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Plant growth and movement | Plant Physiology | NEB class 12 Biology Notes | Botany
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Class 12 Bio

1. Plant Growth and Movement Syllabus

Unit 2: Plant Physiology (this page: chapter 2.5 Plant growth and movement)

2. Plant Physiology
2.1 Water relation: Introduction and significance of diffusion, osmosis, and plasmolysis, ascent of sap, transpiration and guttation.
2.2 Photosynthesis: Introduction and significance, photosynthetic pigments, mechanism (photochemical phase and Calvin-Benson cycle), C₃ and C₄ plants, photorespiration, factors affecting photosynthesis.
2.3 Respiration: Introduction and significance, types, mechanism (glycolysis, Kreb cycle, electron transport system), factors affecting respiration.
2.4 Plant hormones: Introduction, physiological effects of auxins, gibberellins and Cytokinins.
2.5 Plant growth and movement: Concept on seed germination, dormancy, photoperiodism, vernalization, senescence; plant movements (tropic and nastic).

These plant growth and movement notes follow the NEB Class 12 Biology syllabus (+2 Biology, Nepal), chapter 2.5 of Unit 2 Plant Physiology. Practise the multiple choice questions first, then work through the solved short and long answer questions, and finish with the PDF notes for quick revision.

Plant growth and movement notes - Class 12 Biology NEB Unit 2

Figure: Plant growth and movement notes, Class 12 Biology (NEB)

Micro syllabus: 2. Plant Physiology

Describe diffusion, osmosis, plasmolysis, ascent of sap, transpiration, and guttation.
Define photosynthesis and explain its mechanism, pigments, C₃ and C₄ pathways, and influencing factors.
Explain respiration, its types, mechanism, and influencing factors.
Define phytohormones and describe the physiological roles of auxins, gibberellins, and cytokinins.
Describe seed germination, dormancy, photoperiodism, vernalization, senescence, and plant movements.

Read more about plant hormones, seed germination and photoperiodism on Wikipedia. More notes: Class 12 Biology notes, Class 12 Chemistry notes and Class 12 Physics notes.

2. Plant Growth and Movement Notes: Multiple Choice Questions

Question 1. Naturally occurring auxin is

  • a) IAA
  • b) IBA
  • c) NAA
  • d) 2,4-D

Correct Answer: a) IAA

Reason: Indole-3-acetic acid (IAA) is the natural auxin of plants. IBA, NAA and 2,4-D are synthetic.

Question 2. Auxin is transported from

  • a) Root to shoot
  • b) Shoot to root
  • c) Stem to leaves
  • d) Flower to fruit

Correct Answer: b) Shoot to root

Reason: Auxin is made in the shoot tip and moves basipetally (downwards) to the root.

Question 3. Who isolated auxin from the tip of Avena coleoptile?

  • a) Skoog
  • b) F.W. Went
  • c) Kurosawa
  • d) Richmond

Correct Answer: b) F.W. Went

Reason: Went collected auxin from Avena coleoptile tips on agar blocks. Kurosawa studied gibberellins.

Question 4. Which of the following is an effect of auxin?

  • a) Abscission
  • b) Ripening of fruit
  • c) Apical dominance
  • d) Delay of senescence

Correct Answer: c) Apical dominance

Reason: Auxin from the shoot apex stops the growth of lateral buds. Fruit ripening is an effect of ethylene.

Question 5. Development of seedless fruits, induced by auxins, is known as

  • a) Bolting
  • b) Abscission
  • c) Dwarfism
  • d) Parthenocarpy

Correct Answer: d) Parthenocarpy

Reason: Parthenocarpy is fruit formation without fertilisation, so the fruit is seedless.

Question 6. Which auxin is used in killing herbs?

  • a) IAA
  • b) IBA
  • c) 2,4-D
  • d) All of the above

Correct Answer: c) 2,4-D

Reason: 2,4-D is a synthetic auxin used as a weedkiller on broad-leaved weeds.

Question 7. Foolish seedling of rice is caused by

  • a) Auxins
  • b) Cytokinins
  • c) Ethylene
  • d) Gibberellins

Correct Answer: d) Gibberellins

Reason: The fungus Gibberella fujikuroi releases gibberellins, which make the rice seedling grow tall and weak.

