Transport In Plants

Question 1

Why do plants need transport systems

Answer 1

Plants need substances like water, minerals and sugars to live. They also need to get rid of waste substances. , plants are multicellular so factors affecting are 1.Metabolic Demands 2. Size 3. Surface Area to Volume ratio

Question 2

Why do plants need transport systems because of metabolic demands?

Why is the surface area to volume ratio not simple in plants?

Answer 2

Many internal or underground parts of a plant cannot make their own glucose for energy via photosynthesis, so need glucose and oxygen transported to them. Hormones and mineral ions also need to be moved.

The leaves are adapted to have a large surface area to volume ratio, but when taking into account the stems, trunks and roots the overall SA:V ratio may be quite small

Question 3

Why do mineral ions need to be moved around a plant?

Answer 3

So they can be moved to all cells for protein production.

Question 4

Effect of small da v low metabolic demands and size

Answer 4

Exchanging substances by forever diffusion ( from the outer surface to the cells) would be too slow to meet their metabolic needs. So plants need transport systems to move substances to and from individual cells quickly

Question 5

Two types of tissue involved in transport of plants

Answer 5

Xylem N phloem

Question 6

Where are vascular bundles in the stem of a dicot and why?

Answer 6

Near the outside To provide a scaffolding that reduces bending and to give strength n support

Question 7

Where are the vascular bundles in the root of a dicot and why?

Answer 7

In the centre to help the plant withstand the tugging strains that result as the stems and leaves are blown in the wind and support the root as it pushes through the soil

Question 8

What’s the vascular bundle in leaves

Answer 8

Make up a network of veins which support the thin leaves
Main vein found in midrib of leaf to support structure of leaf
It also has Many small, branching veins which spread throughout the leaf and function in both transport and support

Question 9

How is the main vascular bundle structured in the leaf of a dicot?

How is the vascular bundle structured in the stem of a dicot?

Answer 9

Xylem above phloem, vascular bundle roughly circular cross-section

Phloem on the outside, xylem on the inside, separated by a strip called the procambium (or just cambium)

Question 10

What is the bit in the middle of a dicot stem called?

What is the area between vascular bundles in a dicot stem called?

Answer 10

Pith, composed of soft spongy parenchyma cells

Interfasicular parenchyma

Question 11

What is the outermost layer of a plant stem called?

What is the tissue immediately surrounding a vascular bundle in a dicot root called?

What is the outermost layer of a dicot root called?

What layer is found immediately below the exodermis of a plant root?

Answer 11

Epidermis

Endodermis

Exodermis

Epidermis

Question 12

How is the vascular bundle of a dicot root arranged?

What is the area between the vascular bundles and epidermis in a dicot root and stem called?

Answer 12

A ‘X’ shaped xylem with phloem vessels in the gaps of the X, with a ring called the endodermis enclosing all this

Cortex

Question 13

What’s the pericycle
What’s the cambium

Answer 13

primarily found in the roots of plants. It’s located just inside the endodermis and contains meristematic cells that help form lateral roots

A lateral meristem found in stems (and sometimes roots) that produces new xylem and phloem for secondary growth(thickening)

Question 14

Function of xylem tissue

Answer 14

1.Support 2. Transport of water and mineral ions

Question 15

Structure of xylem tissue

Answer 15

Contains xylem vessels-shorter n fatter than tracheids
Tracheids-tapered cells with sloping end walls and pits. Lignified but less efficient. Used for water transport n support
Parenchyma -living cells within thin walls. It stored starch and helps with the lateral movement of water supporting tissue
Fibres -lock narrow thick walled dead cells which provide mechanical strength to cell

Question 16

How does water move though xylem vessels

Answer 16

Water n mineral ions move into and out of the vessels through small pits in the walls which allow sideways movement where there’s no lignin and this is how other cells are supplied with water.

Question 17

Xylem vessel

Answer 17

Long tube like structures formed from elongated dead cells joined end to end.
There are no end walls on these cells as they break down making an uninterrupted tube that allows water to up through the middle easily and form a continuous column.
Cells are dead so they contain no cytoplasm to allow easier flow.

