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PUSAT TUISYEN TELITI 25, Jalan SS 22/11, Damansara Jaya, 47400 Petaling Jaya, Selangor 03-77254002 FORM 3 KSSM SCIENCE CHAPTER 1 COMPREHENSIVE NOTES & TUTORIAL WALTER AARON WONG BSc,...

PUSAT TUISYEN TELITI 25, Jalan SS 22/11, Damansara Jaya, 47400 Petaling Jaya, Selangor 03-77254002 FORM 3 KSSM SCIENCE CHAPTER 1 COMPREHENSIVE NOTES & TUTORIAL WALTER AARON WONG BSc, MSc, MRSB NAME : CLASS :  ABOUT TUTOR WALTER AARON WONG BSc, MSc, MRSB Mr Walter graduated with a BSc (Hons) and MSc in Microbiology from Universiti Kebangsaan Malaysia (UKM). He is currently pursuing his PhD in the same field in Universiti Malaya (UM), conducting research work in waterborne infectious diseases. He is also a member of the Royal Society of Biology in the UK. Mr Walter has also won several awards in scientific communications and was an invited speaker in the ASEAN Emerging Researchers Conference in year 2019 under ASEAN Young Scientists Network, Akademi Sains Malaysia. Mr Walter has 8 years of teaching experience in PT3 / SPM / IGCSE Chemistry and General Science. He makes learning science fun and constantly engages with students during his lessons. CHAPTER 1: STIMULUS AND RESPONSES The Human Nervous System 1. The nervous system is one of the systems found in humans. 2. The human nervous system consists of a network of nerve cells 3. The human nervous system is divided into two parts: Central nervous system (CNS) Peripheral nervous system (PNS) 4. The function of the nervous system is to detect stimuli and send information in the body as well as coordinate body activities. Diagram 1.1: The human nervous system 5. How does the human nervous system work? Imagine someone presses the doorbell. You will be able to hear the bell ringing. In this case, sound is the stimuli. How does your brain react to the sound? The sound that you heard is detected by your ears. Your ear is called the sensory organ. Sensory organs have only 1 function, which is to detect stimuli. The ear will then generate nerve impulse (electrical signal) to the brain The brain then decides what to do by sending a new nerve impulse (electrical signal) to effector to carry out an action.  In this case, the muscles are the effectors. We will use our muscles to walk over to the door and open the door for the person who rang the bell. Walking over to the door and opening the door is known as a response. Here is another example: Imagine, when you look up into the sky and the sun is glaring at you. Your eyes close immediately because of the bright light. Why does this happens?  When too much light (stimulus) enters your eyes, the eyes sense it and sends nerve impulses (electrical signals) to the spinal cord. The spinal cord then sends new nerve impulses (electrical signals) to the muscles on your eyes to close so that lesser light can enter. 6. The brain coordinates many responses every day. 7. There are two types of responses: Voluntary responses (can be controlled by the brain) Involuntary responses (cannot be controlled by the brain) *voluntary responses are also known as voluntary actions *involuntary responses are also known as involuntary actions 8. Example of a voluntary action: 9. Example of an involuntary action: 10. Voluntary actions and involuntary actions are very important in our daily lives. 11. We depend on voluntary actions to carry out our daily tasks. 12. We depend on involuntary actions to survive. Activities in Class to Show the Importance of Voluntary & Involuntary Actions Catching a ruler (voluntary action) Changing size of pupils in our eyes in response to light Stimuli and Reponses in Humans 1. A sensory organ is an organ that detects stimuli. 2. Humans have 5 sensory organs which are the skin, nose, tongue, ears and eyes 3. The ability to sense is the ability of sensory organs to detect stimuli. 4. Each sensory organ is responsible for a different sense. 5. Therefore, humans have five senses which are touch, smell, taste, hearing and sight. Eyes and the Sense of Sight 1. The eye is the sensory organ sensitive to light. 2. We can see the beautiful things around us because we have eyes to detect lights of different colours. 3. The wall of the pupil eyeball consists of three layers: Sclera (outer layer) Choroid (middle layer) Retina (innermost layer) 4. How do we see? The flowchart below will show you how we are able to see the things around us. Ear and the Sense of Hearing 1. Ear is a sensory organ that detects sounds and gives us the sense of hearing. 2. We hear hundreds of different sounds each day. 3. The human ear is divided into 3 major sections: Outer ear, middle ear and inner ear 4. How exactly do we hear sounds? The flowchart below will show you the mechanism of hearing. 5. As a person grows older, their sense of hearing will be weaker. 6. This could be due to the eardrums becoming less elastic so it cannot vibrate as well as it used to. Nose and the Sense of Smell 1. There are thousands of chemicals in the air that we breathe in each day. 2. Some of these chemicals, when dissolve in the mucus on our smell receptors in the nose, will enable us to smell. 3. The nose is a sensory organ that is sensitive to smell. 4. Besides being a sensory organ, the nose also allow air to pass through it to enter our lungs for respiration. 5. There are hairs in the nose that traps dust and microorganisms. 6. How do we smell? The flowchart below shows the mechanism of smell. 7. Have you ever wondered why we cannot smell properly when we have a cold or flu? 8. When we have flu, too much mucus on the smell receptors will prevent the receptors from detecting the chemicals as air flows through. The Tongue and the Sense of Taste 1. The tongue is a sensory organ that gives us the sense of taste. 