Plant Morphology (1).pdf

# Plant morphology, anatomy, and physiology This section delves into the fundamental structural and functional aspects of plants, focusing on meristematic tissues, their properties, and classifications, as well as key transport mechanisms within plants. ### 1.1 Plant morphology Plant morphology is the study of the form and external structure of plants [2](#page=2). ### 1.2 Plant anatomy Plant anatomy is concerned with the internal structure of plants . ### 1.3 Plant tissues Plant tissues are the fundamental building blocks of plant structure [49](#page=49). #### 1.3.1 Meristematic tissues Meristematic tissues, also known as growth tissues, are responsible for plant growth. They consist of actively dividing cells [56](#page=56). ##### 1.3.1.1 Properties of meristematic cells Meristematic cells are characterized by the following properties: * They are small and nearly spherical [52](#page=52). * They possess a dense cytoplasm and relatively few small vacuoles [52](#page=52). * Some cells, termed initials, maintain the meristem as a continuous source of new cells. These initials can undergo mitosis many times before differentiating into specific cell types [52](#page=52). ##### 1.3.1.2 Types of meristems based on origin Meristems can be classified based on their origin: 1. **Promeristem (Embryonic meristem):** This is the first meristem to form, originating from the zygote and found in the embryonic condition [53](#page=53). 2. **Primary meristem:** It originates from the promeristem and is responsible for primary growth, contributing to the formation of the primary plant body [53](#page=53). 3. **Secondary meristem (Lateral meristem):** This meristem arises from cells of the primary permanent tissues that regain their divisional capacity through dedifferentiation. It is typically found on the sides of the plant axis (root and stem) and is responsible for increasing girth [53](#page=53). ##### 1.3.1.3 Comparison of primary and secondary meristems | Feature | Primary meristem | Secondary meristem | | :----------------- | :--------------------------------------------------- | :----------------------------------------------------- | | Presence | Present from the beginning | Formed later during plant development | | Origin of cells | No dedifferentiation involved | Permanent cells transform via dedifferentiation | | Cell size/shape | Small and isodiametric | Elongated | | Vacuoles | Absent | Possess central vacuoles | | Function | Responsible for primary growth | Responsible for secondary growth | | [ ] | [ ] | [ ] | [54](#page=54). ##### 1.3.1.4 Types of meristems based on function Meristems are also classified by their ultimate function: * **Protoderm:** Forms the outermost protective layer, which is the epidermis of the stem or epiblema of the root [55](#page=55). * **Procambium:** Forms the primary vascular bundles, consisting of primary xylem and primary phloem [55](#page=55). * **Ground meristem:** Forms all other parts of the plant body not derived from the protoderm or procambium, including the cortex, endodermis, pericycle, and pith [55](#page=55). ##### 1.3.1.5 Apical and lateral meristems * **Apical meristem:** Occurs at the tips of stems, roots, and their branches. It is a primary meristem. Cell division in apical meristems occurs in various planes leading to growth in length [65](#page=65). * **Lateral meristem:** Found in a lateral position, parallel to the circumference of plant organs. It is a secondary meristem. Cells divide periclinally (in one plane) both on the outer and inner sides resulting in growth in girth and thickness. It gives rise to secondary tissues [65](#page=65). > **Tip:** Apical meristems are responsible for the elongation of plant parts, while lateral meristems contribute to thickening. ### 1.4 Plant transport Plant transport mechanisms are crucial for moving water, minerals, and organic substances throughout the plant [88](#page=88). #### 1.4.1 Ascent of sap The ascent of sap refers to the upward movement of water and dissolved minerals from the roots to the rest of the plant. This process is primarily explained by the **Transpiration pull-Cohesion-Adhesion Mechanism**, proposed by Dixon and Joly [90](#page=90). #### 1.4.2 Apoplastic and symplastic transport Plants utilize both apoplastic and symplastic pathways for the transport of ions and water. * **Apoplastic transport** involves movement through cell walls and intercellular spaces [97](#page=97). * **Symplastic transport** occurs through the cytoplasm of cells, connected by plasmodesmata [97](#page=97). > **Example:** The movement of ammonium ions into the root cylinder can occur via both apoplastic and symplastic routes [97](#page=97). #### 1.4.3 Primary meristems and tissue formation The cells derived from the apical meristem are organized into primary meristems: * **Protoderm:** Develops into the epidermis [52](#page=52). * **Ground meristem:** Forms the ground tissues, including parenchyma, collenchyma, and sclerenchyma cells [52](#page=52). * **Procambium:** Develops into the vascular tissues, xylem and phloem [52](#page=52). --- # Pollen analysis and palynology This topic explores the intricate structure of pollen grains and the scientific discipline of palynology, highlighting its crucial applications in forensic investigations. ### 2.1 Structure of pollen grains Pollen grains are microscopic structures with a complex wall composition and distinct diagnostic features that allow for identification. The pollen wall, known as the