1. Explain the structure and functions of the root.
Answer:
The root is the underground part of the plant that anchors it to the soil and absorbs water and nutrients. The root consists of several parts:
- Root cap: Protects the growing tip of the root and helps in pushing through the soil.
- Root hairs: Extensions of the epidermis that increase surface area for water and nutrient absorption.
- Epidermis: The outermost layer that facilitates the absorption of water.
- Cortex: Stores food and helps in the movement of water and minerals.
- Endodermis: The innermost layer of the cortex, which controls the movement of water into the vascular cylinder.
- Vascular cylinder: Contains xylem and phloem for the transport of water, nutrients, and food.
2. Discuss the different types of roots and their modifications.
Answer:
Roots can be classified into:
- Fibrous roots: Found in monocots, these are made up of many small roots that emerge from the base of the stem (e.g., grasses).
- Taproot: Found in dicots, with a large central root from which smaller lateral roots arise (e.g., carrots).
- Adventitious roots: Roots that arise from unusual places like stems or leaves (e.g., in ivy plants).
- Modified roots: These include:
- Storage roots: Modified to store food (e.g., radishes, sweet potatoes).
- Prop roots: Help support the plant (e.g., corn).
- Aerial roots: Found in plants like orchids, used for support and water absorption from the air.
3. Describe the structure and function of the stem in plants.
Answer:
The stem is the main axis of the plant that supports leaves, flowers, and fruits. It facilitates the transport of water, nutrients, and sugars through vascular tissues. Key components include:
- Epidermis: The outer layer that provides protection.
- Vascular bundles: Contain xylem and phloem, responsible for transporting water, nutrients, and sugars.
- Xylem: Transports water and minerals from the roots to the leaves.
- Phloem: Transports food produced by photosynthesis from leaves to other parts of the plant.
- Cambium: A lateral meristem responsible for secondary growth, producing new xylem and phloem cells.
- Pith: Stores food in some plants, especially in monocots.
4. How does the structure of the stem vary between monocots and dicots?
Answer:
- Monocots: In monocots, vascular bundles are scattered throughout the stem, and there is no distinct central pith. They do not undergo secondary growth.
- Dicots: In dicots, vascular bundles are arranged in a circle, and there is often a distinct central pith. Dicots can undergo secondary growth due to the presence of cambium, leading to the thickening of the stem.
5. Explain the role of cambium in secondary growth of stems.
Answer:
Cambium is a lateral meristem present between the xylem and phloem in dicot stems. It is responsible for secondary growth by producing new cells. Cambium divides to form:
- Secondary xylem (wood): Adds thickness to the stem and transports water.
- Secondary phloem: Carries food from the leaves to other parts of the plant.
As the cambium continues to divide, the plant increases in girth, allowing for the development of thicker stems and stronger vascular systems.
6. Describe the functions of phloem and xylem in the stem.
Answer:
- Xylem: Transports water and dissolved minerals from the roots to the leaves. It consists of tracheids and vessels that provide structural support and facilitate the movement of water.
- Phloem: Transports the products of photosynthesis (mainly sugars) from the leaves to the rest of the plant. Phloem consists of sieve tubes, companion cells, phloem fibers, and parenchyma cells.
7. What are the different types of leaf venation?
Answer:
Leaf venation refers to the arrangement of veins within a leaf:
- Reticulate venation: In dicots, the veins form a network, with the midvein branching into smaller veins (e.g., in a rose leaf).
- Parallel venation: In monocots, the veins run parallel to each other (e.g., in grasses).
8. Discuss the structure of a typical leaf and its function in photosynthesis.
Answer:
The leaf consists of several key parts:
- Epidermis: The outermost layer, usually covered by a waxy cuticle to reduce water loss.
- Mesophyll: Composed of two layers, the palisade mesophyll (where most photosynthesis occurs) and the spongy mesophyll (for gas exchange).
- Vascular tissue (xylem and phloem): Transport water, nutrients, and sugars.
- Stomata: Small openings on the leaf surface that allow gas exchange (CO2 in, O2 out) and transpiration.
Photosynthesis takes place primarily in the palisade mesophyll, where chloroplasts absorb sunlight and convert it into chemical energy.
9. How does the structure of the leaf help minimize water loss in desert plants?
Answer:
Desert plants have several adaptations to minimize water loss:
- Thick cuticle: A waxy layer that reduces water loss through evaporation.
- Reduced number of stomata: Fewer stomata limit transpiration.
