15- PLANT GROWTH AND DEVELOPMENT

CHAPTER NO.15 PLANT GROWTH AND DEVELOPMENT

A151

INTRODUCTION:Growth can be defined as an irreversible permanent increase in size of an organ or its parts or even of an individual cell.Growth is accompanied by metabolic processes (both anabolic and

catabolic), that occur at the expense of energy. e.g., expansion of a leaf is

growth.

Q. How would you describe the swelling of piece of wood when placed in water ?

Ans. Itis an example of imbibition not growth, it is an reversible increase.

Characterstics of plant growth

(1) Plant growth is generally indeterminate because plants retain the capacity for

unlimited growth throughout their life.

This ability of plants is due to the presence of meristems at certain locations in their body. The cells of such meristems have the capacity to divide and self-

perpetuate. The product, however, soon loses the capacity to divide and such cells

make up the plant body.

(2) Plant growth is localised.Reason : Plant growth is restricted to certain locations (apical meristems,intercalary meristems, lateral meristems) within plant body.

(3) Plant_ growth is open. In this form of growth new cells are always being added

to the plant body by the activity of the meristem.

(4) Plant growth is of two types :

(i) Primary growth : Root apical meristem and shoot apical meristem are responsible for the primary growth of the plants and principally contribute to the elongation of the plants along their axis.

(ii) Secondary growth : In dicotyledonous plants and gymnosperms the lateral

meristems (vascular cambium and cork cambium) are responsible for secondary

growth and contribute to the increase in the girth of the organs (root, stem).

Growth is measurable Growth at cellular level, is principally a consequence of increase in the amount of protoplasm. Since increase _in protoplasm is difficult to measure directly, one generally measures some quantity which is more or less proportional to it.Growth is measured by a variety of parameters, they are :

(i) Increase in fresh and dry weight.

(ii) Increase in length e.g., length of pollen tube.

(iii) Increase in surface area e.g., growth in surface area of a leaf.

(iv) Increase in cell number e.g., maize root apical meristem can give rise to more

than 17500 new cells per hour.

(v) Increase in cell size or volume. e.g., cells in a watermelon may increase in size

upto 3,50,000 times.

(vi) Increase in girth e.g., increase in diameters of dicot root and dicot stem.

Methods of growth measurement

(a) By direct observation (b) By auxanometer

Phases of growth

The period of growth is generally divided into three phases, namely :

(i) Meristematic phase

(ii)Elongation phase

(iii)Maturation phase

(i) Meristematic phase : The constantly dividing cells, both at the root apex and

the shoot apex, represent the meristematic phase of growth. The cells in this

region are characterised by :

(a) Cells are small in size with abundant plasmodesmal connections.

(b) Intercellular spaces are absent, if present then very small.

(d) Cells are rich in protoplasm, possess large conspicuous nuclei.

(ii) Elongation phase : The cells proximal to the meristematic zone represent the

phase of elongation. Cells in this region are characterised by :

(a} Increased vacuolation

(b) Cell enlargement

(c} New cell wall deposition

Figure showing detection of zones of elongation by parallel line technique. Zones A,B,C and D behind the apex have elongated the most.

(iii) Maturation phase : The cells more proximal to the phase of elongation

represent the phase of maturation. Cells of this zone, attain their maximal size in

terms of wall thickening and protoplasm modifications.

Growth rates The increased growth per unit time is termed as growth rate. Thus, rate of growth can be expressed mathematically. An organism, or a part of the organism can produce more cells in two ways :

1) Arithmetic growth | |n arithmetic growth cell undergoes mitotic cell division

and produce two daughter cells.Only one daughter cell continue to divide while the

other differentiates and matures. The simplest expression of arithmetic growth is examplified by a root elongating at a constant rate.

In geometric growth cell undergoes mitotic cell division and produce two daughter progeny. Both the progeny cells following mitotic cell division retain the ability to divide and continue to do so. Geometric growth has two phases - Lag and Log phase. When nutrients are limited the growth will be logistic

which show sigmoid growth curve.

Sigmoid growth curve is divided into following three stages :

(a)1 is initial stage, where growth is slow.

(b) MY At this stage growth is rapid at exponential rate.

Here ‘r’ is the relative growth rate and is also the measure of the ability of the

plant to produce new plant material, referred to as efficiency index. Hence, the

final size of w1 depends upon the initial size, w0.If we plot the parameter of growth against time, we get a typical siqmoid or s- curve. A sigmoid curve is a characteristic of living organism growing in a natural environment (limited resources). It is typical for all cells, tissues and organs of plant. It is also idealised for cells in culture.

Q. What kind of a curve can you expect in a tree showing seasonal activities ?

Ans. Sigmoid or S-curve,

LET US KNOW WHAT WE HAVE LEARNT

Q. 1) Which of the following statements are correct regarding growth?

(A) In plants, the form of growth is open and localised

(B) Swelling of piece of wood in water is considered as growth since it involve the

increase in size

(D) Growth, at a cellular level, is a result of increase

in the amount of protoplasm

(1) All the statements are correct

(2) A and B

(3) B, Cand D

(4) A, C and D

Q. 2) Meristematic phase of growth is characterised by :

(1) Increased vacuolation

(2) Maximal size in terms of protoplasmic modifications

(3) Cells those are rich in protoplasm and having thin cell walls with abundant plasmodesmata

(4) Cell enlargement

Q. 3) Which of the following is/are related to the type of growth in which both

the progeny cells, arise from mother cell, retain the ability to divide?

(A) Sigmoid curve

(B) expressed as W1 = WO +rt

(D) Three phases - Lag, exponential and stationary

(1) Aand D

(2) A, B and D

(3) Only C

(4) B and C

Q. 4) The type of growth, in which only one daughter cell among the two (produced by the division of meristem cell) retain the ability to divide, shows which of the following growth curves ?

(A) Linear curve

(B) Sigmoid curve

(D) Bell shape curve

Q. 5) Auxanometer is meant for measuring -

(A) Respiratory activity

(B) Photosynthetic activity

(D) Osmotic pressure

1. All cells of a plant are descendents of the zygote.

2. The leaves, flowers and fruits of the same tree not only have limited dimensions

but also appear and fall periodically and some time repeatedly.

3. Development of a mature plant from a zygote (Fertilized egg) follow a precise

and highly ordered succession of events.

4. Plants retain the capacity for unlimited growth throughout their life.

1. is regarded as one of the most fundamental and conspicuous

characteristics of a living being.

2. Growth at a cellular level is principally a consequence of increase in the amount of ;

1. Define Growth.

2. What is the difference between arithmetic and geometric growth rate?

1. What are different phases of growth and growth rates ?

1. True

2. True

3. True

4. True

1. Growth

2. Protoplasm

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The cells derived from root apical, shoot apical meristems and cambium

differentiate and mature to perform specific functions.During differentiation cells undergo few to major structural changes both in their cell

walls and protoplasms.

Example : To form a tracheary element, the cells would lose their protoplasm. They

also develop a very strong, elastic lignocellulosic secondary cell walls, to carry water to long distances under extreme tension.The living differentiated cells, that by now have lost the capacity to divide can regain the capacity of division under certain conditions. This phenomenon is termed as dedifferentiation.GE Formation of secondary meristems (interfascicular cambium and cork

cambium) from fully differentiated parenchyma cells.

Redifferentiation :Cells of secondary meristems are able to divide and produce cells that once again lose the capacity to divide and mature to perform specific functions. Such cells are called redifferentiated and phenomenon is termed as redifferentiation.

List of tissues in a woody dicotyledonous plant that are the products of

redifferentiation :

: Secondaly xviene -Seconcary philcan

> Cork of ohelient - Secondary colteay or phealloderrmn

Q. How would you describe a tumour ?

Ans. Tumour is a product of dedifferentiation.