exine, is stratified and can possess up to three layers with varying chemical compositions . #### 2.1.1 Pollen wall layers The pollen wall consists of several layers : * **Intine:** The innermost layer, composed of cellulose, which does not survive typical chemical processing for pollen analysis . * **Endexine:** The layer adjacent to the intine. It can be internally laminated or patterned, and its presence may be detectable with light microscopy in some species. Detailed examination of the endexine requires transmission electron microscopy . * **Ectexine:** The outermost layer, containing sporopollenin, and observable under light microscopy. The ectexine is typically structured into three sub-layers : * **Foot layer:** The basal layer . * **Infratectum:** Composed of columns or grains that support the tectum . * **Tectum:** The relatively solid or perforated top layer. Its variability is significant for species differentiation and can either form the surface sculpture or support additional sculptural elements. In rare cases, the tectum may be absent . The variations in width and internal structure of these layers are key diagnostic features for distinguishing between closely related species . #### 2.1.2 Diagnostic features of pollen grains Several external features of pollen grains are used for identification : * **Shape:** Pollen grains exhibit diverse shapes, including spherical, triangular, elliptical, hexagonal, and pentagonal forms, along with variations thereof . * **Aperture type:** Most pollen grains possess one or more small openings, termed apertures, through which male gametes escape. Some pollen types lack apertures and rely on thin wall ruptures for gamete release. Apertures can range from simple pores or slits (colpi) to complex combinations . * **Sculpture:** This refers to the surface ornamentation or pattern of the pollen grain, which is consistent within a species. Sculpture patterns involve variations in surface depressions or protrusions. Common types include : * **Granulate:** Small, sand-like protrusions . * **Echinate:** Spines . * **Verrucate:** Hemispherical, wart-shaped bodies . * **Baculate:** Rod-like structures . * **Reticulate:** A lacelike network . > **Tip:** Understanding the variations in these features is crucial for accurate pollen identification, especially in forensic contexts where subtle differences can be significant . ### 2.2 Palynology Palynology is the study of resistant microscopic structures, including pollen and spores . #### 2.2.1 Forensic significance of palynology The value of forensic palynology stems from four key attributes of pollen and spores : * **Microscopic size:** Their small size allows for easy transfer and detection . * **Vast numbers:** Pollen and spores are produced in immense quantities, increasing the likelihood of their presence and detection . * **Taxonomic identification:** They can be identified to a specific plant taxon, linking individuals or objects to particular locations . * **Resistance to decay:** Pollen and spores are highly resistant to degradation, allowing them to persist over time . Pollen and spores typically range in size from 5 to 200 micrometers ($\mu$m) in diameter, with most falling within the 20 to 70 $\mu$m range . #### 2.2.2 Applications in forensic investigations Pollen analysis, a branch of palynology, offers significant benefits in forensic science : * **Corroborative and associative evidence:** While pollen analysis can contribute to convictions, its primary role is often to provide supporting or associative evidence in criminal cases . * **Investigative leads:** It can generate crucial investigative leads by indicating geographic locations or specific environments . * **Prompting confessions:** In some instances, the presentation of pollen evidence has led to suspects confessing to their crimes . * **Cost-effective evidence:** Palynology can provide law enforcement with simple and inexpensive evidence for case investigations . Pollen can reveal the recent history of a person or object by indicating the geographical regions, countries, or even specific areas within a garden that have been visited, due to the distinct pollen assemblages present in different locations. Furthermore, pollen evidence can help determine the season during which an object acquired the pollen . > **Example:** If a suspect's clothing is found to contain pollen unique to a specific park, this can be used as associative evidence to link them to that location. If the pollen identified is from a plant that only flowers in the spring, it can help establish the timeframe of an event . --- # Diatoms and their forensic significance Diatoms are microscopic, single-celled algae with unique silica cell walls that make them invaluable forensic evidence, particularly in drowning investigations. ### 3.1 Diatom overview Diatoms, classified under the division Chrysophyta (Protista) and phylum Stramenopila/Bacillariophyta (Algae), belong to the class Bacillariophyceae. They are typically small, silicified algae that can exist as individual cells or form filaments, chains, or colonies . #### 3.1.1 The frustule: Diatom cell wall The defining characteristic of diatoms is their cell wall, known as the frustule. The frustule is composed of two overlapping halves, the epitheca and hypotheca, which fit together like a soap case. This silica-based structure is highly intricate, featuring delicate patterns. The frustule is resistant to decay and does not readily break down during decomposition nor is it easily