Biol 200 midterm questions

Question 1

Explain 4 features that can be used to distinguish members of the Domain Bacteria from the Domain Archaea.

Answer 1

a) rRNA sequence

b) Archaeal membrane lipid tails are branched and sometimes linked.

c) Some bacteria can photosynthesize

d) Bacterial cell walls contain some peptidoglycan, Archaea do not.

e) Some Archaea can synthesize** methane.**

f) Some Archaea can live in extremely hot or saline environments.

Question 2

Structure usually relates to function in living organisms. Illustrate this concept by providing
and explaining three broad examples of structural advances in organisms discussed in class or in the text readings in the section of this course that were associated with new evolutionary functions.

Answer 2

i) Flagellum in bacteria permits locomotion.

ii) **Multicellularity **permits the capacity for **specialization of tissues **within an organism (eg. plant roots and shoots)

iii) Membrane-bound organelles permit cellular organization and localizes specific metabolic processes (eg. yeast cell of phylum fungi)

iv) Nuclear membrane permits seperation of transduction from translation and thereby promoting more complex gene regulation.

v)Cytoskeleton permits controlled guidance and **internal movement **within cytoplasm.

vi) Diploid chromosomes permit meiosis and consequently sexual reproduction, as well as heterozygous condition, and the presence and expression of multiple alleles for each gene within a population.

Question 3

Describe 2 distinct features of viruses that allow them to evolve extremely rapidly.

Answer 3

i) Extremely rapid reproduction in host cell

ii) Extremely large number of progeny per reproductive event

iii) Nucleic acid reassortment can occur when two strains infect the same cell (antigenetic shift).

Question 4

Viruses have been detrimental to human societies in many different ways. Support this statement using three separate example.

Answer 4

i) Viruses cause many serious **human diseases **(eg. COVID 19)

ii) Viruses could be used as a bioterrorism weapon (eg. anthrax).

iii) Viruses implicated in many serious animal and plant diseases than have affected human food supply.

Question 5

“We now live, as Earth always has, in an Age of Bacteria. These simplest organisms will dominate our planet (if conditions remain hospitable for life at all) until the sun
explodes.” Stephen J Gould, 1998. This famous biologist considered Prokaryotes as relatively ‘simple’ organisms compared to Eukaryotes. Make two points in favour of, and two points against this conclusion.

Answer 5

Points in favour:

i) no nucleus

ii) no/little membrane compartmentation

iii) unicellular (only)

iv) no cytoskeleton

v) no sexual reproduction

vi) **simple flagella **compared to Eukaryotes

Points against:

i) highly diverse metabolic capacities/ecologies

ii) extraordinary fundamental (DNA sequence for rRNA) genetic diversity

iii) very **rapid growth **under favourable conditions

iv) capacity for very long, highly protected, dormancy

Question 6

Prokaryotes (and some Eukaryotes) are microscopically small. Outline two positive and two negative implications of being microscopically small.

Answer 6

Positives:

i) Rapid reproduction

ii) Extensive easy dispersal

Negatives:

i) Nearby water availability is critical for metabolism

ii) Large surface area to volume ratio means water medium is very viscous - greatly restricting motility.

iii) Small size means they are readily predated on by larger organisms.

Question 7

Prokaryotes were not only essential to the ancestral origins of the Tree of Life, but also to much of its subsequent development and diversification. Make 2 points to support the latter notion that prokaryotes have enhanced diversity among the eukaryotes.

Answer 7

i) Endosymbiosis of 2 prokaryotes gave rise to the first eukaryotes (aerobically respiring, nucleus-containing organisms), which ultimately diversified into many lineages of heterotrophic eukaryotes.

ii) **Endosymbiosis of a heterotrophic eukaryote with a cyanobacteria **(Prokaryote) gave rise to the first photosynthetic eukaryotes, which ultimately diversified into all the members of the higher plants (Archaeplastida).

iii) The diverse and unique metabolic capabilities of prokaryotes is critical to the biogeochemical cycling of many growth-limiting nutrients (N, P, Ca, etc.) and therefore to the ongoing availability of these nutrients to Eukaryotes, thereby providing the resources necessary for their growth and diversification.

iv) Prokaryotes such as cyanobacteria were responsible for greatly increasing the concentrations of oxygen in the atmosphere, thereby providing a critical resource that supports aerobic respiration in the Eukaryotes.

Question 8

Provide 2 reasons to explain why prokaryotes are generally only metabolically active when their cells are in contact with external water.

Answer 8

i) diffusion can supply nutrients and organic matter

ii) diffusion will remove waste excretions

iii) water is necessary as a metabolite

Question 9

Explain what is meant by the term chemoautotroph to describe an organism’s metabolism in terms of its acquisition of energy and carbon, and briefly describe an example of a globally significant biogeochemical reaction that is mediated by a chemoautotroph.

Answer 9

• A chemoautotroph obtains its energy by chemical oxidation of a reduced compound such as Fe+, NH4+, S, CH4, and its carbon by reducing CO2 (or HCO3) gas to an organic compound such as carbohydrates.
• basically: converts inroganic compounds such as carbon dioxide into organic compounds via chemical oxidation.
  Impacts on the biogeochemical cycling of:

i)** iron oxidation **(iron-oxidizing bacteria are responsible for some rusting and rock weathering)

ii) nitrification (nitrifying bacteria convert ammonium in agriculture fertilizer to nitrate that is particularly prone to leaching into aquatic ecosystems causing eutrophication).

iii) methanogenesis (some methanogens convert hydrogen to methane - which is a particularly powerful greenhouse gas).

