This set of Biology Written Test Questions for Medical Entrance Exams focuses on “Mechanism of Absorption of Nutrients – 2”.
1. Where do plants obtain most of their carbon and oxygen?
a) From nitrates in the soil
b) From ammonia in the soil
c) From nitrogen in the atmosphere
d) From carbon dioxide in the atmosphere
Explanation: Plants obtain most of their carbon and most of their oxygen from CO2 in the atmosphere. However, their remaining nutritional requirements are obtained from water and minerals in the soil.
2. Why can’t all minerals be passively absorbed through the roots?
a) They are present in the soil as charged particles
b) The concentration of minerals in the soil is very high
c) Minerals can never be transported
d) Roots only absorb water
Explanation: Unlike water, all minerals cannot be passively absorbed by the roots because the minerals are present in the soil as charged particles which cannot move across the cell membranes. Also, the concentration of the minerals in the soil is usually lower than the concentration of minerals in the roots.
3. How do most minerals enter the root?
a) Through guttation
b) Through transpiration
c) Through Active absorption
d) Through passive absorption
Explanation: Most minerals enter the root by active absorption into the cytoplasm of epidermal cells. This needs energy in the form of ATP. Some ions also move into the epidermal cells passively.
4. What are transport proteins?
a) They are restriction points
b) They are control points
c) They are not present in plants
d) These proteins are present in animals and absent in plants
Explanation: Transport proteins of endodermal cells are control points, where the plant adjusts the quantity and types of solutes that reach the xylem.
5. The root endodermis because of the layer of the cuticle can actively transport ions in all the directions.
Explanation: The root endodermis because of the layer of suberin can actively transport ions in one direction only. Like all the cells, the endodermal cells have many transport proteins embedded in their plasma membrane.
6. After active or passive absorption of all the mineral elements, how are minerals further transported?
a) Transported through guttation
b) Not transported at all
c) Through the transpiration stream
d) Through remobilisation
Explanation: After the active or passive absorption of all the mineral elements, minerals are further transported through the transpiration stream. Transpiration pull is the main mineral transporting force across the entire parts of the plants.
7. Which of the following is not a chief sink for the mineral elements?
a) Young leaves
b) Developing flower
c) Old leaves
d) Developing seeds
Explanation: The chief sinks for the mineral elements are the growing regions of the plant such as apical and lateral meristems, young leaves, developing flowers, fruits and seeds, and the storage organs.
8. Where does the unloading of mineral ions occur in the plants?
a) At the root endings
b) At the stem endings
c) At the root hair cells
d) At the fine vein endings
Explanation: Unloading of mineral ions which are required by the plants for growth and development occur at the fine vein endings through diffusion and active uptake by the plant cells.
9. Generally, from which of the following parts of the plants, the minerals are remobilised?
a) Senescent parts
b) Growing parts of the plant
c) Younger leaves
d) Dead tissues
Explanation: Generally, from the senescent parts of the plants mineral elements are remobilised because as those parts of the plants are going to die, there is no use of those mineral elements as no developmental processes are going to be carried out there.
10. Which of the following element is not remobilised?
Explanation: Elements most readily mobilised are phosphorous, sulphur, nitrogen and potassium. Some elements that are structural components like calcium are not remobilised.
11. How do most of the nitrogen travels in the plants?
a) As ammonia
b) As nitrates
c) As inorganic ions
d) As nitrogen gas
Explanation: Nitrogen generally travels in the plants in the form of inorganic ions, though only some proportion of nitrogen is travelled in this form. Most of the nitrogen is being transported as organic compounds like the amino acids.
12. A small amount of exchange of materials does take place between xylem and phloem.
Explanation: It is true that a small amount of exchange of materials does take place between xylem and phloem because these tissues are not completely isolated from each other. Therefore, it is possible for xylem to carry organic materials while the phloem to carry inorganic nutrients.
13. Which of the following carbohydrates acts as food for the plants?
Explanation: Food, primarily sucrose, is transported by the vascular tissue phloem from a source to a sink. Food in phloem sap can be transported in any required direction.
14. What is understood by the term sink in the plants?
a) The part that needs the food
b) The part that synthesises the food
c) The part that is going to die
d) The part that is going to fall
Explanation: Usually the source is understood to be that part of the plant which synthesises the food, i.e., the leaf, and sink, the part that needs or stores the food. But, the source and the sink may be reversed depending on the season or on the plant’s needs.
15. What is the direction of food in the phloem?
Explanation: The direction of food in phloem is bi-directional as the leaves which synthesise food need to transport the organic materials or the food to the shoot as well to the root apex which lie in the opposite directions.
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