NEET Biology Anatomy of Flowering Plants MCQs Set 14

Answer: (d) Bulliform cells

Explanation:
1. Bulliform cells are large, empty, colourless cells on the adaxial epidermis along the veins of grass leaves.
2. When they lose water, the leaf curls inwards, which minimises water loss.
3. Lenticels, guard cells and bundle sheath cells are different structures.

Teacher's Note:
1. Bulliform cells are motor cells of grass leaves.
2. Their flaccidity makes the leaf roll.

Answer: (a) It forms secondary cortex on its outerside

Explanation:
1. Cork cambium (phellogen) is a couple of layers thick, forms the periderm and gives rise to lenticels.
2. It cuts off phellem (cork) on its outer side and secondary cortex (phelloderm) on its inner side, so the first statement is incorrect.

Teacher's Note:
1. Periderm = phellem + phellogen + phelloderm.
2. Phellem lies outside, phelloderm inside.

Answer: (b) Monocotyledonous stem

Explanation:
1. Many scattered vascular bundles that are conjoint and closed, surrounded by bundle sheath, with a large parenchymatous ground tissue and no phloem parenchyma, are features of the monocot stem.
2. Dicot stems have a ring of open bundles and monocot roots have a polyarch radial arrangement.

Teacher's Note:
1. Scattered closed bundles indicate a monocot stem.
2. Dicot stems have open bundles in a ring.

Answer: (d) Sapwood is the innermost secondary xylem and is lighter in colour

Explanation:
1. Heartwood is dark due to deposition of tannins, resins and oils and gives mechanical support but does not conduct water.
2. Sapwood is the outer, lighter, younger secondary xylem that conducts water and minerals.
3. The statement that sapwood is the innermost xylem is incorrect.

Teacher's Note:
1. Heartwood is inner and dark; sapwood is outer and light.
2. Heartwood is mechanically strong but non-conducting.

Answer: (a) Tissue located below the phloem bundles and a portion of pericycle tissue above protoxylem.

Explanation:
1. In the dicot root, the vascular cambium originates from the tissue just below the phloem bundles and from a portion of the pericycle above the protoxylem.
2. It forms a wavy ring that later becomes circular.

Teacher's Note:
1. Dicot root cambium is entirely secondary in origin.
2. In dicot stems, intrafascicular and interfascicular cambium form a ring.

Answer: (c) Intercalary meristem

Explanation:
1. Intercalary meristem, located at the base of leaves and internodes, allows grasses to regenerate quickly after grazing or mowing.

Teacher's Note:
1. Intercalary meristem is typical for monocots such as grasses.
2. Lateral meristems give secondary growth.

Answer: (d) Water, mineral salts, some organic nitrogen and hormones

Explanation:
1. Xylem translocates water, mineral salts, some organic nitrogen and hormones from roots to the aerial parts.

Teacher's Note:
1. Xylem carries more than just water and minerals.
2. Phloem carries mainly sucrose.

Answer: (d) Bi-directional

Explanation:
1. Phloem transports food, mainly sucrose, from sources to sinks and the direction can change with the season and need, so translocation is bi-directional.
2. Xylem transport is unidirectional.

Teacher's Note:
1. Phloem is bidirectional; xylem is unidirectional.
2. The source-to-sink flow can reverse seasonally.

Answer: (b) Flaccidity of bulliform cells

Explanation:
1. In dry weather bulliform cells lose water and become flaccid, so the leaf blade curls inwards, reducing the surface exposed to transpiration.

Teacher's Note:
1. Turgid bulliform cells keep the leaf open, flaccid ones fold it.
2. This is a xerophytic adaptation in grasses.

Answer: (d) Annual rings are not prominent in trees of temperate region.

Explanation:
1. An annual ring is spring wood plus autumn wood produced in one year.
2. Light early wood and dark late wood are formed by differential cambial activity, which depends on climate.
3. Annual rings are prominent in temperate trees, not absent, so the last statement is not true.

Teacher's Note:
1. Temperate climates have clear seasons, so rings are distinct.
2. Counting rings gives the age of a tree.

Answer: (c) O2

Explanation:
1. Stomatal movement depends on light, CO2 concentration, temperature and water status of the leaf.
2. Oxygen concentration does not directly control guard cell turgor.

Teacher's Note:
1. CO2 and light are the main stomatal regulators.
2. Remember that O2 has no direct effect.

Answer: (d) Endodermis

Explanation:
1. Casparian strips are suberin deposits on the radial and tangential walls of endodermal cells.
2. They force water and minerals to pass through the cells, and not between them.

Teacher's Note:
1. Endodermis acts as a selective barrier due to Casparian strips.
2. Pericycle lies inside the endodermis.

Answer: (b) Secondary xylem

Explanation:
1. The vascular cambium normally cuts off secondary xylem towards the inside and secondary phloem towards the outside.
2. Primary phloem is formed by procambium, and periderm and phelloderm arise from cork cambium.

Teacher's Note:
1. Vascular cambium gives secondary xylem and phloem.
2. Cork cambium gives periderm.

Answer: (c) Epidermis and stele

Explanation:
1. The cortex lies between the epidermis and the stele (vascular cylinder).
2. It is made up of parenchyma and sometimes collenchyma, and its innermost layer is the endodermis.

Teacher's Note:
1. Ground tissue is divided into cortex, pericycle and pith.
2. Stele includes pericycle, vascular bundles and pith.

Answer: (a) Are extensions of xylem parenchyma cells into vessels

Explanation:
1. Tyloses are balloon-like extensions of xylem parenchyma cells into vessels through pits.
2. They block the vessels and are characteristic of heartwood, where they stop the water conduction.

Teacher's Note:
1. Tyloses make heartwood non-conducting.
2. They form from parenchyma cells.

Answer: (d) number of annual rings

Explanation:
1. The age of a tree can be estimated by counting the number of annual rings in a cross section of the trunk.

Teacher's Note:
1. Dendrochronology uses annual rings.
2. One ring forms per year in temperate climates.

Answer: (b) Medullary rays

Explanation:
1. Interfascicular cambium develops from the cells of the medullary rays lying between the vascular bundles, and joins the intrafascicular cambium to form a cambial ring.

Teacher's Note:
1. Intrafascicular cambium is primary, interfascicular is secondary in origin.
2. Together they form a continuous ring.

Answer: (c) Gaseous exchange

Explanation:
1. Lenticels are lens-shaped openings in the periderm of woody stems that allow the exchange of gases between the internal tissues and the atmosphere.

Teacher's Note:
1. Lenticels are formed by cork cambium.
2. They replace stomata in woody parts.