Plant Tissues – PST05210 Basic Pharmacognosy
NTA Level 5 • Semester 2 • PST05210 Plant Tissues Basic Pharmacognosy • Source Session/Topic 3 Full source-text version: all educational wording from the extracted learning source is retained; only presenter/tutor metadata and web-layout noise are removed, while formatting is improved for readability. Session 3: Plant Tissues Total Session Time: 120 minutes Prerequisites • None Learning Tasks By the end of this session students are expected to be able to: • Define Tissue • Classify Plant Tissues • Explain Properties of the Plant Tissues Resources Needed: • Flip charts, marker pens, and masking tape • Black/white board and chalk/whiteboard markers • LDC projector and laptop SESSION OVERVIEW |Step |Time |Activity/ |Content | | | |Method | | |1 |05 minutes |Presentation |Introduction, Learning Tasks | |2 |30 minutes |Presentation |Plant Tissues and their | | | |Brainstorming |Classification | |3 |75 minutes |Presentation |Properties of the Plant Tissues | |4 |05 minutes |Presentation |Key Points | |5 |05 minutes |Presentation |Evaluation | SESSION CONTENTS STEP 1: Presentation of Session Title and Learning Tasks (5 minutes) READ or ASK students to read the learning objectives and clarify ASK students if they have any questions before continuing. STEP 2: Plant Tissues and Their Classification (30 minutes) |Activity: Brainstorming (5 minutes) | | | |Ask students to brainstorm on the following question: | | | |Define a plant tissue | | | |ALLOW few students to respond? | | | |WRITE their responses on the flip chart/ board | | | |CLARIFY and SUMMARISE by using the content below | • A plant tissue may be defined as a group of cells, which are similar in origin, form and function or as a group of dissimilar cells that perform a common function. E.g. phloem elements conduct food • The simple type of plant body is unicellular, in such form; the single cell performs all the vital functions of life. It grows, prepares food, undergoes metabolism, reproduces and completes its span of life • In higher plants, root, stem, leaves and flowers carry out different functions. Due such division of labour, the cells of the plant are differentiated to form different tissues. The different tissues perform different functions • Tissues can be classified into main two types: o Meristematic tissue and o Permanent tissue Scheme below Shows Classification of Plant Tissues Plant Tissue Meristematic Permanent (Mature cells incapable of division) (Cells are capable of division) Simple Complex (Single type of cells) (More than one type of cells) Parenchyma Collenchyma Sclerenchyma Xylem Phloem Xylem vessel Sieve tube Tracheids Companion Cells • Meristematic Tissue (Cells are capable of division) o A meristematic tissue (meristos = divisible) is a group of identical cells that are in a continuous state of division o Some cells produced by meristematic tissue stop dividing and acquire certain changes (differentiation) to become permanent tissues of the plant • Based on location on the plant, the meristem is divided into three types: o Apical meristem ▪ Found at the tips of roots, stem and branches ▪ Functions to increase length of these parts ▪ Divided into three zones • Protoderm – form epidermal tissue • Procambium – form primary vascular tissues • Ground meristem – form cortex and pith o Intercalary meristem o Found in the nodal region, prominently in monocotyledons, e.g. grasses. o It is derived from the apical meristem o Elongates the internodes o Lateral meristem o Found along the longitudinal axis of stem and root o E.g. Vascular cambium and cork cambium (phellogen) o Produces secondary permanent tissues o Increase thickness of stem and root • Permanent Tissue (Mature cells incapable of division) o Are tissues that have temporarily or permanently lost the power to divide o The cells formed by the apical meristem are differentiated into different types of permanent tissues • Based on the constituent cells, the permanent tissue is classified into two types: – o Simple tissue ▪ Tissues made up of cells with similar structure and function ▪ Classified into; • Parenchyma, • Collenchyma and • Sclerenchyma o Complex tissue ▪ A tissue made up of several kinds of cells but all of them function together as a single unit ▪ Classified into; • Xylem tissue o Xylem (Greek word ‘xylos’= wood) o Xylem is made up of four kinds of cells ▪ Tracheids ▪ Vessels or tracheae, ▪ Xylem fibres and ▪ Xylem parenchyma • Phloem tissues o Phloem is composed of four types of cells: ▪ Sieve elements, ▪ Companion cells, ▪ Phloem parenchyma and ▪ Phloem fibres • Companion cells are present only in angiosperms STEP 3: Properties of Plant Tissues (75 minutes) • Characteristics of Meristematic Tissues o May be round, oval, polygonal or rectangular in shape o Are closely arranged without intercellular spaces o Have dense cytoplasm with large nuclei. o Have smaller vacuoles, scattered throughout the cytoplasm. o Their cell walls are thin, elastic and made up of cellulose • Characteristics of Parenchyma Tissues o Generally present in all plant organs o Form the ground tissue in a plant o Is living tissue made of thin walled cells o Is the precursor of all the other tissues o The cell wall is made up of cellulose o Parenchyma cells may be oval, spherical, rectangular, cylindrical or stellate o Parenchyma is of different types o In green parts of the plants, the parenchymatous cells have chloroplasts; they are called chlorenchyma. Its important function is photosynthesis • Characteristics of Collenchyma Tissues o Is a living tissues generally occurring in the dicot stems in two or more layers below the epidermis, these layers form the hypodermis o It also occurs in petiole and pedicel o The cell wall is unevenly thickened, thickening is confined to the corners of the cells o Collenchyma strengthen young organs • Characteristics of Sclerenchyma Tissues o Is a dead tissue; lacks protoplasts o The cells are very thick i.e. have lignified secondary walls (woody) o Sclereids ▪ Sclereids re shorter, fibers are longer ▪ Sclereids have numerous