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Unit notes and practice questions

Grade 11 Biology unit 4

Everything here is for unit 4 of the Grade 11 Biology textbook: what the chapter covers, the short notes, practice questions with their answers, and the lesson video where one exists.

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4
Cards
10
Practice questions on unit 4
113–179
The textbook pages for unit 4

What unit 4 covers

  1. 1.The genetic materials
  2. 2.The structure and function of DNA and RNA
  3. 3.The Structure and function of DNA
  4. 4.3DNA replication
  5. 5.2The structure and function of RNA
  6. 6.The process of cell division
  7. 7.1Cell Division
  8. 8.Protein synthesis
  9. 9.Mendelian inheritance
  10. 10.1Mendelian crosses
  11. 11.2Monohybrid cross
  12. 12.3Dihybrid Cross
  13. 13.4Test Crosses
  14. 14.Sex determination
  15. 15.Non-Mendelian inheritance
  16. 16.1Co-dominance, Incomplete dominance and Multiple alleles
  17. 17.2Rh factor inheritance in humans and its medical importance
  18. 18.3Sex-linked inheritance in humans
  19. 19.4Environmental effects on phenotype
  20. 20.Human pedigree analysis and its importance

Short notes for unit 4

The cards filed under this chapter on the Grade 11 Biology page. Open one at a time.

EnzymeFunction
DNA helicaseUnwinds and separates the two DNA strands
DNA polymeraseAdds complementary nucleotides to growing strand in 5' to 3' direction
RNA primaseSynthesizes RNA primers complementary to DNA strand
DNA ligaseLinks DNA fragments by forming phosphodiester bonds
TopoisomerasePrevents supercoiling ahead of replication fork

When you use it

Use this table to review the specific functions of enzymes acting at the replication fork during the S phase.

Watch out

DNA polymerase cannot initiate synthesis on its own: it requires an RNA primer made by RNA primase and only extends from 5' to 3'.

Drafted from Grade 11 Biology, pages 113-179, then checked twice before it went up

Cross TypeParents GenotypePhenotypic RatioGenotypic Ratio
Monohybrid F2Tt×TtTt \times Tt3:11:2:1
Dihybrid F2RrYy×RrYyRrYy \times RrYy9:3:3:11:2:2:4:1:2:1:2:1
Test cross (Heterozygous)Pp×ppPp \times pp1:11:1
Incomplete/Codominance F2RW×RWRW \times RW1:2:11:2:1

When you use it

Use this table to quickly find expected phenotypic and genotypic ratios for monohybrid, dihybrid, and test crosses.

Watch out

Incomplete dominance and codominance give identical phenotypic and genotypic ratios of 1:2:1 in F2, differing from the classical Mendelian 3:1 ratio.

Drafted from Grade 11 Biology, pages 113-179, then checked twice before it went up

Codon TypemRNA Base TripletFunction
Start codonAUGInitiates translation and codes for Methionine
Stop codonsUAG, UAA, UGASignal termination of protein synthesis

When you use it

Use this table when translating mRNA nucleotide sequences into amino acid chains or finding reading boundaries.

Watch out

Stop codons (UAG, UAA, UGA) do not code for any amino acid: translation halts when a ribosome encounters them.

Drafted from Grade 11 Biology, pages 113-179, then checked twice before it went up

When you use it

Use when identifying whether an organism displaying a dominant phenotype has a homozygous dominant or heterozygous genotype.

Watch out

Always cross the unknown dominant individual with a homozygous recessive individual. If any offspring show the recessive trait, the parent is heterozygous.

Drafted from Grade 11 Biology, pages 113-179, then checked twice before it went up

Practice questions on unit 4

10 multiple-choice questions written against this chapter, each with its answer and the reason. Try one before you open the answer.

Question 1

Which two nitrogenous bases belong to the purine family in a DNA molecule?

  1. A.Adenine and Guanine
  2. B.Cytosine and Thymine
  3. C.Adenine and Thymine
  4. D.Guanine and Cytosine
Show the answer and why

Answer: A Adenine and Guanine

Why

Adenine (A) and Guanine (G) are purines, while Cytosine (C) and Thymine (T) are pyrimidines.

Question 2

Which enzyme is responsible for adding new nucleotides to a growing strand during DNA replication?

