Exam (elaborations)
BOT2601 OCT/NOV 2022 EXAM
- Institution
- University Of South Africa (Unisa)
BOT2601 OCT/NOV 2022 EXAM
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Michelle (Viljoen) ZervasStudent number: 51396491
BOT2601 Exam Oct/Noc
2022-10-14
Question 1.1
Hydromorphic leaves:
have an enlarged aerenchyma and parenchyma tissue with large intercellular
shapes
The patterns of venation have reduced
Gas is present in the vast air passages along with epidermal cells that contain
chloroplast, which improve light absorption and photosynthesis
There may be very little or no scherenchyma present in these leaves
Stomata are present, but they are missing in plants that are permanently
submerged
Halopythic leaves:
The stomata close in order to reduce Na+
Are made up of unique surface glands and hairs that remove NaCl from the
mesophyll cells
Thick leaves
There are many rows of big tightly packed specialized hypodermal cells
Question 1.2
Acidic rain: Acid rain can be defined as rain with a pH below 5.6 and high
concentrations of sulfuric and nitric acids and causes s urface lesions, smaller
mesophyll cells and also the collapse of the epidermal and spongy mesophyll
cells.
Carbon dioxide: As the atmospheric CO2 levels rise, many plant species
change their stomatal density and undergo morphological changes, primarily
to the size and shape of their leaves.
Ozone injury to plants: Ozone is a naturally occurring gas, but too much NO2
in the atmosphere and the combination with O2 in sunlight lead to the
production of more ozone. Leaves that are affected by ozone will have
stipples and bleach patterns on the top of the leaf. The hair density and the
thickness of the epidermal cell walls can change.
UV-B radiation: Plants' physiology and structure are harmed since they are
constantly exposed to various UV-B radiation levels. In an attempt to repair
the damages caused, plants developed mechanisms and a lot of responses to
this stress. Damages caused by the UV-B radiation leads to
, structural changes in the leaves, it also damages the DNA and will lead to
changes in photosynthesis
Gaseous Air pollutants: Cars and factories releases phytotoxins. The
atmospheric gasses that is released from exhaust fumes can dramatically
change leaf anatomy. The leaf structure that is affected can lead to huge
reductions in and chronic tissue damage and growth biomass.
Ionizing radiation: The background radiation released by a number of
radioactive elements causes anatomical changes in a number of plant parts.
Question 1.3
These pollutants can have drastic and broad impact on the structure of leaves
that frequently resulting in major reductions in growth biomass as well as acute and
long-term tissue damage. Stomata are the primary entry point for gaseous air
contaminants into the leaf. The gas inside the mesophyll dissolves in the moist
mesophyll cell walls and creates toxic acids. Some pollutants cause a decrease of
cell membrane semipermeability and causes the mesophyll cell sap to leak into the
intercellular spaces and will than appear as an oiliness on the surface of the injured
leaf. When chloroplasts are distorted, the photosynthesis will reduce because the
lower and upper epidermal cells collapsed. CO2 enrichment shows that leaves of
several species go changes in stomatal density and particularly in the shape of the
leaf. The leaf thickness also increases in enriched CO2 conditions. Some plants
have developed of a second palisade layer can be connected to an increase in
lamina thickness. Decreases in stomatal frequencies are another effect of elevated
CO2 levels. CO2 enhancement shows some irregular variations in radial diameter
and tracheary element length .The warm temperatures, sufficient rainfall and
elevated atmospheric CO2 levels should increase radial stem growth and result in
broader growth rings. The capacity of the leaves to capture and utilise CO2 for the
activities decreases as they thicken.
Question 2.1
Grasses (Poaceae) with the C3 photosynthetic route are more prevalent in
northern latitudes and higher elevations, whereas grasses with the C4
photosynthetic pathway are more prevalent in hotter climes;
C4 grasses have developed biochemical and anatomical characteristics as a
result of their adaptation to high-temperature and high-light settings, which
have an effect on how nutritious they are for herbivorous animals. The tightly
spaced veins in the leaves of C4 grasses are bordered by concentric layers of
bundle sheath cells and mesophyll cells on either side;
C4 grasses usually have lower quantities of photosynthetic enzymes and
lower levels of protein overall compared to C3 grasses because of their higher
photosynthetic efficiency;
Based on the hypothesis that the thick-walled bundle sheath cells of C4
grasses are indigestible and the differences in nutrient levels between the two
grass types, Caswell et al. (1973) proposed that C4 grasses are nutritionally
inferior to C3 grasses;
, The first part of the aforementioned concept has been supported by the vast
majority of studies comparing the nutritional value of C3 and C4 grasses at
ambient CO2 levels: Compared to C4 grasses, C3 grasses typically have
higher concentrations of nonstructural carbohydrates, protein, and water and
lower concentrations of fiber, silica, and toughness;
The C3 photosynthetic pathway grasses are typically regarded as more
nutrient-dense hosts than the C4 grasses, but compared to C4 grasses, the
nutritional quality of C3 grasses is likewise more significantly influenced by
increased atmospheric CO2;
Under conditions of higher CO2, C3 grasses produce more nonstructural
carbohydrates and experience larger nitrogen content reductions;
While protein levels in most C4 grasses were unaffected by raised CO2,
sugar, starch, and fructan, the levels in C3 grasses significantly increased
under elevated CO2 and were linked with a significant decrease in their
protein levels;
Question 2.2
Although recent research suggests that some ruminants digest N-containing
compounds from C3 grasses more effectively than C4 grasses, the evidence
currently available suggests that among grass-chewing insects, the bundle
sheath cell anatomy of C4 grasses either does not impede the digestion of
protein or reduces digestion only by a relatively small amount;
It is evident that greater toughness in several of the species we looked at
cannot be easily explained by increased fiber, even if fiber rose in certain
grasses under increasing CO2;
Leaf thickness, fiber deposition in secondary cell walls, and possibly
nonstructural carbohydrates are just a few examples of the many elements
that might improve SLM, all of which have the potential to increase leaf
toughness;
The higher performance of caterpillars and grasshoppers on a C3 grass was
shown to be mostly attributable to higher nutritional quality, according to
earlier research with a single pair of C3 and C4 grasses
Future atmospheric circumstances will likewise result in C3 grasses
continuing to be more nutrient-rich than C4 grasses. This finding is in line with
the widespread perception that plants with higher protein content and lower C:
N ratios are healthier for both insect and vertebrate herbivores;
Leaf toughness, like fiber, was significantly greater inC4than in C3grasses at
ambient CO
Question 2.3:
At ambient CO2, quantities of nutrients (such as sugars, protein, and water)
are often higher in C3 grasses than in C4 grasses;
The increased CO2 does not have such a significant effect on the nutrition of
C4 grasses compared to C3 grasses whereby the protein levels does not
change very much
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