Biology Notes Fa Fsc Chapter No 10 Form and Function in plants

Form and Function in plants Biology Notes Fa Fsc Chapter No 10 pdf downalod 2021

Biology Notes for class 11 Short Questions Form and Function in plants

Q.2 i) Why insectivorous plants depend on insects?


  Insectivorous plants are not strictly insectivorous, as they consume any animal small sufficiently o be trapped by them; there are larger varieties of pitcher plants that have been declared o consume small rodents and lizards. Further, other types of plant insectivores trap insects on their tacky eaves, let them die and rot naturally, and get benefit from them when the nutrients released are washed into the soil. These plants mainly depend on insects because;

 Insects are an easy source of nitrogen as most insectivorous plants are found in bogs. The soil in these bogs is very wet, high in peat and low on nutrients. To survive in such poor soil, carnivorous plants had to evolve to develop a way to get nutrients, including nitrogen.

Q.2 ii) What do you mean by water potential.


Water potential:

   “Water potential is the possible energy of water in a system likened to pure water when both temperature and pressure are kept the same.”

   Molecules of water possess kinetic energy. Therefore they are in constant motion from one place to another. Water potential is directly proportional to the concentration of water molecules. Greater the concentration of water molecules in a system, greater is the kinetic energy of water molecules. This is called water potential. It is represented by symbol Ψ. Pure water has a maximum water potential.

Q.2 iii) Differentiate between mesophytes and xerophytes.


Mesophytes are the ordinary land plants, which grow under the average condition of moisture.   Xerophytes are desert plants which grow in dry, hot and sandy places with scanty rainfall. 
In a limited supply of water, they close the stomata to prevent loss of water. The stomata are usually very much reduced in number and sunken below the epidermis. 
They have normal roots to absorb water.They have long roots to absorb water. 
Example:  Citrus, brassica, pea, peach, and rose etcExample:     Cactus,  Aloe,  and Zizyphus etc.

Q.2 iv) How turgor provides support to the herbaceous plants.


  Herbaceous plants take in water by endosmosis and become extended, these extended parenchymas are turgid, exert an internal pressure called turgor pressure. Due to this turgor force, these parts remain strong and rigid. If these cells lose water, they also failturgidity, which causes wilting in herbaceous stem and leaves. Therefore, these turgid parenchymas are important for the support and shape of the soft plant.

Q.2 v) Differentiate between primary and secondary growth in plants.


Primary growthSecondary growth
Primary growth takes place by the activities of primary meristematic tissues such as an apical cell, apical meristems, etc.Secondary growth takes place by the activities of secondary meristematic tissues and sometimes by the joint activity of both primary and secondary meristematic tissues.
It results in growth in the length of the plantSecondary growth results in an increase in the diameter of the stem
It occurs in all parts of the plant and all plantsIt occurs in gymnosperms and angiosperms (except monocots).
It is for a short period and stops after complete tissue differentiation occurs in a part of the plant.It continues only in the matured part and occurs after the part of the organ has completely developed

Q.2 vi) Briefly describe the mechanism of formation of annual rings in plants.


Annual rings:

   “The plants of temperate regions accumulate secondary xylem in the form of concentric rings or layers in every year called annual rings.”


  “The annual rings are the growth layers of wood that are produced each year in the stems and roots of trees and shrubs due to secondary growth.”

Mechanism of formation of annual rings in plants:

  The growth occurs in the cambium. In spring, the cambium begins dividing. This creates new tissue and increases the diameter of the tree in two places:

i. Outside the cambium:

     The outer cells become part of the phloem. The phloem carries food produced in the leaves to the branches, trunk, and roots. Some of the phloems die each year and become part of the outer bark.

2. Inside the cambium:

    The inner cells become part of the xylem. These cells contribute most of a tree’s growth in diameter. The xylem carries water and nutrients from the roots to the leaves. These cells show the most annual variation:

  • When a tree grows quickly, the xylem cells are large with thin walls. This earlywood or Springwood is the lighter-coloured part of a tree ring.
  • In late summer, growth slows; the walls of the xylem cells are thicker. This latewood or summerwood is the darker-coloured part of a tree ring. When conditions encourage growth, a tree adds extra tissue and produces a thick ring. In a discouraging year, growth is slowed and the tree produces a thin ring.

