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Wjec Biology Unit 2 > 2.3 Plants > Flashcards

2.3 Plants Flashcards

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1
Q

What are the three levels of transport in plants

A

Cellular uptake
Tissue transport
Whole plant transport

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2
Q

Where are water and ions mainly absorbed

A

Through root hair cells

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3
Q

Function of epidermis in roots

A

Root hair - uptake of water and mineral ions

Protect roots as they grow through soil

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4
Q

Cortex parenchyma function

A

Acts as storage organ

Intercellular spaces allow movement of water and ions

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5
Q

Endodermis function

A

Has waterproof layer to force water and ions into the cytoplasm of the endodermal cells
Controls transport in the xylem

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6
Q

Pericycle function

A

Role in controlling transport into xylem

Site of lateral root growth

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7
Q

Xylem function

A

Transports water and ions from the roots to the stem and leaves.
Provides support for the plant.

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8
Q

Phloem function

A

Transports the products of photosynthesis to the roots from the leaves.

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9
Q

Cambium function

A

Meristematic tissue that can undergo mitosis to produce more xylem and phloem

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10
Q

Look

A

Root

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11
Q

Look

A

Root

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12
Q

Look

A

Root hair cell

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13
Q

Function of cuticle

A

Reduces water loss from evaporation

Transparent to allow light to pass through photosynthesis

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14
Q

Function of epidermis in stem

A

Protection of stem

May have hairs to deter insects/animals from eating them

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15
Q

Collenchyma function in stem

A

Cell walls thickened with cellulose to strengthen the stem while remaining flexible

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16
Q

Cortex parenchyma function in stem

A

Can act as a storage organ

Intercellular spaces allow movement of water and ions and gases.

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17
Q

Pith parenchyma function in stem

A

Thin-walled cells that act as packing tissue

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18
Q

Sclerenchyma function in stem

A

Lignified cells that provide strength and support to the stem

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19
Q

Look

A

Stem

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20
Q

Look

A

Stem

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21
Q

What cell types found in xylem?

A

Xylem vessels
Tracheids
Xylem parenchyma

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22
Q

Xylem vessels function

A

Transport water and minerals from the roots to other parts of a plant
End walls of these break down to form long tubes that extend from roots to stem and leaves

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23
Q

Tracheids function in xylem

A

Provide strength to tissue

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24
Q

Xylem parenchyma function

A

Thin walled, living cells

Act as packing tissue between xylem vessels

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25
Q

What kind of tissue

A

Xylem

26
Q

Which cell types of xylem are dead?

A

Tracheids and xylem vessels

27
Q

What are the walls of tracheids and xylem vessels made up of?

A

Lignin

Impermeable to water

28
Q

Phloem sieve tubes

A

Contain little cytoplasm
Few or no organelles
Cell walls made of cellulose

29
Q

Companion cells

A

Accompany sieve tubes
Provide support to sieve tubes
Involved in transport of substances in and out of sieve tubes
Have many mitochondria- active transport

30
Q

How are companion cells and sieve tubes connected

A

Plasmodemata

31
Q

Look

A

Phloem

32
Q

What are sieve tubes and their function

A

End walls of phloem sieve tubes are perforated by small pores
Strands of cytoplasm pass through the pores from one phloem sieve tubes to next

33
Q

Look

A

Phloem

34
Q

What does the vascular bundle contain

A

Xylem
Phloem
Cambium
Other cells

35
Q

What can root pressure do

A

Push water up the xylem against gravity

36
Q

What is guttation

A

When water that reaches the leaves us forced out which causes a beading of water upon the leaf tips

37
Q

What is root pressure caused by

A
  • active transport of ions into stele - lowers water potential
  • water passively flows into roots - pushing water up
  • gravity acts against it so that very little is formed in tall plants as weight of water pushes down on contents
38
Q

What is the transpiration stream

A

A constant stream of water molecules is formed between roots and leaves

39
Q

Explain the transpiration stream

A
  • stomata opens to let CO2 in
  • water vapour leaves air spaces via stomata
  • water potential is lowered in leaves so a water potential gradient between roots, leaves and outside air
  • water lost by leaves replaced by evaporation of thin layer of water that clings to mesophyll cells
  • as water evaporates it is replaced by water clinging to inside of air spaces
  • a tension on the water in xylem which pulls water to direction of water loss
40
Q

How does cohesion and adhesion affect transpiration stream

A

Cohesion - water is strong enough to transmit the pulling force down to roots
Adhesion - of water to lignin cells of xylem aids in resisting gravity

41
Q

What is transpiration?

