1. Xylem & Phloem Structure Flashcards
(41 cards)
1
Q
see slide 2 for dia of plant vascular system
A
xylem, phloem, root hair cells
2
Q
Why do plants require a transport system?
A
- 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
3
Q
3 reasons why multicellular plants require specialised mass transport systems
A
- Increasing transport distances (due to size)
- SA:V ratio
- Increasing levels of activity (metabolic rate)
4
Q
3 reasons why multicellular plants require specialised mass transport systems: Large transport distances (due to size)
A
- 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
5
Q
3 reasons why multicellular plants require specialised mass transport systems: SA:V ratio
A
- As the size of a plant increases, its SA:V ratio decreases (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 & to remove waste products
- Therefore, they require specialised transport systems
6
Q
How are plants adapted to increase SA:V ratio
A
- Plants have a branching body shape
- Leaves are flat and thin
- Roots have root hairs
7
Q
3 reasons why multicellular plants require specialised mass transport systems: Metabolic rate (increasing activity levels)
A
- 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
8
Q
What are Cotyledons
A
Organs that act as food stores for the developing embryo
9
Q
What are dicot plants
A
- 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
10
Q
What are monocot plants
A
Plants that make seeds that contain 1 cotyledon
11
Q
see slide 11 for comparison between monocot and dicot plants
A
12
Q
What is the vascular system in plants
A
- A plant has a series of transport vessels running through the roots, stems & leaves
- This system of vessels is known as the vascular system
13
Q
What are the types of transport vessels that make up herbaceous dicot vascular systems
A
Xylem & Phloem
- They are arranged tg in vascular bundles in the stem, roots & leaves
14
Q
What are the 2 different plant transport systems
A
- Transpiration system
- Translocation system
15
Q
What is the transpiration system
A
- The movement of water molecules & dissolved mineral ions
- Xylem vessels
- Passive process
16
Q
What is the translocation system
A
- The movement of sugars (sucrose) & amino acids
- Phloem vessel - sieve & companion cells
- Active process
17
Q
Overall water movement in plants
A
- Water is absorbed from soil, but is needed all over the plant
- Water & mineral ions move up stem in xylem
- Water is lost from the leaves
18
Q
Overall sugar (sucrose) movement in plants
A
- Sugars (glucose) are made in leaves but are needed all over the plant
- Sugars (as sucrose) move down stem in phloem
19
Q
What is a vascular bundle
A
- Xylem & Phloem are arranged in vascular bundles in the roots, stems & leaves.
- The arrangement of xylem & phloem is different in different organs
20
Q
Vascular bundle structure
A
- 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)
21
Q
Location of vascular bundles
A
The location of vascular bundles is dependent on which organ they are in as the different organs are under different stresses
22
Q
Location of vascular bundles: In roots
A
- 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
23
Q
Location of vascular bundles: In stems
A
- 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)
24
Q
Location of vascular bundles: In leaves
A
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)
25
see slide 21 for dia of xylem, phloem, cambium
26
Vascular system in a **root**
In the **endodermis** around the vascular bundle of the root, there is a layer of **meristem cells** that form the **pericyclic**.
- This provides a 'drill' like structure, enabling the plant to **push** down into soil
- **Xylem** tissue is strongest so is in centre ( as an 'X')
- **Phloem** in 4 separate sections surrounding the xylem
(slide 22, pg88)
27
Vascular system in a **leaf**
- **Xylem** located on top of **phloem**
- The xylem & phloem make up a **network of veins** which support the thin leaves
- This only applies to to dicotyledonous plants (other plant types have a diff structure)
(slide 23, pg88)
28
Vascular system in the **stem**
- **Xylem** located on the **inside** (in non-wooded plants) & **phloem** on the **outside**
- The xylem & phloem are **near the outside** in stems, to provide **support** that reduces bending
- The **cambium layer** contains **meristem cells**
(slide 25, pg88)
29
Differences in location of vascular bundles in leaves, stem, root
slide 26, pg88
30
Vascular bundles in dicot and monocot STEM
slide 27, 28
31
Function of Xylem tissue
- **Transports water** & dissolved minerals upwards from the root hair cells to the leaves
- This is called the **transpiration stream**
32
Structure of Xylem tissue
- **Long, tube-like** structures formed from cells joined end to end
- A **dead tissue** - no cytoplasm, no nuclei
- **No end walls** making an **uninterrupted tube** - allows water to pass through easily
- Walls contains **spiralised lignin** - gives xylem tissue support, prevents from collapsing inwards (amount of lignin increases as cell gets older)
- **Small pits** in walls (non-lignified areas) - water & ions move into/out of vessels through these non-lignified areas
(pg88)
33
Function of Phloem tissue
Transports **solutes** (dissolved substances), mainly sugars like sucrose, up & down plants
34
Structure of Phloem tissue
Like xylem, phloem is formed from cells arranged in **tubes**. BUT, unlike xylem, its purely a **trasnport tissue** - isn't used for support as well
- Contains **phloem fibres, phloem parenchyma, sive tube elements & companion cells**
35
Structure of Phloem tissue: **Sieve tube elements**
1. These are **living cells** that form the tube for **transporting solutes** through the plant
2. They are joined **end to end** to form **sieve tubes**
3. The **"sieve'** parts are the **end walls**, which have lots of **holes** in them - allowing **solutes** to pass through
4. Unusually for living cells, sieve tube elements have **no nucleus, a very thin layer of cytoplasm & few organelles**
5. The cytoplasm of adjacent cells is **connected** through the holes in the sieve plates
(pg89)
36
Structure of Phloem tissue: **Companion cells**
1. The **lack** of a **nucleus & other organelles** in sieve tube elements, means they **cant survive** on their own. So theres a **companion cell** for **every** sieve tube element
2. Companion cells carry out the living functions for **both** themselves & their sieve cells.
Eg. they provide the energy for the active transport of solutes
37
What is a plant's **vascular system**
Xylem & Phloem make up a plant's **vascular system**. They are found **throughout** a plant & **transport materials** to all parts.
38
Other way of referring to plants with wooded stems
Herbaceous dicotyledonous plants
39
What are transverse cross-sections
- The position of the xylem & phloem in the root, leaf & stem are shown in **transverse cross-sections**.
- This refers to sections cut through each structure at a **right angle** to its **length**
40
What are longitudinal cross-sections
- These are taken **along the length** of a structure.
- For eg, theyre used to show where the xylem & phloem are located in a typical stem (see pg88)
41
Method to dissect plant stems
1. Use a **scalpel** to cut a **cross-section** of the stem (transverse or longitudinal). Cut the sections as **thinly** as possible - thin sections are better for viewing under a microscope
2. Use **tweezers** to gently place the cut sections in **water** until you come to use them. This stops them from **drying out**
3. Transfer each section to a dish containing a **stain**, eg **toluidine blue (TBO)**, & leave for 1min. TBO stains the **lignin** in the walls of the xylem vessels **blue-green**. This will let you see the **position** of the xylem vessels & examine their **structure**
4. **Rinse off** the sections in water & **mount** each one onto a slide
5. Examine the plant tissue under a **microscope** & **draw**
