Science 5 Marks Questions

Parasite	Saprotroph
The organism that grows on the body of another organism and derives nutrients from it is known as a parasite	The organism that obtains nutrients from the dead or decaying organic matter is called saprotroph
The Organism on Which it feeds is called host	They do not feed on a living organism
Examples of parasites are Cuscuta and orchids.	Examples of saprotrophs are fungi and some bacteria.

Replenishment of Nutrients in Soil:
Crops require a lot of nitrogen to make proteins. After the harvest, the soil becomes deficient in nitrogen. Plants cannot use the nitrogen gas available in atmosphere directly. Action of certain bacteria can convert this nitrogen into form readily used by plants. Rhizobium bacteria live in the root nodules of leguminous plants. These bacteria take nitrogen gas from the atmosphere and convert it into water soluble nitrogen compounds making it available to the leguminous plants for their growth.
In return, leguminous plants provide food and shelter to the bacteria as Rhizobium cannot prepare its food. They, thus have a symbiotic relationship. This association is very important for the farmers, as they do not need to add nitrogen fertilisers to the soil in which leguminous plants are grown.

The process by which green plants can prepare their own food is called photosynthesis. Green plants possess chlorophyll in their leaf and utilises carbon dioxide (from air) water, minerals (from soil, through root) as raw material and sunlight as source of energy and convert light energy into chemical energy. The food thus synthesised is in the form of starch (carbohydrate). The overall reaction for photosynthesis can be given as follows:

Experiment to test the presence of starch in leaves: Take two healthy green potted plants of the same type. Keep one potted plant in a dark room for one or two days in order to remove all the starch from the leaves. Keep the other plant in sunlight. Now, take one leaf from each potted plant and put a few drops of iodine solution on them. Then note down the observation.

Plants kept in light and dark conditions: No blue black colour will be observed on the leaves of the plant kept in the dark room. This indicates the absence of starch. Blue black colour will be observed on the leaves of the plant kept in sunlight. This indicates the presence of starch.

Animals like tiger, wolf, lion and leopard are carnivorous and do not eat plants. They hunt and eat herbivorous animals like deer, gaur, bison, zebra, giraffe, etc., which are dependent on plants for food. If there are no plants, herbivorous animals will not be able to survive as they will have no food and would die of starvation. This will ultimately affect animals like tiger, wolf, lion and leopard that depend on herbivorous animals for food. They will have nothing to eat and thus would not survive from this, it can be concluded that all heterotrophs directly or indirectly depend on plants for food and cannot survive without plants.

Plants show two major modes of nutrition, i.e.

1. Autotrophs are those which can synthesise their own food.
2. Heterotrophs are those which are dependent on other plants and animals for their food.

They are of following types:

1. Parasites, e.g. Cuscuta.
2. Saprotrophs, e.g. fungi.

• Take some twigs of an aquatic plant like Hydrilla in beaker filled with water.
• Invert a funnel over the twigs. Invert a test tube filled with water on the stem of the funnel.
• Keep this set-up in sunlight for sometime.
• Air bubbles (oxygen gas) will be seen coming out from the twigs. If this set-up is kept in the dark, no air bubbles will be seen.

This proves that light is necessary for photosynthesis

Column I	Column II
Chlorophyll	Leaf
Nitrogen	Rhizobium
Cuscuta	Parasite
Animals	Heterotrophs
Insects	Pitcher plant