4.6.7Additional lessons
Seed Dispersal and Germination — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 122 of 142
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Dispersal Methods
Dispersal moves seeds away from the parent so that they do not all compete with it.
Wind
- Wind Seeds with wings or parachute-like hairs, such as sycamore and dandelion, are carried away from the parent.
Animal fur
- Animal fur Hooked fruits catch on fur or clothing and are later dropped elsewhere.
Eaten fruit
- Eaten fruit Animals eat fleshy fruits and pass the tough seeds out in their faeces, often far from the parent plant.
Water
- Water Light, waterproof seeds such as coconut float on water currents to new shores.
Explosive
- Explosive Some pods dry and split suddenly, flinging seeds away from the plant.
Section 2 of 5Benefits of Dispersal
Benefits of Dispersal
Less competition
- Less competition Seedlings spread out compete less with the parent and with each other for light, water and minerals.
Colonisation
- Colonisation Seeds reaching new areas can establish plants in unoccupied habitat.
Gene flow
- Gene flow Movement of seeds links populations and spreads alleles between them.
Reduced disease
- Reduced disease Fewer seedlings under the parent lessens the build-up of pests and diseases.
Section 3 of 5Germination
Seeds need water, oxygen for aerobic respiration, and a suitable temperature for enzymes to work.
1
A dormant seed contains an embryo with a radicle, a plumule and food stores in the cotyledons or endosperm, and has a very low metabolic rate.
2
Water enters the seed by imbibition and rehydrates the cells, so metabolism restarts.
3
The embryo releases gibberellin, which stimulates cells to produce amylase.
4
Amylase digests stored starch to maltose, which is converted to glucose to supply energy and building materials.
5
The radicle emerges first and forms the root; the plumule grows upwards into the shoot.
Section 4 of 5Conditions Needed
Water
- Water It activates enzymes, dissolves reserves and allows tissue to swell.
Oxygen
- Oxygen Aerobic respiration releases the large amount of ATP needed for rapid growth.
Warmth
- Warmth Enzymes need a suitable temperature;
- very cold seeds respire too slowly and very hot ones denature enzymes.
Not needed
- Not needed Light is not required for most seeds to germinate, since stored food supports early growth underground.
| Factor | Role in germination |
|---|---|
| Water | Activates enzymes, softens seed coat |
| Oxygen | Supports aerobic respiration |
| Temperature | Allows enzyme-controlled reactions |
Section 5 of 5Exam Checklist & Tips
4.6.7 – Key Points for the Exam
- Seed dispersal Movement of seeds away from the parent plant.
- Germination Start of growth of an embryo in a seed to form a seedling.
- Imbibition Absorption of water by a dry seed.
- Gibberellin Plant hormone that stimulates amylase production during germination.
- Cotyledon Seed leaf containing stored food in many seeds.
Common Mistakes
- Saying that a seed needs light and soil minerals to germinate; stored food supports the first growth.
- Confusing the radicle (root) with the plumule (shoot).
- Stating that dispersal is the same as pollination.
- Saying seeds respire only after germination; dormant seeds respire slowly.
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