MDCAT Biology chapter 16: Biology · Biotechnology MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
30 exam-style questions on Biology · Biotechnology, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Ten Biology · Biotechnology questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Two different primers are added to a PCR mixture because
A
one primer starts the copying and the other primer stops it
B
one binds to each strand, at the two ends of the target
C
one primer copies the DNA and the other copies the RNA
D
two primers make the DNA polymerase work twice as fast
Show answer
Answer: B. After denaturation there are two single strands running in opposite directions; one primer pairs at one end of the target on each strand, so the region between the two primers is copied from both sides in every cycle.
2. Starting from one molecule of double-stranded DNA, what is the smallest number of PCR cycles that gives at least 1000 molecules, if the DNA doubles in every cycle?
A
9
B
10
C
100
D
500
Show answer
Answer: B. After n cycles there are 2n molecules: 29 = 512 is not enough, while 210 = 1024 is. The answer 500 (1000 ÷ 2) treats the growth as adding, not doubling.
3. DNA fingerprinting can identify individuals because it compares
A
the order of genes on chromosome 1, which is unique to each person
B
the genes for haemoglobin, which differ greatly between people
C
repeated non-coding sequences whose repeat number varies
D
the number of chromosomes, which differs between people
Show answer
Answer: C. Short DNA sequences repeated one after another occur at many sites, and the number of repeats at each site varies between people, giving fragments of different lengths. All normal people have 46 chromosomes and the same order of genes.
4. A DNA sample cut with a restriction enzyme gives fragments of 500, 2000 and 5000 base pairs. After electrophoresis, which fragment is nearest to the wells where the sample was loaded?
A
the 500 bp fragment
B
the 2000 bp fragment
C
the 5000 bp fragment
D
all three, side by side
Show answer
Answer: C. The gel acts like a sieve: small fragments slip through quickly and travel farthest, while the largest (5000 bp) moves least and stays nearest the wells.
5. A human gene, including its introns, is 6000 base pairs long; its mature mRNA is 1500 nucleotides long. A cDNA copy made from this mRNA by reverse transcriptase would be about
A
6000 base pairs long, as it includes the introns
B
1500 base pairs long, as it has no introns
C
4500 base pairs long, the length of the introns
D
7500 base pairs long, the gene plus the mRNA
Show answer
Answer: B. cDNA is copied from mature mRNA, from which the introns have already been removed, so it matches the 1500-nucleotide mRNA. Such intron-free genes are used in bacteria, which cannot remove introns.
6. Golden rice has been genetically modified to help reduce
A
iron deficiency anaemia, by producing extra haemoglobin
B
vitamin A deficiency, as its grain makes β-carotene
C
water loss, by closing the stomata during the day
D
insect damage, by producing a toxin in the leaves
Show answer
Answer: B. Golden rice carries genes that make β-carotene (provitamin A) in the grain, giving it a yellow colour; the body converts β-carotene into vitamin A.
7. A plant nursery grows thousands of genetically identical banana plants from small pieces of tissue placed on a sterile nutrient medium. This method of cloning is called
A
DNA fingerprinting
B
cross-pollination
C
gene therapy
D
tissue culture
Show answer
Answer: D. In tissue culture (micropropagation) small pieces of plant tissue grow by mitosis into whole plants identical to the parent. Cross-pollination is sexual and produces variation.
8. A gene is cut out with EcoRI, but its plasmid vector is opened with a different restriction enzyme, BamHI, which leaves different sticky ends. The gene will not join into the plasmid mainly because
A
DNA ligase works only on DNA cut by EcoRI
B
EcoRI makes blunt ends that cannot be joined
C
their sticky ends are not complementary and cannot pair
D
BamHI destroys the antibiotic resistance gene of the plasmid
Show answer
Answer: C. Only complementary sticky ends can base-pair so that DNA ligase can seal them; this is why the gene and the plasmid are normally cut with the same restriction enzyme.
9. A plasmid often used as a vector to carry genes into plant cells is the Ti plasmid, obtained from
A
Escherichia coli
B
Mycobacterium tuberculosis
C
Bacillus thuringiensis
D
Agrobacterium tumefaciens
Show answer
Answer: D. The Ti (tumour-inducing) plasmid of the soil bacterium Agrobacterium tumefaciens naturally transfers part of its DNA into plant cells, so useful genes inserted there reach the plant. Bacillus thuringiensis is the source of the Bt toxin gene.
10. In a gel electrophoresis tank the leads are connected the wrong way round, so the wells are at the positive end. When the current is switched on, the DNA samples will
A
leave the wells into the buffer, away from the gel
B
move through the gel towards the far end as normal
C
move through the gel faster than usual
D
stay in the wells because DNA carries no charge
Show answer
Answer: A. DNA is negatively charged because of its phosphate groups, so it always moves towards the positive electrode; with the anode beside the wells, the DNA moves out of the wells away from the gel and is lost into the buffer.
30, each with the answer and a short explanation, across 2 topics: Recombinant DNA techniques, Applications of biotechnology. Every chapter test draws ten of them, so you can take it many times.
Is the MDCAT Biology chapter 16 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
