G11 Semester 2 Exam

Question 1

Outline the stages of meiosis

Answer 1

Prophase I: Chromosomes condense, the nuclear membrane dissolves, and homologous chromosomes form bivalents where crossing over occurs.
Metaphase I: Spindle fibres from opposing centromeres connect to bivalents and align them along the middle of the cell.
Anaphase I: Spindle fibres split the bivalents and homologous chromosomes move to opposite sides of the cell.
Telophase I: Chromosomes decondense, the nuclear membrane may reform and cell divides to form two daughter cells.

Prophase II: Chromosomes condense, nuclear membrane dissolves and centromeres move to opposite poles.
Metaphase II: Spindle fibres attach to chromosomes and align them to the middle of the cell.
Anaphase II: Spindle fibres separate sister chromatids and move to opposite poles.
Telophase II: Chromosomes decondense, nuclear membrane reforms, cell divides to form four haploid daughter cells.

Question 2

Distinguish between the processes of meiosis and mitosis

Answer 2

Type of cell produced:
Meiosis - sex cells (gametes)
Mitosis - body (somatic) cells

Number of cells produced:
Meiosis - four
Mitosis - two

Number of divisions:
Meiosis - two
Mitosis - one

Ploidy of daughter cells:
Meiosis - haploid
Mitosis - diploid

Genetics of daughter cells:
Meiosis - shows genetic variation due to crossing over and random orientation
Mitosis - are genetically identical

Question 3

Outline the process of DNA profiling

Answer 3

DNA sample is collected and amplified using PCR. Then it is cut into fragments using restriction enzymes and put into gel electrophoresis to differentiate them by size. With visualisation from the gel electrophoresis, it can be used to determine paternity as a child’s DNA is half from the father and half from the mother or forensic investigations by matching DNA from the criminal site and suspects’ DNA.

Question 4

Using a diagram with annotations, explain the transformations of carbon compounds in the carbon cycle. Include equations where applicable

Answer 4

Drawing of the carbon cycle with 6 main processes, photosynthesis, respiration, combustion, decomposition, feeding, and calcium carbonate. Including equations of photosynthesis and cell respiration:
6CO2 + 6H2O –> C6H12O6 + 6O2
C6H12O6 + 6O2 –> 6CO2 + 6H2O + ATP

Question 5

Define species

Answer 5

A group of organisms that can potentially interbreed to produce fertile viable offspring.

Question 6

Define populations

Answer 6

A group of organisms of the same species that are living in the same area at the same time

Question 7

Define communities

Answer 7

A group of populations living together and interacting with each other within a given area

Question 8

Define habitat

Answer 8

The environment in which a species normally lives, or the location of a living organism.

Question 9

Define ecosystem

Answer 9

A community and its abiotic environment

Question 10

Distinguish between autotroph and heterotroph

Answer 10

Autotrophs synthesise their own organic molecules from simple inorganic substances/make their own food with energy derived from sunlight or oxidation of molecules. Heterotrophs obtain their organic molecules from other organisms.

Question 11

Differentiate between the types of heterotrophs (consumer, detritivore, decomposer), with an example each

Answer 11

Consumer: ingest organic molecules from living or recently killed organisms such as mammals (e.g. wolves, bears, humans, etc.)
Detritivore: ingest organic molecules found in the non-living remnants of organisms (e.g. dung beetles, millipedes)
Decomposer: release digestive enzymes and then absorb the external products of digestion (e.g. saprotrophs)

Question 12

Distinguish between herbivores, carnivores, and omnivores

Answer 12

Herbivore: Feeds exclusively on plant matter
Carnivore: Feeds exclusively on animal matter
Omnivore: Feeds on both plant and animal matter

Question 13

Outline the formation of peat/coal

Answer 13

In anaerobic conditions such as waterlogged soils, saprotrophs can only partially decompose organic matter. The remaining carbon-rich material stays within the soil and forms peat. When compressed under sediment, the high pressure and heat force out moisture and turn peat into coal.

Question 14

State the role of the following enzymes of the DNA replication process

Answer 14

Helicase: unwinds and separated double stranded DNA

DNA gyrase: relieves torsional strain created by helicase action to prevent supercoiling

SSB proteins: prevents DNA strands from re-annealing

DNA primase: lays down a short RNA primer to provide an initiation point for polymerisation (DNA pol III can only add nucelotides to the 3’-end of an existing nucleotide chain)

DNA polymerase III: extends the nucleotide chain from the primer

DNA polymerase I: removes and replaced RNA primers with DNA nucleotides

DNA ligase: covalently joins Okazaki fragments together (on lagging strand)

Question 15

Compare the different types of natural selection

Answer 15

Stabilising selection: the intermediate phenotype is favoured at the expense of both extreme phenotypes such as human birth weights.
Disruptive selection: both of the extreme phenotypes are favoured at the expense of the intermediate phenotype such as the pigmentation of a peppered moth.
Directional selection: only one extreme phenotype is favoured at the expense of the other extreme phenotype and the intermediate phenotype such as antibiotic resistance in bacteria.

