MODULE 9 (THE VARIOUS CELL TYPES OF PLANTS)

• Botany is the branch of science that deals with plants, the person who studies structure and function is called a botanist.
• Histology is the science that deals with tissues and the person who studies this is known as Histologist.
• Plant tissues are group into four main types: protective (dermal) tissue, meristematic (embryonic) tissue, mechanical (ground) tissues, and conducting (vascular) tissue.
• The fifth type is called specialized tissue but this is not included as a main tissue. It just acts as an accessory part of the plant but contains many functions.
• Protective tissue covers the surface of the leaves and the living cells of the roots and stems.
• Protective tissue's cells are flattened with their top and bottom surfaces parallel.
• Protective tissues are divided into two: the epidermis and the periderm.
• In animals, the protective covering is the skin whereas in plants it is called the epidermis.
• The dermal tissue system can be specialized to a certain extent.
• The epidermis of the plant's leaves secretes a coating called the cuticle that helps the plant retain water.
• Periderm also called bark, which replaces the epidermis in plants that undergo secondary growth.
• The periderm consists of cork cells and protect and protects the plants from pathogens, prevents excessive water loss and provides insulation in the plants.
• Tissues where cells are constantly dividing are called meristems or meristematic tissues.
• Meristematic is the region that produce new cells. These new cells are generally small, six sided boxlike structures with tiny vacuoles and large nucleus.
• Meristem are divided into three: one is the apical meristems which are located at or near the tips of roots and shoot.
• As new cells form in the meristems, the roots and shoots will increase in length, this vertical growth is also known as primary growth.
• Each apical meristem will produce embryo leaves and buds as well as three types of primary meristems: protoderm, ground meristems, and procambium. These primary meristems will produce the cells that will form from the primary tissues.
• Lateral meristem accounts for the secondary growth in plants which is generally the horizontal growth.
• A good example of secondary growth would be the growth of a tree trunk in girth.
• 2 TYPES OF LATERAL MERISTEMS

  • vascular cambium
  • cork cambium
• Vascular cambium is a thin, branching cylinder, except for the tips where apical meristems run the length of the roots and stems of most perennial plants and many herbaceous plants.
• The vascular cambium is responsible for the production of cells and tissues that increase the thickness, or girth of the plant.
• Cork cambium like vascular cambium is a thin layer that runs the length of roots and stems. The difference that is only found in woody plants, as it will produce the outer bark.
• Intercalary meristems are found in grasses and related plants that do not have vascular cambium or a cork cambium, as they do not increase in girth.
• Intercalary meristem plants do have apical meristems and in areas of leaf attachment called node.
• Intercalary meristem produces new cells and is responsible for increase in length. The intercalary meristem is responsible for the regrowth of cut grass.
• Mechanical or ground tissue are responsible in synthesizing organic compounds, supporting and providing storage for the plant.
• Ground tissue is mostly made of parenchyma cells but also include some collenchyma and sclerenchyma. These three cells complete the ground tissues.
• Parenchyma cells are the most abundant of cell types and found in almost all major parts of higher plants.
• Parenchyma cells are basically sphere shape when they are first made however these cells have thin wall which flatten at the points where many cells are packed together.
• Parenchyma cells divide if they are mature which is vital in repairing damage to plant tissues.
• Some parenchyma cells have many chloroplasts and form the tissues found in the leaves; this type of tissue is called parenchyma which has no chloroplast are generally used for food or water storage.
• Some group of cells are loosely packed together with connected air spaces such as water lilies which are called aerenchyma tissue.
• Collenchyma cells are found just beneath the epidermis, generally they are elongated and their walls are pliable in addition to being strong.
• As the plant grows, these cells and tissues they form, provide flexible support for organs such as leaves and flower parts.
• Good examples of collenchyma plant cells are the "string" from celery that get stuck in our teeth.
• Sclerenchyma tissues have thick tough secondary walls that are embedded with lignin.
• At maturity, most sclerenchyma cells are dead which function for structure and support.
• Sclereids which are randomly distributed throughout other tissues.
• Sclerenchyma cells can occur in two forms:

  • Sclereids
  • Fibers