Chapter 8 - Transport in plants Flashcards
What are xylem vessels?
Xylem vessels transport water and minerals from the root to the stem and leaves and provide support to the plant. They have thick walls with lignin, strengthening the tubes, which helps to support the plant. They have dead cells with no cell contents allowing free passage of water and the cells are joined end to end with no cross walls to form a long, continuous tube.
What are phloem vessels?
Phloem vessels transport sucrose and amino acids made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem.
Where is the xylem and phloem vessels found?
These vessels are arranged throughout the root, stem and leaves in groups called vascular bundles.
How are root hair cells adapted to water uptake in plants?
Root hair cells are single celled extensions of epidermis cells in the root. They grow between soil particles and absorb water and minerals form the soil. Water enters the root hair cells by osmosis. This happens because soil water has a higher water potential than the cytoplasm of the root hair cell. The root hair cell increase the surface area of the cells significantly. This large surface area is important as it increases the rate of absorption of water by osmosis and mineral ions by active transport.
What is the path of water from the soil into the plant?
Osmosis causes water to pass into the root hair cells, through the root cortex, into the xylem and up to the mesophyll cells.
What is transpiration?
Transpiration is the loss of water vapour from leaves. Water evaporates from the surfaces of the mesophyll cells into the air spaces and then diffuses out of the leaves through the stomata as water vapour.
Why is transpiration beneficial to plants?
Transpiration transports mineral ions, provides water to keep cells turgid, provides water to leaf cells for photosynthesis and keeps the leaves cool.
How does transpiration occur?
Water molecules are attracted to each other by cohesion, creating a continuous column of water up the plant. Water moves through the xylem vessels in a continuous transpiration stream from roots to leaves via the stem. Transpiration produces a tension or pull on the water in the xylem vessels by the leaves. As water molecules are held together by cohesive forces, the water is pulled up through the plant as if the rate of transpiration from the leaves increases, water molecules are pulled up the xylem vessels quicker.
How does wilting occur?
Wilting occurs if more water evaporates from the leaves of a plant than is available in the soil to move into the root by osmosis. This is when all the cells of the plant are not full of water, so the strength of the cell walls cannot support the plant and it starts to collapse.
What is translocation?
Translocation is the movement of sucrose and amino acids in the phloem from sources to sinks.
What are sources?
Sources are parts of the plant that release sucrose or amino acids.
What are sinks?
Sinks are parts of the plant that use or store sucrose or amino acids.
How can sources and sinks change?
During a growth period, the storage organs would be the source, and the many growing areas of the plant would be the sinks. After the plant has grown and the leaves are photosynthesizing, they will become the source, and the roots will become the sinks.
