BIOLOGY 2 Marks Questions

Absolute growth rate refers to the measurement and comparison of total growth per unit time. Relative growth rate refers to the growth of a particular system per unit time, expressed on a common basis.

Geometric growth is characterised by a slow growth in the initial stages and a rapid growth during the later stages. The daughter cells derived from mitosis retain the ability to divide, but slow down because of a limited nutrient supply.

The flowering response in short-day plants and long-day plants is dependent on the durations for which these plants are exposed to light. The short-day plant and long-day plant can flower at the same place, provided they have been given an adequate photoperiod.

In arithmetic growth, one of the daughter cells continues to divide, while the other differentiates into maturity. The elongation of roots at a constant rate is an example of arithmetic growth.

The higher plants retain the capacity for unlimited growth throughout their life. This ability of the 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. Therefore, growths in higher plants are open. Also, some of these cells always undergo differentiation after some rounds of cell division. Hence, the differentiation is also open.

1. Abscisic acid is the stress hormone.

• It causes closure of stomata and increases the tolerance of plant to water stress.
• It induces dormancy in seeds and thereby helps the plant to withstand dessication and other unfavourable factors that affect plant growth.

2. 2, 4 dichlorophenoxy aceitic acid.

Sugarbeet is a long day plant. It is because in this plant flowering takes place when the plants are exposed to day length longer than a critical photoperiod.

Plant growth promoters control activities like:

1. Cell division.
2. Cell enlargement.
3. Pattern formation.
4. Tropic movements.
5. Flowering.
6. Seed formation.

It is called apical dominance. Auxin hormone is responsible for this.

Meristematic cells are actively dividing cells which show mitotic divisions, i.e., each chromosome is split lengthwise into two homologous chromatids, which pass equally into daughter cells. Mature cells are incapable of divisions because in these cells differentiation has taken place.

A short-day plant requires a minimum level of darkness in order to flower. In this example, the critical level of daylight is 13hrs, and any level of daylight beyond this will not allow the plant adequate hours of darkness. So the plant will, therefore, not flower when there are 15hrs of exposure of daylight.

The cells is elongation zone are newly formed cells which lose the power of division.They elongate rapidly and increase the length of root.The cells of this region can absorb, water and minerals from the soil.

Natural means of overcoming seed dormancy:

1. Abrasions caused by microbial action.
2. Abrasions because of passage through digestive tracts of animals.

The role of ethylene and abscisic acid is both positive and negative. Ethylene is a simple gaseous PGR. It is synthesised in large amount by tissues undergoing senescence and ripening. It also promotes senescence and abscission of plant organs especially of leaves and flowers. This is its negative effect. As its positive effect, ethylene breaks seed and bud dormancy, initiates germination in peanut seeds, sprouting of potato tubers. It promotes inter-node/ petiole elongation in deep water rice plants. It helps leaves/ inner parts of the shoot to remain above water.

In nature it is broken in the following ways:

1. The hard seed coat is softened over a period of time by microbial action.
2. When the seed passes through the alimentary canal of fruit-eating birds/ animals, the seed coat becomes soft due to the action of digestive juices on it.
3. Abrasions on seed coat are caused by friction with soil and trampling by animals.

1. GA3 is used to speed up the malting process in brewing industry. Gibberellins also promote bolting (internode elongation just prior to flowering) in beet, cabbages and many plants with rosette habit.
2. Gibberellin causes foolish seedling disease in rice because it has the property of internode elongation.

1. Abscisic acid is the stress hormone.
2. The 'bakane' disease is caused by Gibberella fujikuroi.
3.  

• When the apical buds are removed, the synthesis of auxin decreases.
• Auxins are responsible for apical dominance, a phenomenon in which the lateral buds are suppressed to grow into branches.
• In the absence of auxins (apical buds), there is no apical dominance and hence, the lateral buds develop into branches.

