The Structure and Function of Plants Section 1: Levels of Organization in Plants

Levels of Organization in Plants What is a plant? Multicellular: A plant must consist of more than one cell. Eukaryotic: Plant cells must contain a nucleus. Photosynthesis: many plant cells have chloroplast, an organelle that converts sunlight into carbohydrates. Cell Walls: all plant cell have cell walls made of cellulose for support.

Levels of Organization in Plants Structure and Function: Plants have several structures that have evolved to make certain functions possible. "Structure determines function“ Examples: Structure: A cell is long, cylindrical and hollow. Function: Transports substances throughout the plant. Structure: A cell is packed full of chloroplasts. Function: Gathers sunlight for photosynthesis

Levels of Organization in Plants All multicellular organism have the same levels of organization: Cells: the basic unit of structure and function in living things. Tissue: A group of similar cells working together to perform a function. Organ: A group of tissues working together to perform a function. Plant Organs: Roots, Stems, Leaves

Structure of Function of Plant Tissues Each of the 3 organs of the plant (roots, stems and leaves) is made up of three main types of tissue. Dermal Tissue: “skin” of a plant the protective outer covering of a plant. Epidermis: the outermost single layer of cells

Structure of Function of Plant Tissues 2. Ground Tissue: Produce and stores sugars, and provides physical support for the plant. Made up of four different types of cells Parenchyma Structure: Large cells, thin cell walls, large vacuoles. Function: Storage (Stores sugar, starch, and water) b) Chlorenchyma Stucture: parenchyma cells packed with chloroplasts. Function: carryout photosynthesis

Structure of Function of Plant Tissues c) Collenchyma Structure: Have thick, but flexible cell walls. Function: Provides support Ex: Prevents plants from breaking in wind. d) Sclerenchyma Structure: Have extremely thick cell walls, cells are dead at maturity. Function: Provide support Forms seed coats and plants fibers

Structure of Function of Plant Tissues 3. Vascular Tissue: “bloodstream” of a plant circulating water and nutrients There is two types of vascular tissue: xylem and phloem Xylem – Conducts water from roots to the leaves. Phloem – Transports sugar and nutrients from the leaves to the rest of the plant. Cells are shaped like long hollow tubes that run continuously from the roots to the leafs.

Structure of Function of Plant Tissues How does vascular tissue transport water in the plant against the force of gravity? Three possible answers: Root pressure – pressure created from the water moving into the root. Does not exert enough force to lift water up into trees

Structure of Function of Plant Tissues 2. Capillary Action – waters ability to climb up thin tubes. The thinner the tube the higher the water climbs. Xylem cells are just really thin tubes. Even the thinnest tubes can only cause water to climb a few cm. 3. Transpiration – the loss of water through leaves Pulls the water through the plant. The strongest force in water transport.

Structure of Function of Plant Tissues How can water be pulled upward? Water molecules are polar – they have a positive and a negative end. Hydrogen bonds from between the positive and negative charges. Two properties of water Cohesion – attraction between molecules of the same substance Adhesion - attraction between molecules of different substances.

Structure of Function of Plant Tissues How can water be pulled upward? The water molecules are all connected like a chain (cohesion) The water molecules also connect to the sides of the xylem cells (adhesion) Water gets evaporated from the surface of the leave (Transpiration) The chain of water is pulled upward to replace the lost water.

Structure of Function of Plant Tissues Meristem Tissue: regions where cells are rapidly dividing to allow for plant growth. Cells are unspecialized: they all initially look alike Differentiation: Unspecialized cells mature into one of the 3 types of tissue: dermal, vascular or ground.

Structure of Function of Plant Tissues Meristem tissue causes 2 types of plant growth. Primary Growth: Adds length to the plant Apical mersitem: the tip of each stem or root where cells are dividing. What would happen if the stem apical meristem was damaged?

Structure of Function of Plant Tissues b) Secondary Growth: increases the thickness of the plant. Secondary growth takes place at the vascular cambium. Vascular cambium is a single ring of meristem cells. Cells produced inside the vascular cambium become xylem and cells outside become phloem.