Cell walls are thickened w a wood substance=lignin which helps to support the walls and stops them collapsing inwards. Lignin can be deposited in xylem walls in different ways (spiral or distinct rings). These patterns allows flexibility n prevents stem from breaking
Amount of lignin increases as cell gets older
Lignin waterproof so water can’t escape through pits.

Question 18

Why is parenchyma not a developed tissue

Answer 18

parenchyma cells stay alive and flexible w a simple structure
P have no specific adaptations for transport, support, or secretion.
They retain the ability to divide and differentiate, unlike highly specialised cells.
Least specialised but still versatile as Can still differentiate into more complex cell types.

Question 19

Function of phloem tissue

Answer 19

Transports solutes eg sugars like sucrose and amino acids
Made of phloem cells arranged in tubes
Phloem parenchyma-living cells w thin cell walls n large vacuole and it stores sugars which can be used by plant when needed.
Phloem fibres-long dead cells w thickened cell walls made of lignin and provide mechanical strength to cell.
Sieve tube elements-
Companion cells -

Question 21

What do sieve tube events do

Answer 21

Living cells that form the tube for transporting sugars though the plant. They’re joined end to end to form sieve tubes. Sieve parts are the end walls which have lots of holes in them to allow solutes to pass through. They have no nucleus tonopladt and many organelles break down leaving thin layer of cytoplasm and few organelles. Cytoplasm of adjacent cells is connected though the holes in the sieve plates.

Question 22

What are sieve plates

Answer 22

Holes in the end cell walls of sieve tube elements which let the phloem’s contents through

Question 23

What do companion cells do

Answer 23

Lack of a nucleus and other organelles in sieve tube elements means they can’t survive on their own. So there’s a companion cell for every sieve tube element keeping sieve tube alive.
They carry out the living functions for both themselves and sieve cells, provide energy for active transport of solutes ( contains many mitochondria which respiration occurs making atp)

Question 24

In a stained plant tissue what would coulour would the surrounding plant cells
Xylem vessels
Phloem vessels

Answer 24

Surrounding plant cells - pink
Xylem vessels-blue-green
Phloem vessels-pink

Question 25

How to dissect a plant

Answer 25

1)Use a scalpel to cut a cross-section of the stem (transverse or longitudinal). Cut the sections very thin— (best for viewing under a microscope).to use tweezers to hold the stem still whilst you are cutting. 2)use tweezers to gently place the cut sections in water until you come to use them. stops them from drying out 3) Add a drop of water to a microscope slide, add the plant section and carefully add one or two drops of a stain eg toluidine blue and leave for one minute 4)carefully apply a coverslip so you have made a wet mount 5)view the specimen under a light microscope and draw a labelled diagram what you observe

Question 26

How does the transport of water work

Answer 26

1)mineral ions enter root hair cells either by diffusion or active transport depending on the conc gradient=water potential in root hair cells cytoplasm. 2) water enters the plant down the water potential gradient.it will then either 3) move cell to cell by diffusion through plasmodesmata. This is called the symplastic pathway. The water moves through the cytoplasm. 3b) move from epidermis to endodermis by diffusion via the freely permeable cellulose cell wall- this is called the aplastic pathway 4) the waxy casparian strip stops water moving via the apoplastic pathway(controls the movement of water and mineral ions into xylem) so it’s forced into the symplastic pathway to reach the xylem. 5)water moves into xylem by diffusion via pits down a water potential gradient then move upwards due to a transpiration pull+ cohesion +adhesion.(water moves similarly though the leaf tissue once it’s left the xylem reaches air pockets in the spongy mesophyl layer.

Question 27

How does water transport through the plant

Answer 27

1)Mineral ions enter root hair cells by either diffusion or active transport depending on concentration gradient= Lowering the water potential gradient in root hair cell cytoplasm 2)water enters the plant throigh root hair cells then passes through the root cortex via osmosis down the water potential gradient.soil around roots have a high WPG(always water there) and leaves have low(water constantly evaporating from em). Creates a wpg that keeps water moving through plant in right direction from roots to leaves.