1. It is the graphic representation of the total growth against time.
2. The period of time in which growth takes place has been called grand period of growth by Sachs.
3. The rate of growth is not uniform during grand period of growth.
4. If total growth is plotted against time, a S-shaped or sigmoid curve is obtained. It consists of four parts, i.e., lag phase, exponential phase (log phase), phase of diminishing growth and stationary phase.

	Absolute Growth Rate	Relative Growth Rate
1.	The total growth per unit time is absolute growth rate.	The total growth per unit time per unit parameter, is relative growth rate.

The following are the artificial methods of breaking seed dormancy:

1. Abrasions are made in the seed coat mechanically using sand paper, knives, etc.
2. Subjecting the seeds to chilling conditions removes the effect of inhibitor chemicals.
3. The seeds are also exposed to certain light and temperature treatment.
4. Treatment of seeds with gibberellic acid and nitrates helps to overcome the effect of chemical inhibitors.

Man-made means of overcoming seed dormancy:

1. The seed-coat barrier in some seeds can be broken by mechanical abrasions using knives, sandpaper, etc. or by vigorous shaking
2. Effect of inhibitory substances can be removed by subjecting the seeds to chilling conditions or by application of certain chemicals like gibberellic acid and nitrates.
3. Changing environment conditions: like light and temperature.

Meristematic zone is the growing point of root and is subterminal.It is made up of compactly or closely arranged small thin walled isodiametric and meristematic cells which have dense protoplasm.They undergo repeated divisions and produce new cells for the root cap and basal region of the root. Therefore, it is essential for the growth of root.

1. Cells of phellogen or cells of interfascicular cambium.
2. Secondary cortex cells, cells of cork (phellem).

	Arithmetic growth	Geometric growth
1.	In this type of growth one of the two daughter cells formed cells former by mitosis continues to divide.	In this type of growth, both the progeny after mitoses continue to divide.
2.	It is seen in the elongation of root.	It is seen in organs/ issues exponential phase of growth.

• Inhibitor-B, Abscissin II and dormin.
• Now they are all referred to as abscisic acid.

Favourable conditions for seed germination:

1. Proper temperature.
2. Moisture.
3. Sunlight.
4. Oxygen.

1. Florigen is a hypothetical hormone which induces flowering in plants.
2. Gibberellin breaks seed dormancy. It mobilises the enzyme to hydrolyse stored food present in seed at the time of seed germination.

Inhibitors are important to the survival of higher plants in temperate zones where there are extreme variation in weather conditions prevails. Here plants become dormant during harsh winter period and become active plant on corning favourable conditions. Seeds often will not begin to germinate until they have been exposed to cold. The breaking of dormancy and the beginning of growth depend on the release from inhibition of metabolic activities.

In most of the higher plants, growing apical bud inhibits the growth of lateral (axillary buds). This phenomenon is called apical dominance. Removal of short tips (decapitation) normally results in the growth of lateral buds. Decapitation is used in tea plantations to get more leaves from a plant.

Ethylene should be used on rice saplings. Ethylene promotes internode and petiole elongation so the height of the rice plant will be more. Additionally, ethylene also helps in maintaining aerial parts of a plant above the water.

Gibberellins are useful in agriculture in the following ways:

1. Application of gibberellins increases the length of the stem and increases the yield of sugar in sugarcane.
2. Gibberellins delay senescence and prevent the premature fruits drop.
3. It can cause fruits like apple to elongate and improve in shape.

1.  

• Apical dominance is the phenomenon in which the presence of apical buds suppresses the growth of lateral buds into branches.
• Auxin is responsible for this.

2. During drought, abscisic acid signals closure of stomata and thereby checks the loss of water and increases the tolerance of plants to water stress.

Development is the sequence of events that occur in the life history of a cell, organ or organism, which include growth, differentiation, maturation and senescence.

1. In homoblastic development the transition from juvenile to adult phase is gradual.
2. In heteroblastic development the transition is abrupt.

