Question and Answers for BOT2601_Assignment_II_S1_2023.pdf
Question 1:
1 How does the digestibility of C3 and C4 grass species differ? (12)
Answer 1:The given text is a question.
The question is asking about the difference in digestibility between C3 and C4
grass species. C3 and C4 are two types of photosynthetic pathways in plants.
To answer the question in detail, we need to understand the difference between C3
and C4 grass species.
C3 grasses are cool-season grasses that grow in temperate regions. They have a
simpler photosynthetic pathway and are less efficient in producing photosynthesis.
They are usually more digestible and have higher nutritive value.
C4 grasses, on the other hand, are warm-season grasses that grow in tropical
regions. They have a more complex photosynthetic pathway and are more efficient
in producing photosynthesis. They are usually less digestible and have lower
nutritive value compared to C3 grasses.
Therefore, based on the type of grass species, the digestibility can differ. C3 grass
species are usually more digestible compared to C4 grass species due to their
simpler photosynthetic pathway and higher nutritive value.
Question 2:
2 Write the conclusion of C3 and C4 grasses in your own understanding
based on the article below. (20)
TOTAL MARKS = [70]
Answer 2:The text is an instruction given to the reader to write the conclusion of C3
and C4 grasses in their own words based on the article provided. The article may
have information regarding the differences between C3 and C4 grasses, their
characteristics, distribution, and adaptations to different environments.
To answer this instruction, the reader needs to go through the article provided and
understand the information given about C3 and C4 grasses. They should then
summarize the key points in their own words and write a conclusion that
highlights the main similarities and differences between these two types of
grasses.
The reader should also try to explain why these differences matter and what
implications they have for the growth and survival of C3 and C4 grasses. Finally, it is
important to ensure that the conclusion is well-supported by evidence from the
article provided and that it meets the criteria set out in the instructions, such as
the word count and the total marks available.
Question 3:
1 Do protein levels have an influence the nutrition of C3 and C4
grasses? (10)
Answer 3:The following text is a question:
"1 Do protein levels have an influence the nutrition of C3 and C4 grasses? (10)"
The question is asking whether the protein levels have an influence on the
nutrition of two types of grass, specifically C3 and C4 grasses.
To answer this question, research needs to be conducted to determine if there is a
relationship between protein levels and grass nutrition. It is possible that higher
protein levels could lead to better nutrition for the grass, or it may have no effect at
all.
Further studies can be done to investigate the correlation between protein levels
and the nutrition of C3 and C4 grasses. This may require analyzing the chemical
composition of the grasses and conducting feeding trials to determine the
nutritional value of the grasses with differing protein levels.
Overall, the answer to this question is not yet known and requires more research to
determine the potential relationship between protein levels and grass nutrition.
Question 4:
0 M HCl, as described previously (Barbehenn et al., 2004b). The difference in the
amount of sugars (measured with the above procedure) between matched pairs of
hydrolyzed and unhydrolyzed samples was defined as fructan. Starch was
hydrolyzed with a- amylase and amyloglucosidase in the residue remain- ing after
ethanol extraction, and was measured as glucose with a glucose test kit (Hendrix,
1993). All reaction mixtures were scaled to fit in 96-well microtiter plates (200 mL),
using a single aliquot (100 mL) of glucose color reagent to measure all sugars in
each sample. Absorbance measurements were made with a Bio-Rad Benchmark
(Bio-Rad, Hercules, CA, USA) microplate reader at 490 nm. Protein was measured
as total amino acids in 6 M HCl hydrolysates with ninhydrin (N 5 10–20/treatment)
(Barbehenn, 1995). No correction was made for the small overestimation of protein
with this method. Neutral detergent fiber (cellulose, hemicellulose and lignin) was
measured gravimetrically after solubilizing and removing non- fiber compounds (N
5 10/treatment) (Van Soest et al., 1991). TNC was defined as the sum of sugars,
fructan and starch, while total carbohydrate also included structural carbohydrates
(fiber).
Leaf toughness was measured on fresh leaves at the time of plant harvest.
Toughness was measured with a custom-made penetrometer (Barbehenn et al.,
2004b), and was expressed as the mass (g) necessary to punch a 2 mm diameter
hole through a leaf (N 5 20/treat- ment). The middle of the first fully expanded leaf
was tested, while avoiding thickened midribs. Leaves of B. dactyloides were too
narrow to measure with our penetrometer.
Statistical analysis
Measures of the nutritional quality of five C₃ vs. five C₄ grasses were compared by
split-plot nested ANOVA, with photosynthetic pathway, grass species (nested
within photosynthetic pathway) and CO₂ concentration as main effects, and block
and CO₂ × block as random effects (PROC MIXED; SAS, 2000). The full model
included the photosynthetic pathway × CO₂ concentra- tion interaction (to
compare the effect of CO₂ on C₃ vs.