Question 8. Which of the following is not an effect of gibberellins?

  • a) Bolting
  • b) Breaking dormancy
  • c) Stomatal closure
  • d) Synthesis of α-amylase

Correct Answer: c) Stomatal closure

Reason: Stomatal closure is caused by abscisic acid, not by gibberellins.

Question 9. A cytokinin, present in maize endosperm is

  • a) Zeatin
  • b) Zymase
  • c) Morphine
  • d) Naphthalene

Correct Answer: a) Zeatin

Reason: Zeatin was first isolated from immature maize (Zea mays) endosperm.

Question 10. Culture medium, treated with a higher concentration of auxin as compared to cytokinin, induces

  • a) Flowering
  • b) Fruit ripening
  • c) Root development
  • d) Abscission of leaves

Correct Answer: c) Root development

Reason: A high auxin to cytokinin ratio makes callus form roots. A high cytokinin ratio makes shoots.

Question 11. Leaves can be made fresh and green by treatment with cytokinins. This effect is

  • a) Apical dominance
  • b) Dwarfism
  • c) Parthenocarpy
  • d) Delay of senescence

Correct Answer: d) Delay of senescence

Reason: Cytokinins keep chlorophyll and proteins from breaking down, so the leaf stays green longer.

Question 12. Bolting refers to

  • a) Rapid development of roots
  • b) Rapid elongation of internodes
  • c) Rapid production of flowers and fruits
  • d) Pre-mature falling of leaves, flowers and fruits

Correct Answer: b) Rapid elongation of internodes

Reason: Bolting is the quick stem elongation of a rosette plant before flowering, caused by gibberellins.

Question 13. If cotyledons remain under the soil, the seed germination is said to be

  • a) Epigeal
  • b) Hypogeal
  • c) Hypocotyl
  • d) Epicotyl

Correct Answer: b) Hypogeal

Reason: In hypogeal germination the epicotyl grows and the cotyledons stay below ground.

Question 14. Main factor for seed germination is

  • a) Air
  • b) Moisture
  • c) Temperature
  • d) Sunlight

Correct Answer: b) Moisture

Reason: Germination starts with imbibition. Without water the enzymes stay inactive.

Question 15. Hypogeal germination is common in

  • a) Monocots
  • b) Dicots
  • c) Mangrove plants
  • d) Pteridophytes

Correct Answer: a) Monocots

Reason: All monocots show hypogeal germination. Among dicots only gram, pea and groundnut do.

Question 16. Rhizophora exhibits

  • a) Hypogeal germination
  • b) Epigeal germination
  • c) Viviparous germination
  • d) All of the above

Correct Answer: c) Viviparous germination

Reason: Seeds of this mangrove germinate inside the fruit while it is still on the parent plant.

Question 17. Seed dormancy refers to

  • a) Failure of viable seeds in unfavorable environmental conditions.
  • b) Failure of viable seeds in favorable environmental conditions.
  • c) Failure of non-viable seeds in unfavorable environmental conditions.
  • d) Failure of non-viable seeds in favorable environmental conditions.

Correct Answer: b) Failure of viable seeds in favorable environmental conditions.

Reason: A dormant seed is alive but does not germinate even when moisture, temperature and air are suitable.

Question 18. Leguminous seeds fail to germinate due to hard and impervious seed coats. It is known as

  • a) Mechanical dormancy
  • b) Physical dormancy
  • c) Chemical dormancy
  • d) Physiological dormancy

Correct Answer: b) Physical dormancy

Reason: A seed coat that is impermeable to water and gases causes physical (seed coat) dormancy.

Question 19. Flowering in plants, in response to the relative length of day and night, is known as

  • a) Phototaxis
  • b) Phototropism
  • c) Photoperiodism
  • d) Photosynthesis

Correct Answer: c) Photoperiodism

Reason: Garner and Allard (1920) discovered that the length of day and night controls flowering.

Question 20. For flowering in long day plants, the day should be of

  • a) 8-10 hours
  • b) 10-12 hours
  • c) 14-16 hours
  • d) 18-20 hours

Correct Answer: c) 14-16 hours

Reason: Long day plants need a light period of about 14-16 hours in 24 hours. 8-10 hours suits short day plants.