Q. What would you call the parenchyma cells that are made to divide under controlled laboratory conditions during plant tissue culture ?

Ans. It is dedifferentiation and cells are dedifferentiated cells. Differentiation in

plants is open because cells/tissues arising out of the same meristem have

different structures at maturity. The final structure at maturity of a cell/tissue is also determined by the location of the cell within the plant body.GE «Cells postioned away from root apical meristems differentiate as root cap cells, while those pushed to the periphery mature as epidermis.

Development : It is a term that includes all changes that an organism goes

rough during its life cycle from germination of the seed to senescence.

Diagramatic representation of the sequence of processes which constitute the

development of a cell of a higher plant. It is also applicable to tissues/organs.

Plasticity : Plants follow different pathways in response to environment or

phases of life to form different kinds of structures. This ability is called

Example (i) : in cotton, coriander and larkspur.In such plants, the leaves of the juvenile plant, are different in shape from those in mature plant.

Example (ii) : in buttercup (Ranunculus).

In this plant leaves are different in shape produced in air from leaves those

produced in water. (Buttercup is an emergent hydrophyte).

Thus, growth, differentiation and development are very closely related events in the life of a plant. Broadly development is considered as the

Development in plants (i.e., both growth and differentiation) is under the

control of intrinsic and extrinsic factors.

PART A: MULTIPLE CHOICE QUESTIONS

Q.1 Which of the following is an example of plasticity in plants ?

(1) Continuous addition of new cells in plant body.

(2) Cells arising out of the same meritem have different structure at maturity.

(3) Difference in shape of leaves due to phases of life or environment.

(4) Determinate growth in the some plant organs.

Q. 2 Growth is primarily affected by two climatic factors which are ?

(1) Light and temperature

(2) Temperature and relative humidity

(3) Light and wind

(4) Rainfall and temperature

Q.3 In a growing plant, the first phase during the process of growth is -

(1) Cell division

(2) Cell enlargement

(3) Cell differentiation

(4) Cell maturation

Q.4 Which of the following is a characteristic feature of meristematic cells .

(1) Cells are rich in protoplasm

(2) Cell walls are primary in nature

(3) Presence of large conspicuous nuclei

(4) All of the above

Q.5 Plants follows different pathways in response to environment to form different

kinds of structures, that is called :-

(1) Plasticity

(2) Senescence

(3) Photoperiodism

(4) Vernalisation

PART B: TRUE/FALSE

1.All cells of a plant are descendents of the zygote.

2.Plants retain the capacity for unlimited growth throughout their life.

3.Nutrients are required by plants for the synthesis of protoplasm and act as

Source of energy.

PART C: FILLIN THE BLANKS

Given figure shows the sequence of the development process in a plant cell,

identify labelled parts A, B, C and D.

PART C: SHORT ANSWER TYPE QUESTIONS

Q.1 in which terms growth of a pollen tube is measured in?

Q.2 Which phase of growth is represented by root apex & shoot apex?

PART D: LONG ANSWER TYPE QUESTIONS

Q. What are the main differences in differentiation, dedifferentiation and

redifferentiation ? Explain the sequence of growth in a plant cell by ,making

a neat and clean diagram.

ANSWER KEY PART B

1. True

2. True

3. True

ANSWER KEY PART C

1. A= Plasmatic growth

2. B= Differentiation

3. C= Expansion

4. D= Maturation

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In this section, we will discuss about development and developmental

sequences through which a living organism undergoes during its life time.

Development

Development include all those changes in an organism which occur in a

sequence of qualitative changes, towards a higher or more complex state. It

includes all changes, an organism undergoes from birth till death. In development

plant shows a regular sequence of seed germination to growth, differentiation,

maturation, flowering and senesense. Development changes take place at cellular

level. Also, like appearance of chloroplast, when cell come in contact with light.

+Plant development is the process by which the structures originate and

mature as a plant grows. Plant produce new tissues and structures throught

their life from clusters of undifferentiated cells called meristems. Plants undergo different stages.These four stages include different life forms of plant which are as follow:

[Three phases of cell growth are:

The process of development is considered a sum total of growth and differentiation controlled by several intrinsic factors (including genetic and hormonal) and extrinsic factors (including light, temperature, water, oxygen,nutrients etc)

The plant may follow different pathways in response to environment or phases of

life. It leads to formation of various different structures.It occurs due to plasticity in plants like cotton, coriander, larkspur. Leaves of juvenile plants differ in shape from shapes of leaves produced in mature plants.

They are important because plants take in CO2 from the atmosphere and produce

OQ2 in addition plants make up the base of food web by producing their own food

using light, water, CO2 and other chemicals. That is why they are known as

producers or autotrophs.The abrupt change from juvenile to adult phase is called heteroplastic development.

LET US KNOW WHATWE LEARN

MULTIPLE CHOICE QUESTIONS:-

1.Plant produce new tissue only

a. Start of their life

b. Juvenile stage

c. Throughout their life

d. All the above

2.Development stages include

a. Seed germination

b. Maturation

c. Flowering

d. All of the above

3.Senescense is used for

a. Positive growth

b. Negative growth

c. No growth

d. None of the above

4.Development sequences in plant cell

a. Cell division

b. Differentiation

c. Maturation

d. All of the above

5.Plants are important only for

a. Carbon dioxide

b. Oxygen

c. Preparing food

d. All of the above

True/False:-

1. Development changes take place at cellular level.

2. Heterophylly occurs due to plasticity.

FILL IN THE BLANKS:-

1. Heterophylly due to plasticityis presentin

2. Developmentincludes_———_siin an organism during lifecycle.

1. What is development?

2. Write four stages of development.

Long questions:-

1. Explain plasticity and heterophylly.

ANSWER KEY

Mcq

1. Dall of the above

2. Dall of the above

3. B negative growth

4. Dall of the above

5. D all of the above

True/ false

1. True

2. True

Fill in the blanks

1. Buttercup

2. All changes

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INTRODUCTION:Plant Growth Regulators

Plants require light, water, oxygen, minerals and other nutrients for their growth and development. Apart from these external requirements, plants also depend on certain organic compounds to signal, regulate and control the growth of plants. These are collectively called

Plant Growth Regulators or Plant Growth Hormones.There are different types of Plant Growth Regulators, which are also referred to as phytohormones. Let’s learn about them in more detail below.Plant growth regulators are the chemical substances which govern all the factors of

development and growth within plants. Some other names used to refer to it are

phytohormones and plant growth hormones.

Phytohormones are organic compounds which are either synthesized in laboratories or

produced naturally within the plants. They profoundly control and modify the physiological processes like the growth, development, and movement of plants.

Based on their actions, plant growth regulators are broadly classified into two major groups:

1. Plant growth promoters

2. Plant growth inhibtors

Discovery of Plant Growth Regulators

Though it was serendipity, initial steps of the discovery of major plant growth regulators began with Charles Darwin and his son, Francis Darwin. They observed the growth of coleoptiles of canary grass towards the light source-phototropism. Followed by a series of experiments, they concluded the presence of a transmittable substance that influences the

growth of canary grass towards the light. That transmittable substance was what we know as auxin which was isolated later by F.W. Went.Effect of Auxin on Plant Growth

Later, many scientists discovered and isolated different plant growth regulators. Gibberellins or gibberellic acid was formerly found in uninfected rice seedlings and was reported by E.Kurosawa. F. Skoog and Miller discovered another growth-promoting substance named kinetin, which is now known as cytokinins.Plant Growth Promoters Auxins The first phytohormone to be discovered is the Auxin and it was discovered by the biologist Charles Darwin.

