Unit 3.3- Transport in plants

Question 1

Dicotyledonous plants definition:

Answer 1

Plants with two seed leaves and a branching pattern of veins in the leaf

Question 2

Meristem definition:

Answer 2

A layer of dividing cells

Question 3

Phloem definition:

Answer 3

Transports dissolved assimilates

Question 4

Vascular tissue definition:

Answer 4

Consists of cells specialised for transporting fluids by mass flow

Question 5

Xylem definition:

Answer 5

Transports water and minerals

Question 6

Why can plants’ demand for oxygen be met by diffusion?

Answer 6

They are not very active so their respiration rate is low

Question 7

What do plants have a high demand for?

Answer 7

Water and sugars

Question 8

Why do plants need a transport system?

Answer 8

To move:

• Water and minerals from the roots up to the leaves
• Sugars from the leaves to the rest of the plant

Question 9

Why are collenchyma and sclernchyma also found in vascular bundles as well as just xylem and phloem?

Answer 9

They provide strength and support the plant

Question 10

What is the structure of xylem and phloem in the young root?

Answer 10

• Central core of xylem often in the shape of an X
• Phloem is found in between the arms of the X
• This provides strength
• The endodermis is a sheeth of cells around the vascualr bundle
• The medulla is the space in the rest of it (not actually space i think)

Question 11

What is the translocation system?

Answer 11

• The movement of sucrose and amino acids through phloem vessels
• Active process

Question 12

What is the structure of xylem and phloem in the stem?

Answer 12

• Vascular bundles are found near the outer edge of the stem
• The xylem is found in the inner most third
• The phloem is found in the middle third
• The sclerenchyma is found in the outer most third
• The medulla is the bit in the middle
• The cortex is between the bundles
• The collenchyma is a layer around the edge
• The cambium is a layer of meristem cells found between the xylem and phloem. It produces new xylem and phloem

Question 13

What is the difference in the structure of xylem and phloem in the stem in woody and non-woody plants

Answer 13

• In non-woody plants the bundles are separate and discrete
• In woody plants, the bundles are separate in the young stem but become a continuous ring in older stems
• This provides strength and flexibility

Question 14

Companion cells definition:

Answer 14

The cells that help to load the sucrose onto the sieve tubes

Question 15

How are xylem vessels formed?

Answer 15

• Lignin impregnates the walls of the cells forming the xylem vessels
• This makes the walls waterproof which kills the cells
• This leaves a long column of dead cells with no contents
• The lignin strengthens the walls and prevents it from collapsing, keeping it open at all times

Question 16

What does the lignin do in xylem vessels?

Answer 16

• Prevents it from collapsing
• Keeps the vessel open at all times, even when water is in short supply
• The lignin thickening forms patterns in the cell walls. they may be spiral. annular (rings) or reticulate (a network of broken rings). This prevents the vessel from being too rigid and allows some flexibility in the stem or branch

Question 17

What are bordered pits?

Answer 17

• Gaps in the cell wall where lignification is not complete
• The bordered pits in two adjacent vessels are lined up so that water can pass from one vessel to the other
• They also allow water to leave the xylem and move to the living parts of the plant

Question 18

What is phloem tissue made up of?

Answer 18

Sieve tube elements and companion cells

Question 19

What is sap made up of?

Answer 19

Sucrose dissolved in water

Question 20

What are companion cells?

Answer 20

• Found in between sieve tubes
• Large nucleus and dense cytoplasm
• Many mitochondria to produce the ATP needed for active processes
• Carry out the metabolic processes needed to load the assimilates actively into sieve tubes

Question 21

Plasmodesmata definition:

Answer 21

Gaps in the cell wall containing cytoplasm that connects two cells

Question 22

What is the apoplast pathway?

Answer 22

• Does not pass through any plasma membrane into cells
• Therefore the water moves by mass flow rather than osmosis
• Any dissolved mineral ions and salts can be carried by the water

Question 23

What is the symplast pathway?

Answer 23

The water passes through the plasmodesmata from one cell to another

Question 24

What is the vacular pathway?

Answer 24

Water passes through the plasmodesmata from one cell to another but can also pass through the vacuoles in the cells

Question 25

Potometer definition:

Answer 25

A device that can measure the rate of water uptake as a leafy stem transpires

Question 26

Transpiration definition:

Answer 26

The loss of water vapour from the arial parts of a plant, mostly through the stomata in the leaves

Question 27

How does light intensity affect transpiration rate?

Answer 27

In light, the stomata open which increases transpiration

Question 28

How does temperature affect transpiration rate?

Answer 28

Increases it by:

• Increasing the rate of evaporation from the surface
• Increases the rate of diffusion through the stomata because the water molecules have more kinetic energy
• Decreases the water vapour potential in the air, allowing a more rapid diffusion of water molecules out of the leaf

Question 29

How does relative humidity affect transpiration rate?

Answer 29

Higher relative humidity in the air decreases the rate of transpiration

Question 30

How does wind affect transpiration rate?

Answer 30

Air moving outside the leaf will carry more water vapour with it, maintaining a high water vapour potential gradient

Question 31

How does water availability affect transpiration rate?

Answer 31

If there is little water in the soil, then the lost water cannot be replaced. If there is insufficient water in the soil then the stomata close and the leaves will wilt

Question 32

What percentage of water uptake by plants is lost by transpiration?

Answer 32

More than 95%
This means that potometers are reasonably accurate because almost all the water taken by plants will be lost by transpiration

Question 33

What precautions are taken to ensure results from a potometere are accurate?

Answer 33

• Set it up under water to ensure there are no air bubbles in the apparatus
• Ensure the shoot is healthy
• Cut the stem under water to prevent air from entering the xylem
• Cut the stem at an angle to provide a large surface area in contact with the water
• Dry the leaves

Question 34

Adhesion definition:

Answer 34

The attraction between water molecules and the wall of the xylem vessel

Question 35

Cohesion definition:

Answer 35

The attraction between water molecules caused by hydrogen bonds

Question 36

The transpiration stream definition:

Answer 36

The movement of water from the soil, through the plant, to the air surrounding the leaves. The main driving force is the water potential gradient between the soil and the air in the leaf air spaces

Question 37

Endodermis definition:

Answer 37

A layer of cells surrounding the medulla and xylem

Question 38

Assimilates definition:

Answer 38

Substances that have become part of the plant

Question 39

Sink definition:

Answer 39

A part of the plant where assimilates are removed from the transport system

Question 40

Source definition:

Answer 40

A part of the plant that loads materials into the transport system

Question 41

Translocation definition:

Answer 41

The transport of assimilates through a plant

Question 42

Hydrophyte definition:

Answer 42

A plant adapted to living in water or where the ground is very wet

Question 43

Xerophyte definition:

Answer 43

A plant adapted to living in dry conditions