Biology notes
VERY SHORT ANSWER QUESTIONS (30 Questions)
1. Define chromatin.
Chromatin is a complex of DNA and proteins found in eukaryotic cells. It serves to package the DNA into a more compact, dense shape, enabling the regulation of gene expression and DNA replication.
2. Which organelle acts as MTOCs in cilia and flagella?
The organelle that acts as Microtubule-Organizing Centers (MTOCs) in cilia and flagella is the basal body.
3. Which part of the chloroplast contains photosynthetic pigments?
The thylakoid membranes of the chloroplast contain photosynthetic pigments, such as chlorophyll, which are essential for the process of photosynthesis.
4. What is the main function of microvilli?
The main function of microvilli is to increase the surface area of a cell, enhancing its ability to absorb nutrients and other substances.
5. Which synthetic auxin acts as a herbicide?
The synthetic auxin that acts as a herbicide is 2,4-Dichlorophenoxyacetic acid (2,4-D).
6. Which phytohormone exists as a gaseous hydrocarbon?
Ethylene is the phytohormone that exists as a gaseous hydrocarbon.
7. Which mineral deficiency causes "rosette" in plants?
The mineral deficiency that causes "rosette" in plants is typically due to a deficiency in nitrogen.
8. Which mineral deficiency causes "blossom end rot" in tomatoes?
"Blossom end rot" in tomatoes is primarily caused by a calcium deficiency.
9. Define epinasty.
Epinasty is a condition in which the upper side of a plant organ (such as a leaf) grows more rapidly than the lower side, causing the organ to bend downward.
10. Define parthenocarpy.
Parthenocarpy is the natural or artificially induced development of a fruit without fertilization, resulting in seedless fruits.
11. State one structural difference between prokaryotic and eukaryotic cells.
One structural difference between prokaryotic and eukaryotic cells is that eukaryotic cells possess membrane-bound organelles, such as a nucleus, while prokaryotic cells do not.
12. Where is DNA located in a prokaryotic cell?
In prokaryotic cells, DNA is located in the nucleoid region, which is not membrane-bound and contains the cell's genetic material in a single circular chromosome.
13. What type of ribosomes are found in prokaryotes?
Prokaryotes contain 70S ribosomes, which are composed of a 50S large subunit and a 30S small subunit.
14. In which type of cells are microvilli commonly found?
Microvilli are commonly found in epithelial cells, particularly those involved in absorption, such as intestinal epithelial cells.
15. What cytoskeletal protein forms microtubules?
Microtubules are formed from the cytoskeletal protein tubulin, which is a dimer composed of alpha and beta tubulin subunits.
16. Give one difference between cilia and flagella.
One difference between cilia and flagella is their length; cilia are typically shorter and more numerous on the cell surface, while flagella are longer and usually occur singly or in pairs.
17. Name the hormone responsible for phototropism.
The hormone responsible for phototropism is auxin, which regulates plant growth toward light sources.
18. Which hormone increases during water stress?
Abscisic Acid (ABA) is the hormone that increases during water stress, helping plants to respond to drought conditions by closing stomata.
19. Which mineral is required for chlorophyll production?
Magnesium is the mineral required for chlorophyll production, as it serves as a central atom in the chlorophyll molecule.
20. Which mineral is part of ATP?
Phosphorus is the mineral that is part of ATP (adenosine triphosphate), which is a crucial energy currency in cells.
21. What is the primary function of the Golgi body?
The primary function of the Golgi body is to modify, sort, and package proteins and lipids for secretion or delivery to other organelles.
22. Define endosymbiont theory.
The endosymbiont theory posits that certain organelles, specifically mitochondria and chloroplasts, originated as free-living prokaryotes that were engulfed by a host eukaryotic cell, leading to a symbiotic relationship.
23. What is the role of gibberellins in the Green Revolution?
Gibberellins play a crucial role in the Green Revolution by promoting stem elongation, seed germination, and fruit development, enhancing crop yields.