Q.2 vii) List the adaptation in plants to cope with low temperatures.


Adaptations of plants to cope with low temperature: 

   Temperature is one of the most important ecological factors. The variations in temperature range require the plants to adjust themselves to the environment and this is adaptation. Plants possess some morphological and anatomical structures to counter very high or very low temperature. Plants growing in low temperatures may suffer from ill-effects.

1- Well developed bark and short life cycles:

        To manage low temperature, they possess well-developed bark for protection and short life cycles.

2- Changes in solute composition:

       In freezing conditions, changes in the solute composition of cells by producing different polymers of fructose (fructans), which allow the cytosol to super cool without ice forming, though ice crystals may form in the cell-walls.

3- Slow rate of transpiration:

       The leaves and stems are hard and can withstand low temperature. Most of them possess scale leaves and the rate of transpiration is low to retard cooling.

Long Questions

Q.3 i) List the macro and micronutrients of plants. Briefly state the role of each.


Plant nutrition:

  Plants need a variety of nutrients to sustain their daily life processes. Depending upon the amount of each nutrient required.

Types of plant nutrition:

   The mineral nutrients are divided into two main groups.

  • 1. Macronutrients
  • 2. Micronutrients

 1. Macronutrients:

         Macronutrients can be broken into two more groups:

  • a. Primary nutrients
  • b. Secondary nutrients

a. Primary nutrients: 

       The primary nutrients are nitrogen (N), phosphorus (P) and potassium (K). These major nutrients are usually less in soil because plants use these in large amounts for their growth and survival.

i. Nitrogen:

    Nitrogen is necessary for the formation of amino acids, the building blocks of protein. It plays an important role in plant cell division and is vital for plant growth. It is directly involved in photosynthesis and is a necessary component of vitamins. It aids in the production and use of carbohydrates and affects energy reactions in the plant.

ii. Phosphorus:

       Phosphorus is involved in photosynthesis, respiration, energy storage and transfer, cell division, and enlargement and promotes early root formation and growth. It improves the quality of fruits, vegetables, and grains and is vital to seed formation. It helps plants survive harsh winter conditions and increases water-use efficiency.

iii. Potassium:

    Potassium is involved in carbohydrate metabolism and the breakdown and translocation of starches and increases photosynthesis. It also increases water-use efficiency and is essential to protein synthesis. It is important in fruit formation and activates enzymes and controls their reaction rates. Moreover, it improves the quality of seeds and fruit and increases disease resistance.

b. Secondary nutrients:

       The secondary nutrients are calcium (Ca), magnesium (Mg) and sulfur (S). These are usually present in reasonable amounts. Large amounts of calcium and magnesium are added when lime is applied to acidic soils.

i. Calcium:

       Calcium nutrient is utilized for continuous cell division and formation. It is involved in nitrogen metabolism and reduces plant respiration. It helps in translocation of photosynthetic materials from leaves to fruiting organs and also increases fruit set.

 ii. Magnesium:

       Magnesium is a key element of chlorophyll production and improves the utilization and mobility of phosphorus. It is an activator and component of many plant enzymes and increases iron utilization in plants.

iii. Sulfur:

        Sulfur is usually found in sufficient amounts from the slow decomposition of soil organic matter, an important reason for not throwing out grass clippings and leaves. This nutrient is an integral part of amino acids. It helps develop enzymes and vitamins and promotes nodule formation in legumes.

2. Micronutrients:

        Micronutrients are those elements essential for plant growth which are needed in only very small quantities. These elements are sometimes called minor elements or trace elements. The micronutrients include boron (B), copper (Cu), iron (Fe), chlorine (Cl) etc. Recycling of organic matter such as grass clippings and tree leaves is an excellent way of providing micronutrients to growing plants.

i. Boron:

       Boron is essential for germination of pollen grains, the growth of pollen tubes, and seed and cell wall formation. It promotes maturity and it is necessary for sugar translocation.

ii. Chlorine:

     This nutrient interferes with P uptake and enhances the maturity of small grains on some soils.

iii. Copper:

       Copper catalyzes several plant processes. Its major function is in photosynthesis and is helpful during reproductive stages of the plant.  It intensifies colour and improves the flavour of fruits and vegetables. Chlorine is an activator of certain enzymes in plants

iv. Iron:

      Iron Promotes the formation of chlorophyll synthesis and acts as an oxygen carrier. It is helpful in reactions involving cell division and growth.

v. Zinc:

      Zinc is an activator of certain enzymes.

vi. Manganese:

        It is an activator of certain enzymes.

vii. Cobalt:

         It is required by nitrogen-fixing organisms.

