Practical Note On Castor Seed, Cowpea Seed, Groundnut Seed, Sunflower Seed, and Coconut Seed.

THE CASTOR OIL AND JATHROPHA SEEDS

• It is a dicotyledonous endospermous seed
• It has a hard but brittle testa with a thin tegmen under it
• At the narrow end of the seed near the micropyle, there is a white spongy structure called the caruncle
• The hilum is situated near the caruncle
• The hilum and the micropyle are hidden by the caruncle
• Beneath the seed coat is the endosperm, enlarged with mainly oil stores
• The endosperm stores protein and oil
• The embryo is enclosed within the endosperm
• It consists of the radicle, plumule, and the two cotyledons
• The radicle and the plumule are small structures that lie within the cotyledons
• The cotyledons are very flat and papery structures that transfer food from the endosperm to the radicle and plumule during germination.

Type of seed

• Dicotyledonous seed or
• Endospermous seed

Type of germination

• Hypogeal

Drawing of the internal structure of Castor oil seed.

Functions of parts

• Testa protects the seed contents
• Endosperm stores food, mainly oil and protein
• Plumule future shoot
• Radicle future root
• The cotyledons absorb food from the endosperm to the embryo during germination
• It protects the plumule during its passage through the soil
• The cotyledon acts as a photosynthetic organ when exposed to light during germination
• Caruncle absorption of water during germination

Features ensuring successful growth in the castor oil seed

• Food is present in the endosperm
• Cotyledons digest and absorb food for the developing root and shoot
• Curved epicotyl protects the plumule as it grows through the soil
• Cotyledons turn green and undergo photosynthesis
• The roots absorb water and mineral salts
• Caruncle absorbs water necessary for radicle and plumule to germinate

Observable structural differences between castor oil seed and maize grain.

MAIZE GRAIN	CASTOR OIL SEED
Possesses two scars	Possess one scar
Micropyle is absent	Micropyle present
The testa is fused with the wall of the fruit	The testa is separated from the fruit wall
No caruncle	Caruncle present
White/yellow/cream colour	Black/grey/brown colour

Similarities between the internal structure of castor oil seed and maize grain.

Both possess:

• Prominent endosperm
• Reduce cotyledons
• Radicle
• Plumule
• Testa

Differences between the internal structure of castor oil seed and maize grain.

CASTOR OIL SEED	MAIZE GRAIN
Presence of two cotyledons	Presence of one cotyledon
Plumule and radicle sheaths are absent	Plumule and radicle sheaths are present.
Pericarp absent	Testa fused with pericarp
Aleurone absent	Aleurone present
Large leaf-like cotyledon	Small non-leaf-like cotyledon
Endosperm encloses the embryo	Endosperm does not enclose the embryo.

COWPEA SEED

Cowpea is a dicotyledonous non-endospermous seed.

The food nutrients in the cowpea seed are protein, and the food storage tissue is the cotyledons.

Draw the external structure of the cowpea seed.

Observable features of the cowpea

• Testa
• Position of radicle
• Micropyle
• Hilum

Features of the cowpea that can be inherited.

• Shape of the seed
• Size of the seed
• Colour of the hilum
• Thickness of testa

Soak the seed in water for about 24 hours. Using a scalpel, divide the seed longitudinally into two halves and draw the longitudinal section of the seed.

Observable features and their functions

• Plumule develops into a shoot
• Epicotyl supports the first foliage leaves
• The hypocotyl carries cotyledons above the soil
• Radicle develops into roots
• Micropyle movement of air and water
• Testa for protection
• Cotyledon stores food and also carries out photosynthesis in epigeal germination
• The stalk of a broken cotyledon supports the cotyledon

Type of germination

• Epigeal germination

Reason:

• Cotyledons are carried above the soil

Description of Epigeal Germination

• Seed absorbs water and swells
• Testa splits due to the development of the radicle
• Radicle emerges through the raptured testa, grows downwards.
• The hypocotyl elongates quickly
• Pushing the seed out of the soil as a result
• Exposing the cotyledons to sunlight
• Exposed cotyledons turn green and undergo photosynthesis
• The plumule emerges and develops green leaves, which take over photosynthesis
• Cotyledons then shrivel and fall off (after the first foliage leaves have been formed)
• The radicle develops into the root

Testing for protein in cowpea

Method:

• Crush the seed using a pestle and mortar
• Put a small quantity in a test tube
• Add water
• Add an equal volume of Millon’s reagent into the test tube
• Warm the mixture in a water bath.

Observation:

• A white precipitate is formed on the addition of the reagent.
• The precipitate turns red on heating.

Conclusion:

• Protein is present.

Functions of Proteins

• Growth, repair and replacement of worn-out tissue.
• Enzyme formation, e.g. ptyalin
• Hormone formation, e.g. insulin
• Structural materials
• Formation of antibodies.
• Energy sources in the absence of carbohydrates and lipids.
• Formation of haemoglobin

Economic importance of legumes

• Fix nitrogen in the soil
• Cover crop to reduce erosion
• Fodder for animals
• Source of protein
• Used as organic manure
• Source of income

THE GROUNDNUT SEED

The groundnut seed is a dicotyledonous non-endospermous seed.

The food storage tissue is the cotyledons.

Type of germination

• Epigeal germination

Reason:

• Cotyledons are carried above the soil

Food nutrients in groundnut

• Fats and oils
• Proteins

Test for food nutrients in groundnut

Method 1

• Crush the seed with a pestle and mortar
• Rub on filter paper or white paper
• Observe in light
• Translucent mark forms

Conclusion:

• Fats and oils present

Method 2

• Crush the seeds with a pestle and mortar
• Or make a paste of the seeds
• Fetch into a test tube
• Add 2cm³ of distilled water
• Add a few drops of Sudan III solution
• A red-stained layer separates on the surface of the water, which remains uncoloured.

Conclusion:

• Lipid is present

Importance of fats and oils to humans

• Hold and protect vital organs in animals
• Warmth/temperature regulation
• Sources of fat-soluble vitamins (A, D, E, K)
• Formation of cell membranes
• Provide energy
• Used for long-term energy storage
• In the production of sex hormones

Economic importance of groundnut

• Source of food
• Fixes nitrogen in the soil
• Source of income
• Source of raw materials for industries
• Source of oil.

THE SUNFLOWER SEED

It is a dicotyledonous non-endospermous seed, and the type of germination is epigeal.

The sunflower has a one-seeded fruit surrounded by a dry pericarp.

The sunflower is a type of fruit called an achene.

Functions of parts of the sunflower seed

• The pericarp protects the content of the fruit.
• Thin testa protects seed contents
• Plumule develops into the shoot system.
• Radicle develop into the root system.
• The cotyledon stores food for the embryo
• The cotyledon protects the plumule during germination
• Cotyledons act as a photosynthetic organ when exposed to the light during germination

Type of food stored:

• oil
• protein

Economic importance

• Ornamental/beautification
• Source of food
• Source of raw materials for industries
• Source of income
• Source of oil.

COCONUT SEED

Specimen provided

• Edible part of dry coconut (whole) cut longitudinally.

Observable features:

• Brown testa protects the seed
• Milky endosperm stores food for the embryo
• A soft embryo develops into a plant
• Funicle attaches the seed to the endocarp

Classes of food in the coconut fruit/seed

• Water
• Fats
• Carbohydrates (i.e. galactose

Food storage structure is the endosperm

Economic importance of coconut

• Source of food
• Source of oil
• Source of income
• Source of employment
• Pericarp used as fuel

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