Question 28

What does water do after it enters the plant

Answer 28

3A) it then either moves cell to cell by diffusion through plasmodesmata(small channels in cell wall) this is called symplastic pathway. The water moves through the cytoplasm via osmosis( the living parts of the cell) 3b)moves from epidermis to endodermis by diffusion via freely permeable cellulose cell wall this is called the apoplastic pathway. 4) the waxy casparian strip in cell walls stops water moving via the apoplastic pathway (controls movement of water and mineral ions into xylem) so it’s forced into the symplastic pathway to reach the xylem this is useful as it means water has to go through a plasma membrane.(partially p so can control whether substances in water can get through, once past.. 5) water moves into xylem by diffusion via pits down a water potential gradient then moves upwards due to a transpiration pull + adhesion and cohesion. 6)When the water reaches the leaves, it exits the xylem and moves into the surrounding leaf cells, mainly by the apoplast pathway. Water then evaporates from the cell walls into air pockets in the spongy mesophyl layer. When the stomata are open, this water vapor diffuses out of the leaf into the surrounding air, down a water potential gradient. This loss of water from the leaf surface is called transpiration, and it maintains the continuous movement of water through the plant.

Question 29

How does the transpiration pull work

Answer 29

Capillary action = Cohesion-water molecules clog tg due to h bonds. This forms an unbroken column of water. Adhesion-water molecules are attracted to xylem vessels due to H bonds creating strong tension force The force driven by evaporation at the leaves and enables upward movement of water against the pull of gravity

Question 30

What causes root pressure

Answer 30

Root pressure is caused by the active transport of mineral ions from the root cells into the xylem. Decreasing wp so water can flow in by osmosis and this buildup of pressure causes the root pressure. This helps Push water up the xylem in the roots — forces water upward through the xylem vessels helping restore continuous water column. useful at night/ humid conditions when transpiration is low or not happening. It can also Helps release extra water — root pressure can push water out of the edges of leaves through tiny pores, causing water droplets to appear. This is called guttation.

Question 32

What happens to root pressure in low temperatures? What effect do respiratory poisons have on root pressure? Why does root pressure only occur in living roots? How does root pressure show it’s not caused by transpiration?

Answer 32

A: It decreases — because enzymes slow down, so less active transport. A: Root pressure stops — poisons block ATP, which is needed for active transport. A=Because active transport needs living cells to move ions into xylem It still happens at night (when stomata are closed), so it’s not due to water loss from leaves

Question 33

Why does some stomata need to be open at night

Answer 33

Keeping some stomata open helps maintain a low water potential in the leaf, which supports water movement from roots (root pressure and minimal transpiration).

Question 34

Why does transportation happen

Answer 34

Result of gas exchange. plant needs to open stomata to let in CO2 so that it can produce glucose (by photosynthesis). But this also lets water out - there's a higher concentration of water inside leaf than in air outside, so water moves out of the leaf down the WPG when the stomata open. transpiration's = a side effect of the gas exchange needed for photosynthesis.

Question 35

Factors that efc T transpiration rate

Answer 35

1.Light intensity — the lighter it is the faster the transpiration rate. This is because the stomata open when it gets light (the lighter it gets, the wider they open). When it's dark the stomata are usually closed, so there's little transpiration. Temperature — the higher the temperature the faster the must be kept constant. Warmer water molecules have more energy so they evaporate from the cells inside the leaf faster. This increases the water potential gradient between the inside and outside of the leaf, making water diffuse out of the leaf faster. 3. Humidity — the lower the humidity, the faster the transpiration rate. If the air around the plant is dry, the water potential gradient between the leaf and the air is increased, which increases transpiration rate. 4. Wind - the windier it is, the faster the transpiration rate. Lots of air movement blows away water molecules from around the stomata. This increases the water potential gradient, which increases the rate of transpiration.

