Page No - 92
What is the general name of chemical substances which bring about control and coordination in plants ?
Which plant hormone is responsible for the wilting and falling of leaves ?
Abscisic acid is responsible for the wilting and falling of leaves in plants.
Which plant hormone makes a stem (or shoot) bend towards light ?
Where is the auxin hormone made in a plant stem ?
Auxin is made at the tip of the plant stem.
What is the scientific name of sensitive plant ?
Name one plant hormone that promotes growth and another plant hormone which inhibits growth.
A plant hormone that promotes growth is Gibberellin and the hormone that inhibits growth is abscisic acid.
Name one example of the movement of a plant part which is very quick and can be observed easily.
Thigmonastic movement in the leaves of touch-me-not plant is very quick and can be observed easily.
Name the type of chemical substances that control the growth in plants.
What is the stimulus in : (a) phototropism ? (b) geotropism ? (c) chemotropism ? (d) hydrotropism ? (e) thigmotropism ?
Give the scientific terms used to represent the following :
(a) Bending of a shoot towards light.
(b) Growing of roots towards the earth.
(c) Growth of a pollen tube towards ovule.
(d) Bending of roots towards water.
(e) Winding of tendril around a support
Page No - 93
Give one example of the movement of a plant part which is caused by the loss of water (or migration of water).
Give one example each of a plant part:
(a) which is positively hydrotropic as well as positively geotropic.
(b) which is positively phototropic but negatively geotropic.
Which of the following is a growth movement and which is not ?
(a) folding up of leaves of sensitive plant on touching with hand.
(b) folding up of petals of dandelion flower when light fades.
(a) is not growth movement whereas
(b) is growth movement.
Name the plant part :
(a) which bends in the direction of gravity but away from light
(b) which bends towards light but away from the force of gravity
To which directional stimuli do :
(a) roots respond ?
(b) shoots respond ?
Fill in the following blanks :
(a) A plant’s response to light is called…………..
(b) A plant’s response to gravity is called…………..
(c) Plant shoot grows upward in response to…………….
(d) Plant roots grow downward in response to…………..
(e) Tendrils wind around a support in response to……………
(f) Plant roots grow towards…….. and in the direction of force of……………
(g) A root of a plant grows downward. This is known as…………..
(h) ……….is the hormone that causes phototropism in plants
(i) The response of leaves to the sunlight is called……………
(f) Earth, gravity.
Plant parts show two types of movements, one dependent on growth and the other independent of growth. Give one example of the movement in plant parts :
which depends on growth
which does not depend on growth
(a) Bending of stem towards light.
(b) Folding up of leaves of a sensitive plant on touching.
What is a plant hormone ? Name four plant hormones. State one function of each.
The hormones that control and coordinate the activities in plants are called plant hormones. The four types of plant hormones are:
(i) Auxins – It promotes cell enlargement and cell differentiation in plants.
(ii) Gibberellines – It helps in breaking the dormancy in seeds and buds.
(iii) Cytokinins – It promotes cell division in plants.
(iv) Abscisic acid – It promotes the dormancy in seeds and buds.
(a) What does a root do in response to gravity ? What is this phenomenon known as ?
(b) What does a stem (or shoot) do in response to light ? What is this phenomenon known as ?
(a) Root bends downwards in the direction of gravity; positive geotropism. (b) Stem bends towards the light; positive phototropism.
(a) What does a stem (or shoot) do in response to gravity ? What is this phenomenon known as ?
(b) What does a root do in response to light ? What is this phenomenon known as ?
(a) Stem grows upward against the direction of gravity; negative geotropism.(b) Root bends away from light; negative phototropism
(a) What does a Mimosa pudica plant do in response to touch ? What is this phenomenon known as ?
(b) What happens to the dandelion flower (z) during daytime, and (ii) at night ? What is this phenomenon known as ?
(a) In Mimosa pudica plant, the leaves fold up in response to touch. This phenomenon is known as thigmonasty.
(i) A dandelion flower opens up in the morning in bright light. This phenomenon is known is positive photonasty.
(ii) At night, the dandelion flower closes and this phenomenon is known as negative photonasty.
(a) What does a plant root do in response to water ? What is this phenomenon known as ?
(b) What happens to the moonflower (i) during daytime, and (ii) at night ? What is this phenomenon known as ?
(a) The plant root grows towards water and the phenomenon is known as the hydrotropism.
(i) During the daytime the petals of moon flower close when there is bright light.
(ii) At night, when it is dark the petals of moon flower opens up. This phenomenon is known as photonasty.
What is a tendril ? Name the two types of tendrils. What does a tendril do in response to the touch of a support ? What is this phenomenon known as ?
Tendrils are the thin, thread-like growths on the stems or leaves of climbing plants. The two types of tendrils are stem tendrils and leaf tendrils. The tendrils grow towards the things they happen to touch. This phenomenon is known as thigmotropism.
Name the five types of tropisms. How are tropic movements helpful to plants ? Explain with an example.
The five types of tropisms are: Phototropism, Geotropism, Chemotropism, Hydrotropism and Thigmotropism. The various types of tropic movements help the plants to survive. Example even if a seed is planted upside down, its root will grow downwards into earth because it is positively geotropic.
Define chemotropism. Give one example of chemotropism. State whether this example is of positive chemotropism or negative chemotropism.
The growth of a plant part due to chemical stimulus is known as chemotropism. For example the growth of pollen tube towards the ovule induced by a sugary substance as stimulus. This is an example of positive chemotropism.
Distinguish between tropic movements and nastic movements in plants. Give examples to illustrate your answer.
1. These movements are always in the direction of the stimulus.
2. These movements are slow.
3. These movements are exhibited by all parts of a plant. For example, movement of shoot towards the light and not towards gravity.
1. These movements are neither away nor towards the stimulus.
2. These movements are fast.
3. These movements are exhibited by the flat organs (like leaves and petals of flowers) of a plant. For example, the bending and drooping of leaves in ‘Touch-me-not’ plant.
(a) What is meant by nastic movements in plants ? Give one example of nastic movements in plants.
(b) What is the difference between photonasty and thigmonasty ?
(a) The movement of a plant part in response to an external stimulus in which the direction of response is not determined by the direction of stimulus is called nastic movement. Example: The folding up of the leaves of a sensitive plant on touching is an example of thigmonasty.
The non directional movement of a plant part (Usually ) petals of flowers) in response to light is called photonasty
The non-directional movement of a plant part in response to the touch of an object is called thigmonasty
Example: The opening and closing of petals of dandelion flowers in response to the intensity of light.
Example: In Mimosa pudica plant, the leaves fold up in response to touch.