Question 16

Distinguish between phyletic gradualism and punctuated equilibrium

Answer 16

Phyletic gradualism is a speciation that occurs following continuous change at a constant pace over a long period of time. This can be through a gradual accumulation of mutations. Punctuated equilibrium is a speciation that occurs rapidly in bursts with long periods of stability between. In stable periods, characteristics are maintained but this is punctuated by periods of environmental changes

Question 17

Define nucleosome

Answer 17

DNA is complexed with eight histone proteins (an octamer) to form a complex called a nucleosome

Question 18

Outline the role of the nucleosome in DNA transcription

Answer 18

Histone proteins have protruding tails that determine how DNA is packaged within eukaryotic nucleosomes. Through methylation and acetylation, nucleosomes regulate transcription. Acetylation makes DNA less tightly packed and more accessible to transcriptional machinery. Methylation makes DNA more tightly packed and less accessible to transcriptional machinery.

Question 19

Define gene expression

Answer 19

Gene expression is the process where information encoded on a gene is used to create a functional product such as a protein. Expression of a gene is determined by its level of transcriptional activity.

Question 20

Outline the ways gene expression is regulated

Answer 20

Transcription factors and regulatory proteins that mediate RNA polymerase action, nucleosomes, and by being directly methylated to alter gene expression patterns.

Question 21

Identify the three sections of a gene

Answer 21

Promoter - initiation point (where RNA polymerase binds)
Coding Region - sequence that is transcribed
Terminator - termination point

Question 22

Distinguish between introns and exons

Answer 22

Introns are intruding sequences within a gene that are removed prior to translation (not expressed). Exons are the expressing sequences translated into protein.

Question 23

Outline how alternative splicing increases the number of different proteins an organism can produce

Answer 23

Exons can be selectively removed via alternative splicing to produce different protein variants from the same gene - this increases the number of proteins an organism can produce relative to the number of genes

Question 24

Identify a null hypothesis (ecology)

Answer 24

There is no significant difference in the distribution of species (species are not associated)

Question 25

Identify an alternative hypothesis (ecology)

Answer 25

The is a significant difference in the distribution of species (species are associated)

Question 26

If x^2 > 0.05, do we reject or accept null hypothesis (ecology)

Answer 26

There is an insignificant difference meaning we accept null hypothesis

Question 27

If x^2 < 0.05, do we reject or accept null hypothesis (ecology)

Answer 27

There is a significant difference meaning we reject null hypothesis

Question 28

If x^2 > 0.05, are genes linked or unlinked?

Answer 28

Genes are unlinked, accept null hypothesis

Question 29

If x^2 < 0.05, are genes linked or unlinked

Answer 29

Genes are linked, accept alternative hypothesis

Question 30

Write the calculation formula for expected frequencies (genetics)

Answer 30

(Row total x Column total)/Grand total

Question 31

Write the formula for expected frequencies (ecology)

Answer 31

(column total x row total)/grand total

Question 32

Write the chi-squared formula

Answer 32

The sum of (O-E)^2/E

Question 33

List examples of greenhouse gases

Answer 33

Water vapour, carbon dioxide, methane, nitrogen oxides, fluorinated gases (e.g. CFCs)

Question 34

Explain the relationship between greenhouse gases and the greenhouse effect

Answer 34

The greenhouse effect functions to trap heat within the atmosphere and prevent rapid temperature changes. Incoming radiation (from the sun) is shorter wave radiation (e.g. ultraviolet radiation and visible spectrum). The Earth’s surface absorbs this radiation and re-emits it at a longer wavelength (i.e. infrared radiation / heat). Greenhouse gases absorb and re-radiate the longer wave radiation and hence retain heat in the atmosphere. The higher the concentration of greenhouse gases in the atmosphere, the more heat is retained, hence global warming if there are too much greenhouse gases in the atmosphere.

Question 35

Define sex linkage and identify two examples of sex-linked conditions

Answer 35

Sex linkage refers to any gene/trait that is located on the sex chromosome. Two examples of X-linked recessive traits are red-green colour blindness and haemophilia.

Question 36

Identify the causes of variation

Answer 36

Mutations, genetic recombination, gene flow, genetic drift, natural selection, polygenic traits

Question 37

Identify continuous variation in humans

Answer 37

Human height, weight, skin colour

Question 38

Explain the process of evolution

Answer 38

Evolution occurs through the change of allele frequencies. This may happen through random processes such as genetic drifts or differential processes such as natural selection. They may also happen gradually or rapidly over time.

Question 39

Outline a factor that influences genetic drift and identify two conditions by which this factor may occur

Answer 39

Genetic drift is a change in composition of a gene pool due to random events and is impacted by population size. Size affects stability of allele frequencies (high drift is small populations and small drifts in large populations. Two conditions are population bottlenecks when an event reduces the population size and founder effect when a small group breaks away from a larger population to colonise a new territory.

Question 40

Discuss the different types of reproductive isolation

Answer 40

Temporal: occurs when two populations differ in their periods of activity or reproductive cycles such as leopard frogs and wood frogs reaching sexual maturity at different times in the spring hence cannot interbreed with each other.
Behavioural: occurs when two populations exhibit different specific courtship patterns such as the same bird species having different mating songs.
Geographic: occurs when two populations occupy different habitats or separate niches within a common region such as lions and tigers that occupy different habitats and do not interbreed (usually) or frogs that live in land and water.

Question 41

Distinguish between allopatric and sympatric speciation

Answer 41

Allopatric speciation occurs when a geographical barrier physically isolates populations and the two populations being to genetically diverge until they can no longer interbreed. Sympatric speciation is a divergence of species within the same geographical location and the reproductive isolation may be a result of genetic abnormalities.

Question 42

Outline ways evolution can be accelerated

Answer 42

Natural selection, environmental changes such as in population bottlenecks.