Root Structure and Function 1. Root Functions: anchors the plant, absorbs nutrients and holds plant upright. Two types: Taproot – primary root grows long and thick while secondary roots remain small. Fibrous Roots –highly branched so that no root grows larger than the rest. Which root system represents a monocot and which represents a dicot?

Root Structure and Function Dermal Tissue in the Roots The roots covered with dermal tissue called root hairs. Roots hairs are microscopic extension of the outer cells They increase surface area of the root to absord bnutrients and water from the soil.

Root Structure and Function Root hairs have proteins that pump nutrients from the soil into the root. Diffusion: molecules “want” to move to an area of high concentration (the root) to low concentration (the soil). Active transport: using ATP to pump molecules from low concentration (the soil). to high concentration (the root) . What is ATP?

Root Structure and Function After nutrients are pumped into the root, water follows by osmosis. Osmosis is the movement of water molecules through a membrane from high concentration to low concentration. Does not require energy.

Root Structure and Function Gound Tissue in Roots Water and nutrients that enter the root hairs are stored in a layer of ground tissue. What type of ground tissue would you expect to find in a root?

Root Structure and Function Vascular Tissue in the Roots Vascular tissue is always located in the center of the roots. Xylem transports water up to the stem. Phloem transport nutrients to wherever they are needed in the plants. Xylem and Phloem are arranged differently in monocots and dicots. Monocot Dicot

Root Structure and Function Meristem Tissue in the Roots Apical Meristem – adds new cells to the end of the root. Root Cap – protects the apical meristem at it pushes through the soil. What would happen if the apical meristem was damaged.

Stem Structure and Function Stem Functions Produces leaves, branches, and flowers They hold leaves upright to the sunlight They transport substances between throughout the plant. What is the primary function of these stems?

Stem Structure and Function Dermal Tissue in the Stems Woody stems are covered with bark. Bark – all the tissue outside the vascular cambium Phloem: cells that transport sugars, produced outside the vascular cambium. Cork: outer layer of dead, water-proof cells. What is the function of the cork cells?

Stem Structure and Function Vascular Tissue in Stems Vascular tissue in the stems runs from the roots to the leaves carrying water and nutrients. In herbaceous stems vascular tissue is arranged differently in monocot and dicot plants. Dicot Monocot

Stem Structure and Function Vascular tissue in woody stems Xylem cells produced towards the center of the stem form wood Heartwood: older, inactive xylem cells; darker in color Sapwood: newer, active xylem cells, lighter in color Phloem cells are produced towards the outer edge of the stem and fall off as new cells are produced.

Stem Structure and Function Ground Tissue in Stems All types 4 types of ground tissues can be found in the stem depending on the function of the stem. Meristem Tissue in Stems Buds: underdeveloped meristem tissue that produces new stems or flowers. Most buds are protected by scales. Example: Brussel sprouts are enlarged buds

Leaf Structure and Function 3. Leaf Functions: carryout photosynthesis Designed to absorb sunlight Carryout gas exchange (absorb CO2 and release O2) What is the function of these leaves?

Leaf Structure and Function Dermal Tissue in the Leaf Cuticle: the waxy layer on the top surface of the leaf that prevent water loss. Stomata: small pores on the underside of the leaf that allows CO2 in and O2 out. Guard Cells: surround the stomata and control their opening and closing.

Leaf Structure and Function Water can also leave with through the stomata. Transpiration: the loss of water through leaves. The Problem If stomata are open plant loses water but can photosynthesize If stomata are closed the plant save water but cannot photosynthesize Solution: Plants keep the stomata open just long enough to allow photosynthesis but not so long that they lose too much water.

Leaf Structure and Function Vascular Tissue in the Leaf Xylem and phloem are bundled in veins. Monocot leave have parallel viens Dicot leaves have branching viens Ground Tissue in the Leaf Mesophyll is a layer of chlorenchyma cells. What is the function of chlorenchyma cells? Dicots have two layers of mesophyll: palisade and spongy. Monocots only have spongy.

Leaf Structure and Function Cuticle Epidermis Palisade Mesophyll Spongy Mesophyll Vein – Xylem and Phloem Stomata