Alburnum is also called as
A. Autumn wood
B. Heart wood
C. Sap wood
D. Spring wood

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Hint: Alburnum is the recently formed wood found in between the bark and the hardened heartwood present in the trunk of a tree. It is pale yellow or white in color and is a soft part of the wood of the tree. It is responsible for transport of water and minerals to various parts of the plant body.

Complete answer:
Trunk of tree consists of five parts: Cambium, Inner bark, Outer bark, Sapwood and heartwood.

The outermost layer is known as outer bark and is the protective layer of the tree. This outermost layer is dark in color and saves plants from various harsh environmental conditions. Layer just after outer bark is inner bark which consists of phloem tissues which helps in transport of nutrients from roots to shoots and vice versa. Beneath inner bark is cambium which helps in growth of the tree as it contains meristem of the trunk and helps in attaining height of the tree.

Inner to meristem there is a layer called sapwood which contains xylem cells which helps in transportation of water from one part to other part of the tree. The xylem cells are also responsible for storage of starch inside the tree. The centre most region of trunk is called heart wood.

Hence, The correct answer is option (C).

Note: Alburnum is a living layer and contains more moisture content compared to heart wood. It is a layer of secondary wood of a tree from which transportation takes place to every part of the tree. It is light in color compared to outer parts of the trunk. Activity of the cambium ring changes with the change in climatic changes as reactivation of cambium during spring season to form plenty of xylem vessels is known as spring wood. Autumn wood is formed in the winter season and cambium activity is slow.