Plants

Question 1

What are the 3 main reason for transport systems in plants?

Answer 1

1) Metabolic demand - not all parts can photosynthesise, but still need O2, glucose, hormones, and waste removal. e.g. mineral ions need to be transported for protein synthesis for enzyme creation.
2) Size - larger plants have need systems, to transport substances to the highest points. Diffusion alone is not enough.
3) SA:VR - Leaves have a large SA:VR, but stems, roots and trunks have a small SA:VR. Overall means a small SA:VR. Diffusion is not sufficient.

Question 2

What are monocots?

Answer 2

Contain one cotyledon, and usually have long, narrow leaves, with parallel veins. Vascular bundles are scattered.

Question 3

What are dicots?

Answer 3

Contain two cotyledon. Often have broad leaves, and narrow veins. Vascular bundles are scattered.

Question 4

Definition of a cotyledon

Answer 4

Organs which act as food stores for the developing embryo plant, and for the first leaves in germination.

Question 5

What are arborescent dicots?

Answer 5

Woody dicots with lignified tissue. Have a long life cycle.

Question 6

What are herbaceous dicots? What are the transport vessels?

Answer 6

Short life cycle with soft tissue that breaks down easily at the end of life. Vessels are xylem and phloem.

Question 7

Describe the arrangement of vascular bundle in the stems roots and leaves.

Answer 7

Stems - around the edge, to provide strength and support.
Roots - in the middle to help withstand tugging strains.
Leaves - in the midrib along with veins. The xylem is to the surface and the phloem below. Supports broad leaf structure.

Question 8

What is the function of parenchyma?

Answer 8

Packing and supporting tissue. Store food and contain tannin deposits. Tannin is a bitter, astringent - tasting chemical that protects plants from herbivores.

Question 9

Function of the xylem and phloem

Answer 9

Xylem - transport water and mineral ions in transpiration.

Phloem - transport solutes like sucrose and amino acids, in translocation.

Question 10

Describe and explain how the xylem is suited to its function

Answer 10

1) Long hollow tubes with no end cell walls - allows for uninterrupted flow and maximum transport.
2) No cytoplasm due to cells being dead - uninterrupted flow for maximum transport.
3) Secondary walls made of lignin - provides extra mechanical strength, to prevent collapse. Lignin can be in rings, spirals or small areas called bordered pits.
4) Bordered pits - water leaves the xylem into other cells.
5) Parenchyma - contains tannin which prevents the plant being eaten by herbivores.

Question 11

Describe and explain how the phloem is suited to its function

Answer 11

1) Cells joined end to end, to form a hollow structure, as sieve tubes - allows easy transport of solutes.
2) Pores in the sieve tubes - allows solutes to pass through easily.
3) Lack of organelles - no nucleus, tonoplast, ribosomes etc. Only a few mitochondria (for metabolic demand) and plastids remain. Allows more space for solutes to flow.
4) Companion cells - carry out living functions e.g. provide energy for active transport. Connected by plasmodesmata.

Question 12

Define plasmodesmata

Answer 12

Microscopic channels through the cellulose cells walls which link cytoplasm of adjacent cells.

Question 13

What are the tracheary element in the xylem?

Answer 13

Tracheid’s and vessel elements.

Question 14

How does water pass through tracheid’s?

Answer 14

Passes through pits in the cell walls via pit membranes, or through the unlignified portions of cell wall. These pits are known as bordered pits.

Question 15

What properties of water allow tracheid’s to pass water in this way?

Answer 15

Cohesive forces between the H bond in water, and the adhesive forces of the H bonds to the xylem wall.

Question 16

Angiosperm (flowering plants) require more vessels than tracheid’s and efficiency in transport. Why?

Answer 16

Vessels are more effective at transporting, and are much larger than tracheary elements, so can transport more substances in a given volume. Needed due to the high metabolic demand for the creation of fruit/seeds and to keep the plant alive.

Question 17

What is metaxylem?

Answer 17

More mature xylem, typically with broader tracheid’s and vessels with pitted walls.

