Movement Due to Growth in Plants: Hormones & Types

Ans. Phytohormones are the chemical messengers present in plants and are responsible for coordinating growth and movement in plants. They are crucial for plants to perform necessary functions. The main types of plant hormones are:

• Auxin - It is a growth-promoter hormone. It is involved in cell differentiation, cell enlargement and fruit growth.
• Gibberellins - It works in auxin presence. It is involved in processes like seed germination, flower development, root and shoot elongation etc.
• Cytokinins - It promotes cytokinesis in plants. It is also responsible for opening the stomata.
• Abscisic Acid - It is a growth-inhibitor hormone. It promotes wilting and falling of leaves, detachment of fruits and flowers from the plant, closing of stomata etc. 

Ans. When the tip of the tendril comes in contact with an object, the auxin in its tip diffuses to the side away from the support. It promotes cell growth in that region. This side grows faster than the other and becomes longer. Due to this, the tendrils coil around the object and use it as a support. 

Ans. There are three different pathways for the movement of water through the roots:

1. Apoplast Pathway - In the apoplastic route, water moves through the spaces present between the cells and in the cell walls themselves.
2. Symplast Pathway - In the symplastic route, water passes from the cytoplasm of one cell to the cytoplasm of another cell through connections called Plasmodesmata.
3. Transmembrane Pathway - In this pathway, water passes through the plasma membrane of each cell. Water in this route moves through both symplastic and apoplastic pathways.

Ans. Transportation in plants is the process of the transfer of nutrients and water from roots to the entire plant. Water and minerals are transported in plants with the help of two types of tissues:

1. Xylem - It is a long, non-living tube extending from roots to leaves through the stem. The water absorbed by the root hairs transfer from cell to cell and reach the xylem. Through xylem vessels, water is transported to the leaves.
2. Phloem - Phloem contains living cells. It is responsible for the transport of nutrients and sugars produced by the leaves to other areas of the plant. 

There are three ways by which transportation occurs:

• Diffusion - In this process, the substances move from regions of higher concentration to that of lower concentration, without the use of energy. This is a passive process. In plants, transport of gases takes place through diffusion only. 
• Facilitated Diffusion - Facilitated diffusion is also a passive process but it involves protein channels through which molecules pass. These channels are: Uniport, Symport and Antiport. Uniport facilitates the transport of a single solute from one side to another. Symport transports two molecules in the same direction whereas antiport transports two molecules in opposite directions.
• Active Transport - Active transport is the process of transfer of molecules against their concentration gradient by the use of energy. The energy is utilised in the form of ATP and substances are transferred from the region of lower concentration to higher concentration. 

Ans. The movement of plant parts towards the light is called positive phototropism. In this case, the stimulus is light. 

Positive phototropism is shown by plants in the presence of light. Auxin present in the shoot tips diffuses to the side away from light. As auxin promotes cell growth, the side in the shady portion grows longer than the side in front of light. Due to the cell growth, this side bends towards the light. Since the response (movement) is in the direction of stimulus, it is called positive phototropism. 

Ans. The main factors affecting the growth of plants are-

• Light - Plants are autotrophic in nature. They produce food on their own by the process of Photosynthesis. This process requires light in an appropriate amount. Without light, photosynthesis cannot occur. Also, other processes like opening and closing of stomata and chlorophyll synthesis also require light.
• Water - Water is important for the survival of plants. Water is absorbed by the roots of the plant and transported to other parts through xylem vessels. The extra water is lost from the plants by the process of transpiration. Water helps in keeping plants hydrated. 
• Temperature - Plants require an optimal temperature for the process like photosynthesis, transpiration to occur. Temperature lower than the threshold value will slow down the growth of plants. 
• Nutrients - Like animals, plants also require nutrients for their growth and development. Nitrogen, potassium, calcium, sulphur, magnesium etc. are the macronutrients required by plants in large amounts. And nutrients like iron, copper are required by plants in small amounts. Deficiency of these essential nutrients can make plants vulnerable to different diseases and result in stunted growth.

Ans.  Transpiration is the process by which a plant loses water in the form of water vapours through small openings in different parts. This maintains the level of water in the body of the plant. This process also helps in keeping plants cool in hot weather conditions. 

Depending upon the part through which plant loses water, transpiration is of three types:

1. Stomatal Transpiration - When water is lost through stomatal openings, it is called Stomatal Transpiration. A large amount of water is lost by the plants through this route.
2. Lenticular Transpiration - In this type, water is lost through openings called Lenticels present in the bark and twigs of plants. 
3. Cuticular Transpiration - In cuticular transpiration, water is lost by plants through cuticles. Cuticle is a wax-like covering on the surface of leaves. When the stomata are closed, transpiration occurs mainly through cuticles.

Ans. The nutrients essential for growth of plants are mentioned below:

1. Nitrogen - Plants convert nitrogen in the form of nitrate and use it for various processes. Nitrogen is also required during chlorophyll production.
2. Phosphorus - Phosphorus helps in the growth of roots and flowers in plants. It also helps plants cope up with harsh environmental conditions.
3. Sulphur - Sulphur is involved in the production of amino acids, enzymes, seeds etc. It also makes plants disease-resistant.
4. Calcium - Calcium is required in processes through which plants uptake nitrogen. It is also necessary for the development of cell-walls in plants. 
5. Potassium - Potassium is required by plants for growth and strength. It also prevents loss of extra water from plants. 

Ans. The occurrence of two kinds of spores in the same plant is called heterospory. Among them, the smaller spore is called microspore and the larger spore is called megaspore. Heterospory first evolved in pteridophytes. 

Significance of Heterospory

• Heterospory is associated with the sexual differentiation of gametophytes. A microspore develops into a male gametophyte whereas a megaspore develops into a female gametophyte.
• In homosporous pteridophytes spores have to germinate on soil thus face more environmental problems. In heterosporous pteridophytes, spores germinate within the sporangium and the gametophytes are retained inside for variable periods of time. Hence, germinating gametophyte has better chances of survival. This lays the foundation of complete retention of gametophytes within sporophytes in angiosperms and gymnosperms.
• Heterospory is the basis of development of seed habit in higher plants.