Q.3 ii) Explain the movement of water in xylem through TACT mechanism.


Water movement in Xylem through a TACT mechanism:

    Four important forces combine to transport soil solutions (water and mineral ions) from the roots, through the xylem elements, and into the leaves. These TACT forces are:

  • 1. Transpiration
  • 2. Adhesion
  • 3. Cohesion
  • 4. Tension

1. Transpiration:

      Transpiration involves the pulling of water up through the xylem of a plant utilizing the energy of evaporation and the tensile strength of water.

2. Adhesion:

        Adhesion is the attractive force between water molecules and other substances. Because both water and cellulose are polar molecules there is a strong attraction for water within the hollow capillaries of the xylem.

3. Cohesion:

       Cohesion is the attractive force between molecules of the same substance. Water has an unusually high cohesive force due to hydrogen bonding. It is estimated that water’s cohesive force within xylem gives it a tensile strength equivalent to that of a steel wire of similar diameter.

   A combination of adhesion, cohesion, and surface tension allows water-storage water to climb the walls of small diameter tubes like xylem. This is called capillary action. The U shaped surface formed by water as it climbs the walls of the tube is called a meniscus.

4. Tension:

      Tension can be thought of as stress placed on an object by a pulling force. This pulling force is created by the surface tension which develops in the leafs air spaces.

Tension is a negative pressure which creates a force that pulls water from locations where the water potential is greater. The bulk flow of water to the top of a plant is driven by solar energy since evaporation from leaves is responsible for a transpirational pull.

Q.3 iii) Explain the movement of sugars within plants.


  • Movement of sugars in plants:
  • Translocation of organic solutes:

   “The transport of organic solutes from the source of assimilates to the sinks of assimilates is called translocation of organic solutes.”

i. Sugar source:

    “Green leaves are the photosynthetic machinery of the plant. Green leaves are regarded as a source of assimilates because these are the sites of production of sugar during the process of photosynthesis.”

  This sugar is converted into sucrose which is transported out of the leaf to the stem and then upwards to the buds, fruits or seeds and downwards to the roots or the underground stems.

ii. Sugar sinks:

“Sugar sinks are plant organs such as roots, tubers (underground stems), and bulbs (swollen leaves) that consume or store sugars.”


 “The buds, seeds, fruits, roots and the underground stems are together called sinks of assimilates which utilize or store sugar.”

a. Pressure flow mechanism ( Mechanism of translocation of organic solutes):

      Food, primarily sucrose is transported by the vascular tissue called phloem from a source to a sink. Unlike transpiration’s one-way flow of water sap, food in phloem sap can be transported in any direction needed so long as there is a source of sugar and a sink able to use, store or remove the sugar. The source and sink may be reversed depending on the season, or the plant’s needs. Sugar stored in roots may be mobilized to become a source of food in the early spring when the buds of trees, the sink, need energy for growth and development of the photosynthetic apparatus.

   Phloem sap is mainly water and sucrose, but other sugars, hormones and amino acids are also transported. The movement of such substances in the plant is called translocation.

b. Pressure Flow or Mass Flow Hypothesis:

The accepted mechanism needed for the translocation of sugars from source to sink is called the pressure flow hypothesis. As glucose is made at the source it is converted to sucrose (a disaccharide). The sugar is then moved into companion cells and into the living phloem sieve tubes by active transport. This process of loading at the source produces a hypertonic condition in the phloem. Water in the adjacent xylem moves into the phloem by osmosis. As osmotic pressure builds the phloem sap will move to areas of lower pressure.

At the sink osmotic pressure must be reduced. Again active transport is necessary to move the sucrose out of the phloem sap and into the cells which will use the sugar converting it into energy, starch, or cellulose. As sugars are removed osmotic pressure decreases and water moves out of the phloem.

Steps in Pressure Flow or Mass Flow Hypothesis 1

Q.3 iv) Explain the osmotic adjustments of plants in saline soils.