Question 21. Which of the following is a long day plant?

  • a) Rice
  • b) Coffee
  • c) Radish
  • d) Tomato

Correct Answer: c) Radish

Reason: Radish, wheat, cabbage and spinach are long day plants. Rice and coffee are short day plants and tomato is day neutral.

Question 22. A physiological process which causes ageing and the ultimate death of an organism is known as

  • a) Parthenocarpy
  • b) Imbibition
  • c) Senescence
  • d) Vernalization

Correct Answer: c) Senescence

Reason: Senescence is the deteriorative process that ends the functional life of an organ or organism.

Question 23. A process whereby flowering is promoted by a cold treatment given to a fully hydrated seed or to a growing plant is known as

  • a) Parthenocarpy
  • b) Imbibition
  • c) Senescence
  • d) Vernalization

Correct Answer: d) Vernalization

Reason: Vernalization is flowering induced by chilling, also called yarovization.

Question 24. During vernalization, germinating seeds are treated to

  • a) 0-5 °C temperature
  • b) 5-10 °C temperature
  • c) 10-15 °C temperature
  • d) 15-20 °C temperature

Correct Answer: a) 0-5 °C temperature

Reason: Germinating seeds are given cold treatment at 0 °C to 5 °C for days to weeks.

Question 25. Vernalization results in

  • a) Shortening vegetative growth and delay in flowering
  • b) Shortening vegetative growth and early flowering
  • c) Longer vegetative growth and delay in flowering
  • d) Longer vegetative growth and early flowering

Correct Answer: b) Shortening vegetative growth and early flowering

Reason: Cold treatment cuts short the vegetative period, so the plant flowers early.

Question 26. For vernalization, seeds should be

  • a) hydrated and viable
  • b) dehydrated and viable
  • c) hydrated and non-viable
  • d) dehydrated and non-viable

Correct Answer: a) hydrated and viable

Reason: Dry seeds do not respond to cold. The seed must be alive, swollen with water and respiring.

Question 27. Plant movement, independent of external stimuli, is said to be

  • a) Autonomic
  • b) Paratonic
  • c) Tectonic
  • d) Induced

Correct Answer: a) Autonomic

Reason: Autonomic (spontaneous) movements arise from inside the plant. Paratonic movements are induced by stimuli.

Question 28. Autonomic movement of variation is shown by

  • a) Tendrils in climbers
  • b) Leaves in Desmodium
  • c) Leaves in Mimosa pudica
  • d) Insectivorous plants

Correct Answer: b) Leaves in Desmodium

Reason: The lateral leaflets of Desmodium gyrans show turgor movements without any stimulus.

Question 29. Directional and irreversible growth in plants in response to an external stimulus is known as

  • a) Taxis
  • b) Tropism
  • c) Nasty
  • d) Turgor movement

Correct Answer: b) Tropism

Reason: A tropic movement is a growth curvature whose direction depends on the direction of the stimulus.

Question 30. Folding of leaves of the Touch-me-not plant is the best example of

  • a) Nyctinasty
  • b) Thermonasty
  • c) Thigmonasty
  • d) Seismonasty

Correct Answer: d) Seismonasty

Reason: Mimosa pudica leaves fold on shock or touch. This is the seismonastic movement.

3. Plant Growth and Movement Notes: Short and Long Answer Questions

Plant Growth and Movement Notes: Short Answer Questions

Q.1 Define phytohormones and write their features.

Phytohormones (plant growth regulators) are organic chemical substances made in very small amounts in one part of a plant. They move to other parts, where they control growth, development and other physiological processes.

Features:

They are organic compounds made naturally by the plant.
They are made in specific tissues such as shoot tips, root tips and young leaves.
They work in very low concentration.
They are carried through the xylem and phloem to the target cells.
They may promote growth (auxins, gibberellins, cytokinins) or inhibit it (abscisic acid).
Their effect depends on concentration and on how they interact with other hormones.
Q.2 Describe any three physiological effects of auxins.
Apical dominance: auxin made in the shoot apex stops the growth of the lateral buds. Cutting the apex lets the lateral buds grow and the plant becomes bushy.
Cell elongation: auxin makes cells just behind the stem tip grow longer. This causes the bending of stems towards light.
Parthenocarpy: spraying auxin on unpollinated flowers gives seedless fruits, as in tomato and grapes.
Root initiation (extra): IBA and NAA make stem cuttings form roots.
Q.3 Define apical dominance. Name the hormones which induce and suppress apical dominance.