Auxins are one of the most important plant hormones. The chief naturally occurring auxin is indole-3 acetic acid — IAA and other related compounds.The term Auxin is derived from the Greek language meaning to grow.These plant growth regulators are generally produced at the points of stems and roots from where they are transported to other parts of the plants. These plant hormones include both natural and synthetic sources. Indole-3-acetic acid and indole butyric acid are obtained from natural plant sources, whereas naphthalene acetic acid and 2, 4-dichlorophenoxyacetic acid

are obtained from synthetic sources.

Functions of Auxins

1. Facilitate flowering in plants

2. Used in the process of plant propagation.

3. Used by gardeners to keep lawns free from weeds.

4. Involved in the initiation of roots in stem cuttings.

5. Prevention of dropping of leaves and fruits at early stages.

6. Regulate xylem differentiation and assists in cell division.

7. Auxins are widely used as herbicides to kill dicot weeds.

8. Used to produce fruit without preceding fertilization.

9. Promote natural detachment (abscission) of older leaves and fruits.

10.Apical dominance may occur in which the growth of lateral buds is inhibited by the

growth of apical buds. In such cases, the shoot caps may be removed.

11.These are produced by the apex of root and shoot.

Gibberellins:Gibberellins are an extensive chemical family based on the ent-gibberellane structure.The first gibberellin to be discovered was gibberellic acid. Now there are more than 100 types of gibberellins and are mainly gathered from a variety of organisms from fungi to higher plants.They are acidic and are denoted as follows — GA;, GA:, GA;etc.

Functions of Gibberellins

1. Delay senescence in fruits.

2. Involved in leaf expansion.

3. Break bud and seed dormancy.

4. Promote bolting in cabbages and beet.

5. Facilitate elongation of fruits such as apples and enhance their shape.

6. Used by the brewing industry to accelerate the malting process.

7. Used as the spraying agent to increase the yield of sugarcane by elongation of the

stem.

8. In young conifers, utilized to fasten the maturity period and facilitate early seed production

9. Helps in increasing the crop yield by increasing the height in plants such as sugarcane and increase the axis length in plants such as grape stalks.

10.Gibberellins are acidic in nature.

11.It also delays senescence.Cytokinins

These are produced in the regions where cell division occurs, mostly in the roots and shoots.They help in the production of new leaves, lateral shoot growth, chloroplasts in leaves etc.They help in overcoming apical dominance and delay ageing of leaves.

Functions of Cytokinins

1. Break bud and seed dormancy.

2. Promotes the growth of the lateral bud.

3. Promotes cell division and apical dominance.

4. They are used to keep flowers fresh for a longer time.

5. Used in tissue culture to induce cell division in mature tissues.

6. Facilitate adventitious shoot formation and lateral shoot growth.

7. Promotes nutrient mobilization that in turn assists delaying leaf senescence.

8. Helps in delaying the process of ageing (senescence) in fresh leaf crops like cabbage and lettuce.

9. Involved in the formation of new leaves and chloroplast organelles within the plant

cell.

10.Used to induce the development of shoot and roots along with auxin, depending on the ratio.Plant Growth Inhibitors

Abscisic acid It is a growth inhibitor, which was discovered in the 1960s. It was initially called dormant. Later, another compound abscisin-II was discovered and are commonly called as abscisic acid. This growth inhibitor is synthesized within the stem, leaves, fruits,and seeds of the plant. Mostly, abscisic acid serves as an antagonist to Gibberellic acid. It is

also known as the stress hormone as it helps by increasing the plant-tolerance to various types of stress.

Functions of Abscisic acid

1. Stimulates closing of stomata in the epidermis.

2. Helps in the maturation and development of seeds.

3. Inhibits plant metabolism and seed germination.

4. It is involved in regulating abscission and dormancy.

5. It is widely used as a spraying agent on trees to regulate dropping of fruits.

6. Induces seed-dormancy and aids in withstanding desiccation and various undesired growth factors.

Ethylene:Ethylene is a simple, gaseous plant growth regulator, synthesised by most of the plant organs includes ripening fruits and ageing tissues. It is an unsaturated hydrocarbon having

double covalent bonds between and adjacent to carbon atoms.Ethylene is used as both plant growth promoters and plant growth inhibitors. Ethylene is synthesized by the npening fruits and ageing tissues.

Functions of Ethylene Ethylene is the most widely used plant growth regulator as it helps in regulating many physiological processes.

1. Induce flowering in the mango tree.

2. Promotes sprouting of potato tubers.

3. Breaks the dormancy of seeds and buds.

4. Enhances respiration rate during ripening of fruits.

5. Applied to rubber trees to stimulate the flow of latex.

6. Facilitates senescence and abscission of both flowers and leaves.

7. Used to stimulate the ripening of fruits. For example, tomatoes and citrus fruits.

8. Affects horizontal growth of seedlings and swelling of the axis in dicot seedlings.Thus, we see how important are the plant hormones or the plant growth regulators in the growth and development of plants.

LET US KNOW WHAT WE HAVE LEARNT!

PART: A_VERY SHORT ANSWER TYPE QUESTIONS:

(A) MCQs:

1. Coconut milk contains a cytokinin called which promotes plant growth.

a) Naphthalene acetic acid

b) Indole-3-acetic acid

c) Gelatin

d) Zeatin

2. One of the following is not an auxin

a. Indole-3-acetic acid

b. Malic Hydrazide

c. Indole butyric acid

d. Naphthalene acetic acid

3. Seed dormancy is triggered by

a) Indole-3-ethanol

b) Abscisic acid

c) Carbon dioxide

d) None of the above

4. The substances which originates at the tip of stem and control the growth

elsewhere are

(a) vitamins

(b) auxins

(d) florigen

5. Dwarf plants can be made taller by

(a) gibberellins

(b) auxin

(d) vernalin

PART: B FILL IN THE BLANKS:

1. Apical dominance as expressed in dicotyledonous plants is due to the

presence of more in the apical bud than in the lateral ones.

2. In addition to auxin, a must be supplied to culture medium to

obtain a good callus in plant tissue culture.

3. Phenomenen of bolting is caused by plant harmone.

ANSWER KEY: PART—-A

Zeatin

Malic Hydrazide

Abscisic acid

Auxins

Gibberellins

1. Auxin

2. Cytokinin

3. Gibberellic Acid

PART: C SHORT ANSWER TYPE QUESTIONS:

Q.1. What are Plant growth regulators?

Q.2. What are the functions of cytokinins in plant growth?

PART: D LONG ANSWER TYPE QUESTION:

Q.1. What are Auxins? What are its types? Explain their role in plant growth.

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INTRODUCTION:Why do ail of them flower at the same time, that too every year in

the same month?

WHAT IS PHOTOPERIODISM?

Photoperiodism is the sum total of plant's physiological responses to the duration of light received i.e. day length.

It is different from phototropism.

Phototropism is the differential growth of plant in response to light stimuli. For example shoots bend towards the light while

roots bend away from it. Phototropism has no correlation with the duration of light.

In Photoperiodism flowering and other developmental processes are regulated in response to the photoperiods or

day length.

ROLE OF PHOTO PERIODISM:It has significant role in:-

-Most importantly in flowering

-it has significant role in bud dormancy

-control of vegetative _ trait

-tuberization in plants

-bulb formation

-Simultaneous leaf fall in deciduous tree

.dark carbon fixation in CAM plants

THE DISCOVERY THE Concept of Photoperiodism was given by W.W. Garner and HA. Allard of U.S Department of Agriculture, studied

flowering in Maryland mammoth variety of Tobacco plant in 1920.M.M. Variety was a single gene mutant tobacco that didn't

flower in the spring or summer, like wild type.Under controlled experiments, in light-tight boxes where they could manipulate the amount of light and dark, they discovered that flowering only occurred if the day length

(amount of light) was 14 hours or less.

