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Biology > 3.3 > Flashcards

3.3 Flashcards

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1
Q

Why do plants need a transport system?

A
  • Larger plants have a smaller Surface area to Volume ratio. Diffusion is sufficient for oxygen demand but not for other substances
  • Movement of water and minerals from the roots up the leaves
  • Movement of Sugars from the leaves to the rest of the plant
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2
Q

What is the role of the Xylem?

A

Movement of water and soluble mineral ions upwards

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3
Q

What is the role of the Phloem?

A

Movement of assimilates, such as sugars, up or down

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4
Q

What are dicotyledonous plants?

A

Plants with two seed leaves and a branching pattern of veins in the leaf

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5
Q

What is the formation of the Xylem and Phloem in the young root?

A
  • Xylem forms an X shape
  • Phloem is found between the arms of the X

This arrangement provides strength to withstand the pulling forces to which roots are exposed.

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6
Q

What is the endodermis?

A

Around the vascular bundle there is a special sheath of cells called the endodermis. It has a role in getting water into the xylem vessels.

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7
Q

What is the Pericycle?

A

A layer of meristematic cells just inside the endodermis

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8
Q

What is the formation of the Xylem and Phloem in the stem?

A

The vascular bundles are found near the outer edge.

The Xylem is found towards the inside of each vascular bundle.

The phloem is found towards the outside of each vascular bundle

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9
Q

What is Cambium?

A

A layer of meristematic cells that divide to produce new xylem and phloem cells.

It is found in between the xylem and phloem.

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10
Q

What is the formation of the Xylem and Phloem in the leaf?

A

The vascular bundles form the midrib and veins of a leaf.

Within each vein, the xylem is on top of the phloem

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11
Q

Explain why plants do not need a transport system for gases such as oxygen?

A

Plants are not active, so demand for oxygen is low; a leaf is flat, so all tissues are close to the surface; living tissues of stem are also close to surface; diffusion is sufficient to satisfy oxygen demand; oxygen is produced in tissues during photosynthesis.

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12
Q

What does Xylem TISSUE consist of?

A
  • Vessels to carry the water and dissolved mineral ions
  • Fibres to help support the plant
  • Living parenchyma cells which act as packing tissue to separate and support the vessles
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13
Q

What are the features of a Xylem vessel?

A
  • A long column of dead cells with no cellular contents
  • Patterns within the cell wall. These may be spiral, annular, or reticulate.
  • Bordered pits between adjacent vessels
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14
Q

What is the role of Lignin?

A
  • Lignin impregnates the walls of the cells, making them waterproof. This kills the cells.
  • Lignin strengthens the vessel walls and prevents the vessels from collapsing. This keeps the vessels open at all times.
  • Lignin thickening creates patterns in the cell wall. These may be spiral, annular, or reticulate.
  • Incomplete lignification creates boarded pits.
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15
Q

What is the role of the patterns in the cell wall?

A

The patterns allow the xylem to be flexible and to stretch as the plant grows.

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16
Q

What is the role of Bordered pits?

A

The bordered pits between two adjacent vessels allow water to leave one vessel and pass into the next vessel.

They also allow water to leave the xylem and pass into living parts of the plant.

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17
Q

Explain why the flow of water in Xylem vessels is not impeded?

A
  • There are no cross walls
  • There are no cell contents
  • Lignin thickening prevents the walls from collapsing
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18
Q

What does Phloem TISSUE consist of?

A
  • Sieve tube elements
  • Companion cells
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19
Q

What are the features of Sieve Tube Elements?

A
  • Contain very little cytoplasm and no nucleus
  • Contain perforated cross-walls called sieve plates
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20
Q

What is the role of Sieve Plates?

A

The perforations in the sieve plate allow movement of the sap from one element to the next.

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21
Q

What are companion cells?

A

The cells that help to load sucrose into the sieve tubes by carrying out metabolic processes

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22
Q

What are the features of Companion cells?

A
  • Large Nucleus
  • Dense Cytoplasm
  • Numerous Mitochondria
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23
Q

What is the apoplast pathway?

A

Water passes through the spaces in the cell walls and between the cells. It does not pass through any plasma membranes into the cell.

This means that the water moves by mass flow rather than by osmosis.

Also, dissolved mineral ions and salts can be carried with the water.

