Question 1

Define monocotyledons and dicotyledons. List two key differences between them. (5 marks)

Mark Scheme:

1. Definition of Monocotyledons:
   • Monocotyledons, or monocots, are one of the two major groups of flowering plants (angiosperms) characterized by having one cotyledon in their seeds. (1 mark)
2. Definition of Dicotyledons:
   • Dicotyledons, or dicots, are the other major group of flowering plants (angiosperms) characterized by having two cotyledons in their seeds. (1 mark)
3. Difference 1 – Leaf Venation:
   • Monocots: Have parallel venation, where leaf veins run side by side without forming a network.
   • Dicots: Have net-like (reticulate) venation, where leaf veins form a branching network. (1 mark)
4. Difference 2 – Vascular Bundle Arrangement in Stems:
   • Monocots: Vascular bundles are scattered throughout the stem.
   • Dicots: Vascular bundles are arranged in a ring within the stem. (1 mark)
5. Difference 3 – Floral Structure:
   • Monocots: Flower parts are often in multiples of three (e.g., 3 petals).
   • Dicots: Flower parts are often in multiples of four or five (e.g., 5 petals). (1 mark)

Question 2

List three characteristics that distinguish monocotyledons from dicotyledons. (6 marks)

Mark Scheme:

1. Seed Structure:
   • Monocots: Have one cotyledon.
   • Dicots: Have two cotyledons. (1 mark)
2. Leaf Venation:
   • Monocots: Exhibit parallel veins.
   • Dicots: Exhibit net-like (reticulate) veins. (1 mark)
3. Stem Anatomy – Vascular Bundles:
   • Monocots: Vascular bundles are scattered in the stem.
   • Dicots: Vascular bundles are arranged in a ring in the stem. (1 mark)
4. Root System:
   • Monocots: Have a fibrous root system with a network of similarly sized roots.
   • Dicots: Have a taproot system with a dominant central root and smaller lateral roots. (1 mark)
5. Floral Structure:
   • Monocots: Flower parts are often in multiples of three.
   • Dicots: Flower parts are often in multiples of four or five. (1 mark)
6. Pollen Structure:
   • Monocots: Pollen grains usually have one pore or furrow (monosulcate).
   • Dicots: Pollen grains typically have three pores or furrows (tricolpate). (1 mark)

Question 3

Explain the significance of vascular bundle arrangement in monocots and dicots. (5 marks)

Mark Scheme:

1. Monocots – Scattered Vascular Bundles:
   • In monocot stems, vascular bundles are scattered throughout the stem, allowing for flexibility and supporting the plant’s height without the need for secondary growth. (2 marks)
2. Dicots – Ring Arrangement of Vascular Bundles:
   • In dicot stems, vascular bundles are arranged in a ring. This arrangement facilitates secondary growth through the vascular cambium, enabling the stem to increase in thickness and providing structural strength. (2 marks)
3. Functional Implications:
   • The scattered arrangement in monocots supports rapid vertical growth, which is typical for grasses and lilies.
   • The ring arrangement in dicots supports the formation of woody stems seen in trees and shrubs. (1 mark)

Question 4

Describe the structure and function of xylem in dicotyledonous plants. (6 marks)

Mark Scheme:

1. Function of Xylem:
   • Transports water and mineral salts from the roots to the leaves and other parts of the plant. (1 mark)
2. Structure – Vessel Elements and Tracheids:
   • Composed of vessel elements and tracheids, which are hollow, tube-like cells that facilitate efficient water movement. (1 mark)
3. Arrangement in Vascular Bundles:
   • In dicots, xylem is typically located on the upper side of the vascular bundle in stems and leaves. In roots, xylem is arranged in a star shape at the center. (1 mark)
4. Cell Wall Composition:
   • Xylem cells have thick, lignified cell walls that provide structural support and prevent collapse under the negative pressure generated during transpiration. (1 mark)
5. Staining Characteristics:
   • When prepared on slides, xylem often stains red due to the presence of lignin and other compounds. (1 mark)
6. Additional Roles:
   • Provides mechanical support to the plant, contributing to its structural integrity and allowing it to grow tall. (1 mark)

Question 5

Compare the root systems of monocotyledons and dicotyledons. (5 marks)

Mark Scheme:

1. Monocotyledons – Fibrous Roots:
   • Monocots have a fibrous root system, consisting of a network of similarly sized roots that spread out from the base of the plant. This system provides efficient water and nutrient absorption and prevents soil erosion. (2 marks)
2. Dicotyledons – Taproot System:
   • Dicots have a taproot system, featuring a dominant central root that grows deep into the soil, with smaller lateral roots branching off. This system allows for deep water access and stable anchorage. (2 marks)
3. Functional Implications:
   • Fibrous roots in monocots support rapid spread and are typical in plants like grasses.
   • Taproots in dicots provide depth and are common in plants like carrots and oaks. (1 mark)