Question 18

Why do mature xylem vessels not grow?

Answer 18

A vessel undergoes more extensive lignification as development happens in the mature regions of the organ, forming metaxylem.

Question 19

What are the adaptions and functions of a root hair cell?

Answer 19

1) Lots of mitochondria - release energy from glucose during respiration to aid active transport.
2) Small SA:VR - maximises water uptake, increased by elongation.
3) Partially permeable plasma membrane - prevents large molecules entering, as well as maintaining water potential.
4) Each hair has a small surface area - shorter diffusion distance for diffusion and osmosis. Faster process.

Question 20

How do mineral ions taken in by root hairs aid in the uptake of water?

Answer 20

Soil water has a low concentration of dissolved minerals, so has a high water potential. The cytoplasm and vacuolar sap in the root hair cells contain many different solvents, like mineral ions, so the water potential in the cell is lower. This causes water to move into the root hair cells by osmosis.

Question 21

How does water move from the soil to the air, via the plant?

Answer 21

1) Water is absorbed by the rot hair cells at the root tips in the soil.
2) Water enters the xylem from here, with the support of mineral ions to aid water uptake.
3) Water moves up the xylem vessel by cohesion, and is constantly moving against a concentration gradient, from an area with high to an area with low water potential.
4) The water enter the leaf cell and is evaporated in to the air spaces in the spongy mesophyll.
5) Transpiration causes the water to be lost as vapour through the stomata, into the air.

Question 22

Describe the symplast pathway

Answer 22

Movement of water through living spaces of the cell (cytoplasm). When moving into a new cell, water moves through the plasmodesmata. Each cell further away from the roots has a lower water potential, so water is always drawn up (transpiration pull).

Question 23

Describe the apoplast pathway

Answer 23

Movement of water through the cell walls and intracellular spaces, by diffusion. Cohesive and tension forces acting on the cell wall pulls water up the plant by osmosis. This is the fastest movement of water.

Question 24

What is the Casperian strip, and what is its function?

Answer 24

A band of waxy material called suberin that runs around each of the endodermal cells, forming a waterproof layer. This forces water in the apoplast pathway into the cytoplasm and then the symplast pathway. This means water must pass through a partially permeable membrane, which removes nay potentially toxic solutes in the soil water reaching living tissue. Also aids in root pressure.

Question 25

What causes root pressure?

Answer 25

The active pumping of mineral ions into the xylem by osmosis causes root pressure to form.

Question 26

Evidence for active transport in root pressure

Answer 26

1) Cyanide prevents mitochondria forming ATP in respiration. O2 and respiratory substrates are needed for respiration and ATP production. A decrease in ATP production, decreases root pressure.
2) Temperature increase, sees root pressure increase. Suggests an enzyme controlled reaction and an increase in diffusion and osmosis is seen.
3) Xylem sap and water may exude from a cut stem. Xylem sap is forced out of special pores at the end of leaves in some conditions, like overnight when transpiration is low. This is known as guttation.

Question 27

Evidence for Cohesion Tension Theory

Answer 27

Changes in the diameter of trees - diameter shrinks in the day when transpiration and xylem tension are at there peak. At night transpiration and xylem tension are at the lowest and trunk expands. Tested using circumference.
Xylem vessel is broken - cut flower stem are put in water. Air is drawn into the xylem rather than water leaking out.

Question 28

Effect of light intensity on transpiration

Answer 28

Increases with increasing light intensity. Stomata open when light for photosynthesis. With more stomata open, more water vapour can diffuse out, so transpiration increases.

Question 29

Effect of temperature on transpiration

Answer 29

Increasing temperature increases the rate of transpiration. The KE of water molecules increases so evaporation from the spongy mesophyll cells increases.

Question 30

Effect of wind speed on transpiration

Answer 30

Increasing wind speed increases transpiration. Air is trapped by the shape of the leaf. Water vapour accumulates, so water potential around the stomata increases. With more wind, the accumulation will decrease, increasing the diffusion gradient and causing more water to evaporate.