24. Name the receptor for auxin perception in plants.
The receptor for auxin perception in plants is known as TIR1 (Transport Inhibitor Response 1).
25. From which amino acid is IAA primarily synthesized?
Indole-3-acetic acid (IAA), a common auxin, is primarily synthesized from the amino acid L-tryptophan.
26. What is the 9+2 arrangement and where is it found?
The 9+2 arrangement refers to the structural organization of microtubules in cilia and flagella, where nine pairs of microtubules form a ring around a central pair of microtubules.
27. Which hormone class functions as rhizospheric signals to attract mycorrhiza?
Strigolactones are the class of hormones that function as rhizospheric signals to attract mycorrhizal fungi, benefiting plant nutrient uptake.
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8. Which hormone is primarily responsible for inducing fruit ripening in climacteric fruits?
A) ABA
B) GBA
C) Nitrogen
D) Calcium
C) Ethylene
D) NAA
The hormone primarily responsible for inducing fruit ripening in climacteric fruits is Ethylene.
9. From which amino acid is IAA primarily synthesized?
A) Methionine
B) L-tryptophan
C) Zeaxanthin
D) Cysteine
IAA is primarily synthesized from the amino acid L-tryptophan.
13. Which mineral serves as the central atom of a chlorophyll molecule?
A) Iron
B) Zinc
C) Magnesium
D) Manganese
The mineral that serves as the central atom of a chlorophyll molecule is Magnesium.
10. Which hormone class functions as rhizospheric signals to attract mycorrhiza?
A) Strigolactones
B) Gibberellins
C) Cytokinin
D) Ethylene
Strigolactones function as rhizospheric signals to attract mycorrhiza.
14. Whiptail in cauliflower is a specific symptom of deficiency of which mineral?
A) Chlorine
B) Molybdenum
C) Manganese
D) Boron
Whiptail in cauliflower is a specific symptom of boron deficiency.
11. Which hormone is derived from carotenoids and is critical for establishing seed dormancy?
A) Ethylene
B) ABA
C) Gibberellins
D) Auxins
The hormone derived from carotenoids that is critical for establishing seed dormancy is Abscisic Acid (ABA).
15. Which organelle is the largest in a typical animal cell?
A) Mitochondrion
B) Nucleus
C) Golgi body
D) Lysosome
The largest organelle in a typical animal cell is the Nucleus.
12. A farmer observed older leaves showing chlorosis starting from the tips. Which mineral deficiency is this?
A) Iron
This symptom indicates a deficiency of nitrogen.
16. Which process produces the MOST ATP?
A) Glycolysis
B) Fermentation
C) Krebs cycle
D) Oxidative phosphorylation
The process that produces the MOST ATP is Oxidative phosphorylation.
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17. Which organelle possesses digestive enzymes?
A) Vacuole
B) Lysosome
C) Peroxisome
D) Golgi body
The organelle that possesses digestive enzymes is the Lysosome.
22. A centriole has a structure of:
A) 9+2
B) 9 triplets
C) 13 protofilaments
D) 7 doublets
A centriole has a structure of 9 triplets of microtubules.
18. Microtubules are made of:
A) Actin
B) Myosin
C) Tubulin
D) Micron
Microtubules are made of Tubulin proteins.
23. The 9+2 arrangement is found in:
A) Ribosomes
B) Centrioles
C) Cilia and flagella
D) Lysosomes
The 9+2 arrangement is found in Cilia and flagella.
19. If oxygen is absent, cells convert pyruvate into:
A) Acetyl-CoA
B) CO₂
C) Lactate or ethanol
D) FADH2
If oxygen is absent, cells convert pyruvate into Lactate or ethanol.
24. Phytohormones are active at:
A) High concentrations
B) Extremely low concentrations
C) Only in roots
D) Only in leaves
Phytohormones are active at Extremely low concentrations.
20. The Calvin cycle requires:
A) CO2, ATP, and NADPH
B) O2 and FADH2
C) Chlorophyll and light
D) Light and water
The Calvin cycle requires CO2, ATP, and NADPH.