Apical dominance is the control of the apical bud over the lateral (axillary) buds, so that the main stem grows and the side buds stay inactive.

Induced by: auxin (IAA), made in the shoot apex and carried downwards.
Suppressed by: cytokinin, made in the roots. It makes the lateral buds grow and works against auxin.
Q.4 Elaborate bolting and parthenocarpy with suitable examples.

Bolting: It is the sudden, rapid elongation of internodes just before flowering in plants with a rosette habit. Gibberellins cause it. Examples: cabbage, sugar beet.

Parthenocarpy: It is the development of fruit without fertilisation, so the fruit is seedless. Auxins and gibberellins can induce it. Examples: banana, grapes, seedless watermelon, tomato.

Q.5 Classify plants on the basis of photoperiodism and give two examples of each.

Photoperiodism is the response of plants to the relative length of day and night. On this basis plants are of three types:

TypeRequirementExamples
Short day plants (SDP)Short day (8-10 hours) and a long continuous dark period (14-16 hours)Rice, coffee (also soybean, tobacco, chrysanthemum)
Long day plants (LDP)Long day (14-16 hours in 24 hours)Wheat, radish (also cabbage, sugar beet, spinach)
Day neutral plants (DNP)Flower in any photoperiod from 5 to 24 hoursTomato, cotton (also sunflower, cucumber, pea)
Q.6 Point out any four differences between short-day plants and long-day plants.
Short day plantLong day plant
Flowers when the photoperiod is less than the critical day length.Flowers when the photoperiod is more than the critical day length.
Interrupting the light period with darkness does not stop flowering.Interrupting the light period with darkness stops flowering.
Flowering is inhibited if the long dark period is broken by a flash of light.Flowering occurs if the dark period is broken by a flash of light.
A long, continuous, uninterrupted dark period is critical.The dark period is not critical; the light period is.
Also called long night plants (e.g., rice, coffee).Also called short night plants (e.g., wheat, radish).
Q.7 Define senescence and write its significance in plants.

Senescence is the deteriorative process that naturally ends the functional life of an organ, organism or other living unit. Its metabolism is catabolic and finally irreversible, and it ends in death. Example: leaf fall in coconut; death of the whole wheat plant after fruiting.

Significance:

In monocarpic plants the whole plant senesces when seeds are set and dispersed.
Old leaves fall by the abscission layer, so nutrients go to younger leaves.
It helps move nutrients from vegetative parts into the fruits.
Plants escape seasonal stress. Leaf fall in deciduous trees reduces transpiration in the dry season.
Q.8 What do you mean by abscission? Write its significance.

Abscission is the shedding of leaves, flowers and fruits from the plant. It takes place at the abscission zone (abscission layer) at the base of the petiole. There the middle lamella and cell walls dissolve under the action of pectinase and cellulase, and the part falls by its own weight or wind. A corky layer then heals the wound.

Significance:

It diverts water and nutrients to young leaves.
It is a self-pruning process that removes old, injured and diseased parts, including fruits.
It helps to spread fruits and vegetative propagules.
It removes plant parts that contain waste materials.
Q.9 Define vernalization. Write its significance in plants.

Vernalization (yarovization) is the promotion of flowering by cold treatment (0-5 °C) given to a fully hydrated seed or to a growing plant. Dry seeds do not respond. The plant is thought to form a hormone called vernalin.

Significance:

It cuts short the vegetative period and gives early flowering.
It increases resistance to fungal diseases.
It increases cold resistance.
In biennials it induces early flowering and early fruit setting.
Flowering can be induced by grafting, which is used in horticulture.
It helps in crop improvement.