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24
Q

What is the symplast pathway?

A

Water enters the cell cytoplasm through the plasma membrane.

It can then pass through the plasmodesmata from one cell to the next.

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25
Q

What is the vaculoar pathway?

A

Water enters the cell cytoplasm but is able to enter and pass through vacuoles as well.

26
Q

What is transpiration?

A

Transpiration is the loss of water vapor from the aerial parts of a plant, mostly through the stomata in the leaves.

27
Q

What route does water take when leaving a plant?

A
  1. Water enters the leaf through the xylem and moves by osmosis into the cells of the spongy mesophyll. It may also pass along the cell walls via the apoplast pathway.
  2. Water evaporates from the cell walls of the spongy mesophyll
  3. Water vapor moves by diffusion out of the leaf through the open stomata. This relies on the water vapor potential gradient.
28
Q

Why is transpiration important?

A
  • Transports useful mineral ions up the plant
  • Maintains cell turgidity
  • Supplies water for growth, cell elongation and photosynthesis
  • Supplies water that, as it evaporates, can keep the plant cool.
29
Q

What is the effect of light intensity on transpiration?

A
  • In light, stomata open to allow gaseous exchange for photosynthesis.
  • Higher light intensity increases the transpiration rate.
30
Q

What is the effect of temperature on transpiration?

A

A higher temperature will increase the rate of transpiration in three ways. It will:

  • Increase the rate of evaporation from the cell surfaces so that the water-vapour potential in the leaf rises
  • Decrease the relative water vapour potential in the air, allowing more rapid diffusion of molecules out of the leaf
  • Increase the rate of diffusion through the stomata because the water molecules have more kinetic energy
31
Q

What is the effect of relative humidity on transpiration?

A

Higher relative humidity in the air will decrease the rate of water loss.

This is because there will be a smaller water vapour potential gradient between the air spaces in the leaf and the air outside.

32
Q

What is the effect of air movement on transpiration?

A

Air moving outside the leaf will carry away water vapour that has just diffused out of the leaf.

This will maintain a high water vapor potential gradient.

33
Q

What is the effect of water availability on transpiration?

A

If there is little water in the soil, then the plant cannot replace the water that is lost.

If there is insufficient water in the soil, then the stomata close and the leaves wilt.

34
Q

What features of a plant will affect transpiration?

A
  • Leaf surface area - larger surface area provides more surface for evaporation and diffusion.
  • Number of leaves - more leaves provide more surface for evaporation and diffusion.
  • Number of stomata - more stomata allow greater loss of water vapour by diffusion.
  • Thickness of waxy cuticle - thinner cuticle allows more evaporation.
35
Q

What is a potometer?

A

A device that can measure the rate of uptake of water as a leay stem transpires.

36
Q

What is the transpiration stream?

A

The movement of water from the soil, through the plant, to the air surrounding the leaves.

37
Q

What is the pathway of water through the root?

A
  • Water moves into root hair cells
  • The water then moves across the root cortex down a water potential gradient to the endodermis of the vascular bundle.
  • Water may also travel through the apoplast pathway as far as the endodermis, but must then enter the symplast pathway, as the apoplast pathway is blocked by the Casparian strip
38
Q

What is the Casparian Strip?

A

A waxy layer on the endodermis of the root which forces water and minerals to enter the cell cytoplasm through the plasma membranes.

39
Q

How is water moved into the Xylem?

A
  • The plasma membranes contain transporter proteins, which actively pump mineral ions from the cytoplasm of the cortex cells into the medulla and xylem.
  • This makes the water potential of the medulla and xylem more negative, so that that water moves from the cortex cells into the medulla and xylem by osmosis.
  • Once the water has entered the medulla, it cannot pass back into the cortex, as the apoplast pathway of the endodermal cells is blocked by the casparian strip.
40
Q

What process moves water up the stem?

A

Mass Flow

41
Q

What are the three processes that move water up the stem?

A
  • Root Pressure
  • Transpiration Pull
  • Capillary Action
42
Q

How does root pressure affect the movement of water?

A

The action of the endodermis moving minerals into the medulla and xylem by active transport draws water into the medulla by osmosis.

Pressure in the root medulla builds up and forces water into the xylem, pushing the water up the xylem

43
Q

How does transpirational pull affect the movement of water?

