Written Assignment 5


A.Multiple–Choice Questions

Multiple questions

    1. Pressure that develops within a living cell as a result of water entering the cell is called

    2. d

  1. water potential.

  2. plasmolysis.

  3. transpiration pressure.

  4. osmotic pressure.

    1. The cohesion of water molecules and their adhesion to the walls of narrow tubes that results in water rising in the tube help explain

    2. c

  1. the pressure–flow hypothesis.

  2. active transport.

  3. the cohesion–tension theory.

  4. guttation.

  1. Many studies leading to our present knowledge of translocation of food in plants utilized radioactive tracers and

  1. d

  1. aphids.

  2. Mosquitoes.

  3. osmometers.

  4. algae.

  1. High humidity causes


  1. transpiration rates to decrease.

  2. transpiration rates to increase.

  3. leaf hairs to curl.

  4. transpiration to cease altogether.

  1. Water constitutes about what percentage of the weight of young cells? 5 a

  1. 70 percent

  2. 50 percent

  3. 30 percent

  4. 10 percent

  1. Which of the following is a micronutrient in terms of a plant`s mineral requirements?

  1. d

  1. calcium

  2. magnesium

  3. phosphorus

  4. manganese

  1. Relatively uniform loss of color, generally occurring first on older leaves, signifies a deficiency of

  1. d

  1. iron.

  2. nitrogen.

  3. boron.

  4. magnesium.

8 Nitrogen,potassium, calcium, and phosphorus make up about what percentage ofthe nutrient total found in a plant?

  1. a

  1. 70 percent

  2. 50 percent

  3. 30 percent

  4. 10 percent

  1. Stomata are open when the guard cells are turgid.

  1. are flaccid.

  2. are hyperglycemic.

  3. are hypoglycemic.

  4. have a lower solute concentration than their surroundings.

  1. Movement of substances in the phloem is best explained by

10. c

  1. osmosis.

  2. evapotranspiration.

  3. pressure–flow hypothesis.

  4. capillarity.

B.True/False Questions

  1. All substances can pass through a semipermeable membrane at the same rate. 12. false

  2. All plant cell membranes appear to be semipermeable.13. True

  3. During plasmolysis, water leaves a cell`s central vacuole. 14. True

  4. A proton &quotpump&quot is believed to be involved in active transport. 15. True

  5. Imbibition results in the swelling of tissues, whether they are dead or alive. 16. True

  6. Osmotic potential is the minimum pressure required to prevent fluids from moving as the result of osmosis. 17. False

  7. All water leaves a plant via stomata. 18. False

  8. Guttation involves loss of liquid water from a leaf. 19. True

  9. A hydathode is located at the tip of a leaf vein. 20. True

  10. Dew is water that transpired at night. 21. True

C.Discussion Questions

How cana tree, such as the giant sequoia, supply water to its top?

Thegiant sequoia supplies water to the top by using fog. Fog is absorbedthrough the needles of the branches and is thus transported upwardsin the trunk. The tree only grows up the height at which the trunkcan still supply water. For this reason, the tree needs to be in anarea which is very foggy. It is for this reason that the tree growsto be very tall in Sequoia Nt. Park.

Explainhow you would design a study to determine the speed at which foodsubstances in solution move about within a plant.

The stemof the plant could be severed and the stem placed in a coloredsolution. The plant’s xylem will absorb water from the solution andthe movement of this water could be observed as the colour of thestem changes in accordance to the color of the solution. A photometercould also be used to measure the rate at which this takes place.

Describehow osmosis and active transport work to open and close stomata.

Osmosis is the movement ofwater molecules from a region where they are highly concentrated to aregion where they are in lower concentration. When the stomas are ina hypotonic environment, water molecules move into the cellssurrounding it, making them turgid. This causes them to open.

Activetransport is the movement of solute molecules from a region wherethey are in low concentration to a region where they are highlyconcentrated. This process requires energy. When the stomas are in ahypertonic environment, the solute molecules move from the cellssurrounding them into the environs making these cells hypotonic tothe environment. As a result the cells around the stoma become turgidand cause the stoma to open.

Explainthe “dilemma” a leaf faces in maintaining a supply of CO2,minerals, and water without becoming desiccated.

Plantsuse minerals, carbon (IV) oxide and water in the process ofphotosynthesis to manufacture food. These elements all play a role inboth stages of photosynthesis. Water, however, has more functions. Itis lost by the plant to the atmosphere in a process known astranspiration. This process in necessary as it keeps the plant cool.It also helps to maintain a continuous transpiration stream thatfacilitates absorption of water and transportation via the xylem. Thedilemma comes in when the plant is in a very hot place, transpirationwill take place continuously to cool the plant and this water willstill be required for photosynthesis to take place.

The sunprovides the necessary energy to split a water molecule in lightstage of photosynthesis, but at the same time provides the heat thatcauses transpiration to take place at a faster rate. If the waterwill start being lost at a faster rate than it is being absorbed thenthe plant will desiccate. Plants therefore need to maintain thebalance at all times.

Overeagerplant growers add too much “plant food” to their houseplants`soil. Plant food contains mineral salts in a high concentration. Whymight this cause wilting?

Whenthese nutrients are added into the soil, they cause the environmentaround the roots to be hypertonic. This greatly hampers absorption ofwater by the roots since it basically takes place as a result of thehypotonic nature of the environment. This will result in absorptiontaking place at a lower rate than transpiration. As a result, theplant’s processes slow down until wilting eventually takes place.

Describe at least one stomatalmodification or specialized form of photosynthesis that a) aquatic,b) desert, c) tropical, and d) cold–zone plants have that help themadapt to their particular environments.

Aquatic plants have broadleaves with a larger number of stomata than terrestrial plants. Thishelps to increase the rate at which transpiration takes place. thisis necessary because the plant is in an environment with a lot ofwater and will therefore require a means of expelling this excesswater.

Leaves of desert plants havedifferent adaptations to reduce the rate of transpiration. Some ofthese adaptations include the fact that the stoma are placed on thelower side of the leaves and are fewer in number compared to plantsfound in areas with adequate water supply. Some of these leaves rollup, exposing less surface area of stoma to the atmosphere. As aresult transpiration takes place at a reduced rate enabling the plantto conserve water.

Tropical plants have adequatestomata in the upper and lower sides of the leaves. This is becausethe tropical regions are not as dry as desert areas and thereforehave sufficient water. Nevertheless, they need adaptations to caterfor the different seasons. Therefore, some plants contain somehair-like structures that increase the surface area for transpirationin the hot seasons whereas others have reduced leaf sizes for thecold seasons.

Cold-zone plants have stomataladaptations to deal with the extreme temperatures. In most cases theleaves are usually very thin. This reduces the surface area to volumeratio significantly and the rate of transpiration decreases as well.Reducing the rate of transpiration also helps them maintain theprevent heat loss through evaporation.