Transport in Plants

Question 1

What are the 3 reasons plants need transport systems?

Answer 1

metabolic demands
size
surface area

Question 2

Why do a plant’s metabolic demands mean it needs a transport system?

Answer 2

• Glucose and O2 made by photosynthesising parts of plant need to be transported to all cells (ie. underground parts that cannot photo.)
• Waste must be removed
• Hormones made in one part of plant need to be transported to where they act
• Mineral ions absorbed by the root need to be transported to all cells for protein synthesis

Question 3

Why does a plant’s size mean it needs a transport system?

Answer 3

large plants (partic. perennials) need an effective transport system to move substances up and down from roots to topmost leaves

Question 4

Why does a plant’s SA:Vol ratio mean it needs a transport system?

Answer 4

while leaves have a large sa:vol ratio for photo., plants as a whole have a small sa:vol ratio so cannot rely on diffustion alone to supply cells

Question 5

herbaceous

Answer 5

type of dicot with soft tissues and short life cycle

Question 6

dicotyledonous plants

Answer 6

produce seeds with 2 cotyledon halves

Question 7

cotyledons

Answer 7

the two sides of dicotyledonous plant seeds that store nutrients for seed germination and form the first leaves

Question 8

arborescent (woody)

Answer 8

type of dicot with hard lignified tissue and long life cycle

Question 9

vascular system

Answer 9

series of transport vessels running through stem, roots, and leaves

Question 10

why are vascular bundles located in the middle of roots?

Answer 10

to withstand tugging strains

Question 11

what are the layers of the vascular bundle? (outside to inside)

Answer 11

epidermis
cortex (containing parenchyma)
endodermis
pericycle
phloem
xylem

Question 12

what is the function of the pericycle?

Answer 12

contains meristem cells so is able to divide and produce new xylem and phloem elements

Question 13

function of xylem

Answer 13

• transports water and minerals up the stem to the leaves

- supports plant

Question 14

function of phloem

Answer 14

transports sugars and amino acids up and down the plant from leaves (where food is made by photosynthesis) to the cells needed for respiration.

Question 15

structure of xylem vessel

Answer 15

long, hollow column of dead cells (vessel elements) fused end to end
- lignified cell walls

Question 16

function of parenchyma cells

Answer 16

packing tissue;
provides support;
walls permeable to water and dissolved solutes (water travels easily)

Question 17

function of cortex

Answer 17

several layers of undifferentiated cells (parenchyma) between endodermis and epidermis. Contains air spaces.

Question 18

in a root, a vascular bundle contains

Answer 18

xylem

phloem

Question 19

in a stem, vascular bundle contains

Answer 19

xylem
phloem
cambium

Question 20

what is the cambium in a stem?

Answer 20

.

Question 21

what are the three different cell types found in xylem tissue?

Answer 21

• xylem parenchyma
• xylem vessels
• xylem fibres

Question 22

what happens when lignin is put in place in xylem cell walls?

Answer 22

• causes cell contents to die
• reinforces xylem vessels so they do not collapse under transpiration pull
• lignin is impermeable to water

Question 23

what are the three different ways lignin is laid down in the walls of xylem vessels?

Answer 23

rings
spirals
solid tubes with small unlignified sections (pits)

Question 24

function of pits (small holes in lignified xylem cell walls)

Answer 24

allow water to pass sideways into other cells of the plant or to other xylem vessels if one becomes blocked

Question 25

xylem parenchyma function

Answer 25

• Stores food

- Contains tannin- bitter tasting- protects plant from herbivores

Question 26

xylem parenchyma structure

Answer 26

• Thick-walled

- Packs around xylem vessels to provide support

Question 27

xylem fibres structure

Answer 27

• Long cells with lignified secondary walls

- Do not transport water

Question 28

xylem fibres function

Answer 28

Extra mechanical strength

Question 29

sugars are dissolved in water to form

Answer 29

sap

Question 30

phloem structure

Answer 30

• living sieve tube elements lined up end to end to form sieve tubes (long, hollow structure)
• area between elements perforated by sieve plates
• not lignified
• no organelles
• filled with phloem sap

Question 31

purpose of sieve plates in phloem

Answer 31

allow the phloem contents to flow through

Question 32

what happens to all the organelles in the phloem cells?

Answer 32

as pores appear in the cell walls to form sieve plates, the tonoplast and other organelles break down and the nucleus disappears

Question 33

what are linked to phloem cells? how?

Answer 33

companion cells

plasmodesmata (channels through cellulose cell walls linking the cytoplasm of neighbouring cells)

Question 34

function of phloem companion cells

Answer 34

‘life support system’

- very metabolically active

Question 35

phloem companion cells structure

Answer 35

• Large nucleus
• Dense cytoplasm
• Numerous mitochondria
  - Metabolic processes for both companion and sieve tube. e.g. produce ATP for loading sucrose into sieve tubes (active transport). Very metabolically active cells.
• Plasmodesmata link sieve tubes and companion cells. (exchange of materials)

Question 36

what other phloem tissues (aside from companion cells) exist and what is their function?

Answer 36

• Sclereids (cells with extremely thick cell walls)
• Fibres

Both tissues are for support