Comprehensive Study Guide to Flowering Plant Anatomy and Physiology

Cotyledons and Classification of Flowering Plants

A cotyledon is defined as a seed specialised leaf intended for food storage. Flowering plants are categorized into two primary groups based on these structures: monocots and dicots. Monocots possess one seed leaf, while dicots possess two seed leafs. These groups can be further distinguished by their physical characteristics. Monocots exhibit parallell leaf veins and scattered vascular bundles throughout the stem. In contrast, dicots feature net leaf veins and vascular bundles arranged in a ring. Additionally, dicots typically possess a tap root system, with a carrot being a primary example of this root type.

Root Function and Longitudinal Structure

The root system of a plant serves two primary functions: to anchor the plant and to absorb minerals and water. In a longitudal view of a root, several layers and zones are visible. The outermost layer is the epidermis (dermal tissue), which contains root hairs for absorption. Internally, the root contains the cortex (ground tissue) and the vascular bundle, which consists of xylem and phloem. The xylem is specifically referred to as xylem vasculr tissue.

The development of the root is divided into four functional segments. The bottom-most part is the root cap, which provides protection as the root grows. Above this is the meristem, the site of cell production. Following the production zone is the zone of elongation, where cells increase in size. Finally, there is the zone of differentiation, where cells specialize into their specific functions. Ground tissue and the cotyledor storage areas are also critical components of the early plant structure.

Flower Anatomy and Reproductive Processes

The flower is the organ responsible for sexual reproduction, which involve gametes. The male part of the flower is the stamen, which produces pollen (the male gamete). The stamen is composed of the anther and the filament. The female part of the flower is the carpel, which produces the egg (the female gamete). The carpel consists of the stigmala (also referred to as stigma), the style, and the ovary. Pollination is defined as the transfer of pollen from the anther to the stigma. Flowering plants are categorized by their reproductive strategies into insect pollinated flowers and wind pollinated flowers, which differ in the positioning and structure of their anthers, filaments, stigmas, styles, and ovaries.

Leaf Function, Structure, and Anatomy

The primary function of the leaf is photosynthesis. To support this, leaves are typically thin with a large surface area to maximize light absorption. Additional functions include gas exchange, transpiration, food storage, waste removal, and vegetative propagation, which is a form of asexual reproduction. Within the leaf veins, xylem vessels deliver water for the process of photosynthesis, while phloem transports the produced food elsewhere in the plant. Stomata are tiny pores on the leaf surface that facilitate gas exchange and transpiration.

The internal anatomy of the leaf is highly specialized. The top layer is covered by a wary cuticle, followed by the upper epidermis. Below this is the palisade mesophyll cell layer, which is densely packed with chloroplasts for photosynthesis. Underneath the palisade layer is the spongy mesophyll cells, which are separated by air spaces to allow for gas movement. The bottom of the leaf consists of the low epidermis, which contains guard cells that regulate the opening and closing of the stomata. Vascular tissue is embedded within these layers, and ground tissue provides the structural matrix of the leaf.

Dermal, Vascular, and Ground Tissues

Dermal tissue covers the plant like a skin. It is usually one cell thick, known as the epidermis, but can form a thicker layer known as cork. This tissue is composed of dermal tissue cells, guard cells, and trichomes. Its main function is to protect the cell. A waxy cuticle may be present on the surface to prevent water loss, while specialized dermal structures like root hairs absorb water and minerals.

Vascular tissue is responsible for transport throughout the plant via vascular bundles. Xylem is a dead tissue that transports water and minerals. It is composed of two main structures: tracheids and vessels. Tracheids have tapered ends and contain lignen and pits, while vessels also contain lignen and pits. Phloem is a living tissue (due to the presence of companion cells) that transports food. Translocation is the specific term for the movement of food from one part of the plant to another. Phloem contains sieve tube elemnt, sieve plates, companion cells with a nucleus, and sieve tubes containing cytoplasm.

Stem Structure, Meristems, and Tissue Arrangement

The stem supports the aerial parts of the plant and facilitates transport, moving water from roots to leaves and food from leaves to roots. If the stem is green, it can also perform photosynthesis. The stem anatomy includes the node (the point on the stem where a leaf is attached), the internode (the space between two nodes), and buds, which are the sites of new leaf, stem, or flower growth. Lenticles are specialized pores on the surface of the stem used for gas exchange.

Ground tissue, or cortex, is found between the dermal and vascular tissue in both stems and roots. It is responsible for photosynthesis, supporting the plant, and water storage. Meristematic tissue is found at the tips of the roots and shoots and is responsible for growth. These cells are very small and unspecialised, essentially acting as stem cells that later become dermal, vascular, or ground tissue as the plant grows. The arrangement of vascular bundles in the stem varies by type: in a dicot stem, the vascular tissue is arranged in a ring, whereas in a monocot stem, the vascular bundles are scattered throughout the ground tissue.