1. The cells would lose their protoplasm.
2. They develop thick, elastic, lignocellulosic secondary cell wall.

1. Seed dormancy is defined as the inherent or endogenous blocks in the seed that do not allow the seed to germinate even under favourable conditions.
2. It is caused by:

1. The presence of hard seed coat, which is impervious to gases and/ or water.
2. The presence of certain inhibitory chemicals in the seed.
3. Immature embryo.

Most fruits however develop only from the ovary and are called true fruits. Although in most of the species, fruits are the results of fertilization, there are a few species in which fruits develop without fertilization. Such fruits are called parthenocarpic fruits. Banana is one such example. Parthenocarpy can be induced through the application of growth hormones (like gibberellins and auxin) and such fruits are seedless. Auxins induce parthenocarpy in tomatoes.

In some plants, certain structures show different forms, in response to environment or to phases of life. This ability is known as plasticity. For example, in cotton, coriander and larkspur, leaves of juvenile plant are different in shape compared to leaves in mature plants. This is called heterophylly. In buttercup shape of leaves produced in air is different from that produced in water.

1. Naphthalene acetic acid.
2. Indole butyric acid.
3. 2, 4 dichlorophenoxy acetic acid.
4. Abscisic acid.

This is the phenomenon of more cell division taking place in shoot apex or root apex. The growth in apical regions prevents other parts from growing Horticulturists use this property to grow plants with more branches by cutting off the apex. This helps in channelizing resources to other areas of plant rather than to the apex.

1. Heterophylly is the phenomenon in which a plant bears different shapes of leaves.
2.  

1. Environmental heterophylly.
2. Developmental heterophylly.

The root apex and shoot apex show elongation phase. They have apical meristem which has cells undergoing continuous cell division. This leads to elongation and growth of the apical region of shoot and root.

Plasticity is the ability of plants to follow different pathways in response to environment or phases of life to different structures. Ex.- Heterophylly in plants like cotton, buttercup, etc.

Growth in plants is indefinite because they have the capacity for unlimited growth throughout their life. This ability of the plants is due to the presence of meristems at certain locations. This type of growth is exhibited by roots, stem and their branches and is called open form of growth.

The compounds, which can be converted into auxins, are called auxin precursors. The compounds, which inhibit the actions of auxins, are termed anti-auxins. The auxins, which can easily be extracted, are called free auxins. And auxins, which are hard to extract and need the use of organic solvents, are referred to as bound auxins.

He should use Gibberellins. Gibberellins help increase the size of apples. Moreover, they also delay senescence so apple can be left on branches for a longer duration This will give the orchard owner enough time to wait for good market conditions.

Water:

• It is necessary to maintain turgidity of cells that helps in extension of growth.
• Water provides the medium for the biochemical or enzymatic reactions that are necessary for growth activities.

Nutrients:

• They act as source of energy.
• They are required for the synthesis of protoplasm as they are constituents of biomolecules.

Internal causes of seed dormancy:

1. Impermeable and hard seed coat.
2. Presence of chemical inhibitors, such as absicissic acid, phenolic acid, para ascorbic acid, etc.
3. Immature embryo.

1. The diagram shows shoot apex of a dicotyledonous plant.

2. Part 1 is showing inner cellular mass of shoot apex known as corpus. Cells of corpus are large and divide in different planes. Cells derived from corpus form procambium and ground meristem.

A-Lag phase, B-Log phase and C-Steady phase.

• Plant growth is indeterminate, as plants retain the capacity to grow throughout their life; this ability is due to the presence of meristems, where cells have the capacity to divide and self-perpetuate.
• Plants show open form of growth, i.e., the form of growth, where new cells are continuously added to the plant body by the activity of meristems; hence, plant growth is unique.

If a short day plant is artificially given long and uninterrupted dark period, it flowers even under long day conditions. Similarly, if a long day plant is artificially given long photoperiods, it flowers even under short day conditions. Thus, it is possible that a short day plant and a long-day plant growing in the same locality are made to flower on the same day of the year by providing suitable photoperiodic conditions artificially.