Question 6

Explain the role of phloem in the transport system of dicotyledonous plants. (5 marks)

Mark Scheme:

1. Function of Phloem:
   • Transports organic solutes (e.g., sucrose) from source tissues (primarily leaves) to sink tissues (e.g., roots, fruits, growing shoots) where they are used or stored. (1 mark)
2. Structure – Sieve Tubes and Companion Cells:
   • Composed of sieve tube elements, which are elongated, living cells connected end-to-end by sieve plates.
   • Companion cells are closely associated with sieve tube elements, providing metabolic support. (2 marks)
3. Vascular Bundle Arrangement:
   • In dicots, phloem is typically located on the lower side of the vascular bundle in stems and leaves. (1 mark)
4. Transport Mechanism – Pressure Flow:
   • Utilizes the pressure flow mechanism, where the loading of sugars into the phloem increases osmotic pressure, drawing in water and creating a turgor pressure that drives the flow of phloem sap towards sink tissues. (1 mark)

Question 7

List and describe three types of permanent tissues in dicotyledonous plants. (6 marks)

Mark Scheme:

1. Parenchyma:
   • Function: Involved in storage (e.g., starch, water), photosynthesis (especially in leaves), and secretion.
   • Structure: Thin-walled cells with large intercellular spaces, living at maturity.
   • Location: Found in most plant organs, especially in leaves, stems, and roots. (2 marks)
2. Collenchyma:
   • Function: Provides flexible support to growing parts of the plant, such as young stems, leaves, and petioles.
   • Structure: Modified parenchyma cells with unevenly thickened cell walls, primarily composed of cellulose and pectin, allowing for strength and flexibility.
   • Location: Typically found under the epidermis in growing regions. (2 marks)
3. Sclerenchyma:
   • Function: Provides rigid support and structural strength to mature plant parts.
   • Structure: Lignified cells with thick, tough cell walls, often dead at maturity. Includes fibers and sclereids.
   • Location: Found in mature stems, veins of leaves, and seed coats. (2 marks)

Question 8

Describe the structure and function of sieve tube elements in dicotyledonous plants. (5 marks)

Mark Scheme:

1. Structure – Elongated Cells:
   • Sieve tube elements are elongated, living cells arranged end-to-end to form continuous sieve tubes. (1 mark)
2. Sieve Plates:
   • They have perforated end walls called sieve plates that allow for the flow of phloem sap between adjacent sieve tube elements. (1 mark)
3. Lack of Organelles:
   • Sieve tube elements lack nuclei and most organelles, reducing flow resistance and maximizing space for nutrient transport. (1 mark)
4. Association with Companion Cells:
   • Each sieve tube element is paired with a companion cell through plasmodesmata, facilitating metabolic support and maintenance of phloem function. (1 mark)
5. Function – Transport of Sugars:
   • They transport organic nutrients (mainly sucrose) from source tissues (e.g., leaves) to sink tissues (e.g., roots, fruits). (1 mark)

Question 9

Explain how the arrangement of vascular bundles in dicot stems supports secondary growth. (5 marks)

Mark Scheme:

1. Ring Arrangement of Vascular Bundles:
   • In dicot stems, vascular bundles are arranged in a ring, positioning xylem internally and phloem externally. (1 mark)
2. Presence of Vascular Cambium:
   • The vascular cambium is located between the xylem and phloem within each vascular bundle, responsible for secondary growth (increase in stem thickness). (1 mark)
3. Secondary Xylem and Phloem Formation:
   • The vascular cambium produces secondary xylem (wood) towards the inside and secondary phloem towards the outside, allowing the stem to thicken while maintaining the arrangement of vascular tissues. (1 mark)
4. Support from Sclerenchyma Fibers:
   • Sclerenchyma fibers surround the vascular bundles, providing additional structural support and strength to withstand mechanical stresses. (1 mark)
5. Facilitation of Continuous Transport:
   • The ring arrangement and secondary growth ensure that the transport of water, minerals, and sugars can continue efficiently as the stem increases in girth. (1 mark)

Question 10

Compare the epidermis in stems and roots of dicotyledonous plants and describe its functions. (5 marks)

Mark Scheme:

• Structure – Single Cell Layer:
  • Both stems and roots have an epidermis composed of a single layer of cells covering the outer surface. (1 mark)
• Protection Function:
  • The epidermis protects the plant from water loss, pathogens, and physical damage. (1 mark)
• Presence of Root Hairs (in Roots):
  • In roots, the epidermis extends into root hairs, which increase the surface area for water and mineral absorption. (1 mark)
• Cuticle in Stems:
  • The epidermis in stems often has a cuticle, a waxy layer that further reduces water loss and provides an additional barrier against environmental stresses. (1 mark)
• Trichomes (in Stems):
  • Stems may have trichomes (hair-like structures) on the epidermis that provide protection against herbivores and reduce transpiration. (1 mark)

