IB MYP 4-5 Biology Chapter 2 : Transformation–Practice Questions

Question:

What do these enzymes do?
Nitrate reductase
Iodotyrosine deiodinase
Phosphoglucose isomerase

▶️Answer/Explanation

Ans: 

  • Nitrate reductase reduces/transfers electrons to nitrate/converts nitrate to nitrite.
  • Iodotyrosine deiodinase removes iodine from iodotyrosine.
  • Phosphoglucose isomerase converts glucose phosphate to fructose phosphate.

Question:

What is the difference between phenylalanine and tyrosine?

▶️Answer/Explanation

Ans: Phenylalanine has an extra OH (hydroxyl) group on its phenyl ring.

Question:

The enzyme that catalyses this reaction is called phenylalanine hydroxylase (PAH). What happens in a hydroxylation reaction?

▶️Answer/Explanation

Ans: In a hydroxylation reaction, a hydroxyl group (OH) is added or removed from a molecule.

Question:

The genetic disease phenylketonuria (PKU) results in very low levels of the enzyme PAH. What will be the effect on concentrations of phenylalanine and tyrosine in the body?

▶️Answer/Explanation

Ans: The concentration of phenylalanine will rise/be too high and the concentration of tyrosine will fall/be too low.

Question:

PKU has some harmful effects on the development of babies, so a blood test is routinely done a few days after birth.

a) What treatment could be given to babies with PKU to avoid the harmful effects?

▶️Answer/Explanation

Ans: Give the baby a diet containing low amounts of phenylalanine.

b) Why is it not necessary to test babies, or start this treatment, before birth?

▶️Answer/Explanation

Ans: The mother’s metabolism can control concentrations of phenylalanine and tyrosine when the baby is in the uterus.

Question:

Describe the difference in structure between the two monosaccharide sugars glucose and galactose.

▶️Answer/Explanation

Ans: The OH group on the lefthand carbon (C4) is pointing down in glucose and up in galactose.

 

Question:

Lactose synthase is the enzyme which catalyzes the production of lactose, using glucose and galactose as substrates. Explain the need for different enzymes to synthesize and digest lactose.

▶️Answer/Explanation

Ans: Having different enzymes for synthesizing and digesting lactose allows the body to control which process occurs; synthesis happens by a different pathway; synthesis involves using energy from ATP because it is an endothermic process; lactose is synthesized from galactose diphosphate plus glucose whereas lactose is digested to galactose plus glucose.

Question:

Predict what will happen to lactose in the intestines of adults who do not produce the enzyme lactase.

▶️Answer/Explanation

Ans: Lactose is not digested (by human enzymes/digestive juices); bacteria/microbes in the gut digest the lactose.

Question:

Explain how lactase secretion in adulthood could have become common in populations that keep cattle or other mammals and drink their milk.

▶️Answer/Explanation

Ans: Adults that continue to secrete lactase into adulthood have an advantage; they are better nourished on a diet containing milk; they avoid harmful effects of lactose intolerance; they are healthier so produce more children; their children inherit the trait of secreting lactase in adulthood.

Question:

Deduce whether the reactions that change ethanol into ethanoic acid are oxidations or reductions.

▶️Answer/Explanation

Ans: Ethanol to ethanal is an oxidation; ethanal to ethanoic acid is also an oxidation.

Question:

Explain the reason for different enzymes in the two reactions.

▶️Answer/Explanation

Ans: The substrates/reactants have different shapes/chemical properties so different active sites are needed for them to bind and react; the chemical reaction that occurs is different so a different specific catalyst is needed.

Question:

Suggest a reason for not converting ethanol to ethanoic acid in just one reaction.

▶️Answer/Explanation

Ans: No enzyme exists that does the transformation in one step; a series of small transformations is more likely to occur correctly than one major one.

Question:

Using an atlas if necessary, identify three countries with a high frequency of the ALDH*504Lys and three countries with a low frequency.

▶️Answer/Explanation

Ans: High frequency: Japan; China; South Korea; Low frequency: any country not in East Asia.

Question:

Almost all Japanese, Chinese and Korean people have ADH1C, a variant of the ADH enzyme.

▶️Answer/Explanation

Ans: Concentrations of ethanal will be much higher after drinking alcohol than in people with nonvariant forms of ALDH1 and ALDH2.

This variant converts ethanol to ethanal much more efficiently than other forms of the enzyme. Explain the consequences of having a combination of both ADH1C and ALDH*504Lys.