Plant Growth and Movement Notes: Long Answer Questions

Q.1 Discuss the effects of gibberellins in dormancy, flowering and plant growth.
Dormancy: gibberellins break seed and bud dormancy. They make the aleurone layer produce α-amylase, which digests starch and feeds the embryo. Abscisic acid does the opposite and keeps seeds dormant.
Flowering: they cause bolting (rapid elongation of internodes) in rosette plants like cabbage. They can replace the cold treatment or long day needed for flowering.
Plant growth: they make internodes elongate, so dwarf plants grow tall. They also increase leaf and fruit size.
Q.2 Describe the role of cytokinins in tissue culture and agriculture.

In tissue culture:

Cytokinins make cells divide (cytokinesis).
Equal auxin and cytokinin make an undifferentiated mass of cells called callus.
More cytokinin than auxin makes shoots form. More auxin than cytokinin makes roots form. This is used in micropropagation.

In agriculture:

They delay senescence, so leafy vegetables and cut flowers stay fresh and green longer.
They overcome apical dominance, so crops branch more.
They help seed germination and fruit setting.
Q.3 Describe the seed germination process in brief.

Germination is the irreversible process in which the embryo of a seed becomes active and grows into a seedling. It needs water, a suitable temperature, oxygen and, for some seeds, light. It has these steps:

1) Imbibition: the seed takes in water through the micropyle. It swells, the seed coat bursts and hydrolytic enzymes become active.
2) Respiration: the seed respires actively and needs oxygen. A deeply buried or waterlogged seed gets too little oxygen.
3) Light: many forest seeds germinate only when light reaches them.
4) Temperature: seeds germinate within a range of temperature, mostly around 16-32 °C.
5) Scarification: the seed coat is weakened by fire, soaking or an animal’s gut, so the seedling can come out.
Mobilisation of reserves: gibberellins break dormancy and help digest reserve food. Abscisic acid inhibits germination.
Growth of the embryo axis: the radicle grows down to form the root and the plumule grows up to form the shoot.

Types: in hypogeal germination (all monocots, gram, pea) the epicotyl grows and the cotyledons stay in the soil. In epigeal germination (bean, castor, sunflower, cucumber) the hypocotyl grows and lifts the cotyledons above the soil. In viviparous germination (Rhizophora) the seed germinates inside the fruit on the parent plant.

Q.4 Mention the factors of seed dormancy. Write the advantages of seed dormancy.

Factors (types) of seed dormancy:

Physical dormancy: the hard seed coat is impermeable to water and gases, as in legumes, olive, peach and cherry.
Mechanical dormancy: the seed covering is too strong for the radicle to push through, as in walnut shells and stone fruit pits.
Chemical dormancy: inhibitors such as phenols, coumarin and abscisic acid are present in the fruit or seed covering, as in citrus, tomato and grapes.
Morphological dormancy: the embryo is underdeveloped and needs time to grow, as in celery.

Advantages:

It helps the seedling survive environmental stress.
It allows the formation of a seed bank.
It makes germination happen together, so the plants are at the same stage for cross-pollination.
It helps seed dispersal, for example when the seed coat is scarified in a bird’s or animal’s gut.
Q.5 Write about autonomic growth movement in plants.

Autonomic movements happen without any external stimulus. Autonomic growth movements are due to unequal growth in different parts of an organ. They are irreversible. They are of four types:

Nutation: a nodding movement of the growing stem tip of twiners (pea, bean). Growth is faster on one side and then on the other, so the tip rotates in the same direction.
Circumnutation: in spirally growing stems and tendrils the region of fastest growth moves round the growing point and makes spiral coils.
Epinasty: faster growth on the upper side of an organ, as in the opening of young leaves.
Hyponasty: faster growth on the lower side, as in circinate coiling and closed sepals and petals of a flower bud.

The other autonomic movements are movements of variation (turgor changes, reversible, e.g., leaflets of Desmodium gyrans).

Q.6 Define paratonic or induced movements. Mention its types with an example of each.

Paratonic (induced) movements are movements caused by an external stimulus such as light, gravity, touch or temperature. They are of two types:

Tropic movements: directional growth curvatures. The direction of the stimulus decides the direction of the response. Example: stem bending towards light (phototropism).
Nastic movements: turgor or growth movements whose direction does not depend on the direction of the stimulus. Example: folding of Mimosa pudica leaves on touch (seismonasty).
Q.7 What is tropism? Describe its types with an example of each.

