Class 12 NIOS Biology Chapter 9 Solutions provide complete answers to terminal exercises for effective revision. This chapter highlights essential biology topics that form a strong base for higher studies. Each solution is explained step by step to improve clarity and exam preparation.
These solved exercises serve as a reliable guide for students aiming to score well in exams. By practicing them, learners gain confidence and improve their understanding of Class 12 NIOS Biology.
NIOS Biology Chapter 9 Solutions
1. Which element can be obtained from both mineral and non-mineral sources?
Nitrogen
2. Deficiency of which essential element causes yellowing of leaves in certain plants, and why?
Magnesium is said to be an essential element because it is essential for the formation of the chlorophyll molecule. Its deficiency causes yellowing of leaves.
3. Why is magnesium included among essential elements?
Magnesium is said to be an essential element because it is essential for the formation of the chlorophyll molecule. Its deficiency causes yellowing of leaves.
4. What are the criteria of essentiality of elements?
To determine which one is an essential element, the following criteria are used:
- (i) An essential element is necessary for normal growth and reproduction of the plant, and should be a part of the essential metabolites for plant growth.
- (ii) The requirement of the element is very specific, and it cannot be replaced by another element.
- (iii) The element is directly or indirectly involved in the metabolism of a plant.
- (iv) In the deficiency of an essential element, the plant would exhibit specific symptoms of deficiency, and the plant would recover from its symptoms if supplied with the deficient element.
5. Differentiate between micro and macro nutrients.
- Micronutrients: Required in minute quantities, like 0.1 mg per gram of dry matter or less than that. Also called dry matter as trace elements. E.g.. Manganese, Boron, Copper, Cobalt, Molybdenum, etc.
- Macronutrients are required in relatively large quantities, like one to 10 milligrams per gram of dry matter. Carbon, Oxygen, Hydrogen, Phosphorus, Potassium, etc.
6. Why do biologists grow plants using by hydroponics technique?
Hydroponics is the technique of growing plants in a nutrient solution in the complete absence of soil. It helps scientists determine the essentiality of minerals. Here, seedlings are made to grow in water containing the known nutrients in a particular proportion. Vigorous bubbling of the air is routinely done to provide sufficient oxygen to the root system. The culture solutions may contain all essential nutrients except the one whose importance is to be identified. Then the plant growing in it is compared to the one growing with all essential nutrients (control experiment).
7. Explain the uptake of mineral nutrients by the plants.
Plants absorb a large number of minerals from the soil. The uptake of mineral ions by the roots may be passive or active.
- (a) Passive Absorption: It is the initial and rapid phase wherein ions are absorbed into the “outer space of the cells, through the apoplast pathway. It does not require the use of any metabolic energy.
- (b) Active Absorption: It is the second phase of ion uptake. The ions are taken in slowly into the ‘inner space’, the symplast of cells. It needs the expenditure of metabolic energy.
The movement of ions is called flux. When the ions move into the cells, it is called influx, and the outward movement of ions is called efflux.
The mineral ions absorbed by the root system are translocated through the xylem vessels to other parts of the plant.
8. Give the deficiency symptoms of nitrogen, phosphorus, and potassium.
- Deficiency of Nitrogen causes chlorosis, the loss of chlorophyll, leading to the yellowing of leaves. It may also cause a delay in flowering.
- Deficiency of Phosphorus causes stunted growth and premature fall of leaves.
- Deficiency of Potassium causes cell division inhibition, stunted growth, and premature fall of leaves.
9. Differentiate between the different modes of heterotrophic nutrition in plants.
Non-green organisms that do not synthesise their food and depend on other organisms and sources for their energy needs are called heterotrophs, and such nutrition is called heterotrophic nutrition. Heterotrophic organisms are classified into saprophytes and parasites.
- Saprophytes are those plants that grow and live on dead organic matter, including animal and plant remains. Most of these plants secrete some extracellular enzymes (enzymes secreted and poured out on food), which break down the complex organic compounds into simple forms. The simple forms are then absorbed by the plants. Saprophytes include mainly fungi and bacteria; the Indian pipe plant, Monotropa, found in the Khasi hills of our country, is a saprophyte.
- Parasitic Plants: Dodder (Cuscuta), known locally as Amarbel/Akashbel, is a parasitic plant that lacks both chlorophyll and leaves. It is a yellow-colored climber that attaches itself to the host. It gives out haustoria, or the suckers that get attached to the phloem of the host and derive nutrition. Cuscuta does not have roots in the mature condition. It produces bunches of whitish or yellowish bell-shaped flowers.
10. Write notes on:
- (i) Aeroponics
- (ii) Insectivorous plants
- (iii) Active absorption of minerals by plants
- Aeroponics: Aeroponics is a technique of growing plants with their roots supplied with moisture present in the air. Rooted plants are placed in a special type of box. The shoots of the rooted plants are exposed to air, and the roots are inside the box, having a computer-controlled humid atmosphere. The roots are sprayed/misted for short durations with a hydro-atomized pure water/nutrient solution.
- Insectivorous plants are autotrophic plants but develop adaptations to trap insects to supplement the deficiency of Nitrogen in the soil.
Active absorption of minerals by plants: It is the second phase of ion uptake. The ions are taken in slowly into the ‘inner space’, the symplast of cells. It needs the expenditure of metabolic energy.
