NTA Level 5 • Semester 2 • PST05210

Morphology of the Seed

Basic Pharmacognosy • Source Session/Topic 10

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Session 10: Morphology of the Seed

Total Session Time: 60 minutes

Prerequisites

• None

Learning Tasks

By the end of this session students are expected to be able to:

• Define a seed

• Describe the structure of a seed

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board and chalk/whiteboard markers

• LCD projector and Laptop

SESSION OVERVIEW

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning objectives and clarify

ASK students if they have any questions before continuing.

STEP 2: Definition of a Seed (10 minutes)

|Activity: Brainstorming (5 minutes) |

| |

|Ask students to brainstorm on the following question: |

| |

|What is a seed? |

| |

|ALLOW few students to respond? |

| |

|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARIZE by using the content below |

• Seed is the structure formed by plants from a ripened ovule after

fertilization

• There numerous sizes and shapes of seeds

• Seeds are formed within a fruits of gymnosperm and angiosperms

• Seeds may be formed from orthotropous ovules, campylotropous or

anatropous ovules

STEP 3: Structure of a Seed (35 minutes)

|Activity: Small Group Discussion (10 minutes) |

| |

|DIVIDE students into small manageable groups |

| |

|ASK students to discuss on the following question |

|Write down the external structures found on a seed |

| |

|ALLOW students to discuss for 15 minutes |

| |

|ALLOW few groups to present and the rest to add points not |

|mentioned |

| |

|CLARIFY and SUMMARIZE by using the contents below |

• Basic parts of a seed are the embryo, endosperm and the seed coat

External structures of a seed

o Seed coat

▪ Most seeds have two seed coats

▪ Testa (the outer seed coat)

• Outer most protective layer of the seed –form the seed coat

• Protects the seed

• Thickness varies with type of seed

▪ Tegmen

• The inner seed coat

o Funicle or stalk

▪ A structure that attaches the seed to the placenta

o Micropyle

▪ An opening that marks position of the radicle

o Hilum

▪ Scar left by the funiculus (attachment to the embryo)

o Raphe

▪ Fibrovascular tissue formed by adhesion of funicle and testa

o Aril

▪ Expansion of placenta or funicle over the surface of the seed

▪ Formed in some seeds

o Elaiosome

▪ Fleshy structures rich in lipids and proteins attached to the

seed

o Caruncle or Strophiole

▪ A structure that arises from the testa near the hilum

• Internal structures of a seed

o Embryo

▪ The immature plant within the seed from which a new plant grows

• Made up of cotyledons

o One cotyledon in monocotyledons plants

o Two cotyledons in almost all dicotyledons and two or more

in gymnosperms

• Has radicle and plumule

▪ Endosperm

• A tissue that forms beginning of food storage of a plant

• Consists of two parts, one part stores starch and the other

part stores proteins

• Exalbuminous seeds

o Seeds with no endosperm at maturity e.g. sunflower

• Albuminous seeds

o Have endosperm at maturity e.g. castor seed

STEP 5: Key Points (5 minutes)

• Seed is the structure formed by plants from a ripened ovule after

fertilization and occurs in many shapes and sizes

• Seeds may be formed from orthotropous ovules, campylotropous or

anatropous ovules

• The seed consists of a seed coat which covers the seed and made up of the

testa and tegmen

• The internal of a seed consists of the embryo and endosperm

• In some seeds the endosperm is absorbed and absent at maturity forming

exalbuminous seeds while in albuminous seeds the endoperm persists

STEP 6: Evaluation (5 minutes)

• What is a micropyle?

• What are the functions of a seed coat?

References

Trease, G. E., Evans, W. C., & Evans, D. (2009). Trease and Evans

pharmacognosy. London: Saunders.

Joanne Barnes et al (2002), Herbal medicines 3rd Edition: Pharmaceutical

Press

Wallis, T. E. (2005). Textbook of pharmacognosy. New Delhi: CBS.

Robbers, J. E., Speedie, M. K., Tyler, V. E., & Tyler, V. E. (1996).

Pharmacognosy and pharmacobiotechnology. Baltimore: Williams &

Wilkins.

Heinrich, M., Kinghorn, A. D., Maizels, D., Gibbons, S., & Phillipson, J.

D. (2012). Fundamentals of pharmacognosy and phytotherapy. Edinburgh:

Churchill Livingstone/Elsevier.

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