Module 3.1.3 Transport In Plants

Question 1

Why do plants have transport systems?

Answer 1

Moves substances between the leaves, stem & roots

Question 2

Why is there a need for transport systems in plants?

Answer 2

Metabolic demands - photosynthesis happens in the leaves although many internal & underground parts of the plant dont photosynthesis & need nutrients & wastes removed
Size - some plants small but some are very large so effective transport systems required to move substances up & down the plant
SA:V - Leaves are adapted for a large SA:V (photosynthesis) but other components dont so they cannot rely on diffusion

Question 3

What are dicotyledonous plants?

Answer 3

Plants that makes seeds that contain cotyledons - organs that act as food stores for the developing embryo plant & 1st form leaves when the seed germinates

Question 4

What is the difference between herbaceous & woody dicot plants?

Answer 4

Herbaceous - soft tissues & live a relatively short life
Woody - hard lignified tissues & long life cycle

Question 5

What are the 2 main transport vessels in herbaceous dicots?

Answer 5

The phloem & xylem

Question 6

Where & how are the transport tissues arranged in the plant?

Answer 6

In vascular bundles in the leaves, stem & roots

Question 7

What is the 2 main functions of the xylem?

Answer 7

Transport of water & mineral ions
Support

Question 8

Is the xylem made from dead or living tissue?

Answer 8

Dead

Question 9

What is the structure of the xylem?

Answer 9

Long hollow tube made by several columns of cells fusing together end to end
Walls contain lignin - support

Question 10

What are the 2 other tissues associated in the xylem in herbaceous dicots?

Answer 10

Xylem parenchyma
Xylem fibres

Question 11

What is the xylem parenchyma?

Answer 11

Tissue that stores food & contains tannin deposits (bitter chemical that protects plant tissues from attacks

Question 12

What is the xylem fibres?

Answer 12

Tissues with long cells with lignified secondary walls to provide mechanical strength

Doesn’t transport water

Question 13

What is the function of the phloem?

Answer 13

Transports sugars & amino acids needed for cellular respiration & synthesis of other useful molecules from the leaves to around the plant

Question 14

What other supporting tissues does the phloem contain?

Answer 14

Fibres & sclereids - cells with extremely thick cell walls

Question 15

What is the 2 components of the phloem tube?

Answer 15

Sieve tube element
Companion cells

Question 16

What is the structure of the sieve tube element?

Answer 16

Hollow structure made of many cells joined end to end
Not lignifies
Walls are perforated to form sieve plates
Mature phloem cells have no nucleus

Question 17

What is the function of the sieve tube element?

Answer 17

Lets the phloem contents through
As large appear, the tonoplast, nucleus & other organelles break down so the phloem becomes a tube filled with phloem sap

Question 18

What is the structure of the companion cells

Answer 18

Form with sieve tube elements & linked by many plasmodesmata
Have their nucleus & all their organelles
Very active

Question 19

What is the function of the companion cells

Answer 19

Function as a ‘life support system’ for the sieve tube cells as they have lost most of their normal cell’s functions

Question 20

What are some adaptions of leaves?

Answer 20

Have a large SA for capturing sunlight & carrying out photosynthesis
Waxy cuticle - waterproof (prevents leaves from loosing water rapidly & constantly by evaporation from their surfaces)

Question 21

Why is it important that gases move in & out of the air?

Answer 21

For photosynthesis to occur

Question 22

What does the stomata do?

Answer 22

Allows CO2 & O2 to move in & out of the leaf down a concentration gradient due to diffusion

Question 23

What allows the stomata to open & close?

Answer 23

The guard cells

Question 24

What happens when the stomata are open?

Answer 24

Gas exchange in & out the leaf & water moves out by diffusion

Question 25

What is the loss of water by diffusion?

Answer 25

Transpiration - inevitable consequence of gas exchange

Question 26

Why do stomata need to be open all the time?

Answer 26

Cellular respiration happens day & night

Question 27

Describe the transpiration stream

Answer 27

Water enters a plant by osmosis & is transported up the xylem until it reaches the leaves. Then it moves by osmosis across membranes & by diffusion in the apoplast pathway from the xylem through the cells of the lead where it evaporates from the freely permeable cellulose cell wall of the mesophyll cells into the leaves into the air spaces

Question 28

What is the word equation for photosynthesis?

Answer 28

Water + carbon dioxide -light-> glucose & oxygen

Question 29

Where does photosynthesis occur?

Answer 29

In chloroplasts in palisade cells

Question 30

How do the reactants for photosynthesis enter the plant?

Answer 30

Water -> xylem vessel through osmosis
Carbon dioxide -> diffuses through the stomata of guard cels across the spongy mesophyll towards palisade cells

Question 31

What are glucose & O2 used for in a plant?

Answer 31

The sinks (respiring tissues)

Question 32

What is translocation?

Answer 32

The movement of assimilates e.g. sucrose from the source to the sinks of plants through the phloem

Question 33

Describe translocation & active loading

Answer 33

The H+ ions move into the palisade cell from the companion cell, through the proton pump by active transport. This increases the concentration of the H+ ions in the palisade cell. Sucrose then moves into the companion cell through the H+ sucrose co-transporter. This is usually done by diffusion but if there is a high concentration of sucrose in the companion cell, the sucrose will be pumped across the membrane by active transport. This increases the concentration of sucrose in the companion cell. This sucrose then moves into the phloem through the plasmodesmata by diffusion which lowers the water potential of the cell. This then causes water to then move into the phloem by osmosis.

Question 34

What is the difference between water potential & hydrostatic pressure?

Answer 34

Water potential -> the potential energy of water in the system to pure water

Hydrostatic pressure -> the concentration of molecules

Question 35

Describe transpiration

Answer 35

Water vapour moves out of the stomata of the guard cells through evaporation which lowers the water potential. The water in the roots is cohesive so the molecules bond together with weak hydrogen bonds. Water also has an adhesive force with the xylem walls, due to it being reinforced with lignin. This causes the transpiration stream to move as one body. Furthermore, there is root pressure in the roots as water moves into the root hair cell through active transport which creates a high hydrostatic pressure which makes the water cohesive. This creates a tension & a transpiration pull where the water is pulled up the xylem from the roots to the leaves for photosynthesis.