Transport of Food and Minerals in Plants PDF

# Chapter 1: Transport of Food and Minerals in Plants ## Warm Up Anjana asks Priya, "How do plants eat and drink?" ## Learning Objectives * Introduction * Transport in Single-celled and Basic Multicellular Plants * Transportation in Higher Plants (Conduction) * Structure and Roles of Xylem and...

# Chapter 1: Transport of Food and Minerals in Plants ## Warm Up Anjana asks Priya, "How do plants eat and drink?" ## Learning Objectives * Introduction * Transport in Single-celled and Basic Multicellular Plants * Transportation in Higher Plants (Conduction) * Structure and Roles of Xylem and Phloem * Osmosis * Transpiration * Root Pressure * Understanding Active Transport * Essential Minerals in Plants ## Introduction All organisms rely on essential substances like food, water and oxygen to stay alive. Plants need sunlight, water, and carbon dioxide for photosynthesis. These materials must be transported throughout the plant. In addition, waste products must be removed. This is handled by a transport mechanism that differs from organism to organism. **The Movement of Subtances** Transport refers to the movement of individuals or items from one location to another. In biology, when we refer to transport, we mean the movement of food, water, and minerals throughout the plant. ## Transport in Single-celled and Basic Multicellular Plants Diffusion plays a key role in material transportation in unicellular organisms like *Chlamydomonas* and basic multicellular plants like *Spirogyra*. Diffusion is characterized by the movement of molecules from an area of higher concentration to an area of lower concentration until they are evenly distributed. ## Transportation in Higher Plants (Conduction) In multicellular advanced plants, the transport mechanism is more sophisticated. Simple diffusion cannot meet the transportation needs of these plants. Higher plants possess specialized tubes, namely xylem and phloem, which form vascular or conducting tissues. - Water and minerals move upwards from the roots to the different sections of the plant through the stem via the xylem. - The food material produced in the leaves travels in a soluble form through the phloem to the entire plant body. ## Structure and Roles of Xylem and Phloem ### Xylem * **Characteristics:** Xylem is multifaceted. It has parenchyma cells (living cells with thin walls) and sclerenchymatous cells (dead cells with thick walls). * **Tracheids** are elongated, non-living cells that taper. They have walls thickened with lignin, except for some areas called pits. * **Vessels** resemble cylindrical tubes stacked end-to-end. Their end walls can dissolve, either partially or wholly, creating a continuous channel. These non-living cells also have lignified walls. * **Roles:** * Xylem primarily directs water and minerals from roots throughout the plant. * Both tracheids and xylem fibers help with structural reinforcement. * Xylem parenchyma aids in the accumulation of starch and other compounds. ### Phloem * **Characteristics:** Phloem is intricate, made up of both parenchyma cells and sclerenchymatous cells. * **Presence:** Phloem is located throughout the plant. * **Roles:** * The primary role of the phloem is to transport food substances from leaves to different plant parts and storage structures. * Phloem parenchyma assists in organic matter storage. * Phloem fibers give structural support to the plant. ## Water Conduction by Roots Roots play a dual role: * Securing the plant in the soil. * Drawing in water and nutrients from the soil. Root hairs are tiny, single-celled projections found near the tip of the root. These are the primary sites of water and nutrient uptake, which occurs through a mechanism termed **osmosis**. ## Osmosis Osmosis refers to the movement of water molecules from a region of higher concentration to one of lower concentration through a selective barrier known as a semipermeable membrane. It is a specific form of diffusion that solely involves water molecules ($Fig. 1.8$). * When two solutions are separated by a semipermeable membrane, water molecules can freely move through its tiny openings. However, larger solute molecules are restricted because they are too large to pass through this selective barrier. * A **semipermeable membrane** (or partially permeable membrane) is a thin barrier with small pores. It selectively allows certain substances to move across while blocking others. Typically, it permits the flow of solvent molecules but prevents larger solute molecules from crossing (e.g. the plasma membrane of a cell, egg membranes, and cellophane paper). * **Ascent of Sap:** Water is absorbed into plant cells through **osmosis**. * Plant cell membranes serve as **selective barriers:** only allowing certain molecules to pass. * The liquid within a cell's **vacuole**, known as **cell sap**, is rich in solutes. * Because the soil has a higher water concentration relative to root hair cells, water enters these cells through osmosis. * As water accumulates, the concentration of the sap inside the vacuole becomes diluted. * Consequently, water continues to move from one cell to its neighboring cell through osmosis. * This movement continues until the water reaches the plant's xylem. Once there, it travels upward from cell to cell, defying gravity, propelled by **transpiration**. ## Transpiration Transpiration is the process where plants release water vapor from their leaves into the atmosphere ($Fig. 1.11$). * As leaves release water, more is drawn up from the plant's xylem, creating a continuous flow from the roots to the tips. This upward water movement is driven by what's known as the **"transpiration pull."** * Plants take in more water through their roots than they need for functions like growth and photosynthesis. The excess water is released into the environment via transpiration, primarily through **leaf pores called stomata**. * Though only a fraction of the absorbed water is utilized for photosynthesis and maintaining the plant's structure, transpiration plays an important role in cooling the plant and protecting it from excessive sunlight. This not only cools the plant but also moderates the immediate environment. ## Root Pressure Root pressure describes the force that pushes water from a plant's root cells into the xylem, creating a pressure build up ($Fig. 1.12$). This pressure plays a role in moving water through the plant, especially up the stem and into the leaves. ## Understanding Active Transport Active transport is a process where molecules move against their concentration gradient across a membrane, requiring energy ($Fig. 1.13$). One example in plants is the absorption of minerals by root hairs. Even though the soil has a lower concentration of minerals than the root hair cells, these minerals are still absorbed into the cells with the help of energy. In contrast, water's passive absorption from the soil happens due to the pull of transpiration, where roots are merely absorbing without expending energy. Passive transport doesn't use energy. ## Essential Minerals in Plants Plants source minerals from the atmosphere, water and primarily the soil. When plants and animals decompose, they return these minerals to the soil. While plants contain many elements, only specific ones are vital for their health, termed as **essential elements**. * In total, 16 such elements are recognized. Based on their requirement, these elements are divided into two categories: * **Macronutrients:** Needed in significant amounts. Examples include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, sulphur, calcium, magnesium, and iron. * **Micronutrients:** Needed in minimal amounts, often referred to as trace elements. Some examples are chlorine, copper, and boron. * Minerals are crucial for plant growth. * They offer vital nourishment to plants. * Without minerals, plants cannot fully undergo either their growth or reproductive stages. * A lack of certain minerals can cause disorders in plants that can be remedied only by providing the missing mineral. ## New Words: * **Diffusion:** The movement of molecules from high to low concentration. * **Xylem:** The vascular tissue for water and mineral transport. * **Phloem:** The vascular tissue for food substance transport. * **Osmosis:** The movement of water across a semipermeable membrane. * **Transpiration:** The release of water vapor from plant leaves. * **Root Pressure:** The force pushing water into the xylem. * **Active Transport:** The movement against a concentration gradient, requiring energy. * **Macronutrients:** The elements needed in significant amounts for plants. * **Micronutrients:** The elements needed in small quantities for plants.