Transport in plants

Question 1

Identify the 2 type of vascular tissues

Answer 1

• Xylem

- Phloem (sieve tube elements&companion cells)

Question 2

Functions of xylem

2 pts

Answer 2

• conducts water and dissolved mineral salts from the roots the stem and leaves
• provide mechanical support for plant

Question 3

Structure of xylem

6 pts

Answer 3

• made up of many dead cells fused together at the ends to form a long hollow tube (do not contain protoplasm)
• the hollow tubes are called xylem vessels
• xylem tissues consist mainly of xylem vessels
• continuous lumen with no cross-walls or protoplasm
• lignin deposits in inner walls of xylem vessels
• lignin deposited in form of rings, spirals, or whole vessel lignified except for regions called pits (diff patterns of lignifications)

Question 4

Functions of xylem

2 pts

Answer 4

-conducts water and dissolved mineral salts from the roots the stem and leaves

Question 5

Structure of xylem

6 pts

Answer 5

• made up of many dead cells fused together at the ends to form a long hollow tube
• the hollow tubes are called xylem vessels
• xylem tissues consist mainly of xylem vessels
• continuous lumen with no cross-walls or protoplasm
• lignin deposits in inner walls of xylem vessels
• lignin deposited in form of rings, spirals, or whole vessel lignified except for regions called pits

Question 6

Why are there different patterns of lignifications?

2 pts

Answer 6

• annular (rings) and spiral usually younger plants

- pitted usually when plant is older and more matured

Question 7

Why are there are holes in the lignifications?

2 pts

Answer 7

• transport and to allow water and mineral salts to move out to sides e.g to side branches
• also move to phloem to help push sucrose down

Question 8

How is the xylem adapted for its functions?

Answer 8

• empty lumen without protoplasm or cross-walls enables water to move easily thru lumen
• walls are lignified to prevent collapse of vessels

Question 9

Function of phloem

Answer 9

-transports manufactured food such as sucrose and amino acids from leaves to other parts of plant

Question 10

Structure of phloem

2 pts

Answer 10

• consists of 2 main types of cells: sieve tube elements and companion cells
• other cell types present: phloem parenchyma cells and phloem fibres

Question 11

Structure of sieve tube

5 pts

Answer 11

• elongated cells
• lack nuclei
• thin layers of cytoplasm (diff between xylem&sieve tube cells)
• sieve tube elements made of sieve tube cell joined end to end to form sieve plate in between
• sieve plates are cross-walls with many small sieve pores

Question 12

Structure of companion cells

2 pts

Answer 12

• narrow, thin-walled cells
• contain cytoplasm and numerous mitochondria (aerobic repiration, release energy, needed to transport sucrose and amino acid

Question 13

Purpose of companion cell

2 pts

Answer 13

• mature sieve tube cells does not have most of its organelles (e.g. central vacuole, nucleus, mitochondria etc)
• companion cell helps to keep sieve tube cell alive by providing it with nutrients and energy

Question 14

How is the sieve tube (phloem) adapted for its function?

3 pts

Answer 14

• sieve tube elements have very little protoplasm, arranged to form a continuous column
• this reduces resistance for flow of substances within phloem
• pores within sieve plates allow rapid flow of sucrose and amino acids

Question 15

How is the companion cell (phloem) adapted for its function?
(2 pts)

Answer 15

• companion cells contain numerous mitochondria (aerobic respiration)
• produce energy to allow sucrose and amino acids to be actively transported to sieve tubes
• every phloem sieve tube cell has an associated companion cell to ensure its survival

Question 16

How are vascular tissues organised in stems (arrangement of xylem&phloem)

Answer 16

-in a dicotyledonous stem, xylem and phloem grouped tgt to form vascular bundles

Question 17

How are vascular tissues organised in stems (cambium)

4 pts

Answer 17

• phloem lies outside xylem
• tissue called cambium lies between them
• cambium cells divide and differentiate to form new xylem and phloem tissues
• allows thickening of stem

Question 18

How are vascular tissues organised in stems (pith)

Answer 18

-vascular bundles arranged a ring around central region called the pith

Question 19

How are vascular tissues organised in stems (outer layer)

2 pts

Answer 19

• stem covered by a layer of cells called epidermis

- epidermal cells protected by waxy, waterproof cuticle (reduces evaporation of water from stem)

Question 20

How are vascular tissues organised in stems (cortex)

2 pts

Answer 20

• cortex is the region between vascular bundle and epidermis
• both pith and cortex are storage tissues

Question 21

How are vascular tissues organised in roots (arrangement of phloem&xylem)
(2 pts)

Answer 21

• in a dicotyledonous root, xylem and phloem not bundled tgt
• alternate with each other

Question 22

How are vascular tissues organised in roots (cortex)

3 pts

Answer 22

-cortex of root is a storage tissue
-innermost layer of root cortex is called endodermis
(endo=inside, epi=outside)
-endodermis controls what goes into xylem (like a gate)

Question 23

How are vascular tissues organised in roots (outer layer)

2 pts

Answer 23

• epidermis of root is outermost layer of cells

- also known as piliferous layer

Question 24

How are vascular tissues organised in roots (root hair)

2 pts

Answer 24

• each root hair is a tubular outgrowth of an epidermal cell
• outgrowth increase SA:V of root hair cell

Question 25

Define translocation | 4 pts

Answer 25

- the transport of manufactured food substances (sucrose&amino acids) in plants - bi-directional - food substances can move either down phloem tissues of shoots to roots - can also go up the phloem tissues of shoots to leaves

Question 26

Direction of translocation | 7 pts

Answer 26

- direction depends on demand and supply of sucrose - not all food produced is used by leaves - excess glucose stored in storage organs, often in lower portions of plant - sucrose&amino acids translocated from leaves to storage area, food move down shoot - environmental conditions not favourable, photosynthesis cannot occur optimally (e.g. during winter) - storage organ becomes main source of food - food translocated from lower parts of plant to higher parts

Question 27

How can translocation be studied? | 3 pts

Answer 27

- using aphids - "ringing" experiment - radioactive isotopes

Question 28

Translocation studies: Using aphids (steps)

Answer 28

1. Anaesthesise aphid with CO2 while it is feeding on stem 2. Cut off its body such that its proboscis remains in plant tissue 3. Analyse liquid that exudes from cut end of proboscis 4. Section the portion of stem that contains the proboscis and examine it under a microscope

Question 29

Translocation studies: Using aphids (why it is necessary to anaesthesise aphids)

Answer 29

- to enable body of aphid to be cut off while aphid is feeding - ensures proboscis remains in phloem sieve tube - if stylet severed, sap will continue to flow from plant due to hydrostatic pressure within sieve tube

Question 30

Explain how structure of root hair cell helps them to perform their functions in uptake of water&minerals (3 pts) (Practice paper question)

Answer 30

- each root hair is a tubular outgrowth of an epidermal cell, outgrowth increases SA:V, more water taken in at faster rate - RHC have large no. of mitochondria, release energy for active transport of mineral salts (not water) - large central vacuole with a cell membrane (tonoplast) prevent leakage of cell sap, increase conc gradient for faster diffusion

Question 31

Explain how water moves thru shoot and into air | 3 pts) (Practice paper question

Answer 31

- osmosis occurs from xylem to mesophyll cells and out of cells - water evaporates from thin film arnd cells into intercellular spaces - water vapour diffuses out of stomata