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Unit notes and practice questions

Grade 12 Biology unit 4: Evolution

Everything here is for unit 4 of the Grade 12 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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10
Practice questions on unit 4
161–235
The textbook pages for unit 4

What unit 4 covers

  1. 1.Evolution: definition, theories and evidence
  2. 2.Natural selection: definition, types and examples
  3. 3.Human evolution
  4. 4.Mutation, genetic drift and gene flow
  5. 5.Causes of species extinction
  6. 6.Renowned anthropologists in Ethiopia
  7. 7.Renowned evolutionists in Ethiopia

Short notes for unit 4

The cards filed under this chapter on the Grade 12 Biology page. Open one at a time.

Speciation TypePrimary Isolating EventGeographic Status
Allopatric speciationPhysical geographic barrier separates populationsGeographically isolated
Sympatric speciationReproductive barrier develops within same habitatGeographically overlapping

When you use it

Use when determining whether new species formed due to geographic separation or within the same territory.

Watch out

Sympatric speciation does not require physical barriers. It occurs via polyploidy or reproductive isolation in the same place.

Drafted from Grade 12 Biology, pages 161-235, then checked twice before it went up

When you use it

Use when distinguishing postzygotic reproductive outcomes in evolutionary biology questions.

Watch out

In hybrid inviability the embryo dies before reproductive maturity, while in hybrid sterility the hybrid matures into an adult but cannot produce fertile gametes.

Drafted from Grade 12 Biology, pages 161-235, then checked twice before it went up

PatternAncestryResulting Traits
Divergent evolutionCommon ancestorHomologous traits become increasingly different
Convergent evolutionDifferent ancestryAnalogous traits evolve due to similar environments
Parallel evolutionRelated ancestrySimilar traits develop independently in similar niches

When you use it

Use when identifying whether shared traits in organisms arose from common descent or similar selection pressures.

Watch out

Convergent evolution produces analogous structures in unrelated species, not homologous structures from a common ancestor.

Drafted from Grade 12 Biology, pages 161-235, then checked twice before it went up

BarrierCategoryMechanism
Habitat isolationPrezygoticLiving in different ecological niches prevents mating
Temporal isolationPrezygoticBreeding at different times or seasons
Behavioral isolationPrezygoticDistinct courtship calls or mating rituals
Mechanical isolationPrezygoticStructural incompatibility of reproductive organs
Gametic isolationPrezygoticSperm and egg chemically incompatible
Hybrid inviabilityPostzygoticZygote fails to develop and dies in embryo stage
Hybrid sterilityPostzygoticOffspring develops to adult but is infertile
Hybrid breakdownPostzygoticFirst generation fertile but subsequent generations weak

When you use it

Use to classify barriers that prevent interbreeding between different species before or after fertilization.

Watch out

Prezygotic barriers stop fertilization from occurring. Postzygotic barriers act only after a hybrid zygote has formed.

Drafted from Grade 12 Biology, pages 161-235, then checked twice before it went up

Selection TypePhenotypic EffectPopulation Impact
Stabilizing selectionFavors intermediate phenotypesReduces variation around the mean
Directional selectionFavors one extreme phenotypeShifts the mean character value in one direction
Disruptive selectionFavors both extreme phenotypesSplits population into two distinct peaks

When you use it

Use when analyzing how selective pressures change the distribution of phenotypes in a population.

Watch out

Disruptive selection selects against the average phenotype, not against the extremes.

Drafted from Grade 12 Biology, pages 161-235, 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

In Francesco Redi's experiment, what did the open jar contain after some days?

  1. A.Nothing at all
  2. B.Maggots
  3. C.Fish
  4. D.Mice
Show the answer and why

Answer: B Maggots

Why

Redi left one jar open and covered the others. Days later the open jar contained maggots, while the covered jars did not. This helped to disprove spontaneous generation.

Question 2

Which of the following best defines evolution?

  1. A.A change in the body size of one individual during its lifetime
  2. B.The movement of people from one town to another
  3. C.A change in the genetic composition of a population over successive generations
  4. D.The death of every member of a species
Show the answer and why

Answer: C A change in the genetic composition of a population over successive generations

Why

The textbook defines evolution as a change in the genetic composition of a population over successive generations. The key idea is the population and the generations, not one individual.

Question 3

In which year did Lamarck propose the theory of inheritance of acquired characters?

