Question 1: State the location and function of different types of meristems.
- Apical Meristem is located at root apex and shoort apex and its function is longitudinal growth.
- Intercalary Meristem is located between mature tissues and its function is repair.
- Secondary Meristem is located on the periphery of root and stem, and its function is secondary growth.
Question 2: Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.
Answer: Cork cambium is a meristematic tissue which develops in the cortex region of mature stem. Cork cambium is formed to replace the broken epidermal layer of stem. The cells cut off on the outer side by cork cambium become cork. Hence, it can be said that the cork cambium is a tissue which forms cork.
Question 3: Explain the process of secondary growth in the stems of woody angiosperms with the help of schematic diagrams. What is its significance?
Answer: The cambial ring becomes active and starts cutting off new cells; both on the inner and the outer sides. The cells which are cut off towards the pith mature into secondary xylem. The cells which are cut off towards the periphery mature into secondary phloem. The cambium is usually more active on the inner side than on the outer side. Hence, a large number of secondary xylem is produced compared to the secondary phloem. The secondary xylem; thus produced soon forms a compact mass.
While the cambial ring forms the major portion during secondary growth in woody stem, the broken epidermal layer is replaced by the activity of cork cambium.
Secondary growth is necessary for growth in girth of the stem. Moreover, secondary growth also provides additional mechanical strength to the stem.
Question 4: Cut a transverse section of young stem of a plant from your school garden and observe it under the microscope. How would you ascertain whether it is a monocot stem or a dicot stem? Give reasons.
Answer: If the vascular bundles are arranged in a ring then it is a dicot stem. If the vascular bundles are scattered, then it is a monocot stem.
Question 5: The transverse section of a plant material shows the following anatomical features - (a) the vascular bundles are conjoint, scattered and surrounded by a sclerenchymatous bundle sheaths. (b) phloem parenchyma is absent. What will you identify it as?
Answer: Monocot stem
Question 6: Why are xylem and phloem called complex tissues?
Answer: Since xylem and phloem are composed of more than one type of cells, hence they are called complex tissues.
Question 7: What is stomatal apparatus? Explain the structure of stomata with a labeled diagram.
Answer: The minute pores present in the epidermis of leaves are called stomata. A stoma is composed of two guard cells; which are bean-shaped. The guard cells are dumbbell-shaped in grasses. The outer wall of guard cells is thin and the inner walls are highly thickened. Chloroplast is present in the guard cells. The guard cells regulate the opening and closing of stomata. A few specialized epidermal cells may be present near the guard cells. These specialized cells are called subsidiary cells. The stomatal aperture, guard cells and subsidiary cells together make the stomatal apparatus. Transpiration and exchange of gases are regulated by stomata.
Question 8: Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.
Answer: Following are different tissue systems in flowering plants; along with tissue names in each system:
- Epidermal Tissue System: Epidermis, Stomata
- Ground or Fundamental Tissue System: Paraechyma, Sclerenchyma and Collenchyma
- Vascular or Conducting Tissue System: Phloem and Xylem
Question 9: How is the study of plant anatomy useful to us?
Answer: The study of plant anatomy helps us in understanding the internal structure of a plant. We learn to appreciate the vast complexity of structures in a simple looking plant. Study of plant anatomy also helps us in understanding the evolution which has taken place among the plants.
Question 10: What is periderm? How does periderm formation take place in the dicot stems?
Answer: The meristematic tissue which develops to replace the worn out epidermis of dicot stem is called cork cambium or phellogen. The phellogen cuts off cells on both sides. The outer cells differentiate into cork or phellem. The inner cells differentiate into secondary cortex or phelloderm. Cork is impervious to water due to suberin deposition in the cell wall. The cells of secondary cortex are parenchymatous. Phellogen, phellem and phelloderm are collectively called periderm.
Question 11: Describe the internal structure of a dorsiventral leaf with the help of labeled diagrams.
Answer: Dorsiventral (Dicotyledonous) Leaf
There are three main parts in the leaf lamina of a dorsiventral leaf, viz. epidermis, mesophyll and vascular system.
Epidermis: The epidermis covers both the upper and lower surfaces. The upper epidermis is called adaxial epidermis, while the lower one is called abaxial epidermis. Cuticle is distinct. A higher number of stomata are present on the abaxial epidermis than on the adaxial epidermis. Stomata may be absent also in the adaxial epidermis.
Mesophyll: The tissue between the two epidermises is called mesophyll. The mesophyll is composed of parenchyma and contains chlorophyll. There are two types of cells in the mesophyll, viz. palisade parenchyma and spongy parenchyma. The palisade parenchyma is placed adaxially. It is made up of elongated cells; which are arranged vertically and parallel to each other. The spongy parenchyma is situated below the palisade parenchyma and extends to the lower epidermis. There are numerous large spaces and air cavities between the cells of spongy parenchyma.
Vascular Bundle: The vascular bundles can be seen in the veins and the midrib. Vascular bundles are surrounded by a layer of thick-walled bundle sheath cells. Vascular bundles are of different sizes because of reticulate venation.