2.4 Stems Flashcards Preview

RHS Level 2 Module R2101 > 2.4 Stems > Flashcards

Flashcards in 2.4 Stems Deck (22)
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1

Stems give rise to which TWO types of buds, and what do they do?

Apical bud - surrounds the growing tip of a shoot - (shoot apical meristem)

Axillary bud - forms in angle between leaf and stem - responsible for branching as they develop into side shoots.

2

Stems - what is a node?

Points at which leaves and axillary buds occur.

Permanent stem between the nodes is called the internode.

3

Stems - what is the leaf scar?

Once leaves fall off they leave a scar where the leaf joined the stem.

4

Stems - what are lenticels?

Pores in the cork (woody) that allow gas exchange, allowing cortex to "breathe".

5

What is the primary function of a stem

To hold leaves and flowers in optimum positions

Transport between roots and leaves

6

How does the stem develop?

From germination the stem develops from the Plumule (embryonic shoot)

In seedlings, the stem-like part of the shoot between the cotyledons and first true leaves is called the Epicotyl.

True stem then develops to produce mature leaves and flowers.

Increases in length through cell division and expansion.

Herbaceous growth uses cell expansion to thicken.

Woody growth uses secondary thickening (girth) through the action of the vascular cambium (also in roots).

7

How do Monocots strengthen?

Secondary growth occurs randomly throughout stem (vascular bundles are scattered throughout ground tissue)

No secondary thickening

Most monocots are herbs so don't undergo complex processes

Results can be strong, flexible, fibrous stems (think bamboo!) - with outer sheaths

8

How do Dicots strengthen?

Through secondary thickening (woody growth) - in woody plants!

Mechanical strength - allows for huge, strong growth

During growth, cells of the Vascular Cambium grow and join up to form a central ring - a complete lateral meristem.

This lateral meristem lays down Secondary phloem on the outside and Secondary xylem on the inside

This Secondary Xylem is dead tissues which forces apart the primary xylem and phloem

Cork cambium forms and begins to produce cork - an important part of the bark.

9

Other functions of stems:

Storage

Climbing

Reproduction

Organisation

Mechanical strength

Photosynthesis

Height

Defence

10

Reasons for stem HEIGHT

Leaves reach light

Flowers exposed to pollinators

Pollen and seeds dispersed better

11

Examples of stem STORAGE

Swollen stems of desert plants (cacti / euphorbia)

Underground stem tubers - e.g potatoes

Corms - swollen, tuber-like stem bases - store starch over winter - PERENNATION!

12

When do stems aid photosynthesis?

When leaves are absent - e.g. succulents

13

How do stems aid in defence?

Prickles on stems

Stinging hairs

14

Benefits of climbing stems...?

Plant gains height without having to develop woody tissues

Twining species wrap around other plants for support

15

What are stems' roles in reproduction?

Portions of stem can produce clones

Stolons (runners) run above ground and produce roots and shoots

Rhizomes are creeping stems underground and produce new shoots at nodes

Corms produce new corms (cormels) from short stolons underground

16

How do stems function in water transport

Water moves in the xylem upwards only, by transpirational pull, to form a continuous column of water.

Can happen by way of adhesion of water molecules to xylem vessel wall.

17

Differences between a woody and herbaceous stem (3):

Woody stems undergo secondary thickening - herbaceous do not

Woody stems develop bark (cork) whereas herbaceous retain the epidermis

Woody stems have a central cylinder of xylem and phloem, whereas herbaceous stems have xylem and phloem arranged in a ring of vascular bundles

18

Where does starch storage take place in young dicot stem?

In the pith and the cortex

19

Where does mineral transport take place in stem?

In the xylem

20

Where does cell division take place in stem?

In the vascular cambium

21

Differences between monocot and dicot stems (4)

Monocot stems have randomly scattered vascular bundles whereas dicots have them arranged in a ring

Monocot stems are herbaceous and non-woody, whereas dicot stems can be woody and herbaceous

Monocot stems have no vascular cambium, whereas dicot stems do (dicots undergo secondary thickening.

Monocot stems have stomata in epidermis; dicot stems have lenticels in bark.

22

Stem adaptations:

Rhizome - horizontal stem below the surface - produces new shoots at nodes.

Corm - compressed underground stem - produces new corm above old one.

Stem tuber - underground stem from which new plants arise at “eyes”.

Stolon/runner - horizontal stem which runs along the ground surface and roots at nodes or along its length.

Sucker - vertical stem which arises from roots.