Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Tissue is a group of cells that are similar in structure and/or work together to achieve a particular function.
Meristematic Tissues are tissues whose cells are capable of cell division. Based on their location, they are classified as: 1. Apical Meristem (at growing tips of stems and roots, increasing length), 2. Intercalary Meristem (at the base of leaves or internodes), and 3. Lateral Meristem (increases the girth/diameter of the plant).
Cells of Meristematic tissue are very active, have dense cytoplasm, thin cellulose walls, and prominent nuclei. They lack vacuoles because they do not need to store food or waste as they are constantly dividing.
Permanent Tissues are formed from meristematic tissues that take up a specific role and lose the ability to divide. This process is called differentiation.
Simple Permanent Tissues consist of one type of cell: 1. Parenchyma (thin-walled, provides support and stores food, includes Chlorenchyma for photosynthesis and Aerenchyma for buoyancy), 2. Collenchyma (thickened at corners with pectin, provides flexibility and mechanical support), 3. Sclerenchyma (dead cells, thickened with Lignin, provides stiffness and strength).
Complex Permanent Tissues consist of more than one type of cell working together: 1. Xylem (transports and minerals vertically, consists of tracheids, vessels, xylem parenchyma, and xylem fibres), 2. Phloem (transports food from leaves to other parts, consists of sieve tubes, companion cells, phloem parenchyma, and phloem fibres).
The vascular bundle is the collective term for the conduction system composed of Xylem and Phloem.
📐Formulae
💡Examples
Problem 1:
A student observes a plant tissue under a microscope. The cells are dead, have extremely thick cell walls made of Lignin, and have no internal space. Identify the tissue and its function.
Solution:
The tissue is Sclerenchyma.
Explanation:
Sclerenchyma cells are dead at maturity. The deposition of Lignin makes the walls very thick, providing mechanical strength and stiffness to parts like the husk of a coconut or the hard covering of seeds.
Problem 2:
Why do meristematic cells lack vacuoles while permanent parenchyma cells have large central vacuoles?
Solution:
Meristematic cells are in a constant state of division and do not store nutrients or waste, whereas Parenchyma cells function as storage units.
Explanation:
Vacuoles provide turgidity and store substances like , amino acids, and sugars. Since meristematic cells are primarily concerned with DNA replication and cell division, a large vacuole would occupy space and hinder the rapid division process.
Problem 3:
Contrast the direction of flow in Xylem and Phloem.
Solution:
Xylem: Unidirectional (upward). Phloem: Bidirectional (upward and downward).
Explanation:
Xylem transports and minerals from the roots to the leaves. Phloem transports photosynthetic products (like sucrose, ) from the 'source' (leaves) to the 'sink' (roots, fruits, and growing points).