the person eating the crop
• B. The introduced gene may spread by pollen to wild relatives or to non modified fields
• C. GM crops cannot reproduce at all
• D. GM crops always give lower yields than ordinary varieties

Explanation: Gene flow through pollen is a documented and measurable risk, and it can create herbicide resistant weeds or contaminate the crop of a neighbouring farmer who is not growing the modified variety. Eaten DNA is digested into nucleotides like any other DNA, so it does not enter human cells, and yields are usually equal or higher. Separating real risks from imaginary ones is the point of this question.

98. To obtain a human gene without its introns, genetic engineers make a DNA copy of the mature messenger RNA using

• A. DNA ligase
• B. restriction endonuclease
• C. reverse transcriptase
• D. DNA helicase

Explanation: Reverse transcriptase, taken from retroviruses, builds a complementary DNA strand on an RNA template, and since the introns have already been spliced out of mature mRNA the resulting cDNA is a continuous coding sequence. This matters because a bacterium has no splicing machinery and could not process a gene containing introns. Ligase and restriction enzymes join and cut DNA but cannot copy RNA.

99. Which of the following is an ethical rather than a technical objection to human cloning?

• A. The success rate of nuclear transfer is very low
• B. Cloned animals have often shown health problems
• C. The technique needs a large number of donor eggs
• D. A cloned child would be created as a copy of someone else rather than as an individual

Explanation: The first three statements are practical limitations that better technique might eventually overcome, whereas the last concerns human dignity and would remain even if the method became perfectly safe. Distinguishing the two kinds of objection matters, because only the ethical one explains why reproductive cloning of humans is banned outright rather than merely regulated. Therapeutic cloning to grow tissues is judged separately.

100. The wall of the left ventricle is much thicker than that of the right ventricle because it

• A. holds a far larger volume of blood
• B. must pump blood against the much greater resistance of the systemic circuit
• C. contains more valves than the right ventricle
• D. receives blood at a higher pressure from the left atrium

Explanation: Both ventricles eject the same volume with each beat, but the left has to drive blood through the whole body while the right only sends it to the lungs a short distance away and at low pressure. More cardiac muscle means a higher pressure can be generated, which is why the left wall is roughly three times thicker. Blood enters both ventricles from the atria at low pressure.