Plant Anatomy Questions and Answers

Answer: D

All four features occur together in the dicot stem.

In a young dicot stem the endodermis is rich in starch grains and is called the starch sheath (i). The vascular bundles are conjoint (xylem and phloem on the same radius), collateral (phloem outside xylem) and open, with cambium between them (ii). The protoxylem faces the centre, so the xylem is endarch (iii). Between the bundles run parenchymatous medullary rays (iv).

Roots, dicot or monocot, have radial bundles with exarch xylem. A monocot root has no cambium. A dicot leaf has collateral veins without cambial activity and no medullary rays, since it has no pith around which the bundles form a ring.

Answer: B

It is Kranz anatomy.

In \(\mathrm{C}_{4}\) plants such as maize and sugarcane, the vascular bundles are surrounded by a ring of large bundle sheath cells rich in chloroplasts, with mesophyll cells arranged around them. The German word Kranz means wreath, after this ring-like arrangement. It allows carbon dioxide to be fixed in the mesophyll and concentrated in the bundle sheath for the Calvin cycle.

'Cratz' and 'Yarwood' anatomy are not botanical terms, and dendrochronology is the dating of wood by tree rings.

Answer: A

Continuous cambial activity gives diffuse porous wood.

Where the cambium works at a steady rate through the year, as in many tropical trees, it produces vessels of much the same size throughout, scattered evenly across the wood. That even distribution is called diffuse porous wood, and such wood usually shows no sharp growth rings.

Ring porous wood forms where cambial activity is seasonal: large vessels are made in spring and small ones later, giving a distinct ring. Semi ring porous wood is the intermediate case, and 'fibrous wood' is not a category of vessel arrangement.

Answer: C

Gymnosperm wood is Manoxylic and Pycnoxylic.

Manoxylic wood is soft and loose, with wide parenchymatous rays and much parenchyma, as in cycads. Pycnoxylic wood is dense and compact, with narrow rays and little parenchyma, as in conifers such as Pinus.

Homoxylic describes wood made of tracheids without vessels, a feature shared by almost all gymnosperms, so it does not divide them into two types. Polyxylic describes a stem with several rings of vascular tissue, as in Cycas, which is a feature of the stele rather than a type of wood.

Answer: B

The key's answer is both ring porous and diffuse porous wood.

In temperate and seasonal climates the cambium is active in spring and summer and slows or stops in winter. Each season's activity lays down early wood and late wood, which is what produces annual (growth) rings. Those seasonally produced rings are found in both ring porous wood, where large vessels are concentrated in the early wood, and diffuse porous wood, where vessels of similar size are spread across the ring.

So naming only ring porous or only diffuse porous wood gives half the picture that the key accepts. Heteroporous is not a standard wood type from cambial seasonality.