They called the Maryland mammoth a short -day plant because it required a light period shorter than a critical length to flower.

CLASSIFICATION INTO SDP, LDP and DNP. Short-day plants flower when daylight is less than a critical length. They flower in the late summer, fall, or early winter.

-Long-day plants flower when daylight is increasing. They flower in the spring and early summer.-Day-neutral plants do not flower in response to day light

changes. They flower when they reach a particular stage of maturity or because of some other cue like temperature or

water, etc. this is the most common kind of flowering pattern.

WHAT IS THE PLANT ACTUALLY MEASURING?

In 1940 it was found that photoperiodism has nothing to day length-it is completely dependent on a critical night length.

These findings initially reported from experiments on cocklebur are as:-

1. The critical night length for the cocklebur is 8 hours: as long

as the cocklebur plant has at least 8 hours of continuous darkness, it will flower.

2. What was originally called a short-day plant is actually long-night plant.

3. If the night is punctuated by light for a few minutes, then it will not flower!

Long-day plants are actually short-night plants!

. Similarly, what were once thought to be long-day plants are actually short-night plants: they flower only when the night is

shorter than a critical length.A few minutes of light during the night will shorten the night length, therefore causing flowering to occur!

CRITICAL DAY LENGTH -CRITICAL day length is the photoperiod required to induce

flowering.It varies from species to species.-Example — Xanthium (SDP) requires a critical day length of 15.5 hrs. (15.5 light/8.5 dark). If the gets less than 8.5 hours of Dark. It fails to flower..Critical Photoperiod must not be exceeded in short day plants and should always be exceeded in long day plants.There is no relation with total day length.A Single Photoperiodic cycle which induce flowering-Inductive

Cycle and its effect is called PHOTOPERIODIC INDUCTION.

The above observations indicate presence of some pigment in the leaf which must be photoreversible.Several experiments indicate that light is absorbed by a photo

reversible pigment-Phytochrome.

This is a bluish bili protein and exists in two inter convertible form-Pr and Pfr.

Pr form of Phytochrome absorbs red light and converts into Pfr form.The Pfr form of Phytochrome absorbs far red light and

converts to Pr form under continuous darkness.

MECHANISM OF PHOTOPERIODISM:

This process involves following steps:

1. Perception: by leaves

2. Transmission: Stimulus from leaf to shoot apex

3. Evocation: Occurrence of flowering at apex There are two important aspects.

Phytochrome is a photo or light receptor because it receives light. It is a chemical or pigment that receives light.

Stimulus: Some scientists say that it is a florigen produced in Jeaves and transmitted to stem apex and cause flowering (It is hypothetical substance).

LET US KNOW WHAT WE HAVE LEARNT!

PART A: VERY SHORT ANSWER TYPE QUESTIONS:

A. MULTIPLE CHOICE QUESTIONS:

1. influences the process of flowering in plants.

(a) Photoperiod

(b) Water in the soil

(d) Amount of green pigment

2. A plant that require not less than 10 hours of light to flower

is called .

(a) Day-neutral plant

(b) Short day plant

(d) None of the above

3. When the dark period of short-day plants is interrupted by brief exposure of light, then the plant .

(a) Produces more flowers

(b) Will not bear any flowers

(d) Produces flowers immediately

4. In which of the following living species, phytochrome, the blue-green pigment is found?

(a) Algae

(b) Fungi

(d) Vascular cryptograms

5. Which is the site for perception of light/dark duration?

a) Leaves

b) Stem

c) Roots

d) Apical bud

B.TRUE/FALSE:

1. Plants are able to measure the duration of exposure to light.

2. Duration of light period is more important than the duration of

dark period.

3. The two forms of the phytochrome are photochemically inconvertible.

C.FILL IN THE BLANKS:

1. The hormone responsible for flowering is

2. Wheat is a....... day plant.

ANSWER KEY: PART-A

A. MULTIPLE CHOICE QUESTIONS:

1. (a)

2. (c)

3. (b)

4. (c)

5. (a)

B. TRUE/FALSE:

1. True

2. False

3. True

C. FILL IN THE BLANKS:

1. Florigen

2. Long day

PART B: SHORT ANSWER TYPE QUESTIONS:

Q1. What is photoperiodism? Give its historical background.

Q2. What is critical period? Explain.

Q3. What are phytochromes? Give their mechanism of action.

Q4. Would a defoliated plant respond to photoperiodic cycle? Why?

PART C: LONG ANSWER TYPE QUESTIONS:

Q1. Give classification of plants on the basis of photoperiodic responses.

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INTRODUCTION:VERNALIZATION: is meeting the cold temperature requirement of

some temperate plants artificially, so as to reduce the duration of their

vegetative phase nd initiate onset of reproductive phase or flowering.

SEED DORMANCY is the internal inhibition of otherwise viable seed even when it is placed in most favourable conditions. Non-germination of a viable seed due to non-availability of proper environmental conditions is called

VERNALIZATION:Many species especially many biennials and perennials are induced to flower by the exposure of low temperature. They grow vegetatively during the warm

season, receive the low temperature treatment during winter and grow further

to bear flowers and fruits in the following warm season which varies from species to species.A biennial plant grows only vegetatively during the first season and will not initiate flowering until it has been exposed to prolonged periods of

low temperature of the winter.Many biennials are photoperiodically sensitive and require sensitive and require long days in order to complete the flowering process, even after cold treatment has been given.

The biennial or winter types normally fail to produce flowers until they have over wintered in the field. By vernalisation, in such winter varities

flowering can be produced flowers until they are planted. The biennial or winter types normally fail to produce in the same year.The site of vernalization is believed to be shoot apical meristem.Vernalization effect is reversible and the reverse process is called devernalization.If vernalized seed or plant is kept at high temperature, the effect of vernalization is completely removed. As the stimiulus can be translocated via a graft union, it is

postulated that a hormone is esponsible for transmitting the vernalized stimulus

called i.

REQUIREMENTS OF VERNALIZATION:-Continous low temperature for a few days.Actively dividing cells.Proper nourishment.

Proper hydration Aerobic respiration.

1) It reduces the vegetative period of the plant.

2) It prepares the plant for flowering.

3) It induces the synthesis of gibberlins.

4) It can remove the kernel wrinkles in wheat.

5) It increases the resistance of plants against cold and diseases.Lysenco a Russian worker 1938 used the term Vernalization for a low temperature promotion of flowering in plants.

SEED DORMANCY It is the internal inhibition of otherwise viable seed even when it is placed in most favourable conditions. Non-germination of a viable seed due to non-availability of proper environmental conditions is called

CAUSES OF SEED DORMANCY:-impermeable and hard seed coat e.g. apple, chenopodium, Xanthium.

Inhibitors:- Ferulic acid present in tomato juice does not allow seeds to germinate. Other inhibitors include ABA, secondary plant products like phenolic inhibitors. They may occur in seed coat, embryo or endosperm.EE |) Evanthis hiemalis the embryo is immature at the time of seed shedding.

Excess salts:- They cause dormancy in seeds of Atriplex.HE. - The embryo is mature but the seed requires a period of dry

storage for gaining the ability to germinate e.g. oat, barley, wheat.

