Transport In Plants

• Plants need to be able to transport water, carbon dioxide, oxygen and minerals.
• Root hairs are found at the tip of roots. Root hairs have thin walls and occur in large numbers to increase surface area. They absorb water by osmosis.
• Water diffuses from the root hair into the ground tissue. It then diffuses from ground tissue into the xylem in the center of the root. Water moves up through the stem to leaves and flowers.
• As water enters a root by osmosis, the build up of water in the roots causes root pressure. This pushes water up through small plants.
• Transpiration is the loss of water vapour due to evaporation from the leaves of a plant. Transpiration takes place through the stomata. As each water molecule is pulled through the xylem cells by osmosis, the next water molecule is pulled also. Water is pulled through the plant by transpiration.
• A Cohesion Tension model allows large amounts of water to move quickly from roots to leaves in warm conditions. It can move 220 litres in one hour up through a plant.
• Using the Cohesion Tension Model, water evaporates from the xylem out through the stomata into the air. During transpiration, each water molecule is pulled through the xylem. Due to cohesion the next water molecule is pulled along. The tension between the water molecules allows it to be pulled up to 145 meters.
• Leaves control the rate of transpiration by having cuticles that do not allow water to pass through. Stomata are located on the lower surface of leaves to reduce water loss. Each stomata is surrounded by two guard cells.
• High temperatures, high wind, and high carbon dioxide concentrations are all environmental conditions affecting stomata.
• High levels of carbon dioxide causes stomata to close.
• Guard cells open and close the stoma by changing shape.
• Stomata allows for gas exchange to be carried out. Once inside the leaf, the CO2 diffuses from the air spaces into the mesophyll.
• Oxygen diffuses from the mesophyll into the air spaces and out through the stomata.
• Water vapour diffuses out from the leaf through the stomata.
• Lenticels are openings in the stems of plants that allow gas exchange. Oxygen diffuses inwards through the lenticel. CO2 and water vapour diffuse outwards.
• Minerals are absorbed from the soil by root hairs in a process called active transport. Root hairs have a lot of mitochondria to supply energy.
• Dicot plants can have large tap roots to store food E.g. carrots
• Potato plants produce an underground stem to store food. These are called tubers.
• Onions, daffodils and tulips all produce bulbs. A bulb is an underground stem that has swollen fleshy leaves to store food.