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Plant Structure and Function The Fascinating World of Plant Structure With added feature: Plant Function See it today! Now in Technicolor. Root Structure and Function • There are two types of root systems: – Taproot - one root grows much larger than the other roots with many small roots growing from it. • These roots usually grow deep into the soil to get water and nutrients. – Fibrous roots - a dense network of many thin string-like roots. • These roots spread out to absorb water and nutrients that are close to the surface. Root Structure and Function • Root Growth – The first root to grow from a seed is called the primary root. – As it grows downward other roots grow from it, called secondary roots. – Both types of roots have root hairs, which increase the surface area of the root. – The root tip is covered with a root cap which protects it as the meristem tissue grows. • The root cap also lubricates the root so it can move through the soil easier. Root Structure and Function • Parts of a Root: (From the outside/in) – Epidermis - Outer layer • The root hairs grow out of this layer. – Cortex - This layer stores food and water. – Vascular tissue - This is made up of xylem and phloem. • Xylem carries water and minerals from the soil to the leaves. • Phloem carries food from the leaves to other parts of the plant, including the roots. Root Structure and Function • Specialized Roots – Aerial root - Absorbs water from the air. – Prop root - This supports the stem and leaves of the plant. Aerial Roots Prop Roots Stem Structure and Function • Stems are made up of the same four tissues that make up the roots. – Epidermis – Cortex – Vascular Tissue - Xylem and Phloem • A layer that is different from the roots is the pith -a layer of cells in the center of the stem that store water. Stem Structure and Function • The stems are of two types: – Herbaceous - soft, green and filed with water. • Most of these plants live only a few weeks, a year at the most. • They do not grow very tall, usually 2 meters (6.5 feet) tall at the most. • They have the Xylem and Phloem in vascular bundles. – In Dicots the bundles are arranged in a ring. – In Monocots the bundles are scattered in the cortex. – The Xylem is always on the inside, Phloem to the outside. Stem Structure and Function – Woody Stem - These are usually non-green, thicker and harder than herbaceous stems. • These plants grow tall. • The parts of this stem are (from outside/inward) – Cork (Bark) - Dead layer of cells that protects the plant from disease, bacteria, and fungi. – Cortex (Bark) - Stores food and water. – Phloem (Bark) - Carries food from the leaves to the roots and other parts of the plant. – Cambium - This is meristem tissue, this part grows. » Outer part forms new phloem cells. » Inner part forms new xylem cells. – Xylem - Carries water and nutrients to the leaves. – Pith - Dead xylem cells, forms the wood of the tree. Stem Structure and Function • Stem Growth – The xylem goes through two growth periods a year: • Spring - Large xylem cells produced. • Summer - Small xylem cells produced. • Together they form the annual rings. – These show the age of the tree. – Stems grow in lengths from buds: • Terminal Bud - at the tip of the branch. • Lateral Bud - forms new leaves, branches and flowers. Leaf Structure and Function • Most leaves are broad and flat, which is called the blade of the leaf. • The blade is attached to the stem by a stalk called the petiole. – Some plants do not have a petiole, because their leaves are directly attached to the stem. – In most leaves the petiole becomes the main vein of the leaf. • The veins of the leaf carry the food, water, and nutrients. • The veins are made of vascular tissue. Leaf Structure and Function • Plants have either a simple leaf or a compound leaf. – Simple - this has one blade and one petiole. – Compound - this has a blade divided into smaller parts, leaflets. Leaf Structure and Function • Leaf Layers (Top of leaf to bottom of leaf) – The leaf has an upper epidermis covered by a thin waxy layer, the cuticle, that protects the leaf from drying out and from insects and disease. – Below the upper epidermis is a layer of cells called the palisade layer: • This is made up of parenchyma cells that contain chlorophyll. • Most of the photosynthesis takes place here. • The veins run through this layer. Leaf Structure and Function – The next layer is the spongy layer. • This layer contains many air spaces. • Gas is exchanged in this area. – The next layer is the lower epidermis. • This layer contains small openings