Question:

Alcoholics are addicted to alcohol and tend to consume excessive amounts of it. In populations where ALDH*504Lys occurs, the frequency is much lower among alcoholics than non-alcoholics. Suggest a reason for this trend.

▶️Answer/Explanation

Ans: People with ALDH2*504Lys have high ethanal concentrations after drinking ethanol; causing unpleasant effects due to the toxicity of ethanal; so they tend to avoid alcohol; and do not become alcoholic; vice versa for those who do not have the variant gene.

Question:

Average alcohol consumption in liters per year is much lower in China (6.7 l/year) than in the USA (9.2 l/year), Canada (10.2 l/year) or Russia (15.1 l/year). Suggest reasons for this, based on what you know about the enzymes metabolizing alcohol.

▶️Answer/Explanation

Ans: Fewer alcoholics; less binge drinking; worse hangovers; less culture of alcoholdrinking; effects of ethanal deter drinking alcohol.

Question:

Do our enzymes affect our identity?

▶️Answer/Explanation

Ans: Yes because they influence significant aspects of our identity such as alcohol drinking or abstinence.

Question:

A gene called GNRH1 on chromosome 8 is transcribed in the first stage of GnRH production – what are the other stages?

▶️Answer/Explanation

Ans: Messenger RNA/mRNA moves out from the nucleus to the cytoplasm; mRNA binds to a ribosome; translation of RNA to protein/polypeptide; base sequence converted to amino acid sequence; release of GNRH from the ribosome.

Question:

How many amino acids are there in the chain – eight, ten or twelve?

▶️Answer/Explanation

Ans: Ten (There is an error in the book one nitrogen atom in the peptide chain is shown red rather than blue, making it harder to find the number of amino acids by counting the number of times the sequence NCC is repeated in the backbone of the polypeptide.)

Question:

A chain of amino acids as short as this is usually called an oligopeptide, rather than a protein. What is an advantage of using oligopeptides or small proteins as hormones, rather than large proteins?

▶️Answer/Explanation

Ans: Easier to transport a smaller molecule; less resources/amino acids used; receptor molecule to which the hormone binds can be smaller.

Question:

What are the similarities and differences in the data for the three hormones shown in the graph?

▶️Answer/Explanation

Ans: All three hormones rise and fall in concentration; four times in 15 hours; all rise and fall at about the same times; GnRH always rises first; LH always rises higher; FSH rises for a longer time before falling again.

Question:

GnRH causes secretion of LH and FSH. What evidence for this is there in the graph?

▶️Answer/Explanation

Ans: GnRH increases in concentration before LH and FSH rise.

Question:

One of the effects of LH is to cause the testes to secrete more testosterone. Testosterone causes production of sperm and also secondary sexual characteristics such as pubic hair. At approximately what age do you expect the hypothalamus to start secreting GnRH?

▶️Answer/Explanation

Ans: At the age when boys begin puberty/10/11/12/13/14/15.

Question:

What would happen if a boy was lacking the GNRH1 gene?

▶️Answer/Explanation

Ans: The boy would not enter puberty/develop secondary sexual characteristics (unless artificially stimulated).

Question:

a) Calculate the difference in body mass between the groups raised in high and low water.

▶️Answer/Explanation

Ans: 1.9 1.2 = 0.7 grams

b) Explain the difference in body mass.

▶️Answer/Explanation

Ans: Grow to a larger size before metamorphosis in high water.

Question:

Using all the data in the table, explain how western spadefoot toad tadpoles respond to a low-water environment.

▶️Answer/Explanation

Ans: More corticosterone is produced in low water; causing production of more thyroid hormone receptor proteins; more thyroid hormone is produced in low water; which activates receptor
proteins by binding; and the activated receptors bind to specific genes in the nucleus; activating them; activated genes cause metamorphosis.

Question:

Suggest advantages to the western spadefoot toad of being able to metamorphose at different times in response to water levels.

▶️Answer/Explanation

Ans: Metamorphosis happens before the water disappears; but there is growth to the largest possible size before metamorphosis.

Question:

If a cell with different versions of two genes carries out meiosis, there are four possible combinations of genes in the cells produced. Calculate the number of possible combinations for each
of these numbers of genes with different versions:

a) 3 

▶️Answer/Explanation

Ans: 23 = 8

b)

▶️Answer/Explanation

Ans: 24 = 16

c) 10

▶️Answer/Explanation

Ans: 210 = 1024

d) 1,000

▶️Answer/Explanation

Ans: 21000 (which is a very large number!)

