3.3 Transport In Plants

Question 1

what are the 3 attributes of dicotyledonous plants

Answer 1

• Have 2 seed leaves
• Leaf veins form a net pattern
• Vascular bundle in a diffinite ring

Question 2

what are the 3 needs for TS

Answer 2

Metabolic demands: Not all cells carry out photosynthesis. Mineral ions absorbed by roots need to be transported to all cells to make proteins. Hormones made in one part of the plant may need to be transported.

Size: Some plants are very large as they continue to grow. This means effective transport systems are required to carry substances great distances.

Surface area to volume ratio: Due to adaptations of leaves, they have high surface area to volume ratio, but many components like trunks lead to lower surface area to volume ratio, which means it can’t rely on diffusion to supply substances to cells

Question 3

what is a vascular system

Answer 3

Dicotyledonous plants have a series of transport vessels running through the system e.g. roots, leaves, stems

Question 4

what are vascular bundles

Answer 4

there are two main types of transport vessels, which are arranged together to make a vascular bundle. They are Phloem & Xylem Vessels

Question 5

where are the vascular bundles found in the stem and what is the arrangement

Answer 5

• Vascular Bundles are found around the edge to give strength & support
• The Xylem in on inside while Phloem is on outside

Question 6

where is the vascular bundle located in a leaf and what is the arrangement

Answer 6

• above Midrib of the leaf which helps carry vascular tissues through the organ & help support the structure
• Xylem is above the Phloem

Question 7

Where is the vascular bundle in root locates & what is the arrangements

Answer 7

• The Vascular arrangement is located in the centre to help withstand forces
• Xylem is in the centre and is a cross shape while the phloem is found around the Xylem vessel

Question 8

what does xylem vessel do

Answer 8

Transports dissolved mineral and water ions and provides structural support.

Question 9

what 4 tissues are found in xylem vessels

Answer 9

1. Vessels
2. Tracheid
3. Parenchyma
4. Fibres

Question 10

what are the qualities of vessels

Answer 10

Long hollow tubular cells to form hollow structure, joined end to end with perforated plates in between. The lignification of this can be reticulate or spiral, which gives some flexibility in the vessels.

Question 11

what are the qualities of Tracheids

Answer 11

Elongated cells with lignified cell wall. Mature cell walls are dead an empty. The pits allow rapid transport of water from 1 cell to another.

Question 12

what are the qualities of Parenchyma

Answer 12

Packs around Xylem vessels which store food and contain tannin deposits, which has bitter taste to protect it from herbivores.

Question 13

Qualities of Xylem vessel fibres

Answer 13

Long lignified cells which don’t transport water but provide mechanical strength and support. There are pits in the woods to allow water to leave. The lignified cell walls provide mechanical strength but causes cells to be killed.

Question 14

what is lignification and the new structure

Answer 14

Lignin is deposited into cell wall to make them waterproof while killing the cells and causing the contents to decay, forming a long column of dead cells. These are useful as they prevent the collapse of Xylem as they strengthen the vessels.

Question 15

what is the outward physical appearance of lignin

Answer 15

Formed in patterns like spirals, rings, or reticulate shapes and allow some flexibility in the stem and branch.

Question 16

what does phloem do

Answer 16

Transports assimilates from source to rest of plant and transport amino acids.

Question 17

Sieve Tube Elements

Answer 17

Elongated cells end to end to form a tube have lost most of their organelles, leaving more space to flow of molecules. The end walls have perforations called sieve plates which allow sub to move to the next cell then layer of cytoplasm in the cell wall.

Question 18

Companion Cells

Answer 18

Form with sieve tube elements, contain small cells and a large nucleus and then cytoplasm. There are many mitochondria from active cells to provide energy required to load and unload sucrose into and out of thief tube elements. Linked to the sieve tube element by Plasmodesmata which links the two cells together.

