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Plants - Seed Dispersal and Germination

Grade 6Cambridge (IGCSE)

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Germination is the process by which a seed begins to grow into a new plant. It requires three specific conditions: Water (H2OH_2O), Oxygen (O2O_2), and Warmth (Optimal Temperature).

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The seed structure includes the testa (seed coat), the embryo (consisting of the radicle and plumule), and the cotyledon (food store).

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The radicle is the part of the embryo that develops into the root system, while the plumule develops into the shoot system.

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Seed dispersal is the movement or transport of seeds away from the parent plant to reduce competition for light, space, and nutrients such as Nitrates (NO3−NO_3^-) and Magnesium (Mg2+Mg^{2+}).

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Wind Dispersal: Seeds are often light and have adaptations like wings (e.g., sycamore) or hairs (e.g., dandelion) to increase air resistance.

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Animal Dispersal: Can be internal (eating fleshy fruits and excreting seeds) or external (seeds with hooks/burrs that stick to fur).

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Water Dispersal: Seeds are buoyant and waterproof, allowing them to float (e.g., coconuts).

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Explosive Dispersal (Ballochory): Pods dry up and burst open, flinging seeds away (e.g., pea pods).

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During the initial stages of germination, the seed performs aerobic respiration using stored glucose: C6H12O6+6O2→6CO2+6H2O+EnergyC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy}.

📐Formulae

Percentage Germination=(Total seeds germinatedTotal seeds planted)×100\text{Percentage Germination} = \left( \frac{\text{Total seeds germinated}}{\text{Total seeds planted}} \right) \times 100

6CO2+6H2O→lightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{\text{light}} C_6H_{12}O_6 + 6O_2

Rate of Germination=ΔNumber of germinated seedsΔtime (days)\text{Rate of Germination} = \frac{\Delta \text{Number of germinated seeds}}{\Delta \text{time (days)}}

💡Examples

Problem 1:

An experiment was conducted where seeds were placed in a test tube with boiled, cooled water and a layer of oil on top at 25∘C25^\circ C. Will the seeds germinate?

Solution:

No, the seeds will not germinate.

Explanation:

Boiling water removes dissolved Oxygen (O2O_2), and the oil layer prevents more O2O_2 from entering from the air. Since aerobic respiration is required for germination, the lack of O2O_2 prevents the process even if H2OH_2O and warmth are present.

Problem 2:

A student plants 50 mung bean seeds. After 5 days, 42 seeds have successfully produced a radicle. Calculate the percentage germination.

Solution:

Percentage=4250×100=84%\text{Percentage} = \frac{42}{50} \times 100 = 84\%

Explanation:

The percentage is calculated by dividing the successful germinations by the total sample size and multiplying by 100.

Problem 3:

Identify the dispersal method for a seed that is small, light, and possesses a feathery structure.

Solution:

Wind Dispersal.

Explanation:

Feathery structures increase the surface area of the seed, allowing it to be carried easily by air currents away from the parent plant.