Question 36

Equipment used to measure transpiration rates

Answer 36

Potometer- it measures water uptake of a plant and how diff factors affect transpiration rate Using it: 1.Cut a shoot underwater to prevent air from entering the xylem. Cut it at a slant to increase the SA available for water uptake. 2. Assemble the potometer in water and insert the shoot under h20, so no air can enter. 3. Remove the apparatus from the h20 but keep end of the capillary tube submerged in a beaker of water. 4. Check that apparatus is watertight and airtight. 5. Dry the leaves, allow time for the shoot to acclimatise and then shut the tap. 6. Remove the end of the capillary tube from beaker of h20 until one air bubble has formed, then put the end of the tube back into the water. 7.record starting position of bubble 8.start a stopwatch and record the distance moved by the bubble per unit time, e.g. per hour. rate of air bubble movement is an estimate of the transpiration rate 9. Only change one variable at a time all other conditions must b constant.

Question 37

What are xerophytes

Answer 37

Plants which can tolerate low water availability to low rain fall or high winds such as a desert or an ice/snow covered region. Adaptations are to conserve as much water as possible. Which helps maintain the WPG slowing down rate of transpiration. Eg marram grass n cacti

Question 38

Adaptations of xerophytes

Answer 38

rolled leaves, leaf hairs and stomata sunk in pits= all trap water yapour, increasing humidity around the stomata = V gradient to slow water loss by diffusion • thick waxy cuticle which is impermeable to water= preventing evaporation through the epidermal layer • stomata opening at night and closed at midday =when evaporation rate would be highest [reversed stomatal rhythm). • deep roots =to reach water far underground which are aiso shallow spreading to collect occasional rainfall • leaves reduced to spines or curled =with minimum surface area for transpiration • reduced no of stomata =to reduce transpiration rate • storage of water =in succulent tissues

Question 39

What are hydrophytes

Answer 39

Plants that can tolerate high levels of water and are either partially or fully submerged in water Adaptations are to absorb as much 02 n light as possible Eg water lily

Question 40

Adaptations of hydrophytes

Answer 40

Leaf shape: the submerged leaves have a LARGE SA =for maximum light absorption a maximum rate of photosynth • Lack of protective layer: the epidermal layer has V LITTLE IF ANY, cuticle, as water loss is not a problem. Xylem tubes: very few or absent as ALL SURFACE CELLS ABSORB H20 nutrients & dissolved gases by diffusion from surrounding h20. • Location of stomata: the green pigment containing chloroplasts & stomata are also found only on the upper surface of the leaf. • No strengthening tissue: stems and leaf petioles are normally supported by water. Mechanical support would be disadvantageous as It would limit flexibility in the event of changes in water level or water movements. • Roots: often also reduced and their main function is anchorage. root hairs are OFTEN ABSENT and the roots themselves may be entirely missing. * Air pockets: MANY to ensure leaves float on the waters surface to rapidly exchange gases and capture light energy

Question 41

How is Marram Grass specially adapted to survive in a very dry environment?

Answer 41

-stomata sunk in pits, =sheltered from the wind. trapping moist air in pits slowing transpiration down by lowering the WPG. -a layer of 'hairs' on the epidermis trapping moist air round stomata, which reduces the WPG between leaf n air slowing down transpiration -hot/windy condition they roll leaves trapping moist air slowing down trans and reduces exposed SA for losing h20 and protects stomata from wind -thickly waxy later on epidermis to reduce water loss by evaporation

Question 42

Differences between xerophytes and hydrophytes

Answer 42

Xero- roots deep and shallow and covers large SA to inc water uptake. Hydro-reduced roots and anchorage absent Xero-thick cuticle to reduce water loss Hydro-little cuticle -water loss ain’t no problem Xero-air pockets are rolled leaves to inc humidity reducing h20 loss Hydro-many air pockets to ensure leaves float Xero-stomata -rolled leaves to reduce sa Hydro-stomata on upper surface of leaf Leaf structure- rolled spines to reduce SA for water vapour loss Large SA to max light absorption

Question 43

Halophytes

Answer 43

Can tolerate high levels of salt lose soil and low levels of O2. Roots fully submerged in h20 most of day =anoxic. Adaptations are to reduce internal salt level stay upright and absorb as much O2 as possible Eg mangroves

