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IP Secondary 3 Biology > Chapter 5 - Transport in Plants > Flashcards

Chapter 5 - Transport in Plants Flashcards

1
Q

Pith and cortex (function)

A

Store food substances (e.g. starch)

The size of the pith and cortex will vary depending on the plant

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2
Q

Epidermis (structure)

A

A layer of cells which cover the stem

Protected by waxy, waterproof cuticle → reduces evaporation of water

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3
Q

Xylem (function)

A

Conducts water and dissolved mineral

salts from the roots to stem and leaves

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4
Q

Xylem (structure)

A
  • Long hollow tube stretching from the root to the leaf
  • Made of many dead cells
  • Long and empty lumen, without cross-walls or protoplasm
  • Walls are thickened with lignin
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5
Q

Sieve tubes (structure)

A
  • Consist of sieve tube cells/elements which are columns of elongated, thin-walled living cells
  • Degenerate protoplasm
  • No nucleus, no vacuole and most organelles are also lost
  • Thin cytoplasm which is connected to cells above and below through sieve plates
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6
Q

Lignin (function)

A

Provides mechanical support for the plant

Prevents collapse of the plant

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7
Q

Lignin (structure)

A
  • Hard and rigid substance

- Can be annular, spiral or pitted

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8
Q

Phloem (function)

A

Transports manufactured food (sucrose and amino acids) from the leaves to other parts of the plant

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9
Q

Phloem (structure)

A

A column of sieve tubes and companion cells

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10
Q

Companion cells (function)

A
  • provide nutrients → keep sieve tube cells alive
  • many mitochondria → provide energy for transporting sugars from the mesophyll cells into sieve tubes by active transport
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11
Q

Sieve plates

A
  • presence of pores → rapid flow of manufactured food substances through sieve tubes
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12
Q

Cambium

A
  • thickening of stem
  • between the phloem and xylem
  • cells divide and differentiate to form new xylem and phloem tissues
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13
Q

Dissolved mineral salts (ions) enter root hair cells by diffusion when…

A

concentration of certain ions and mineral salts in the soil solution is higher than in the cell sap

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14
Q

Dissolved mineral salts (ions) enter root hair cells by active transport when…

A

concentration of certain ions in the soil solution is lower than in the cell sap
(ions are pumped into the cells)

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15
Q

During active transport, ions are ________ into cells

A

pumped

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16
Q

After entering the root hair cells, dissolved mineral salts (ions) continue to move through the root cells by ________ until they reach the xylem cell

A

diffusion

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17
Q

Water enters root hair cells from the soil by ________

A

osmosis

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18
Q

Osmosis process: thin film of liquid around soil particles

  • is a ________ solution of ________
  • has ________ water potential
A
  • dilute, mineral salts

- less negative

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19
Q

Osmosis process: cell sap

  • is a ________ solution of ________
  • has ________ water potential
A
  • concentrated, sugars and salts

- more negative

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20
Q

Water transport between plant cells through cell wall = ________ pathway

A

apoplast

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21
Q

Water transport between plant cells through cytoplasm = ________ pathway

A

symplast

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22
Q

Water transport between plant cells through vacuole = ________ pathway

A

vacuolar

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23
Q

Plasmodesma

A

Small channels that directly connect the cytoplasm of neighbouring plant cells to each other to facilitate transport of materials

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24
Q

Entry of water _________ the cell sap in root hair cell.
Cell sap in root hair cell has a ________ negative water potential compared to that in inner root cells.
Water moves from root hair cell to the inner root cells via ________ until it reaches the vascular cylinder.

A

dilutes
less
osmosis

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25
Q

Casparian strip (structure)

A

a belt of waxy material in the endodermal layer

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26
Q

Casparian strip (function)

A

blocks the passage of water and ions via the apoplast pathway
(regulates the flow of water)

27
Q

Describe root pressure

A

Active transport of ions into the vascular cylinder → Positive pressure → Inward movement of water into the region → Upward push of xylem sap

28
Q

Describe capillary action

A

Adhesive and cohesive nature of water → Upward movement of water

29
Q

Define “cohesion”

A

hydrogen bond between water molecules

30
Q

Define “adhesion”

A

hydrogen bond between water molecules and cell wall of xylem vessel in stems

31
Q

Define transpiration

A

The loss of water vapour from the aerial parts of the plant, through the stomata of the leaves

32
Q

Define transpiration pull

A

The negative pressure (tension) or ‘suction force’ generated by transpiration

33
Q

Water lost through transpiration are:

A
  • excess water absorbed from the soil and not used by the plant
  • water produced by plant cells during respiration
34
Q

Movement of water inside a leaf

A

→ Water continuously moves out of the mesophyll cells to form a thin film of moisture over their surfaces
→ Water evaporates from this thin film of moisture and moves into the intercellular air spaces. Water vapour accumulates in the large air spaces near the stomata (sub-stomatal air spaces)
→ Water vapour then diffuses through the stomata to the drier air outside the leaf (=transpiration)
→ As water evaporates from the mesophyll cells, the water potential of the cell sap decreases. The mesophyll cells begin to absorb water by osmosis from the cells deeper inside the leaf. These cells, in turn, remove water from the vein (xylem vessels).
→ This results in a suction force which pulls the whole column of water up the xylem vessel

35
Q

What happens in the leaf during transpiration?

