Answers to biology exercise

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Answers to biology exercise

  1. 1. Answers to Biology Exercise
  2. 2. Question 1 <ul><li>1) Which region contains structures that are responsible for the transport of water? </li></ul>(R) Note: Structure R is referring to the Xylem Vessels, while Structure S is the phloem. There is a need to differentiate and remember the positions of the vessels in leaf, stem & root (Refer to your lecture slides)
  3. 3. Question 2 <ul><li>2) The structure labelled X ______________ </li></ul>(Prevents water loss) Note: Most of you answered this correctly Cuticle
  4. 4. Question 3 <ul><li>3) Translocation refers to the ____________ </li></ul>(movement of manufactured food from the leaves to the rest of the plant ) Note: Most of you answered this correctly
  5. 5. Question 4 <ul><li>4) Xylem tissue in plants is responsible for the transport of </li></ul>(water and mineral salts) Note: All of you answered this correctly Do not confuse mineral salts with food substances such as sucrose and amino acids
  6. 6. Question 5 <ul><li>5) The roots absorb water through </li></ul>(Root hairs) Note: Some of you answered this incorrectly. Root hairs are specialized structures that aid in absorption of water (Recall their adaptations) Epidermal cells do not directly participate in absorption of water & mineral salts as these cells become the tubular outgrowth of the root hairs
  7. 7. Question 6 <ul><li>6) Much of the transpiration in plants occur through the </li></ul>(Stomata) Note: Some of you answered this incorrectly. Transpiration in plants occur in the leaves as well as the stem. Leave – Stomata transpiration & Cuticular Transpiration (Cuticle does not totally prevent water loss) Stem – Lenticular transpiration (Lenticels are pores present on the stem which allow water vapour to move out of the stem) Minimal transpiration occurs through cuticular & lenticular transpiration (aids in cooling)
  8. 8. Question 7 <ul><li>7) Transpiration takes place from </li></ul>(only the aerial parts) Note: Most of you answered this incorrectly ( leaves ) See previous slide explanations. Not all parts of the plants allow transpiration, the roots do not transpire. They are adapted to water & mineral salts absorption. Aerial parts refer to the parts of plants above the ground excluding the roots.
  9. 9. Question 8 <ul><li>8) The main function of the companion cells is to </li></ul>(produce energy for translocation) Note: Some of you answered this incorrectly You need to know what companion cells are associated with, they are associated with phloem and contains many mitochondria. Transport of water in Xylem vessels does not require energy as there are forces which help to push (Root pressure), pull (Transpiration pull) & capillary action to direct water upwards the plant.
  10. 10. Question 9 <ul><li>9) Which of the following factors does not increase the rate of transpiration? </li></ul>(high humidity) Note: Some of you answered this incorrectly Does not increase = decrease You need to understand which factor will cause the layer of air around the leaves to have higher water content, hence having a more gentle water potential gradient between the leaves and the surrounding atmosphere. With a gentle water potential gradient, water vapour cannot move out of the leaves as fast when compare to a steeper water potential gradient
  11. 11. Question 10 <ul><li>10) Mineral salts are absorbed into the roots by </li></ul>(active transport) Note: Some of you answered this incorrectly ( diffusion, osmosis ) Recall root pressure – Dissolved mineral salts in the soil usually have lower concentration as compare the root cells. The root cells (root hair cells & cortical cells) are actively transporting mineral salts into the cortex and into the xylem vessels. Increase solute concentration = lower water potential within the root, hence water is able to enter the root through osmosis.
  12. 12. Question 11 <ul><li>11) The opening and closing of stomata is due to </li></ul>(turgor pressure of guard cells) Note: All answered this correctly.
  13. 13. Question 12 <ul><li>12) Stomata are present on the ____________ of the leaves. </li></ul>(mainly lower surface) Note: Some of you answered this incorrectly (lower surface only) Please read the question properly. Sometimes, student makes mistake by rushing into the question without reading and understanding all the MCQ choices. Depending on the types of plant, stomata can also be found on the upper surface of leaves. However, for most land dicot plants, stomata are found mainly on the lower surface. What would happen if most of the stomata are found on the upper surface and are exposed to direct sunlight? Hint: Think about how transpiration will be affected.