The seed dormancy can be overcome by both natural and man made methods:The seed coat barrier in some seeds can be broken by mechanical abrasions using knives, sandpaper etc.Vigorous shaking

Naturally these are caused by microbial action Passage through digestive tracts of animals.Effect of inhibitory chemicals can be removed by subjecting the seeds to

chilling conditions or by application of certain chemicals like gibberllic

acid and nitrates.Changing the environmental conditions, such as light and temperaturecan also help remove seed dormancy.

LET US KNOW WHAT WE HAVE LEARNT!

PART: A_VERY SHORT ANSWER TYPE QUESTIONS:

1. MCQs:

1. Process of Vernalization can be induced by:-

(a) cytokinin

(b) swim

(d) gibberellices acid

2. Seed dormancy allows plant to

(a) develop healthy seeds

(b) overcome unfavorable climatic conditions

(d) prevent deterioration of seed

3. Which hormones breaks the dormancy in potato tubers

(a) auxin

(b) gibberellins

(d) abscisic acid

4. Which of the following structure in the seed coat that prevent water and oxygen

entry into seed by their induced dormancy?

(a) strophiolar plug

(b) pericarp

(d) epicarp

5. Seed dormancy is due to:

(a) IAA

(b) starch

(d) abscissic acid

2. FILL IN THE BLANKS;-

1. Winter wheat requires temp. for subsequent flowering.

2. Vernalin is a substance.

3. pigment is involved in germination of photoplastic seeds.

4. Bienniel plants complete their life cycle in years.

5. plant exhibit dormancy due to immature embryo.

3. TRUE FALSE --

1. Vernaline Harmone is responsible for Vernalization.

2. Vernalization effect is reversible.

3. Dormancy helps the seeds to germinate during unfavorable conditions.

4. Pigment phytochrome is involved Vernalization.

5. Biennials grow vegetatively in second year and produce flower in 3 years.

1. MCQs:

1. (d); cytokinin

2. (b); overcome unfavourable conditions

3. (b); gibberllins

4. (a); strophiolar plug

5. (d); abscisic acid

2. FILL UPS:

1. 0-5°C

2. Hormonal

3. Phytochrome

4. Two

5. Orchids

3. TRUE /FALSE:

1. True

2. True

3. False

4. False

5. False

PART: B SHORT ANSWER TYPE QUESTIONS:

Q1. Define Vernalization?

Q2. What is the role of gibberellins in seed dormancy?

Q3. How can the effect of Vernalization be removed?

Q4. What are sites of Vernalization?

PART: C LONG ANSWER TYPE QUESTIONS:

1. How do farmers use the dormancy of seeds for its advantage?

A157

RECAPITULATION:Growth and Development

Growth is an irreversible permanent increase in size of an organ or it's

parts or even of an individual cell. It can be defined as the increasing of

plant volume or mass with or without formation of new structures as

organ tissue or cell organelle for e.g. expansion of a leaf is the growth.

Development includes all changes that an organism goes through during its life cycle from germination of the seed to senescence.

PHOTOPERIODISM Photoperiodism is the physiological reaction of plants to the length of night or a dark period. Some plants that are explorer to light for a period exceeding well defined critical duration. These plants are called I.

Some plants are exposed to light for a period less than the critical duration before the flowering is intimated in them. These plants are NE.The critical duration is different for different plants.

There are many plants which are not affected by light duration. Such plants are

called day a

Question/Answers:-

1. Define growth, differentiation, development, dedifferentiation,

redifferentition, determinate growth , meristem and growth rate.

Ans]. The permanent and irreversible change in any part of plant with respect to size, form, weight and volume is called growth.

BE development is defined as a process in which there is qualitative change towards a higher or more complex state.GE. the chemical or morphological change of meristem cell to become permanent cell is called differentiation.HE. the process by which permanent cells regain the ability to divide is called dedifferentiation.BE. the differentiation of the differentiated cell or tissue is called redifferentition.

plant growth in which the main stem ends in an inflorescence or other reproductive structure and stops continuing to elongate

indefinitely with only branches from the main stem having further and similarly

restricted growth.BE. |t is a region of plant tissue, found chiefly at the growing tips of roots and shoot and the cambium, consisting of actively dividing cells forming new tissue.GE the measurement and comparison of total growth per unit time is

called absolute growth rate .The growth of a given system per unit time expressed

on a common basis is called relative growth rate.

2. Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant?

Ans. The growth in plant is measured by a variety of parameters such as:

i. Increase in length or girth.

ii. Increase in fresh or dry weight.

iii. Increase in area or volume. Any individual measurement is sufficient.

a) When a seed is germinated and allowed to grow in dark then there is rapid elongation. At the same time the dry weight of the seedling decreases because it utilizes the reserved food stuff to grow. A dry weight measurement in such condition will be misleading. Growth measured by the total weight of plant can also be misleading as the water content of a plant frequently.

3. Describe briefly:

i. Arithematic growth

ii, Geometric growth

iii. Sigmoid growth curve

iv. Absolute and relative growth rate

Arithematic growth: - It is the growth in which meristematic cells divide and form

two daughter cells. One of these cells differentiates to form a permanent cell while the other remains meristematic and divides and redivides to form a number of

cells.

Geometric growth:- Such growth occurs in higher plants and their organs measured in size or weight.

Sigmoid growth curve:- If geometric growth is plotted against time, it shows a

sigmoid growth curve. It has following phases:-

a. eteReaeiss — In this phase growth is slow.

b. [epdotelatcialtrclmelatekis] — In this phase growth is very fast. Also called

as log phase.

C. SiceCNaeaesS — In this phase growth rate becomes slow and finally stops.

Absolute and relative growth rate:- The measurement and comparisons of total

growth per unit time is called absolute growth. The growth of a given system per

unit time expressed on a common basis is called relative growth rate.

4. List five main groups of natural plant growth regulators. Write a note on

discovery, physiological functions and agricultural/horticultural application

of any one of them.

Ans.glalmelgeyauandceleieiegs.- The organic substances which are synthesized in

minute quantity in one part of the plant and transported to other part, where they

influence specific physiological process are called plant growth regulators.

The five groups of natural plant growth regulators are as follows:-

AUXINS:The term auxins include all those chemical substances which promote growth of

stem or coleoptile sections and decapitated coleoptiles. But in the same

concentration these are in capable of causing growth on intact plant. The principal naturally occurring auxin is indole-3-acetic acid (IAA).Mcoueny- F.W. Went was the first person to name the substances of tip of plant as auxin. Koagl and Haagen Smith in 1931 isolated a substance from human urine,that is auxin-A and then in 1934 auxin-B from corn germ oil. Thimann in 1936 isolated IAA from Rhizopus suinus and then from Avena coleoptiles and otherplants.Physiological functions Cell enlargement — Auxins cause elongation of cells in shoot.Cell division — Auxins induces cell division activity in cambium.Differentiation — Auxins induce early differentiation of xylem and phloem in tissue culture experiments.Root initiation — In general, auxins initiate rooting but inhibit the growth of

roots.Apical dominance — Thiamann and Skoog reported that IAA is responsible

for apical dominance.

Agricultural importance:-

1. Fruit formation — Auxins enhance the size of carpel and hence early fruit

formation takes place.

2. Senescence — Auxins retard the process of senescence.

3. Abscission — Auxins retard the abscission of leaves, fruits and branches etc.

4. Parthenocarpy — Auxins induce parthenocarpic development of fruits an such fruits are seedless.

5. what do you understand by photoperiodism and vernalisation. Describe

their significance.

Ans - It is the physiological developmental response of plants to the length of night and dark period.Significance —Plants can be made to flower through artificial supply of light or darkness.It gives us Knowledge about which is useful in breeding programmes.Knowledge of photoperiodism is required for determining the crop pattern of an area. Many plants require cold treatment for their flowering,

pretreatment of germinating seeds with low treatment to induce flowering is called

as vernalisation.Significance —Itreduces the vegetative period of plant.

