All flowering plants produce seeds. The seeds are a tiny part of a plant which gives rise to a new plant. Different seed is found in different shapes, sizes, and colors. It can be a pip (like an apple), a nut (in walnut), or a bean (pea, pulses). Let’s find out more about it.
Parts of Seeds
A seed has the following parts:
- Seed coat: It is the outer covering the of seed. It protects the internal parts.
- Seed leaves or cotyledons: Cotyledons are present inside the seed. Cotyledons absorb the food from the parent plant and store it for the embryo. They also protect the embryo. Some seeds have two seed leaves like gram, pea, bean, etc. Such seeds are called dicot or dicotyledonous. Some seeds have only one seed leaf. They are called monocot or monocotyledonous.
- Embryo or baby plant: It is present inside the seeds which develop into a new plant. The embryo gives rise to a baby shoot (plumule) and root (radical).
Structure of a seed (Source: Shutterstock)
Take four shallow dishes. Place cotton in each dish. Take a few gram seeds and put some of them on each dish. Now, follow the steps gives below for each dish.
- Dish 1: Keep this dish in a place where it gets an adequate amount of air and warmth. The cotton should be moist.
- Dish 2: Place the second dish in the refrigerator and keep the cotton moist.
- Dish 3: Place it where it can get an adequate amount of air and warmth. Do not wet the cotton.
- Dish4: Place it where it can get adequate sunlight. Keep the seed and the cotton covered with water.
Result: We will see in this activity the seed germinate only in jar B because jar B had water, air, and warmth required for the seed to germinate. Jar A did not have warmth or sunlight. Jar C there was no air for seed. In jar A, the seed did not get water. This shows that if any condition is missing, the seed will not grow into new plants. So air, water, and sunlight are the conditions necessary for germination.
Germination of a Seed
Germination means the development of a seed into a new plant. All seeds do not germinate. Only those which get suitable conditions grow into new plants. The conditions necessary for a seed to germinate are:
- Air to breathe.
- Water to make the seed coat soft. This enables the baby plant to break the seed coat open and come out.
- Warmth to make its cells active.
Germination occurs in following stages:
- The seeds absorb water through the seed hole. The cells of the embryo start dividing and increasing in size.
- The seed coat breaks open and the root (radical) sprout and grows downwards.
- Then the shoot (plumule) start growing upwards, which later produces stem and leaves.
- When the seedling grows green leaves, it starts making its own food.
- By this time, cotyledons dry up and fall. The seedling then develops into a new plant.
Germination of seed (Source: Shutterstock)
Dispersal of Seed
Plants are fixed to the ground. They cannot move from place to place. If all the seeds of a plant fall and germinate near it, they will not get favourable conditions for growth. Therefore, it is necessary for them to get scattered and grow away from the parent plant. The scattering of seed for growing away from their parent plant is called dispersal of a seed.
There are some natural agents that help in scattering the seeds away from the parent plant. These are wind, water, animals and by the explosion of fruits. Some seeds and fruits develop a special structure that helps them in dispersal.
Seeds that are small in size and light in weight are dispersed by wind. Cotton, Madar, and dandelion seeds are dispersed by wind. They have fine, long hair around them. So, they are easily carried away by the wind.
Seed dispersal by wind (Source: Shutterstock)
Seeds of plants growing in water or near water bodies are dispersed by water. These seeds are light in weight and are able to float in water. The spongy fruit of lotus and fibrous outer covering of coconut make them light. This helps a seed float on water and move long distances.
Dispersal by water (Source: Shutterstock)
Many fruits and seeds are spread by animals, birds, and humans. Humans and animals eat fruits and throw away their seeds. These grow into a new plant. Squirrels collect nuts and bury them. When the conditions become favourable, these nuts grow into new plants.
Birds eat fruits sometimes the seeds come out in their droppings undigested. Some seeds get stuck to their beaks while eating fruits. When they rub their beaks, the seeds fall down and later on grow into new plants.
Seed dispersal by animals (Shutterstock. com)
4. Explosion of fruits
Pods of some fruits like peas, beans, and balsam burst open or explode when dry, thus scattering their seeds.
An explosion of fruit (Source: Shutterstock)
Q1. Which of the following food crop came from other countries?
- Green Chilli
- All of the above
Sol. Potato is originated in the area of southern Peru and extreme northwestern Bolivia. It is an edible tuber which contains a high amount of carbohydrates. Tomato is originated from Peru, Bolivia, Chile, and Ecuador. It is an edible fruit. It is used in making salads, juice, sauces. Green chillies are originated in Mexico. It is used to spice up the food. Thus, the correct answer is option D.