Tropism is a directional, slow and irreversible growth movement of a plant organ, caused by an external stimulus. The response is towards the stimulus (positive) or away from it (negative). It is seen in organs of radial symmetry such as the shoot and root.

TypeStimulusExample
PhototropismLightStem bends towards light (positive); root grows away (negative)
GeotropismGravityPrimary root grows down (positive)
HydrotropismWaterRoots bend towards water
ChemotropismChemicalsPollen tube grows through the style towards the embryo sac
ThigmotropismContactTendrils coil round a support
ThermotropismTemperaturePlant parts curve towards a normal temperature
Q.8 Describe the nastic movements shown by Drosera and Mimosa pudica.

Nastic movements are quick, turgor-based movements in dorsiventral organs. The direction of response is fixed by the organ, not by the direction of the stimulus.

Drosera (sundew): it shows thigmonasty (haptonasty). When an insect touches the glandular hairs of the leaf, the hairs bend inwards over it and trap it.
Mimosa pudica (touch-me-not): it shows seismonasty. On touch or shock the leaflets fold and the petiole droops. The pulvinus at the leaf base loses water and turgor quickly, so the leaf collapses; it recovers when turgor is restored.

4. Plant Growth and Movement Notes PDF

PDF Notes 1: Plant Physiology (Unit 2)

PDF Notes 2: Plant Growth and Movement (Chapter 2.5)

5. Plant Growth and Movement: Frequently Asked Questions

What is plant growth and movement? (Plant growth and movement notes)
Plant growth and movement is chapter 2.5 of Unit 2 Plant Physiology in Class 12 Biology. It covers seed germination, seed dormancy, photoperiodism, senescence, abscission, vernalization and plant movements (tropic and nastic).
What are the types of seed germination?
There are three types: hypogeal (cotyledons stay under the soil, as in all monocots, gram and pea), epigeal (cotyledons come above the soil, as in bean and castor) and viviparous (the seed germinates inside the fruit on the parent plant, as in Rhizophora).
What is seed dormancy and why is it useful?
Seed dormancy is the failure of a viable seed to germinate even in favourable conditions. It helps the seedling survive stress, forms a seed bank, synchronises germination and aids seed dispersal.
What is photoperiodism?
Photoperiodism is the response of plants, mostly flowering, to the relative length of day and night. It was discovered by Garner and Allard in 1920. Plants are short day, long day or day neutral.
Which are examples of short day, long day and day neutral plants?
Short day: rice, coffee, soybean. Long day: wheat, radish, cabbage. Day neutral: tomato, cotton, sunflower.
What is vernalization?
Vernalization is the promotion of flowering by cold treatment (0-5 °C) of a hydrated seed or growing plant. It shortens the vegetative period and gives early flowering.
What is the difference between senescence and abscission?
Senescence is the ageing process that ends the life of an organ or plant. Abscission is the shedding of leaves, flowers and fruits at the abscission layer. Senescence of a leaf usually comes before its abscission.
What is the difference between tropic and nastic movements?
Tropic movements are slow growth curvatures whose direction depends on the direction of the stimulus, as in phototropism. Nastic movements are quick turgor movements whose direction does not depend on the stimulus, as in Mimosa pudica.
What are autonomic movements?
Autonomic movements occur without any external stimulus. They include growth movements (nutation, circumnutation, epinasty, hyponasty) and movements of variation (Desmodium leaflets).
Where can I download Plant growth and movement notes PDF for Class 12 Biology?
You can read and download the PDF notes in the View PDF section of this page. It has the Plant Physiology unit notes and the Plant Growth and Movement chapter notes (Asmita Publication based, NEB syllabus).
Is this Class 12 Biology book PDF for Nepal NEB?
Yes. The notes follow the NEB Class 12 Biology syllabus of Nepal and the Asmita Publication textbook, Unit 2 Plant Physiology.
Where can I find the Plant physiology Class 12 notes PDF free download?
The Plant Physiology unit PDF in the PDF notes section can be viewed and downloaded free. It covers water relation, photosynthesis, respiration, plant hormones and plant growth and movement.

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