BIOLOGY PRACTICAL ON ONION BULB AND RHIZOME OF GINGER.

Onion Bulb

Habitat of the Specimen (onion bulb)

• School farm
• garden

Examples of other plants with bulbs

• Garlic
• Spider lily.

Biological classification of the Specimen (onion)

• Division Angiospermophyta
• Class Monocotyledoneae

Reason for class;

• Leaves with parallel venation

Agricultural classification of the Specimen (onion)

• Cash crop

Food nutrients in the Specimen

• Sugars
• Vitamins

Observable adaptive features of the Specimen (onion bulb)

• Scale leaves for protection
• Buds for vegetative propagation
• Adventitious roots for anchorage and absorption of water and mineral salts
• Fleshy leaves store food

Ecological importance of the onion bulb

• Vegetative propagation
• Source of food/ stores food
• Perennating organ
• Source of nutrients

Economic importance of onion bulb

• Food/spice
• Medicinal
• Source of income

Method of preservation of the Specimen

• Drying
• Freezing
• Irradiation

Functions of the observable features in the longitudinal section of a Sprouting Onion Bulb

• Stem supports leaves
• Fleshy leaves store food
• Scale leaves protect bulb
• Terminal bud develops into foliage leaves
• Lateral buds develop into daughter bulbs
• Foliage leaves undergo photosynthesis
• Adventitious roots provide anchorage and absorption of water and mineral salts from the soil

Similarities between Onion Bulb and Rhizome.

• Presence of scale leaves
• Presence of adventitious roots
• Presence of buds
• Presence of swollen with food

Differences between a Bulb and a Rhizome.

BULB	RHIZOME
Short vertical stem	Long horizontal stem
Presence of fleshy storage leave	Absence of fleshy leaf
Leaves arranged in concentric ring	Leaves are not arranged in concentric ring
Short internode	Long internode
Absence of leaf scars	Presence of leaf scars
Lateral buds are covered	Lateral buds are exposed
Presence of cluster of adventitious roots	Adventitious roots are spaced

Similarities between Onion bulb and Aloe vera

• Leaves are basal rosette
• Leaves in concentric arrangement
• Succulent leaves
• Reduced stem

Similarities between Onion bulb and Talinum sp

• Both possess:
• Succulent leaves
• Stem
• Buds
• Roots

Differences between a Bulb and Talinum sp.

Onion Bulb	Talinum sp.
Rosette of leaves	Alternate leaf arrangement
Buds are enclosed	Buds are exposed
Scale leaves present	Scale leaves absent
Foliage leaves absent	Foliage leaves present
Flat reduced stem	Elongated and erect stem
Adventitious roots	True root system

RHIZOME

Biological significance of rhizome

• Horizontal stem stores food
• Underground stem
• Nodes and internodes
• Buds for vegetative propagation
• Organ for vegetative propagation
• Scale leaves for protection
• Adventitious roots for vegetative propagation

Observable features which classify the rhizome as an underground stem.

• Presence of nodes and internodes
• Presence of axillary buds and terminal buds
• Presence of adventitious roots
• Presence of scale leaves.

Ecological importance of rhizome of ginger

• Stores food
• Vegetative propagation/reproductive organ
• Perennating organ

Economic importance of rhizome of ginger

• Medicinal
• Spice
• Food
• Cash crop
• Source of income

Food substances in rhizome of ginger

• Starch
• Minerals
• Vitamins

Observable adaptive features of rhizome of ginger

• Scale leaves for protection
• Buds for vegetative propagation
• Adventitious roots for anchorage and absorption of water and mineral salts.
• Swollen stem stores food

Rhizome can be propagated by;

• cutting/vegetative propagation.

Reason:

• Presence of lateral.
• Presence of axillary buds.
• Presence of stem with swollen food.

Advantages of vegetative propagation in plants

• Only one parent is needed to produce offspring.
• No need for agents of pollination and dispersal
• Offspring are genetically identical to parent
• Desirable characters are passed on to offspring
• Easy establishment of offspring because offspring use food reserves from the parent plant
• Rapid growth in the young plant as the plant is less affected by unfavourable weather conditions.
• Early maturity of offspring.

Disadvantages of vegetative propagation

• No new varieties are produced.
• Offspring have reduced resistance to diseases (reduced strength and vigour) due to lack of variety.
• Undesirable genetic characters are easily passed on to offspring.
• Overcrowding may lead to competition among parents and offspring.
• Absence of colonization of new areas
• Destruction of many individuals by disasters such as fire and flood is likely

Similarities between a Rhizome and a Talinum plant

They both possess;

• Nodes
• Internodes
• Leaf scars
• Buds
• Leaves

Differences between a Rhizome and a Talinum plant

Rhizome	Talinum sp.
Scale leaves present	Scale leaves absent
Foliage leaves absent	Foliage leaves present
Horizontal stem	Vertical stem
No flower	Flower present
Adventitious roots	True roots.
Storage underground stem	Swollen storage taproot.

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