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OCR Biology AS Level > 3.3 - Transport in Plants > Flashcards

3.3 - Transport in Plants Flashcards

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1
Q

Why do plants need a transport system?

A

Larger, multicellular plants have a large Surface Area: Volume ratio (SA:V) so it requires a specialised exchange surface/transport system.

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2
Q

What are 4 key components that plants need to transport?

A
  1. Oxygen
  2. Water
  3. Sugars
  4. Minerals
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3
Q

What are the 2 types of specialised vascular tissue?

A

XYLEM and PHLOEM

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4
Q

What does the XYLEM transport and in which direction?

A

The xylem transports water and minerals UP the plant (from the roots)

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5
Q

What does the PHLOEM transport and in which direction?

A

The phloem transports ASSIMILATES (i.e. sugars) UP and DOWN the plant

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6
Q

What are dicotyledonous plants?

A

Plants with TWO seed leaves

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7
Q

How are vascular tissue organised in dicotyledonous (dicot) plants?

A

Organised in BUNDLES

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8
Q

What other tissues are contained in vascular bundles?

What are their roles?

A

Collenchyma and sclerenchyma - for strength and support

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9
Q

How is the vascular bundle arranged in the young root?
Give 7 features
(keywords: xylem,phloem,medulla,cortex, endodermis,pericycle)

A
  • Circular bundle
  • Xylem is arranged in a “star”/”X” shape
  • Phloem is embedded between the arms of the xylem
  • Medulla is the space within the xylem and phloem
  • Cortex is the furthermost outer layer
  • Endodermis which is an outer layer, within cortex
  • Pericycle which is in within the endodermis
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10
Q

What is the role of the endodermis in the young root vascular bundle?

A

Transports water into the xylem

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11
Q

What is the role of the pericycle in the young root vascular bundle?

A

Contains meristem cells that can divide into xylem and phloem

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12
Q

Why is the xylem distributed so widely as an X-shape in the young root vascular bundle?

A

Helps with strength

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13
Q

How is the vascular bundle arranged in the stem (10)?

A
  • curved, hexagonal bundle
  • The xylem, phloem and sclerenchyma are arranged in little stacks
  • These stacks create a ring within the bundle
  • The xylem is located in the innermost layer of the stack
  • The phloem is located in the middle layer of the stack
  • The sclerenchyma, which is there for support, is located in the top layer of the stack
  • The stacks also contain cambium (meristem cells) in between the xylem and phloem
  • Medulla is the space around the stacks
  • Cortex is the outermost layer
  • Collenchyma is within the cortex
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14
Q

How is the vascular bundle arranged in the stem (3)?

A

(this is from a cross-sectional perspective of the leaf)

  • xylem and phloem form a curved layer called a central midrib
  • xylem is on the inside, phloem on the outside
  • veins are distributed across the leaf
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15
Q

How do you stain a plant (e.g. celery) to see the xylem?

A

Put the celery in coloured water - the xylem will be stained

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16
Q

What are 3 components that make up the xylem?

A
  1. Vessels to transport water and minerals
  2. Fibres to support the plant
  3. Some parenchyma to separate and support the xylem vessel
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17
Q

What are xylem vessels?

A

Hollow tubes within parenchyma which is formed by the laying down of a substance called lignin that surrounds the walls of the cells.

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18
Q

How is the xylem vessel formed (3)?

A
  • Lignin makes the walls waterproof and thus kills the cells.
  • The end walls and contents of the cells decay
  • This leaves a long column of dead cells with no contents
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19
Q

What are the 3 ways of lignin arrangements?

A
  1. SPIRAL lignification - lignin is arranged in a spiralling shape
  2. ANNULAR lignification - lignin is arranged in discrete rings across the xylem vessel
  3. RETICULATE lignification - lignin is arranged in a network of broken rings
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20
Q

What are places of incomplete lignification called?

What does this allow?

A

BORDERED PITS - allows water to travel from one vessel to the next vessel or into other living parts of the plant

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21
Q

Give 7 adaptations of xylem vessels.

A
  1. A continuous column is formed for water to move
  2. Narrow tubes so the water column does not break easily and capillary action (upwards movement of water) is effective
  3. Bordered pits to allow water to move from vessel to vessel
  4. Lignification allows xylem to stretch and bend
  5. No cross-walls
  6. No cell contents
  7. Lignin supports the walls from collapsing
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22
Q

What are the two components that make up phloem tissue?

A
  1. SIEVE TUBE ELEMENTS

2. COMPANION CELLS

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23
Q

Describe the structure and their roles of the sieve tube elements in the phloem (3).

A
  • No nucleus and no cytoplasm which allows for mass flow of sap (sucrose dissolved in water)
  • Thin walls
  • Contains perforated cross-walls called SIEVE PLATES which allow movement of water from element to element.
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24
Q

Describe the structure and their roles of companion cells.

A
  • Loads sugars onto the sieve tube elements
  • Large nucleus, dense cytoplasm
  • Contain many mitochondria to load the sucrose
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25
Q

What are the cytoplasmic bridges between plant cells called?

