Transport in Plants.docx

**[Organisation and the Vascular Structures]** **[Plants]** [Structure of flowering plant] (1) [Seeds]*\ *Most flowering plants arise from a seed which consists of an embryo surrounded by a testa (seed coat). The embryo consists of one or two cotyledons (seed leaves), a plumule, a radicle, and s...

**[Organisation and the Vascular Structures]** **[Plants]** [Structure of flowering plant] (1) [Seeds]*\ *Most flowering plants arise from a seed which consists of an embryo surrounded by a testa (seed coat). The embryo consists of one or two cotyledons (seed leaves), a plumule, a radicle, and sometimes an endosperm.\ If seeds have a healthy supply of water, oxygen, and a suitable temperature, they will germinate. [Roots\ ]*Structure\ *- If the radical persists, it will give rise to a tap root whose branches will form lateral roots. Tap roots are normally large obvious, e.g., carrots and parsnips.\ - If the radical does not persist, adventitious fibrous roots arise from the base of the young stem e.g., grass.\ - Adventitious roots are roots that develop from any part of the plant that is not derived from the radicle e.g., Ivy. *Root Growth\ *- The apical meristem, near the tip of the root, divide by mitosis. The cells produced at the front of the meristem produce a structure called the root cap. This becomes slimy and lubricates the passage of the root through the soil. It protects the apical meristem of the root from abrasion.\ - The cells formed at the rear of the apical meristem acquire vacuoles and elongate, pushing the tip of the root forwards. This is called the zone of elongation.\ - Once fully elongates, the cells on the outside of the root produce root hairs. These have a large surface area to absorb water and minerals.\ - Cells near the core of the root differentiate into vascular tissue, xylem and phloem. This is called the zone of differentiation.\ - The cells mature in the zone of maturation.\ A diagram of a structure Description automatically generated(2) *Functions of the Root\ *- Anchorage: The root anchors the plant in the ground, preventing it from being blown over or washed away.\ - Uptake of minerals: Roots absorb water and minerals from the soil.\ - Food storage: Any excess food produced by the leaves is transported to the roots through the phloem to be stored for later use. This process is called translocation. Food can be stored in the form of sugars or starch. The stored food can be used at night when the plant is no longer photosynthesising. It can also be used so that they can grow quickly in the spring. Parsnips use this type of storage.\ - Vegetative propagation: Roots can be used to produce new plants that are identical to the parent plant. [Stem\ ]*Structure\ *The stem is a cylinder that rises vertically from the ground. Most stems are solid, but a few are hollow. Some stems also twine around other plant stems. Leaves arise from various points on the stem called nodes. The length of stem between successive leaves is called the internode. Buds are miniature compressed stems and are found at various places on the stem. There are two types of buds;\ - Terminal buds: Often called apical buds, found at the ends of stems and are responsible for elongation. Sometimes they are directed by hormones to form flowers instead of new stems.\ - Axillary buds: Found in the axils of leaves. The axil is the angle between the petiole and the stem. Axillary buds are usually dormant. They can grow into side stems or branches when they are far enough away from the terminal bud, or if the terminal bud is removed. *Functions of the Stem\ *- Support: The stems hold the leaves and flowers in place so that they can carry out their functions efficiently\ - Transport: The stem transports water and minerals upwards in a tissue called xylem. Transports food and other materials up and down the stem in a tissue called phloem\ - Food storage: Some plants store food in their stems e.g., potato\ - Vegetative reproduction: In strawberries, some stems grow across the surface of the ground. These are called runners and form new plants where a bud touches the ground [Leaf\ ]*Structure\ *- Most leaves consist of a stalk called the petiole, and a flattened blade-like portion called the lamina. The veins of the leaf are raised areas, usually on the underside, caused by the vascular bundles.\ - In monocots, these run parallel to each other. In dicots, they are branched.\ - In many leaves there is a larger vein running up the centre called the midrib.\ - The angle formed between the petiole and the stem is called the axil. The bud on this is called the axillary bud. *Function of the Leaf\ *- Photosynthesis: The primary function of leaves. Most leaves have a large surface area to capture the maximum amount of light.\ - Food storage: Some plants, such as cabbage and onion, store food.