It prepares the plant for flowering.

It induces the synthesis of Gibberilins.

It can remove the kernel wrinkle in wheat.

6. Why abscissic acid is known as stress hormone?

Ans. Abscissic acid stimulates the closer of stomata in the epidermis and

increases the tolerance of plants to various kinds of stresses. Hence it is called Stress Hormone. ABA plays an important role in plants water stress and during drought condition. It has been observed that the concentration of ABA increases in the leaves of plants facing stresses.

7. ‘Both growth and differentiation in higher plant are open’. Comment.

Ans. Plant growth is a unique feature because of capacity of plant to grow through their life. This ability is due to presence of meristems at certain location which have the capacity to divide and self-perpetuate. This form of growth where new cell are always being added to plant body by the activity of meristem is called open form of growth.Differentiation in plant is also considered to be open due to the fact that cell or tissue arising out of the same meristem has different structures at maturity. The final structure at maturity is determined by the location of cell within.

8. Both a short day plant and a long day plant can flower simultaneously in a

given place. Explain.

Ans. A short it day plant can flower only after it receive light below a critical day

length while a long day plant can flower only after it receive lignt above a critical day length.Both plants (short day plants and long day plants) will be flowering naturally at the same place when these have day length of 12 hours.

9. Which one of the plant growth regulator would you use if you were asked

to:

i. Induce rooting in a twig — Auxin

ii. Quickly ripen a fruit — Ethylene

iii. Delay of senescence — Cytokinin

iv. Induce growth in axillary bud — Gibberellins

v. Bolt a rosett plant — Gibberellins

vi. Induce immediate stomatal closure in plant — Abscisic acid

10. Would a defoliated plant respond to photoperiodic cycle ? Why?

ANS. No, the defoliated plant does not respond to photoperiod. This is because

the site of perception of light / dark duration is the leaves. This has been

hypothesized that there is a hormonal substance which is responsible for flowering which migrate from leaves to shoot apices to induce flowering. This occurs only when the plants are exposing to necessary inductive photoperiod.

11. Which would be expected to happen if?

i. GA3 is applied to rice seedlings.

ii. Dividing cells stop differentiating.

iii. A rotten fruit gets mixed with unripe fruits.

iv. You forget to add cytokinin to the culture medium ?

Ans. 1. Elongation of hypocotyl takes place. This elongation is due to the cell

division and cell elongation.

2. If dividing cells stop the division then they gets differentiated into mature cells to perform specific function. This act of leading to maturation is termed as

differentiation.

3. Ripening of fruit takes place.

4. If we forget to add cytokinin to the culture medium then cell division will not take place. As a result of this, culturing will stop.

A158

RECAPITULATION GROWTH:An irreversible permanent increase in the size of an organ or its parts or even individual cell is called growth. It is accompanied by metabolic processes (both anabolic and catabolic).

CHARACTERSTICS OF PLANT GROWTH Plant growth is indeterminate because plants retrain the capacity for unlimited growth throughout their life.Plant growth is localised.

Plant growth is open.Plant growth is of two types — primary growth and secondary growth.

GROWTH IS MEASURABLE Growth is measured by variety of parameters.Increase in fresh and dry weight.Increase in length e.g. length of pollen tube.Increase in surface area e.g. growth in surface area of a leaf.

Increase in cell number e.g. in maize root.

Increase in cell size and volume e.g. In watermelon.

PHASES OF GROWTH Plant growth has three phases.

Meristematic phase: The constantly dividing cells both at root apex and shoot apex represent the meristematic phase of growth.

Elongation phase: The cells proximal to the meristematic zone represent the elongation phase of growth.

Maturation phase: The cells more proximal to the phase of elongation represent the maturation phase of growth.

GROWTH RATE The increased growth per unit time is termed as growth rate.It is either arithmetic or geometric.In arithmetic growth cell undergoes mitotic cell division and produce two daughter cells. Only one daughter cell continues to divide while other differentiates and mature.In geometric growth cell undergoes mitotic cell division and produce two daughter

cells. Both the daughter cells retain the capacity to divide and continue to do so.

CONDITIONS FOR GROWTH WATER Plant cells grow in size by cell enlargement which in turns requires water.

OXYGEN: Oxygen helps in releasing metabolic energy essential for growth activities.

NUTRIENTS: Macro and micro nutrients are required by plants for synthesis of protoplasm and act as source of energy.

TEMPERATURE: Every plant has an optimum temperature range best suited for its growth.

ENVIRONMENTAL SIGNALS :LIGHT: Light is stimulus for shoot growth.

GRAVITY: Gravity is stimulus for root growth.

DIFFERENTIATION The cells derived from root apical meristems, shoot apical meristems and cambium differentiate and mature to perform specific functions. The act leading to maturation is termed as differentiation.

e.g. To form treachery elements, the cells would lose their protoplasm.

DEDIFFERENTIATION The living differentiated cells which by now have lost the ability to divide can regain the capacity of division under certain conditions. The phenomenan is termed as dedifferentiation.e.g. formation of secondary meristems from fully differentiated parenchyma cells.

REDIFFERENTIATION Cells of secondary meristems are able to divide and produce cells that once again lose the capacity to divide and mature to perform specific functions. Such cells are called redifferentiated cells and phenomenon is called redifferentiation.e.g. secondary xylem and secondary phloem.

DEVELOPMENTAll changes that an organism goes through during its life cycle from

germination of seed to senescence are termed as development.

PLASTICITY Plants follow different pathways in response to environment or phases of life to form different kinds of structures. This is called plasticity.

PLANT GROWTH REGULATERS The plant growth regulators (PGRs) are small, simple molecules of diverse chemical composition.

The PGRs are of two types- growth promoters and growth inhibitors.

AUXINS Auxin is a plant growth promoter. Precursor of auxin is tryptophan. Zinc is also essential for the biosynthesis e.g. auxin.PHYSIOLOGICAL EFFECTS OF AUXIN

It promotes apical dominance.It promotes flowering.It promotes abscission of older mature leaves and fruits.It induces parthenocarpy in tomatoes.It controls xylem differentiation.It helps in cell division.

GIBBERELLINS Gibberellin is a plant growth promoter.

PHYSIOLOGICAL EFFECTS OF GIBBERELLINS

Gibberellins promote intermodal elongation just prior to flowering.Improve yield in sugarcane.Improve shape in apple.Improve yield in grapes.Early maturity in conifers.

Speed up the malting process in brewing industry.Breaking up of seed dormancy.

CYTOKININS Cytokinins are the plant growth promoters.

PHYSIOLOGICAL EFFECTS OF CYTOKININS

They promote cytokinesis.They overcome apical dormancy.They help in delaying of senescence.Help to produce new leaves.

Help to produce chloroplast in leaves.

Promote lateral shoot growth and adventitious shoot formation.

ETHYLENE Methionine is a precursor of ethylene. It is a plant growth promoter.

PHYSIOLOGICAL EFFECTS OF ETHYLENE

It enhances the fruit ripening.It promotes the senescence and abscission of plant organs especially of leaves and fruits.

It breaks seed and bud dormancy.It increases the absorption surface.It induces flowering.

ABSCISIC ACID It is a plant growth inhibitor. Carotenoid is the precursor of abscisic acid.PHYSIOLOGICAL EFFECTS OF ABSCISIC ACID It acts as general plant growth inhibitor.It inhibits seed germination.It stimulates closing of stomata.

PHOTOPERIODISM The response of plants to periods of day and night is termed as

photoperiodism.

SHORT DAY PLANTS : Plants require the exposure to light for a period less than critical duration are called short day plants.