Question 10

Describe two lines of evidence supporting the hypothesis that life evolved in deep sea thermal vents.

Answer 10

i) **thermophiles **are particularly frequent at the base of the Tree of Life (deep sea vents are hot).

ii) the reducing conditions in vents are consistent with the biochemical traits of early life forms (heterotrophic, and anaerobic).

iii) most of the fundamental housekeeping (cellular maintenance) proteins and biochemical processes seem to have a heritage reflecting a hydrothermal environment??

iv) UV levels are low in vents relative to the ocean surface, meaning nucleic acid degradation was minimal.

v) something really convoluted with pH

Question 11

Make 4 points in favour of the view that viruses are not living organisms.

Answer 11

i) require a host cell to replicate
ii) do not grow either by size increase or by dividing
iii) cannot respond to external stimuli
iv) lack cellular structures
v) lack capacity to metabolize independently

Question 12

Elucidating the fundamental biology of viruses has been beneficial to human societies in many different ways. Give 1 example to demonstrate this point, and clearly explain the societal benefit.

Answer 12

i) understanding **smallpox **and its relation to cowpox led to the development of vaccines as an immunization preventative medical procedure.

ii) understanding that many viruses function as bacteriophages has resulted in the development of very important tools in molecular biology to conduct gene transfers and cloning.

iii) understanding the role of the external viral spike proteins that serve as antigens during human infection has provided the basis for developing mRNA vaccines such as for COVID-19.

Question 13

The life cycles of all sexually reproducing organisms can be classified into three principal types. Name the generalized life cycle of the type which applies to the Red algae.

Answer 13

Alternation of generations

Question 14

Sketch a very simple conceptual diagram to illustrate this general life cycle, clearly indicating all multicellular and unicellular forms in the haploid and diploid phases as appropriate, as well as fertilization and meiosis (but no need to draw the specific organisms or any other details)

Answer 14

look at the diagram.

Question 15

Some Red algal species have evolved a modified version of the above life cycle with three multicellular forms. Illustrate this particular type of life cycle using a new diagram that highlights the differences compared to your answer above, and write a short description to explain the key features of this particular life cycle.

Answer 15

• Tetrasporophyte: just another diploid lump shooting off the sporophyte before the meiosis that makes the spores.
• The first multicellular diploid form may produce specialized spores (by mitosis) that disseminate and eventually germinate into a second multicellular diploid form on which some of cells undergo meiosis to produce haploid spores. Those spores can germinate to produce multicellular haploid forms.

Question 16

Suggest a reason why these triphasic red algal species may have evolved this capacity for two separate diploid stages.

Answer 16

Members of the Red Algae group do not have a flagellum in the gamete/spore stage, although it seems that their common ancestor with other algal groups did. Perhaps the** flagellum is ineffective for gamete motility in the turbulent coastal surface water** environments in which these organisms grow, and therefore it has been lost over evolutionary time. The production of multiple successive diploid forms may be a means to **maximize the numbers of sporophytes that will each contain some cells that undergo meiosis **thereby increasing the numbers of individual male and female gametophytes and thus gamete production and the **likelihood of compatible mating and successful fertilization.
**
TLDR:
- red algae exist in turbulent environments (strong currents) so flagella are useless.
- Instead, they make lots of gametes so that there is a higher chance that some will probably meet and fetilize.

Question 17

Explain two lines of evidence indicating that some Euglenoids gained the capacity to photosynthesize by secondary endosymbiosis?

Answer 17

Review: Chloroplasts in the photosynthetic euglenoids were acquired through (secondary) endosymbiosis by an ancestral heterotrophic euglenoid host of anancestral green algal cell that itself was a result of (primary) endosymbiosis by an ancestral heterotrophic eukaryotic host of a cyanobacterium that became an ancestral chloroplast.

Evidence includes the facts that photosynthetic Euglenoids have chloroplasts that:

a) contain chlorophyll b

b) are contained by a triple layer of plasma membranes

c) some presumably less advanced (more ancestral) Euglenoids are heterotrophs

Question 18

Construct and describe a phylogenetic tree based on rRNA sequence data that includes a grazing cow and at least three of the major groups of organisms that you would expect to find on or within that animal.

Answer 18

i) Ruminant bacteria branch off first in its own group
ii) ruminant methanogen archaea branch off next in its own group
iii) new group: grass branch off first, then chytrid fungi, then cow.

Question 19

Name the type of sexual life cycle that is followed by all members of the Kingdom Fungi.

Answer 19

Zygotic meiosis

Question 20

Indicate where the processes of cytoplasmic fusion (plasmogamy) and nuclear fusion (karyogamy) occur in the above diagram using labelled arrows.

Answer 20

In this fungus (within the Zygomycota), once mating begins, cytoplasmic fusion (plasmogamy) is immediately followed by nuclear fusion (karyogamy) during
formation of the zygospore… i.e. DURING the mating of gametangia leading to the zygospore…..i.e. nuclear fusion occurs very soon after cytoplasmic fusion where the arrow is above the word ‘zygospore’ above.

Question 21

Briefly describe an ecological context that can promote the onset of sexual reproduction in these fungi.

Answer 21

The fungus is likely to begin sexual reproduction producing the zygospore once either:
a) the food resource is depleted
b) the environment conditions become harsh
c) an appropriate sexually compatible mate is detected.

Question 22

Fungi are more important than bacteria and archaea as decomposers of dead plant and animal organic matter in terrestrial ecosystems. Make 3 points to support this
statement.

