The document describes how living organisms, including plants and animals, respond to environmental stimuli through various mechanisms and movements. It categorizes plant responses as tropic (directional) or nastic (non-directional) and explains specific types like phototropism, geotropism, hydrotropism, chemotropism, and thigmotropism, each responding to different stimuli. Additionally, it discusses the role of phytohormones in regulating plant growth, development, and physiological responses.

2.  All living organisms respond to environmental stimuli.
 Animals have nervous system and endocrine system for
control and coordination.
 Plants also respond to stimuli by secreting chemicals.
 Plants exhibit some movements.

3. Movements
of Plants
Directional
or Tropic
movements
Non-directional
or Nastic
movement
Occur in the
direction of the
stimulus
Non growth
movement,
independent of
stimulus

4.  The movements do not
depend on the direction
from the stimulus acts.
 Example - when someone
touches the leaves of
mimosa, the leaves begin to
fold up and droop.

5. Leaves before touching Leaves after touching

6.  The drooping of Mimosa leaves
is independent of the direction
from which the leaves are
touched.
 Such movements usually
happen due to change of water
balance in the cells.
 When leaves of mimosa are
touched, the cells in the leaves
lose water and become flaccid
which results drooping of
leaves.

7.  Plants respond to stimuli
slowly by growing in a
particular direction.
 Example - Plants like the
pumpkin, cucumber etc.
plant climb up fences by
means of tendrils.

8. Types of Trophic movements
Phototropism (light)
Geotropism (gravity)
Hydrotropism (water )
Chemotropism (chemicals)
Thigmotropism (touch)

9.  Phototropism is the growth
of plants in response to light.
 Positive phototropism –
Shoots respond by bending
towards light.
 Negative phototropism -
Roots respond by bending
away from light.
Phototropism
Response of the plant to
the direction of light

10. Geotropism
 Geotropism is the
movement of a plant in
response to gravity (either
downwards or upwards).
 Positive geotropism – Roots
grow towards the ground
 Negative geotropism -
Shoots by growing away
from the ground.
Plant showing Geotropism

11. Hydrotropism
 Hydrotropism is a growth
response in which the
direction is determined by
the stimuli of water.
 Example - Roots grow
towards the source of water.
Plant showing
Hydrotropism

12.  Chemotropism is a
growth movement of a
plant part in response to
chemical stimulus.
 Example - Growth of
pollen tubes towards
ovules
Flower showing
Chemotropism

13.  Thigmotropism is the
directional growth of a
plant part in response to
the touch stimulus of an
object.
 Climbers produce tendrils
which move towards a
source of support in order
to coil around it and help
the plant to climb.
Thigmotropism
Plant showing
Thigmotropism

14.  Plants hormones, also called Phytohormones, are
chemicals produced within the plant in a low
concentrations and diffuse all around the cell.
 Phytohormones regulate plant growth,
development and response to the environment.

15. Types of Phytohormones
Auxins
Gibberellins
Cytokinins
Abscisic acid
Ethylene

16.  Auxins are synthesised by the growing apices of the stem
and root.
 It promotes cell elongation and growth of stem and root.
 It causes apical dominance.
 It induces rooting on stem cutting.
 Gibberellins are hormones that help in the growth of
the stem, seed germination, bolting, and flowering.
 It induces parthenocarpy.
 It’s application overcomes the genetic dwarfism.
 It breaks up the dormancy of seeds.

17. Cytokinins are hormones present in the areas of rapid
cell division, such as fruits and seeds.
 It promotes cell division and cell enlargement.
 It promotes the germination of seeds.
Abscisic acid is a hormone that inhibits the growth in
various parts of plants.
 It inhibits cell growth and cell division.
 It causes dormancy of buds and seeds.
 It induces wilting of leaves and closure of stomata.
Ethylene is a gaseous plant growth regulator.
 It plays role in ripening of fruits.