Question 31

Effect of humidity on transpiration

Answer 31

Increasing humidity decreases the rate of transpiration. The amount of water in the air compared to total conc. of water the air can hold is the relative humidity. The water potential gradient decreases inside the leaf and the outside air, so more evaporation takes place.

Question 32

Effect of soil water availability on transpiration

Answer 32

A high availability means no water stress, but a low means a plant is under stress. Transpiration reduces when there is water stress.

Question 33

What are the two types of potometer?

Answer 33

Mass potometer - measure transpiration through loss of mass.

Moving bubble potometer - measure water uptake by the root.

Question 34

Describe and explain the process of measuring transpiration rate with a moving bubble potometer

Answer 34

1) Cut a shoot underwater to prevent air from entering the xylem. Do at a slant to increase SA for water absorption.
2) Assemble the potometer in water and insert the shoot underwater. Avoids unwanted air bubbles in the xylem.
3) Check apparatus is water and airtight. Dry the leaves, allow time for the shoot to acclimatise and then shut the tap. This prevents anomalous results.
4) Remove end of capillary tube from the beaker of water so 1 air bubble forms. Put the end of the tube back in the water. Record starting position. Allows the vol. of water to be measured.
5) Start a stopwatch and record the distance moved by the bubble per unit time. The rate of movement is an estimate of transpiration rate.
6) Only change 1 variable at a time. Don’t want a limiting factor to make results void.

Question 35

What is Fick’s law?

Answer 35

Rate of diffusion (directly proportional) surface area x conc. difference /thickness of membrane

Question 36

Define translocation

Answer 36

Movement of nutrients around a plant. Usually refers to the transport of sucrose, amino acids or other molecules in the phloem. Can occur in either direction (bi-directional). An active process requiring energy.

Question 37

What is a source?

Answer 37

Where assimilates are made (high concentration) e.g. sucrose, but also green leaves and stems, storage organs, food stores in seeds. Sucrose makes up 20-30% in phloem sap.

Question 38

What is a sink?

Answer 38

Where assimilates are used up (lower concentration) e.g. growing roots, cell meristems that are actively dividing, food stores like seeds, fruit etc.

Question 39

Describe the process of active loading

Answer 39

1) In companion cell, ATP is used up to actively transport hydrogen ions out of the cell and to surrounding tissue.
2) This sets up a concentration gradient - more H+ ions in surrounding tissue than in companion cells.
3) A H+ ion binds to a co-transporter protein in companion cell membrane and re-enters the cell (down conc. gradient).
4) Sucrose molecule binds to protein at the same time. The movement of H+ ion also moves sucrose into cell, against a conc. gradient.
5) Sucrose molecule transported out of companion cell to sieve tube in same process.

Question 40

Why is active loading required?

Answer 40

Used to move substances into companion cells from surrounding tissues, and from companion cells into sieve tubes, against a conc. gradient.

Question 41

Evidence for translocation

Answer 41

Advances in microscopy means adaptations can be seen of companion cells.
Poisoning of mitochondria in companion cells stops translocation.
Flow of sugars is 10000 times faster than diffusion alone.
Aphids can feed on cut phloem. Proven that phloem sap is forced out through the stylet. Fluid from the aphid can be tested.

Question 42

Describe the movement of sucrose from the source to sink after active loading

Answer 42

1) Lots of sucrose in the top part of the phloem, lowering water potential in the sieve tubes.
2) Xylem lies next to the sieve tube elements. Water potential is higher in the xylem.
3) Higher water potential in xylem, so water enters sieve tube via osmosis, increasing water volume of sieve tube.
4) Sieve tube element has an increase in hydrostatic pressure between source and sink. Water will move down towards the sink.

Question 43

Describe how the sucrose moves into the sink

Answer 43

1) Glucose and sucrose are constantly used by the sink.
2) Sucrose is actively transported to the sink, increasing water potential of sieve tube.
3) Solutes at sink end have left, so water potential increases. H2O exits sieve tube via osmosis, lowering hydrostatic pressure.
4) H2O leaving, maintains a high to low hydrostatic pressure between top and bottom of sieve tube, so consistent toward pull happens.

