Anatomy of Flowering Plants – Class 11 Biology Notes
Introduction to Plant Anatomy
Anatomy refers to the study of the internal structure of plants. In this chapter, we will examine the various types of tissues and tissue systems in plants, focusing on their organization and functions. Understanding plant anatomy helps in understanding how plants grow, transport water and nutrients, and protect themselves.
Plants have specialized tissues organized into tissue systems, which work together to carry out specific functions.
1. Plant Tissues
There are two main types of plant tissues:
- Meristematic Tissues
- Permanent Tissues
1.1. Meristematic Tissues
Meristematic tissues are responsible for the growth of plants. These tissues consist of actively dividing cells and are mainly found in regions of growth, such as tips of roots, stems, and branches.
Types of Meristematic Tissues:
- Apical Meristem: Located at the tips of roots and stems, responsible for the primary growth (increase in length).
- Lateral Meristem: Located along the sides of stems and roots, responsible for secondary growth (increase in thickness).
- Examples: Vascular cambium and cork cambium.
- Intercalary Meristem: Found at the internodes or base of leaf blades, responsible for the growth of leaves and stems.
Characteristics of Meristematic Tissue:
- Cells are small, thin-walled, and living.
- Cells have a large nucleus and cytoplasm.
- Lack intercellular spaces.
1.2. Permanent Tissues
Permanent tissues are composed of cells that have completed their division and are specialized to perform specific functions. These tissues can be classified into simple permanent tissues and complex permanent tissues.
Simple Permanent Tissues:
These tissues consist of similar types of cells and are involved in storage, photosynthesis, and support.
- Parenchyma:
- Structure: Thin-walled cells, large intercellular spaces.
- Functions: Storage of food and water, photosynthesis, and secretion.
- Example: Mesophyll cells in leaves, storage cells in roots.
- Collenchyma:
- Structure: Unevenly thickened cell walls, living cells with little intercellular space.
- Functions: Provide mechanical support and flexibility to growing parts of the plant.
- Example: Stems and petioles of herbaceous plants.
- Sclerenchyma:
- Structure: Thick, lignified cell walls, dead cells at maturity.
- Functions: Provide rigidity and strength to the plant.
- Example: Sclereids in fruits (e.g., in pears) and fibers in hemp.
Complex Permanent Tissues:
These tissues consist of different types of cells working together for the transport of water, minerals, and food.
- Xylem:
- Structure: Composed of tracheids, vessels, xylem fibers, and xylem parenchyma.
- Function: Conducts water and minerals from roots to other parts of the plant.
- Types of Xylem Cells:
- Tracheids and Vessels: Hollow and dead at maturity, conduct water.
- Xylem Parenchyma: Living cells, store water and nutrients.
- Xylem Fibers: Provide structural support.
- Phloem:
- Structure: Composed of sieve tubes, companion cells, phloem fibers, and phloem parenchyma.
- Function: Transports food (mainly sugars) from leaves to other parts of the plant.
- Types of Phloem Cells:
- Sieve Tube Elements: Main conducting cells, lack a nucleus.
- Companion Cells: Provide metabolic support to sieve tube elements.
- Phloem Parenchyma: Store food.
- Phloem Fibers: Provide strength.
2. Tissue Systems in Plants
Tissues in plants are organized into three main tissue systems, which perform various physiological functions:
2.1. Epidermal Tissue System
- Structure: Composed of a single layer of cells that cover the plant body.
- Function: Protects the plant from external damage and prevents water loss.
- Components:
- Epidermal Cells: Flattened cells with a protective cuticle.
- Stomata: Pores that regulate gas exchange and water loss.
- Trichomes: Hair-like structures that provide protection and reduce water loss.
2.2. Vascular Tissue System
- Structure: Composed of xylem and phloem tissues.
- Function: Transport of water, minerals, and food throughout the plant.
- Components:
- Xylem: Transports water and dissolved minerals.
- Phloem: Transports food (mainly sugars) produced during photosynthesis.
2.3. Ground Tissue System
- Structure: Composed of parenchyma, collenchyma, and sclerenchyma.
- Function: Involved in storage, photosynthesis, and structural support.
- Components:
- Parenchyma: Storage and photosynthesis.
- Collenchyma and Sclerenchyma: Provide structural support.
3. Secondary Growth in Plants
Secondary growth refers to the increase in the girth of stems and roots and occurs in plants that have lateral meristems. This process is mainly carried out by two types of meristems:
- Vascular Cambium: Responsible for the production of secondary xylem (wood) and secondary phloem.
- Cork Cambium: Produces cork cells that form the bark and protect the plant.
Secondary growth is common in dicots and gymnosperms but not in monocots.
MCQs – Anatomy of Flowering Plants
1. Which of the following tissues is responsible for the transport of water in plants?
a) Phloem
b) Xylem
c) Collenchyma
d) Sclerenchyma
Answer: b) Xylem
2. Which tissue provides flexibility and support to growing parts of the plant?
a) Xylem
b) Phloem
c) Collenchyma
d) Sclerenchyma
Answer: c) Collenchyma
3. The cells of which of the following tissues are dead at maturity?
a) Xylem
b) Phloem
c) Parenchyma
d) Collenchyma
Answer: a) Xylem
4. What is the primary function of phloem in plants?
a) Transport of water
b) Transport of food
c) Storage of food
d) Photosynthesis
Answer: b) Transport of food
5. Which of the following is not a type of meristematic tissue?
a) Apical meristem
b) Lateral meristem
c) Intercalary meristem
d) Xylem
Answer: d) Xylem
6. The protective layer of cells covering the plant body is part of:
a) Vascular Tissue System
b) Epidermal Tissue System
c) Ground Tissue System
d) Meristematic Tissue System
Answer: b) Epidermal Tissue System
7. Cork cambium is responsible for:
a) Formation of xylem
b) Formation of phloem
c) Formation of secondary phloem and bark
d) Formation of cambium cells
Answer: c) Formation of secondary phloem and bark
8. Which of the following plant tissues is responsible for storing food?
a) Xylem
b) Phloem
c) Parenchyma
d) Collenchyma
Answer: c) Parenchyma
9. In plants, the water and food transport systems are known as:
a) Epidermis
b) Vascular tissue system
c) Ground tissue system
d) Meristematic tissue system
Answer: b) Vascular tissue system
10. Which of the following tissues is found in the vascular bundle of plants?
a) Phloem
b) Xylem
c) Both phloem and xylem
d) Collenchyma
Answer: c) Both phloem and xylem