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7th standard cbse science​

Answer 1

Required Answer:

$\boxed{\begin{array}{c|c|c}\sf Agents&\sf Examples&\sf Explanation\\\huge\frac{\qquad}{}&\huge\frac{\qquad }{}&\huge\frac{\qquad}{}\\\underline{\sf{ \: \: \: \: \: \: \: Wind \ \: \: \: \: \: }}&\underline{\sf{Maple,Grasses}}&\underline{\sf{light \: and \: winged \: seeds}} \\ \\\underline{\sf{ \: \: \: \: \: \: Water \: \: \: \: }}&\underline{\sf{Coconut}}&\underline{\sf{Having \: fibrous \: structure}} \\ \\\underline{\sf{ \: \: \: \: Animals \: \: \: \: }}& \underline{\sf{xanthium}}&\underline{\sf{spiny \: structures \: with \: hook}}\\ \\\underline{\sf{ \: \: \: \: Explosion\: \: \: \: }}& \underline{\sf{pea}}&\underline{\sf{having \: fruits \: that \: can \: burst }}\end{array}}$

Explanation:

Dispersal by wind:

• Seeds that are light in weight and that have hair like structures are dispersed by wind.
• Maple, grasses and madar are dispersed by wind.

Dispersal by water:

• Some seeds and fruits have fibrous structure that help them to float and resulting seed dispersal.
• Fruit of coconut is dispersed by water.

Dispersal by animals:

• Some seeds and fruits have spiny structures that help them to stick on the body of the animals. In this ways, they get dispersed by animals as they carried away far with them and fall of to the ground.
• Xanthium is dispersed by animals.

Dispersal by explosion:

• Some seeds and fruits have such a structure that they may burst open.
• Seeds of peas and castor are dispersed by explosion.

Answer 2

Required Answer :

$\boxed{\begin{array}{c|c|c} \bf Agents & \bf Examples & \bf Explanation \\ & & \bf (Type \ of \ seed \ \& \ structure) \\ \sf \dfrac{\qquad \qquad \qquad \qquad}{Wind} & \sf \dfrac{\qquad \qquad}{Dandelion, Sycamore } & \sf \dfrac{\qquad \qquad \qquad \qquad}{Very \: light \: and \: have \: wings \: or \: fine \: hair \: on \: them} \\ \sf \dfrac{\qquad \qquad \qquad \qquad}{Water} & \sf \dfrac{\qquad \qquad}{Coconut, Lotus} & \sf \dfrac{\qquad \qquad \qquad \qquad}{Have \: fibrous \: structure} \\ \sf \dfrac{\qquad \qquad \qquad \qquad}{Animals} & \sf \dfrac{\qquad \qquad}{ Xanthium, Tiger's \: Claw} & \sf \dfrac{\qquad \qquad \qquad \qquad}{Have \: spiny \: structures \: with \: hooks} \\ \sf \dfrac{\qquad \qquad}{Explosive \ Mechanism} & \sf \dfrac{\qquad \qquad}{Pea, Balsam} & \sf \dfrac{\qquad \qquad \qquad \qquad}{Have \: fruits \: that \: can \: explode } \end{array}}$

Explanation :

What is Dispersal? ☆

The process of scattering away of seeds or fruits away from the parent plant is called dispersal.

Dispersal by wind ☆

• Some seeds are very light and have wings or fine hair on them. Such seeds are easily carried away by wind.

• Seeds such as Dandelion and cotton seeds have fine hair attached on them which act like parachutes, and some seeds such as Sycamore have wings that help them to float in air and move to far - off places.

Dispersal by water ☆

• A lot of plants grow in and around water bodies. Seeds and fruits of these plants, such as coconut and lotus are usually carried by the flowing water to far - off places. Coconuts are hollow from inside and are covered with rough hair. This makes them light to float and travel in water. The lotus fruit has a spongy part that helps it to float.

Dispersal by animals ☆

• Some seeds have hooks, spines or stiff hair. These help the seeds to stick to the hair in the bodies of animals, feathers, of birds, or also to our clothes. These seeds are then carried from one place to another.

• Often birds and some animals swallow seeds while eating fruits such as berries. The seeds come out when they excrete.

• Seeds also get dispersed when we eat fruits and then throw away the seeds such as mangoes, guavas, papaya etc

Dispersal by explosion ☆

• The fruits of some plants such as pea and balsam, explode when they dry. This scatters the seeds away from the parent plant

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