Chapter 8 Flashcards
State the functions of xylem and phloem
Xylem is responsible for taking up water and mineral ions from the roots to the leaves and phloem is responsible for supplying glucose made by photosynthesis from the leaves to the roots
Identify the position of xylem and phloem as seen in sections of roots, stems and leaves, limited to non-woody dicotyledonous plants
Identify root hair cells, as seen under the light microscope
What is the function of root hair cells?
to absorb mineral ions and water
State the pathway taken by water
they start through the root via absorption and osmosis by the root hair cells, they are then passed through the root cortex cells by osmosis into the xylem; where they are then taken upwards in the stem and eventually reach the mesophyll cells in the leaf for photosynthesis.
Investigate, using a suitable stain, the pathway of water through the above-ground parts of a plant
What is the point of the large surface area of root hairs?
the large surface area of root hairs increases the rate of the absorption of water by osmosis and ions by active transport
transpiration
loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata
Explain how water vapour loss is related to the large surface area of cell surfaces, interconnecting air spaces and stomata
A large surface area of cell surfaces means more water vapour can leave, the interconnecting air spaces contain the water vapour and the stomata open and close to release to keep water vapour from escaping into the environment.
Explain the mechanism by which water moves upwards in the xylem in terms of a transpiration pull that draws up a column of water molecules, held together by cohesion
The water in the xylem is pulled upwards via a transpiration pull. As water is evaporates, is used in respiration and is used to prevent the plant from wilting, there is less water in the leaves, more is supplied through the xylem vessels via tension. When there is a continuous flow of water from the roots to the leaves through the xylem, that is called a transpiration stream. This only works with cohesion and adhesion. Cohesion is when the water molecules are attracted to each other sticking together and adhesion is when the water molecules are attracted to the inside of the xylem vessel
Explain how and why wilting occurs
The stomata close up to reduce transpiration when there is not enough water. If the plants still do not get water, it will start to wilt. When they lose too much water they no longer become turgid or full of water. and start to droop since it is no longer being supported.
Investigate and describe the effects of variation of temperature and humidity on transpiration rate
translocation
the movement of sucrose and amino acids in phloem from regions of production (source) to regions of storage OR to regions where they are used in respiration or growth (sink)
Explain that some parts of a plant may act as a source and a sink at different times during the life of a plant
The leaves of a plant respire to produce glucose and that glucose is then transported down to the roots. This means the source is the leaves and the sink is the roots. However, in spring, due to winter, there is starch stored in the roots. In order to have energy to grow their new leaves, the starch is transformed into sucrose and is transported from the roots to the leaves. In transpiration, it is always from the roots to the leaves.
