Important Notes For NEET Biology – Anatomy of Flowering Plants

Plant Tissues

• Meristematic tissue: Cells divide actively.
• Apical meristem: Occurs at the tip and produces primary tissues, e.g. dermal, vascular, and ground tissues.
• Intercalary meristem: Occurs in grasses between matured tissues.
• Lateral meristem: Produces secondary tissues, e.g. cambium.
• Permanent tissue: Cells that don’t divide further after attaining their specialized structure and function.
• Simple tissue: Only one type of cells having the same structure and function.
• Complex tissue: More than one type of cells that work in coordination.

Types of Permanent Tissue

Simple Tissue

• Parenchyma
  • Structure: Cells are mostly isodiametric with thin cell walls made up of cellulose.
  • Function: Photosynthesis, secretion, storage.
• Collenchyma
  • Structure: Closely packed cells with no intercellular spaces; deposition of cellulose, hemicellulose, and pectin in the cell wall.
  • Function: Mechanical support; chloroplast-containing cells assimilate food.
• Sclerenchyma
  • Structure: Elongated cells with thick lignified cell walls; dead cells with no protoplasm; present as fibers or sclereids.
  • Function: Provide mechanical support; present in the seed coat, pulp, and walls of fruits.

Complex Tissue

• Xylem
  • Structure: Made up of tracheids, vessels, xylem fibers, and xylem parenchyma; vessels and tracheids are the main transporting material.
  • Function: Conducts water from roots to stem and leaves.
• Phloem
  • Structure: In angiosperms, phloem is made up of companion cells, sieve-tube elements, phloem parenchyma, and phloem fibers; in gymnosperms, albuminous and sieve cells are present.
  • Function: Transports food.

Epidermal Tissue System

• Comprises the outer covering of the plants, such as the epidermis, cuticle, stomata, epidermal extensions; trichomes in the stem and root hairs.
• Stomata regulate gaseous exchange and water loss by transpiration.
• Guard cells are bean-shaped in dicots and contain chloroplasts; grasses have dumb-bell-shaped guard cells.
• Root hairs are unicellular; trichomes are multicellular.

The Ground Tissue System

• Forms the major bulk of tissues between epidermal and vascular tissues, e.g. cortex, pericycle, pith.
• Contains simple tissues.
• Mesophyll of leaves is a ground tissue with chloroplast.

The Vascular Tissue System

• Consists of complex tissues of xylem and phloem.
• Dicots have cambium present between xylem and phloem of the vascular bundle, forming secondary vascular tissues.
• Dicots have an open vascular bundle; monocots have a closed type of vascular bundle, i.e., cambium is absent.
• Roots have a radial arrangement of vascular bundles; stem and leaves have a conjoint arrangement of vascular bundles.

Root Structures

Dicotyledonous Root

• Epiblema is the outermost layer with root hair.
• Cortex ends with the innermost layer endodermis, which contains suberin forming Casparian strips.
• Pericycle gives rise to lateral roots and vascular cambium.
• Two to six vascular bundles present; radial and exarch vascular bundles.

Monocotyledonous Root

• Similar to dicot root but polyarch xylem bundles are present.
• Large pith and no secondary growth.

Stem Structures

Dicotyledonous Stem

• Outer epidermis with cuticle; trichomes and stomata may be present.
• Cortex consists of hypodermis, cortical layer, and endodermis containing starch grains.
• Vascular bundles arranged as a ring; conjoint, open, and with endarch protoxylem.

Monocotyledonous Stem

• Hypodermis is sclerenchymatous.
• Vascular bundles are scattered, conjoint, and closed.

Leaf Structures

Dicotyledonous Leaf (Dorsiventral)

• Reticulate venation; epidermis on both surfaces with more stomata on the abaxial epidermis.
• Mesophyll differentiated into palisade and spongy parenchyma cells.
• Vascular bundles surrounded by bundle sheath cells.

Monocotyledonous Leaf (Isobilateral)

• Parallel venation; stomata equally distributed on both sides.
• Mesophyll not differentiated; bulliform cells present in grasses.
• Vascular bundles of the same size.

Secondary Growth

• Due to dividing lateral meristems; characterized by an increase in thickness.
• Cambium forms secondary xylem and phloem.
• Earlywood and latewood form annual rings indicating tree age.
• Heartwood is hard, durable, and resistant to insects; sapwood conducts water.
• Cork cambium forms cork (phellem) and secondary cortex (phelloderm); suberin makes cork waterproof.
• Bark includes all tissues exterior to vascular cambium.
• Lenticels help in gaseous exchange.
• Absent in monocots but present in gymnosperms.

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