3.3. Transport in plants Flashcards
1
Q
What is a dicotyledonous plant?
A
A plant with two seed leaves ans a branching pattern of veins in the leaves.
2
Q
What is the meristem?
A
A layer of dividing cells.
3
Q
What is the phloem?
A
Transports dissolved assimilates.
4
Q
What is the vascular tissue?
A
Consists of cells specialised for transporting fluids by mass flow.
5
Q
What is the xylem?
A
Transports water and minerals.
6
Q
Why do plants need a transport system?
A
Plants need a transport system to move:
- water and minerals from the roots up to the leaves.
- Sugars from the leaves to the rest of the plant.
7
Q
What does the plants vascular tissue consist of?
A
- Xylem tissue- transports water and soluble mineral ions up the xylem.
- Phloem tissue- transports assimilates, such as sugars up and down the phloem.
8
Q
What may the vascular bundle contain to provide strength and support for the plant?
A
Collenchyma and sclerenchyma.
9
Q
What does the vascular bundle look like in the root of a plant?
A
The vascular bundle is found in the centre of the root. There is a central core of xylem in the shape of an X. The phloem is found in between the arms of the X-shaped xylem tissue. This arrangement provides strength to withstand the pulling forces to which roots are exposed to.
10
Q
What is found around the vascular bundle in the roots?
A
Around the vascular bundle is a special sheath of cells called the endodermis. The endodermis has a key role of getting water into the xylem vessels.
Just inside the endodermis is a layer of meristem cells called the pericycle.
11
Q
What does the vascular bundle look like in the stem?
A
The vascular bundle is found near the outside of the edge of the stem.The xylem is found towards the inside of each vascular bundle and the phloem towards the outside. In between the xylem and the phloem, is a layer of cambium (a layer of meristem that divides into new xylem and phloem).
12
Q
How may the vascular bundles look different in the stems of woody and non-woody plants?
A
In non-woody plants, the bundles are separate and discreet. In woody plants, the bundles are separate in young stems, but become a continuous ring in older stems.
13
Q
What does the vascular bundle look like in the leaf?
A
The vascular bundle form the midrib and veins of a leaf. A dicotyledonous leaf has a branching network of veins that get smaller as they spread away from the midrib. Within each vein, the xylem is located on top of the phloem.
14
Q
What does the dissection of plant material to examine the distribution if vascular tissues require?
A
Staining the tissues.
15
Q
What is a companion cell?
A
The cells that help to load sucrose into the sieve tubes.
16
Q
What are the sieve tube elements?
A
They make up the tube in the phloem tissue the carry sap up and down the plant. The sieve tube elements are separated by the sieve tube plates.
17
Q
What do xylem tissues consist of?
A
- Vessels to carry water and dissolved minerals.
- Fibres to support the plant.
- Living parenchyma cells which act as packing tissue to separate the support the vessels.
18
Q
How do xylem vessels form?
A
As xylem vessels develop, lignin impregnates the walls of the cells, making the walls waterproof. This kills the cells. The end walls and contents of the cells decay, leaving a long column of dead cells with no contents.
19
Q
What does the lignin provide the xylem vessel?
A
Strengthens the vessel and prevents the vessels from collapsing. This keeps the vessel open at all times when water may be in short supply.
20
Q
How does the lignin strengthen the xylem?
A
The lignin thickening forms a pattern in the cell wall. These may be spiral, angular or reticulate. This prevents the vessel from being too rigid and allows some flexibility of the stem to branch.
21
Q
Where in the xylem vessel may lignification not be complete?
A
In some places, lignification is not complete, leaving gaps in the cell wall. These gaps from bordered pits. The bordered put in two adjacent vessels the aligned to allow water to leave one vessel and pass into the next vessel.
22
Q
How are xylem vessels adapted to their function?
A
- They are made from dead cells aligned end to end to form a continuous column.
- The tubes are narrow, so that the water column does not break easily and capillary action can be effective.
