Plant structure and growth

Topic 9.1

Assessment Statements• 9.1.1 Draw and label plan diagrams to show the distribution of tissues in

the stem and leaf of a dicotyledonous plant.• 9.1.2 Outline three differences between the structures of dicotyledonous

and monocotyledonous plants.• 9.1.3 Explain the relationship between the distribution of tissues in the leaf

and the functions of these tissues.• 9.1.4 Identify modification of roots, stems, and leaves for different

functions: bulbs, stem tubers, storage roots, and tendrils.• 9.1.5 State that dicotyledonous plants have apical and lateral meristems.• 9.1.6 Compare growth due to apical and lateral meristems in

dicotyledonous plants.• 9.1.7 Explain the role of auxin in phototropism as an example of the

control of plant growth.

Review of land plantsPlant group Major featuresNon-vascular land plants

• no conducting tissue• often grouped together as bryophytes• usually small and grow close to the ground• include mosses, liverworts, and hornworts

Seedless vascular plants

• well-developed vascular tissue• do not produce seeds• include horsetails, ferns, club mosses, and whisk ferns

Seeded vascular plants

• most living plants are in this group• seeds contain an embryo, a supply of nutrients, and a protective outer coat• have extensive vascular tissue and include some of the world’s largest organisms

Seeded vascular plants• Gymnosperms – have seeds that do not develop within

an enclosed structure• Angiosperms – have seeds that develop within a

protective structure

AngiospermTissue type DescriptionDermal tissue • outer covering which protects against

physical agents and pathogenic organisms• prevents water loss and may have specialized structures for various purposes

Ground tissue • consists mostly of thin-walled cells that function in storage, photosynthesis, support, and secretion

Vascular tissue • xylem and phloem carry out long-distance conduction of water, minerals, and nutrients within the plant and provide support

Meristematic tissue• All 3 tissue types derive from meristematic tissue• Composed of aggregates of small cells that have the

same function as stem cells in animals• When these cells divide, one cell remains meristematic

(initial) while the other (derivative) is free to differentiate and become part of the plant body

Root tissue

• Absorbs mineral ions and water from the soil

• Anchor the plant• Provide food storage

epidermis

cortex

xylem

phloemendodermis

Stem tissue

• Plant region where leaves are attached

• Area where leaf joins is called a node and the area between two nodes is called the internode

Leaf tissue

• Involved in photosynthesis

• Consist of the blade and a stalk called the petiole that attaches the blade to the stem

Cuticle (wax)

Upper epidermis

Palisade mesophyll

Spongy mesophyll

Stomatal pores

phloem

xylem

Vascular bundle

Functions of tissues in relation to their position in the leaf1. The palisade mesophyll is located in the upper portion of the leaf

where light is most available. The cells of this region are chloroplast rich, thus allowing for maximal photosynthesis.

2. Veins are distributed throughout the leaf so as to transport raw materials and products of photosynthesis. The veins occur roughly in the middle of the leaf so as to be near all cells.

3. The spongy mesophyll is located just superior to the stomata allowing continuous channels for gas exchange.

4. The stomatal pores are on the bottom of the leaf. This area receives less light with a resulting lower temperature. The lower temperature minimizes water loss from the pores and the plant.

Monocotyledonous and dicotyledonous plantsMonocots DicotsParallel venation in leaves Netlike venation pattern in leaves

3 flower parts or multiples of 3 4 or 5 flower parts or multiples of 4 or 5

Seeds contain only one cotyledon (seed leaf)

Seeds contain two cotyledons (seed leaves)

Vascular bundles arranged throughout the stem

Vascular bundles arranged as a ring in the stem

Root system mainly fibrous Root system involves a taproot (main root)

Pollen grain with one opening Pollen grain with three openings

Leaf venation

Flowers

Embryos

Stems

Roots

Pollen

RootsRoot modification Description and exampleProp roots Thick adventitious roots that grow from

the lower part of the stem and brace the plant (ex: corn)

Storage roots Specialized cells within the root store large quantities of carbohydrates and water (ex: carrots and beets)

Pneumatophores(air roots)

Produced by plants that live in wet places, these roots extend above the soil or water surface and facilitate oxygen uptake (ex: mangroves)

Buttress roots Large roots that develop near the bottom of trees to provide stability (ex: fig tree)

Prop, storage, pneumatophore, or buttress?

StemsStem modification Description and exampleBulbs Vertical, underground stems consisting

of enlarged bases of leaves that store food (ex: onions)

Tubers Horizontally growing stems below ground that are modified as carbohydrate-storage structures (ex: potatoes)

Rhizomes Horizontal stems that grow just below the surface to allow plant spreading (ex: ginger plant)

Stolons Horizontal stems growing above ground that allow a plant to reproduce asexually (ex: strawberry plants)

Bulb, tuber, rhizome, or stolon?

LeavesLeaf modification Description and exampleTendrils Structures that coil around objects to

aid in support and climbing (may also be formed from modified stems) (ex: pea plants produce tendrils from leaves)

Reproductive leaves Produce tiny plants along the leaf margins that fall to the ground and take root in the soil (ex: kalanchoe plants)

Bracts or floral leaves Coloured modified leaves that surround flowers and attract insects for pollination (ex: poinsettia)

Spines Reduce water loss, may be associated with modified stems that carry out photosynthesis (ex: cacti)

Meristems• Plants show growth throughout their entire life• Continual pattern of growth is referred to as

indeterminate• Some plants are annuals and complete their life cycle in

one year• Other plants are biennials and take two years to

complete their life cycle• Perennials live many years and when they die it is

usually due to infection or some environmental factor• Reason for indeterminate growth is due to meristematic

tissue

Dicot meristematic tissue: apical and lateral• Apical meristems

• Occurs at tips of roots and stems

• Produces primary tissues and causes primary growth which allows the root to extend throughout the soil

• Allows stem to grow longer

• Herbaceeous, non-woody stems and roots

• Lateral meristems• Allow growth in

thickness of plants• Woody plants• Two types

• Vascular cambium produces xylem/phloem and secondary xylem which produces wood

• Cork cambium produces cork cells of outer bark

Overview of primary and secondary growth

Phototropism• Tropisms are growth or movement responses to

directional external stimuli• may be positive (towards stimulus) or negative (away

from stimulus)• Common stimuli: chemicals, gravity, touch, and light• Phototropism means plant growth in response to light• Plant stems exhibit positive phototropism and roots

demonstrate negative phototropism

Auxins• Auxins are plant hormones that cause the positive

phototropism of plant shoots and seedlings• found in the embryos of seeds, the meristems of apical

buds and young leaves• Work only on plant cells that have auxin receptors• Increase flexibility of plant which enables cell elongation

on the side of the shoot necessary to cause growth towards the light

• Auxin is redistributed to the stem side away from the light source causing a curvature toward the light source

• Called indoleacetic acid (IAA)