Transport in plants

Question 1

Why do plants need a transport system?

Answer 1

High metabolic demands

Size

Small SA:V ratio

Question 2

What are dicotes?

Answer 2

Dicotyledonous plants

Make seeds with 2 cotyledons (food stores for developing plant embryos)

Have vascular bundles = transport system)

Question 3

Describe cross-section of a stem?

Answer 3

Xylem = inner side of vascular bundle

Phloem = outer side of vascular bundle.

Epidermis = outer layer

Cortex = between epidermis + ring of vascular bundle

Parenchyma = inside ring

vascular bundles on the edge = strength and support.

Question 4

Describe cross section of the root?

Answer 4

Exodermis = outer layer
Epidermis = middle layer
Endodermis = inner layer

Xylem = x shape
Phloem = outside x shape

Question 5

Describe cross section of leaf?

Answer 5

Xylem on top

Phloem underneath

Question 6

Describe function of the xylem?

Answer 6

Transports water + mineral ions up the plant (transpiration pull)

Supports the plant
~~> lignin deposited onto cell wall keeping it rigid (no organelles so cells = dead)

Withstand pressure of water uptake

Question 7

Structure of xylem:

Answer 7

Cell walls completely broken down to form hollow tube

Water moves up xylem

Lignified cell wall = provides mechanical strength (rings/spirals)

Non-lignified pits = allow H2O + mineral ions to leave xylem.

Question 8

Role of xylem parenchyma?

Answer 8

Stores food

Contains tannin = bitter chemical

Defence against herbivores

Question 9

Function of phloem:

Answer 9

Transports assimilates (sucrose) from source to sink of plant.

Alive: for active transport + translocation

Requires energy

Question 10

Why is sucrose transported instead of glucose?

Answer 10

Less reactive

Not used up in respiration

Question 11

Structure of phloem:

Answer 11

Cell wall partially broken down

Individual cell = sieve tube element

Plasmodesmata = gaps that link cytoplasm of adjacent cells

Companion cell =keeps phloem alive
Involved in translocation.

Question 12

How does water enter a plant?

Answer 12

Through root hair cell (increases SA)

Higher water potential in soil

Question 13

Describe symplast pathway?

Answer 13

Water enters root hair cell via osmosis

Travels through cortex via living parts of cell (cytoplasm) + plasmodesmata until it reaches xylem vessel

Maintains steep WP gradient

Water moves down WP gradient

Question 14

Describe the apoplast pathway?

Answer 14

Water = absorbed into cell wall of root hair cell

Travels through cortex via non-living parts of cell. (Cell wall) –> reaches endodermis layer

Moving via mass flow –> area of high hydrostatic pressure to low hydrostatic pressure.

Question 15

How does water move across endodermis?

Answer 15

Casparian strip = waxy suberin

Defence mechanism

Waterproof

Forces water to move into symplast pathways across partially permeable membrane

—–> filters out toxins

Question 16

How does water get loaded into xylem?

Answer 16

Move mineral ions into xylem first.

Active transport = ATP

Lower WP in xylem

Moves water into xylem by osmosis down WP gradient.

Generates root pressure

Pushes water up xylem. (cohesion + adhesion)

Question 17

What is the evidence of AT and root pressure?

Answer 17

Poison —> prevent the production of ATP
~~ Cyanide = no energy supply = the root pressure disappears.

• Root pressure increases with a rise in temperature and falls with a fall in temperature,
  — > chemical reactions involved

Oxygen or respiratory substrates fall = root pressure falls.