affected by enzymatic or acidic tests performed during postmortem examinations . #### 3.1.2 Habitat and distribution Diatoms are predominantly aquatic organisms, found in oceans, brackish water, and freshwater environments. They can also inhabit moist terrestrial locations. Their small size, widespread abundance, and ubiquitous distribution make them easily transferable into the body through aspiration or openings like nostrils, ears, and mouth . #### 3.1.3 Reproduction and other characteristics Diatoms reproduce primarily through asexual binary fission, though sexual reproduction also occurs. They are autotrophic, meaning they produce their own food. Diatoms are generally non-motile, but some species are capable of limited movement along a substrate via mucilaginous secretions through a slit-like groove called a raphe. They can exist as phytoplankton (in the water column) or as benthos (attached to substrata) . #### 3.1.4 Classification by symmetry Diatoms are broadly categorized into two orders based on their symmetry and valve shape : * **Centrales (now Biddulphiales):** These diatoms exhibit radial symmetry, with valve striae arranged around a central point, annulus, or areola. Round Centrales have radial markings . * **Pennales (Bacillariales):** These diatoms display bilateral symmetry, with valve striae arranged in relation to a line, often appearing as pinnate (feather-like) markings. Elongated Pennales are known for their gliding motion . > **Example:** Images of a Centrate diatom and a Pennate diatom are available on page 135 . ### 3.2 Forensic significance of diatoms Diatoms are considered "Golden Standards" in forensic science for solving drowning cases. Their presence, or absence, in a victim's body can provide crucial evidence regarding the circumstances of death . #### 3.2.1 Diatoms and drowning investigations Drowning occurs when a person is submerged in a fluid, leading to the ingress of water and its components into the body. Because diatoms do not naturally occur within the human body their detection in internal organs or tissues strongly suggests ante-mortem drowning in a water body containing these microorganisms. The types of diatoms found in a victim can also correlate with the physiochemical nature of the environment where the drowning occurred . > **Tip:** The resistance of diatom frustules to decomposition and postmortem tests makes them highly reliable indicators, even in cases of heavily decomposed bodies . #### 3.2.2 Applications in other forensic scenarios Beyond drowning, diatoms can serve as vital evidence in cases involving skeletonized or dismembered bodies, helping to reconstruct events and potentially solve crimes. Their unique siliceous structure and widespread distribution offer a distinct advantage in linking victims to specific aquatic environments . --- # Plant growth and development This section explores the fundamental biological processes that govern how plants grow and develop from a single cell into a mature organism. ### 4.1 Introduction to plant growth and development Plant growth is defined as an irreversible increase in size, which is usually measured by cell division and cell enlargement. Development encompasses all the changes that occur during a plant's life, from germination to senescence. These processes are intricately regulated by genetic factors and environmental cues, allowing plants to adapt to their surroundings and complete their life cycles . ### 4.2 Principles of plant growth Plant growth primarily occurs at specific regions called meristems, which contain actively dividing cells. These meristems can be apical, located at the tips of shoots and roots, or lateral, contributing to secondary growth in woody plants . * **Cell division:** The process by which a single cell divides into two or more daughter cells, increasing the number of cells in the plant . * **Cell expansion:** The enlargement of cells, driven by the uptake of water into the vacuole, which increases turgor pressure and stretches the cell wall. This is a critical component of irreversible growth in plants . > **Tip:** While cell division increases cell number, cell expansion is often responsible for the significant increase in plant size. ### 4.3 Plant development Development in plants involves a series of distinct stages, including germination, vegetative growth, reproductive growth, and senescence. These stages are orchestrated by hormones and environmental signals . * **Germination:** The process by which an embryo within a seed begins to grow and develop into a seedling, usually initiated by water, oxygen, and appropriate temperature . * **Vegetative growth:** The period of growth and development where the plant produces leaves, stems, and roots, focusing on increasing biomass . * **Reproductive growth:** The stage where the plant transitions to flowering and producing seeds or fruits, ensuring the continuation of the species . * **Senescence:** The programmed aging and eventual death of plant parts or the entire plant, often following reproduction . ### 4.4 Hormonal regulation of growth and development Plant hormones, also known as phytohormones, are chemical messengers that regulate virtually all aspects of plant growth and development. Key plant hormones include : * **Auxins:** Primarily involved in cell elongation, apical dominance, root formation, and tropisms (e.g., phototropism) . * **Gibberellins:** Promote stem elongation, seed germination, and flowering . * **Cytokinins:** Stimulate cell division and