Question

The upper surface of a leaf is dark green when compared to the lower surface of the leaf. The presence of which tissue near the upper epidermis is responsible for this?
A. Palisade
B. Spongy
C. Collenchyma
D. Vessels

Answer 1

Hint: The plant body has three types of tissue systems- epidermal or tegumentary. Fundamental or ground and vascular or fascicular tissue system. Ground tissue forms the bulk of the plant body and consists of parenchymatous, collenchymatous, sclerenchymatous and glandular tissues.

Complete answer:
> Collenchyma is the tissue of the primary body and the cells of this tissue are living and have protoplasm. The cell walls of the cells show localized thickening due to presence of pectin hemicellulose and cellulose material. Presence of cellulose and pectin substances in the cell wall accounts for high water absorbing capacity to the cells.
> Xylem vessels are long tubes like with both their end walls perforated or dissolved. Each cell appears circular, oval, or sometimes polygonal in cross-section with very wide lumen. These cells are dead and they lose their protoplasm due to deposition of the lignified secondary wall.
> Vessels are chief conducting tissues of vascular plants that translocate water and dissolved mineral nutrients from roots to the leaves. They also provide mechanical support to the plants.
The mesophyll tissue in the leaves is the bulk of tissue lying between the upper and lower epidermis. It consists of parenchyma cells containing abundant chloroplasts and is separated by intercellular spaces.
> Palisade and spongy parenchyma are differentiated layers of mesophyll tissues.
The palisade us made up of compactly arranged columnar cells elongated at right angles to the leaf epidermis. The spongy parenchyma on the other hand consists of loosely arranged cells with wide intercellular spaces.
Palisade tissue contains a high amount of chloroplasts and it provides upper epidermis dark green color.

So the correct answer is A. Palisade.

Note: Plants are autotrophic in nature i.e. they prepare their own food through the process of photosynthesis. They require sunlight, water and carbon dioxide for this process. They have chlorophyll pigments in their chloroplasts in their cells that help in trapping light. This chlorophyll pigment gives green color to the plant.