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biology: unit 3 > 3.3: Transport in plants > Flashcards

3.3: Transport in plants Flashcards

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AP® Biology flashcards
1
Q

What makes up a stem?

A
  • Cortex
  • Epidermis
  • Parenchyma
  • Phloem
  • Xylem
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2
Q

What makes up a root?

A
  • Exodermis
  • Epidermis
  • Xylem
  • Phloem
  • Endodermis
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3
Q

What is a xylem and what are the features?

A

Tissue that transports minerals and ions up the plant (transpiration stream)

  • Supports the plant
  • Dead - no organelles makes it a hollow tube
  • Lignin - to withstand pressure of water uptake
  • Non lignified pits - to allow water an mineral ions to leave xylem
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4
Q

What is the xylem parenchyma?

A

Stores food
Contains tannin (bitter chemical)

  • This is a defence against herbivores
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5
Q

What is a phloem?

A

Transports assimilates (sugars) from source to sink

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6
Q

Why is sucrose transported in the phloem?

A

It is less reactive so it is not used up in respiration

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7
Q

What are features of the phloem?

A

Alive - can do active transport which is important for translocation

  • Sieve tube elements
  • Sieve plate
  • Companion cell - keeps phloem alive and is involved in translocation
  • Plasmodesmata - gap that links cytoplasm of adjacent cells
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8
Q

What is transpiration?

A

Loss of water vapour by evaporation?

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9
Q

What are advantages and disadvantages of transpiration?

A

Advantages:
Cools down plants - water vapour absorbs heat
Causes transpiration stream - delivers water and mineral ions

Disadvantages:
Loss of water - lose tugor pressure which causes wilting and reduces the SA of leaves and stem exposed to surrounding environment - reduces transmission

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10
Q

Watrer vapour moves out of the cell becoming water vapour and will diffuse out of the stomata: Causes

A
  1. WP to decrease in one cell
  2. Other cell with higher WP will have its water be drawn to first cell
  3. Original cell with higher WP will have lower compared to third one
  4. Third cell will have its water be drawn to second cell
  5. This continues until it reaches the xylem
  6. The pull of water from the root up to the stem, through the xylem is the transpiration stream
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11
Q

Where does cohesion and adhesion occur in transpiration?

A

Cohesion - HB between water molecules causes it to stick together
Adhesion - HB between water molecules and walls of xylem

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12
Q

What are the factors that affect transpiration?

A
  • Temperature
  • Windy conditions
  • Light intensity
  • Humidity
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13
Q

What does temperature do to transpiration?

A

Molecules including water have higher KE and move faster
Increases the water concentration gradient

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14
Q

What does windy conditions do to transpiration?

A

The air movement blows the H2O molecules on the inside of the leaf away.
Therefore move away faster

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15
Q

What does light intensity do to transpiration?

A

More stomata will open, for more CO2 to enter, for more photosynthesis to occur and H2O to leave

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16
Q

What does humidity do to transpiration?

A

There are more water molecules in the air
Reduces the water concentration gradient between leaf and air

17
Q

What is the apoplast pathway?

A

Movement of water through cell wall by tension

18
Q

What is the symplast pathway?

A

Movement through cytoplasm (diffusion) and plasmodesmata (osmosis)

19
Q

What is the casparian strip?

A

In the endodermal cell and its made of waxy suberin
Waxy - apoplast pathway no longer works

  • Water goes through symplast pathway
20
Q

What are the steps of water transport in plants?

A
  1. H2O moves across root cells in apoplast or symplast pathway
  2. H2O moves across endodermis - moves through apoplst pathway + meets casparian strip
  • H2O forced from cell wall into cytoplasm and carry on in SP (Plasma membrane)
  1. H2O moves in xylem
  • Move ions into xylem by active transport therefore water potential decreases in xylem
  • H2O moves into xylem by osmosis down a water potential gradient
  • Root pressure is generated - pushes H20 up xylem
21
Q

Where does phloem loading occur?

A

Apoplast pathway

22
Q

What is translocation?

A

Transport of assimilates from source to sink

23
Q

What occurs in translocation?

A
  1. H+ pumped out of companion cell through H+ pumps by active transport (increases H+ outside of companion cell)
  2. H+ wants to diffuse back into CC so gets co-transportted with sucrose into CC through co-transporters
  3. Sucrose diffuses from CC into sieve tube element through plasmodesmata (decreases WP inside the STE)
  4. H2O moves into STE by osmosis (generates tugor pressure for mass flow)
24
Q

What is mass flow?

A

Assimilates flow from source to sinks down pressure gradient

25
Q

What happens in phloem unloading?

A
  1. Sucrose diffuse from phloem to sinks because it has a low sugar concentration
  2. Sucrose is moved to other cells or converted to other forms - maintains concentration gradient between cells and phloem
  3. Loss of assimilates increases WP of STE
  • H2O moves out into cells by osmosis or enters xylem’s transpiration stream
26
Q

What are adaptions of root hair cells?

A

Large surface area due to shape - increases water uptake for osmosis
Permanent vacuole containing cell sap, which is more concentrated than soil water - ensures a high water potential gradient is maintained

27
Q

What are xerophytes?

A

Plants with adaptations to reduce water loss and are therefore found in locations with limited water, for example, the desert

  • Marram grass is found on sand dunes, which despite being next to the ocean, there is limited water due to sand beiing so porrous
28
Q

What are adatations of xerophytes?

A
  • Curled leaves to trap moisture to increase local humidity
  • Hairs to trap moisture to increase local humidity
  • Sunken stomata to trap moisture to incease local humidity
  • Thicker cuticle to reduce evaporation
  • Large root network to reach more water
29
Q

What are hydrophytes?

A

Plants which live in or on water, so require adaptations to survive in an excess of water

  • Water lillies grow on the surface of water
30
Q

What are advantages of hydrophytes?

A

Ensures no additional water us retained in the plant and efficient water loss:

  • Short roots
  • Very thin to no waxy cuticle
  • Stomata permenantly open and in the top surface of lead

Ensures light is still absorbed for photosynthesis:

  • Leaves being large, wide and on the surface of leaf
31
Q

What is root pressure?

A
  • As water moves into the roots by osmosis it increases the volume of liquid inside the root and therefore the pressure inside the root increases. This is known as root pressure
  • This increase in pressure in the roots forces water above it upwards (positive pressure)
32
Q

What happens in mass flow?

A
  1. The sucrose in the STE has decreased the water potential
  2. Water moves to STE which creates high hydrostatic pressure
  3. Water acts as as medium to transport he assimilates from an areas of high hydrostatic pressure to low
  4. Once it reaches an area of low HSP the sucrose is used by cells and surroounding tissures
  5. Sucrose diffuses from the STE to surrounding tissues which decreases its WP
  6. Water moves from STE to surrounding tissues by osmosis down a WP gradient

biology: unit 3 (3 decks)

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