[Science Form 2] Eye On Defects

A person with normal vision sees distant and close objects clearly. To maintain a clear image of the object on the retina, the thickness of one's eye lenses changes, in a process called accommodation.


However, for some people, clear vision is not achieved because of defects. Common vision defects are:

1. Short-sightedness (myopia)
2. Long-sightedness (hypermetropia or hyperopia)
3. Astigmatism
4. Colour-blindness
5. Lack of accommodation (presbyopia)

********************

1. Short-sightedness (Myopia)

People with myopia are not able to clearly see objects that are far away. This is because light rays focus in front of the retina, a result from the fact that eye is not able to focus light rays further back, despite maximum flattening of its lenses. Short-sightedness mainly affects a person's ability to look at distant objects where the light rays come straight (or parallel) into the eyes.

Short-sighted eye

Corrected short-sightedness

Short-sightedness is corrected by using glasses with concave lenses, which diverge light rays before they enter the eye.


2. Long-sightedness (Hypermetropia or Hyperopia)

People who are long-sighted can clearly see objects that are far away, but they have trouble seeing objects near them. If you are long-sighted, near objects may be so blurry that you cannot do tasks such as reading or sewing. Long-sightedness occurs when the eye does not bend light correctly. This causes the image of an object to focus behind the retina, instead of directly on it, thus resulting in a blurred image.

Long-sighted eye

Corrected long-sightedness

Long-sightedness is corrected by using glasses with convex lenses, which converge light rays.

3. Astigmatism

Astigmatism is caused by an irregular surface of the cornea, or a lense that is not evenly curved. As a result, the vertical and horizontal rays from the image cannot be focused at the same time. Both images may fall short of the retina, or one before the retina while the other behind it. Hence, terms such as compound hyperopic, compound myopic or mixed astigmatism. A person suffering from astigmatism may see certain parts of an object more clearly than others.

Astigmatic eye

Corrected astigmatism

Astigmatism can be corrected by either wearing glasses with cylindrical lenses, or surgery.

4. Colour-blindness

To understand what causes colour-blindness, you need to know about the cone cells or colour receptor cells in your eyes. These cone cells are on your retina, an area the size of a postage stamp that is at the back of your eye.

You have red, blue and green cones, which are sensitive to those colours and combinations of them. You need all three types to see colours accurately. When your cones do not work properly, or you do not have the right combination, your brain does not get the right message about which colours you are seeing. To someone who is colour-blind, a green leaf might look tan or grey. This defect cannot be corrected because it is hereditary.


5. Lack of Accommodation (Presbyopia)

The term presbyopia means "old eye" and and is a vision condition involving the loss of the eye's ability to focus on both near and far objects. It is a condition that occurs as part of normal aging, because when a person get older, one's eye lense becomes harder and less elastic. The muscles in the ciliary body also loss their ability to contract and relax. Presbyopia occurs gradually over a number of years and is usually noticeable by age 40-45.

Presbyopia is corrected by wearing glasses with bifocal lenses to see near and far objects clearly.


*******************

[Science Form 2] Air Pressure

Since air has mass, the atmosphere pushes against all thing on Earth, including us! This "pressing down" of the atmosphere is called air pressure or atmospheric pressure.

Drinking through a straw

When you drink through a straw from an open glass of water, air pressure allow the water to travel up the straw. By sucking on the straw, you are reducing the air pressure inside your mouth.

While sucking in the straw, the air pressure in your mouth is less than the air pressure outside of the straw - in the room and in the glass. The outer air pressure pushes down on the water in the glass and this forces the water up the straw.

Can you predict what will happen if you put an airtight over the glass of water?

No matter how hard you suck, the water will not go up the straw. Why? Well, when air pressure on the water is blocked, there is no air pressure to help push the water up your straw. The air can't get to the water to push on it, so it doesn't go up the straw.



Unclogging the sink with a plunger

A plunger is made of a long stick and a bell-shaped, sturdy rubber cup on one end. The rubber cup of the plunger is set onto the draining hole of the sink to create a seal.

