This document discusses limitations of sight, types of vision, and stimuli and responses in plants. It covers: 1) Two types of limitations of sight - blind spots and optical illusions. 2) Two types of vision - monocular vision involving one eye and stereoscopic vision involving two eyes. 3) Four types of tropic responses in plants - phototropism, geotropism, hydrotropism, and thigmotropism which are responses to light, gravity, water, and touch respectively.

2.  Limitations of sight
 There are basically 2 types of limitations of sight
a) Blind spot
b) Optical illusion
 Blind spot
a) Occurs when image falls on the blind spot of
the eye
Pg 29 – blind spot test

3.  Optical illusion
a) Occurs when our brain can’t interpret what we
see accurately

8.  Monocular and Stereoscopic Vision
 Monocular Vision
a) Vision involving one eye only
b) Animals of prey usually have such vision to
detect the presence of predator easily
c) Has wider vision

9.  Stereoscopic Vision
a) Vision involving two eyes
b) Animals of predator usually have such vision to
enable them to estimate distance accurately
c) Can view objects in 3 dimension too
Distance finger test

10.  Devices to overcome limitation of sight
Microscope Magnifying Binoculars Telescope
glass
X-ray Ultrasound Periscope

12. shoot
Why do shoot grows upwards
and towards the sun while
stem roots grow downward and
towards water in soil?
root

13. Why do climbing plants coil their
tendrils around nearby objects?
tendrils

14.  Tropic responses
 Tropic responses are responses by plants towards
stimulus and is dependent on the direction of
stimulus.
 4 types of tropic responses:
a) Phototropism (light)
b) Geotropism (gravity)
c) Hydrptropism (water)
d) Thigmotropism (touch)

15.  Phototropism (light)
a) It is plants’ response towards light
b) Shoot shows positive phototropism (move
towards light)
c) Root shows negative phototropism (move away
from light)
d) It is to allow shoot to get more sunlight for
photosynthesis

16.  Geotropism (gravity)
a) It is plants’ response towards gravity
b) Shoot shows negative geotropism (move upwards)
c) Root shows positive geotropism (move downwards)
d) It is to allow root to get water and for support

17.  Hydrotropism (water)
a) It is plants’ response towards water
b) Shoot shows negative hydrotropism (move away
from water)
c) Root shows positive hydrotropism (move towards
water)
d) It is to allow root to get water
water in
soil

18.  Thigmotropism (touch)
a) It is plants’ response towards touch when in
contact with objects
b) Take place in tendrils of plant when wrapping
around the object
c) Stems and tendrils exhibit positive
thigmotropism
d) Function is to reach a higher position to obtain
sunlight. It also serves as support to plants
e) Usually in climbing plants

19.  Nastic movements
 Nastic movements are responses by plants towards
stimulus and is not dependent on the direction of
stimulus.
 There are many stimuli that can cause nastic
movements such as light (photonasty), touch
(thigmonasty), temperature (thermonasty) etc.
http://www.youtube.com/ http://www.youtube.com/
watch?v=ymnLpQNyI6g watch?v=0V7_YT_RDh0
Venus flytrap Oxalis nastic
movement

20. Stimuli and Responses in Plants
Response Stimulus Root response Shoot response Function
Phototropism Light Negative Positive Obtain light
Geotropism Gravity Positive Negative Obtain water and mineral
salts
Hydrotropism Water Positive Negative Obtain water and mineral
salts
Thigmotropism Touch - - Obtain protection, support &
light
Nastic movement does not depend on the
direction of stimulus. Examples of plant
with nastic movement are mimosa pudica
and Venus flytrap.