Plant Stem Flashcards
2.41 State the primary functions of stems
State the primary function of stems:
- Hold leaves in optimum position for photosynthesis
- Hold flowers in optimum position for pollination
- Transportation of water, food, nutrients and plant hormones around the plant
- storage of nutrients
- production of new living tissue from buds and shoots
Stems may be herbaceous or woody
2.42 Produce a drawing to show a transvers section through a young dicotyledonous stem to show the following internal features:
- epidermis,
- cortex,
- cambium,
- phloem,
- xylem,
- pith,
- vascular bundles
Drawing showing internal features of a young dicot stem, including
- epidermis,
- cortex,
- cambium,
- phloem,
- xylem,
- pith,
- vascular bundles
2.42 Produce a drawing to show a transvers sction through a young dicotyledonous stem to show the following external features:
- lenticels,
- nodes,
- axillary buds,
- apical buds,
- scale scars,
- leaf scars
Drawing of a transvers section showing external features of a young dicot stem to include:
- lenticels,
- nodes,
- axillary buds,
- apical buds,
- scale scars,
- leaf scars
2.42a Describe the structure and state function of the stem epidermis
Description: stems are enclosed by the epidermis, a single layer of cells that forms aboundry between the plant and the external environment. The epidermis contains stomata (pores) which allow gas exchange enabling photosynthesis & respiration for the cells within
Function: stem epidermis protects the stem. It protects against water loss, regulates gas exchange and damage / attack
2.42b Describe the structure and state function of the stem cortex
Description: stem cortex
Function: stem cortex
2.42c Describe the structure and state function of the stem cambium
Decription: stem cambium produces wood & cork ?
Function: stem cambium
2.42d Describe the structure and state function of the stem phloem
Description: stem phloem are long tube like cells (sieve tubes) They have cellulose walls and are living unlignified cells with no nucleus. The end walls are only partially broken down to leave sieve-like structures (sieve plates) at intervals along the sieve tubes. Each has a companion cell which regulates the movement of water through the sieve tube. Phloem is typically found to the outside of the xylem in most species
Function: stem phloem transport of water and food from the leaves to the rest of the plant
2.42e Describe the structure and state function of the stem xylem
Drescription: stem xylem are the woody element of the vascular bundle. They are long wide open ended cells with very thick lignified walls, able to withstand the high pressures of water and solutes
Function: stem xylem support the transport of water, nutrients & plant hormones from the roots to the rest of the plant. Xylem tissue also provides physical support
2.42f Describe the structure and state function of the stem pith
Description: stem pith
Function: stem pith
2.42g Describe the structure and state function of the stem vascular bundle
Description: stem vascular bundle , comprised of the phloem, xylem and vascular cambium each is contained by a bundle sheath
- moncots have vasular bundles scattered through the stem
- dicots have vascular bundles arranged near the periphery around the central core of pith
Function: stem vascular bundles transport water, soluable minerals, food and plant hormones around the plant
2.42h Describe the structure and state function of the stem lenticels
Description: When a stem becomes woody a corky layer develops between the epidermis and the phloem forming a waterproof and gas-tight bark layer. Lenticels are breaks in the cork layer made up os loose cells which allow the passage of gasses and moisture.
Function: lenticels enable gas exchange in woody stems
2.42i Describe the structure and state function of the stem nodes
Description: nodes (leaf joints) the position where leaves and axillary buds are attached to the stem, Sometimes slightly swollen. The section between the nodes is call the internode
Function: nodes hold leaves and buds onto the stem
2.42k Describe the structure and state function of the stem axillary bud
Description: axillary bud (lateral bud) are usually formed in the leaf axils, the point at which the leaf joins the stem. They may remain dormant for some length of time only becoming active when needed for growth
Function: axillary bud (lateral bud) have the potential to form sideshoots, and flowers
2.42l Describe the structure and state function of the stem apical bud
Description: apical bud (terminal bud) appear at the tip of a stem enclosed within a group of densley packed scales, and contains a meristem from which lenghtwise vegetative growth or a flower will emerge. Their growth exerts a level of control over the lateral buds lower down due to its production of growth regulating homrmones (apical dominance). If apical dominace is lost, buds lower down will start to grow more strongly in an effort to replace the apical bud. Gardeners may utilise this response to create bushy growth
Function: apical bud from which the stem grows and elongates, the site of meristematic tissue where cell division takes place.
2.42m Describe the structure and state function of the stem scale scar
Description: scale scar (girdle scar) indicates where last year’s apical bud was positioned. Useful in determining which part of th estem is current, 1 yr old, 2 yr old wood when pruning. Girdle scar is formed due to the close proximity of the bud scales on the stem when they are dropped at the start of growing season
Function: scale scar bud scales protect the apical meristem from damage and waterloss
2.42n Describe the structure and state function of the stem leaf scar
Description: leaf scar is the mark left behind where the leaf stalk, petiole, was attached to the stem. The dark dots are the sites of where the vascular bundles were attached to the stem and have since healed
Function: leaf scar to prevent the loss of fluids from the plants vascular system
2.43a Describe how the stem is adapted to perform other functions including: protection
Stem adaptations to perform other functions such as protection include:
- thorns are modified branches growing from axillary buds have a connection to the vascular system e.g Crataegus spp.
- prickles are specalised outgrowths from the epidermis, and easily rubbed off e.g. Rosa spp. Prickles also facilitate scrambling over other vegetation
2.43b Describe how the stem is adapted to perform other functions including: storage / perennation
Stem adaptations to perform other functions such as storage and perennation include:
- Corms: compressed underground shoots in which the whole stem is swollen with food . Covered by dry scale leaves, underneather are nodes, internodes and axillary buds e.g. Crocus
- Stem tubers: have vestigial nodes and axillary buds which grow into shoots. They can photosynthesise, thereby colouring green which roots can not e.g. Begonia
- Rhizomes: stems which are growing horizontally, usually underground, sometimes just above ground. Nodes and internodes clearly seen along the stem as well as adventitious roots e.g. Iris germanic
2.43c Describe how the stem is adapted to perform other functions including: climbing
Stem adaptations to perform other functions such climbing include: Twining stems wind around each other upright structures for support, either clockwise or anticlockwise. Such twining stems can become large and woody which are then called lianes e.g. Wisteria passiflora
2.43d Describe how the stem is adapted to perform other functions including: natural vegetative reproduction
Stem adaptations to perform natural vegetative reproduction include:
- Stolons / runners horizontal stems which grow just above the ground and root at nodes along the stem or at stem tips producing plantlets e.g. Fragaria
- Rhizomes stems growing horizontally, as the stem branches new rhizomes are formed from lateral buds each with a shoot at its tip, enabling the plant to spread e.g. Festuca rubes
- Stem tubers e.g. Solanum tuberoses
