Transcript Transport
The plant gets it food from the light energy. The plants do not get it food from the soil. The leaves of plant make food by photosynthesis. During photosynthesis, plants use light energy, carbon dioxide and water to make food. The food produced is in the form of sugar. A gas called oxygen is given out in the process of photosynthesis. SUNLIGHT CARBON DIOXIDE + WATER GLUCOSE + OXYGEN CHLOROPHYLL Most leaves are green because they contain a green pigment, called chlorophyll, which able to trap sunlight. The plant uses the light energy trapped by the chlorophyll to make food. The water which plants need to make food is absorbed by the roots of the plants from the surroundings. Chlorophyll Bubbles can be seen on underside surfaces of the leaves. On a leaf surface, there are many tiny openings, called stomata( singular: stoma) which allow gases to enter or leave. More stomata are found on the underside of a leaf. That is why you see air bubbles coming out from the underside of the leaf when you soak in warm water. Carbon dioxide from the air enters the leaf through the stomata. The carbon dioxide is used for photosynthesis. Oxygen produced during photosynthesis and not used by the plant leaves through the stomata. Plants lose water in the form of water vapors to the surrounding through these tiny openings too. Close Stomata Open Stomata For plants to maintain themselves, they need regular supply of various things. Therefore, plants need a TRANSPORT SYSTEM. Xylem and Phloem are two separate sets of tubes for transporting materials around the plant. They are independent of each other and are found in every part of the plant. However, they are usually found close together. A group of xylem vessels and phloem tubes is called a VASCULAR BUNDLE. Xylem Vessels - Xylem helps to support plants and take up water: Xylem vessels are like a long drainpipe. Xylem Vessel They are made from dead hollow cells, joined end to end without any end walls between them, forming a long open tubes. Xylem vessels run from the roots of a plant, right up through the stem and spread out into every leaf. They carry water and minerals from the root up to the leaves. This is known as TRANSPIRATION STREAM. Xylem vessels contain no cytoplasm or nuclei. Side walls of Xylem vessels are strong and firm containing lignin, which gives the plant support and keeps it upright. Wood is made almost entirely of lignified xylem vessels. Phloem Tubes - carry food materials which the plant has made and needs: Phloem contain sieve-tube elements. Phloem Tube Sieve tube elements have no nucleus, but contain cytoplasm. They do not have any lignin in their cell walls. Made from living cells, joined end to end, with punctured end-plates so that materials can flow through. Each sieve tube element has a companion cell next to it. Companion cell has many organelles, except the nucleus. It is thought that companion cells help the sieve tube elements with some of their requirements. Phloem tubes carry food made in the leaves to all other parts of the plant, in either direction. The growing part of the plant, in the root tips and shoot tips, receives regular supply of sugars, fats, proteins etc. by the phloem tubes to/from storage organs in the roots. In summary, Phloem carries food to/from the roots for growth and storage from other parts of the plants. Xylem transports water and minerals from the roots up to the leaves. Xylem and Phloem vessels are used to carry different things around the plant.