NCERT Class 11-Biology: Chapter –6 Anatomy of Flowering Plants Part 8

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Question 4:

Assume that a pencil box held in your hand, represents a plant cell. In how many possible planes can it be cut? Indicate these cuts with the help of line drawings.

Answer:

Assuming a plant cell division it can be cut vertically, horizontally and diagonally.

Thus, it can be cut into three planes, through three axes, i.e., x, y and z.

Three Planes and Three axea

Three Planes and Three Axea

When any plane passes through the central axis of the plant cell, it divides the cell into two identical halves; it is called Radial Symmetry (figure below shows radial symmetry)

Two identical Halves

Two Identical Halves

If the plant cell can be divided into identical left and right halves in only one vertical plane, exhibit bilateral symmetry (figure below shows bilateral symmetry)

One vertical plane, exhibit bilateral symmetry

One Vertical Plane, Exhibit Bilateral Symmetry

Question 5:

Each of the following terms has some anatomical significance. What do these terms mean? Explain with the help of line diagrams.

a. Plasmadesmoses/ Plasmodesmata

b. Middle lamella

c. Secondary wall

Answer:

a. Plasmodesmata – A microscopic channels between two cells through the cell wall are called Plasmodesmata. Plasmodesmata allow transport of materials between two cells. They are protoplasmic strands between adjacent plant cells.

Plasmodesmata

Plasmodesmata

b. Middle lamella – It is a layer in the cell wall and is made of calcium pectate (mainly) and magnesium pectate. It helps in cementing between two neighbouring cells. During ripening a fruit becomes soft and pulpy due to dissolution of middle lamella.

c. Secondary wall – this is a non-extensible layer. It is made of hemicelluloses. It provides rigidity to the cell. The cell wall of a young plant cell is capable of growth, which gradually diminishes as the cell matures and the secondary wall is formed on the inner (towards membrane) side of the cell. Secondary cell wall may have the deposition of lignin. Secondary wall helps in the differentiation of the cell.

Secondary wall

Secondary Wall

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