- Modified leaves: Some desert plants have small, thick, or needle-like leaves to reduce surface area.
- Succulent leaves: Store water in their thick, fleshy tissues.
10. Explain the role of stomata in plants and how they regulate gas exchange.
Answer:
Stomata are small pores in the leaf epidermis, surrounded by guard cells. They regulate gas exchange by opening and closing:
- Open stomata: Allow CO2 to enter for photosynthesis and release oxygen.
- Closed stomata: Prevent water loss through transpiration and protect against excessive water evaporation. The opening and closing of stomata are controlled by environmental factors like light, humidity, and CO2 concentration.
11. Describe the different types of plant tissues and their functions.
Answer:
- Meristematic tissue: Responsible for growth. Found in apical, lateral, and intercalary regions.
- Permanent tissue: Forms after differentiation. Includes:
- Simple tissues: Parenchyma, collenchyma, and sclerenchyma, which provide storage, flexibility, and strength.
- Complex tissues: Xylem (transports water) and phloem (transports food).
12. What is the function of the root cap in a plant’s root system?
Answer:
The root cap is a protective structure that covers the growing tip of the root. It helps protect the delicate meristematic cells behind it from mechanical damage as the root pushes through the soil. It also secretes mucilage to ease the movement of the root through the soil.
13. Compare and contrast the structure of monocot and dicot stems.
Answer:
- Monocot stems:
- Vascular bundles are scattered throughout the stem.
- No secondary growth due to lack of cambium.
- Stems are generally herbaceous (non-woody).
- Dicot stems:
- Vascular bundles are arranged in a circle around the central pith.
- Presence of cambium leads to secondary growth, making them woody.
- Develop secondary tissues like bark and wood.
14. How does the vascular tissue in the root differ from the stem?
Answer:
In the root:
- The xylem and phloem are located in the vascular cylinder at the center of the root.
- The phloem is located externally, and xylem is situated centrally. In the stem:
- Vascular bundles are scattered in monocots or arranged in a ring in dicots.
- Xylem and phloem are found together in vascular bundles, with cambium in between.
15. What is the importance of secondary growth in plants?
Answer:
Secondary growth is essential for increasing the girth of plants. It occurs due to the activity of the cambium, leading to the formation of new xylem and phloem tissues. This growth is crucial for woody plants as it allows for thicker stems, which provide better support and the capacity to transport more water, nutrients, and food.
16. Discuss the differences between simple and complex permanent tissues in plants.
Answer:
- Simple permanent tissues: Composed of one type of cell. Examples include:
- Parenchyma: Involved in storage and photosynthesis.
- Collenchyma: Provides support and flexibility in growing parts.
- Sclerenchyma: Provides strength and rigidity.
- Complex permanent tissues: Made of different types of cells. Examples include:
- Xylem: Responsible for water transport.
- Phloem: Responsible for transporting food.
17. How does the structure of leaves help in regulating photosynthesis?
Answer:
Leaves are structured to maximize photosynthesis:
- The palisade mesophyll contains chloroplasts that absorb sunlight and carry out photosynthesis.
- The spongy mesophyll allows for the diffusion of gases (CO2) required for photosynthesis.
- The vascular tissue transports water to the leaf and distributes sugars produced during photosynthesis.
18. What are the various types of leaf modifications seen in plants?
Answer:
Leaf modifications include:
- Tendrils: Modified leaves that help in climbing (e.g., pea plants).
- Spines: Modified leaves in cacti to reduce water loss (e.g., in cacti).
- Storage leaves: Modified to store water or food (e.g., in onions).
- Bracts: Leaf-like structures around flowers for protection and attraction (e.g., poinsettia).
19. How does the structure of the stem enable plants to support leaves and flowers?
Answer:
The stem provides support through its rigidity and flexibility, facilitated by tissues like collenchyma and sclerenchyma. It elevates leaves to access sunlight for photosynthesis and positions flowers for pollination. The vascular tissues (xylem and phloem) ensure that the stem can support the transport of water, nutrients, and food to the leaves and flowers.
20. Explain the role of vascular cambium in the plant.
Answer:
Vascular cambium is a lateral meristem responsible for the production of secondary xylem and phloem, contributing to the thickening of stems and roots. It divides to produce new vascular tissues, allowing for the plant’s continued growth in diameter, and is critical in plants that exhibit secondary growth, such as trees.
These questions and answers provide a thorough understanding of plant anatomy, specifically the structures of roots, stems, and leaves, and their functions in plant growth and development.