A
  • Water diffuses from xylem to the neighbouring cells in the spongy mesophyll layer
  • Water dissolved into the thin layer of moisture surrounding the spongy mesophyll cells
  • Water vapour leaves via stomata
36
Q

What happens in the stem during transpiration?

A
  • Loss of water vapour from leaves creates a ‘suction force’ = transpiration pull which draws water up the stem
37
Q

What happens in the root during transpiration?

A
  • Water moves into root hair cells by osmosis

- Water moves from root hair cells to neighbouring cells in the root by osmosis until it reaches the xylem vessel

38
Q

What is a transpiration stream?

A

Upward movement of water molecules from roots to leaves

39
Q

Rate of transpiration increases when… [4]

A
  1. humidity is low
  2. there is wind/air movement
  3. temperature is high
  4. there is light
40
Q

Why does humidity affect transpiration?

A

When humidity is low,

air is dry and water vapour diffuses out from the leaves faster

41
Q

Why does wind affect transpiration?

A
  • Wind blows away the water vapour that diffuses out from the leaves
  • Maintains the water vapour concentration gradient
42
Q

Why does temperature affect transpiration?

A

When temperature is high,

rate of evaporation increases

43
Q

Why does light affect transpiration?

A

When there is light,

stomata open and more water vapour can diffuse out

44
Q

Importance of transpiration pull [5]

A
  1. Draws water and mineral salts from roots to stem and leaves
  2. Removes latent heat of vapourisation → cools the plant
  3. Water is used by leaves during photosynthesis
  4. Keep cells turgid to spread out the leaves widely to trap sunlight
  5. Replace water lost by cells
45
Q

How can the rate of transpiration be measured?

A
  1. Using a spring balance
  2. Using a potometer

(for detailed set-ups, check slides or textbook)

46
Q

Spring balance: How to use the results to calculate rate of transpiration?

A

loss in mass / time taken

units: g/h

47
Q

Potometer: How to use the results to calculate rate of transpiration?

A

change in volume of water in column / time taken

units: cm^3/min

48
Q

In a normal, healthy plant, …

A
  • Leaves are __ and the cells are turgid

- Spread out widely

49
Q

In a wilted plant, …

A
  • Leaves are folded and cells are plasmolysed
    (lost of turgor pressure)
  • Folded up
50
Q

Wilting

A

→ Plant cells lose water vapour faster than the roots can absorb water (i.e rate of transpiration > rate of water absorption)
→ Turgor pressure in plant cells decreases
→ Cell membrane and cytoplasm shrinks away from cell wall
→ Plant cells become plasmolysed/flaccid
→ Stem becomes soft and limp and leaves are folded up

51
Q

Xerophytic plants: What are adaptations do they have? [3]

A
  • The upper epidermis on the outside of the leaf has a thick cuticle and no stomata
  • Stomata are confined to furrows in the inner surface of the leaf, where they are sheltered from air currents
  • The inner epidermis has many stiff hairs
52
Q

Xerophytic plants: How do the adaptations help in the harsh environment?

A

Results in humid air becoming trapped inside the rolled leaf, reducing the rate of transpiration

53
Q

Xerophytic plants: Leaf unrolls when ________, but rolls up when transpiration is _______
Rolling is brought about by ________ in the leaf cells

A

water is available
excessive
osmotic changes

54
Q

What is translocation?

A

Transport of manufactured food and amino acids in plants

55
Q

Sugars are transported from ________ to ________ via phloem

A

sources

sinks

56
Q

What are sources?

A

Plant organs in which sugar is being produced by photosynthesis or the hydrolysis of starch

57
Q

What are sinks?

A

Organs which consume or store sugar

e.g. roots, buds, stems, fruits

58
Q

What is translocation?

A

The transport of manufactured food substances such as sucrose and amino acids in plants

59
Q

Mechanism of translocation

A

→ Active transport of sucrose into the sieve tube at the source reduces water potential inside the sieve-tube elements
→ Inward movement of water into the phloem by osmosis
→ Generates a positive pressure that forces the sap to flow along the tube
→ The pressure is relieved by the unloading of sugar and the consequent loss of water at the sink
→ Xylem recycles water from sink to source (in leaf-to-root translocation)

60
Q

What is the hypothesis behind the mechanism of translocation?

A

Bulk flow by positive pressure (pressure-flow hypothesis)

61
Q

“Ringing” experiment: to show phloem as the translocation tissue

A
  1. Cut of a complete ring of the bark, including the phloem and the cambium, from the stem of a twig
  2. Place the twig in water with the ring immersed
  3. Set up another twig that has a cut ring above water
  4. Set up a control with an unringed twig
  5. Observe for swellings
62
Q

Swellings will be formed ________ the cut region due to accumulation of ________

A

above

food substances

63
Q

Using aphids: to show phloem as the translocation tissue

A
  • Aphids feed on plant juices
  • Studies have shown that aphids insert their stylet into the phloem sieve tube to feed on the sugars
    → Shows that translocation of sugars and amino acids occurs in phloem
64
Q

Using isotopes and autoradiography: to show phloem as the translocation tissue

A
  1. Provide a leaf with carbon dioxide containing radioactive carbon (14C)
  2. During photosynthesis, glucose formed contains 14C
  3. Expose a section of the cut stem onto an X-ray film
    → Only the phloem will show radioactivity

IP Secondary 3 Biology (8 decks)

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