Flowering Plant Structure: Cells and Tissues

• Flowering plants, also known as angiosperms, exhibit a complex internal structure crucial for their survival and reproduction
• This structure is primarily composed of cells, tissues, and organ systems working together to perform various functions

Plant Cells

• Plant cells are the fundamental building blocks of plant tissues and organs
• They are eukaryotic cells with distinct features, including a cell wall, chloroplasts, and a central vacuole
• The cell wall, composed mainly of cellulose, provides structural support and protection to the cell
• Chloroplasts are the sites of photosynthesis, where light energy is converted into chemical energy in the form of glucose
• The central vacuole stores water, nutrients, and waste products, maintaining cell turgor pressure and regulating cell size
• Plant cells differentiate into various specialized cell types, each with specific functions, such as parenchyma, collenchyma, sclerenchyma, xylem, and phloem cells

Plant Tissues

• Plant tissues are groups of similar cells performing a specific function
• Plants have four main tissue types: epidermal, ground, vascular, and meristematic tissue
• Epidermal tissue forms the outer protective layer of the plant, covering the leaves, stems, and roots
• It protects the plant from water loss, mechanical damage, and pathogen invasion
• Ground tissue makes up the bulk of the plant and performs various functions include photosynthesis, storage, and support
• Parenchyma, collenchyma, and sclerenchyma are the main types of ground tissue cells
• Vascular tissue is responsible for transporting water, minerals, and sugars throughout the plant
• Xylem transports water and minerals from the roots to the rest of the plant, while phloem transports sugars from the leaves to other parts of the plant
• Meristematic tissue is composed of undifferentiated cells that can divide and differentiate into other tissue types
• Apical meristems are found at the tips of roots and shoots and are responsible for primary growth, increasing the length of the plant
• Lateral meristems, such as the vascular cambium and cork cambium, are responsible for secondary growth, increasing the thickness of the plant

Plant Organs

• Plant organs are structures composed of different tissues working together to perform specific functions
• The main plant organs are roots, stems, leaves, flowers, fruits, and seeds

Roots

• Roots anchor the plant in the soil and absorb water and nutrients from the soil
• They also store food and water
• The root system consists of a main root and lateral roots branching off from it
• The root tip is protected by a root cap, which helps the root penetrate the soil
• Root hairs, extensions of epidermal cells, increase the surface area for water and nutrient absorption

Stems

• Stems support the leaves, flowers, and fruits and transport water and nutrients between the roots and the leaves
• Stems contain vascular bundles, which consist of xylem and phloem tissues arranged in a specific pattern
• The arrangement of vascular bundles varies depending on the type of plant
• Stems may also have specialized structures such as nodes, internodes, buds, and lenticels
• Nodes are the points where leaves attach to the stem
• Internodes are the regions between nodes
• Buds are undeveloped shoots that can develop into new leaves, stems, or flowers
• Lenticels are pores in the stem that allow gas exchange

Leaves

• Leaves are the primary sites of photosynthesis in plants
• They are responsible for capturing sunlight and converting it into chemical energy
• Leaves have a flattened blade called the lamina and a stalk called the petiole
• The lamina contains veins, which are vascular bundles that transport water and nutrients and provide support
• The epidermis of the leaf is covered by a waxy cuticle, which prevents water loss
• Stomata are pores in the epidermis that allow gas exchange

Flowers

• Flowers are the reproductive structures of angiosperms
• They are responsible for producing seeds
• A flower consists of four main parts: sepals, petals, stamens, and carpels
• Sepals are the outermost parts of the flower, protecting the developing bud
• Petals are usually brightly colored and attract pollinators
• Stamens are the male reproductive organs, consisting of a filament and an anther, which produces pollen grains
• Carpels are the female reproductive organs, consisting of an ovary, style, and stigma
• The ovary contains ovules, which develop into seeds after fertilization

Fruits

• Fruits develop from the ovary after fertilization
• They protect the seeds and aid in their dispersal
• Fruits can be classified as simple, aggregate, or multiple, depending on their origin
• Simple fruits develop from a single ovary
• Aggregate fruits develop from multiple ovaries in a single flower
• Multiple fruits develop from the ovaries of multiple flowers

Seeds

• Seeds are the mature ovules that contain the embryo and stored food
• They are responsible for propagating the plant
• Seeds have three main parts: the embryo, the endosperm, and the seed coat
• The embryo is the young plant that will develop into a new plant
• The endosperm is the stored food that nourishes the embryo
• The seed coat is the outer protective layer of the seed

Vascular System

• The vascular system in plants is like the circulatory system in animals
• It is responsible for transporting water, minerals, and sugars throughout the plant
• The vascular system consists of two main types of vascular tissue: xylem and phloem
• Xylem transports water and minerals from the roots to the rest of the plant
• Xylem cells are dead at maturity and form long, hollow tubes
• Phloem transports sugars from the leaves to other parts of the plant
• Phloem cells are living at maturity but lack a nucleus and other organelles
• They are connected by sieve plates, which allow the flow of sugars between cells

Plant Nutrition

• Plants require a variety of nutrients for growth and development
• These nutrients are obtained from the soil through the roots
• The essential nutrients for plants are divided into macronutrients and micronutrients
• Macronutrients are required in large amounts, while micronutrients are required in small amounts
• The macronutrients include nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur
• The micronutrients include iron, manganese, zinc, copper, boron, molybdenum, and chlorine
• Plants also require water for photosynthesis, transpiration, and other processes

Plant Hormones

• Plant hormones are chemical messengers that regulate plant growth and development
• They are produced in small amounts and transported to other parts of the plant where they elicit a response
• The main types of plant hormones are auxins, gibberellins, cytokinins, abscisic acid, and ethylene
• Auxins promote cell elongation, apical dominance, and root formation
• Gibberellins promote stem elongation, seed germination, and flowering
• Cytokinins promote cell division, lateral bud growth, and leaf expansion
• Abscisic acid promotes dormancy, inhibits growth, and closes stomata during water stress
• Ethylene promotes fruit ripening, leaf abscission, and senescence

Plant Responses to the Environment

• Plants are constantly responding to changes in their environment
• These responses can be short-term or long-term
• Short-term responses include changes in gene expression, enzyme activity, and hormone levels
• Long-term responses include changes in growth, development, and reproduction
• Plants respond to a variety of environmental stimuli, including light, gravity, temperature, water, and touch
• Phototropism is the growth of a plant towards or away from light
• Gravitropism is the growth of a plant in response to gravity
• Thigmotropism is the growth of a plant in response to touch
• Plants also have defense mechanisms to protect themselves from herbivores and pathogens
• These defense mechanisms include physical barriers such as thorns and spines, as well as chemical defenses such as toxins and repellents

Explore the internal structure of flowering plants (angiosperms), focusing on the roles of cells, tissues, and organ systems. Learn about cell walls, chloroplasts, and vacuoles within plant cells. Discover specialized cell types like parenchyma, collenchyma, and xylem.