A

The loss of water by evaporation from the leaves must be replaced by water coming up from the xylem.

Water molecules are attracted to each other by forces of cohesion. These cohesion forces are strong enough to hold the molecules together in a long chain or column.

As the molecules of water are lost at the top of the column, the whole column is pulled up as one chain.

The pull from above creates tension. Hence the cohesion-tension theory.

44
Q

How does Capillary action affect the movement of water?

A

Adhesion holds the water molecules within the xylem to the side of the xylem vessel.

Because the xylem is very narrow, these forces can pull the water up the sides of the vessel.

45
Q

How does water actually leave the leaf?

A

Water evaporates from the cells lining the cavity immediately above the gaurd cells.

This lowers the water potential in these cells, causing water to enter thme by osmosis froom neighbouring cells.

In turn, water is drawn in from the xylem in the leaf by osmosis.

46
Q

What are the general adaptations of terrestrial plants?

A
  • A waxy cuticle on the leaf will reduce water loss due to evaporation through the epidermis
  • The stomata are on the undersurface of a leaf so as to reduce evaporation due to direct heating
  • Most stomata are closed at night
  • Some plants lose their leaves in water when temperatures are too low for photosynthesis
  • Long tap roots to reach water underground
  • Low water potential in leaves to reduce evaporation
47
Q

What is a xerophyte?

A

A plant adapted to living in dry conditions

48
Q

What are the adaptations of Cacti?

A
  • The leaves are reduced to spines. This reduces the surface area of the leaves which reduces transpiration
  • The stem is green for photosynthesis
  • The roots are widespread in order to take advantage of rainfall
49
Q

What are the adaptations of Marram grass which lives in sand dunes?

A
  • There is a thick waxy cuticle to reduce evaporation
  • Spongy mesophyll is very dense so there is less surface area for evaporation
  • Leaves are rolled longitudinally to increase humidity to reduce evaporation
50
Q

What is a hydrophyte?

A

A plant adapted to living in water or where the ground is very wet

51
Q

What are the general adaptations of water-based plants?

A
  • Large air spaces in the leaf. This keeps the leaves afloat so they can absorb sunlight.
  • The stomata are on the upper epidermis so that they are exposed to the air to allow gaseous exchange
  • The leaf stem has many large air spaces. This helps with buoyancy, but also allows oxygen to diffuse quickly to the roots for aerobic respiration.
52
Q

How do water-based plants transpire?

A

Many plants contain specialized structures at the tips of their leaves called hydathodes.

These structures can release water droplets which may then evaporate from the leaf surface.

53
Q

What are assimilates?

A

Substances that have become a part of the plant

54
Q

What is the sink?

A

A part of the plant where those materials are removed from the transport system (Phloem).

55
Q

What is the source?

A

A part of the plant that loads materials into the transport system (Phloem).

56
Q

What is translocation?

A

The transport of assimilates throughout a plant

57
Q

How is sucrose moved into the sieve tubes?

A
  • Glucose is converted to sucrose
  • H+ ions are actively transported out of the companion cells
  • Sets up a H+ concentration gradient
  • They can only diffuse back into the companion cell through co-transport of H+ and sucrose
  • As the concentration of sucrose in the companion cell increases, it can diffuse through the plasmodesmata into the sieve tube
58
Q

How does sucrose move through the phloem?

A

Sucrose moves through by mass flow/ bulk transport.

The solution is called sap, and it can be made to flow either up or down the plant as required

59
Q

What causes movement as the Source?

A
  • As sucrose moves into the phloem the water potential decreases. This causes water to move into the phloem.
  • The hydrostatic pressure then increases at the source. This sets up a pressure gradient.
  • Sap moves from higher hydrostatic pressure to lower hydrostatic pressure.
60
Q

How is the sucrose unloaded?

A
  • Diffusion of sucrose from phloem to surrounding cells
  • Occurs wherever cells need glucose / sucrose
  • Water leaves phloem to surrounding cells / xylem
  • Results in lower hydrostatic pressure
61
Q

What causes movement as the Sink?

A
  • Sucrose can be removed by either diffusion or by active transport.
  • This increases the water potential, so that water moves out of the sieve tube into the surrounding cells. This reduces the hydrostatic pressure in the phloem at the sink.

Biology (6 decks)

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