Module 3: Transport in Plants

Question 1

Why do plants need transport systems?

Answer 1

*multicellular
*small surface area:volume ratio
*high metabolic rate
*need substances
*need to remove waste products
*exchanging substances by direct diffusion is too slow

Question 2

What tissues make up the plant’s vascular system?

Answer 2

Xylem and phloem

Question 3

Where is the xylem found in roots?

Answer 3

In the centre.

Question 4

Where is the phloem found in roots?

Answer 4

Surrounding the xylem in the centre.

Question 5

What is the function of the xylem and phloem in roots?

Answer 5

Provide support for the root as it pushes through the soil.

Question 6

Where is the xyelm and phloem found in stems?

Answer 6

Near the outside.

Question 7

What is the function of the xylem and phloem in stems?

Answer 7

Provide ‘scaffolding’ to reduce bending.

Question 8

Where is the xylem and phloem found in leaves?

Answer 8

Make up a a network of veins.

Question 9

What is the function of the xylem and phloem in leaves?

Answer 9

Provide support to thin leaves.

Question 10

What are transverse cross-sections?

Answer 10

Sections cut though the structure at a right angle to the length.

Question 11

What are longitudinal cross-sections?

Answer 11

Sections cut through the sturcture along the length.

Question 12

What is the main function of xylem tissue?

Answer 12

Transports water and minerals in solution.

Question 13

Which way does movement happen in xylem tissue?

Answer 13

Up the plant, from the roots to the leaves.

Question 14

What is the other function of xylem tissue?

Answer 14

Support.

Question 15

What is xylem tissue made up of?

Answer 15

Several different types of cells.

Question 16

What do xylem vessels do?

Answer 16

Transport the water and minerals in solution.

Question 17

Describe the cells of xylem vessels.

Answer 17

Dead with no cytoplasm.

Question 18

Describe the structure of xylem vessels.

Answer 18

Long, tube like structures formed from vessel elements joined end to end, with no end walls, forming a continuous tube.

Question 19

What are the cell walls of xylem vessels thickened with?

Answer 19

Lignin.

Question 20

What is lignin?

Answer 20

A woody substance that thickens xylem vessel cell walls.

Question 21

What does lignin do?

Answer 21

Helps to support xylem vessels and stops them collapsing inwards.

Question 22

How is lignin deposited in cell walls?

Answer 22

In different ways, e.g. in spirals or in distinct rings.

Question 23

What happens to the lignin in a cell as it ages?

Answer 23

Amount increases.

Question 24

How does water and ions move in and out of xylem vessels?

Answer 24

Through small pits in the walls where there is no lignin.

Question 25

What is the only function of phloem tissue?

Answer 25

Transports solutes around plants.

Question 26

What is the main substance that phloem tissue transports?

Answer 26

Sugars, such as sucrose.

Question 27

Which way does transport happen in phloem tissue?

Answer 27

Both up and down.

Question 28

What is the structure of phloem tissue?

Answer 28

Cells arranged in tubes.

Question 29

What four things does phloem tissue contain?

Answer 29

*phloem fibres *phloem parenchyma *sieve tube elements *companion cells

Question 30

What are sieve tube elements?

Answer 30

Living cells joined end to end to form sieve tubes.

Question 31

What is a sieve tube?

Answer 31

The tube in phloem tissue for transporting.

Question 32

What is unusual about sieve tube elemtns?

Answer 32

They are living cells but have no nucleus, only a thin layer of cytoplasm and few organelles.

Question 33

How is the cytoplasm of adjacent sieve tube elements joined?

Answer 33

Through holes in the sieve plates.

Question 34

What do the end walls of the sieve tube elements form?

Answer 34

Sieve plates.

Question 35

What is the purpose of sieve plates?

Answer 35

They have many holes, allowing solutes through.

Question 36

What is the function of companion cells?

Answer 36

Carry out the living functions for their sieve cells as well as themselves.

Question 37

Why are companion cells needed?

Answer 37

Sieve tube elements lack a nucleus and other organelles so cannot survive on their own.

Question 38

What does every sieve tube element have one of?

Answer 38

A companion cell.

Question 39

What is the method for dissecting a plant stem?

Answer 39

1. use a scalpel to cut a cross-section of the stem as thinly as possible 2. use tweezers to place the sections in water until needed 3. transfer each section into a dish containing stain and leave for 1 minute 4. rinse off the sections with water and mount onto a slide

Question 40

When dissecting a plant stem, why are the sections placed in water until needed?

Answer 40

To prevent them from drying out.

Question 41

What is an example of a stain used for plant stems?

Answer 41

Toluidine blue O (TBO)

Question 42

What does toluidine blue O stain?

Answer 42

Lignin in xylem vessels blue-green, allowing us to see the position and structure.

Question 43

What are the four factors affecting rate of transpiration?

Answer 43

*temperature *light *humidity *wind

Question 44

How does temperature affect rate of transpiration?

Answer 44

*increasing temperature increases rate of transpiration *warmer water molecules have more energy, so evaporate from the cells inside the leaf faster *this increases water potential between the inside and outside of leaf *so water diffuses out of the leaf faster

Question 45

How does light affect rate of transpiration?

Answer 45

*increasing light intensity increases rate of transpiration *the stomata open when it gets light so carbon dioxide can diffuse into the leaf for photosynthesis *when it's dark, the stomata close so there's little transpiration as water cannot diffuse out the stomata

Question 46

How does humidity affect rate of transpiration?

Answer 46

*decreasing the humidity increases the rate of transpiration *of the air around plant is dry, the water potential gradient between the leaf and air is increased *this increases transpiration

Question 47

How does wind affect rate of transpiration?

Answer 47

*increasing wind increases rate of transpiration *lots of air movement blows away water molecules around the stomata *this increases the water potential gradient *this increases rate of transpiration