25. Plant Growth Regulators (PGRs) are:
A) Naturally occurring hormones only
B) Synthetic compounds only
C) Both natural and synthetic compounds
D) Always proteins
Plant Growth Regulators (PGRs) are both natural and synthetic compounds.
21. Centrioles are composed of:
A) Actin filaments
B) Microtubules
C) DNA
D) Cellulose
Centrioles are composed of Microtubules.
26. Auxins are chemically:
A) Diterpenes
B) Indole derivatives
C) Sesquiterpenes
D) Adenine derivatives
Auxins are chemically Indole derivatives.
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27. The most abundant natural auxin is:
A) ABA
B) IAA
C) GA₁
D) ACC
The most abundant natural auxin is IAA (Indole-3-acetic acid).
28. Gibberellins break:
A) Dormancy
B) Chlorophyll
C) ATP
D) Roots
Gibberellins break dormancy.
33. Ethylene is synthesized from:
A) Tryptophan
B) Methionine
C) Adenine
D) Chlorophyll
Ethylene is synthesized from Methionine.
29. GID1 is a receptor for:
A) Auxins
B) ABA
C) Gibberellins
D) Ethylene
GID1 is a receptor for Gibberellins.
34. Climacteric fruits show:
A) No respiration change
B) Respiration spike
C) Dormancy
D) Chlorosis
Climacteric fruits show a respiration spike.
30. Cytokinins stimulate:
A) Senescence
B) Cytokinesis
C) Abscission
D) Dormancy
Cytokinins stimulate Cytokinesis.
35. ABA induces:
A) Stomatal opening
B) Stomatal closure
C) Fruit ripening
D) Stem elongation
ABA induces Stomatal closure.
31. High auxin/cytokinin ratio promotes:
A) Shoots
B) Roots
C) Senescence
D) Ripening
A high auxin/cytokinin ratio promotes Shoots.
36. Strigolactones are derived from:
A) Tryptophan
B) Carotenoids
C) Methionine
D) Adenine
Strigolactones are derived from Carotenoids.
32. Ethylene is:
Ethylene is a phytohormone involved in various plant processes including fruit ripening and leaf senescence.
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37. Strigolactones inhibit:
A) Root growth
B) Axillary bud outgrowth
C) Photosynthesis
D) Respiration
Strigolactones inhibit Axillary bud outgrowth.
39. Boron deficiency causes:
A) Terminal bud death
B) Chlorosis in old leaves
C) Purple stems
D) Lodging
Boron deficiency causes Terminal bud death.
38. Sulphur deficiency appears first in:
A) Old leaves
B) Young leaves
C) Roots
D) Seeds
Sulphur deficiency appears first in Young leaves.
40. Nickel is essential for:
A) Urease enzyme
B) Chlorophyll
C) GA signaling
D) Root hairs
Nickel is essential for Urease enzyme activity.
PART C: SHORT ANSWER QUESTIONS (15 Questions)
Instructions: Answer each question in 3-5 sentences.
SA 1. Define the endosymbiont theory and name two organelles that support this theory.
The endosymbiont theory proposes that certain organelles, specifically mitochondria and chloroplasts, originated as free-living bacteria that were engulfed by ancestral eukaryotic cells, leading to a mutually beneficial symbiotic relationship. Evidence supporting this theory includes the double membrane structures of these organelles, their own circular DNA resembling bacterial DNA, and the presence of 70S ribosomes similar to those found in prokaryotes.
SA 2. Write a few lines about the structure and function of the cell surface membrane.
The cell surface membrane, also known as the plasma membrane, is primarily composed of a phospholipid bilayer with embedded proteins, carbohydrates, and cholesterol. This structure allows the membrane to be fluid and flexible, facilitating selective permeability to ions and molecules, cell signaling, and maintaining the internal environment of the cell.
SA 3. What is the role of gibberellins in the Green Revolution?