- bordered pits in the lignified walls allow water to move sideways from one vessel to another.
- Lignin deposited in the walls in spiral, annular or reticulate patterns allow xylem to stretch as the plant grows, and enables stem the branch.
23
Q
Why isn’t the flow of water impeded in the xylem vessel?
A
- There are no cross-walls.
- There are no cell contents, nucleus or cytoplasm.
- Lignin thickening prevents walls from collapsing.
24
Q
What does the phloem transport?
A
Assimilates (mainly sucrose and amino acids).
25
What is the phloem made up of?
Phloem tissue consists of sieve tubes- made up of sieve tube elements - and companion cells.
26
What is the structure of a phloem vessel?
**Elongated sieve tube elements** are lined up end to end to form **sieve tubes.** They contain **no nucleus and very little cytoplasm**, leaving space for **mass flow of sap** to occur. At the ends of the sieve tube elements are **proliferated cross-walls called sieve plates**. The sieve tubes are usually 5/6 sided.
27
What is the function of the sieve plates?
They serve as a mechanism to block the sieve tubes after injury or infection. The pores in the sieve plate rapidly become blocked with the deposition of callose. This prevents the loss of sap and inhibits the transport of pathogens around the plant.
28
What are companion cells and where can they be found?
In between sieve tubes are companion cells. they each have a **large nucleus and dense cytoplasm**. They have **numerous mitochondria** and **produce ATP** needed for active processes. The companion cells carry out metabolic needed to **load assimilates into the sieve tubes**.
29
What are plasmodesmata?
Gaps in the cell wall containing cytoplasm the connects two cell walls.
30
Are cellulose cell walls permeable to water?
Cellulose cell walls are **fully permeable to water**.
31
How can water move across plant cells?
Water can pass across the **cell wall** and through the partially permeable **plasma membrane** into the **cell cytoplasm** or even into the **vacuole**.
32
What is it called when the cytoplasm of one cell is connected to another?
A cytoplasmic bridge or a plasmodesmata.
33
What is a cytoplasmic bridge?
Cell junctions at which cytoplasm of one cell is connected so that of another through a gap in their cell walls. These junctions are also called plasmodesmata.
34
How many possible pathways are there for water to travel through a plant?
3.
35
What are the 3 pathways water can take through a plant?
* The apoplast pathway.
* The symplast pathway.
* The vacuolar pathway.
36
What is the apoplast pathway?
Water passes through **the spaces in the cell walls and between cells**. It does not pass through any plasma membranes into the cells. This means the water moves by mass flow not osmosis. Dissolved mineral ions ans salts can be carried with the water.
37
What is the symplast pathway?
Water enters the **cytoplasm through the plasma membrane**. It can then pass through the plasmodesmata from one cell to the next.
38
What is the vacuolar pathway?
This is similar to the symplast pathway, but the **water is not confined the the cytoplasm** of the cells. It is able to **enter the vacuoles** instead.
39
What causes a plant to take up water?
A plant will take up water by osmosis. This is because the water potential in the cell is more negative than the water potential of the water- water molecules will move down the water-potential gradient into the cell.
40
Why wont a plant cell carry on absorbing water till in bursts?
Because it has a strong cellulose cell wall it will not burst. Instead once the cell in full of water, it is described as being turgid. The water inside the cell starts to exert a pressure on the cell wall, called the partial pressure, as the pressure potential builds up, in reduces the influx of water.
41
What will happen if you put a plant in a salt solution with a very low water potential?
The plant will loose water by osmosis. As water loss continues, the cytoplasm and vacuole shrink. Eventually, the cytoplasm no longer pushes against the cell wall. If the cell continuous to loose water, the plasma membrane will loose contact with the cell- known as **plasmolysis**. This tissue in now flaccid.
42
What can we call this process?
Plasmolysis.
43
How does water travel to adjacent plant cells?
**Through osmosis**, water molecules will move from the cell with a higher water potential to the cell with a more negative water potential.
44
What is adhesion?
The attraction between water molecules and the walls of the xylem vessel.
