1. Xylem & Phloem Structure

Question 1

see slide 2 for dia of plant vascular system

Answer 1

xylem, phloem, root hair cells

Question 2

Why do plants require a transport system?

Answer 2

• A transport system ensures that all the cells of a plant receive a sufficient amount of nutrients (eg. Water, minerals, sugars to live)
• Plants are fairly big & have a relatively small SA:V ratio, but have a high metabolic rate
• This is achieved by the combined action of XYLEM tissue and PHLOEM tissue

Plants that have specialised transport systems are known as VASCULAR PLANTS

Question 3

3 reasons why larger organisms require specialised mass transport systems

Answer 3

• Increasing transport distances (due to size)
• SA:V ratio
• Increasing levels of activity (metabolic rate)

Question 4

3 reasons why larger organisms require specialised mass transport systems: Increasing transport distances (due to size)

Answer 4

• Every cell in a plant requires water, glucose & mineral ions.
• The roots of a plant take in water & mineral ions while the leaves produce glucose by photosynthesis
• These molecules need to be transported to other parts of the plant (glucose is transported as SUCROSE in plants)
• This large transport distance makes simple diffusion a non-viable method for transporting substances all the way from the exchange site to the rest of the organism
  - Diffusion wouldn’t be fast enough to meet the metabolic requirements of cells

Question 5

3 reasons why larger organisms require specialised mass transport systems: SA:V ratio

Answer 5

• As the size of a plant INCREASES, its SA:V ratio DECREASES. This is bc volume increases much more rapidly than SA as size increases
• This means is has relatively less SA available for substances to diffuse through, so the rate of diffusion may not be fast enough to meet its cells’ requirements
• Large plants therefore cannot rely on diffusion alone to supply their cells with substances (sa food & oxygen) & to remove waste products
• This is why they require specialised transport systems

Question 6

How are plants adapted to increase SA:V ratio

Answer 6

• Plants have a branching body shape
• Leaves are flat and thin
• Roots have root hairs

Question 7

3 reasons why larger organisms require specialised mass transport systems: Metabolic rate (increasing activity levels)

Answer 7

• Larger organisms are not only more physically active but they also contain more cells than smaller organisms
• A larger no. of cells results in a higher level of metabolic activity
  - As a result, the demand for oxygen & nutrients is greater & more waste is produced
• Plant cells & tissues have a much lower metabolic rate than animal cells
  - Therefore their demand for oxygen for anaerobic respiration is reduced

Question 8

What are Cotyledons

Answer 8

Organs that act as food stores for the developing embryo

Question 9

What are Dicot plants

Answer 9

• Plants that make seeds that contain 2 cotyledons
  There are 2 main groups of dicots:
  
  • Herbaceous dicots (non-woody stem) eg daisies
  • Woody dicots eg oak

Question 10

What are monocot plants

Answer 10

Plants that make seeds that contain 1 cotyledon

Question 11

see slide 11 for comparison between monocot and dicot plants

Question 12

What is the vascular system in plants

Answer 12

• A plant has a series of transport vessels running through the roots, stems & leaves
• This system of vessels is known as the vascular system

Question 13

What are the types of transport vessels that make up herbaceous dicot vascular systems

Answer 13

Xylem & Phloem
- They are arranged tg in vascular bundles in the stem, roots & leaves

Question 14

What are the 2 different plant transport systems

Answer 14

• Transpiration system
• Translocation system

Question 15

What is the transpiration system

Answer 15

• The movement of water molecules & dissolved mineral ions
• Xylem vessels
• Passive process

Question 16

What is the translocation system

Answer 16

• The movement of sugars (sucrose) & amino acids
• Phloem vessel - sieve & companion cells
• Active process

Question 17

Overall water movement in plants

Answer 17

1. Water is absorbed from soil, but is needed all over the plant
2. Water & mineral ions move up stem in xylem
3. Water is lost from the leaves

Question 18

What does xylem do

Answer 18

Transport water & mineral ions up from roots

Question 19

What does phloem do

Answer 19

Transport food (sucrose) up from leaf

Question 20

Overall sugar (sucrose) movement in plants

Answer 20

1. Sugars (glucose) are made in leaves but are needed all over the plant
2. Sugars (as sucrose) move down stem in phloem

Question 21

What is a vascular bundle

Answer 21

• Xylem & Phloem are arranged in vascular bundles in the roots, stems & leaves.
• The arrangement of xylem & phloem is different in different organs

Question 22

Vascular bundle structure

Answer 22

• There is a layer of cambium in between xylem & phloem, that is meristem cells which are involved in production of new xylem & phloem tissue
  (see slide 17, 18 for dia)

Question 23

Location of vascular bundles

Answer 23

The location of vascular bundles is dependent on which organ they are in as the different organs are under different stresses

Question 24

Location of vascular bundles: In roots

Answer 24

• In roots, the vascular bundle is found in the centre
  XYLEM: in the centre core
  EFFECT: This helps the roots withstand the pulling strain they are subjected to as the plant transport water upwards & grows
  PHLOEM: on the edges of the centre core

Question 25

Location of vascular bundles: In stems

Answer 25

• In stems, the vascular bundles are located around the outside
  XYLEM: on the inside (closest to centre of the stem) to help support the plant
  PHLOEM: on the outside (closest to the epidermis)

Question 26

Location of vascular bundles: In leaves

Answer 26

In leaves, the vascular bundles form the midrib & veins and therefore spread from the centre of the leaf in a parallel line.
XYLEM: on the upper side of the bundles (closest to upper epidermis)
PHLOEM: on the lower side of the bundles (closest to lower epidermis)

Question 27

see slide 21 for dia of xylem, phloem, cambium

Question 28

Vascular bundles in roots

Answer 28

In the endodermis around the vascular bundle of the root, there is a layer of meristem cells that from the pericyclic.
- this provides a ‘drill’ like structure, enabling the plant to push down into soil
- xylem tissue is strongest so is in centre (X)
- phloem in 4 separate sections
(slide 22)

Question 29

Vascular bundles in leaf

Answer 29

• Xylem located on top of phloem
• This only applies to to dicotyledonous plants (other plant types have a diff structure)
  (slide 23)

Question 30

Vascular bundles in stem

Answer 30

• Xylem located on the inside (in non-wooded plants)
• Provides additional support to the stem
• The cambium layer contains meristem cells
  (slide 25)

Question 31

Differences in location of vascular bundles in leaves, stem, root

Answer 31

slide 26

Question 32

Vascular bundles in dicot and monocot STEM

Answer 32

slide 27, 28

Question 33

Structure of xylem

Answer 33

• A dead tissue - no cytoplasm, no nuclei
• Hollow tubes - no end walls, allows water to pass through easily
• Cell wall contains spiralised lignin - gives tissue high strength, prevents collapse
• Pits in wall (non-lignified areas) - water/ions move into/out of vessels through these

Question 34

Function of xylem

Answer 34

• Transports water & dissolved minerals upwards from the root hair cells to the leaves
• This is called the transpiration stream

Question 35

What is xylem

Answer 35

Very long, tube-like structures formed from cells joined end to end

Question 36

Lignin in relation to time

Answer 36

The mount of lignin in xylem increases as cell gets OLDER