تشريح النبات: المحاضرة الثالثة

Study Notes

Plant Anatomy Course: This is the third lecture.
Plant Cell Structure: The plant cell is composed of living (protoplast) and non-living components.
Protoplast: The living content of the plant cell including vacuoles, cell sap, starch granules, nucleus, nuclear membrane, cell structures (aleurone, plastids), oils, fats, crystals, nucleolus, nucleoplasm, Golgi bodies, pigments and other organic substances, ribosomes, and other organelles.
Non-Protoplast Components: Non-living components include the cell wall, cytoplasm and plasma membranes.
Cell Wall: Primarily composed of cellulose and other materials.

Vacuole Description: Mature plant cells contain one or more large vacuoles. They are filled with an aqueous solution (cell sap) and enclosed by a semi-permeable membrane (inner plasma membrane). The cell sap is about 98% water and includes dissolved or colloidal substances like proteins, carbohydrates, organic acids, pigments, and other materials.
Vacuole Formation: Vacuoles begin as small droplets in meristematic cells, gradually enlarging and filling with cell sap as the cell matures. The increasing vacuole compresses the cytoplasm, pushing it towards the cell wall, forming a thin layer that lines the mature cell wall.

Carbohydrates: These can be dissolved in the cell sap or non-dissolved. Examples of dissolved carbohydrates include glucose, fructose (monosaccharides), and sucrose (disaccharides). Inulin is a polysaccharide found in some plant cell saps. Other, less common sugars in some plants include dextrins, mannitol, and pentosans. Starch granules are important storage polysaccharides.
Starch Granules: Microscopic structures formed from several layers with varying densities, surrounding a central point called the hilum. The hilum is noticeable in the starch of potatoes, wheat, and legumes, and less distinct in other types.
Concentric and Eccentric Hilum: Starch granules can have a hilum at the centre (concentric), or offset from the centre (eccentric).
Simple and Compound Granules: Starch granules can have one hilum (simple) or more (compound), and compound granules are made from multiple smaller granules with or without shared outer layers.
Semi-Compound Granules: These granules have a more complex structure, with multiple granules enclosed by a shared starch layer. They are often seen in potato tubers.
Starch Granule Shape: The shape of starch granules varies depending on the plant species, can be round as in potatoes, or elongated with tangential fissures as in beans, or branched as in maize.

Proteins: Proteins are present in cell sap, especially in oil-rich seeds. They convert into aleurone grains as the seed dries and matures.
Aleurone Grains: Microscopic structures encircled by a membrane, containing a mixture of non-crystalline protein and crystalline protein bodies (crystalloids).
Crystalloids: Larger, polygonal protein bodies.
Globoids: Smaller, spherical bodies comprising proteins and phosphorus.

Organic Acids: These are dissolved in the cell sap, and result from metabolic processes. Examples include citric, malic, and tartaric acid.
Calcium Oxalate Crystals: Insoluble calcium oxalate crystals have different forms (solitary, star-shaped druses, or needle-shaped raphides), in various plant parts.
Calcium Carbonate: These crystals, like cystoliths, are seen in the tissues of certain plants. Their formation involves a stalk of cellulose that extends from the apex of the cell. These can be detected using dilute hydrochloric acid which dissolves the structure and liberates carbon dioxide.

Anthocyanins: These pigments are dissolved in the cell sap, giving colours to petals and other parts.
Glycosides: These complex organic compounds yield glucose and/or ring-shaped organic compounds upon hydrolysis.
Mucilage: Some plants have a viscous cell sap that contains mucilage.
Tannins: These are complex compounds which are considered a source of energy for metabolic processes. Some believe tannins protect from insects and fungi.
Alkaloids: These are cyclic compounds containing nitrogen and are found in various plant species, often with medicinal uses.
Latex: A milky fluid composed of resins, gums, and carbohydrates created by certain plants