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RHS Level 2 Certificate
Year 1 Week 5: Stems and Leaves
Quiz answers
1. Cytoplasm - Jelly like substance that contains and supports the organelles
Mitochondria – Organelle that is the site of respiration.
Nucleus - Contains the DNA and RNA of the cell
Vacuole - Contains water, some nutrients and cell waste products - helps the cell maintain its shape.
Chloroplast - The site of photosynthesis within the cell
Middle lamina -Membrane that physically connects cells
together into plant tissues. 2. The release of stored energy from carbohydrate in the
mitochondria for use by the plant.
3. At the meristems (apical and lateral)
Quiz answers
4. The DNA of the cell and the location of the cell in the plant.
5. (a) tissue that transports water and dissolved mineral nutrients from roots
(b) tissue that transports sugars/carbohydrate made during photosynthesis from the leaves
6. All except (a)
7. (a) and (c)
8. (a)
9. (c)
10. ? What did you chose?
Learning objectives
1. Stems – structure and purpose1.1 Describe how the stem develops.1.2 Describe different types of buds and state where they occur in the plant.1.3 Identify the two elements of the vascular system and name their purposes1.4 Describe transverse sections of the young dicotyledon stem, should
include the location of the following: epidermis, cortex, xylem, phloem, pith, cambium, vascular bundles, endodermis.
1.5 Describe how the stem is adapted in order to perform specific functions.2. Leaves – structure and purpose2.1 Describe the structure of the leaf.2.2 Describe how leaf shape, size, form and colour can vary.2.3 Describe how leaves are adapted in order to perform certain functions2.4 Describe transverse sections of the young dicotyledon leaf; this should
include the location of the following: epidermis, xylem, phloem, vascular bundles, palisade & spongy mesophyll, cuticle, stomata.
Stems – Structure and Purpose
o What are stems for?o support for leaves and flowers – competition for
light and access for pollinatorso transport of water and nutrients around the plant
o What is the internal structure of the stem?o Stem vascular systemo Differences between stem and roots?o Differences between monocot and dicot stems?
Stems – vascular system
Vascular system in a number of bundles – in a dicot root there is a single vascular bundle, in a monocot there is a regular circular arrrangment.
Monocots in the stem – scattered irregularly Dicots in the stem – arranged regularly around
the circumference Xylem (in both)– located on the ‘inside’ of the
bundle Phloem (in both) – on the ‘outside’ Vascular cambium – meristematic tissue that
generates new xylem and phloem.
Young Dicot stem
Stem Adaptations
Water storage – e.g. Opuntia sp. Thorns for protection - Crataegeus
monogyna (Common Hawthorn) Dormancy – storing food to allow avoidance
of hostile conditions over winter or during summer drought e.g. Zingiber officinale (Ginger ) has a rhizome, Solanum tuberosum ssp. Tuberosum (potato) has stem tubers
Climbing – stems twine to aid the plant in climbing e.g. Wisteria sinensis.
Buds – different types
Apical bud – at the tip of the shoot. Axillary buds – at the joint between leaf and
stem (at the node). Usually dormant or leaf producing.
Fruit buds – produce flowers, usually a distinct shape and form, differing from…
Wood buds – produce new stems, sometimes only if the apical bud is removed.
Fruit or wood?
Leaves –function and structure (1)
Function of leaves – photosynthesis
External structure – Petiole– Lamina– Midrib– Veins
Leaves –function and structure (2)
Cuticle –waxy layer on surface that slows water loss
Epidermis – cells that form ‘skin’ of leaf
Palisade cells – arranged like picket fence, contain chloroplasts
Chloroplasts – site of photosynthesis
Spongy mesophyll – packing cells, allow water vapour and other gasses through
Stomata – active control of entry and exit of gasses and water vapour.
Phloem – dissolved sugars Xylem – water and mineral nutrients
Leaf – internal structure
Stomata
Pairs of specialised guard cells on either side of small openings in the underside of leaves and in soft stems.
Guard cells swell when the plant has enough water – pulling apart to open the stomata and allowing water vapour and waste gasses out and oxygen and CO2 in.
When water levels fall the guard cells empty and the stomata close to conserve water.
Electron-micrograph of lettuce stomata
Leaf Adaptations
Tendrils or suckers – for climbing e.g. Lathyrus odoratus
Leaf Hairs – for protection from the sun e.g. Stachys byzantina
Spines – for protection from grazing animals e.g. Ilex aquifolia
Food storage – for over-wintering, e.g. Narcissus spp.
Attracting pollinators – modified, highly coloured leaves known as bracts surround insignificant flowers e.g. Euphorbia pulcherima.
Leaf adaptations (2)
Leaf fall for deciduous trees – recovery of chemical components of chlorophyll; formation of abscission layer, a layer of weak cells; vascular bundles plugged; leaf fall.
Juvenile trees retain dead leaves, protects buds
Leaf form and leaf arrangement (phyllotaxy)
Various different leaf forms – known by different descriptive names to enable clear identification
Phyllotaxy is the name for the arrangement of leaves on a plant. Prevents the leaves from shading each other.
Learning outcomes
1. Stems – structure and purpose1.1 Describe how the stem develops.1.2 Describe different types of buds and state where they occur in the plant.1.3 Identify the two elements of the vascular system and name their purposes1.4 Describe transverse sections of the young dicotyledon stem, should include the
location of the following: epidermis, cortex, xylem, phloem, pith, cambium, vascular bundles, endodermis.
1.5 Describe how the stem is adapted in order to perform specific functions.2. Leaves – structure and purpose2.1 Describe the structure of the leaf.2.2 Describe how leaf shape, size, form and colour can vary.2.3 Describe how leaves are adapted in order to perform certain functions2.4 Describe transverse sections of the young dicotyledon leaf; this should include
the location of the following: epidermis, xylem, phloem, vascular bundles, palisade & spongy mesophyll, cuticle, stomata.