Gibberellins played a crucial role in the Green Revolution by promoting cell elongation, seed germination, and flowering in various crops. Their application allowed for increased plant height and facilitated earlier harvests, contributing to higher agricultural yields and improved food security.
SA 4. Write the names of all macronutrients (including structural elements) required by plants.
The macronutrients required by plants include Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), and Sulfur (S). These elements are vital for various physiological functions such as growth, enzyme function, and structural integrity of the plant.
SA 5. State the functions of any two essential elements in plant metabolism.
Nitrogen is an essential element that is vital for the synthesis of amino acids, nucleic acids, and chlorophyll, and is crucial for plant growth and development. Phosphorus is important in energy transfer through ATP, nucleic acid synthesis, and root development, ensuring proper plant metabolism and function.
SA 6. Define phytohormones and give two examples of growth promoters.
Phytohormones, also known as plant hormones, are organic compounds that regulate physiological processes in plants at low concentrations. Examples of growth promoters include Auxins, which stimulate cell elongation, and Gibberellins, which promote seed germination and stem elongation.
SA 7. Describe the role of auxin in phototropism.
Auxin is a plant hormone that plays a pivotal role in phototropism by promoting cell elongation on the side of the plant that is away from the light source. This unequal distribution of auxin results in the bending of the plant toward light, allowing for optimal light absorption for photosynthesis.
SA 8. State two of the triple responses of ethylene in plants.
Two of the triple responses of ethylene in plants include increased stem elongation and increased lateral expansion of stems, which lead to the bending of the plant as it grows towards light. Additionally, ethylene triggers the inhibition of root elongation, allowing for a more stable and supportive growth structure.
SA 9. Give examples of two primary macronutrients and their role in plants.
Two primary macronutrients are Nitrogen and Phosphorus. Nitrogen is crucial for chlorophyll production and the formation of amino acids, while Phosphorus plays a key role in energy transfer as part of ATP and contributes to root development and flowering.
SA 10. Differentiate between prokaryotic and eukaryotic ribosomes.
Prokaryotic ribosomes are 70S in size, comprised of a 50S large subunit and a 30S small subunit, while eukaryotic ribosomes are larger at 80S, consisting of a 60S large subunit and a 40S small subunit. Additionally, prokaryotic ribosomes are found freely in the cytoplasm, whereas eukaryotic ribosomes can be found attached to the endoplasmic reticulum or free in the cytoplasm.
SA 11. What is the function of the Golgi body in protein processing?
The Golgi body, or Golgi apparatus, is responsible for the modification, sorting, and packaging of proteins synthesized in the endoplasmic reticulum. It glycosylates proteins, adds carbohydrate chains, and creates vesicles to transport the modified proteins to their designated locations within or outside the cell.
SA 12. Explain the term "niche construction" with one example.
Niche construction refers to the process by which organisms modify their environment, creating new niches that affect the survival and evolution of themselves and other species. An example of niche construction is beavers building dams, which create ponds that alter the local ecosystem and provide habitat for various species.
SA 13. What is the significance of the 9+2 arrangement in cilia and flagella?
The 9+2 arrangement in cilia and flagella is significant because it provides the structural framework necessary for their movement. The nine pairs of microtubules surrounding a central pair enable the coordinated bending and waving motion that propels the cell or moves fluid across surfaces.
SA 14. Describe the role of magnesium in plants and the deficiency symptoms.
Magnesium plays a crucial role in plants as a central component of chlorophyll, facilitating photosynthesis. Deficiency symptoms include interveinal chlorosis, where leaf tissue turns yellow while veins remain green, leading to poor growth and reduced yield.
SA 15. Define climacteric fruits and give two examples.
Climacteric fruits are fruits that continue to ripen after being harvested due to a surge in ethylene production and respiration. Examples include bananas and tomatoes, both of which exhibit changes in texture, color, and flavor post-harvest.
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PART D: ESSAY TYPE QUESTIONS (20 Questions)
(6 Points Each OR as Specified)
Instructions: Answer each question in detail. For questions with options, choose either A or B. If both are attempted, only the best answer will be considered.