A

Process by which plants give off water vapour through openings in their leaves

42
Q

How is water lost

A

Mainly - stomatal opening in leaves
Water used during photosynthesis
Water retained in cells for support
Water produced through respiration

43
Q

When will plants wilt

A

Water loss exceeds water uptake

Leaves and stems lose turgor pressure

44
Q

Conditions for plants to wilt

A

Hot
Sunny
Windy

45
Q

How does temperature affect rate of water uptake in plants

A

More temperature
More kinetic energy
Faster diffusion, evaporation and osmosis

46
Q

How does humidity affect water uptake in plants

A

More humid
More water vapour in the air
Decreases water potential gradient
Less water molecules diffuse out the cell

47
Q

How does wind speed affect rate of water uptake in plants

A

Wind speeds increases
Water vapour on surface of leaf is blown away
Water potential gradient in and out the leaf increases
Higher rate of diffusion

48
Q

How does light intensity affect rate of water uptake of plants

A

More light intensity
Rate of photosynthesis in guard cells of stomata increase
Stomata more likely to open
Higher rate of diffusion of water from leaf

49
Q

How to prove water is lost from leaves

A

Anhydrous cobalt paper
Dark blue - no water
Pink - absorbs water

50
Q

How to measure water loss

A

Measure loss of mass over time
Need layer of oil on surface of water to prevent evaporation
Shoot cut underwater to ensure air doesn’t enter xylem

51
Q

How to measure water uptake

A

Use a potometer

Rate of water uptake = length of bubblexpi(radius) squared / time taken

52
Q

What is translocation

A

Process of moving the products of photosynthesis from where they are made or stored to other parts of the plant

53
Q

What is main mechanism of phloem transport

A

Mass flow hypothesis

54
Q

Mass flow hypothesis during daytime?

A
  1. Glucose produced during photosynthesis- SOURCE. Glucose converted into sucrose
  2. Sucrose is passed into phloem sieve tubes through a number of routes
  3. Water potential of sieve tubes lowered
  4. Water moves into sieve tubes from xylem through osmosis (hydrostatic pressure increases close to source so sieve tube contents move down tube whilst carrying sucrose)
  5. Roots and growth points have high requirements for glucose for storage/respiration SINKS. Sucrose is unloaded into tissues where it’s converted into glucose/starch/ other carbohydrates
  6. Increasing sugar concentration in the tissues of sinks lowers water potential and water moves out the phloem via osmosis
  7. Excess water enters xylem
55
Q

Mass flow hypothesis during the night

A
  • no photosynthesis
  • all tissues need glucose for respiration - become SINKS
  • storage organs become SOURCE
  • translocation direction is reversed
56
Q

Evidence against mass flow hypothesis

A

• real hydrostatic pressure not as high as calculated
• sieve plates slow down transport through sieve tubes and reduce hydrostatic pressure
• The mass flow hypothesis suggests that ATP is only involved in the loading of the sieve tubes and that
movement through the sieve tubes is passive - evidence shows that sieve tubes use ATP along their
whole length and this suggests that the process is active.
• It has been found that substances move in opposite directions at the same time in the same phloem sieve
tube.
• Some substances move at different rates in the same sieve tube even when moving in the same
direction.

57
Q

Alternative theories mot mass flow

A

Electro-osmosis
Cytoplasmic streaming
Protein contraction/ peristalsis
All active

58
Q

Investigating translocation through ringing

A

Removing bark and phloem from stem
OR
Leaving different widths of bark intact
• wider strip = higher mass of carbohydrate transported to lower parts of the plant

Concluded
• transport from leaves must be in phloem - swelling above removal of phloem
• sugars must be transported in phloem - top of shoot unaffected so obtaining sugars for respiration and other materials for growth - lower part of stem and roots grow less well as sugars dont get to them from leaves

59
Q

Investigating translocation through use of radio-isotopes

A

Exposing leaves to radioactive CO2
Substances made of photosynthesis would be radioactive - becomes exposed under X-ray
Black regions in phloem
Concluded
• transport of carbon compounds from leaves is bi-directional - above and below site of photosynthesis using 14CO2
• photosynthesis products transported in phloem - radioactive compound only detected in phloem

60
Q

Investigating translocation using aphids

A

Aphids feed by inserting stylet into phloem sieve tube
Stylet (mouthpart) is hollow so used to feed on sugar-rich contents of phloem
If aphids anaesthetised body can be removed and leaving stylet in place
Fluid is produced from cut end of stylet and can be collected
Content composed mainly sugars and amino acids
Rate of transpiration can be determined by exposing leaves to radioactive CO2 or roots to radioactive ions

Wjec Biology Unit 2 (5 decks)

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