Question:

Identical twins have the same combinations of genes as each other. Consider this hypothesis: identical twins are the result of two sperms with identical combinations of genes fertilizing two eggs with identical combinations of genes. Is this likely? If not, can you suggest a better hypothesis?

▶️Answer/Explanation

Ans: Not likely; one sperm fuses with one egg; one zygote produced; zygote divides by mitosis to form an embryo; embryo splits into two parts; each part develops as a separate embryo.

Question:

If identical twin men married identical twin women, would all their offspring be the same?

▶️Answer/Explanation

Ans: Offspring not all the same; no more similar than siblings.

Question:

Explain the reasons for greater genetic diversity among children of mixed-race parents, compared with same-race parents.

▶️Answer/Explanation

Ans: More genetic diversity.

Summative assessment: Heritable variation and identity

In humans, the 23rd pair of chromosomes determines whether we are male or female. Males have one large X and one small Y chromosome. Females have two X chromosomes. In females, the
two X chromosomes pair up in the early stages of meiosis. Despite being different in structure along most of their lengths, X and Y chromosomes have the same structure at their ends, allowing them to be paired when meiosis happens in males. X chromosomes carry far more genes than Y chromosomes, but the gene SRY, carried by the Y chromosome, sets off a significant transformation.

Question:

The diagram below shows the sex chromosomes in a testis cell at the start of the first division of meiosis. Draw diagrams to show where these chromosomes would be at

a) the end of the first division of meiosis

▶️Answer/Explanation

Ans: One cell contains the X and the other contains the Y chromosome; both of these chromosomes have two strands/chromatids.

b) the end of the second division of meiosis

▶️Answer/Explanation

Ans: Two cells have X chromosomes and two have Y; each of these chromosomes has one strand/chromatid.

Question:

SRY codes for a protein of 204 amino acids called TDF (testis determining factor). Outline the processes that transform the base sequence of SRY into the amino acid sequence of TDF.

▶️Answer/Explanation

Ans: SRY gene is transcribed; mRNA copy of base sequence produced; mRNA passes out from nucleus to cytoplasm; mRNA binds to ribosome; translation; ribosome converts base sequence of mRNA into amino acid sequence of TDF.

Question:

Until human embryos are four to six weeks old there are no visible differences between males and females. The embryonic gonads could develop into ovaries or testes. TDF is a transcription
factor that binds to DNA in specific places to activate certain genes. These genes prevent the embryonic gonads from developing into ovaries and instead cause them to develop into testes. The developing testes secrete the hormone testosterone.

a) Deduce what causes the embryonic gonads in a female embryo to develop into ovaries.

▶️Answer/Explanation

Ans: SRY gene not present; TDF not produced; genes preventing ovary formation not activated by TDF.

b) Suggest some of the changes that testosterone will cause during the development of a male embryo.

▶️Answer/Explanation

Ans: Development of testes; scrotum; sperm duct; seminal vesicle/prostate gland; penis.

Investigating amylase

This reaction happens in the mouth:

The amount of amylase in saliva can be assessed by testing how long it takes for a sample of saliva to digest all the starch in a measured quantity of starch solution. You can use the following protocol:

Question:

a) Choose one of these hypotheses:
There is more amylase in the saliva of girls than boys.
There is more amylase in the saliva of boys than girls.
There is no difference between the amount of amylase in the saliva of girls and boys (null hypothesis).

▶️Answer/Explanation

Ans: Most plausible hypothesis is no difference between boys and girls; same amount of starch in the diet; same need for amylase/starch digestion.

Explain the reasons for your choice of hypothesis. 

b) Describe how you plan to test your hypothesis, including control of variables. 

▶️Answer/Explanation

Ans: Same saliva collection method; same volume of saliva used in testing; same temperature repeats/test saliva from more than one boy and girl.

c) Either using your actual results, or results supplied by your teacher, calculate average rates of starch digestion, showing your working clearly.

▶️Answer/Explanation

Ans: Time taken to digest starch measured in seconds/converted to seconds; amount of starch digested correctly calculated as volume of starch solution (cm3) × starch concentration (mg cm3) (1% starch is 10 mg cm3); rate of starch digestion = mass of starch digested (mg)/time taken (seconds); calculate average rates for girls and for boys.

d) Use whatever chart or graph you think is most appropriate to display the rates.

▶️Answer/Explanation

Ans: Mean rate of starch digestion on y axis with scale and legend; boys and girls on X axis; two bars only plotted (not a bar for each saliva sample; range bars to show the highest and lowest rates for boys and for girls).

e) Evaluate your hypothesis using the results of the experiment. 

