Transport in Plants - Biology

Identity root hair cells, as seen under the light microscope, and state their functions

The root hair cell basically helps absorb water and inorganic ions from the soil via osmosis, which we touched upon in Unit 2, Movement in and out of cells.

State that water is transported from the roots to leaves through the xylem vessels

Water is transported from the roost to the leaves through the xylem vessels.

identify the position of xylem and phloem as seen in sections of roots, stems and leaves, limited to non-woody dicotyledonous plants.

Xylem Tissue and Phloem Tissue In the diagram directly below, Xylem is shown as 8 (red circles), whilst Phloem is shown as 9 (blue circles)

Define transpiration as loss of water vapour from planı leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata

(Transpiration is the evaporation of water at the surfaces of the mesophyll cells followed by loss of water vapour from plant leaves, through the stomata. )

define translocation in terms of 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)

- This is the movement of sucrose and amino acids in the phloem tubes of the plant - Glucose is very important as it makes many other important nutrients. - For Example, Glucose is used to make sucrose. Sucrose then enters the phloem - The phloem then transports the sucrose all across the leaf where it can be made use of.

Transpiration

- Transpiration is the evaporation of water from the surface of a plant Or • Transpiration is the loss of water from the plant in the form of water vapour. - Transpiration mostly occurs from the leaves. - The leaves are the major evaporation sites because of the huge number of microscopic holes in their surface through which water vapour can escape. - These holes are called "stomata' and are open in light to allow the entry of carbon dioxide for photosynthesis. The loss of water vapour through these open stomata is the price the plant pays to get carbon dioxide. - Beyond the stomata, the leaves and stems have a water-proof covering to reduce evaporation and so conserve water.

Investigate and describe the effects of variation of temperature and humidity on transpiration rate

Humidity: Humidity is basically a measure of the amount of water vapour in the air. Remember, unit 2, when we talked about difference in concentration and diffusion? If the air outside is very humid, then that means that there is a high concentration of water vapour in the surroundings, which will create a concentration gradient between the inside of the plant and the surroundings. The surroundings has loads of water vapour, so there would be less concentration gradient for the water to transpire to, so the rate of transpiration will decrease in humid environments. All in all, increased humidity decreases rate of transpiration. Temperature: When the temperature is high, molecules have more kinetic energy and move faster, hence allowing evaporation to occur faster. This increases the rate of transpiration. Light Intensity: When there is high light intensity, the stomata will open up to allow carbon dioxide in for photosynthesis, so there will be more chance for water molecules to escape the stomata into the surroundings via transpiration. In the dark, where little photosynthesis occurs, the stomata's are closed, hence little transpiration occurs in the dark.

Investigate, using a suitable stain, the pathway of water through the above-ground parts of a plant

Investigation: To Show the Path of Water Through Plant Tissue a) Place a small seedling into a beaker containing water that is dyed red. Leave the plant in bright light at room temperature in a breeze. Note that the red dye enters the roots and travels up the stem and into the leaves. Note that the red dye travels along the veins of the leaf. If sections of the root, stem and leaf are examined under the microscope the xylem tissue is seen to be red in colour - xylem transports the water. b) Cut the base, non-leafy end, of a fresh stalk of celery under water. Place the cut end into a beaker of water stained with red food dye. Leave the celery stalk in bright light at room temperature in a breeze. Note the red lines moving up the stalk and then along the veins of the leafy parts. Cut across the stalk and note the curve of red dots close to the outer edge. If a thin section is examined under the microscope it is the xylem which has been stained red in colour.

Reminders for the investigation (question 6)

Role of Water in Plants a) An essential component of all plant cells - plant cells are about than 90% water. b) Water is needed as a raw material for photosynthesis; the leaves are the major sites of photosynthesis. c) Water is needed to transport of food and mineral nutrients through the plant. d) The support of soft, non-woody parts depends on a good water supply to the cells. Source of Water for the Plant The soil is the reservoir of water the plant draws on to satisfy its demands for water. The soil is also the plant's source of mineral nutrients. The roots are well adapted to absorb water and mineral nutrients from the soil. After absorption, water is transported up the plant to the leaves in a specialised tissue called xylem. The mineral nutrients are water-soluble and they are carried in solution up through the plant with the water.

Relate the structure and functions of root hairs to their surface area and to water and ion uptake.

The elongated section of the root hair, which you can clearly see on the diagram (the extended bit which looks like something...yes, you know what i'm talking about now), basically provides a large surface area for the absorption of water and inorganic ions. Additionally, the membrane of the root hair cell is semi-permeable. What that means is basically only minerals and water can go through the membrane, but no necessarily go back out.

State the pathway taken by water through root, stem and leaf as root hair, root cortex cells, xylem and mesophyll cells

The process of water traveling from the soil to leaves is rather simple, so you'll just have to memorize this. 1. There is a high water potential in the soil and not-so-high water potential in the root hair cell, as the root hair cell has a very concentrated cell-sap. Because of this, osmosis occurs and water and inorganic ions move from the soil to the root hair cells, down a concentration gradient. 2. The inorganic ions and water travel to the xylem tube, which is responsible for traveling the products up to the leaves. 3. The xylem vessel transports the water and inorganic ions (minerals) up the xylem tube from the root to stem through a process called transpiration, against gravity. 4. The water and inorganic ions leave the xylem and is absorbed by the cells in the leaves.

Transpiration Stream

Transpiration Stream Each plant is full of water from the tips of the roots to the tips of the leaves. The roots are in direct contact with the water in soil. Water has the great ability to glue itself to itself. Evaporation of water from the leaves "pulls' on the column of water all the way through the plant into the soil. As water is lost from the leaves it pulls water up the plant and pulls water from the soil into the roots. The upward flow of water in the plant is called the transpiration stream. The faster the evaporation of water i.e. transpiration, the faster the transpiration stream and the faster the absorption of water from the soil.

Explain the mechanism by which water moves upwards in the xylem in terms of a transpiration pull, helping to create a water potential gradient that draws up a column of water molecules, held together by cohesion

Water transport up the plant requires something that will allow it to work against gravity. Visualize the xylem tube. The water is flowing upwards right, from the soil to the xylem tube. In order to work against gravity, water travels via this process called Capillary Action, which allows liquids to flow liquids to flow through narrow spaces such as the xylem tube without the assistance of gravity. According to wikipedia, Capillary Action works "because of inter-molecular attractive forces between the liquid and solid surrounding surfaces; If the diameter of the tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and adhesive forces between the liquid and container act to lift the liquid"

State the functions of xylem and phloem

Xylem vessels transport water and dissolved minerals from the root up to all the other parts of the plant. Xylem transports water and mineral nutrients up the plant, ending at the leaves. Xylem is composed of long empty but water-filled dead cells. The dead xylem cells, with their missing end walls, form long open microscopic pipes from the roots to the margins of the leaves. The water, with the dissolved mineral nutrients, travels through these pipes being pulled by the evaporation of water from the leaves - the plant does not have to work to transport water. Because xylem is so hard and strong it also plays an important role in the support of the plant. In woody plants the wood is mostly composed of xylem. Phloem Vessels: The function of Phloem Vessels is to transport food nutrients such as glucose from the leave to other parts of the plant. Phloem transports food in the form of a sugar solution. Food is transported from the leaves to the other parts in summer. In early spring food is transported from the roots to all the growing points and especially for the formation of new leaves. Phloem is composed of living cells - the plant has to work to transport food. Phloem is a soft tissue and in woody stems it is in the bark.