LONG DAY PLANTS : Plants require the exposure to light for a period exceeding a well-defined critical duration is called long day plants.

DAY NEUTRAL PLANTS : Plants in which there is no such correlation between exposure to light duration and induction of

flowering response. Such plants are called day neutral plants.

VERNALISATION It refers to the promotion of flowering by a period of low temperature.

REQUIREMENTS FOR SUCCESS OF VERNALISATION

Actively dividing cells.Period of low temperature treatment.Aerobic respiration.

Optimum hydration.Optimum nutrition.

SIGNIFICANCE Vernalisation prevents precocious reproductive development late in the growing season and enables the plant to have enough time to reach maturity.SEED DORMANCY Failure of a viable seed to germinate even when given all the favourable environmental conditions is known as seed dormancy.

REASONS OF SEED DORMANCY Impermeable and hard seed coat.Immature embryo.Presence of chemical inhibitors like abscisic acid, phenolic acid etc.METHODS OF BREAKING OF SEED DORMANCY Action of sunlight.Action of heat.Passing seeds through digestive tracts of animals.Stratification.Scarification.

Soaking overnight in water.

LET US KNOW WHAT WE HAVE LEARNT!

PART: A VERY SHORT ANSWER TYPE QUESTIONS:

a) MCQs:

1. Formation of secondary meristems from fully differentiated parenchyma is

an example of:

(a) Differentiation

(b)Redifferentiation

(c)Dedifferentiation

(d)Maturation

2. Which plant hormone is responsible for fruit ripening?

(a)Auxin

(b)Gibberellins

(c)Cytokinins

(d)Ethylene

3. Which among the following is plant growth inhibitor?

(a)Abscisic acid

(b)Auxin

(c)Ethylene

(d)Gibberellins

4. Plants which requires the exposure to light for a period less than critical

duration are:

(a) Long day plants

(b) Short day plants

(d) None of the above

5. Failure of a viable seed to germinate even when given all the favourable

environmental conditions is known as:

(a) Seed dormancy

(b) Vernalisation

(d) None of the above

b) FILL UPs:

1. The constantly dividing cells at root apex and shoot apex

represent ............... phase of growth.

2. ........ iS Stimulus for shoot growth.

3. Gravity is stimulus for ...... growth.

c) TRUE/FALSE:

1. To form treachery elements, cells would lose their

protoplasm.

2. Gibberellins is a plant growth inhibitor.

3. Oxygen helps in releasing metabolic energy.

ANSWER KEY: PART-A

a)MCQs:

1. (c) Dedifferentiation

2. (d) Ethylene

3. (a) Abscisic acid

4. (b) Short day plants

5. (a) Seed dormancy

b) FILL IN THE BLANKS:

1. Meristematic

2. Light

3. Root

c) TRUE/ FALSE:

1. True

2. False

3. True

PART: B SHORT ANSWER TYPE QUESTIONS:

1. What are the different phases of growth?

2. Define growth rate. Explain its types.

3. Explain physiological effects of Cytokinins.

PART:C LONG ANSWER TYPE QUESTIONS:

1. What do you understand by seed dormancy? Discuss the reasons of seed dormancy and methods to break it.

A159

INTRODUCTION:

DIGESTIVE SYSTEM:Digestion is the process of breaking down complex food particles into simpler forms to absorb nutrients.The complex of digestive processes gradually breaks down the foods eaten until they are in a form suitable for absorption.

After absorption, nutrients are used to synthesize body constituents.They provide the raw materials for the manufacture of new cells, hormones and enzymes, and the energy needed for these and other processes and for the disposal of waste materials.

The human digestive system consists of the alimentary tract and accessory

organs.The alimentary canal begins at the mouth, passes through the thorax, abdomen, and pelvis and ends at the anus. Itis thus a long tube through which food

passes. The parts include:

1. Mouth

2. Pharynx

3. Oesophagus

4. Stomach

5. Small intestine

6. Large intestine

7. Rectum

8. Anus

1. MOUTH The mouth or oral cavity is bounded anteriorly —by the lips, posteriorly — it is continuous with the oropharynx.The palate forms the roof of the mouth and is divided into the anterior hard palate and the posterior soft palate. The uvula is a curved fold of muscle covered with mucous membrane, hanging down from the middle of the free border of the soft

palate.It consists of the following important parts:

The tongue is a voluntary muscular structure that occupies the floor of the mouth.It is attached by its base to the hyoid bone and by a fold of its mucous membrane covering, called the frenulum, to the floor of the mouth. It has numerous papillae (little projections), having sense of taste, called the taste buds. The tongue plays an important part in: mastication (chewing), deglutition (swallowing), speech, taste.

The teeth

Teeth have thecodont attachment, i.e.embedded in a jaw bone socket.

Diphyodont: Two sets of teeth during a

lifetime. The deciduous or milk teeth (20) are replaced by permanent adult teeth (32).

Heterodont: There are four different types of teeth. Incisors (8, for biting), Canines (4, fortearing), Premolars (8, for crushing and grinding), molars (12, for making smallerpieces). The dental formula is 2123/2123; it represents the upper and lower half of the jaw.

2. PHARYNX Food passes from the oral cavity into the pharynx then to the esophagus below.The pharynx is divided for descriptive purposes into three parts, the nasopharynx,oropharynx, and laryngopharynx. The epiglottis (a cartilaginous flap) blocks the entry of food into glottis, the opening of trachea (windpipe).

3.OESOPHAGUS It is a long tube that opens into the stomach, which is regulated by a muscular gastro-oesophageal sphincter.

4.STOMACH It is ‘J’ shaped structure for storage and digestion of food. It secretes HCI to kill the bacteria. It is divided into four parts:

1.Cardiac — where oesophagus opens

2.Fundic

3.Body- central region

4 Pyloric- opens in the small intestine

At the distal end of the pylorus is the

pyloric sphincter, guarding the opening

between the stomach and the duodenum. Inner walls of stomach bears rugae (longitudinal folds).

5. SMALL INTESTINE It is the longest part of the alimentary canal. Pyloric sphincter connects the stomach to the small intestine. It has three parts:

1. Duodenum: It is about 25 cm long and ‘C’ shaped. Secretions from the gall

bladder and pancreas are released into the duodenum through a common structure, the hepatopancreatic ampulla, and the opening into the duodenum is guarded by the hepatopancreatic sphincter of Oddi.

2. Jejunum: It is the middle section of the small intestine and is about 2m long.

3. lleum, or terminal part, is about 3 meters long and ends at the ileo-caecal valve.Finger like villi are seen at the mucosa. Each villus has brush bordered columnar epithelial layer provided with microvilli. It increases the surface area for absorption.Villus consists of capillary network and a small lymph vessel (lacteal).

6. LARGE INTESTINE It also has three parts:

Caecum- itis a blind sac,which hosts microbes and has vermiform appendix (a

vestigial organ) attached to it.It is well developed in herbivores and small in man.

Colon- it consists of four parts; ascending, transverse,sigmoid and descending Rectum- opens out of the body through the anus.

7. Anus Anus is guarded by anal sphincter (circular voluntary muscles).

LET US KNOW WHAT WE HAVE LEARNT!

PART: A VERY SHORT ANSWER TYPE QUESTIONS:

A. MULTIPLE CHOICE QUESTIONS

Ques.1. Which of the following correctly represents the normal adult human

dental formula?

a) 3131/3131

b) 2133/2123

c) 2123/2123

d) 3133/3133

Ques. 2. The portion of the small intestine that is attached to the pylorus of

the stomach is:

a) duodenum.

b) colon.

c) jejunum.

d) ileum.

