P3 Science - Life Cycles of Plants

What Are Life Cycles?

Plants reproduce to ensure the continuity of their own kind.
Most plants reproduce by seeds. Of these plants, most are flowering, but some, like firs and pines, are non-flowering and store their seeds in cones instead.
Some plants, however, reproduce by spores. These plants include ferns and mosses.

🌲 Pine trees store their seeds in cones instead of flowers — they're non-flowering plants that still reproduce by seeds!

Flowering Plants

Flowering plants reproduce by seeds and they share the same basic life cycle.

🌰 Seed Under the right conditions, the seed will germinate into a new plant

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🌱 Young Plant (Seedling) Leaves, stem and roots develop

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🌻 Adult Plant Develops flowers and fruits

♻️ The life cycle is a circle — the adult plant produces new seeds, which grow into new plants, and the cycle continues forever!

Germination

For most seeds, the basic conditions needed for germination are:

💧 Water

🌬️ Air (Oxygen)

☀️ Warmth

💡 Seeds do NOT need light to germinate — they don't have leaves yet to trap light! Instead, they rely on food stored in their seed leaves.

Set-up	Conditions	Result	Why?
P	Moist cotton wool, 25°C, well-lit room	✓ Germinated	Has water, air/oxygen, and warmth
Q	Moist cotton wool, 2°C (refrigerator)	✗ Did not germinate	No sufficient warmth
R	Dry cotton wool, 25°C, well-lit room	✗ Did not germinate	No water
S	Moist cotton wool, 25°C, dark room	✓ Germinated	Has water, air/oxygen, and warmth (light not needed)
T	Airtight box + oxygen absorber, moist cotton wool, 25°C	✗ Did not germinate	No air/oxygen

Only the seeds in Set-ups P and S germinated as they had water, air/oxygen and warmth — all three conditions needed for germination.

Parts of a Seed

🛡️ Seed Coat

The seed coat is a thin outer layer that protects the seed.

🌾 Seed Leaf

The fleshy part of the seed that stores food. It provides the seedling with stored food for growth before the seedling grows true leaves to trap light to make its own food.

🌱 Root (Embryonic)

The root is the first to grow out and its appearance marks the germination of the seed. It grows towards and absorbs water, which is needed for further plant development.

🥜 The two halves of a peanut are actually seed leaves packed with stored food — that's why peanuts are so nutritious!

Growth

When a seed germinates, the root appears first, followed by the shoot (consisting of the leaves and stem).
During the initial stages of development, the seedling obtains food from the seed leaves.
Once the leaves emerge, however, the seedling can make its own food.
When all the stored food in the seed leaves is used up, the seedling depends solely on its leaves to trap light and make food.

🌰 Seed Dormant, waiting for right conditions

🌱 Root Emerges Germination begins — root grows first

🪴 Shoot Grows Seed leaf provides stored food

🌿 True Leaves Plant can now make its own food

📊 Common Graphs: Mass of Seed Leaf vs Shoot Over Time

Seed leaf mass: Food stored in the seed leaf will be used by the seedling for growth (as the seedling has not grown true leaves to trap light to make its own food by photosynthesis). Hence, the mass of the seed leaf decreases over time.

Shoot mass: The shoot of the seedling grows over time. Hence, the mass of the shoot increases over time.

📈 On a graph, you'll see two lines going in opposite directions — seed leaf mass goes DOWN while shoot mass goes UP until true leaves develop!

Adult Plants

The plant is at the adult stage when it starts to produce flowers and bear fruits.
The fruits contain seeds which will grow into new plants.

🍎 An apple is a fruit that contains seeds — when the apple falls and rots, those seeds can sprout into brand new apple trees!

📝 Key Takeaways

Topic	Key Point
Purpose of Reproduction	To ensure the continuity of their own kind
Life Cycle Stages	Seed → Young Plant (Seedling) → Adult Plant
Germination Conditions	Water, Air (Oxygen), and Warmth — light is NOT needed
Seed Coat	Protects the seed
Seed Leaf	Stores food for the seedling before true leaves grow
Root (Embryonic)	First to emerge — marks germination; absorbs water
Growth Stages	Root appears first → seedling uses stored food → true leaves grow → plant makes its own food via photosynthesis

P3 Life Cycles of Plants 🌱🌻