Saturday, March 5, 2011

Science Form 2 : World Through Our Senses

1.1 Sensory Organs and Their Functions

1.2 Sense of Touch

1. Skin is the sensory organ that can detect touch, pain, pressure, heat and cold
2. Consists of 3 main layer:
    a) epidermis – outer layer
    b) dermis – inner layer
    c) fatty layer - insulator
3. Structure of human skin

4. Function of different receptors:
    a) pain receptors - detect pain
    b) touch receptors - detect light touches
    c) heat receptors - detect heat
    d) cold receptors - detect cold
    e) pressure receptors - detect pressure

1.3 Sense of Smell

1. Nose is the sensory organ for smell that can detect chemicals in the air.
2. Smell receptors located at the top of nasal cavity.
3. The nasal cavity lined with mucous that is important to dissolve chemicals
4. Structure of human nose.

5. Detection of smells
    => Chemicals in the air enter the nasal cavity, dissolved in in the mucus to stimulate smell receptors.
    => Smell receptord produce impulse and send the messages to the brain.
    => Brain interprets the messages
    => Smell identified

1.4 Sense of Taste

1. The tongue is sensory organ related to the sense of taste
2. 4 basics taste: sweet, salty, sour and bitter

3. The surface of tongue covered with taste buds.

4. Each taste bud contains many taste receptors.
5. Saliva dissolve chemicals to be detect by taste receptors
6. Sense of taste is helped by sense of smell

1.5 Sense of Hearing

1. Ears are the sensory organs of hearing that can detect sound.
2. Human ears has 3 main parts:
    a) Outer ear; pinna, ear canal, eardrum
    b) Middle ear; ossicles (hammer, anvil & stirrup), oval window and Eustachian tube.
    c) Inner ear; cochlea, auditory nerve and semicircular canals.

1.6 Sense of Sight

1. Sensory organs for sight are the eyes, which sensitive to light.
2. The wall of the eyeball is made up of 3 layers:
    a) Sclera – tough, outer layer
    b) Choroid – black, middle layer
    c) Retina – sensitive to light, innermost layer


1.7 Understanding light and sight

1.7.1 Reflection and refraction of light
1.  Take place when light rays fall on the surface of an opaque object and bounce off it.
2.  Plane mirrors and shiny metals are good light reflectors
3.  Flat and smooth surface reflects light in regular patterns (regular reflection)

4.  Irregular surfaces like paper and cloth will reflects scattered in different directions of reflected light.(diffused reflection)

5.  The law of reflection states:
     i) angle of incidence = angle of reflection
                                 i = r
    ii) Incident ray, reflected ray and normal are at the same plane

6.  Applications of the reflection of light
   . a) Periscopes – used in submarines
     b) Kaleidoscope
     c) Mirrors
7.  Refraction of light occurs when light travels through different media at certain angle
8.  Refraction occur when the speed of light changes
9.  The speed of light decreases when light enters a denser medium
10.The speed of light increases when light enters a less dense medium
      A) From less dense to a denser medium
           i) The light refracted towards the normal
          ii) Angle of incident is bigger than the angle of refraction

     B) From Denser to a less dense medium
          i) The light refracted away from normal
         ii) Angle of incident is smaller than the angle of refraction

11. Phenomena of the refraction of light:

1.7.2 Vision defects and ways to correct them

1. Normal vision can see close and near objects clearly
2. The thickness of the lens is changed when looking at near or distant object
3. Focusing object:

4.Short-sightedness (myopia)
   a) See near objects clearly but distant objects are blurred.
   b) The lens is too thick
   c) The eyeball is too long

5. Correcting short-sightedness

6. Long-sightedness (hypermetropia)
    a) See distant objects clearly
    b) Can’t focus on near object
    c) The eye lens too thin
    d) Eyeball too short

7. Correcting long-sightedness

8. Comparison between short-sightedness and long-sightedness

9. Astigmatism
    - Caused by the irregular surface of the cornea or lens not evenly curved
    - Image cannot be focused at same time
    - Image formed distorted and not clear.
    - Can be corrected by wearing cylindrical lenses

1.7.3 Limitation of sight
         A. Blind spot - the point where the optic nerve enters the retina; not sensitive to light
         B. Optical illusions
              - Caused by disturbances to the impulses going to the brain
              - The brain cannot interpret accurately the information sent bye eye.
         C. Stereoscopic and monocular vision
              i) Stereoscopic vision
                 - Both eyes in front of the head
                 - Overlapping
                 - Smaller field of vision
                 - Give 3 dimensional (3D), can estimate distance accurately
                 - Most predators and human

              ii) Monocular vision
                 - One eye at each side of the head      
                 - Do not overlap
                 - Wider field of vision
                 - Does not give 3D view, cannot estimate distant accurately.
                 - Most prey

1.7.4 Device to overcome limitation
         - Example of device to overcome limitation of sight:

      Magnifying glass                                                                 Binocular


1.8 Understanding sound and hearing

1. Properties of Sound
    - Sound is form of energy
    - Produced by vibrations
    - When and object vibrates, kinetic energy is changed to sound energy.
    - Medium (solid, liquid, gas) is needed for sound to travel.
    - Sound cannot travel through vacuum.
    - Sound can be reflected by hard and smooth surfaces. (metal, glass, brick wall)
    - Reflection of sound is called echoes
    - Soft and porous surface can absorb sound. (carpets, curtains, cotton, sponge
2. Hearing defects
    - temporary loss - the earwax in the auditory canal block sound waves.
    - total hearing loss - ossicles fused together, damaged cochlea by local infections or by
      exposured to loud sound.
3. Ways to rectifying hearing defects
    - uses syringes and warm water to remove wax
    - puntured eardrum can be repair by surgery
    - implanted electronic gadget

4. Limitation of Hearing

5. Ways to overcome hearing limitations

                Earphones                                                 Stethoscope                        

                                                                         Loud Speaker

6. Stereophonic hearing
    - Ability to hear using both ears
    - Enables to detect the direction of the sound accurately
    - Important for the survival of animals especially for prey

1.9 The stimuli and responses in plants

1. Two types of responses: tropism and nastic movement.
     A. Tropism
          - Growth response in a particular direction
          - Occurs slowly, not noticeable
          - 4 types :
             i) Phototropism – light
                - Response of plant towards light
                - Shoot grow towards light (positive phototropism) while root grow away light 
                  (negative phototropism)

             ii) Geotropism – gravity
                 - Response of plant towards gravity
                 - Roots grow downwards (positive geotropism) and shoot grow upwards (negative geotropism)

             iii) Hydrotropism – water
                  - Response of plant towards water
                  - Root grow towards water (positive hydrotropism) and shoot grow away from water (negative hydrotropism)

             iv) Thigmotropism – touch or contact
                 - Plant response towards touch or contact
                 - Root grow away from solid objects such as stones
                 - Stem or tendrils grow towards the objects that come into contact with.

     B) Nastic Movements
         - Response part of plant towards touch, light and heat
         - Does not depend on the direction of the stimulus
         - Movement is reversible
         - Example: Mimosa pudica, Venus fly trap

2. Importance of plant responses
    - To ensure plant get their basic need.
    - Plant depend on phototropism to get sunlight for photosynthesis.
    - Geotropism and hydrotropism enables the plant to obtain water and minerals salt.

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Sathish Rajan said...

very helpful

Ng Zhi Wei said...

Best notes in history

John Wick said...

Two types of responses: tropism and nastic movement. gladys

Pavi Pavithran said...


雯雯1220 BChrisJW said...

best notes ever

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