differentiation, and influence shoot growth and leaf senescence . * **Abscisic acid (ABA):** Involved in dormancy, stress responses (like drought tolerance), and seed maturation . * **Ethylene:** A gaseous hormone that promotes fruit ripening, senescence, and abscission (shedding of leaves and fruits) . ### 4.5 Environmental influences on growth and development Plants respond to a variety of environmental factors that significantly influence their growth and development. These include : * **Light:** Essential for photosynthesis and also acts as a signal for photomorphogenesis, influencing germination, flowering, and stem elongation . * **Water:** Crucial for cell turgor, photosynthesis, and nutrient transport; water availability directly impacts growth rates . * **Temperature:** Affects metabolic rates, enzyme activity, and can trigger developmental transitions like flowering and dormancy . * **Nutrients:** Essential elements required for cellular processes, hormone synthesis, and structural integrity . * **Gravity:** Plays a role in root and shoot orientation (gravitropism) . > **Example:** A plant bending towards a light source (phototropism) is a direct result of the hormone auxin accumulating on the shaded side, causing those cells to elongate more rapidly than cells on the illuminated side . --- ## Common mistakes to avoid - Review all topics thoroughly before exams - Pay attention to formulas and key definitions - Practice with examples provided in each section - Don't memorize without understanding the underlying concepts

| Term | Definition | |------|------------| | Meristem | A tissue in plants composed of actively dividing cells, responsible for plant growth and the formation of new tissues and organs. | | Mitosis | The process of cell division in eukaryotic cells, resulting in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of growth and repair. | | Differentiation | The process by which a less specialized cell becomes a more specialized cell type, occurring multiple times during the development of a multicellular organism as the organism changes from a simple embryonic form into complex specialized systems and tissues. | | Epidermis | The outermost layer of cells in plants, providing a protective covering for the body of the plant and playing a role in gas exchange and water regulation. | | Vascular tissues | The tissues in plants that conduct water and nutrients throughout the plant body. These include xylem and phloem. | | Xylem | The vascular tissue in plants that conducts water and dissolved nutrients upward from the root and also helps to support the plant. | | Phloem | The vascular tissue in plants that conducts sugars and other metabolic products downward from the leaves to where they are needed. | | Promeristem | The earliest and most undifferentiated meristematic tissue, originating from the zygote and responsible for initiating new growth. | | Primary meristem | Meristematic tissues that arise from the promeristem and are responsible for the primary growth (increase in length) of the plant. | | Secondary meristem | Meristematic tissues that arise from dedifferentiated cells of permanent tissues and are responsible for secondary growth (increase in girth) in plants. | | Dedifferentiation | The process by which a specialized cell reverts to a less specialized, meristematic state, enabling it to divide and form new tissues. | | Apical meristem | Meristems located at the tips of roots and shoots, responsible for the primary growth in length of the plant. | | Lateral meristem | Meristems located along the sides of roots and shoots, responsible for secondary growth, increasing the plant's girth. | | Protoderm | The outermost primary meristem, which develops into the epidermis. | | Procambium | A primary meristem that develops into the primary vascular tissues, xylem and phloem. | | Ground meristem | A primary meristem that gives rise to the ground tissues of the plant, including parenchyma, collenchyma, and sclerenchyma. | | Palynology | The scientific study of pollen and spores, including their composition, dispersal, and significance in various fields like paleontology, archaeology, and forensics. | | Pollen grain | The microscopic male gametophyte of seed plants, typically a powdery or sticky substance containing the male reproductive cells. | | Exine | The tough outer layer of the pollen wall, composed of sporopollenin, which is highly resistant to degradation. | | Sporopollenin | A complex biopolymer that forms the primary component of the exine of pollen and spores, providing exceptional resistance to environmental degradation. | | Aperture | A small opening or pore on the surface of a pollen grain, through which the pollen tube grows during germination. | | Diatom | A single-celled alga belonging to the class Bacillariophyceae, characterized by a unique cell wall composed of silica called a frustule. | | Frustule | The rigid, silica-based cell wall of a diatom, composed of two overlapping valves, which persists after the cell's death. | | Raphe | A slit-like groove or channel on the valve of some diatoms, through which mucilage is secreted to enable movement. | | Benthic | Relating to or occurring at the bottom of a body of water, such as a lake or ocean. | | Phytoplankton | Microscopic, photosynthetic organisms that drift in bodies of water, forming the base of aquatic food webs. | | Limnology | The scientific study of the biological, chemical, and physical characteristics of inland waters, such as lakes, ponds, and rivers. |