Section 1: Cell Biology (Questions 1-7)
A. Write a detailed note on the Nucleus. (Structure: 3 Marks, Functions: 3 Marks)
The nucleus is a membrane-bound organelle that contains the cell’s genetic material. Structurally, it is surrounded by a nuclear envelope, which consists of two lipid bilayers with nuclear pores that regulate the passage of substances. The nucleoplasm houses chromatin and a nucleolus, which synthesizes ribosomal RNA. Functionally, the nucleus serves as the control center for cellular activities, regulating gene expression and mediating the replication of DNA during cell division.
B. Write detailed notes on the cell membrane (3 Marks) and the fluid mosaic model (3 Marks)
The cell membrane, or plasma membrane, is a phospholipid bilayer embedded with proteins, cholesterol, and carbohydrates. It serves as a barrier controlling the movement of substances in and out of the cell while facilitating communication through receptor proteins. The fluid mosaic model describes the cell membrane as a dynamic and flexible structure, where lipids and proteins can move laterally within the layer, contributing to the membrane's functionality and adaptability in response to environmental changes.
C. Write any 6 differences between prokaryotic cells and eukaryotic cells. (6 Marks)
Nucleus: Prokaryotic cells lack a true nucleus; DNA is found in the nucleoid region, while eukaryotic cells have a membrane-bound nucleus.
Size: Prokaryotic cells are generally smaller (0.1 - 5.0 micrometers) compared to eukaryotic cells (10 - 100 micrometers).
Organelles: Prokaryotic cells lack membrane-bound organelles, whereas eukaryotic cells contain organelles such as mitochondria and the endoplasmic reticulum.
Cell Division: Prokaryotic cells divide by binary fission; eukaryotic cells divide by mitosis and meiosis.
Ribosomes: Prokaryotic ribosomes are 70S, while eukaryotic ribosomes are 80S.
Cell Wall: Most prokaryotic cells have peptidoglycan cell walls, while eukaryotic cell walls, where present (as in plants and fungi), are made of cellulose and chitin, respectively.
D. Explain the structure of the Golgi complex (3 Marks) and its functions (3 Marks).
The Golgi complex consists of a series of flattened, membranous sacs called cisternae, stacked together. The structure is polar, with a cis face (receiving side) facing the endoplasmic reticulum and a trans face (shipping side) facing the plasma membrane. The functions of the Golgi complex include the modification of proteins through glycosylation, sorting and packaging of proteins into vesicles for transport to various destinations, and the synthesis of certain polysaccharides.
E. Draw a neat labeled diagram of a eukaryotic animal cell as seen under an electron microscope. Label all organelles. (6 Marks)
Student should insert their diagram here.
F. Describe the structure and function of mitochondria. In your answer include:
a) Double membrane structure and cristae (2 Marks)
The mitochondria have a double membrane structure with an outer membrane that is smooth and an inner membrane that is highly folded into structures called cristae. These folds increase the surface area for the electron transport chain and ATP synthesis.b) Role in ATP production (2 Marks)
Mitochondria are known as the powerhouse of the cell because they generate ATP through oxidative phosphorylation, utilizing energy produced during the breakdown of glucose and other nutrients.c) Evidence for the endosymbiont theory (2 Marks)
Evidence supporting the endosymbiont theory includes the presence of circular DNA within mitochondria, similar to prokaryotic genomes, and the fact that mitochondria possess their own ribosomes for synthesizing some of their proteins, resembling the 70S ribosomes of bacteria.
G. Compare and contrast the structure and function of chloroplasts and mitochondria. (6 Marks)
Chloroplasts and mitochondria both have a double membrane structure. Chloroplasts contain thylakoid membranes stacked into granum where photosynthesis occurs, while mitochondria contain cristae that house the components of the electron transport chain for ATP production. Chloroplasts are involved in converting light energy into chemical energy (photosynthesis), predominantly found in plant cells, while mitochondria are responsible for ATP production through cellular respiration, present in nearly all eukaryotic cells, including plants and animals.