Answer 22

i) fungi have a hyphal growth form that allows them to grow toward and within their substrate.

ii) Fungi are not as dependent as bacteria on the immediate proximity of water and nutrients to support metabolism during decomposition because they can translocate water and nutrients within their hyphae from moist or fertile sources elsewhere, and therefore can decay relatively dry, nutrient-poor substrates.

iii) As a eukaryote, fungi are capable of sexual reproduction meaning that in each successive generation, they can generate relatively high levels of genetic diversity as compared to bacteria… and therefore they can evolve relatively quickly to adapt to diverse decomposer niches on land.

iv) **Fungi can synthesize specialized wood decay enzymes.
**
v) Fungi may be better adapted than bacteria to dispersal on land because they can produce large fruiting bodies to release spored into the air and so disperse to other organic matter substrates.

vi) Plant colonisation of land occured long after bacteria evolved, and at about the same time as the earliest land fungi (~1 bya). Therefore, both fungi and bacteria have had the chance to evolve on organic substrates on land for about the same time. As a result, the earlier origin of bacteria may not have been any particular advantage.

Question 23

Compare and contrast fungal and vascular plant reproduction by describing three distinctive features of the genetics and lifecycles of the Kingdom Fungi.

Answer 23

i) sexual reproduction is by zygotic meiosis in most fungi, whereas vascular plants have an alternation of generations life cycle.

ii) Zygotic (diploid) stage in fungi is unicellular and often represents the dormant highly protected stage of the life cycle that is favoured when environmental conditions are not favourable for growth.

iii) cytoplasmic (plasmogamy) and nuclear (karyogamy) fusion are substantially separated in time in many fungi (e.g. Ascomycota and Basidiomycota), meaning there is a distinct and **prolonged dikaryotic phase.
**
iv) Asexual reproduction is extremely common i most fungi, but in a much smaller proportion of vascular plants.

Question 24

The Kingdom Fungi contains many distinctive biological features compared to the other eukaryotic Kingdoms. **List 4 clearly separate and distinct biological characteristics of the Fungi to support this statement.**

Answer 24

i) **Dikaryotic cells** (containing 2 distinct haploid nuclei) are common and are even the **dominant life stage in the Basidiomycota.** ii) **Hyphae can be coenocytic** (cells not divided by cell walls, or only partially separated because of cell wall perforations). iii) Individual **fungi can extend across a very wide range of spatial scales** (microns to kilometers). iv) **Fungi have a very wide variety of feeding habits.** Wood decomposers; Nematode trapping fungi; Fungi that are parasitic on other fungi; fungi that parasite insects etc. v) **Fungi represent a very large number of the total species on Earth** (expected total number on Earth is second only to insects). vi) **Fungi can produce a very wide range of specialized enzymes and metabolites **(eg. can decompose lignin in wood). vii) Fungi form a very diverse range of **symbiotic partnerships.** viii) **Fungi have cell walls made of chitin**

Question 25

‘Dry rot’ refers to decomposition of wood in a dry environment by certain fungi. Outline two distinctive features of these fungi that allow them to achieve this process?

Answer 25

i) Fungi have the capacity to **translocate water and nutrients along the mycelium from hyphae that are in contact with moist areas elsewhere** to other hyphae that are actively decomposing completely dry wood. ii) Certain dry rot fungi can **synthesize substantial liquid water as a byproduct of glycolysis.** iii) Dry rot fungi can synthesize highly **specialized wood-decaying enzymes.**

Question 26

Describe the structure of a crustose lichen in cross-section by explaining each of the four layers in sequence from the top surface to the base.

Answer 26

Sandwich structure with: 1) Thin relatively dense layer of fungal tissue on top. 2) Algal layer 3) a thicker more 'spongey/open/porous' fungal layer 4) a thin fungal layer

Question 27

Explain the function of the fungal inner layer.

Answer 27

The inner layer of low density fungal tissue provides excellent **water uptake and storage.**

Question 28

Indicate how lichens acquire their supplies of carbon and sulfur and which symbiont participant is involved in each case.

Answer 28

i) **Alga fixes CO2 during photosynthesis, **some of which is used for its own metabolism and some of which is **translocated to the fungus.** ii) **Lichens get sulfur from the air **(atmospheric deposition of particles) **and rain**. Tiny sulfur particles in the air settle onto the lichen, or sulfur dissolves in rainwater. The top layer of the lichen, made of fungus **(fungal layer), absorbs this sulfur.**

Question 29

Diversity begets diversity. Explain this central concept of the course.

Answer 29

The evolution of diverse traits among species enhances the potential for subsequent evolution of further diversity in traits, and ultimately often **leads to increased numbers of species**.

Question 30

Illustrate the concept that 'diversity begets diversity' using 4 clearly separate and distinct examples that you have learnt about in this course.

