IGCSE Biology Paper-3: Specimen Questions with Answers 332 - 332 of 358

Passage

Fig. shows a diagram of a cross-section of a dicotyledonous leaf, as seen using a light microscope.

Dicotyledonous Leaf

Question 332 (1 of 4 Based on Passage)

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Name tissue A and cell B.

Explanation

A — Palisade mesophyll

B — Stomata

Dorsi-ventral leaves are found in dicots. These are generally horizontal and sunlight falls on their upper surface (ventral surface or adaxial surface) .

The important anatomical features of dorsiventral leaves are:

  • Upper epidermis: It is single-layered. It is covered with a thick cuticle. It has more stomata than the lower epidermis.
  • Mesophyll: It is differentiated into an upper palisade parenchyma and spongy parenchyma. The cells of the palisade parenchyma are cylindrical in shape and are compactly arranged. They have chloroplasts and, therefore, photosynthesize. They also check transpiration. The spongy parenchyma is loosely arranged with large intercellular spaces. They also contain chloroplasts and carry out photosynthesis.
  • Vascular bundle: There is one prominent vascular bundle and several small ones. The size of the vascular bundles is dependent on the size of the veins. The veins vary in thickness in the reticulate venation of the dicot leaves. It has phloem towards the lower (abaxial) side and xylem towards the upper (adaxial) side. The vascular bundle is enclosed by thick walled bundle sheath.
  • Lower epidermis: It is single layered and has less stomata or may be absent.
T. S. Dicot Leaf