Transport in plants

• Plants have branching shapes. This gives them a large surface area in relation to their volume.
• Plants absorb water through their roots and this water must be transported up to the leaves. This transportation system is called the xylem.
• Plants have a second transport system called the phloem. Phloem transports sucrose and amino acids from the leaves to the other parts of the plant.
• A xylem vessel is like a long pipe. It is made of many hollow, dead cells that are joined end to end.
• The ends of the walls in the xylem are open.
• Xylem vessels run from the roots of the plant up to the stem, before branching out into every leaf.
• Xylem vessels help to keep the plant upright because their walls are very strong.
• Phloem tubes are made form many cells joined end to end.
• A group of xylem vessels and phloem tubes is called a vascular bundle.
• Vascular bundles are found in the leaves, roots, and shoots of a plant.
• Vascular bundles help to support the plant.
• The root is covered in a layer of epidermis.
• Root hairs do not live for very long, so as they grow they are replaced with new ones.
• Root hairs are tiny but there is a large number of them, meaning that they have a large surface area which increases the rate at which they can absorb water and ions.
• Water moves into a root hair through osmosis.
• Root hairs are at the end of the root and the xylem vessels are in the center. Before the water cab be taken to the rest of the plant, it must go through the xylem vessels.
• Water travels by osmosis through the cortex, from cell to cell. Some of the water also seeps between the spaces of the cells or through the cell walls. Eventually it reaches the xylem vessels in the middle of the root.
• Once the water reaches the xylem vessels, it moves up the xylem due to the pressure.
• Transpiration: the loss of water vapor from plant leaves by evaporation of water at the surface of the mesophyll cells followed by diffusion of water vapor through the stomata.
• The mesophyll cells in the leaf are covered with a thin film of moisture.
• When the film of moisture on the mesophyll cells evaporates, the water vapor diffuses out of the cell through the stomata.
• The many air spaces inside the leaf increases the rate of evaporation, causing more water to be drawn up the xylem vessels and speeding up the flow of water.
• The stomata allows water vapor to diffuse easily out of the cell when open. This reduces the water potential inside the leaf which make more water evaporate from the surfaces of the mesophyll cells.
• The faster a plant transpires, the faster it will take up water.
• Transpiration increases as temperature increases.
• Transpiration decreases as humidity increases.
• Some of the organic food material that the plant makes is transported through the phloem tubes. It is carried from the leaves to whichever part of the plant needs it.
• The part from which the organic materials are being translocated from is called the source. The part from which the organic materials are being translocated to are the sink.