Question 44

Halophytes adaptations

Answer 44

Complex root system-Knee roots stabilize mangroves in shifting soil. Vertical roots that spring up to act like snorkels when submerged and pores in bark contain hydrophobic substances so when submerged water can’t flood into roots Secretors by getting rid of salt or non sec by blocking salt w chemical barrier or storing to balance WP Viviparity-Offspring germinate to inc chances of survival when attached to parent

Question 45

What’s translocation

Answer 45

Movement of dissolved substances (eg sugars like sucrose and amino acids) to where needed in plants. Dissolves substances are called assimilated this is an energy requiring process in phloem Moves substances from source to sinks

Question 46

What’s source and sinks

Answer 46

Source -where it’s made so high concentration of substance there Sink-where irs used up (low concentration of substance there) Sources =photosynthetic leaves or tubers Sinks-non photosynthetic, respiring tissues,meristems or tubers

Question 47

How do assimilates move

Answer 47

Mass flow Added to phloem by sources Removed from phloem by sinks

Question 48

Mass flow hypothesis

Answer 48

AT is used to actively load the solutes (e.g. sucrose from photosynthesis) into the sieve tubes of the phloem at the source (e.g. the leaves). This lowers the WP inside the sieve tubes, so water enters the tubes by osmosis from the xylem and companion cells. This creates a higher hydrostatic pressure inside the sieve tubes at the source end of the phloem. At the sink end, cell sap(water n sucrose) moves down the pressure gradient(mass flow) solutes are removed from the phloem to be used up. This happens by diffusion (passive) as the solutes are at a higher conc in the phloem than they are in the surrounding tissue at sink. removal of solutes inc the WP inside sieve tubes, so water also leaves the tubes by osmosis. This lowers the HS pressure inside the sieve tubes. Maintaining pressure gradient from the source end to the sink end. This gradient pushes solutes along the sieve tubes towards sink. When they reach the sink the solutes will be used (e.g. in respiration) or stored (e.g. as starch). The higher the concentration of sucrose at the source, the higher the rate of translocation.

Question 49

How does active loading work

Answer 49

1) in companion cells actively pump H+ into surrounding tissues out of cell through AT and this is fueled by hydrolysis of atp. This sets up conc gradient as there’s more H+ ions in surrounding tissues than comp cell 2) H+ diffuses back into companion cells down H+ conc gradient binding with sucrose via a cotransporter protein via facilitated diffusion.movement of H+ ions is used to move the sucrose molecules into cell against conc gradient. 3) inc conc of sucrose in companion cells,so it diffuses out via plasmodesmata into sieve tube elements/phloem vessels via simple diffusion.

Question 50

What’s co transport

Answer 50

Co-transport: Two substances move together across a membrane. •One moves down its gradient (high to low). •The other moves up its gradient (low to high). Eg: Sucrose enters phloem using energy from Na⁺ moving down its gradient.

Question 51

Pressure at source and pressure at sinks according to mass flow

Answer 51

Source - high HS PRESSURE sucrose actively loaded-inc wp-water moves in sinks - LOW HS PRESSURE- sucrose actively leaves ,water p inc so water leaves

Question 52

What adaptation do companion cells have to aid active loading at the source?

Answer 52

Many mitochondria: Provide the ATP needed for active transport. Plasmodesmata: Allow for easy communication and exchange of substances between the companion cells and sieve tube elements. Proton pumps to create a gradient that helps move sucrose into the phloem.

Question 53

Evidence for active loading

Answer 53

1)ATP needed: Companion cells have many mitochondria, showing energy is used. 2.Proton pumps: These create a gradient to move sucrose. 3.Temperature: The process stops at low temperatures, needing energy. 4.Cyanide effect: Cyanide blocks ATP and stops sucrose loading.

Question 54

Evidence of translocation in phloem

Answer 54

Phloem is made of sieve tubes and companion cells, designed for transporting sugars and nutrients.

Question 55

2 main reasons we are unsure about mass flow hypothesis

Answer 55

Lack of clear evidence for pressure gradients: It’s difficult to directly measure the pressure gradients in phloem, making it hard to confirm how exactly sugars move. Transport speed issues: The speeds at which sugars move in the phloem don’t always match what the mass flow hypothesis predicts, suggesting other factors may be involved.