3.1.3 Transport In Plants

Question 1

Structure and function of root hair cell?

Answer 1

Collect water and mineral nutrients that are present in the soil and take up these in solution up through the roots to the rest of the plant.

Question 2

Structure and function of epidermis?

Answer 2

Protects against water loss, regulates gas exchange, secretes metabolic compounds, and absorbs water and mineral nutrients

Question 3

Structure and Function of Piliferous layer?

Answer 3

Region of the epidermis of the root; produces abundant root hairs and is involved in the uptake of water and nutrients

Question 4

Structure and function of endodermis?

Answer 4

A single layer of cells that borders the cortex of a root. The endodermis functions allows the root to select what gets into the vascular core.

Question 5

Structure and function of the cortex?

Answer 5

The outermost layer of the stem or root of a plant. It transports materials into the central cylinder of the root through diffusion and stores food in the form of starch

Question 6

Structure and Function of the casparian strip?

Answer 6

A band of waterproof tissue that is found on the side and walls of the endodermis of roots. The strip prevents the water from entering the pericycle except through the cytoplasm of endodermal cells. This may be important in producing root pressure

Question 7

Structure and Function of pericycle?

Answer 7

Provide support,structure + protection cells surround the xylem and phloem in the stem

Question 8

What is the symplast pathway?

Answer 8

The symplast pathway is where water moves between cytoplasm/vacuoles of adjacent cells across the cortex of the root.

Question 9

What is the apoplast pathway?

Answer 9

the apoplast pathway can only take water a certain way; near the xylem, the Casparian strip forms an impenetrable barrier to water in the cell walls, and water must move into the cytoplasm to continue. Through the cell walls of the cells.

Question 10

What are the connecting passages called?

Answer 10

Plasmodesmata

Question 11

What is a monocotyledonous plant?

Answer 11

1 seed leaf

Question 12

What is a dicotyledonous plant?

Answer 12

2 seed leaves

Question 13

What are parenchyma?

Answer 13

Packing cells of the plant?

Question 14

What does the position of the vascular bundle determine?

Answer 14

In the stem, the position of the vascular bundle (in a ring) helps to support the stem against sideways forces

Question 15

Why is water important?

Answer 15

It is a substrate for photosynthesis

It is a pathway for transport of mineral ions through the plant

It provides support through turgidity

Evaporation may help to cool leaf surfaces

Question 16

Describe the process of water transport through the plant?

Answer 16

Water enters the root hair cells by osmosis. This happens because soil water has a higher water potential than the cytoplasm of the root hair cell. Water is drawn from the cells in the xylem to replace that which has been lost from the leaves.

Water molecules inside the xylem cells are strongly attracted to each other. There is strong cohesion between the molecules because of hydrogen bonding. A continuous column of water is therefore pulled up the stem in the transpiration stream by evaporation from the leaves.

As water travels through the xylem in the stem and leaf, it is being replaced by water taken up by the roots.

Question 17

Atmospheric conditions affecting transpiration?

Answer 17

Wind

High Temperatures

Low Humidity

High Light Intensity

Question 18

What are the 2 functions of the xylem?

Answer 18

Support and transport of water and mineral ions

Question 19

Structure and function of Xylem?

Answer 19

Dead cells when functioning in the xylem.
Long and hollow; several columns of cells fusing together end to end
No end cell walls = hollow tube
Tannin deposits

Lignificad secondary walls = provide extra mechanical strength. Lignin found in rings, spirals or tubes.
Bordered pits without lignin where water leaves the xylem and moves into other cells of the plant.

No nucleus, no cytoplasm, no vacuoles one lignified cells.

Waterproof due to lignin

Question 20

What tissue is the phloem made out of?

Answer 20

Living tissue

Question 21

What is the function of the phloem?

Answer 21

Transporte food in organic solutes from the leaves.

Supplies cells with sugars and amino acids needed for cellular respiration and the synthesis of other molecules.

Question 22

How many ways can transport travel in the phloem?

Answer 22

2 ways

Question 23

What is the structure of sieve tube elements in the phloem?

Answer 23

Cells joined end to end to form long hollow structure.
Not lignified.
Walls perforate today form sieve plates which are porous.
Filled with phloem sap.
Mature cells have no nucleus.

Question 24

What structures do companion cells form in phloem?

Answer 24

Form with sieve cells.
Liked to elements by plasmodesmata.
Maintained nucleus and organelles because companion cells are metabolically active.
Function like a life support system for plants.

Question 25

What are the 3 mechanisms of water transport?

Answer 25

Capillarity
Root pressure
Cohesion tension theory

Question 26

Explain capillarity

Answer 26

Against the force of gravity., narrow diameter.
Strong intermolecular forces of attraction between water molecules- cohesion.

