2023-07-21-BIOL254-W1-Notes .docx

LECTURE 2: PRINCIPLES OF PLANT PHYSIOLOGY Internal Organisation of a Stem (Shoot) Anatomy of a Eudicot Stem The first thing you will find is the dermal tissue or epidermis whether you are dealing with stem root or leaves. The next thing is bundles or clusters also known as vascular tissues, the thi...

LECTURE 2: PRINCIPLES OF PLANT PHYSIOLOGY Internal Organisation of a Stem (Shoot) Anatomy of a Eudicot Stem The first thing you will find is the dermal tissue or epidermis whether you are dealing with stem root or leaves. The next thing is bundles or clusters also known as vascular tissues, the third thing will be the ground tissue. Names are assigned to regions of the ground tissues, and they are pith (plant tissue in the middle of the stem), Cortex (cells in-between two neighbouring vascular tissue or bundles). The basic makeup of the plant body weather a eudicot or monocot is the same that is you will find the dermal tissue, the ground tissue and the vascular tissue but the appearance and how the tissues are distributed are different. In eudicot you always find vascular bundles close to the dermal tissues. The larger cells are the xylem, the smaller cells are phloem and do not have the red staining, the phloem cells are between the fibres and the xylem and do not have the same cell wall chemistry as the xylem and fibre. The fibre cells are close to the dermal tissue, they are smaller than the xylem cell and have the red staining. Principle: in dicot and monocot stems or root, you can find the same types of tissues and cells. They have the same basic makeup. Anatomy of a Eudicot Root This looks very different from the eudicot stem. The dermal tissue – epidermis. In the centre of the root section, you will find cells larger and with particular cell chemistry reacting to stains. In the centre, you’ll find xylem cells and phloem cells and fibre cells. These vascular tissues are found in the middle of the root. The ground tissue contains the cortex and endodermis. The xylem tissue forms some sort of pole in the middle of the root, a large ground tissue outside the vascular tissue and underneath the dermal tissue. Zooming to the centre of the root section, the big cells with thickened cell wall compared to some other cells are the xylem cells. There is no nucleus. The xylem tissue forms a cross like appearance. Wherever you see a xylem tissue, you are likely to see a phloem cell close by. A single layer of cell that marks the boundary of the centre of the cell is called the endodermis. Well within the endodermis is a single layer of cell called the pericycle. The endodermis and endodermis form the boundary of the vascular tissues. Why is endodermis such as distinctive layer, cos all the surrounding cortical cells are large. Anatomy of a Monocot Root The monocot root has the dermal tissue known as the epidermis. The vascular tissue that is xylem is in the central part of the roots characterized by large cells. The ground tissue – cortical cells are large. wherever you see xylem cells, you are expected to find phloem cells nearby and they are usually smaller. Parenchyma Cell In the ground tissues, you will find the parenchyma cells. These cells make up the ground tissue. They ground tissue do not have any special cell wall chemistry, they are empty looking because of one big central vacuole filled with liquids. Depending on the cell we can find a nucleus. They are usually large, of different shapes and usually bigger than other cells in the root or stems. Epidermis The epidermal cells are tightly packed. They form a continuous layer of external protection. There is no airspace, there is no gaps. The epidermis of leaves is of interest to us because they are two types - the upper epidermis and the lower epidermis. The same principle of the epidermal cells applied in the leaves which is they are tightly packed and no gabs between them. Fibre Cells In the vascular bundles, you’ll find cells smaller than the xylem tissues that has the same cell chemistry as the xylem tissue as they get stained with same colour as the xylem. The fibre cells are closer to the dermal tissue while the xylem is closer to the pith. Meristematic Tissues Meristematic tissues localised in specific parts of the plant body. These tissues are found at the growing shoot tip and root tip of a plant. If you cut longitudinal sections, you’ll be able to see this shoot and root meristems. The cells tend to be small and do not have any vacuole or empty space. They are clustered together at a particular area at the growing point of the shoot or root. International Organization of Root Tip At the tip of the root, you find a shield or group of cells called the root cap. Their function is to protect the meristem. After the root cap cells, you will find cells at the quiescent centre where the root meristem is. These group of cells keep on producing new cells. In the centre of the root, you start to see cell different from the rest called provascular tissue which would later develop to xylem and phloem cells. Protoderm cells are cells that will later become the dermal tissue at the mature part of the root.