45
What is cohesion?
The attraction between water molecules caused by the hydrogen bonds.
46
What is the outermost layer of layer of cells in a root called?
The epidermis.
47
What does the epidermis of a root contain? What are these?
Root hair cells. These are cells with long extensions that increase the surface area of the root.
48
What do root hair cells absorb?
Mineral ions and water from the soil.
49
Why must water travelling though the apoplast pathway join the symplast pathway before reaching the vascular bundle?
The apoplast pathway is blocked by the **Casparian strip.**
50
How does water travel from the soil to the vascular bundle?
The water moves across the root cortex **down a water-potential gradient** to the endodermis of the vascular bundle.
51
How is water absorbed by a root hair cell?
Mineral ions are actively absorbed from the soil, lowing the water potential of the cytoplasm. This causes water to be absorbed by osmosis.
52
Via what processes is water transported from the root hair cell to the vascular bundle?
Water moves across root cortex by **osmosis** and via **apoplast pathway**.
53
What does the Casparian strip do?
Blocks the apoplast pathway between the cortex and the medulla.
54
What is the role of the Casparian strip blocking the apoplast pathway?
It ensures that water and dissolved ions have to pass into the cell cytoplasm through the plasma membranes.
55
How is mineral ions transported from the cortex to the medulla and xylem?
The **plasma membranes contain transporter proteins**, which actively pump mineral ions from the cytoplasm of the cortex cells into the medulla and xylem.
56
How does the water move from the cortex cells in to the xylem?
Once the mineral ions have been actively transported into the medulla and xylem, the **water potential becomes more negative,** causing water form the cortex cells to the medulla and xylem via **osmosis**. Once the water has entered the medulla, it **cannot pass back into the cortex** as the apoplast pathway is blocked by the Casparian strip.
57
By water process is water transported up the xylem?
By mass flow- a flow of water and mineral ions in the same direction.
58
What three processes help move water up the stem?
* Root pressure
* Transpiration pull
* Capillary action
59
How does root pressure help movement of water up the stem?
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 water up the xylem**. Root pressure can push water a few metres up the stem, but cannot account for water getting to top of tall trees.
60
What is the transpiration pull?
The loss of water by evaporation from the leaves must be replaced by water coming up the xylem.
61
How does the transpiration pull help move water up the stem?
**Loss of water from evaporation** from the leaves **must be replaced** by water coming up 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.** As molecules are **lost at the top of the column**, the whole **column is pulled upwards** as one chain. The pull from above, creates tension in the column of water.
62
Why is it important that the xylem is strengthened by lignin? (transpiration pull)
The transpiration pull creates pressure is the vessels, therefore, it being strengthened by lignin, stops it from collapsing.
63
What is the cohesion-tension theory?
**The transpiration pull**- because this involves **cohesion** between water molecules and **tension** in the column of water.
It relies on the plant maintaining an unbroken column of water all the way up the xylem vessel, then the water column can still be maintained though another vessel via the bordered pits.
64
How does capillary action help water move up the stem?
**Adhesion** causes an attraction between the water molecules and the walls of the xylem vessel. Because the **xylem vessels are very narrow**, these f**orces of attraction can pull the water up the side of the vessel**.
65
How does water leave the leaf?
Most of the **water leaves the leaf as vapour from the stomata**. A tiny amount of water will leave via the waxy cuticle. Water evaporates from the cell lining the cavity immediately above the guard cells. This **lowers the water potential in these cells**, causing **water to enter them by osmosis** by neighboring cells.
66
What is a hydrophyte?
A plant adapted to living in the water or where the ground conditions are very wet.
67
What is a xerophyte?
A plant adapted to living in dry conditions.
68
What can we call a plant adapted to living in dry conditions?
A xerophyte.
69
What can we call a plant adapted to living in the water or where the ground conditions are very wet
A hydrophyte.
70
What must plants living on land be adapted to do?
* Reduce their loss of water.
* Reduce the water that is lost.