Question 11

Explain the significance of having a single cotyledon in monocotyledonous plants. (5 marks)

Mark Scheme:

1. Seed Structure:
   • Monocotyledons have one cotyledon in their seeds, which serves as the initial food storage for the developing seedling. (1 mark)
2. Early Growth Adaptation:
   • The single cotyledon often develops into a leaf, which begins the process of photosynthesis early in the seedling stage. (1 mark)
3. Nutrient Storage and Transfer:
   • The cotyledon stores nutrients that are mobilized during germination to support the initial growth of the seedling. (1 mark)
4. Simplified Vascular System:
   • Having one cotyledon is associated with a simpler vascular arrangement in monocots, which complements their parallel venation and scattered vascular bundles. (1 mark)
5. Growth and Development:
   • The single cotyledon contributes to the rapid vertical growth typical of monocots, such as grasses, by efficiently allocating resources for early development. (1 mark)

Question 12

Describe the structure and function of the endodermis in dicotyledonous roots. (5 marks)

Mark Scheme:

1. Structure – Location and Composition:
   • The endodermis is a single layer of cells located just inside the epidermis and surrounding the vascular tissue in dicot roots. (1 mark)
2. Casparian Strip:
   • The endodermal cells possess a Casparian strip, a band of suberin and lignin that blocks the passive flow of water and solutes through the cell walls. (1 mark)
3. Selective Absorption:
   • The Casparian strip forces water and dissolved minerals to pass through the plasma membranes of endodermal cells, allowing the plant to regulate and selectively absorb nutrients. (1 mark)
4. Barrier Function:
   • Acts as a barrier to prevent the backflow of substances, ensuring that minerals and water are directed into the xylem for transport. (1 mark)
5. Regulation of Ion Uptake:
   • The endodermis plays a crucial role in regulating ion uptake, maintaining ion balance, and preventing harmful substances from entering the vascular system. (1 mark)

Question 13

Compare the vascular bundle arrangement in monocots and dicots and explain how it affects their growth. (6 marks)

Mark Scheme:

1. Monocots – Scattered Vascular Bundles:
   • In monocot stems, vascular bundles are scattered throughout the stem. (1 mark)
2. Dicots – Ring Arrangement of Vascular Bundles:
   • In dicot stems, vascular bundles are arranged in a ring. (1 mark)
3. Impact on Growth – Monocots:
   • The scattered arrangement in monocots allows for flexibility and supports rapid vertical growth without secondary thickening. (1 mark)
4. Impact on Growth – Dicots:
   • The ring arrangement in dicots facilitates secondary growth through the vascular cambium, allowing stems to increase in thickness and develop woody structures. (1 mark)
5. Support and Structural Integrity – Monocots:
   • Scattered vascular bundles provide distributed support, enabling monocots like grasses to remain rigid despite lack of secondary growth. (1 mark)
6. Support and Structural Integrity – Dicots:
   • The ring arrangement supports the formation of wood, enhancing the plant’s structural integrity and ability to withstand environmental stresses. (1 mark)

Question 14

Describe the structure and function of sclerenchyma in plant tissues. (5 marks)

Mark Scheme:

1. Structure – Cell Wall Composition:
   • Sclerenchyma cells have thick, lignified cell walls that provide rigidity and strength. (1 mark)
2. Types of Sclerenchyma:
   • Includes fibers (long, slender cells) and sclereids (short, irregular cells). (1 mark)
3. Function – Structural Support:
   • Provides mechanical support to the plant, contributing to rigidity and structural integrity. (1 mark)
4. Location:
   • Found in mature stems, veins of leaves, seed coats, and other hard tissues. (1 mark)
5. Role in Plant Stability:
   • Enhances the plant’s ability to withstand physical stresses such as wind and gravity, ensuring overall stability. (1 mark)

Question 15

Explain the role of the vascular cambium in dicotyledonous plants. (5 marks)

Mark Scheme:

1. Definition and Location:
   • The vascular cambium is a type of lateral meristem located between the xylem and phloem in dicot stems and roots. (1 mark)
2. Secondary Growth Function:
   • Responsible for secondary growth, which increases the thickness or diameter of stems and roots. (1 mark)
3. Production of Secondary Xylem:
   • The cambium produces secondary xylem (wood) towards the inside, contributing to the plant’s woodiness and structural support. (1 mark)
4. Production of Secondary Phloem:
   • Simultaneously, it produces secondary phloem towards the outside, enhancing the plant’s nutrient transport capacity. (1 mark)
5. Contribution to Plant Longevity:
   • Allows dicot plants, especially woody plants, to continue growing in diameter throughout their lifespan, supporting tall and robust structures. (1 mark)