    “A halophyte is a salt-tolerant plant that grows in waters of high salinity, coming into contact with saline water through its roots or by salt sprays, such as in saline semi-deserts, mangrove swamps, marshes and sloughs and seashores.”

Osmotic adjustment in halophytes in saline soil:

  Halophytes can grow in a soil containing a large percentage of common salt and therefore occur on seashores forming a special type of vegetation called mangrove. They are salt tolerators and not salt lovers. Although there is plenty of water in the soil, water absorption is fairly difficult due to an abundance of salts in the soil water. Hence they show physiological drought and show xerophytic characters. The stems contain well-developed water storage tissues.

  The leaves are covered with thick cuticles to prevent evaporation of water.


   Salsola (saltwort) and Rhizophora.

Q.3 v) Describe the structure of supporting tissues in plants.


Supporting Tissues in Plants:

   The development of stable supporting elements has been an important prerequisite for the evolution of large terrestrial organisms. The architectural design of the plant is very complex. Thin petioles carry heavy and flat laminas, stems support leaves, flowers and fruits. All plant organs are exposed to mechanical strains.

Types of supporting tissues in plants:

  • i. Parenchyma
  • ii. Collenchyma
  • iii. Sclerenchyma

i. Parenchyma:

   Parenchyma is relatively unspecialized vegetative cells and a kind of simple tissue found in the epidermis, cortex and pith. The whole body of lower plants (Bryophytes) is made up of these issues.

Characteristics of parenchyma tissues:

  • They usually have thin primary walls but no secondary walls.
  • They have a large central vacuole surrounded by a peripheral layer of cytoplasm. They are loosely packed with intercellular spaces in leaves and green herbaceous stem.
  • They contain chloroplasts, therefore, photosynthesis largely occurs in these cells.
  • They take in water by endosmosis and become extended and turgid and exert an internal pressure called turgor pressure
  • Due to this turgor pressure, these parts remain firm and rigid. If these cells lose water, they also lose turgidity, which causes wilting in herbaceous stem and leaves. Therefore, turgid parenchyma is important for the support and shape of the soft plant.

ii. Collenchyma:

    The collenchyma is the typical supporting tissue of the primary plant body and growing plant parts. The name collenchyma derives from the Greek word “kolla” meaning “glue”, which refers to the thick, glistening appearance of the walls in fresh tissues.

   Collenchyma cells have unequally thickened primary walls, especially when observed in cross-sectional view. The different thickness patterns of the wall are a characteristic feature formed during elongation. There are four primary types of collenchyma: angular, annular, lamellar (or plate), and lacunar.

 Characteristics of collenchyma tissue:

  • They are also living tissues, more elongated structurally similar to parenchyma except that their walls are irregularly thickened. The thickened area is usually more prominent at edges.
  • Collenchyma is characteristically found in leaves and elongating stems. In leaves, it appears as strands, often located above and below major veins, as well as in petioles and sometimes leaf blade margins.
  • In stems, it appears as a hollow cylinder around vascular tissues, or as peripheral longitudinal strands.

iii. Sclerenchyma:

        The other true supporting tissue is the sclerenchyma. It is their hard, thick walls that make sclerenchyma cells important strengthening and supporting elements in plant parts that have ceased elongation.

   The term “sclerenchyma” is derived from the Greek “sclerosis” meaning “hard”.

Types of sclerenchyma cells:

  Two groups of sclerenchyma cells exist:

  • 1- Fibres
  • 2- Sclereids

       Their walls consist of cellulose and/or lignin. Sclerenchyma cells are the principal supporting cells in plant parts that have ceased elongation.

1- Fibres:

      Sclerenchyma fibres are of great economic importance since they constitute the source material for many fabrics (flax, hemp, jute, ramie). The difference between fibres and sclereids is not always clear. Transitions do exist, sometimes even within the same plant.

   Fibres arise from meristematic tissues. Cambium and procambium are their main centres of production. They are often associated with the xylem of the vascular bundles. The fibres of the xylem are always lignified. Fibres that do not belong to the xylem are basted (outside the ring of cambium).