A

Plasmodesmata

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26
Q

What are 3 pathways that water can take when travelling through the roots?

A
  1. APOPLAST: Where water goes in between the cell walls of the cell
  2. SYMPLAST: Where water moves through the cytoplasm
  3. VACUOLAR: Where water moves through the cytoplasm but passes through the vacuoles
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27
Q

What is transpiration?

A

Loss of water vapour from the aerial parts of the plant

especially leaves

28
Q

Where in the leaves is water vapour lost? Give 2 locations.

A
  • some in the cuticle

- most from the stomata

29
Q

What are stomata?

A

Pores on the underside of the leaf which open in the day to allow for gas exchange for photosynthesis - this allows water to be evaporated out.

30
Q

How is water vapour lost (3)?

A
  1. Water enters the leaf via the xylem and moves via osmosis to the spongy mesophyll cells.
  2. Water evaporates from the cell walls of the spongy mesophyll.
  3. Water vapour moves by diffusion out of the leaf through the stomata, relying on a WATER VAPOUR POTENTIAL GRADIENT (high water vapour molecules in the leaf compared to outside so they will move to the outside)
31
Q

Give 4 reasons why Transpiration is beneficial.

A

When water vapour is lost, it must be replaced from below. This draws water up the stem. This allows:

  1. Transportation of useful mineral ions up the plant
  2. Maintenance of cell turgidity
  3. Supply of water for growth, cell elongation and photosynthesis
  4. Supply of water so that, as it evaporates, can keep the plant cool on a hot day.
32
Q

What are the 5 environmental factors that affect the rate of transpiration?

A
  1. Light intensity
  2. Temperature
  3. Relative humidity
  4. Air movement (wind)
  5. Water availability
33
Q

Explain how light intensity affects the rate of transpiration.

A

When there’s light, the stomata open to allow gas exachange for photosynthesis whilst losing water vapour.
Increasing light intensity increases the rate of transpiration.

34
Q

Explain how temperature affects the rate of transpiration (3).

A

Increases the rate of transpiration in three ways:

  1. Increases the rate of evaporation from the cell surfaces so that the water-vapour potential rises in the leaf
  2. Increases the rate of diffusion through the stomata because the water vapour molecules have more Kinetic Energy
  3. Decrease the relative water-potential in the air so diffusion rate increases from the leaf to the outside.
35
Q

Explain how relative humidity affects the rate of transpiration.

A

Higher humidity in the air will decrease the rate of transpiration because there will be a smaller water vapour potential gradient between the air spaces in the leaf and the air outside.

36
Q

Explain how air movement (wind) affects the rate of transpiration.

A

Air moving outside the leaf will carry away water vapour that has just diffused out of the leaf.
This maintains a steep water vapour potential gradient.

37
Q

Explain how water availability affects the rate of transpiration.

A

If there is a lack of water in the soil, the plant cannot replace the water that has been lost.
Also, if there is insufficient water in the soil then the stomata close and the leaves wilt.

38
Q

What is a potometer?

A

A piece of apparatus that can be used to estimate the rate of transpiration by measuring the rate of water uptake by a leafy shoot.

39
Q

Explain how a potometer measures the rate of transpiration (3).

A
  1. Water vapour lost by the leaves is replaced from the water in the capillary tube of the potometer.
  2. The movement of the meniscus at the end of the water column can be measured.
  3. To observe how different environmental factors affect the rate of transpiration, set the potometer under various conditions (e.g. for humidity place the shoot within a plastic bag)
40
Q

State 5 precautions when measuring the rate of transpiration to take to ensure valid results.

A
  1. Set it up under water to makes sure there are no air bubbles inside the potometer
  2. Ensure that the shoot is healthy
  3. Cut the stem under water to prevent air entering the xylem.
  4. Cut the stem at an angle to provide a large surface area in contact with the water.
  5. Dry the leaves
41
Q

Using calculations, explain how you can measure the rate of transpiration (2).

A
  1. Use the ‘Volume of a Cylinder’ equation in the context of the CAPILLARY TUBE (the long tube in the potometer): V = πrl where ‘r’ is the radius of the tube and ‘l’ is the length of the tube
  2. The rate of transpiration is the volume calculated over time taken (Rate = Volume / Time)
42
Q

Explain how the transpiration stream works ACROSS THE ROOT works (5).

A
  1. Mineral ions are absorbed from the soil, making the water potential of cytoplasm more negative.
  2. Water enters the root hair cell by osmosis
  3. Water moves across the root cortex by osmosis via the apoplast pathway
  4. At the end of the root, a layer called the Casparian strip blocks water flow in the apoplast pathway - water must enter via the symplast or vacuolar pathway.
  5. Water/ions enter the medulla and then the xylem.
43
Q

What is the name of the process in which water travels up the stem?

A

Mass Flow

44
Q

What force drives water up the stem?

A

Root pressure

45
Q

What property of water allows it to climb up the xylem (transpiration pull) ?

A

Cohesion - when water molecules are attracted to each other and thus carry themselves as one large column along the xylem

46
Q

In the context of transpiration pull, why is it necessary that xylem vessels are strengthened by lignin?

