STEMS (ps8) Flashcards
State the primary functions of stem
The primary function of plant stems are to:
Hold leaves in perfect position for photosynthesis- so that they receive adequate air and sunlight
Transport water and minerals from the roots to the leaves, and sugars from the leaves to other parts of the plant /organs
Hold the flowers above the ground in the best position for pollination by wind and insects
Hold fruits in perfect position for dispersal
Describe the structure of the stem, and state the functions of its components
INTERNAL STRUCTURE To include drawing of a transverse section through a young dicotyledon stem and must show the following: Epidermis Cortex Cambium Phloem Xylem Pith Vascular bundle
External structures to include Lenticels Nodes Axillary buds apical buds Scars (scale and leaf)
External features of stem.
Describe
(ALANIS external stem- how to remember )
Apical bud Lenticels Axillary bud Nodes Internode Scars (scale and leaf)
APICAL BUD
The apical bud is a collection of developing leaves tightly packed around the APICAL MERISTEM, an area of rapid cell division, elongation and differentiation.
Contains meristematic tissue and is protected by modified leaves called scales.
The terminal bud firms the PRIMARY GROWTH POINT of shoots. During dormant seasons the terminal bud is surrounded by BUD SCALES that are known as modified leaves.
Also known as the LEADER BUD.
LENTICELS
Lenticel is a pore on the surface of a stem of some plants allowing gas exchange.
AXILLARY BUD
also contains meristematic tissue and is covered by scales.
They are found in the angle formed between each leaf and the stem, and are embryonic side shoots. Most axillary buds are dormant as the presence of the apical bud inhibits their development, a phenomenon called APICAL DOMINANCE. Under certain conditions axillary buds do develop, forming vegetative branches either with their own terminal buds or bearing flowers. Growth of the axillary buds can be stimulated by removal of the terminal bud, PINCHING OUT, resulting in more bushy growth.
NODE
The region of the stem at which the leaves are attached - there is a greater volume of vascular bundles and meristematic tissue
INTERNODE
Part of stem between nodes without anything growing, lack of meristematic tissue, only used for transport of water and sugars
SCARS (leaf/bundle/terminal bud scale)
A leaf scar is the mark left by a leaf after it falls off the twig. It marks the site where the petiole attached to the stem. A leaf scar is typically found below a branch as branches come from axillary buds located above leaf scars.
Bundle scars are circular or barred regions within the leaf scar where bundles of vascular tissue that had connected the leaf and the stem broke off.[2] The number of bundle scars in a leaf scar is sometimes used as an identifying mark as they are often consistent across a species.
Terminal bud scale scars
bud scale scars are the scars remaining after the bud scales fall off
INTERNAL FEATURES IF STEM
EPIDERMIS
Made up of a single layer of closely packed cells covered ina waxy cuticle. Stomata are found in the epidermis of young stems, to allow for gaseous exchange.
After secondary thickening the epidermis of the stem is replaced by an impermeable bark. The bark is perforated by areas of loosely packed cells called LENTICELS that allow gaseous exchange
CORTEX
The cortex gives structure to the stem and consist of loosely packed parenchyma cells. It maybe green and therefore capable of photosynthesis
CAMBIUM
Is found between the phloem and xylem of some plants . It is meristematic, dividing to form new xylem and phloem in a process know as SECONDARY THICKENING which allows for the lateral growth of stems.
PHLOEM
Transports the food manufactured in photosynthesis both up and down the plant.
XYLEM
Is responsible for the transport of water and dissolved minerals through the plant, from the roots to them stem and then the leaves.
PITH
Pith is made up of Parenchyma cells which have a packing and food storage function, in older stems pith also stores waste products- pith is only found in dicots.
VASCULAR BUNDLES
A collection of phloem and xylem cells .The vascular bundle is just below the epidermis in stems . In dicots vascular bundles include cambium between the phloem and xylem cells. The cambium is a meristematic tissuei
Describe how the stem is adapted to perform other functions. Drawer modification table , MODIFICATION FUNCTION NAME (2-3 plants for each)
MODIFICATIONS
Twining stems
Function -for climbing to receive an amount if light
Name-
Calystegia sepium (hedge bindweed) anti
Wisteria sinensis,(anti-clockwise) as all northern hemisphere
wisteria florabunda (clockwise) Southern Hemispheres Lonicera periclymenum (honeysuckle)
TENDRILS
function - climbing
Name: Bryonia alba
PRICKLES & THORNS
(Prickles do not have connection to vascular bundles- outgrowth of epidermis)
(Thorns outgrowth of inner tissue/ vascular bundles)
Function- to protect/for protection
Name: Rosa rugosa, (prickles)
Crataegus monogyna (thorns)
Thorns may become a secondary stem or spar- can produce flowers or fruits)
STEM TUBER (modified swollen stem)
Function- to store food/ starch/ carbohydrate
Name- Solanum tuberosum (potato )
CORM
Function- to store food/ starch/ carbohydrate
Name- Crocus speciosus (bierbersteins crocus)
RHIZOME
(Underground stem which grows horizontally)
Function- to store food/ starch/ carbohydrate
Name- Iris x germanica
STOLON
Function - vegetative propagation
Name- Fragaria x ananassa (strawberry)
RUNNERS
Function - vegetative propagation
Name- Rubus fruticosus