Question 19

what 3 adaptations allow for water to move into roots

Answer 19

1. Each RHC has high SA:V
2. Each hair has a thin surface layer through which diffusion & osmosis can happen quickly
3. Concentration of solutes in cytoplasm of RHC maintain the water potential gradient between soil & cell

Question 20

what is the Symplost Pathway

Answer 20

Water in cytoplasm moved into other cell cytoplasm which are connected by plasmodesmata via diffusion. This pathway is driven by water potential gradient as water moves from root hair cells which have constant supply of water from soil causing increase water potential in her cell allowing it to travel to plant cells via osmosis. In addition, the next adjacent plant cell has lower water potential than current one, allowing for water to be constantly transported forward. This pathway is much slower as there is higher resistance due to organelles.

Question 21

Apoplast Pathway

Answer 21

Water moves within cells and spaces between the cell walls. Cellulose cell wall has relatively open structure allowing water to move between cellulose fibres. Since water molecules being attracted due to hydrogen bonds via cohesion as water is moved along cells more moves along with it. This pathway is much faster as there is less resistance.

Question 22

explain movement of water across endodermis

Answer 22

• In endodermis there is a band of waterproof material of waxy suberin called Caparian Strip
• Water can no longer move through the apolost pathway and passes the cell membrane into cytoplasm to become part of S-pathway.
• This allows cell membrane to control which substances can enter Xylem and allows toxins to be filtered out
• Once they pass the strip the water can move back into cell wall

Question 23

Explain the movement of water into the xylem vessel

Answer 23

Mineral ions are moved into Xylem via active transport. This then reduces water potential in the Xylem. Due to higher water potential and endodermis and lower water potential in Xylem the water moves into Xylem via water potential gradient. This generates root pressure, which pushes up water into Xylem

Question 24

3 Evidences for the role of Active Transport in root pressure

Answer 24

Some poisons, such as cyanide, affect mitochondria and prevent production of ATP. If cyanide is applied to root cells, there is no energy supply. The root pressure disappears.

Root pressure increases with a rise in temperature an falls with falling temperatures, suggesting chemical reactions are involved.

If levels of oxygen or respiratory substrates fall, root pressure falls.

Question 25

what is transpiration

Answer 25

Loss of water vapour by evaporation through stomata.

Question 26

Simple explaination of transpiration

Answer 26

During photosynthesis, the stomata is open to allow exchange of carbon dioxide and oxygen. Water vapour in the leave then diffuses out the leaf through stomata due to lower level of water vapour in the air. Stomata open and closes to control amount of water last.

Question 27

Explain the process in the Transpiration stream

Answer 27

Water molecules evaporate from surface of mesophyll into airspaces in the leaf and move out stomata into air via diffusion. This lowers the potential of cells, so water moves from adjacent cell via osmosis. This is repeated across leave to the Xylem where water leaves excellent by osmosis into cells

Question 28

what is the cohesion-tension theory

Answer 28

Water molecules form hydrogen bonds with carbohydrates in walls of Xylem vessels, which is known as adhesion. Water molecules from hydrogen bonds with each other, so they tend to stick together and move together due to the attraction between them pulling them closer, which is called cohesion. The combined effects allow water to move up narrow tubes against gravity.

Question 29

How does light intensity effect transpiration

Answer 29

Higher light intensity causes the stomata to open and more of them to open. This increases the rate of the amount of water diffusing out.

Question 30

how does humidity effect transpiration

Answer 30

A high humidity will reduce the rate of transpiration since it reduced the water vapour potential gradient. This will lead to reduced water vapour diffusing out the stomata.

Question 31

2 ways in which temperature effects transpiration

Answer 31

Increase of temperature causes higher kinetic energy of water molecules and therefore increase rate of evaporation from spongy Mr Phil into airspaces.

Increase in temperature also causes there to be more water vapour outside the leaf, leading to higher humidity.

Question 32

how does air movement effect transpiration

Answer 32

More wind will move any water vapour away from leave creating a low humidity environment.

Question 33

what is translocation

Answer 33

Transport of assimilates and organic nutrients in Phloem tissue from the source to the sink, and this process requires metabolic energy in the form of ATP.