\ - Excretion: The waste products of metabolism are stored in the leaves, and then discarded when the leaves fall. [Flowers\ ]*Structure and Function\ *- Flowers are the organ of sexual reproduction. Large, brightly coloured, and scented flowers attract pollinators. Small and dull flowers are pollinated by the wind. [Plant Tissue Types] [Dermal Tissue\ ]- Protective outer covering of the plant.\ - In older plants, can have a layer of cork that acts as an insulating and protective layer. Called the epidermis in young plants.\ - Pores in the epidermis of leaves called stomata allow for gaseous exchange and transpiration.\ - The stem of woody plants have pores for gaseous exchange called lenticels. [Ground Tissue\ ]Ground tissue has a variety of functions including:\ - Photosynthesis: In leaves, ground tissue form the cells of the spongy mesophyll layer and palisade mesophyll. These cells contain chloroplasts and his is where most photosynthesis occurs\ - Storage: In stems and roots, ground tissue is used for storage of food and water. In stems, it forms the endosperm\ - Protection: Ground tissue fills space and provides protection\ - Support: In non-woody plants, ground tissue contributes to rigidity when it is turgid [Vascular Tissue\ ]Vascular tissues are complex and are composed of several types of cells. Two of these are Xylem and Phloem. [Xylem\ ]*Structure -- Xylem Vessels\ *- Found in angiosperms\ - Narrow so that capillary action is at a maximum\ - Heavily lignified and therefore dead when mature\ - Lignin gives them strength to withstand the negative tension of water transport\ *Structure -- Tracheids\ *- When mature, are thickened with a polymer called lignin, which is both waterproof and strong. These are described as lignified.\ - Lignified cells are dead and contain no cell contents\ - Have tapered ends and are perforated to allow the easy movement of water and dissolved minerals from one cell to the next\ - Pits contain no lignin, pits allow the lateral movement of water within the stem *Function of Xylem\ *- Xylem transports water and dissolved minerals up the stem\ - Lignin supports the plant by holding up the plant against the pull of gravity [Phloem\ ]*Structure -- Sieve Tube Cells\ *- Have no nucleus, ribosomes, cytoskeleton, and no large vacuoles. The lack or organelles makes transport through them easier.\ - Sieve tube cells end in perforated sieve plates, and these can transport dissolved substances in either direction.\ *Structure -- Companion Cells\ *- Have a nucleus and control the adjoining sieve tube element through special pores called the plasmodesmata.\ - Companion cells pump sugar into the phloem in leaves *Function of Phloem\ *- Transport of food and hormones (auxins) to all plant cells from the leaves\ - Companion cells controls the activities of the sieve tubes [Meristematic Tissue\ ]The areas of the plant where there is rapid cell division by mitosis to produce new tissue in the form of unspecified cells. There are two types of meristematic tissue. [Apical Meristems\ ]- Responsible for growth in length of stems, shoots, and roots\ - Found at the tips of shoots in the apical bud and in axillary buds\ - In roots, they are found immediately behind the root cap in the zone of division [Lateral Meristems\ ]- Responsible for growth in width of stem. They are known as cambium and there are three different types:\ - Vascular Cambium\ - Inter-fascicular Cambium\ - Cork Cambium [Differences between Monocotyledons and Dicotyledons] A monocot is a plant whose seed contains one seed leaf e.g., daffodils. A dicot is a plant whose seed contains two seed leaves e.g., geraniums. Monocot Dicot -------------------------------------------------------------------------------- ----------------------------------------------------------------------------- Have strap-shaped leaves Leaves ae broader than they are long and are irregular in shape The veins in the leaf run parallel to the sides Veins are spread out in different directions and are branches When flowers are present, they usually have floral parts in multiples of three Floral parts in multiples of four or five Most are herbaceous Both herbaceous and woody species Vascular bundles are scattered throughout the stem Vascular bundles are arranged in a ring around the outer region of the stem [Mandatory Practical -- Prepare and examine microscopically the transverse section of a dicotyledonous stem] \- Collect a herbaceous stem\ - Trap the stem between two pieces of carrot to hold it steady\ - Wet the stem to lubricate the movement of the backed blade and make it easier to slice without damaging the structure of the stem\ - Using a backed blade, cut away from yourself for safety\ - Cut the sections as thinly as possible\ - Place the thinly cut slices in water to keep the cells turgid\ - Lift the thinnest sections you can find with a paintbrush\ - Place the section on a clean slide and add a drop of iodine stain\ - Lower a coverslip onto the section at an angle to prevent air bubbles\ - Turn on the microscope light\ - Examine the slide at low power, focusing with the coarse focus knob\ - Examine at high power, focusing with the fine focus knob\ - Draw what you see.