2. The surface of the tongue is covered with taste buds. 3. Each taste bud contains many taste receptors. 4. Taste receptors are sensitive to the chemicals in food. 5. The tongue has 5 types of taste receptors: Sweet Sour Salty Bitter Umami (savoury taste) 6. These taste receptors are distributed all over the tongue. 7. This means that the ability to taste is not restricted to a single part of the tongue. 8. The higher the number of taste buds that you have, the more number of taste receptors on your tongue. 9. This means that people with higher number of taste buds are more sensitive to taste and can taste food better. 10. How do we taste food? The flowchart below will show you the mechanism of tasting: Skin and the Sense of Touch 1. The skin is a sensory organ that detects touch. 2. There are thousands of receptors on the skin. 3. These receptors are sensitive to certain stimuli such as: Pain Touch Temperature Pressure 4. The diagram below will show you the cross-section of the human skin and their various receptors. 5. The skin on different parts of the body has different degrees of sensitivity. 6. The parts of the skin that are very sensitive to the touch stimuli are the fingertips, the back of the neck, lips and ear pinna. 7. Parts of skin that are less sensitive to the touch stimuli are the elbow and knee. 8. The sensitivity of the skin depends on: a) The number of receptors present The higher the number of receptors present, the more sensitive the skin. The nearer the receptors are to each other, the more sensitive the skin is to stimuli b) The thickness of the epidermis The thinner the epidermis, the more sensitive the part of the skin 9. Blind people can read Braille by feeling the surface of the paper, due to the high sensitivity of their fingertips. 10. Injections are usually given on the forearms and buttocks because the skin in these areas are less sensitive to touch and pain compared to the skin on other parts of the body. Limitation of Senses 1. Humans cannot see bacteria with the naked eyes, neither can we see the surface of moon clearly. 2. This means our sense of sight has limitations. 3. The limitation of senses is the limitation of our body to detect stimuli. 4. Sometimes, the limitation of senses is due to the defects in the sensory organs or the process of ageing which affects hearing and sight in humans. 5. Let us explore the limitations of sight and hearing. Limitation of Sight There are two types of limitations of sight, they are, optical illusions and blind spots. Optical illusion 1. Optical illusions make what we see different from the true situation. 2. The brain cannot make accurate interpretations of the information sent by the receptors in the eye. 3. Figure 1.16 below shows a few examples of optical illusions The blind spot 1. The eyes cannot detect an image that falls on the blind spot. 2. The blind spot is the part of the retina that is not sensitive to light. 3. Image cannot be seen because the blind spot does not have photoreceptors. 4. What causes limitation of sight? 5. Limitation of sight can be caused by the following factors: Defective eyes Ageing 6. For a person with normal vision, light which enters the pupil falls on the retina. 7. Conditions that affect vision include: short-sightedness long-sightedness astigmatism presbyopia. 8. To solve the problem above, corrective measures can be taken to restore a clear vision. Limitations of Hearing 1. Similar to the sense of sight, the sense of hearing also has its limitations. 2. Human can only detect sounds in the frequency range of 20 Hz to 20 000 Hz. 3. What causes hearing to be affected? Ossicles in the middle ear fused together due to infection Inelastic eardrum due to ageing  Constant exposure to sounds and loud music can damage the sound receptors in the cochlea. 4. Can limitations of hearing be overcome? 5. There are several ways to improve the sense of hearing. 6. A person who has partial hearing loss can still hear with corrective measure but if a person is completely deaf, corrective measures cannot be used. 7. A person’s hearing can be improved through surgery or by wearing a hearing aid. A hearing aid can amplify the sound to make a person hear better Technology and Inventions to Overcome Limitations of Senses 1. There are also many other instruments to overcome limitations of sight and hearing. 2. Some of the instruments created by scientist to overcome limitations of sight and hearing can be seen below: Stimuli and Response in Plants 1. Plants respond to light, gravity, water and touch stimuli. 2. There are two types of responses: tropism and nastic movements. 3. Tropism (a) is a growth response in a direction (b) involves certain parts in a plant, for example, shoot and root (c) affects the direction of the responses, which depends on the direction of the stimuli 4. Tropism can be divided into positive tropism and negative tropism. 5. Plants responses are very important to ensure the continuity and survival of plants. The Importance of the Responses Towards Stimuli in Other Animals 1. Carnivores and herbivores have different types of vision. 2. Carnivores have stereoscopic vision while herbivores have monocular vision. Stereophonic and Range of Hearing in Animals 1. Humans can only detect sound in the frequency range of between 20 Hz until 20 000 Hz. 2. Animals have different range of hearing frequencies. 3. Animals have sensory organs that ensure its survival on the Earth. 4. Different adaptations of animals allow different types of animals to survive in the environment.