Class 7 Science

Plant Nutrition: Nitrogen Fixation

Synthesis of other nutrients

Plants need proteins and fats besides carbohydrate. Proteins are nitrogenous substances which contain nitrogen. Although nitrogen is present in abundance in atmosphere, but plant cannot absorb atmospheric nitrogen. Plant gets nitrogen from soil. Certain types of bacteria called rhizobium, are present in soil. They convert gaseous nitrogen into usable form and release it into the soil. Plants absorb these soluble forms of nitrogen along with water and other minerals through roots.

Sometimes farmers add nitrogenous fertilizer to their field to fulfill the need of nitrogen. In this way plants gets fulfillment of nitrogen along with other nutrients. After the fulfillment of all nutrients plants synthesize proteins and fats.

Review Questions

Question 1: What are the nutrients other than carbohydrates which are required by plants?

Answer: Proteins and fats are the nutrients, other than carbohydrates, which are required by plants.

Question 2: In which form do plants absorb nitrogen?

Answer: Plants absorb soluble form of nitrogen.

Question 3: Why do farmers add nitrogenous fertilizers to the soil?

Answer: Farmers add nitrogenous fertilizers to the soil to fulfill the requirement of nitrogen for plants. Nitrogen is necessary to synthesize proteins.

Question 4: Which microorganism helps to provide nitrogen to the plants?

Answer: A certain type of bacteria called rhizobium helps to provide nitrogen to the plants.

Question 5: How do plants absorb nutrients other than carbohydrates from the soil?

Answer: Other nutrients are available in the soil in the form of minerals. Plants absorb these minerals from soil, along with water.

Modes of Nutrition in non-green plants

Heterotrophic Mode of Nutrition in Plants

Some plants do not have chlorophyll. Hence, they cannot synthesize their food by themselves. Such plants are known as non green plants. They depend on other organisms for food. Such plants use the heterotrophic mode of nutrition. Some of them are called parasite. A parasite is an organism which lives on or inside the body of another organism and takes shelter and food from that organism. The host, in this case, is always at loss.

Plants that do not have chlorophyll are called non-green plants. Plants, which live on other plants for food, are called parasitic plants.

Parasite (Parasitic Plant): Plants that get their food from other plants by living on them are called parasite. Example; Cuscuta, mistletoe.

Cuscuta is a vine-like plant with yellowish stem. It twines around big trees, like banyan tree. Cuscuta gets nutrition from the tree on which it lives. The tree upon which it climbs and lives is called the host. Here, banyan is the host and cuscuta is the parasite.

Some plants are total parasite while some are partial parasite.

A total parasite fully depends on other plants for their nutrition. For example - cuscuta.

Partial parasite: Partial parasite is a parasite that receives a part of its nutrients from host. For example, mistletoe bears green leaves. It synthesizes its own food, but receives water and mineral from the host plant.

Review Questions

Question 1: What do you understand by parasitic plants?

Answer: A plant which lives on another plant and takes nutrients is called a parasitic plant.

Question 2: Give some examples of parasitic plants.

Answer: Cuscuta and mistletoe

Question 3: Why some plants are called parasites?

Answer: Some plants are unable to prepare their own food and need to take food from another plant. Hence, they are called parasites.

Question 4: What is the mode of nutrition in non-green plants?

Answer: Non-green plants show heterotrophic mode of nutrition.

Question 5: What do you understand by non-green plants?

Answer: A plant which lacks chlorophyll is called non-green plant.

Question 6: What do you understand by host?

Answer: An organism which provides shelter and nutrition to another organism is called a host.

Question 7: What is partial parasite?

Answer: A parasite which depends for some of the nutrients; on another organism; is called a partial parasite.

Question 8: Give example of partial parasitic plants?

Answer: Mistletoe