Answer 30

i) **Diversity in bacterial metabolism permitted primary endosymbiosis** because the process involved those particular bacteria that had evolved a capacity for **aerobic respiration.** This primary endosymbiosis ultimately **gave rise to the first heterotrophic eukaryote**s and so was a starting point for extraordinary subsequent diversification across the Eukarya. ii) **Diversity in the evolution of the photosynthetic bacteria resulted in some that produced oxygen (cyanobacteria)** ultimate resulted via primary endosymbiosis in the first photosynthetic eukaryotes which went on to diversify greatly. iii) **Diversity in the evolution of the photosynthetic bacteria resulted in some that produced oxygen (cyanobacteria)** ultimately paving the way for **oxygen accumulation in the atmosphere and therefore selection for aerobic metabolism which spurred the evolution of diverse aerobic heterotrophs across the Eukarya.** iv) **Diversity in unicellular members of the Archaeplastida** was a necessary precursor to the **secondary and tertiary endosymbiosis whereby some dinoflagellates and other heterotrophic protists acquired photosymbionts **which subsequently led to substantial diversification within these algal groups. v) **Diversity in prokaryotic fission** (i.e. mutation) probably **led to the evolution of diploidy** which paved the way for **polyploidy** which has been such an important mechanism for **speciation in higher plants.** vi) **Diversity in the evolution of diploidy also paved the way for sexual reproduction **and the incipient processes of recombination and meiosis that generate further genetic diversity, and therefore usually **enhanced phenotypic and species diversity across all Eukarya. ** vii) **Diversity in primitive roots (rhizoids) **in certain green algae were a **precursor to the evolution of much more advanced roots **in the highly diverse vascular plants.

Question 31

The diagram above illustrates a fundamental life cycle trend in the evolution of diversity across the Tree of Life since life first originated. a) Describe the trend across the four life cycles using appropriate biological terminology

Answer 31

**i)** The first organisms were **prokaryotes with single copies of their chromosomes** and thus only capable of **reproduction by fission** resulting in two daughter cells that were almost genetically identical (except for mutation) in each life cycle. **ii)** The evolution of **diploidy** meant some cells in the life cycle could **contain chromosomes in pairs**, ultimately paving the way for the **evolution of meiosis and hence sexual reproduction, and the zygotic meiosis life cycle.** **iii)** The trend in **sexually reproducing organisms** (i.e. those capable of diploidy) from the zygotic meiosis life cycle, to those with the **alternation of generation life cycle,** and ultimately to those organisms with the **gametic meiosis life cycle** essentially reflects an **evolutionary trend from organisms spending most of their life cycle in the haploid phase, to organisms that spend most of their life cycle being in the diploid phase.**

Question 32

Explain the significance of the trend pattern in terms of the evolution of biodiversity across the Tree of Life.

Answer 32

**i)** **Compared to prokaryotic fission**, **sexual reproduction results in extraordinary genetic diversity** in progeny in each successive generation. - Since the haploid cells produced from meiosis are all genetically unique because they are produced by processes of recombination/cross-over, and independent assortment, and random fertilization in the first place, **each generation in a species that reproduces sexually is markedly different from all previous ones**. - This genetic diversity generally **enhances phenotypic diversity on which evolutionary selection pressures could act to promote diversification in structure and function,** including speciation. **ii)** Furthermore, diploidy results in two alleles for each gene per individual, and multiple alleles within a population. Thus the **range of phenotypes within a population is therefore much higher in diploids compared to haploid organisms and so more extensive diversification is promoted.** - **The extended diploid phase of the alternation of generations life cycle and even more so in the gametic meiosis life cycle** relative to the more ‘primitive’ zygotic meiosis in essence extends the diploid proportion of the life cycle, and therefore **the period in which selection can act on the phenotypic diversity described above.** **iii)** The result of this general trend is **the evolution of increased organism complexity across the Tree of Life over time along a gradient from asexual reproducing organisms to sexual reproducing organisms** with the zygotic meiosis life cycle, then those with the alternation of generation life cycle, and ultimately the largest complexity in those organisms with the gametic meiosis life cycle. TLDR: - prokaryotic fission to sexual reproduction = more genetic diversity each generation because cells produced from meiosis are genetically unique (cuz recombination). - genetic diversity = phenotypic diversity - phenotypic diversity = something for evolution pressure to act on = promotes structural and functional diversity - diploidy = 2 alleles in each gene per individual so lots of alleles in the population = larger range of phenotypes - idk

Question 33

The biological functioning of both aquatic and terrestrial ecosystems is primarily dependent on energy derived from photosynthesis. a) Write out the ‘equation of life’ that includes both autotrophic and heterotrophic components and includes energy inputs and outputs.

Answer 33

(HCHO)n + O2 = (+light)= CO2 + H2O + Energy

Question 34

Why are most photosynthetic organisms in aquatic systems generally small and structurally undifferentiated compared to their counterparts on land?

Answer 34

i) **The water medium in aquatic environments provides buoyancy to keep the photosynthesizing organism up close to the top surface where light availability is highest**, and where there is **ready diffusion of critical nutrients such as N, P, and dissolved CO2. **Consequently, there is **no selection pressure for complex structural tissues**, and furthermore **unicellular organisms are ideal because they have a relatively large surface area to volume ratio for nutrient uptake and waste release.** ii) By contrast, **on land, photosynthetic organisms are generally multicellular** to produce multiple **specialized structural tissues to acquire and compete for the resources they need**. For example, to access a water supply, most plants are rooted in the soil. **The resulting immobility means they develop into populations of individuals that cannot escape from direct competition with each other for light, water, and nutrients.** Hence there is an evolutionary **selection pressure to grow tall to reach the canopy and avoid shading of the light resource by other species,** meaning the development of considerable stem structural tissue in the shoot, which then must be supported by substantial anchoring root structural tissue belowground.

Question 35

Electricity generation facilities in many parts of the world today are dependent on diverse ancestral members of the Fern group (Pteridophytes). Explain this statement.

