Very important questions on biology for your next science exam

69. The chemical substance P is made and secreted by the meristematic tissue at the tip of stem (or shoot) of a plant. The chemical substance P is responsible for a phenomenon Q in plants in which the stem bends towards a source of light. The same chemical substance P has an opposite effect on the root of a plant. It causes the root of a plant to bend away from the source of light in a process called R.

(a)What is the chemical substance P?

(b) State whether P prefers to remains in the sunlit side of a stem or in shade.

(c)What is the effect of substance P on the rate of growth of (z) a root, and (ii) a stem?

(d) What is the name of process (i) Q, and (ii) R?

(e) What is the general name of chemical substances like P? Name another substance which belongs to this class of chemical substances.

70. A potted plant is growing in a transparent glass jar. In this plant, X and Y are the two growing parts having a lot of meristematic tissue. It is observed that the part X of this plant exhibits positive geotropism but negative phototropism. On the other hand, part Y of this plant exhibits negative geotropism but positive phototropism.

(a)Name the part X of plant.

(b) Name the part Y of plant.

(c)Which part of the plant, X or Y, will exhibit positive hydrotropism?

(d) Which part of the plant, X or Y, can have tendrils on it?

(e) Which phytohormone causes the part X to exhibit negative phototropism?

71. There are three plants A, B and C. The flowers of plant A open their petals in bright light during the day but close them when it gets dark at night. On the other hand, the flowers of plant B open their petals at night but close them during the day when there is bright light. The leaves of plant C fold up and droop when touched with fingers or any other solid object.

(a)Name the phenomenon shown by the flowers of (i) plant A, and (ii) plant B.

(b) Name one flower each which behaves like the flower of (i) plant A, and (ii) plant B.

(c) Name the phenomenon exhibited by the leaves of plant C.

(d) Name a plant whose leaves behave like those of plant C.

(e) Which plant/plants exhibit the phenomenon based on growth movements?

72. While conducting experiments to study the effect of various stimuli on the plants, it was observed that the roots of a plant X grow and bend towards two stimuli A and B but bend away from a third stimulus C. The stem of the plant X, however, bends away from stimuli A and B but bends towards the stimulus C. The stimulus B is known to act on the roots due to too much weight of the earth. Keeping these points in mind, answer the following questions:

(a) What could stimulus A be?

(b)Name the stimulus B.

(c)What could stimulus C be?

(d)The branches of a fallen tree in a forest grow straight up in response to two stimuli. What could be these two stimuli out of A, B and C ? Also name these two stimuli.

73. P and Q are two types of plants having weak stems which cannot stand upright on their own. The plants P and Q have organs R and S respectively which can grow towards any support which they happen to touch and wind around that support. It is observed that organ R originates from the leaves of the plant whereas organ S originates directly from the stem of the plant.

(a) What is (i) R, and (ii) S?

(b) What is the name of growth movement exhibited by the organs R and S?

(c) Name the stimulus involved in this case.

(d) State whether the behaviour of organs R and S is a tropic movement or a nastic movement.

(e) Name one plant like P and another plant like Q.

74. The top part A of the flask-shaped reproductive organ X in the flower of a plant secretes a surgery substance into its lower part B which goes towards the bottom part C of the flask-shaped organ. When a tiny grain D coming from the top part E of another reproductive organ Y in the flower falls on part A, it grows a long tube F through the organ X in response to the sugary substance and reaches the bottom part C of flask- shaped organ to carry out fertilisation.

(a) What is (i) organ X, and (ii) organ Y, inside the flower?

(b) Name parts (i) A (ii) B, and (iii) C, of flask-shaped organ.

(c) Name (i) grain D, and (ii) part E of organ Y.

(d) Name the tube F.

(e) What is the phenomenon of growing a long tube in response to a sugary substance in the process of fertilisation in a flower known as?

75. P, Q, R and S are four major types of phytohormones. P is a phytohormone which functions mainly as a growth inhibitor. It promotes the wilting and falling of leaves. Q, R and S are phytohormones which all promote growth of plants in various ways. Q is responsible for the phenomenon of phototropism in plants. R is involved mainly in shoot extensions. The phytohormone S helps in breaking the dormancy of seeds and buds. What are P, Q, R and S? Give one reason each for your choice.

76. A potted plant having straight parts A and B was placed horizontally on its side as shown in Figure (i). After a few days it was observed that the parts A and B of the plant acquire new positions as shown in Figure (ii).

(a) Name the phenomenon exhibited by the position of plant parts A and B in Figure (ii)

(b) Name the stimulus (other than sunlight) which causes plant part A to grow and bend upwards, and plant part B to bend downwards.

77. When the leaves of a sensitive plant are touched with a finger, they fold up and when light fades at dusk, the petals of a dandelion flower close.

(a) State one way in which the above two processes are similar.

(b) State two ways in which the above two processes differ.

Answers:

69. (a) P is auxin hormone (b) In shade (c) (i) Decreases the rate of growth of root (ii) Increases the rate of growth of stem (d) (i) Positive phototropism (ii) Negative phototropism (e) Plant hormones; Gibberellin 70. (a) Root (b) Stem (or Shoot) (c) X (d) Y (e) Auxin 71. (a) (i) Photonasty (ii) Photonasty: (b) (i) Dandelion flower (ii) Moonflower (c) Thigmonasty (d) Sensitive plant (Mimosa pudica) (e) A j and B 72. (a) Water (b) Gravity (c) Light (d) B and C; Gravity and Light (or Sunlight) 73. (a) (i) Leaf tendril (ii) Stem tendril (b) Thigmotropism (c) Touch (of support) (d) Tropic movement (e) Organs like P (leaf tendrils): Pea plant; Organs like Q (stem tendrils) : Bitter gourd plant 74. (a) (i) Carpel (ii) Stamen (b) (i) Stigma (ii) Style (iii) Ovary (c) (i) Pollen grain (ii) Anther (d) Pollen tube (e) Chemotropism 75. P is abscisic acid; Q is auxin; R is gibberellin ; S is cytokinin 76. (a) Geotropism (b) Gravity 77. (a) Both are nasties (or nastic movements) (b) In the folding of leaves of sensitive plant, stimulus is touch but in the folding of petals of dandelion flower, stimulus is light; Folding of leaves of a sensitive plant is not a growth movement but the closing of petals of a dandelion flower is a growth movement.