9.1 plant structure & growth

9.1 Plant Structure & Growth

Topic 9 Plant Science

Plant Structure & Growth 9.1.1 Draw and label plan diagrams to show the distribution

of tissues in the stem and leaf of a dicotyledonous plant. (Either sunflower, bean or another dicotyledonous plant with similar tissue distribution should be used).

Note that plan diagrams show distribution of tissues (for example, xylem, phloem) and do not show individual cells. They are sometimes called “low power” diagrams.

Plant Structure & Growth 9.1.2 Outline three differences between the structures of

dicotyledonous and monocotyledonous plants.

Teachers should emphasize three differences between monocotyledonous and dicotyledonous plants (examples include: parallel versus net-like venation in leaves, distribution of vascular tissue in stems, number of cotyledons, floral organs in multiples of 3 in monocotyledonous versus 4 or 5 in dicotyledonous, fibrous adventitious roots in monocotyledonous versus tap root with lateral branches in dicotyledonous).

Plant Structure & Growth 9.1.3 Explain the relationship between the distribution of

tissues in the leaf and the functions of these tissues.

This should be restricted to dicotyledonous plants. The functions should include: absorption of light, gas exchange, support, water conservation, and the transport of water and products of photosynthesis.

9.1.4 Identify modifications of roots, stems and leaves for different functions:

bulbs, stem tubers, storage roots and tendrils.

Plant Structure & Growth 9.1.5 State that dicotyledonous plants have apical and lateral

meristems. Apical meristems are sometimes referred to as primary

meristems, and lateral meristems as cambium. Meristems generate new cells for growth of the plant.

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.

Plant Classification There are FOUR main groups of plants. These can be easily identified by studying their

external structure: Phylum Bryophyta

Bryophytes (mosses and liverworts) Phylum Filicinophyta

Ferns Phylum Coniferophyta

Conifers Phylum Angiospermatophyta

Angiosperms (flowering plants)

Angiospermophytes - Flowering Plants Highly variable structure;

Tiny herbaceous to large trees They have roots, stems and leaves An advanced vascular system Can form woody tissue Can grow up to 100m in height Seeds are produced Seeds develop from ovules inside ovaries. The ovaries are

part of flowers. Fruits develop from the ovaries to disperse the seeds.

Angiospermophytes - Flowering Plants

Monocotyledons and Dicotyledons Angiosperms can be divided onto two classes. Classification depends upon the number of seed leaves

(cotyledons) which they have in their seeds. The TWO classes are:

Monocotyledons One seed leaf Leaves usually have parallel veins Includes: grasses, cereals

Dicotyledons Two seed leaves Leaves are usually net veined Often grow to a large size: most trees, roses, many garden plants

Monocotyledons and Dicotyledons The IBO guide states:


Structure of a Dicotyledons Plant Roots:

Root hairs for absorbing water and mineral nutrients.

Stem: Transportation of water

from the roots to the leaves Transportation of the sugars

from the leaves to the roots Leaves:

Main site of photosynthesis Buds (terminal and axillary)

Site of new growth

Root Structure of a Dicotyledon Plant Plants absorb potassium, phosphate, nitrates and other mineral ions

from the soil The concentration of these ions is much higher inside the roots, so

they are absorbed by active transport. Root hairs provide a large surface are for mineral ion uptake. Because of the high solute concentration in root cells, water moves

into the roots cells by osmosis. Most of the water absorbed by the roots is drawn by the transpiration

pull into the xylem vessels in the centre of the root. To reach the xylem, water has to cross the cortex. There are two routes for the water to take to reach the xylem vessels:

The symplastic route Water moves from cell to cell via the cytoplasm

The apoplastic route Water moves along the cell walls

Root Structure of a Dicotyledon Plant

Stem Structure of a Dicotyledon Plant

Stems connect the leaves, roots and the flowers of plants They transport materials between them using xylem and

phloem tissue. Xylem transports water and dissolved nutrients Phloem transports the products of photosynthesis

Stems support the aerial parts of the plant Xylem tissue provides support especially in woody stems In dicotyledonous plants, the vascular bundles are

arranged in a ring around the outer part of the stem Xylem on the inside. Phloem on the outside.

Stem Structure of a Dicotyledon Plant

Leaf Structure of Dicotyledon Plant

Modifications of roots, stems & leaves Tendrils are usually specialized stems or leaves that are

used by climbing plants for support, attachment and cellular invasion by parasitic plants, generally by twining around suitable hosts.

Food Storage in Plants Bulbs, stem tubers & storage roots are used for food

storage. Many plants develop a food storage organ in which food

is stored. Examples include:

potatoes, carrots, corms, bulbs

The steps in food storage are: Photosynthesis in the leaves produce glucose. The sugars are translocated in the phloem from the leaves to the

storage organ. The sugars are converted into starch, proteins and other organic

compounds for storage.

Food Storage in Plants

Ref: IB Biology, OSC

Meristems 9.1.5 State that dicotyledonous plants have apical and lateral




See your notes for explanation

Phototropism 9.1.7 Explain the role of auxin in phototropism as an

example of the control of plant growth.

See your notes for explanation

IBO guide: 9.1.1 Draw and label plan diagrams to show the distribution

of tissues in the stem and leaf of a dicotyledonous plant. (Either sunflower, bean or another dicotyledonous plant with similar tissue distribution should be used).

Note that plan diagrams show distribution of tissues (for example, xylem, phloem) and do not show individual cells. They are sometimes called “lowpower” diagrams.

IBO guide: 9.1.2 Outline three differences between the structures of

dicotyledonous and monocotyledonous plants.


IBO guide: 9.1.3 Explain the relationship between the distribution of

tissues in the leaf and the functions of these tissues.

This should be restricted to dicotyledonous plants. The functions should include: absorption of light, gas exchange, support, water conservation, and the transport of water and products of photosynthesis.

9.1.4 Identify modifications of roots, stems and leaves for different functions:

bulbs, stem tubers, storage roots and tendrils.

IBO guide: 9.1.5 State that dicotyledonous plants have apical and lateral




9.1.7 Explain the role of auxin in phototropism as an example of the control of plant growth.

9.1 plant structure & growth

Technology