Answer 35

- The Pteridophytes include lycophytes, horsetails and ferns all of which grew in abundance in tree-like forms in the Carboniferous period about 360-290 mya ago. - **Growth conditions were ideal** in terms of warm temperatures and lots of rainfall and so huge forests developed. - **The fallen dead plant matter from these forests accumulated in low-lying areas where coverage by swamp water made conditions anaerobic and so restricted their decomposition**. - These accumulations became large and then protected and buried by subsequent sediment deposits, where they were **pressurised and heated from the Earth’s mantle, resulting in their eventual transformation over geological time to coal.**

Question 36

When seed plants first appeared on land in a world dominated by plant groups whose evolution had been focussed on the sporophyte stage, most of their evolution and diversification and subsequent speciation involved selection in favour of strategies that served to propel their genes into future generations through evolution of various features of the gametophyte stage. **Describe the five main plant traits that resulted from this selection.**

Answer 36

The traits that evolved included: **1) ****Gametophyte stage reduced even further to just a few cells.** **2) Heterospory** – physically different male and female gametophytes that could then go on to develop into highly specialised structures (pollen and ovule respectively). 3) **Pollen as a wind-dispersal mechanism** for the male gametes. 4) **Ovules retained on the parental sporophyte** and therefore protected but immobile. 5) **The seed** itself which depended on the evolution of the previous 4 traits for its appearance.

Question 37

Spores in the seedless plants were the principal mechanism for dispersal in all plants for the first 100 million years after land colonization. Re-write the following statement with the blanks filled in appropriately: In spore-bearing plants, spores are produced by ___osis from specialized cells on the __ploid _____ophyte and may disperse and germinate to produce a multicellular __ploid _____ophyte .

Answer 37

In spore-bearing plants, spores are produced by **meiosis** from specialized cells on the **diploid sporophyte** and may disperse and germinate to produce a multicellular **haploid gametophyte**.

Question 38

The evolution of the seed trait gave the seed plants a huge evolutionary selection advantage over spore-bearing plants in the terrestrial environment. Name two specific features of seeds, and in each case explain one evolutionary fitness benefit of that feature compared to spores.

Answer 38

**i) protective outer seed coat** allows for dormancy for days to years, until conditions are favourable for germination. ii) The **seed’s internal nutrient-storing cells** are nutrient reserves that allow the germinating seed to fully establish itself **without immediate reliance on its environment.** iii) The **seed’s embryo** **is deeply protected **by both the external surface seed coat and the internal nutrient-rich enclosing tissue.

Question 39

“Agriculture is in fact a brilliant if unconscious evolutionary strategy on the part of certain plants and animals to get humans to advance their interests” (Michael Pollan, Omnivores Dilemma, 2006). Write a series of logically ordered statements to explain the evolutionary biology underlying this statement using the example of maize (sweet corn; Zea mays) arising from its ancestral ancestor Teosinte (both pictured above) within the Grass family.

Answer 39

- Maize evolved from an ancestral grass plant (Teosinte) that is native to C. America. - **Teosinte produces a small cob at the top of the plant and each kernel is covered by a hard coating. ** - Ongoing selection by central American indigenous farmers of wild mutants resulted in a plant with the female (inflorescence) part moved from the shoot tip to halfway down the plant, and wrapped in a dense husk. - Subsequent **farmer-derived selection resulted in dramatic increases in cob size and loss of the hard coating around the ancestral Teosinte kernels.** Apparently, ‘artificial’ (i.e. human) selection of mutations in just 5 ancestral Teosinte genes achieved the transformation. - Humans dispersed corn to new locations. - In summary, corn is an example of a plant that has **evolved to become desirable to humans** and hence has become a focus of agriculture, and therefore been an extraordinarily successful species in terms of global areal expansion and cover density.

Question 40

Trade-offs are a very common feature in evaluating the fitness benefits and costs of particular evolutionary traits. Evergreen needle-leaf and deciduous broad-leaf tree species tend to occupy distinctly different habitat-types. The former are generally slow-growing and more abundant at relatively high latitudes and altitudes (e.g. boreal and alpine habitats where soil moisture can be scarce at some times of year), whereas deciduous broadleaf trees tend to be faster-growing but confined to lower latitude and altitude sites where soils are usually more moist. a) Name representative species (common or scientific name) of an evergreen needle-leaf tree and of a deciduous broad-leaved tree that might be found growing on the Queen’s campus.

Answer 40

i) Pine ii) Cedar iii) Spruce iv) Fir v) Maple vi) Oak vii) Ash viii) Beech

Question 41

By considering the trade-off associated with their differences in leaf surface area/volume ratio, e**xplain why each of these tree groups is best adapted to the soil moisture characteristics of their particular habitat-type.** **In your answer, be sure to clearly specify both the benefit as well as the associated cost for why evergreen needle-leaved species tend to dominate on relatively dry soils** (2 x 1 marks), **and a specific benefit and a cost for why deciduous broad-leaved species tend to dominate on more moist soils **(2 x 1 marks).

Answer 41

*Evergreen* - Evergreen needle-leaf trees have a relatively **small leaf surface area relative to volume** and the benefit of this trait is that it **minimizes leaf water loss**. - Therefore, it allows these species to **dominate in habitats where soil moisture is scarce** (desiccation-resistant). - The disadvantage of small leaf surface area relative to volume is that **photosynthetic capacity is low, resulting in relatively slow growth rates.** *Decidiuous* - Deciduous broadleaf tree leaves have a relatively **large surface to volume ratio** and the benefit of this trait is that it provides **high leaf area for photosynthetic activity**, and therefore these species have relatively **high growth rates**. - However, the disadvantage is that these species have relatively **high water demands and therefore generally do not grow well in habitats with habitats where soil moisture can be scarce** at some times of year (such as high latitude and altitude sites).

