2101 - Stems

Question 1

What is a Stem?

Answer 1

Plant organ which connects the roots of a plant to its leaves and flowers.
Distinguished externally from roots by the presence of leaves and buds from their axils.

Question 2

Functions of a Stem

Answer 2

Holding leaves in optimum position for Photosynthesis and adequate air.
Transport of Water and Minerals from roots to the leaves.
Transport of Sugars from the leaves to other parts of the plant.
Holding flowers in optimum position for pollination by wind, insect or other vector.
Storage of starch… Solanum tuberosum (potato)

Question 3

External features of a Stem

Answer 3

Apical Bud (terminal bud)
Axillary Buds
Nodes
Internodes
Lenticels
Terminal bud scale scars
Leaf scars

Question 4

Shoot

Answer 4

Term for Stem and leaves together.

Question 5

External features of a Stem - Apical Bud

Answer 5

Contains the shoot apical meristem, surrounded by developing leaves.
Secretes auxins which suppress growth of axillary buds and creates Apical Dominance.

Question 6

External features of a Stem - Axillary Bud

Answer 6

An undeveloped shoot (a bud) which develops in the leaf axil.
Remains suppressed until Apical dominance is removed and it can grow a new stem.

Question 7

External features of a Stem - Node

Answer 7

The point of attachment of a leaf to a stem.

Question 8

External features of a Stem - Internode

Answer 8

The section between nodes on the stem.
Development determined by environmental constraints.
(between nodes only not bud scars and nodes)

Question 9

External features of a Stem - Leaf Scar

Answer 9

Where leaf petiole has detached from the stem. Corky layer.

Axillary buds found directly above the leaf scar.

Question 10

External features of a Stem - Terminal Bud Scale Scar

Answer 10

Indicator of the start/end of a season’s growth.

Question 11

External features of a Stem - Lenticel

Answer 11

Pore in the stem of woody plants.
Allow gaseous exchange between tissues beneath the stem surface and the atmosphere.
(hole through the epidermis)

Question 12

Internal features of a Stem

Answer 12

Epidermis
Cortex
Cambium
Phloem
Xylem
Pith
Vascular Bundle

Question 13

Internal features of a Stem - Epidermis

Answer 13

Single Cell layer. Covered with waxy cuticle made of Cutin to protect young stem from waterloss, pest and disease.
Replaced by corky bark (produced by the cambium) after secondary thickening.

Question 14

Internal features of a Stem - Cambium

Answer 14

Found between the Xylem and Phloem of some plants.
Meristematic, responsable for lateral growth of stems and secondary thickening.
(Divides to create new Xylem & Ploem)

Question 15

Internal features of a Stem - Xylem

Answer 15

Responsible for transport of water and minerals through the plants. No end walls, so become continuous hollow tube, strengthened by lignin.
Travels up only. Passive physical process.

(lignified cells = wood)

Question 16

Internal features of a Stem - Phloem

Answer 16

Transports sugars manufactured during photosynthesis to other areas of the plant.
(Areas in need, or to perhaps storage organs such as bulbs and tubers).
Contains sieve tubes and companion cells.
Up and Down. Active process, expends energy.
Called Translocation.

Question 17

Internal features of a Stem - Pith

Answer 17

Central tissue in the stem.
Contains Parcenchyma cells.
Is a packing tissue adding body to the stem, it can also have a storage function.

Question 18

Internal features of a Stem - Cortex

Answer 18

Outer layer between the Epidermis and the ring of Vascular Bundles.
Similarly to the Pith may act as strengthening and or storage tissue. It may also be capable of Photosynthesis.

Question 19

Monocot Stems

Answer 19

Monocots Vascular Bundles are scattered.

Monocots have no vascular cambium, so are not capable of secondary thickening. Therefore cannot increase number of Vascular Bundles after development.

Some Monocots can expand through Parenchyma division and irregular Lignification. Though this is not the same as True Wood.

Question 20

Dicot Stems

Answer 20

Dicotyledon stem vascular bundles arranged in rings.

Has Vascular Cambium to create new Xylem and Phloem, therefor can increase in lateral growth and create True Wood or Secondary Thickening.

Question 21

Stem Adaptions - Twining Stems

Answer 21

Twining their stems around a support.
Climbing/Support for plant and height enables better light, air and pollination availability.

Loincera periclymenum (Honeysuckle)
Wisteria sinensis

Question 22

Stem Adaptions - Tendrils

Answer 22

Tenrils with self adhesive pads
Parthenocissus quinquefolia (Virginia Crepper)

Question 23

Stem Adaptions - Prickles

Answer 23

Can be used for climbing/support and also protection. Growth from the epidermal tissue.

Rosa rugosa

Question 24

Stem Adaptions - Thorns

Answer 24

Modifcation from the Axilary bud.

Pyracantha coccinea
Crataegus monogyna

Question 25

Stem Adaptions - Corm

Answer 25

Layers of modified stem for perennation.
Provide food for next seasons growth.

Crocosmia ‘Lucifer’

Question 26

Stem Adaptions - Rhizome

Answer 26

Ground level modified stem for perennation.
Horizontal stem.

Also for Asexual (vegetative) reproduction.
Short internodes with new shoots from the top axially bud and many roots from the lower axially bud.

Iris germanica (Bearded Iris)

Question 27

Stem Adaptions - Stem Tuber

Answer 27

Potato.

Solanum tuberosum

Question 28

Stem Adaptions - Water Storage

Answer 28

Echinocactus grusonii

Question 29

Stem Vegetative reproduction

Answer 29

Runners - Stolons
Stems with long internodes that produce new plants form the end of the stem

Fragaria spp. (Strawberry)

Question 30

Climbing (NOT ONLY STEMS)

Answer 30

Twining - Stem
Twining petiole - Leaf
Prickles - Stem
Thorns - Stem
Spines - Leaf
Tendrils - Stem/Leaf
Adventtious Roots - Root