  1. A.DNA ligase
  2. B.DNA polymerase
  3. C.Topoisomerase
  4. D.RNA primase
Show the answer and why

Answer: B DNA polymerase

Why

DNA polymerase adds free nucleotides to a growing DNA strand in the correct sequence using the template strand.

Question 3

During which stage of interphase does DNA replication take place?

  1. A.G1 phase
  2. B.G0 phase
  3. C.S phase
  4. D.G2 phase
Show the answer and why

Answer: C S phase

Why

The S phase (synthesis phase) is the period of interphase when DNA replicates to form sister chromatids.

Question 4

Which codon serves as the start or initiator codon for protein synthesis?

  1. A.UAA
  2. B.UAG
  3. C.UGA
  4. D.AUG
Show the answer and why

Answer: D AUG

Why

AUG is the start codon that initiates protein synthesis. UAA, UAG, and UGA are stop codons.

Question 5

During which step of mitosis do sister chromatids separate at the centromere and move to opposite poles?

  1. A.Prophase
  2. B.Metaphase
  3. C.Anaphase
  4. D.Telophase
Show the answer and why

Answer: C Anaphase

Why

In anaphase, the centromeres split and spindle fibers pull the separated sister chromatids toward opposite poles of the cell.

Question 6

In which phase of meiosis does crossing over occur between non-sister chromatids?

  1. A.Prophase I
  2. B.Metaphase I
  3. C.Anaphase I
  4. D.Prophase II
Show the answer and why

Answer: A Prophase I

Why

Homologous chromosomes pair up and form chiasmata to exchange genetic material (crossing over) during prophase I of meiosis.

Question 7

When Gregor Mendel self-crossed heterozygous tall pea plants (Tt x Tt), what phenotypic ratio appeared in the F2 generation?

  1. A.1 tall : 3 short
  2. B.3 tall : 1 short
  3. C.1 tall : 2 short
  4. D.9 tall : 3 short
Show the answer and why

Answer: B 3 tall : 1 short

Why

Crossing Tt with Tt produces 3 tall plants (TT and Tt) for every 1 short plant (tt), giving a 3:1 phenotypic ratio.

Question 8

A farmer in Wollo crosses a red shorthorn cow with a white shorthorn bull. All the offspring show a roan coat color where both red and white hairs are expressed. What type of inheritance is this?

  1. A.Complete dominance
  2. B.Incomplete dominance
  3. C.Codominance
  4. D.Sex determination
Show the answer and why

Answer: C Codominance

Why

Codominance occurs when both alleles in a heterozygote express themselves equally at the same time, producing the roan coat pattern.

Question 9

A student in Addis Ababa wants to find the genotype of a pea plant with purple flowers (dominant trait, P). To perform a test cross, what should this plant be crossed with, and what result proves it is heterozygous (Pp)?

  1. A.Cross with a homozygous dominant plant (PP); all offspring have purple flowers.
  2. B.Cross with a homozygous recessive plant (pp); offspring show a 1:1 ratio of purple to white flowers.
  3. C.Cross with a heterozygous plant (Pp); all offspring have white flowers.
  4. D.Cross with a homozygous recessive plant (pp); all offspring have purple flowers.
Show the answer and why

Answer: B Cross with a homozygous recessive plant (pp); offspring show a 1:1 ratio of purple to white flowers.

Why

A test cross involves breeding with a homozygous recessive individual (pp). If the parent is heterozygous (Pp), half the offspring will be purple (Pp) and half will be white (pp), a 1:1 ratio.

Question 10

According to the law of independent assortment, what four types of gametes are produced by a dihybrid plant with the genotype YyRr?

  1. A.YY, yy, RR, rr
  2. B.Yy, Rr, YR, yr
  3. C.YR, Yr, yR, yr
  4. D.YY, YR, yr, rr
Show the answer and why

Answer: C YR, Yr, yR, yr

Why

Because the alleles for each gene sort independently into gametes, each gamete receives one allele from each gene pair, giving four equal possibilities: YR, Yr, yR, and yr.

The app holds 12 questions on this unit, marked as you go. These are the first 10.

The textbook pages for unit 4

Unit 4 runs from page 113 to page 179 of the Ministry of Education edition.

Ministry of Education edition, English, 294 pages

Download the PDF

All Grade 11 Biology short notes

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