Question 42

Trillium species, Daffodils and Lilies are all members of the Monocot plant group. **Describe two common structural features of the flowers in this group.**

Answer 42

i) **Radial symmetry** ii) Floral parts in **threes** iii) Embryo that produces **single cotyledon**

Question 43

Describe a distinctive characteristic feature of the emerging germinating embryo in this plant group (monocots).

Answer 43

- All monocots have **a single cotyledon leaf.** - So on germination **this single leaf is the first structure to emerge.** - By contrast, the the germinating embryo of the Eudicota all have two emerging leaves (cotyledons). | 2 marks so u have to include both the first 2 points

Question 44

Describe the typical mature leaf shape of this plant group (monocots).

Answer 44

i) Leaves are usually **long and often narrow.** ii) Leaves **terminate in a single-point** (i.e. without indentation (grass-like as compared with a Eudicot maple leaf for example). (Leaf veins are usually parallel) | 2 marks

Question 45

Nitrogen and Phosphorus are both essential elements for all living organisms. **Indicate two important and functionally different biochemical molecules for each of these two elements.**

Answer 45

*Nitrogen * - Amino Acids (and therefore proteins) - Nucleotide bases (eg. ATCG) in DNA/RNA - Chlorophyll prgments - ammonium - nitrate *Phosphorus* - ATP energy - Phospholipids in membranes - Nucleotide phosphoribose backbone in DNA/RNA - Phosphate sugars in metabolism - Bones in vertibrates (made of calcium phosphate)

Question 46

Name two other (i.e. not nitrogen or phosphate) essential nutrients that vascular plants generally obtain from soil.

Answer 46

i) Potassium ii) Calcium iii) Magnesium iv) Sulphur v) Iron

Question 47

Some plant species have evolved specialized traits to obtain significant components of their nutrition from animals or from other plants. Explain this statement by **describing 3 distinct examples that were discussed in lecture or in the textbook readings of plant nutrient acquisition involving other organisms.**

Answer 47

i) **Sundew** plants **trap flies with sticky glues on their leaves,** and then slowly **digest the trapped insects by** **exuding digestive enzymes.** ii) **Pitcher** plants form **funnel-like shoots that trap insects and even frogs**. The **slippery coating on the inside coupled with a multitude of downward point hairs prevent escape.** Digestive enzymes in the funnel’s internal liquid pool at the base decompose the prey. iii) **Genlisea** has highly **modified underground leaves that curl over on themselves into ‘split straw’ like pipes** that trap soil organisms and digest them. iv) **Mistletoe** is an example of parasitic plant that **feeds on other plants by tapping into the branch phloem tissue.** v) ‘Indian pipe’ plants have a root system that taps into the mycorrhizae that are functionally associated with other nearby plant species thereby gaining its carbon etc. for growth. In fact it gains sufficient carbon in that parasitic way, that it has dispensed over evolutionary time with the capacity to make chlorophyll and therefore to photosynthesize.

Question 48

Angiosperms contain enormous structural diversity. **Give 2 distinct examples of conventional roots that have become modified by evolution into other structures.**

Answer 48

i) Evolution within the angiosperms has resulted in modification of **conventional roots into storage roots** (e.g beetroot) ii) **Prop roots** (e.g. maize) iii) **Green roots** (e.g. epiphytes such as orchids) iv) **Cluster roots** (e.g. Proteaceae of phosphorus-impoverished soils).

Question 48

Some plants can have relatively low root:shoot biomass ratios. **Explain the evolutionary selection pressure that would lead toward evolution of a low root:shoot biomass ratio, and describe the likely environmental properties of a habitat-type where such evolution would likely occur.**

Answer 48

- **Shoots are critical to providing photosynthetic capacity, while roots provide access to soil nutrients and water.** - A plant species is likely to evolve toward biomass allocation to organs that enhance uptake of the most growth-limiting resources. - An environment that has **low light**, and perhaps **moderate to high soil fertility is likely to result in the evolution of a low root:shoot biomass ratio** because the belowground resources are likely to be less growth-limiting than light availability. - Such environments include the understory of forests – especially tropical forest - A low root:shoot biomass ratio means a plant allocates a smaller proportion of its biomass to its roots compared to its shoots.

Question 49

Angiosperms contain enormous structural diversity. Give two distinct examples of leaves that have become modified by evolution into other structures.

Answer 49

Evolution within the angiosperms has resulted in modification of leaves into: i) tendrils ii) hairs iii) reproductive leaflets iv) spines v) storage leaves (such as in onion)

Question 50

When a potato is stored in a cupboard or dark area for too long, the “eyes” of the potato will often produce new shoots. Based on this information, and the basic structural design of plants, **explain how we know that a potato tuber is an example of a structurally specialized underground shoot and not a structurally specialized root.**

Answer 50

- **A potato is the swollen end of an underground stem** (a rhizome). - Stems consist of modular growing units of internode, leaf, node, and axillary meristem. - **Potato eyes are the axillary meristems on the main swollen underground stem**, and if the potato is stored for an excessively long time, **the axillary meristems will become active and produce new shoot buds** (known as ‘eyes’ – that can develop into mature shoots (i.e. consisting of stems and leaves)) that are in effect branches from the original potato tuber stem.