2- Sclereids:

       Sclereids are variable in shape. The cells can be isodiametric, prosenchyma, forked or branched. They can be grouped into bundles, can form complete tubes located at the periphery or can occur as single cells or small groups of cells within parenchyma tissues. But compared with most fibres sclereids are relatively short.

Characteristic examples:

  Stone cells (called stone cells because of their hardness) of pears (Pyrus communis) and those of the shoot of the wax plant (Hoya carnosa). The cell walls fill nearly all the cell’s volume. The shell of many seeds like those of nuts as well as the stones of drupes like cherries or plums are made up from sclereids

Q.3 vi) Explain the role of important plant growth hormones.


Plant growth hormones (Phytohormones):

    “Phytohormones are organic substances which are naturally produced in plants that control the growth or other physiological functions, at a site remote from its place of production and acting in extremely minute quantities.”

Types of phytohormones:

   There are five major growth hormones namely;

  • 1. Auxins
  • 2. Gibberellins
  • 3. Cytokinins
  • 4. Abscisic acid
  • 5. Ethylene

1. Auxins:

    Auxin is a Greek word, which means to increase. Naturally occurring auxin is a hormone that is produced in the apical meristems of shoots and the tips of coleoptiles. Indole acetic acid with other related compounds is collectively called auxin.

Functions of auxins:

    Auxins control and regulate many physiological processes.

  • Auxin travels by diffusion toward the base of the plant, where it controls the lengthening of the shoot and the coleoptile, chiefly by promoting cell elongation.
  • Studies indicate that its effect on cell elongation is achieved in some indirect way by a relaxation of the cellulose fibrils of the cell wall, permitting the cell to expand.
  • Auxin also plays a role in the differentiation of vascular tissue and initiates cell division in the vascular cambium.
  • It often inhibits growth in lateral buds, thus maintaining apical dominance.
  • The same quantity of auxin that promotes growth in the stem inhibits growth in the main root system.

2. Gibberellins:

      The gibberellins were first isolated from a parasitic fungus that causes abnormal growth in rice seedlings. They were subsequently found to be natural growth hormones present in many plants.

The function of Gibberellins:

  • The most dramatic effects of gibberellins are seen in dwarf plants, in which the application of gibberellins restores normal growth, and in plants with a rosette form of growth, in which gibberellins cause bolting.
  • Gibberellins cause seed germination in grasses.
  • In the barley seed, the embryo releases gibberellins that cause the aleurone layer of the endosperm to produce several enzymes, including alpha-amylase, which breaks down the starch stored in the endosperm, releasing sugar. The sugar nourishes the embryo and promotes the germination of the seed.
  • It can break the dormancy of the seed and cancels the effects of the inhibitory substances.
  • In apples and grapes, the exogenous application causes more fruit sets.
  • Gibberellins promote flowering, help in growing seedless grapes and improve the storage life of bananas etc.

3. Cytokinins:

      The cytokinins were first discovered as a consequence of their capacity to promote cell division and bud formation in cultures of plant tissues. They are chemically related to certain components of nucleic acids.

Functions of cytokinins:

  • Cytokinins can also act along with auxin to cause cell division in plant tissue culture.
  • In tobacco pith cultures, a high concentration of auxin promotes root formation, while a high concentration of cytokinins promotes bud formation.
  • In intact plants, cytokinins promote the growth of lateral buds, acting in opposition to the effects of auxin.
  • Cytokinins prevent senescence in leaves by stimulating protein synthesis.

3. Abscisic acid:

       “Abscisic acid is a plant hormone, which has important roles in seed development and maturation.”

Functions of Abscisic acid:

  • Abscisic acid causes bud dormancy and seed dormancy.
  • It inhibits the active growth of seedling flowering in long-day plants and promotes abscission.
  • During stress conditions (water deficiency or drought), the concentration of abscisic acid increases which causes stomata to close and facilitates an influx of water into the roots.
  • Therefore, abscisic acid is also called stress hormone that helps plants cope with adverse conditions.

4. Ethylene:

       “Ethylene is a gaseous hormone diffused through the plant in air spaces.”

Functions of ethylene:

  • It inhibits root growth and development of axillary buds when present in high concentration.
  • Ethylene also stimulates fruit ripening and induces several aspects of senescence in plant cells and organs.
  • The mechanics of leaf abscission involve decreasing auxin and increasing ethylene production.