called stomatas (the singular of “stomatas” is stomata). • The small openings regulate the exchange of gases. • Two bean-shaped cells, guard cells, surround and control the size of the stomata. – When the guard cells swell, the stomata opens. – When the guard cells shrink, the stomata closes. Leaf Structure and Function • Plants lose water through the stomata in their leaves in a process called transpiration. • Specialized leaves – Needles – Spines of a cactus decrease the surface area of the leaf to prevent water lose. – Vines have tendrils to help them attach to objects. – Carnivorous plants have special leaves to trap insects or other organisms. Cactus Spines Tendrils Carnivorous Plant Venus Fly Trap Pitcher Plant Flower Structure and Function • Parts of a flowers: – The green leaf-like structures that surround and protect the petals are called sepals. – The petals surround the male and female reproductive organs. • The petals of some plants are used to attract pollinators. – The male reproductive organ is called the stamen, a thin stalk that contains the anther, where pollen is produced. • The sperm cells are contained inside the pollen grains. Flower Structure and Function – The female reproductive organ is called the pistil. • Several stamens usually surround the pistil. • The bottom of the pistil is called the ovary, which contains ovules, where the eggs are produced. • Pollination – The transfer of pollen grains from the stamen to a pistil. • Self-pollination - pollen from the same plant is transferred to the pistil. • Cross-pollination - when the pollen from another plant is transferred to the pistil. Flower Structure and Function • After pollination the pollen grain develops a pollen tube. – The tube grow the entire length of the pistil. – The sperm cell then travels down the tube to the ovary. • When the sperm cell comes in contact with the egg’s cell fertilization occurs. – The embryo plant then begins to develop. – As the embryo grows the ovary gets larger. Seeds and Fruits • A fertilized ovule is called a seed. – The seed contains an embryo plant and stored food for the embryo. • The seed that is formed remains inside the ovary and we call this the fruit. – All fruits contain seeds. Seeds and Fruits • Seed Dispersal: – Some plants have fruits that are light and shaped for travel by air (wind). • Maple Tree, Ash Tree, or Elm tree - wing-like structures • Dandelion and Milkweed - cotton-like structures Seeds and Fruits – Some plants have fleshy fruits and animals disperse them. • Berries - animals eat them and the seeds are dispersed in the animals waste. Seeds and Fruits – Some plants have fruits that float on water. • Milkweed - air-filled pod • Coconut Seeds and Fruits – Some plants have hook-like fruits that stick to the fur of animals. • Burdock • Smooth beggartick or Smooth bur marigold (boogie lice) Seeds and Fruits • Seed Germination – The growth of an embryo plant from a seed is called germination. – The two main requirements for germination are warmth and moisture. Plant Growth and Responses • The basic growth requirements for all plants are: – Light • To carry out photosynthesis. • Not all plants require the same amount of light. • The amount of sunlight a plant receives determines the time that it will flower. – Summer flowering plants are long-day plants, they need at least 12 hours of light a day. – Fall flowering plants are short-day plants, they need less than 12 hours of light a day. – If the plant flowers anytime they are day-neutral plants, amount of light is not a requirement. Plant Growth and Responses – Water • Not all plants need the same amount of water. • Too much water kills a cactus. • Too little water kills a fern. – Minerals • The main minerals that plants need to survive are: – Nitrogen (Nitrates) – Phosphorous (Phosphates) – Potassium • These minerals are found in fertilizers. Plant Growth and Responses – Proper Temperature • The seeds will not germinate until the soil is warm. • Most plants grow best in temperatures between 10oC and 38oC (50oF and 100oF). • Growth Hormones – Any organic chemical that makes an organism grow is a growth hormone. – Growth hormones are located in the root tips, lateral buds, and terminal buds of the plants. • Most plants are taller than they are wide because the terminal bud makes hormones that prevent the lateral bud from growing too fast. Plant Growth and Responses • Tropism – The response to a stimulus is called tropism. • Phototropism - Growth towards light. • Geotropism - Stems grow up and roots grow down. • Thigmotropism - Response to touch, like tendrils growing around an object.