Question 51

Some plants such as grasses can have a total root surface area as much as 130 times more than the total shoot surface area. **a) Explain the evolutionary selection pressure that would lead toward evolution of such a high proportion of root surface area.**

Answer 51

- **Surface area is a primary determinant of nutrient uptake.** - A plant species is likely to evolve toward preferential allocation to new growth of surface area of tissue that would **enhance uptake of the most growth-limiting resources.**

Question 52

Some plants such as grasses can have a total root surface area as much as 130 times more than the total shoot surface area. **b) Describe the likely environmental properties of a habitat-type that would promote such evolution.**

Answer 52

- **An environment that has low soil nutrients, low soil moisture, and perhaps high light**, is likely to result in the evolution of a **high root:shoot surface area ratio** because the belowground resources are likely to be most growth-limiting. - Such environments include **grasslands, savannah, deserts.**

Question 53

The concept of species is central to biology. Define the term as it is generally applied to animal populations in their natural environment. ## Footnote (past year)

Answer 53

A group of populations whose members can interbreed with one another and **produce fertile offspring**, but cannot interbreed with populations of other such groups. ## Footnote 0.5 marks for: can interbreed 0.5 marks for: cannot interbreed with populations of other such groups

Question 54

Briefly explain one difficulty associated with the standard species definition when it is applied to each of the following: i) some plants; ii) prokaryotes ## Footnote (past year)

Answer 54

i) Some plant species can** hybridise with each other and produce fertile progeny**, but are still generally **considered separate species.** ii) Prokaryote populations do not interbreed in the sense described above, and yet they clearly group into ‘strains’ according to similar physiologies etc. - Their **reproduction is asexual via mitosis. ** - Unidirectional DNA/RNA transfer among and within strains may occur via conjugation or transduction.

Question 55

There are ~20 times more heterotrophic than autotrophic species on Earth. Suggest** two **reasons which might explain this observation. ## Footnote (past year)

Answer 55

i) **Heterotrophs have a wider potential food base because they can rely on consumption of other heterotrophs as well as autotrophs** (i.e. they can occupy multiple positions in trophic food webs). ii) **Heterotrophs evolved before autotrophs** and therefore have had more evolutionary time to diversify. iii) Heterotrophs evolved and diversified under anaerobic conditions and later diversified to adapt to aerobic environments (i.e. **they have been exposed to more widely varying niches). ** iv) **Competition for growth-limiting food resources in heterotrophs has led to strong diversification** (e.g. lignin degraders; Sympatric Galapagos finches specializing on particular seeds). By contrast, **this selection pressure does not apply as strongly to autotrophs because they are ‘self-feeders’.**

Question 56

A green algal species that has separate gametophyte and sporophyte stages of similar duration and size in its life cycle. The green algal species has a life cycle named ________________________, and so the haploid stage of the diagram would be ____________________(greatly enhanced/greatly reduced/largely unchanged) and is _____-cellular (unicellular/multicellular), the ____________ stage would be ____________________ (greatly enhanced/greatly reduced/largely unchanged), and the ____________ stage would be ____________________ (greatly enhanced/greatly reduced/largely unchanged), and is _____-cellular (unicellular/multicellular). ## Footnote (past year)

Answer 56

The green algal species has a life cycle named **alternation of generations**, and so the haploid stage of the diagram would be **largely unchanged**(greatly enhanced/greatly reduced/largely unchanged) and is **multi**-cellular (unicellular/multicellular), the **dikaryotic**stage would be **greatly reduced** (greatly enhanced/greatly reduced/largely unchanged), and the **diploid** stage would be **largely unchanged** (greatly enhanced/greatly reduced/largely unchanged), and is **multi**-cellular (unicellular/multicellular).

Question 57

# A nice fluffy dog: The dog species has a life cycle named ________________________, and so the haploid stage of the diagram would be ____________________(greatly enhanced/greatly reduced/largely unchanged) and is _____-cellular (unicellular/multicellular), the ____________ stage would be ____________________ (greatly enhanced/greatly reduced/largely unchanged), and the ____________ stage would be ____________________ (greatly enhanced/greatly reduced/largely unchanged), and is _____-cellular (unicellular/multicellular). ## Footnote (past year)

Answer 57

The dog species has a life cycle named **gametic meiosis**, and so the haploid stage of the diagram would be **greatly reduced**(greatly enhanced/greatly reduced/largely unchanged) and is **uni**-cellular (unicellular/multicellular), the **dikaryotic **stage would be **greatly reduced** (greatly enhanced/greatly reduced/largely unchanged), and the **diploid** stage would be **greatly enhanced** (greatly enhanced/greatly reduced/largely unchanged), and is **multi**-cellular (unicellular/multicellular).

Question 58

The Sunflower (Helianthus annuus) is a member of the Asteraceae family, and is an example of a species with a composite flower (inflorescence). Describe three characteristicstructural features of composite flowers. ## Footnote (past year)

Answer 58

**i) Individual flowers all bunched together** into a cluster - the flowering head (i.e. the inflorescence). ii) Individual flower size tends to be **very reduced in size compared to other families.** iii) Morphological differentiation of flowers into **'disc-types' in middle and 'ray-types' around the circumphrence edge** is common. iv) Individual **flowers open in temporal sequence** - often in an inward-moving spiral sequence. v) Superficially at least, composite flowers typically appear to have **radial symmetry** (not bilateral).

