THE MAIZE GRAIN AS A BIOLOGICAL SPECIMEN.

Maize grain is not a seed, but rather a fruit.

It is referred to as a fruit because its outer wall is formed from the fusion of the testa and the fruit wall.

Maize grain is monocotyledonous and endospermous.

Type of fruit

• Caryopsis

Reasons

• A one-seeded fruit in which the pericarp is dry and fuses with the seed coat

Class of food

• carbohydrate,
• protein

It is essential to note that starch is not a class of food. Starch is a suitable answer for a food nutrient or a type of food

Food storage tissue

• Endosperm stores starch.
• Aleurone stores protein

Functions of starch in animals

• Source of energy,
• Structural components.
• Converted to lipids

Type of germination

• Hypogeal

To test for starch

• Use a pestle and mortar
• Grind
• Add water
• Add a few drops of iodine solution
• Blue-black colour
• Starch is present

How do you remove starch from seeds?

• Soak in water for one day (24hours)
• The amount of starch in a germinating seed decreases because the starch is used up for respiration and building of cells

#01

Maize is an endospermous seed, meaning it stores food (starch) in the endosperm.

• If dry maize grain is cut into two and a few drops of iodine solution are added on the cut surface, a black colour forms due to the presence of starch in the endosperm.
• If the seed is soaked in water for 24 hours, the enzyme amylase in the endosperm is activated, allowing it to digest starch into maltose. After some time, Sugar is then transported by the cotyledon to the embryo for respiration and germination
• If iodine solution is dropped immediately on the cut surface of maize grain soaked in water for 24 hours, blue black colour forms due to the presence of starch in the endosperm
• If iodine solution is dropped on the cut surface of a sprouted maize grain, no blue-black colouration will be observed due to the absence of starch in the endosperm.
• If the sprouted maize grain is boiled in Benedict solution, brick red precipitates will be formed in the endosperm, cotyledon and axis of the embryo (the link between the cotyledon and the plumule and radicle).
• If a dry maize grain is boiled in Benedict’s solution, no brick red precipitate forms because there is no water to activate amylase to digest starch into maltose (sugars)

Draw 6cm to 8cm of the external structure of the maize grain

Observable features/characteristics of maize grains.

• Fruit wall
• Position of endosperm
• Remains of style
• Position of scutellum
• Position of the embryo
• Point of attachment to the cob.

#02

SPECIMEN:

• Soak some maize grains overnight.
• Remove and allow sprouting (to germinate) in moist cotton wool for three days
• Select six of the germinated maize grains into a petri dish and label A
• Select six dry maize grains into a separate petri dish and label B.

QUESTIONS

a)

i)

• Using pestle and mortar, grind the germinating seeds in A, add water and filter.
• Label the filtrate A.
• Write your observation
• Divide A into two halves, about 2cm³ in separate test tubes.
• Label the test tubes A1 and A2

ii)

• Using pestle and mortar, grind six dry seeds in B, add water and filter.
• Label the filtrate B.
• Record your observation

b)

• Boil B in a water bath for 5 minutes.
• Record your observation
• Divide B into two halves, about 2cm³ in separate test tubes.
• Label the test tubes B1 and B2

c)

i). Add 2 to 3 drops of iodine solution into each of A1 and B1. Record your observation

ii). Add about 2cm³ of Benedict solution to equal volumes of A2 and B2 separately and heat in a water bath. Record your observation

d)

i) What conclusion can you draw from this experiment?

ii) Explain your observation and conclusion

iii) Name any natural enzyme involved.

e) Name the class of food present in maize grain

f) Explain your result and conclusion

g) Physiological and environmental factors affecting sprouting in maize

ANSWERS.

a)

i) Cloudy solution forms

ii) Turbid solution forms

b)

• A turbid solution of B turns a colloidal suspension on boiling

c)

	Test	Observation	Conclusion
i.	A1 + Iodine solution	No blue-black colour forms	Starch is absent
	B1 + Iodine solution	Blue-black colour formed.	Starch present
ii.	A2 + Benedict’s solution and warmed	Brick-red precipitate forms	Reducing sugar is present.
	B2 + Benedict’s solution and warmed	No brick-red precipitate forms	Reducing sugar is absent.

d)

i) A contains reducing sugar

ii) B contains starch

iii) Amylase

e)

• Carbohydrate

f)  Explanation of result

• Water activates enzymes in dry seeds when soaked in water
• Starch in soaked seeds is converted into sugars.
• Starch is insoluble in cold water but dissolves to form a colloidal suspension on warming.

g). Environmental and physiological factors affecting germination in maize

• Moisture or water
• Oxygen
• Warmth (Suitable Temperature)
• Enzymes
• Hormones

Soak maize grain in water for about 36 hours. Remove it, cut it longitudinally into two halves. Make a label drawing 8cm – 10cm of one half of the sectioned maize grain.

Functions of parts.

• Fused pericarp and testa for protection.
• Endosperm stores food for the embryo.
• Cotyledon secret enzymes convert food in the endosperm.
• Cotyledon absorbs food from the endosperm and transfers it to the radicle and plumule.
• Plumule develops into the shoot system of the plant.
• Radicle develops into the root system of the plant.
• Coleoptile protects the plumule during growth.
• Coleorhiza protects the radicle.
• Epithelium of the cotyledon secretes enzymes to digest the endosperm

#03

SPECIMEN:

• MAIZE GRAIN INFESTED WITH FUNGI (MOULDY)

QUESTIONS

• Identify the specimen
• Describe the specimen
• Factors enhancing the state of the specimen
• Effects on public health
• Effects on food security
• Ecological significance
• Methods to prevent the conditions

ANSWERS

Description of specimen:

• It is a maize grain
• It is soft
• Discoloured
• Mouldy

Environmental conditions that trigger the growth of fungus on maize grain

• Presence of fungal spores in the air.
• Suitable temperature for enzymatic activity
• Moisture/high relative humidity to activate enzymes to digest food

The effects of the phenomenon on public health

• Food contamination
• Diseases
• Reduces nutrient value
• Reduces nutrient value
• Toxins
• Reduces taste
• Unpleasant odour
• Cause foodborne diseases

Effects on food security

• Wastes food
• Food poisoning
• Makes seeds less viable to germinate
• Reduces Economic value
• Source of contamination for other food materials

Ecological significance.

• Seeds will not germinate
• Poisonous to animals
• Source of spores to other grains

Methods to prevent the conditions

• Dry grains well before storage.
• Remove infested grains from the container or room.
• Store grain in a dry environment.

Pests affecting maize

• Weevil,
• Termite,
• Rats
• Grasscutter
• mouse
• birds

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