Lesson 1 Plant Structure, growth, and development
Three groups of secondary metabolites:
1. Alkaloids
Alkaloids are secondary metabolites. They are primarily composed of nitrogen and
are widely used in medicine. Most alkaloids have a bitter taste or are poisonous
when ingested
Function for the plant: Used by humans:
- Protect against insects - Food (e.g., coffee)
- Protect against plants that grow nearby - Medicine
2. Terpenoids
Terpenoids are made of isoprene units and are found in all plants. They are the
largest group of secondary metabolites and some of them are volatile, which means
they evaporate easily (e.g., essential oils)
Function for the plant: Used by humans:
- Protect against heat and damage - Medicine (taxol)
- Attract pollinators - Rubber
- Waste products - Perfume
- Aromatherapy
3. Phenols
Phenols consist of a hydroxyl group (-OH) attached to an aromatic ring. Phenols are
found in nearly all parts of the plant and in every plant on the planet (e.g.,
flavonoids: anthocyanins, flavones and flavanols)
Function for plant: Used by humans:
- Antioxidants - Food
- Protection against environmental stress - Medicines
- Attraction of pollinators - Dyes
Plants have a hierarchical organization
Plants have organs, which consist of tissues. Tissues consists of cells
❖ Shoot system:
- Important for the production of sugars (photosynthesis)
- Reproductive organs are found in the shoot system
- Transport of water, minerals and products of photosynthesis
❖ Root system:
- Anchoring the plant
- Absorbing minerals and water
- Stores carbohydrates
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,Root system
A root is an organ with important functions:
- Anchoring the plant
- Absorbing minerals and water
- Storing carbohydrates
❖ The primary root is the first root to emerge
❖ The primary root branches to form lateral roots, which improve anchorage and
water absorption
❖ The tap root develops from the primary root and prevents the plant from toppling
❖ Root hairs near the root top increase the surface area of the root
❖ Difference between lateral roots and adventitious roots:
o Lateral roots develop from the tap root
o Adventitious roots don’t develop from the taproot, they develop from stems
or leaves
Many plants have root adaptations with specialized functions. For example:
1. Maize: important for heavy plants, to stabilize it
2. Sugar beet: root is used as storage for sugars
3. Mangrove: grows against gravity. Important for absorption of oxygen
4. Strangles Fig and Ficus Socotrana: root is used as stabilization
Shoot system
The stem is an organ consisting of the growing shoot tip, or apical bud.
It causes elongation of a young shoot
❖ The shoot system consists of an alternating system of
- Nodes: the point at which leaves are attached to internodes
- Internodes: the stem segments between nodes
❖ The axillary bud is a structure that has the potential to form a
lateral branch, thorn, or flower
Many plants have modified stems. They are all recognizable by
their axillary buds. For example:
1. Rhizome (rootstock): how to recognize root from
rootstock? → on the roots you will never see axillary buds
2. Tuber: when we eat a potato, we’re not eating the roots, but
the tubers. They have the axillary buds, but they are removed
3. Stolon: for propagation, to form new plants which will be a
complete copy of the mother plant
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,Leaves
The leaf is the main photosynthetic organ of most vascular plants.
Leaves generally consist of a flattened blade and a stalk called the
petiole, which joins the leaf to a node of the stem
Function of leaves:
- Intercept light
- Exchange gasses
- Dissipate heat: transpiration
- Defend the plant from herbivores and pathogen: trichomes
In classifying angiosperms (plants that produce flowers and seeds), taxonomists (scientist
concerned with classification) may use leaf morphology as a criterion
Simple leaves have 1 petiole joined to its stem with an axillary bud. Compound leaves
mainly have blades, which is joined to small petioles to the main petiole. They also have an
axillary bud
How to distinguish a simple leaf from the compound leaf?
Look between the petioles. If there is no axillary bud between the leaves, it means that the
petiole is part of the compound leaf. If you see an axillary bud, it means that it’s 1 particular
leaf
Modified leaves
Some plant species have evolved modified leaves that serve various functions.
For example:
1. Spines: no photosynthetical function. The spines are mainly made by
stem. The spines protect cacti and reduce transpiration
2. Tendrils: modified leaves of pea/bean plant. They can attach to
a specific surface to help them climbing
3. Reproductive leaves: some plants reproduce
themselves by forming small leaves that will
fall down, and form clones
4. Storage leaves: they contain starch and material, and they are
leaves
Dermal, vascular and ground tissue systems
❖ Each plant organ has dermal, vascular and ground tissues
❖ Each of these three categories forms a tissue system
❖ Each tissue system is continuous throughout the plant
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, - The dermal tissue system consists of the epidermis
- The vascular tissue system facilitates the transport of materials through
the plant and provides mechanical support
- Tissues that are neither dermal nor vascular are the ground tissue system.
Most common tissue: storage and photosynthesis
Dermal tissue system
o In non-woody plants, the dermal tissue system consists of the epidermis. A waxy
coating called the cuticle helps to prevent water loss from the epidermis.
o In woody plants, protective tissues called periderm replace the epidermis in older
regions of stems and roots
Trichomes are outgrowth of the
shoot epidermis and can help with
reducing water loss and insect
defense
Vascular tissue system
The vascular tissue system facilitates the transport of material through the plant
and provides mechanical support. It contains of the xylem and phloem:
- Xylem transports water and dissolves minerals upward from roots into the
shoots
- Phloem transports sugars from where they are made to where they are
needed
In angiosperms, the stele of the root is a solid central vascular cylinder
Vascular tissue in stems
In most of dicots, the vascular bundle is in a ring
Vascular tissue in roots
Stele: vascular tissue from a stem or a root
The vascular cylinder appears as a lobed core of xylem with
phloem between the lobes (dicots)
The ground tissue, mostly parenchyma cells, fills the cortex,
the region between the vascular cylinder and epidermis.
The innermost layer of the cortex is called the endodermis. The endodermis
regulates passage of substances from the soil into the vascular cylinder
Ground tissue system
Tissues that are neither dermal nor vascular are the ground tissue system.
Ground tissue internal to the vascular tissue is the pith – ground tissue external
to the vascular tissue is the cortex
Ground tissue includes cells specialized for storage, photosynthesis and support
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