Question 34

what is a source

Answer 34

loads assimilates into phloem

Question 35

what is a sink

Answer 35

unloads assimilates from phloem

Question 36

3 Sources of Assimilates

Answer 36

Green leaves and green stems.

Food stores in seeds when they germinate.

Storage organs that unload stores at the beginning of growth.

Question 37

3 Sinks of Assimilates

Answer 37

Meristems data actively dividing.

Roots that are actively growing or actively absorbing mineral ions.

Parts of a plant that are laying down food stores, such as developing seeds, fruit or storage organs.

Question 38

Explain the 4 steps in the Phloem Loading phase

Answer 38

Hydrogen ions are pumped out the companion cell to report on pumps by active transport. This creates a high concentration gradient of hydrogen ions in outside the companion cells in the leaf.

Hydrogen ions diffuse back into the companion cell with sucrose through Co transporters.

Since there is high level of sucrose in companion cell, it diffuses into sieve tube elements through plasmodesmata which decrease the water potential in STE

As a result, water moves into the sea. Tube elements by osmosis which generates charger pressure for mass flow.

Question 39

what is the one step of mass flow translocation

Answer 39

Mass flow assimilates flow from source to sink down pressure gradient.

Question 40

What happens in Phloem Unloading

Answer 40

Sucrose diffuses from phloem into the sinks.

In the sink, sucrose is moved to other cells or converted to other forms to maintain concentration gradient between cells & phloem

Lots of assimilates increase water potential of sieve tube elements, which causes water to move into cells via osmosis or enters Xylem transpiration stream.

Question 41

what are Xerophytes

Answer 41

Plants in dry habitats that have evolved a wide range of adaptations that enable them to live & reproduce in places where water availability is very low

Question 42

10 adaptations of Xerophytes

Answer 42

Thick Waxy cuticle: Reduces the rate of water loss from the leaf surface

Sunken Stomata: Many Xerophytes have their stomata located in pits which reduces air movement, producing a microclimate of still humid air that reduces water vapour potential gradient and so reduces transpiration

Reduced number of stomata: Many Xerophytes have reduced number of stomata, which reduced their water loss by transpiration, but also reduced their gas exchange capabilities.

Reduced leaves: By reducing the leaf area, water loss can be greatly reduced. The leaves of conifers are reduced to thin needles. These narrow leaves, which are almost circular in cross section, have greatly reduced surface area to volume ratio, minimising the amount of water loss and transpiration.

Hairy Leaves: Some Xerophytes have very hairy leaves that, like the spines of some cacti, create a microclimate of still humid. Reducing the water vapour potential gradient and minimising the loss of water by transpiration from the surface of the leaf.

Curled Leaves: The growth of code or rolled leaves reduces water loss by transpiration. This confines all the stomata within a microenvironment of still humid air to reduce diffusion of water vapour from the stomata.

Succulents: Succulent plants store water in specialised parent IMA tissue in their stems and roots. They get their name because, unlike other plants, they often have swollen or fleshy appearance. Water is stored when it is in plentiful supply and then use in times of drought.

Leaf loss: When water is not available, they simply lose their leaves.

Root adaptations: Many Xerophytes have root adaptations that help them to get as much water as possible from the soil. Long tap roots growing deep into the ground can penetrate several metres so they can access water that is a long way below the surface.

Avoiding the problem: Some plants are adopted to cope with the problem of low water availability by avoiding the situation entirely by becoming dormant or die, then germinate & grow rapidly when water is available again

Question 43

what are Herophytes

Answer 43

Plants that have adapted to living in wet saturate conditions like being submerged or on the surface of water

Question 44

What are 5 adaptations of Herophytes

Answer 44

Very thin or no waxy cuticle: hydrophytes do not need to conserve water as there is plenty available, so water lost by transpiration is not an issue

Many opens stomata: Maximising the number of open stomata will lead to more loss of water through transpiration.

Reduced structure of plant: The water supports the leaves & flowers so there is no need for strong supporting structures

Wide & flat Leaves: Have wide surface area to increase diffusion of water out the leaf

Small Roots: Water can diffuse directly into stem and leaf tissue so there is less uptake required by roots