Mass Transport In Plants Flashcards

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1
Q

Water - Describe the cohesion-tension
theory of water transport in the
xylem. (5)

A
  1. Water lost from leaf because of transpiration /
    evaporation of water (molecules) / diffusion from
    mesophyll / leaf cells;
    OR
    Transpiration / evaporation / diffusion of water
    (molecules) through stomata / from leaves;
  2. Lowers water potential of mesophyll / leaf cells;
  3. Water pulled up by xylem (creating tension);
  4. Water molecules cohere / ‘stick’ together by
    hydrogen bonds;
  5. (forming continuous) water column;
  6. Adhesion of water (molecules) to walls of xylem;
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2
Q

Water - T A potometer measures the rate of water
uptake rather than the rate of transpiration.
Give two reasons why the potometer does not truly
measure the rate of transpiration
(2)

A
  1. Water used for support / turgidity;
    Accept: water used in (the cell’s) hydrolysis or
    condensation (reactions) for one mark.
  2. Water used in photosynthesis;
  3. Water produced in respiration;
  4. Apparatus not sealed / ‘leaks’;
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3
Q

Water - Give two precautions the students should have taken when setting up the potometer to obtain reliable measurements of water uptake by the plant shoot. (2)

A
  1. Seal joints / ensure airtight / ensure watertight;
    Answer must refer to precautions when setting up the apparatus
    Ignore: references to keeping other factors constant
  2. Cut shoot under water;
  3. Cut shoot at a slant;
  4. Dry off leaves;
  5. Insert into apparatus under water;
  6. Ensure no air bubbles are present;
  7. Shut tap;
  8. Note where bubble is at start / move bubble to the
    start position;
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4
Q

Sucrose - Describe the transport of carbohydrate in plants. (5)

A
  1. (At source) sucrose is transported into the
    phloem/sieve element/tube;
  2. By active transport
    OR
    By co-transport with H+;
    Accept co-transport with hydrogen/H ions
  3. By companion/transfer cells;
  4. Lowers water potential in phloem and water enters by osmosis;
    For ‘phloem’ accept ‘sieve element/tube’.
  5. (Produces) high (hydrostatic) pressure;
  6. Mass flow;
  7. Transport from site of photosynthesis to respiring
    cells
    OR
    Transport from site of photosynthesis to storage organ
    OR
    Transport from storage organ to respiring cells;
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5
Q

Sucrose - Use your understanding of the mass flow hypothesis to explain how pressure is generated inside this phloem tube (3)

A
  1. Sucrose actively transported (into phloem);
  2. Lowering/reducing water potential
    OR
    More negative water potential;
  3. Water moves (into phloem) by osmosis (from
    xylem);
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6
Q

Sucrose - Phloem pressure is reduced during the hottest part of the day. Use your understanding
of transpiration and mass flow to explain why (3)

A
  1. High (rate of) transpiration/evaporation;
  2. Water lost through stomata
    OR
    (High) tension in xylem;
  3. (Causes) less water movement from xylem to phloem
    OR
    Insufficient water potential in phloem to draw water from xylem;
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