71
What adaptions may terrestrial plants have to reduce water loss?
* **A wavy cuticle** on the leaf will **reduce water loss due to evaporation** through the epidermis.
* **Stomata are often found on the under-side of a leaf**, not the top. This reduces the evaporation due to direct heating from the sun.
* Most **stomata closed at night**, when there is no light for photosynthesis.
* **Deciduous plants lose their leaves in the winter**, when the group may be fros4n and temperatures are too low for photosynthesis.
72
What sort of plant is marram grass?
Xerophyte.
73
What do adaptations of marram grass include?
* **Leaf is rolled longitudinally** so air is trapped inside and air becomes humid, reducing water loss from leaf.
* There is a **thick waxy cuticle** on the outside of the rolled leaf, reducing evaporation.
* **Stoma are on the inside of the rolled leaf** so they are protected by the enclosed air space.
* **Spongy mesophyll is very dense** with few air spaces- so there is less surface area for evaporation.
74
what adaptations do cacti have to live in arid conditions?
* They are **succulents so they store water in their stems** which become fleshy and swollen- the stem is often ribbed or fluted so it can expand when water us available.
* **Leaves are reduced to spines**, reducing the surface area, therefore less water loss by transpiration.
* **Green stem** for photosynthesis.
* **Roots are widespread** to take advantage of any rainfall.
75
What are some features of xerophytic plants allowing them to survive in arid conditions?
* **Closing stomata** when water availability is low to reduce water loss and so reduce need to take up water.
* Some have **low water potential inside their leaf cells** by maintaining a high salt concentration in the cells. The low water potential reduces the evaporation of the water from the cell surfaces as the **water potential gradient between leaf cells and air is reduced.**
* Have **long tap roots** so they can reach water deep underground.
76
What is an example of hydrophytes?
Water lilies
77
What issues may a hydrophytic plant may face?
May face issues such as getting **oxygen** to their submerged tissues and keeping **afloat**.
78
What adaptations may a water lily have?
* **Many large air spaces in leaf**- keeps the leaves afloat so they are in air and can absorb sunlight.
* The **stomata are on the upper epidermis**, so they are exposed to the air to allow gaseous exchange
* **The leaf stem has many large air spaces**, helping with buoyancy, but also allows oxygen to diffuse quickly to the roots for aerobic respiration.
79
why may it be hard fort a hydrophytic plant to respire?
Water will not evaporate into water or air that has high humidity. If water cannot leave the plant, then the transpiration stream stops and the plant cannot transport mineral ions up to the leaves.
80
How can hydrophytic plants respire?
Many of these plants contain specialised structures at the tips or margins of their leaves called **hydathodes**. These structures can **release water droplets** which may then evaporate from the surface of the leaf.
81
Define transpiration.
The loss of water from the aerial parts of a plant. Mostly through the stomata in the leaves.
82
Why is water evaporating from the top of the leaf limited?
Because of the waxy cuticle.
83
What is the typical pathway taken by most water leaving the leaf?
* Water enters the leaf through the xylem, and **moves by osmosis** into the cells of the spongy mesophyll. It may also pass through along the cell walls via the **apoplast pathway**.
* **Water evaporates** from the cell walls of the spongy mesophyll.
* Water **vapour moves via diffusion** out of the leaf through the **open stomata**, which relies on a difference on the concentration gradient of water vapour in and and of the leaf. (**water potential gradient**).
84
Why is transpiration important?
* Transports useful mineral **ions** up the plant.
* maintains cell **turgidity**.
* Supplies water for growth, cell elongation and **photosynthesis**.
* Supplies water, as it evaporates, can keep a **plant cool** on a hot day.
85
What factors affect the rate of transpiration? (5)
* **Light intensity**- In light, the stomata open to allow gaseous exchange for photosynthesis= more transpiration.
* **Temperature**
* **Relative humidity**
* **Air movement**
* **Water availability**- If there is little water available, plant cannot replace the water that is lost- can lead the the stomata closing and leaf wilting.