C₄ grasses) and the CO₂ concentration × species inter- action (to compare the effect
of elevated CO₂ on individual species within each photosynthetic path- way). Small,
but significant, differences in some measures were observed between years for L.
multi- florum and B. curtipendula (e.g., hexose in both species, sucrose in B.
curtipendula, and fructan in L. multiflorum) (Table 1), precluding the pooling of
data across years. Therefore, data from 2001 were used for these two species in the
overall comparison because of the larger sample sizes available during this year.
The normality of residuals was tested with PROC UNIVARIATE (SAS, 2000). Where
necessary (hexose, toughness and bio- mass), log transformations were used to
normalize the residuals. If residuals could not be normalized (sucrose, fructan and
water), the significance of main effects was determined with Kruskal–Wallis tests
(Wilkinson, 2000). Kruskal–Wallis tests were also used to compare the ratios of total
carbohydrates : protein among the four photosynthetic pathway × CO₂
concentration groups. Pairwise differences within grass species between CO₂
treatments were examined by differences of least-squares means (SAS, 2000), or by
Kruskal– Wallis tests when data could not be transformed. Toughness in C₃ and C₄
grasses was compared using ANCOVA, with fiber as the covariate, to compare the
slopes of the regression lines (Fig. 3) (SAS, 2000).
Results
C₃ grasses contained higher levels of hexose sugars (glucose and fructose) and
sucrose at ambient CO₂ than did C₄ grasses (Table 1, Fig. 1a, b). By contrast, C₄
grasses contained higher levels of starch at ambient CO₂ than did C₃ grasses. Thus,
the levels of TNC (sugars, starch and fructan) were not significantly different
between the C₃ and C₄ grasses at ambient CO₂ (Table 1, Fig. 1e).
Levels of each of the nonstructural carbohydrates in the C₃ grasses increased
significantly under elevated CO₂ (Tables 1 and 3, Fig. 1a–d). Hexose, sucrose, starch
and fructan increased 48%, 63%, 63% and 202%, respectively. Storage carbohydrates
(starch and fructan) increased most consistently in the C₃ grasses, although in two
species in which starch did not increase significantly (F. arundinacea and E.
canadensis) sugars increased instead. Although levels of fructan tripled on average
in C₃ grasses under elevated CO₂, their absolute levels remained relatively low,
constituting no more than 7% dry weight (Table 1, Fig. 1c).
Nonstructural carbohydrates in the C₄ grasses in- creased to a smaller extent under
elevated CO₂ than they did in the C₃ grasses, producing significant photosynthetic pathway × CO₂ concentration interactions
Ⓒ 2004 Blackwell Publishing Ltd, Global Change Biology, 10, 1565–1575
Answer 4:The text is a statement that describes a scientific experiment and its
results. The experiment compares the nutritional quality of C₃ and C₄ grasses
under ambient and elevated CO₂ concentrations. The levels of hexose sugars,
sucrose, and starch were higher in C₃ grasses at ambient CO₂, while the levels of
storage carbohydrates (starch and fructan) increased most consistently in C₃
grasses under elevated CO₂. The levels of nonstructural carbohydrates in C₄ grasses
increased to a lesser extent under elevated CO₂ than in C₃ grasses, producing
significant photosynthetic pathway × CO₂ concentration interactions. The statistical
analysis involved a split-plot nested ANOVA, Kruskal-Wallis tests, and ANCOVA,
which were used to compare and analyze the data.
Question 5:
2 Explain in your own words how do CO2 affects the nutrition of C4 grass? (15)
Question 3
Answer 5:The given text is a question.
The question asks to explain in your own words, how CO2 affects the nutrition of C4
grass. CO2 is an important component of the atmosphere, but the increasing levels
of CO2 can have significant impacts on plant growth and nutrition. C4 grasses are
a group of plants that have a unique photosynthetic pathway. These plants are
adapted to high-light and warm environments, and they have a different way of
conducting photosynthesis, which is more efficient in water conservation.
When the levels of CO2 are increased, the stomatal conductance of C4 plants
decreases, which leads to less water loss and improved water-use efficiency. The
high levels of CO2 can increase the photosynthetic rate of C4 plants and enhance
their growth, which can lead to an increase in nitrogen uptake and assimilation.
However, prolonged exposure to high levels of CO2 can have several negative
impacts on plant nutrition. The increased carbon uptake can lead to a decrease in
the levels of other essential nutrients such as nitrogen, potassium, and calcium,
which can adversely affect plant growth and development.
In summary, the increase in CO2 levels can have both beneficial and detrimental
effects on the nutrition of C4 grass, and it depends on the duration and
concentration of the CO2 exposure.