Flowering Plants

“Angiosperms, sometimes known as flowering plants, are a large class of plants that develop flowers to facilitate sexual reproduction. They have distinguishing characteristics, including producing seeds inside fruits and having reproductive organs inside flowers. “

Parts of Flowering Plants

The name list of parts of Flowering Plants is as follows;

• Roots
• Stem
• Leaves
• Flowers
• Petals
• Sepals
• Stamen
• Pistil
• Ovules
• Fruit

To understand the Structure and Function of Flowering plants we will discuss Leaf, Stem, and Roots in detail.

Plant Leaf

• The leaf is attached to the stem by a leaf stalk, which continues into the leaf as a midrib.
• The midrib is the central vein that runs along the center of a leaf. Branching from the midrib is a network of veins that deliver water and salts to the leaf cells and carry away the food made by them. As well as carrying food and water, the network of veins forms a kind of skeleton that supports the softer tissues of the leaf blade.
• The leaf blade (or lamina) is broad and has a vertical section through a small part of a leaf blade.

The Layers of Leaf are as follows:

Cuticle

The outer surface of leaves and other plant parts like stems and fruits are covered in a waxy covering called the cuticle. Its primary purpose is to shield the plant from numerous biotic and abiotic challenges, including UV radiation, water loss, and UV rays. It is made up of a complex mixture of cutin and waxes.

• Cutin and waxes are the two main constituents of the cuticle. Cutin is a polymer comprised of glycerol and fatty acids, whereas waxes are made up of long-chain aliphatic chemicals.
• As these cells mature, a continuous cuticle layer is produced because they bleed wax and cutin onto their outer surface.
• The cuticle’s main job is to keep the plant’s water from evaporating. Its wax is hydrophobic, so it prevents plants from being dehydrated. The cuticle also protects against UV rays, viruses, and herbivores.
• The cuticle’s thickness varies depending on the plant’s species and the environment it grows. While plants in moist areas may have thinner cuticles to promote greater gas exchange, arid climates often have thicker cuticles to avoid water loss.
• Several plants have developed unique cuticle adaptations to help them survive in harsh settings. For instance, some desert plants have a thick, multilayered cuticle that helps keep water from evaporating, while others have specific wax crystals that reflect sunlight and help the plant stay cool.

Epidermis

The epidermis (as shown in Fig 1.2) is a single layer of cells on the upper and lower surfaces of the leaf. The epidermis helps to keep the leaf’s shape. The closely fitting cells reduce evaporation from the leaf and prevent bacteria and fungi from getting in. There is a thin waxy layer called the cuticle over the epidermis, which helps to reduce water loss.

Stomata

Stomata (singular form: stoma) are structures found in the leaf epidermis. A stoma comprises two guard cells surrounding an opening, also known as a stomatal hole. The guard cells’ turgor and morphology can change, causing the stomatal hole to open or close. Stomata only appear in the lower epidermis of the majority of dicotyledons. The stomata are evenly distributed on both sides of the leaf in monocotyledons, narrow-leaved plants like grasses.

• Generally, stomata are open during daylight hours but closed during the evening, and most of the night, they allow carbon dioxide to diffuse into the leaf, where it is used for photosynthesis.
• The carbon dioxide supply to the leaf cells is virtually cut off if the stomata close and photosynthesis ceases. But, many species close their stomata when it’s dark, and there isn’t any photosynthesis.
• The cell wall adjacent to the stomatal pore is thicker and less flexible than other cell parts. So, even though the guard cell, which contains chloroplast, attempts to expand because, to the increased turgor, the thick inner wall cannot. The stomatal pore between the guard cells is opened due to the guard cells curving as a result.

Mesophyll

Mesophyll refers to the tissue that lies between the upper and lower epidermis. It comprises two zones: the bottom, spongy mesophyll, and the upper palisade mesophyll. Palisade cells often have a lengthy shape and a large number of chloroplasts. The form and fit of the permeable mesophyll cells vary, and there are numerous air holes between them.

• Making food through photosynthesis is the job of the palisade cells and, to a lesser extent, the spongy mesophyll cells. To create sugar molecules, their chloroplasts connect carbon dioxide and water molecules using the energy they get from the sun.
• The mesophyll cells use carbon dioxide during daylight when photosynthesis is quick. As a result, the amount of carbon dioxide in the air gaps decreases, and more carbon dioxide diffuses in through the stomata from the outside air.
• The diffusion of carbon dioxide continues through the air gaps to the cells. Moreover, as a consequence of photosynthesis, these cells create oxygen. Oxygen diffuses via the stomata as the air spaces’ oxygen concentration rises.

Palisade Mesophyll

The palisade mesophyll (as shown in Fig 1.4) is a layer of elongated, tightly packed cells found in the leaves of plants. It is located beneath the upper epidermis and above the spongy mesophyll. It is responsible for the Photosynthesis occurring in leaves because it contains Chloroplast. The arrangement of the cells in the palisade mesophyll allows for efficient light absorption and carbon dioxide exchange.

Veins or Vascular Bundles

The veins transport the water to the mesophyll cells, where it is used to produce sugar through photosynthesis. Because the concentration of free water molecules in a leaf cell, which contains sugars, will be lower than the concentration of water in the water vessels of a vein, the mesophyll cells take in the water by osmosis. When leaf veins extend out, every cell is close to a water source. The phloem cells of the veins receive the sugars produced in the mesophyll cells, and they then transport the sugars out of the leaf and into the stem.