86
What can you call the devise used to measure the rate of water uptake from a plant?
A potometer.
87
What is a potometer?
A device That can measure the rate of water uptake as a leafy stem respires.
88
How can you measure the rate of photosynthesis?
Using a potometer, water vapour lost by the leaves is replaced by water in the capillary tube. The movement of the bubble at the end of the tube can be measured.
To study different environmental factors and there effect on transpiration, you can set up the equipment up in different conditions, e.g, one by a fan.
89
When using a potometer, what precautions must be taken?
* Set it up under water to make sure there is no bubbles in the apparatus.
* Ensure the shoot is healthy.
* Cut them stem under water to prevent air entering the xylem.
* Cut the stem at an angle to provide a large surface area in contact with the water.
* Dry the leaves.
90
How can you measure the volume of water taken up by the plant?
The rate of transpiration is the volume calculated by the time take. Rate= volume/ time.
91
What are assimilates?
**Substances that have been made by the plant**, using substances absorbed by the environment; e.g. sugars(mainly transported as **sucrose**) and **amino acids**.
These substances have become part of the plant.
92
What is a sink?
part of a plant where those materials are removed from the transport system; e.g. the roots receive sugars and store them as starch.
93
What is a source?
A part of the plant that loads materials into the transport system; e.g. the leaves photosynthesise and the sugars are moved to other areas of the plant.
94
What is translocation?
The transport of assimilates throughout the plant.
95
By what process is sucrose loaded into the seive tube?
By as active process.
96
Where does the energy needed for transporting sucrose into the sieve tubes come from?
It involves the use of energy from ATP in the companion cells. The energy is used to transport **hydrogen ions out of the companion cells**. This increases their concentration outside of the cell- leading to a **concentration gradient** is created. The **hydrogen ions then diffuse back** into the companion cells through special **cotransporter proteins**. These proteins only allow movement of hydrogen ions if they are **accompanied by sucrose molecules**. This is known as **cotransport**.
97
What is cotransport?
Cotransport, also known as secondary active transport, one molecule is moving down its concentration gradient ,carrying a second molecule with it against the second molecule's concentration gradient.
98
How is sucrose loading cotransport? How does this lead to sucrose into the sieve tube?
It results in the hydrogen ions being actively transported out of the cells, then moves sucrose against its concentration gradient.
As the concentration of sucrose in the companion cells increases, it can diffuse into the sieve tube through the plasmodesmata.
99
What sort of movement is the movement of sucrose in the sieve tube?
Mass flow.
100
What is the solution in the sieve tube called?
Sap.
101
How is the flow caused in the sieve tubes?
The flow is caused by the **difference in hydrostatic pressure** between the two ends of the tube, which p**roduces a pressure gradient**. **Water enters** the tube at the **source**, increasing the pressure, and **water leaves** at the **sink**, reducing the pressure- therefore, the sap flows from the source to the sink.
102
How is hydrostatic pressure caused at the source?
At the source, sucrose enters the sieve tube, making the **water potential more negative**. This leads to water molecules from the surrounding tissues moving in by osmosis. This **increases the hydrostatic pressure.**
103
Where in a plant may sucrose be loaded into into the sieve tube?
* In early spring, this could be the roots, where energy stored as starch is converted into sucrose and moved to other parts of the plant for growth.
* The leaf- sugars made during photosynthesis are converted to sucrose.
104
Where in a plant may be a sink?
Anywhere that removes sucrose from the phloem sieve tube. The sucrose could be used for respiration and growth in a meristem, or could be converted into starch for storage in the roots.
105
How is a hydrostatic pressure created at the sink?
Where sucrose is being used in the cells, it can diffuse out of the sieve tube via the plasmodesmata- it can also be removed by active transport. The removal of sucrose from the sap, increases the the water potential so water moves out to the surrounding cells, creating a lower hydrostatic pressure.
106
What is mass flow in the phloem?
All the sap in one sieve tube is all moving in one direction.
