R2101 2.4 Describe the structure and state the functions of stems

Question 1

Main functions of a stem (5)

Answer 1

1. Support for plant
2. Spaces out leaves for air and sunlight to maximise photosynthesis
3. Holds flowers above ground to help with pollination
4. If green, helps with photosynthesis
5. Is the link between roots (where food is stored and minerals and water are taken up) and the leaves (where water is lost and food manufactured)

Question 2

What are the spaces between nodes called?

Answer 2

Internodes

Question 3

What is a shoot?

Answer 3

Collective name for the stem and all its attachments

Question 4

What is a bud? What do they consist of (2)?

Answer 4

A bud is a compact undeveloped shoot. Consists of:
1. Crowded overlapping immature leaves. The outside has thicker leaves that form bud scale which protect from drying and damage.
2. Minute buds - precursors

Question 5

What are the two positionally type of buds?

Answer 5

1. Apical (or teminal) at the tip of a shoot
2. Axillary - off to the side

Question 6

What is a leaf scar and why is it useful?

Answer 6

A leaf scars shows where a leaf or fruit has been attached

It is useful in identifying some plants in winter with bare stems. e.g. Aesculus (horse chesnut) has very distinct leaf scars

Question 7

Four main areas of tissue in the stem?

Answer 7

1. Epidermis
2. Cortex
3. Vascular tissue
4. Pith

Question 8

What are lenticals? (4)

Answer 8

1. Blister like breaks in the surface of the skin
2. Is a pathway through which gases can diffuse to the living cells of the bark
3. Replace stomata when the epidermis gives way to a waterproof and gas tight bark layer
4. Shape and form can be distinctive in indentification of some species e.g. Prunus serrula

Question 9

What are growth rings? What do they show?

Answer 9

1. On the surface of the stem show where one years growth has ended and the next years begins.
2. The growth ring is the bud scale scar where the terminal bud scales were attached to the shoot before the next year’s growth started. This can be helpful in pruning.

Question 10

Epidermis (2)

Answer 10

1. Produces waterproof waxy layer made of cutin on its surface called the cuticle
2. Pores called stomata punctuate its surface. Guard cells control the opeing and closing of these pores

Question 11

Cortex (3)

Answer 11

1. Beneath the epidermis and largely made up of parenchyma
2. Help maintain plant shape
3. Inside the cortex are a ring of vascular bundles in dicots and the vascular bundles are scattered throughout the stem in moncots

Question 12

Pith

Answer 12

Central zone of the stem, mostly parenchyma cells. May sometimes breakdown to give a hollow stems.

Question 13

Vascular bundle - Xylem

Answer 13

1. Contains long wide open-ended cells with thick lignified walls to withstand high pressure of water

Question 14

Vascular bundle - phloem

Answer 14

1. Long tube like cells called sieve tubes
2. Transport food
3. Have cellulose cell walls - not lignified
4. Do not contain nucelus
5. End walls only partially broken down to produce sieve plates
6. Companion cells regulate the flow of liquids through the sieve tube

Question 15

Vascular bundle - vascular cambium (dicots)

Answer 15

1. This is a lateral meristem
2. Dividing cells producing more xylem and phloem tissue to increase the girth of the stem of woody plants as it grows - secondary thickening

Question 16

Vascular bundle - support (dicots)

Answer 16

Arranged in ring which gives strength and support to the stem in the much the same way steel rods do in reinforced concrete

Question 17

Role of apical bud

Answer 17

1. Where growth is inititated
2. Also give rise to small leaves (bud scales) to protect the meristem

Question 17

Role of apical bud

Answer 17

1. Where growth is inititated
2. Also give rise to small leaves (bud scales) to protect the meristem
3. Deep inside the bud is a tiny mass of cells - each with a conspicuous nucleus but no vacuole. These make up the apical meristem, and this is where cells divide to produce new tissues.

Question 18

Role of axilliary buds

Answer 18

1. Have their own apical meristems which often give rise to side branches
2. Located lower down the stem in the angle of the leaf

Question 19

What are twining stems

Answer 19

1. Wind around structures for support
2. Can be either clockwise or anitclockwise (e.g. Wisteria floribunda)
3. Can become large and woody. Then are called lianes

Question 20

What are thornes?

Answer 20

1.Modified branches growing from axillary buds
2. Discourages herbivores
3. e.g. Crataegus ssp

Question 21

What are prickles?

Answer 21

1. Specialised outgrowths of stem epidermis
2. Easily rubbed off
3. Both protect the plant and help it scramble over other vegetation
4. e.g. Roses

Question 22

What are rhizomes?

Answer 22

1. Organ of perennation
2. Stem grow horizontally underneath and sometime just above the ground
3. Nodes and internodes can be clearly seen along the stem
4. e.g. Iris germanica
5. Have thickend contractile roots which help pull them to an appropriate level in the soil

Question 23

What are corms?

Answer 23

1. Organ of perennation
2. Compressed underground shoots in which stem is swollen with strach
3. Have dry scale leaves on their outer surface
4. Each year a new corm forms on top of an old one
5. Have thickend contractile roots which help pull them to an appropriate level in the soil
6. e.g. Crocus

Question 24

What are stem tubers?

Answer 24

1. Organ of perennation
2. Formed at the end of rhizomes
3. Distinguised from root tubers by having vestigial nodes and axillary buds which grow into shoots
4. Can turn green exposed to sunlight (roots cannot)
5. e,g, Solanum tuberosum

Question 25

What are stolon?

Answer 25

1. A lateral stem that grows horizontally over the surface of the soil
2. Will produce adventitious roots at some of its nodes
3. It produces adventitious buds and subsquently new plants along its length
4. e,g, Fragaria
5. The stolon feeds the new plant until it becomes self-sufficient, then dies back

Question 26

Difference between stolon and a runner?

Answer 26

Runner only puts down roots at its tip

Question 27

What is a sucker?

Answer 27

1. Upright shoots arising from the root (Not a stolon)

Question 28

How stems use hairs?

Answer 28

1. Help them climb to spread seeds widely
2. e.g. Galium aparine

Question 29

Examples of where buds help identification (3)

Answer 29

1. *Fraxinus excelsior *has black buds
2. Fagus sylvatica has long and pointed buds
3. Magnolia buds are hairy