Question 44

Evidence for mass flow

Answer 44

Tracers - radioactively label carbon. Carbon in the glucose created from photosynthesis, turns x-rays black. Can observe cells /areas of the phloem that transport sucrose.
Ringing - shows sucrose accumulation above a ring of bark removed. The accumulation bulges.

Question 45

Why might this theory of mass flow be wrong?

Answer 45

Not all solutes in the phloem move at the same rate. Sucrose always seems to move at the same rate, regardless of the concentration at the sink. No one is sure on the role of sieve plates in the process.

Question 46

Define hydrophyte and give an example

Answer 46

Plants that are either partially or completely submerged in water - have a high water availability, e.g. water lillies.

Question 47

Define xerophyte and give an example

Answer 47

Plants that live in areas where water availability is low, e.g. cacti or marram grass.

Question 48

Define mesophyte and give an example

Answer 48

Able to take up sufficient water to replace transpiration e.g. most plants.

Question 49

5 adaptations of xerophytes

Answer 49

1) Reduced SA:VR - smaller surface on which evaporation can happen on is reduced. Reduced transpiration rate.
2) Thick waxy cuticle - Covers epidermis to reduce water loss by evaporation.
3) Hairs and spikes - Traps a layer of still air, creating a microclimate. This reduces the water potential gradient, reducing water loss by transpiration.
4) Ability to store water - store water on swollen stems or thick fleshy leaves. High conc. of pentose compounds hold H2O. Reduces water loss by transpiration.
5) Stomata - Sunken to reduce air movement, trapping a layer of air in a microclimate, reducing water potential gradient, and transpiration.

Question 50

How and why do mesophytes prevent water loss?

Answer 50

A waxy cuticle is on both sides of the leaf, which traps moisture inside, preventing transpiration. Stomata are only on the lower epidermis, to reduce factors which increase transpiration rate. Stomata are also closed at night.

Question 51

Adaptations of hydrophytes

Answer 51

1) Air spaces - enables leaves and flowers to float on water, and to store O2.
2) Stomata mainly on surface - maximise no. for gaseous exchange. No risk to plant of loss of turgor as water is always available.
3) Stem flexibility - water supports the leaves and flowers, so no need for strong supporting structures. Helps reduce damage by water currents.
4) Thin waxy cuticle - don’t need to conserve water as it is always in plentiful supply.
5) Wide, flat leaves - spread out to increase SA:VR, to capture as much light as possible for photosynthesis.

Question 52

Marram Grass Adaptations

Answer 52

1) Sunken stomata in pits - reduce air movement around stomata, creating a water potential gradient, reducing transpiration.
2) Hinge (bulliform) cells - lose turgidity and collapse in dry conditions, becoming curled. Reduces air movement and increases humidity, reducing transpiration.
3) Hairs on epidermis trap water vapour, reducing water potential gradient between leaf and air, reducing transpiration.
4) Thick, waxy cuticle - on epidermis, to reduce water loss by evaporation, as this layer is waterproof.

Question 53

How can stomata be investigated? Method 1

Answer 53

1) Small drop of water on a microscope slide.
2) Hold the leaf with the surface to be examined.
3) Tear the leaf to reveal part of the epidermis.
4) Place the leaf on microscope slide and examine.

Question 54

How can stomata be investigated? Method 2

Answer 54

1) Paint surface of leaf with nail varnish.
2) Allow to dry.
3) Peel varnish off with forceps.
4) Place on a dry microscope slide and examine.

Question 55

How to calculate density of stomata per unit area

Answer 55

No. stomata x (density of stomata / area of F.O.V (Pi x r2))

Question 56

Why are the methods useful?

Answer 56

Count no. of stomata that are open and closed.
Adaptions of plant to environment can be observed.
Effects of changing environment.
No., density and distribution on upper an lower epidermis can be measured / estimated.