Q.3 vii) Classify plants based on photoperiodism and give examples.



  “The relative length of the day and night to which the plant is exposed is called photoperiod and the response of the plant to photoperiod is the photoperiodism.”

   The relative lengths of the day and night to which the plants are exposed have remarkable effects on the behaviour of plants particularly on the development of flowers.”

Classification of plants based on photoperiodism:

   According to photoperiodism, plants are classified into three types which are;

  • 1. Short-day plants
  • 2. Long day plants
  • 3. Day-neutral plants

1. Short-day plants:

        Short day plants produce flowers in early spring when the day length is shorter than a critical value. For short-day plants, the critical value is maximum for flowering.

Examples of short-day plants:

  Tobacco, Dahlia, Soya bean and Chrysanthemum etc.

2. Long day plants:

     Long day plants produce flowers in summer when the day length is longer than a critical value. For long-day plants, the critical value is a minimum value for flowering.

Examples of long-day plants:

    Hibiscus, beet, spinach and potato etc.

3. Day-neutral plants:

     Day-neutral plants are independent of the day length and therefore not affected by the day length. They produce flowers whenever they become mature, irrespective of the day length.

Examples of day-neutral plants:

   Maize, tomato, sunflower, and cucumber etc.

Q.3 viii) Describe the mechanism of opening and closing of stomata.


Mechanism of opening and closing of stomata:

  Mechanism of opening and closing of stomata can be studied by the following most accepted theories.

1. Starch sugar theory:

      According to this hypothesis, photosynthesis occurs in light by absorbing carbon dioxide which lowers the H+ ion of cell sap and pH of guard cells is increased. High pH favours the activity of enzyme phosphorylase which converts starch into glucose and phosphate. It dissolves in the medium and increases the concentration of cell sap.

   This causes an increase in the osmotic pressure of guard cells and its diffusion pressure deficit (DPD) also increases which result in the movement of water into the guard cells from surrounding cells. Guard cells become turgid and swell. Thus the stomata open.

  During the dark, the level of carbon dioxide in the substomatal cavity is increased which results in the decrease in the pH of guard cells. At low pH, glucose is converted back to starch in the presence of enzyme phosphorylase. Synthesis of starch leads to the dilution of cell sap by consuming its dissolved glucose molecule. Thus, the osmotic pressure of cell sap is decreased and its DPD (diffusion pressure deficit) is decreased. The turgid cells lose water to surrounding cells and become flaccid and stomata close.

2. Theory of K+ ion transport:

       In the presence of light, starch is converted into phosphorylated hexoses and then to phosphoenol pyruvic acid which combines with carbon dioxide to produce malic acid. Malic acid dissociates into malate anion and H+ ion in the guard cell. H+ ions are transported to epidermal cells and K+ ions are taken into the guard cells in exchange of H+ ions. An increased concentration of K+ ions and malate ions in the vacuole of guard cells causes sufficient osmotic pressure to absorb water from surrounding cells. It results in the opening of stomata.

  In the dark, carbon dioxide concentration is increased in the substomatal cavity which prevents proton gradient across the protoplasmic membrane in guard cells. As a result, active transport of K+ ions into guard cells ceases. As soon as the pH of guard cells decreases the abscisic acid inhibits K+ ion uptake by changing the diffusion and permeability of guard cells. Malate ion in the guard cell cytoplasm combines with H+ ion to produce malic acid. These changes cause a reversal of the concentration movement. So the K+ ion is transported out of guard cells into the surrounding epidermal cells. The osmotic pressure of the guard cell is decreased which results in the movement of water from guard cells to surrounding cells and guard cells become flaccid and stomata close.

Biology Class 11 Notes for pdf


Definition: “The sum total of all the processes involved in taking and the utilization of elements through which growth, repairing, and maintenance of activities in organisms is accomplished is called nutrition.”

Question: What is Nutrient, write its types.


Definition: “Nutrient is a food or any substance that supplies elements to the body necessary for metabolism.”

Example: proteins, carbohydrates, lipids, minerals, vitamins.

Type of Nutrients

Mineral nutrients are two type


Definition: “The type of nutrient which is required in a large amount to a body is known as a macronutrient.”

Biology Notes fa fsc Chapter No 9 Diversity Among Animals


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