Plant Reproduction » Food Reserves in Seeds

What you'll learn this session

Study time: 30 minutes

The importance of food reserves in seeds
The main types of food reserves: starch, proteins and oils
How seeds store and use these food reserves
The structure of seeds in relation to food storage
How to test for different food reserves in seeds
The role of food reserves in germination

Introduction to Food Reserves in Seeds

Seeds are amazing packages of life! They contain everything a young plant needs to start growing before it can make its own food through photosynthesis. Think of seed food reserves like a packed lunch that helps the seedling survive until it can feed itself.

Key Definitions:

Food reserves: Stored nutrients in seeds that provide energy and building materials for the developing embryo during germination.
Cotyledons: Seed leaves that often store food reserves (especially in dicotyledonous plants).
Endosperm: Nutritive tissue in seeds that stores food reserves (especially in monocotyledonous plants).
Germination: The process by which a seed develops into a seedling.

🌱 Why Seeds Need Food Reserves

Seeds need food reserves because:

The embryo can't photosynthesise while underground
Energy is needed for cell division and growth
Building materials are required for new cells and tissues
The seedling needs to grow quickly to reach light
Food reserves help seedlings survive in competitive environments

📖 Where Food is Stored

Food reserves are stored in different parts of the seed:

Dicot seeds (e.g., beans, peas): Mainly in the cotyledons
Monocot seeds (e.g., corn, wheat): Mainly in the endosperm
Some seeds also store food in the perisperm (tissue derived from the nucellus)

Types of Food Reserves in Seeds

Seeds store food in three main forms: carbohydrates (mainly starch), proteins and lipids (oils and fats). Different seeds have different proportions of these reserves based on their evolutionary history and growing conditions.

🍞 Starch

What it is: A complex carbohydrate made of many glucose molecules linked together.

Function: Provides energy for the growing seedling.

Found in: Cereal grains like wheat, rice and corn (70-80% starch).

Test: Iodine solution turns blue-black when starch is present.

🥚 Proteins

What they are: Large molecules made of amino acids.

Function: Provide building materials for new cells and enzymes.

Found in: Legumes like peas, beans and lentils (20-40% protein).

Test: Biuret test turns violet when protein is present.

🥛 Oils and Fats

What they are: Lipids made of fatty acids and glycerol.

Function: High-energy storage that provides more energy per gram than carbohydrates.

Found in: Nuts, sunflower seeds, flax seeds (up to 60% oil).

Test: Emulsion test with ethanol and water shows cloudy white emulsion.

Seed Structure and Food Storage

The structure of a seed is perfectly designed to protect and nourish the embryo. Let's look at how different types of seeds store their food reserves.

🥑 Dicotyledonous Seeds

Examples: beans, peas, sunflowers

Have two cotyledons (seed leaves)
Cotyledons are usually large and thick, storing most of the food
Little or no endosperm present at maturity
Example: In a bean seed, the large fleshy cotyledons contain starch and protein

🌽 Monocotyledonous Seeds

Examples: corn, wheat, rice

Have one cotyledon (seed leaf)
Cotyledon is usually thin and not the main storage organ
Large endosperm that stores most of the food
Example: In a corn seed, the endosperm contains starch while the embryo contains oil

Case Study: The Amazing Coconut

The coconut is one of the most impressive examples of food storage in seeds. This giant seed contains:

Coconut water - liquid endosperm that provides hydration and nutrients
Coconut meat - solid endosperm that's rich in oils (about 35%) and some protein
Enough food reserves to support growth for months

This extensive food storage allows coconuts to travel across oceans, germinate on distant shores and establish new palm trees - a brilliant survival strategy!

How Seeds Use Their Food Reserves

When a seed germinates, it doesn't just use up its food reserves all at once. There's a carefully controlled process that ensures the seedling has energy until it can photosynthesise.

The Germination Process

During germination, seeds convert their stored food into usable forms:

Activation of enzymes: Water absorption (imbibition) activates enzymes in the seed.
Breakdown of reserves:
- Amylase enzymes convert starch to glucose
- Protease enzymes break down proteins into amino acids
- Lipase enzymes break down oils into fatty acids and glycerol
Transport to growing regions: These smaller molecules move to areas of the embryo that are actively growing.
Energy release: Glucose is used in cellular respiration to release energy for growth.
Building new tissues: Amino acids are used to build new proteins for the growing seedling.

🔬 Testing for Food Reserves

You can investigate what food reserves are present in different seeds with these simple tests:

Starch test: Crush seed and add iodine solution - blue-black colour indicates starch
Protein test: Crush seed, add sodium hydroxide solution followed by copper sulfate solution - purple colour indicates protein
Oil test: Crush seed between filter paper - translucent spot indicates oil

🌱 Practical Applications

Understanding seed food reserves has important applications:

Agriculture: Selecting crops with appropriate food reserves for different growing conditions
Food production: Using seeds with high protein or oil content for human nutrition
Conservation: Understanding how long seeds can remain viable in seed banks
Biotechnology: Modifying seeds to enhance nutritional content

Comparing Food Reserves in Different Seeds

Seeds vary dramatically in their food reserve composition based on their evolutionary history and ecological niche:

🌾 Cereal Grains

Main reserve: Starch (70-80%)

Examples: Wheat, rice, corn

Advantage: Quick energy release for rapid growth

🥫 Legumes

Main reserve: Protein (20-40%) and starch

Examples: Peas, beans, lentils

Advantage: Materials for building new tissues

🥜 Nuts and Oilseeds

Main reserve: Oils (up to 60%)

Examples: Sunflower, peanut, flax

Advantage: Compact high-energy storage

Did You Know?

Seeds can store their food reserves for incredibly long periods! The oldest seed successfully germinated was a 2,000-year-old date palm seed discovered at Masada in Israel. Named "Methuselah," this seed had preserved its food reserves well enough to grow into a healthy palm tree after two millennia!

Summary: Why Food Reserves Matter

Food reserves in seeds are crucial for:

Providing energy for germination when the seed can't yet photosynthesise
Supplying building materials for new cells and tissues
Helping the seedling establish quickly in competitive environments
Allowing seeds to remain viable for long periods
Supporting human nutrition through crops with different nutritional profiles

Next time you eat a bean, a grain of rice, or a sunflower seed, remember that you're consuming the food reserves that would have fed a growing plant. These amazing packages of nutrients are one of nature's most successful innovations!

🧠 Test Your Knowledge!