Chemical Coordination in Plants

Question 1

define stimuli

Answer 1

changes either in the external or internal environment of an organism

Question 2

define responses

Answer 2

the resulting actions caused by stimuli

Question 3

define hormones

Answer 3

they are produced in one area of a plant, transported around the body of the plant and have their effects at a location far away from the site of their production. they work as messengers.

Question 4

main areas of growth/cell division in plants

Answer 4

meristems (just behind the tip of a root or shoot)

Question 5

hormones of plants are called

Answer 5

phytohormone

Question 6

define auxin

Answer 6

powerful growth stimulants, effective at low concentrations. they are present in more actively growing regions.

Question 7

main natural auxin found in plant

Answer 7

IAA (indole 3-acetic acid)

Question 8

functions of auxins

Answer 8

1. promote growth of stem, root, fruits by cell elongation. (hormone induces cell wall loosening)
2. delay leaf senescence(falling)
3. promote growth of apical buds, and inhibit lateral buds
4. induce rooting in the cutting of plants like rose
5. induce fruit formation without fertilization, like apples and tomatoes

Question 9

define apical dominance

Answer 9

suppression of growth of lateral buds by apical buds

Question 10

define parthenocarpy

Answer 10

development of fruits without fertilization, brought about by auxins

Question 11

formula of Gibberellic acid

Answer 11

GA3

Question 12

location of gibberellins

Answer 12

meristematic regions like stem apex, root apex, buds, seeds

Question 13

functions of gibberellins

Answer 13

1. promote growth of internodes by stem elongation
2. break seed dormancy and initiate germination
3. induce parthenocarpy
4. delay senescence
5. enhance longitudinal growth of internodes in dwarf plants

Question 14

location of cytokinins

Answer 14

produced in root tips and transported through xylem.
found in germinating seeds, developing fruits, embryo.

Question 15

functions of cytokinins

Answer 15

1. stimulate plant growth by cell DIVISION (even in non-meristematic tissues)
2. expansion of cotyledons in seeds
3. break seed dormancy
4. promote chlorophyll synthesis
5. delay senescence
6. INHIBIT apical dominance

Question 16

only hormone which is a gas at ordinary temperature

Answer 16

ethylene

Question 17

site of synthesis and action of ethylene

Answer 17

produced in fruits, and stay in same fruit (more ethylene produced in meristematic tissues)

Question 18

functions of ethylene

Answer 18

1. reduction in cell elongation!
2. acceleration of senescence
3. ripening of fruits
4. promoting root growth
5. initiate germination
6. inducing flowering in mango

Question 19

most widely used plant growth hormone in agriculture

Answer 19

ethylene

Question 20

define abscisic acid (ABA)

Answer 20

growth retarding hormone found in angiosperms, gymnosperms, pteridophytes, mosses.

Question 21

location of ABA

Answer 21

chloroplasts of leaves

Question 22

functions of abscisic acid

Answer 22

1. plant growth inhibitor by slowing down metabolism
2. induces seed dormancy
3. accelerates senescence (ageing) and abscission (falling) of leaves, flowers
4. stimulates closure of stomata and increases tolerance

Question 23

difference between senescence and abscission

Answer 23

senescence: ageing
abscission: falling

Question 24

stress hormone

Answer 24

abscisic acid (increases tolerance to stress)

Question 25

define tropism

Answer 25

the direction of response is related to direction from which stimulus comes. such a response is called tropism

Question 26

define tropic movement

Answer 26

growth movements occurring in response to unidirectional external stimuli in a plant part

Question 27

define phototropism

Answer 27

movement towards light

Question 28

how do auxins play an important role in phototropism

Answer 28

help in bending a shoot towards source of light, by getting accumulated in the part of the shoot which is not facing the light. promotes cell elongation in this area, causing shoot to bend towards source of light

Question 29

define geotropism

Answer 29

growing towards the earth's gravity (AKA gravitropism)

Question 30

how can geotropism be demonstrated in the lab

Answer 30

clinostat

Question 31

define hydrotropism

Answer 31

movement of plant parts in response to water or moisture

Question 32

define thigmotropism

Answer 32

growth movement of plant parts in response to touch stimulus

Question 33

how does thigmotropism work

Answer 33

stimulus is perceived by tendril tips and is then transmitted to basal parts. entire tendril becomes sensitive to stimulus.

Question 34

define chemotropism

Answer 34

growth of plant organs in response to chemicals

Question 35

sunflowers exhibit what kind of tropism

Answer 35

heliotropism