Attraction between water and sides of vessel - adhesion

Capillarity cannot act alone due to the maximum height capacity travelled by capillarity.

Question 27

Explain root pressure theory?

Answer 27

Result of active secretion of ions across endodermal cells of the root and subsequence osmotic flow.

Again root pressure is too small to act alone but does play a contributory role.

Question 28

Explain the cohesion tension theory?

Answer 28

When a water molecule is lost via transpiration another one is pulled along by the processes of cohesion and tension. Water is polar which means that molecules are attracted to one another which creates surface tension.
Transpiration pull which utilises capillary action and the inherent surface tension is the primary mechanism of water movement in plants.

Question 29

How does the gradient of water potential change as you’ve towards the stomata?

Answer 29

The gradient of water potential decreases as you move towards the stomata as water leaves the stomata in the form of water vapour

Question 30

What is transpiration?

Answer 30

Transpiration: is the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by the diffusion of water vapour through the stomata

Question 31

What is translocation?

Answer 31

Translocation is the movement of organic compounds from where they are made at their source, to where they are required at their sink. It is an active process which can be used to transport phloem up or down the plant.

Question 32

Examples of sources?

Answer 32

Green leaves
Stems
Storage organs
Food stored in seeds

Question 33

Examples of sinks?

Answer 33

Growing roots
Active processes
Meristem cell activity
Developing stores eg fruits

Question 34

What graph proves the cohesion tension theory?

Answer 34

Dendograph

Question 35

What kind of process is translocation?

Answer 35

An active process

Question 36

Explain the process of translocation in plants?

Answer 36

Aerobic respiration in the mitochondria produces ATP
H+ ions are pumped out

Cotransporter protein or proton pump

H+ ions then return to companion cells with a sucrose molecule
This sucrose then diffuses into sieve tube elements

Question 37

What is the mass flow hypothesis?

Answer 37

The mass flow Hypothesis suggests that there is a passive movement of sucrose from the phloem where it is most concentrated to other areas like growing tissues were sucrose is less concentrated i.e. the sink

Question 38

Explain the mass flow hypothesis?

Answer 38

Source cells (mesophyll cells) produce sucrose during photosynthesis which decreases the water potential of the cell. Water diffuses vía osmosis from the xylem down a w.p gradient.

Causes hydrostatic pressure to build up and sucrose molecules to be forced out of the cell into the phloem.

Pressure pushes sucrose down towards the sink cells = mass flow hypothesis

At the sink cell, the sucrose is either used for respiration or converted into insoluble starch for storage.

Question 39

Evidence that the phloem is the tissue for translocation?

Answer 39

Ringing / girdling
Carbon-14 labelled sucrose (radioactive tracers)
Experiments using aphids

Question 40

At what point are stomata closed?

Answer 40

When water leaves the guard cells and therefore the guard cells are flaccid

Question 41

At what point are stomata open?

Answer 41

Stomata are open when the guard cells are turgid, filled with water.

Question 42

Mechanism for the opening of the stomata?

Answer 42

Blue light
ATP —> ADP + Pi
This reaction produces energy to pump H+ ions out = active transport
PROTON PUMP

H+ ions renter taking Cl- ions through passive transport > co transport
Potassium back in to balance charges
Decrease w.p
Water enters vía osmosis down a w.p gradient

Question 43

Explain the adaptation of sunken stomata?

Answer 43

Creates a chamber of humidity which Traps water vapour and keeps humidity high. This reduces the W.p gradient which reduces evaporation. As a result transpiration is reduced.

Question 44

Explain how a covering of leaf epidermal hairs helps xerophytes survive in their habitat?

Answer 44

The presence of hers creates a chamber of high humidity to trap water vapour.This reduces a w.p gradient which reduces evaporation. As a result of reduced evaporation the transpiration rate is also reduced.

Question 45

Explain why water loss from a plant is unavoidable?

Answer 45

Transpiration, and resulting water loss, is unavoidable as the leaves’ stomata need to be open to let in carbon dioxide for photosynthesis.

Question 46

Adaptations of hydrophytes?

Answer 46

Thin / no waxy cuticle - transpiration is not an issue

Presence of aerenchyma

Stem hypertrophy

Submerged dissected leaves

Location of stomata

Question 47

What are aerenchyma and what do they do?

Answer 47

Aerenchyma is a modified parenchyma, where the cells are arranged with regular air spaces or air chambers to facilitate diffusion of gases to provide buoyancy to aquatic plants such as lotus and water hyacinth.

Question 48

How does the location of stomata on hydrophytes and xerophytes differ?

Answer 48

Xerophytes - lower surface to reduce transpiration rate

Hydrophytes-