Section 2: Evolution (Questions 1-6)
A. Explain the theory of natural selection as proposed by Charles Darwin and describe how it leads to evolution over time. (6 Marks)
The theory of natural selection, formulated by Charles Darwin, posits that individuals within a species exhibit variation in many traits, and those traits that confer a survival or reproductive advantage are more likely to be passed on to future generations. Over time, this process leads to gradual changes in the population, enhancing adaptations to their environment and resulting in the evolution of new species. Individuals that are better adapted to their environment survive and reproduce more successfully, while those less suited to their environment are less likely to produce viable offspring.
B. Describe the major stages of animal evolution from water to land and the key adaptations that enabled this transition. (6 Marks)
The transition from water to land in animal evolution involved several major stages:
Advent of Amphibians: The first vertebrates to adapt to life on land were amphibians, which evolved from lobe-finned fish during the Devonian period.
Adaptations: Key adaptations included the development of lungs for breathing air, limbs for movement on land, and skin that can prevent excessive dehydration.
Tectonic Events: Geological changes led to new habitats, which provided diverse environments for animals to inhabit, promoting the radiation of species.
C. Compare and contrast Lamarckism and Darwinism. Include the key principles of each theory and explain why Lamarck's theory was rejected. (6 Marks)
Lamarckism, proposed by Jean-Baptiste Lamarck, suggests that organisms can pass on traits acquired during their lifetime to their offspring, exemplified by the idea that giraffes' long necks evolved as a result of stretching to reach leaves. In contrast, Darwinism emphasizes the role of natural selection in evolution, asserting that only inherited traits can impact survival and reproduction. Lamarck’s theory was rejected due to a lack of genetic evidence supporting the inheritance of acquired traits, whereas Darwin’s theory is supported by vast evidence from genetics, fossil records, and observations of natural selection in action.
D. Explain the process of allopatric speciation using an example. Include the role of geographic isolation and reproductive isolation in your answer. (6 Marks)
Allopatric speciation occurs when a population is geographically isolated, leading to the divergence of species through evolutionary processes. An example is Darwin's finches on the Galápagos Islands; as they became isolated on different islands, they adapted to different environments, leading to variations in beak sizes and shapes corresponding to food sources. Geographic isolation restricts gene flow between populations, while reproductive isolation mechanisms can develop over time, such as changes in mating behaviors or timing, reinforcing speciation.
E. Describe the theory of biogenesis in detail. In your answer include:
a) The definition (2 Marks)
Biogenesis is the hypothesis that living organisms arise from pre-existing living matter, as opposed to abiogenesis, which suggests life can originate from inanimate substances.b) The historical background of the debate on spontaneous generation (2 Marks)
Historically, spontaneous generation was the prevailing belief that living organisms, such as insects and mice, could arise from non-living matter. This idea was challenged by experiments demonstrating that life does not spontaneously emerge from decaying matter.c) Key experiments that disproved spontaneous generation (2 Marks)
Key experiments include Francesco Redi's demonstration that maggots on meat come from fly eggs and Louis Pasteur's experiments that showed microbial growth only occurred in boiled broth exposed to air, providing evidence that microorganisms come from other microorganisms.
F. Describe the experiments that disproved spontaneous generation, including the contributions of Francesco Redi and Louis Pasteur. Explain the significance of these experiments to modern biology. (6 Marks)
Francesco Redi conducted an experiment using jars of meat to demonstrate that flies, not spontaneous generation, produced maggots. He covered some jars to prevent flies from landing on the meat, resulting in no maggots, while open jars had maggots. Louis Pasteur further disproved spontaneous generation using swan-neck flasks to show that boiled broth remained sterile when protected from airborne contaminants, despite being exposed to air. The significance of these experiments is immense as they established the principles of microbiology and led to the germ theory of disease, which underpins modern medical practices and hygiene.