▶️Answer/Explanation

Ans: Difficult to determine whether starch is fully digested; gradual colour change of iodine from blueblack to orange; variability of results; more repeats needed; comment on whether the differences are significant; other valid comment based on actual data obtained/used.

The genetic basis of amylase activity

Question:

a) The gene that codes for salivary amylase is AMY1. This gene is located on chromosome 1. Explain why we might expect there to be two copies of this gene in all humans.

▶️Answer/Explanation

Ans: Humans have diploid nuclei/cells; two copies of chromosome 1 per nucleus; one copy of AMY1 on each chromosome 1.

b) Many humans inherit more than two copies of AMY1. This is because of tandem repeats of the gene on a chromosome passed in a gamete from one or both parents. Tandem repeats are sequences of bases in DNA that are repeated, with the repeats adjacent to each other.

The scatter graph below shows the number of copies of AMY1 in a sample of 50 European-American individuals and also the concentration of amylase (AMY1 protein) in their saliva.

i) State the minimum, maximum and median number of AMY1 copies.

▶️Answer/Explanation

Ans: Minimum is 2 copies; maximum is 15; median is 7.5.

ii) Outline the relationship between the number of copies of AMY1 and the concentration of amylase.

▶️Answer/Explanation

Ans: The more copies of AMY1, the higher the concentration of amylase; positive correlation; variation in the data/not linear relationship.

iii) Explain the reasons for this relationship

▶️Answer/Explanation

Ans: AMY transcribed more often with more copies; more mRNA for amylase; more translation of mRNA for amylase/more amylase secreted in saliva.

c) The European-American population traditionally eats a high starch diet. Six other populations were investigated, three that traditionally eat low starch diets and three that eat high starch
diets. The cumulative frequency graph below shows the results.

i) What trend does the data in the graph show?

▶️Answer/Explanation

Ans: Populations that eat a high starch diet have more copies of AMY1 (on average); Japanese, Hadza and EuropeanAmerican all show this trend.

ii) Suggest an explanation for this trend.

▶️Answer/Explanation

Ans: Better starch digestion with more amylase; more glucose/energy obtained from high starch diets; selective advantage/more successful/more offspring produced; offspring inherit more copies of AMY1 gene.

Genetic counseling and color blindness

Question:

Red-green color blindness is the condition where a person has difficulty in distinguishing between red and green wavelengths of light. The commonest form is deuteranomaly, in which the pigment that normally absorbs green light instead absorbs yellow, orange or red light. The frequency of deuteranomaly can be as high as 6% of males and 0.4% of females in some populations.

a) Suggest reasons for testing a person to see if they have red- green color blindness.

▶️Answer/Explanation

Ans: Helps to understand a person’s identity; helps to predict difficulties a person may have; allows help to be given to minimize difficulties; might suggest particular occupations should be avoided; avoid dangers due to inability to distinguish colours; difficulty distinguishing traffic light colours/other specific example of any of these reasons.

b) The two genes required for normal red and green vision are located next to each other on the X chromosome. These genes are very similar in base sequence. They code for different versions of the protein opsin. This protein binds to retinal to form a light-absorbing pigment. Three differences in base sequence cause three differences in amino acid sequence in opsin, which cause the pigment to absorb either red or green light.

Deuteranomaly is due to the presence of a changed version of the gene coding for the green-absorbing opsin.

From the information that you have been given, write an explanation of the probable causes of deuteranomaly for a young boy with this condition. Try to use clear and simple language that he would understand.

▶️Answer/Explanation

Ans: You inherited your genes from your parents; you inherited tiny differences in one of your genes; this gene should allow you to recognize the colour green; but because of the differences your version of the gene tells you that the green is the same colour as red.

c) Genetic counselling is offered to parents who might have a child with a genetic condition. If a husband has deuteranomaly and his wife has normal vision, explain advice that should be given about the chances of

i) a son inheriting the condition 

▶️Answer/Explanation

Ans: No chance of a son inheriting the condition; because the gene is on the X chromosome and fathers pass on their Y chromosome to their sons.

ii) a daughter inheriting it.

▶️Answer/Explanation

Ans: Daughter will not have the condition; because they inherit a normal version of the gene from their mother; but they will carry one copy of the deuteranomaly gene (which they could pass on to their children).

d) Discuss the effects on identity that having a genetic condition such as deuteranomaly might have.

▶️Answer/Explanation

Ans: Good to be different/other positive reaction; depression/regret/other negative reaction; reluctance to pass gene on to children; altered life expectations/plans for the future.

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