Question 16

Discuss the differences in pollen structure between monocots and dicots and their significance. (5 marks)

Mark Scheme:

1. Monocots – Monosulcate Pollen:
   • Monocot pollen grains typically have one pore or furrow (monosulcate). (1 mark)
2. Dicots – Tricolpate Pollen:
   • Dicot pollen grains usually have three pores or furrows (tricolpate). (1 mark)
3. Significance – Monocots:
   • The single pore facilitates pollen tube growth in a specific direction, aiding in efficient fertilization. (1 mark)
4. Significance – Dicots:
   • The three pores allow for more flexible pollen tube growth, enabling successful fertilization across a variety of flower structures. (1 mark)
5. Taxonomic Importance:
   • Pollen structure is used as a taxonomic characteristic to differentiate between monocotyledonous and dicotyledonous plants. (1 mark)

Question 17

Explain how secondary growth occurs in dicots but not in monocots. (5 marks)

Mark Scheme:

1. Presence of Vascular Cambium:
   • Dicotyledons possess a vascular cambium, a lateral meristem responsible for secondary growth. (1 mark)
2. Secondary Growth Mechanism:
   • The vascular cambium produces secondary xylem and secondary phloem, increasing the stem’s diameter. (1 mark)
3. Lack of Vascular Cambium in Monocots:
   • Monocotyledons typically lack a vascular cambium, preventing secondary growth and thus limiting stem thickening. (1 mark)
4. Structural Adaptations:
   • Monocots rely on fibrous root systems and scattered vascular bundles for support, avoiding the need for secondary thickening. (1 mark)
5. Impact on Plant Form:
   • As a result, dicots can develop woody stems and increase in girth, while monocots remain herbaceous or develop limited thickening. (1 mark)

Question 18

Describe how the root system of dicotyledonous plants provides advantages in water and nutrient uptake compared to monocots. (5 marks)

Mark Scheme:

1. Taproot System:
   • Dicots have a taproot system, featuring a dominant central root that grows deep into the soil, providing access to deep water sources. (1 mark)
2. Lateral Roots:
   • Smaller lateral roots branch off the taproot, increasing the surface area for water and nutrient absorption. (1 mark)
3. Anchorage and Stability:
   • The deep and extensive root system offers strong anchorage, enhancing the plant’s stability against environmental stresses like wind. (1 mark)
4. Resource Exploration:
   • Taproots can penetrate deeper soil layers, accessing minerals and nutrients that are unavailable to plants with only fibrous roots. (1 mark)
5. Symbiotic Relationships:
   • The taproot system often forms symbiotic relationships with mycorrhizal fungi, further enhancing nutrient uptake efficiency, especially for phosphorus. (1 mark)

Question 19

Compare the epidermis structure in monocots and dicots and explain its functions. (5 marks)

Mark Scheme:

1. Epidermis Structure – Monocots:
   • Monocots have an epidermis with cuticle and may contain trichomes (hair-like structures) for protection and reducing water loss. (1 mark)
2. Epidermis Structure – Dicots:
   • Dicots also have an epidermis with a cuticle, but may have additional structures like stomata and trichomes for gas exchange and protection. (1 mark)
3. Cuticle Function:
   • In both monocots and dicots, the cuticle is a waxy layer that prevents water loss and protects against pathogens. (1 mark)
4. Presence of Root Hairs (in Roots):
   • In roots, the epidermis extends into root hairs, which increase the surface area for water and nutrient absorption. (1 mark)
5. Trichomes Function:
   • Trichomes on the epidermis provide protection against herbivores and can reduce transpiration by reflecting excess light and trapping moisture. (1 mark)

Question 20

Explain the importance of phloem in distributing energy within dicotyledonous plants. (5 marks)

Mark Scheme:

• Transport of Sugars:
  • Phloem transports sugars (e.g., sucrose) produced in the leaves to sink tissues such as roots, fruits, and growing shoots. (1 mark)
• Energy Distribution:
  • The transported sugars provide energy for cellular respiration, growth, and development in various parts of the plant. (1 mark)
• Support of Metabolic Processes:
  • Sugars delivered by phloem are used in biosynthetic pathways for cellulose synthesis, protein synthesis, and other metabolic activities. (1 mark)
• Storage:
  • Phloem transports sugars to storage organs like roots and fruits, where they are stored as starch or other energy reserves. (1 mark)
• Coordination of Growth:
  • Efficient sugar distribution ensures that all parts of the plant have the necessary energy resources to grow, repair, and reproduce, maintaining overall plant health and development. (1 mark)