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Plant Hormones (Questions 1-7)
A. Write a note on auxins and gibberellins including their synthesis (3 Marks) and physiological functions (3 Marks).
Auxins, primarily Indole-3-acetic acid (IAA), are synthesized mainly in the apical meristems of plants and are involved in regulating cell elongation, phototropism, and apical dominance. Gibberellins, such as Gibberellic acid (GA₁), are synthesized in young tissues and are crucial for processes including stem elongation, seed germination, and breaking dormancy. Both auxins and gibberellins significantly impact plant growth and development through their promotion of cell division and elongation.
B. Write a detailed note on ABA and Ethylene including their synthesis (3 Marks) and physiological functions (3 Marks).
Abscisic Acid (ABA) is synthesized from carotenoid precursors and is recognized for its role in stress responses, particularly in regulating stomatal closure to prevent water loss during drought conditions. Ethylene, synthesized from Methionine, plays a critical role in fruit ripening, leaf senescence, and the triple responses to mechanical stress. Together, ABA and Ethylene help plants adapt to environmental changes and manage stress effectively.
C. Explain the role of phytohormones in the following processes:
a) Fruit ripening (2 Marks)
Phytohormones like Ethylene promote the ripening of climacteric fruits by triggering metabolic changes that enhance color, aroma, and texture, making them more palatable.b) Seed dormancy and germination (2 Marks)
Gibberellins break seed dormancy by stimulating enzymes that promote the mobilization of stored nutrients, enabling successful germination under favorable conditions.c) Response to water stress (2 Marks)
ABA increases during water stress and promotes stomatal closure to minimize water loss, thus helping the plant retain moisture during drought conditions.
D. Describe the signaling mechanism of auxin, including the role of TIR1 receptors and Aux/IAA repressors. (6 Marks)
The signaling mechanism of auxin involves the binding of auxin to TIR1 receptors located in the cell nucleus, which leads to the ubiquitination of Aux/IAA repressors. The degradation of Aux/IAA allows the activation of auxin-responsive genes, facilitating various developmental processes such as elongation and differentiation. This mechanism allows plants to respond dynamically to changes in their environment by modulating gene expression in response to auxin concentration.
E. Discuss the dual role of strigolactones as both endogenous hormones and rhizospheric signals. Include their agricultural application in "suicidal germination." (6 Marks)
Strigolactones act as endogenous hormones that regulate shoot branching and root growth while also serving as rhizospheric signals to attract mycorrhizal fungi, promoting nutrient uptake. In agriculture, they can induce suicidal germination of parasitic plants, such as Striga species, that rely on host plants for nutrients. This can be an effective strategy for managing parasitic weed infestations in crops, promoting sustainable agricultural practices.
F. Compare the signaling components and primary effects of any three plant hormones: auxin, gibberellin, and abscisic acid. (6 Marks)
Auxin: Signaling involves TIR1 receptors leading to gene activation; primary effects include regulation of cell elongation, apical dominance, and phototropism.
Gibberellin: Involves DELLA proteins, with gibberellin binding resulting in degradation of DELLA repressors; primary effects include promoting stem elongation, seed germination, and flowering.
Abscisic Acid (ABA): Signaling is mediated by receptor proteins leading to inhibiting growth and promoting stomatal closure; its primary effects are critical for plant stress responses, particularly during drought.
G. Explain how knowledge of plant hormones is applied in:
a) Tissue culture (2 Marks)
Plant hormones are utilized in tissue culture to induce cell differentiation and organogenesis, allowing for the regeneration of whole plants from tissue samples. Auxins and cytokinins are often used to promote root and shoot development.b) Herbicide development (2 Marks)
Synthetic auxins are applied as herbicides to regulate plant growth improperly in unwanted species, leading to their death while leaving desirable crops unharmed through selective destruction of plant tissues.c) Fruit storage and ripening control (2 Marks)
Knowledge of ethylene's role in ripening allows for the artificial regulation of fruit rip