Plant Stem

The stem is part of a plant that connects the roots to the leaves and maintains the plant. It is in charge of moving glucose, nutrients, and water between the leaves and the roots. The xylem, phloem, cambium, and epidermis are only a few tissues found in the stem. Several plant species have stems that might be cylindric, flattened, or thorny in shape, size, or texture. Specific plant stems are significant in flowering and fruit production, among other aspects of sexual reproduction.

The parts of the Plant Stem are as follows:

Epidermis

Like the leaf epidermis, this is a single layer of cells that helps keep the shape of the stem and cuts down the loss of water vapor. Stomata in the epidermis allow the tissues inside to take up oxygen and eliminate carbon dioxide. In woody stems, the epidermis is replaced by bark, consisting of many dead cells.

Vascular Bundles

Vascular bundles comprise groups of specialized cells that conduct water, dissolved salts, and food up or down the stem. The vascular bundles in the roots, stem, leaf stalks, and leaf veins all connect to form a transport system throughout the entire plant. The two primary tissues in the vascular bundles are called the xylem and phloem. Food substances travel in the phloem; water and salts travel mainly in the xylem. The cells in each tissue form elongated tubes called vessels (in the xylem) or sieve tubes (in the phloem), surrounded and supported by other cells.

The components of Vascular Bundles are as follows:

Xylem definition

“A plant tissue called the Xylem carries water and minerals from the roots to the vegetative portion of the Plant. It consists of specialized cells grouped in tubes that run the length of the Plant. Transpiration is the process by which water moves through the Xylem to all parts of the Plant.”

• It comprises specialized cells, such as tracheids and vessel components, that are arranged in a network of tubes that run the length of the plant.
• Water can be transported effectively through the xylem because the cells are dead at maturity and have no cytoplasm or other organelles.
• Lignin is a complex polymer that the plant uses to strengthen and support the xylem cell walls.
• Turgor pressure, which is essential for plant growth and development, is another function of the xylem.
• According to the type of plant and its surroundings, the xylem has a distinct structure with various adaptations for various environments.
• The roots, stem, and leaves of vascular plants commonly contain xylem.

Vessels

The cells in the xylem which carry water become vessels. A vessel comprises a series of long cells joined end to end. Once a region of the plant has ceased growing, the end walls of these cells are digested away to form a continuous, fine tube. At the same time, the cell walls are thickened and impregnated with a substance called lignin, which makes the cell wall very strong and non-permeable. Since these lignified cell walls prevent the free passage of water and nutrients, the cytoplasm dies. This does not affect the path of water in the vessels. Xylem also contains many elongated, lignified supporting cells called fibers.

Phloem

“A plant tissue called the Phloem is responsible for moving nutrients, especially carbohydrates, from the leaves to the rest of the plant. It is composed of specialized cells, such as companion cells and sieve tube components.“

• Sugars, amino acids, and other nutrients are transported from the leaves to the rest of the plant by a tissue called phloem.
• It comprises specialized cells, such as companion cells and sieve tube components, that are placed in a network of tubes that run the length of the plant.
• Phloem contains mature living cells connected by pores known as sieve plates that permit the passage of nutrients.
• Instead of transpiration, like in the xylem, pressure gradients and active transport move nutrients through the phloem.
• Companion cells provide sieve tube components with metabolic support, assisting in maintaining the flow of nutrients.
• Depending on the type of plant, phloem has different structural characteristics.

Sieve Tubes

The conducting cells in the phloem remain alive and form sieve tubes. Like vessels, they are formed by vertical columns of cells. Perforations appear in the end walls, allowing substances to pass from cell to cell, but the cell walls are not lignified, and the cell contents do not die, although they do lose their nuclei. The perforated end walls are called sieve plates.

Cortex and Pith

The cortex is the tissue between the vascular bundles and the epidermis. Its cells frequently contain starch. Chloroplasts are found in the outer cortical cells of green stems, which use photosynthesis to produce food.

The pith is the term for the stem’s interior tissue. Similar to how several blown-up balloons packed firmly into a plastic bag would create a rather stiff structure, the cells of the pith and cortex serve as packing tissues and aid in supporting the branch.

Plant Roots

In contrast to the stem, where the vascular bundles form a cylinder in the cortex, the vascular bundle is located in the core of the root. From the root to the stem, the Xylem transports minerals and water. The phloem transports food from the stem to the root.

The basic components of Plant Roots are as follows:

Root Cap

The root cap (as shown in Fig 1.7) is a structure found at the tip of a plant’s root. It comprises specialized cells that protect the growing tip of the root. The root cap helps the root penetrate the soil by secreting a lubricating substance. It also senses gravity and helps to orient the root in the direction of growth. The root cap cells are constantly replaced as the soil wears them away. The Root Cap comprises numerous layers of cells at the tip of the root. When the root tip is forced through the soil, these cells are continuously replenished at the same rate they are worn away.

Root Hairs

“Little, hair-like structures called “root hairs” are seen on the roots of plants. They expand the root’s surface area and facilitate water and nutrient uptake from the soil.“

In a region above the root tip, where the root has just stopped growing, the outer layer cells produce tiny, tube-like outgrowths called root hairs. These can just be seen as a soft layer on the roots of seedlings grown in moist air. The root hairs grow between the soil particles and stick closely to them in the soil. The root hairs take water from the soil by osmosis and absorb mineral salts (as ions) by active transport.

The large number of tiny root hairs significantly increases the absorbing surface of a root system. The surface area of the root system of a mature rye plant has been estimated at 200 m². The other surface provided by the root hairs was calculated to be 400 m². Root hairs remain alive for only a short time. The root region just below a root hair zone produces new roots, while the root hairs at the top of the area are shriveling. Above the root hair zone, the cell walls of the outer layer become less permeable. This means that water cannot get in so quickly.

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