Topic 1.7Limitation of sight

Limitations of sight

There are basically 2 types of limitations of sighta) Blind spotb)Optical illusion

Blind spota) Occurs when image falls on the blind

spot of the eye

Pg 29 – blind spot test

Optical illusion

a) Occurs when our brain can’t interpret what we see accurately

Monocular and Stereoscopic Vision

Monocular Visiona)Vision involving one eye onlyb)Animals of prey usually have such vision

to detect the presence of predator easilyc)Has wider vision

Stereoscopic Vision

a)Vision involving two eyesb)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

Devices to overcome limitation of sight

Microscope

Magnifying glass

Binoculars

Telescope

PeriscopeUltrasound

X-ray

Topic 1.9Responses and

Stimuli in Plants

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

shoot

root

stem

Why do climbing plants coil their tendrils around nearby objects?

tendrils

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)

Phototropism (light)

a) It is plants’ response towards lightb)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

Geotropism (gravity)

a) It is plants’ response towards gravityb)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

Hydrotropism (water)

a) It is plants’ response towards waterb)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

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

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.

Venus flytrap

Oxalis nastic movement

http://www.youtube.com/watch?v=ymnLpQNyI6g

http://www.youtube.com/watch?v=0V7_YT_RDh0

Stimuli and Responses in PlantsResponse 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.