  14. 14. Question 13 <ul><li>13) Explain the processes involved in the movement of water from the soil into the conducting tissue of a plant root. (7) </li></ul>Plants absorb water from the roots through the root hair cells that are elongated so as to increase surface area to volume ratio for faster absorption of water. This process is done through osmosis for water, while active transport for the mineral salts. For osmosis, water moves through a partially permeable membrane of the root hair cell down a concentration gradient, from high water potential to a low water potential. This is possible because the sap in the root hair cell is relatively concentrated with a solution mineral salts as they are actively transported into the root cells from the surrounding soil . Therefore, it creates a lower water potential, allowing water to enter. Now, the root hair cell has a high water potential compared to that of the next cell. Water moves through osmosis to the next cell and the process repeats. This process is known as root pressure.
  15. 15. Question 13 <ul><li>13) Explain the processes involved in the movement of water from the soil into the conducting tissue of a plant root. (7) </li></ul>Note: Include keywords such as osmosis for water and active transport for mineral salts. The question states movement of water within the root only, you do not need to mention capillary action and transpiration pull. It is good to mention that root hair helps to increase the rate of water absorption due to the large surface area to volume ratio
  16. 16. Question 14 <ul><li>14) Products of photosynthesis, such as sucrose, are translocated via the phloem from the sites of production in green leaves to places where they are utilised, such as seeds, fruits, roots and new leaves. These places are known as 'sinks'. Describe the pathway by which a sucrose molecule is transported from the leaf to a sink such as a fruit. </li></ul>The leaf manufactures sucrose through photosynthesis. The sucrose is then transported into the phloem by active transport whereby energy is provided by the companion cells. The water potential in the phloem then become lower than that in the xylem, and hence water enters the phloem through osmosis. The sucrose mixes with the water and form a solution. It is then transported to the sink; where there is an increase demand for sucrose, via pressure flow. Sucrose is transported into the sink by active transport. Water is also attracted into the sink through osmosis which subsequently returned into the xylem vessels.
  17. 17. Question 14 <ul><li>14) Products of photosynthesis, such as sucrose, are translocated via the phloem from the sites of production in green leaves to places where they are utilised, such as seeds, fruits, roots and new leaves. These places are known as 'sinks'. Describe the pathway by which a sucrose molecule is transported from the leaf to a sink such as a fruit. (4) </li></ul>Note: Include keywords such as active transport of sucrose from the leaf into the phloem, pressure flow causes the movement of sucrose molecules to be transported to regions which demand sucrose Active transport must be mentioned when sucrose gets transported into the phloem from the source & from the phloem into the sink
  18. 18. Question 15 <ul><li>15a) What does the potometer directly measure? </li></ul><ul><li>(Measures the rate of water uptake by plant) </li></ul><ul><li>Incorrect – Measures the rate of transpiration </li></ul><ul><li>b) Name the process by which water is lost from the shoot. </li></ul><ul><li>(Transpiration) </li></ul><ul><li>Shoot is referring to the stems, leaves and budding flowers </li></ul><ul><li>Incorrect – Lenticular, stomata, cuticular transpiration (Read the question carefully, use general term to identify the process) </li></ul>
  19. 19. Question 15 <ul><li>c) Suggest reasons why the measurement in (a) is not necessarily the same as the rate of the process stated in (b). </li></ul><ul><li>Water is also used during photosynthesis where food substances are manufactured. The water is also stored within the plant for growth and maintaining its turgidity. </li></ul><ul><li>d) State and explain 2 factors that might affect the shoot's rate of water loss. </li></ul><ul><li>Humidity – Affect the amount of water concentration surrounding the plant </li></ul><ul><li>Wind speed - Affect the amount of water concentration surrounding the plant </li></ul><ul><li>Temperature – Affect the rate of evaporation of water and the degree of water saturation in the air </li></ul><ul><li>Light Intensity- Affect the size of the stomata </li></ul><ul><li>(Elaborate – Refer to lecture slides) </li></ul>

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