Question 59

Describe a characteristic genetic feature of composite inflorescence flowers and clearly explain why it is evolutionarily advantageous compared to flowers of most other families within the Angiosperms. ## Footnote (past year)

Answer 59

- **The ovary of each flower contains its own set of ovules that each contain a female gametophyte** that has been produced by meiosis, and that ultimately results in the egg. - Therefore, **not only are all the eggs in each flower genetically distinct from each other, but they are also genetically distinct from the eggs within ovules in neighbouring flowers** within the composite flowerhead/inflorescence. - This arrangement provides **extraordinary genetic diversity within a single composite flower and therefore enormous genetic variability in resulting progeny onwhich evolution by natural selection can act.** ## Footnote (past year)

Question 60

The Kingdom Plantae phylogeny contains groups of species that differ greatly in speciation rates over the time since they first evolved. **Support this statement by comparing the Bryophytes (e.g. mosses) and the Angiosperms (flowering plants) in terms of relative differences in number of species, and relative differences in duration of evolutionary time.** ## Footnote (past year)

Answer 60

- **Bryophytes first appeared early** in the terrestrial plant flora (over 400 million yearsago – a detail not required in the answer) compared to the **Angiosperms which appeared relatively late** (160 million years ago – a detail not required in the answer), **but have relatively few species and compared to the extraordinarily large number of flowering plant species (angiosperms).** - TLDR: **bryophytes appeared earlier than angiosperms, but angiosperms have more species.**

Question 61

Describe **2** distinct reasons which help to explain why the Angiosperms (flowering plants) have particularly high speciation rates compared to the other major plant groups. ## Footnote (past year)

Answer 61

i) Selection for increased efficiency of sexual reproduction in the terrestrial environment where moisture is often restricting resulted in **evolution toward the reduced gametophyte stage**, and the evolution of the seed, and pollen, flower, fruit and double fertilization....) that were all **associated with major changes in flower structure and therefore enhanced speciation within the flowering plant group**. ii) **Appearance of insects in the evolutionary environment** provided for the potential of **coevolution** (insect-mediated pollination) that **promoted speciation within the flowering plant group.** iii) Angiosperms coevolved alongside increasingly diverse and advanced insect and larger herbivores and microbial pathogens. This coevolution often resulted in an evolutionary ‘arms race’ of increasingly sophisticated plant defences, that were subsequently matched by new herbivore protection/avoidance mechanisms and pathogen traits, all of which tended to promote speciation.

Question 62

Light + Inorganic (CO2) ## Footnote (past year)

Answer 62

**Photoautotroph** (eg. Pine trees, Red algae)

Question 63

Inorganic (CO2) + Chemical (via oxidation) ## Footnote (past year)

Answer 63

**Chemoautotroph** (eg. iron-oxidizing bacteria)

Question 64

Light + Organic (compounds containing reduced C) ## Footnote (past year)

Answer 64

**Photoheterotroph** (eg. mitochondria, mycorrhizal fungi)

Question 65

Chemical (via oxidation) + Organic (compounds containing reduced C) ## Footnote (past year)

Answer 65

**Chemoheterotroph**(eg. beetles)

Question 66

why do insects have so many species?

Answer 66

- they evolve faster due to short life span, more pregeny, more niches to occupy (because they are smaller, predated on, consume resources).

Question 67

What's biodiversity

Answer 67

the study of the many different ways that organisms have found to complete their lifecycle.

Question 68

gram + cell wall

Answer 68

- thick peptidoglycan cell wall - plasma membrane - provides protection

Question 69

gram - cell wall

Answer 69

- thin peptidoglycan layer - plasma membrane - peptidoglycan - **have periphasic space!!** = degree of seperation between outer membrane and plasma membrane - this allows buffer zone, detox proteins

Question 70

Exaption

Answer 70

taking something already had and modifying for new purpose. eg. the citric acid cycle

Question 71

abiotic conditions

Answer 71

stuff like temperature, dry, wet etc.

Question 72

abiotic conditions

Answer 72

predators, competition etc.

Question 73

bacteria have been evolving longer than fungi, why are there more fungal species?

Answer 73

because they can do sexual reproduction = diversity

Question 74

Why are we more successful in treating bacterial diseases compared to fungal diseases?

Answer 74

- because fungi are much more similar to humans. - fungi have evolved defenses

Question 74

alga and fungus symbiosis

Answer 74

*Alga with fungus:* - alga feeds carbs to the fungus - fungus protects alga and stable water supply - parasitic for one algae - mutualistic for the while colony (controlled parasitism) *Alga without fungus:* - little leakage of carbs from alga without the fungus. - so grows quicker without the fungus

Question 75

80% of all vascular plant species form associations with mycorrhizae (fungus - root symbiosis)

Answer 75

Advantage for plant: - surface area to volume ratio - hyphe have high surface area to volume ratio (acquire more nutrients) - protects against pathogens

Question 76

What were the first land plants like?

Answer 76

- short (didnt have the structural tissue to grow taller) - spread quickly because no competetion

Question 77

Boundary layer

Answer 77

- zone of calm air that aurrounds each lead - retains moisture - higher CO2

Question 78

Why the fleshy structure around seed in apple?

Answer 78

to attract animals - animal eats - moves to new location - poops

Question 79

why produce root hairs?

Answer 79

to maximise surface area for water uptake

Question 80

steps in zygotic meiosis

Answer 80

- **vegetative myecelium** (left circle) - miosis (middle circle) - **sporangium **(right of circle) - **gametangium **(top right of circle) - mating (arrow going to zygospore) - zygospore (right box) - meiosis (under zygospore) - germination (after meiosis)