Ques. 3. In which layer of intestine, villi are present?

a) muscularis.

b) submucosa.

c) mucosa.

d) serosa.

Ques. 4. The teeth used for crushing or grinding food:

a) incisors

b) molars

c) premolars

d) canines

B. Fill in the blanks:

1) is the dentition in which teeth is embedded in sockets of jaw bones.

2) Caecum is in size in case of herbivores.

C. True /False:

1) Finger like projections villi in intestine are help in increasing the surface area of

absorption.

2) Epiglottis blocks the entry of food into windpipe

ANSWER KEY: PART- A

A. Multiple choice Questions:

1. (c) the normal adult human dental formula is 2123/2123.

2. (a) The portion of the small intestine that is attached to the pylorus of the

stomach is the duodenum .

3. (c) Villi are seen at mucosa of the intestine.

4. (c) The premolars teeth are used for crushing or grinding food.

B. Fill in the blanks:

1) Thecodont

2) large

C. True/ false:

1) True.

2) True

PART: B SHORT ANSWER TYPE QUESTIONS:

Ques.1. Explain the terms;

(i) Thecodont (ii) heterodont

Ques. 2. Write the parts of stomach in human.

Ques.3. Why villi are present in intestine and not in the stomach?

PART: C LONG ANSWER TYPE QUESTIONS:

Ques.1. Describe the alimentary canal of man?

A160

INTRODUCTION: DIGESTIVE GLANDS:To bring about the chemical simplification of food, digestive juices are secreted by

the different glands. The digestive glands associated with the alimentary canal

include majorly the salivary glands, the liver and the pancreas.

These are exocrine glands that secrete saliva. Saliva is mainly produced by three

pairs of salivary glands which are:-

(i) |The parotids (largest of the three glands , present on either side of the

cheek),

(ii) |The sub-maxillary ( present

at lower jaw) and

(iii) The sub-linguals (below the

tongue) These glands situated just outside the buccal cavity secrete salivary juice

into the buccal cavity. The saliva

breaks down the starch into sugars.

LIVER if It is the largest gland in the body, an exocrine gland. The liver is a reddish brown gland situated in the upper part of the abdomen on the right side.

Ithas two lobes i.e. right and left

lobe. It is a double membrane

structure.The hepatic lobules are the

structural and functional units of

liver containing hepatic cells hepatocytes). Each lobule is also

covered by a thin connective, tissue sheath called the Glisson’s capsule.

Hepatocytes secrete bile juice that is stored in a sac called the gall bladder. The bile plays an important role in the digestion of fats.

Functions of liver:-

(i) RBC production

(ii) Emulsification of fats

(iii)produces heparin for preventing clotting of blood

(iv) bile activates lipases, etc.

GALL BLADDER:- it is small pear shaped organ situated near the liver. The

bile secreted by the hepatic cells passes through the hepatic ducts and is stored

and concentrated in a thin muscular sac called the gall bladder.

The duct of gall bladder (cystic duct) along with the hepatic duct from the liver,forms the common bile duct.The bile duct and the pancreatic duct open together into the duodenum as the common hepato-pancreatic duct which is guarded by a sphincter called the sphincter of Oddi.The pancreas is a large cream coloured gland located just below the stomach. The pancreatic juice acts on carbohydrates and proteins and changes them into simpler forms.The pancreas is a compound (both exocrine and endocrine) elongated organ situated between the limbs of the‘U’ shaped duodenum.The exocrine portion secretes an alkaline pancreatic juice containing enzymes and the

endocrine portion secretes hormones, insulin and glucagon.The partly digested food now reaches the lower part of the

small intestine where the intestinal juice [succus entericus]completes the digestion of all components of the food.

The glands of stomach are called gastric glands. These are present in the mucosa of the stomach. These are:-

1. Mucus or goblet cells (secretes

alkaline mucus)

2. Peptic cells or chief or zymogenic cells (secretes inactive gastric enzymes)

3. Parietal or oxyntic cells (secretes HCl)

INTESTINAL GLANDS:The epithelium of intestine bears a large number of glands and is located on villi. In general the secretion of intestinal juice is called succus entricus. These glands are shown in the picture. Others glands are:-

(a)Brunner’s glands are present in duodenum.

(b)Crypts of leiberkuhn in mucus portion

bacteria.

DIGESTION OF FOOD The process of digestion involves the conversion of large , complex and non- diffusible substances into respective simpler forms. It starts in buccal cavity and continues till the anus of large intestine.

DIGESTION IN BUCCAL CAVITY In buccal cavity, the mastication of food with the help of teeth and tongue and also

swallowing takes place. The saliva contains enzymes: - salivary amylase and

lysozyme.

Salivary amylase

(i) Starch (polysaccharide ==—=—=—=—==>_ Maltose (disaccharide)

pH6.8

(ii) Lysozyme in saliva helps in destroying harmful bacteria.

Digestion — Enzyme Action in Stomach

The stomach stores the food for 4-5 hours. The food mixes thoroughly with the

acidic gastric juice of the stomach by the churning movements of its muscular wall

and is called the chyme.

The proenzyme [inactive precursor of an enzyme] pepsinogen, on exposure to

hydrochloric acid gets converted into the active enzyme PEPSIN, the proteolytic

enzyme of the stomach.Pepsin converts proteins into proteoses and peptones

(peptides). The mucus and bicarbonates present in the gastric juice play an

important role in lubrication and protection of the mucosal epithelium from highly concentrated hydrochioric acid. HCl provides the acidic pH (pH 1.8) optimal for

pepsins.Rennin is a proteolytic enzyme found in gastric juice of infants which helps in the digestion of milk proteins.Small amount of lipases are also secreted.

DIGESTION — ENZYME ACTION IN SMALL INTESTINE: The digestive juices from liver (Bile), pancreas (pancreatic juice), and small intestine ( intestinal juices) are released into small intestine to bring out the further chemical simplification of food.The pancreatic juice contains inactive enzymes — trypsinogen, chymotrypsinogen,

procarboxypeptidases, amylases, lipases and nucleases.Trypsinogen is activated by an enzyme, enterokinase, secreted by the intestinal mucosa into active TRYPSIN, which in turn activates the other enzymes in the pancreatic juice.

The bile released into the duodenum contains bile pigments (bilirubin and biliverdin), bile salts, cholesterol and phospholipids but no enzymes. Bile helps in emulsification of fats, i.e., breaking down of the fats into very small micelles. Bile also activates LIPASES. Small amounts of lipases are secreted by gastric glands.Bile from liver

Fats > Emulsification The intestinal mucosal epithelium has goblet cells which secrete mucus. The secretions of the mucosa along with the secretions of the goblet cells constitute the intestinal juice. This juice contains a variety of enzymes like disaccharidases (e.g., maltase), dipeptidases, lipases, nucleosidases, etc. Hormonal control of the secretion of digestive juices is carried out by local hormones produced by the gastric and intestinal mucosa.

The breakdown of biomacromolecules mentioned above occurs in the duodenum region of the small intestine. The simple substances thus formed are absorbed in the jejunum and ileum regions of the small intestine.The undigested and unabsorbed substances are passed on to the large intestine.

LET US KNOW WHAT WE HAVE LEARNT!!

PART: A VERY SHORT ANSWER TYPE QUESTIONS:

(MULTIPLE CHOICE QUESTIONS

Ques.1 The HCI in gastric juice converts:

(a) Disaccharide to monosaccharide

(b) Pepsinogen to pepsin

(d) Polypeptide to peptide

Ques.2 Enterokinase helps in the conversion of:

(a)Lactose to Sucrose

(b)Trypsinogen into trypsin

(c)Pepsinogen into pepsin

(d)Proteins into polypeptide