A

The lignin prevents the vessel from collapsing under the tension that the water creates

47
Q

What property of water allows water to attract along the sides of the xylem vessel?

A

Capillary action - ADHESION. This is the attraction of water molecules to the sides of the xylem vessel.

48
Q

Give 5 structural/behavioural adaptations in which terrestrial plants can reduce their water losses.

A
  1. Waxy cuticle reduces water loss/evaporation through the epidermis
  2. Stomata are found on the underside of the leaves - reduces evaporation due to direct heating from the Sun
  3. Most stomata are closed at night
  4. Deciduous plants lose their leaves in winter
49
Q

What are Xerophytes?

A

Plants that are adapted to live in dry conditions

50
Q

Give 2 examples of xerophytes?

A
  1. Marram grass

2. Cacti

51
Q

State 5 adaptations of marram grass (Ammophila).

A
  1. Leaf is rolled longitudinally so that the air trapped inside the leaf is humid to reduce water loss.
  2. Thick waxy cuticle on the outside of the leaf to reduce evaporation
  3. Stomata are on the inner side of the leaf
  4. Stomata are in pits in the lower epidermis, folded and covered with hair - reduces air movement so reduces air loss
  5. Dense spongy mesophyll, few air spaces - less surface area for water evaporation
52
Q

State 4 adaptations for cacti.

A
  1. They are succulents- stems are ribbed/fluted for expansion
  2. Leaves are reduced to spines to reduce the SA of leaves to reduce water loss
  3. Stem is green for photosynthesis
  4. Roots are very widespread to take advantage of as much water underground as possible
53
Q

What are some features, other than adaptations of marram grass/cacti, do xerophytes perform (3)?

A
  1. Stomata is closed when water availability is low to reduce water loss
  2. Some plants have a low water potential in their leaf cells by maintaining a high salt concentration in the cell to reduce water loss (less steep water potential gradient)
  3. Very long tap root to reach water deep underground
54
Q

What are Hydrophytes?

A

Plants that are adapted to living in water or where the ground is wet.

55
Q

What 2 issues do hydrophytes face?

A
  1. The plants are submerged so they need to find a way of getting oxygen to their tissues.
  2. They also need to keep their leaves in the sunlight for photosynthesis.
56
Q

Give 1 example of a Hydrophyte.

A

Water lillies (family Nymphaeales)

57
Q

State 3 adaptations of water lillies.

A
  1. Many large air spaces in the leaf for buoyancy
  2. Stomata on the upper epidermis so that they’re exposed to the air to absorb sunlight
  3. Stem has many large air spaces to allow oxygen to diffuse quickly to the roots for respiration (also helps for buoyancy)
58
Q

How do hydrophytes transpire?

A

They have structures at the tip of the leaves called HYDATHODES which release droplets which can evaporate from the leaf surface

59
Q

What is TRANSLOCATION?

A

The movement of assimilates throughout the plant, occurring in the phloem.

60
Q

What is a SOURCE?

A

Parts of the plant that LOADS materials (e.g. sucrose) into the transport system

61
Q

Give 1 example of a source and explain why it is one.

A

Leaves - they photosynthesise and the sugars produced are moved to other plants of the plant

62
Q

What is a SINK?

A

Parts of the plant that REMOVES the materials from the transport system

(think of sinks as ‘selfish’ compared to sources)

63
Q

Give 1 example of a sink and explain why it is one.

A

Roots - they receive sugars (from photosynthesis) and store them as starch

Note: roots can also be sources because they can convert the starch back into sugars in the winter.

64
Q

Describe the whole process of Active Loading of sucrose (7).

A
  1. H+ ions are actively pumped from the companion cells using ATP (energy) made by mitochondria.
  2. High concentration of H+ ions enter back into the companion cells via facilitated diffusion through contransporter proteins BUT ONLY IF THEY HAVE SUCROSE.
  3. High concentration of sucrose in the companion cells enters the sieve tube element via diffusion through the plasmodesmata.
  4. Water also enters the phloem by osmosis and this facilitates BULK FLOW of sucrose + water. This increases the HYDROSTATIC PRESSURE in the sieve tube element.
  5. Sap moves down the source (the phloem/sieve tube) from a high hydrostatic pressure to a lower hydrostatic pressure at the SINK.
  6. Sucrose is removed from the sieve tube to the surrounding cells so it increases the water potential in the sieve tube.
  7. Water moves out of the sieve tubes and reduces the hydrostatic pressure.
65
Q

Compare, in terms of differences, of translocation and transpiration. State 4 features for each process.

A

TRANSLOCATION:

  1. ACTIVE process
  2. The force it relies on to drive the materials is HYDROSTATIC PRESSURE
  3. It’s a PUSH of materials
  4. Affected by poisons

TRANSPIRATION:

  1. PASSIVE process
  2. The force it relies on to drive the materials is the COHESION-TENSION theory
  3. It’s a PULL of materials (tension = pulling)
  4. Not affected by poisons

OCR Biology AS Level (13 decks)

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