Plant Biology - Plant Anatomy
PLANT TISSUES
Plant body is made up of cells which aggregate and from tissues. Various tissues aggregate to from tissue system and organs. Plant tissues are of 2 types – Meristematic and Permanent tissue.
MERISTEMATIC TISSUE:
Dividing tissue present in the growing regions of the plant is called meristematic tissue. Depending on the region where they are present, they are classified as apical, lateral and intercalary.
- Apical meristem is present at the growing tips of stems and roots and increases the length of stem and the root.
- Lateral meristem is present in between two permanent tissues and increases the girth of the stem and root.
- Intercalary meristem is present at the base of the leaves or internodes on twigs.
According to the origin and development of meristematic tissues, they are classified into three different categories.
· Meristematic cells located at the shoot apex or root apex are made up of small and similar cells, is called as prometistem
· A tissue which is meristematic right form its origin is called primary meristem
· Meristem tissue which develops through transformation of a permanent tissue is called a secondary meristem.
Meristems tissues are very active and have dense cytoplasm, thin cellulose walls and prominent nuclei. They lack vacuoles.
PERMANENT TISSUE:
Cells of Meristematic tissue differentiate to form different types of permanent tissue. They take up a specific role and lose the ability to divide. This process of taking up a permanent shape, size and a function is called differentiation. There are two types of permanent tissue – Simple and complex tissue.
Simple permanent tissue
Simple permanent tissues are made up of one kind of cells and are homogenous in nature. A few layers of cells from the basic packing tissue are called parenchyma – a type of permanent tissue. It contains loosely packed living cells which provide support and stores food. It contains unspecialized cells with thin cell walls.
Ø Chlorenchyma – parenchyma which contains chlorophyll and performs photosynthesis is called as chlorenchyma.
Ø Aerenchyma – parenchyma containing large air cavities to give buoyancy to the plants to help them float is called aerenchyma.
Ø Collenchyma – provides support and is irregularly thickened at the corners.
Ø Sclerenchyma – provides stiffness to the plant with long narrow walls due to lignin.
The outmost layer of the permanent tissue is called epidermis made up of a single layer of cells and provides protection against water loss. The entire surface of a plant is covers by epidermis cells.
Epidermis cells on the aerial parts of the plant secrete a waxy, water-resistant layer on their outer surface and protect water loss, mechanical injury and invasion by parasitic fungi. Epidermal cells are relatively flat and their outer ad side walls are thicker than the inner wall.
Epidermis of leaves contains pores which is called stomata. Stomata are enclosed by two kidney shaped cells called guard cells. They are necessary for exchanging gases with the atmosphere and losing water in the form of water vapor (transpiration).
Epidermal cells of the root contain long hair like parts that greatly increase the total absorptive surface area and absorb the water.
In desert plant, epidermis contains thick waxy coating of cutin – a chemical substance with waterproof quality on its outer surface.
Complex permanent tissue
Tissues made of more than one type of cells which coordinate to perform a common function are called complex permanent tissue. They are associated with function of conduction, so also called as conducting tissues. It contains vascular bundle. Xylem and phloem are the conductive tissues.
Ø Xylem – conducts water to different parts of the plant body. It consists of tracheids, vessels, xylem parenchyma and xylem fibers
Ø Phloem – conducts food. It consists of sieve tubes, companion cells, phloem fibers and the phloem parenchyma. Sieve tubes are tubular cells with perforated walls. Phloem transports food from leaves to other part of the plant.
Self study:
Q-1: Match the following
| A |
B |
| Meristematic |
Tissue that conduct food in different parts of plant |
| Permanent |
Tissue that conduct water in different parts of plant |
| Xylem |
Dividing tissues present on the growing region of the cell |
| Phloem |
Differentiated meristematic tissue for special functioning |
Answer:
| A |
B |
| Meristematic |
Dividing tissues present on the growing region of the cell |
| Permanent |
Differentiated meristematic tissue for special functioning |
| Xylem |
Tissue that conduct water in different parts of plant |
| Phloem |
Tissue that conduct food in different parts of plant |
Q-2: Epidermis of leaves contains ………. Which is surrounded by two ………cells
- Stomata and guard
- Xylem and Phloem
- Endocarp and mesocarp
- Parenchyma and Collenchyma
Answer: Epidermis of leaves contains pores which is called stomata. Stomata are enclosed by two kidney shaped cells called guard cells
Q-3: Name the parenchyma tissue that contains chlorophyll and performs photosynthesis.
- Sclerenchyma
- Collenchyma
- Chlorenchyma
- Aerenchyma
Answer: Chlorenchyma is a parenchyma tissue which contains chlorophyll and performs photosynthesis.