  1. A.1809
  2. B.1668
  3. C.1748
  4. D.1924
Show the answer and why

Answer: A 1809

Why

The textbook says Lamarck proposed the theory of inheritance of acquired characters in 1809. The other years belong to other events in the chapter: Redi's experiment (1668), Needham's report (1748) and Oparin's first ideas (1924).

Question 4

About how far off the coast of Ecuador are the Galapagos Islands?

  1. A.60 miles
  2. B.120 miles
  3. C.1,200 miles
  4. D.600 miles
Show the answer and why

Answer: D 600 miles

Why

The textbook states that the Galapagos Islands are about 600 miles off the coast of Ecuador in South America.

Question 5

Which pair of structures is an example of homologous structures?

  1. A.The wing of a bird and the wing of a mosquito
  2. B.The forelimb of a human and the flipper of a whale
  3. C.The wing of a bat and the wing of a bird
  4. D.The wing of a bat and the wing of a mosquito
Show the answer and why

Answer: B The forelimb of a human and the flipper of a whale

Why

Homologous structures are similar in structure but do different jobs. The forelimbs of humans, whales, cats and bats have the same basic bone pattern, even though they are used in different ways. The three other pairs are wings, which do the same job but have very different structures, so they are analogous.

Question 6

Which statement best explains why the wings of a bird and the wings of a mosquito cannot show that the two animals share a common ancestor?

  1. A.They have the same function but very different structures, so they evolved separately.
  2. B.They are both covered with feathers.
  3. C.They have the same bones arranged in the same way.
  4. D.They are both found in the same fossil layer.
Show the answer and why

Answer: A They have the same function but very different structures, so they evolved separately.

Why

These are analogous structures. They do the same job, but their anatomy is very different. The bird wing has bones inside and feathers, while the mosquito wing has neither. Because they are so different, they evolved separately and do not show a shared ancestor.

Question 7

According to the chapter, how often do resistance mutations usually occur in bacteria?

  1. A.In every bacterium
  2. B.In about 1 in 10 bacteria
  3. C.In less than 1 in a million bacteria
  4. D.In exactly half of all bacteria
Show the answer and why

Answer: C In less than 1 in a million bacteria

Why

The textbook says that acquiring resistance is a very rare event. Resistance mutations usually occur in less than 1 in a million bacteria. Once a resistant bacterium exists, it can survive antibiotics and reproduce while its non-resistant neighbours are killed.

Question 8

Which of the following is NOT one of the three postulates of Neo-Darwinism?

  1. A.Genetic variability
  2. B.Natural selection
  3. C.Reproductive isolation
  4. D.Inheritance of acquired characters
Show the answer and why

Answer: D Inheritance of acquired characters

Why

The three postulates of Neo-Darwinism are genetic variability, natural selection and reproductive isolation. Inheritance of acquired characters is part of Lamarck's theory, not Neo-Darwinism.

Question 9

Why are mules infertile?

  1. A.The chromosomes of the mule are not homologous, so meiosis does not occur in its germ cells.
  2. B.Mules cannot grow or develop at all.
  3. C.Mules have no chromosomes.
  4. D.Horses and donkeys never mate with each other.
Show the answer and why

Answer: A The chromosomes of the mule are not homologous, so meiosis does not occur in its germ cells.

Why

A mule is a hybrid of a female horse and a male donkey. A horse's egg has one more chromosome than a donkey's sperm cell. The mule can grow and develop, but its chromosomes are not homologous, so meiosis does not occur in its germ cells and it cannot produce sex cells.

Question 10

How does polyploidy help a plant hybrid that is infertile?

  1. A.It removes extra chromosomes from the hybrid's cells.
  2. B.It stops all sexual reproduction in the hybrid.
  3. C.It doubles the chromosome number, so the chromosomes can form homologous pairs in meiosis and the hybrid becomes fertile.
  4. D.It makes the hybrid exactly the same as its parent species.
Show the answer and why

Answer: C It doubles the chromosome number, so the chromosomes can form homologous pairs in meiosis and the hybrid becomes fertile.

Why

Many hybrids cannot form homologous pairs during meiosis, so they cannot make sex cells. If the chromosome number doubles, all chromosomes can pair up. Meiosis and sex-cell formation can then take place, and the hybrid is fertile. This is why polyploidy has been important in plant evolution.

The app holds 11 questions on this unit, marked as you go. These are the first 10.

The textbook pages for unit 4

Unit 4 runs from page 161 to page 235 of the Ministry of Education edition.

Ministry of Education edition, English, 358 pages

Download the PDF

All Grade 12 Biology short notes

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