The plunger stick is then pushed down, inverting the rubber plunger cap and forcing the air that was in the plunger cap into the pipe.

The plunger is then pulled back, sucking air and water up with it, causing a vacuum. This abrupt force of air and water pressure helps loosen a clog in the pipes and gets the sink water draining again.

It may take several repeated motions of pushing and pulling back on the plunger to loosen the clog.

[Science Form 2] Experiments On Air Pressure At Home

Experiment!

Have you ever tried carrying out experiments on air pressure at home? Let's see how we can inflate a balloon inside a bottle.

Inflate a balloon inside a bottle? Is that possible?

All you need is a bottle, a bowl, some hot water, some ice-cold water and a balloon.

Now, let's start the experiment.

1. Fill the bottle with hot water.
2. Fill the bowl with the ice-cold water.
3. Let both sit for one minute.
4. Empty out the bottle.
5. Stretch the balloon over the mouth of the bottle.
6. Set the bottle in the bowl of cold water.

This is what you would observe... an inverted inflated balloon in the bottle!

How do we explain this phenomena?

First of all, air contracts and takes up less room when cooled. Similarly, it expands when it gets hot. The hot water heats the bottle. When the bottle is poured out, the heated bottle then heats the air in it. When the bottle is placed in the bowl of cold water, the air inside the bottle cools and contracts, causing the air pressure inside the bottle to decrease. When this happens, the higher air pressure outside the bottle causes the air outside to be drawn in, pulling the balloon in and inflating it inside the bottle.

[Science Form 2] Difference Of Acids & Alkalis

Scientists use something called the pH scale to measure the strength of an acidic or alkaline liquid. Although there may be many types of ions in a solution, the pH focuses on the concentration of hydrogen ions (H⁺) and hydroxide ions (OH^-). The scale goes from values very close to 0 through 14.

Distilled water is 7. Acids can have a pH of between 0 and a number very close to below 7, while alkalis have a pH of between a number very close to above 7 and 14.

Most of the liquids we find every day have a pH near 7. They are either a little below or above that mark. If we go into a chemistry lab, we could find solutions with a pH of 1 and others with a pH of 14.

There are also very strong acids with pH values of below 1, such as battery acid. Alkalis with pH values of near 14 include drain cleaners and sodium hydroxide (NaOH). These chemicals are corrosive and very dangerous.

Also you can easily tell if a substance is an acid or not by its effect on litmus paper. Blue litmus paper is used for testing acids. If wet blue litmus paper turns red, the substance is acidic. Wet red litmus paper is used to test alkalis, which will turn the paper blue.

Properties of acids and alkalis that distinguish them from other substances

Acids

• have a sour taste and feel like water.
• turn litmus solution red, as well as turn blue litmus paper red.
• have pH numbers less than 7.
• react with metals, forming hydrogen and a salt.
• react with carbonates, forming a salt, water and carbon dioxide.
• react with alkalis, forming a salt and water.

Alkalis

• feel soapy to touch and taste bitter.
• turn litmus solution blue, as well as turn red litmus paper blue.
• have pH numbers greater than 7.
• react with ammonium compounds to give off ammonia gas (except for ammonia).
• react with acids, forming a salt and water.
• do not react with metals and carbonates.

[Science Form 2] Importance Of Biodiversity

Biodiversity is not only important to the environment, but also to the well-being of Man.

Importance of biodiversity to Man.

1. Raw materials.
   Many plants and animals provide various goods of products to humans, many of which play important roles in human economies.
   
   
2. Food
   Plant and animal diversity provides a variety of food for Man.
   
   
3. Medicines and herbs
   Many plants are rich sources of traditional and modern medicines. These are used to treat and prevent diseases.
   
   
4. Genetic diversity
   The wealth of gene pools increases diversity in future generations. Eg: for better crops.
   
   
5. Ecology
   All species are supported by the interactions among other species, each providing an ecological value to another such as pollination, nutrient cycling and also the regulation of the atmosphere and climate.
   
   Plant and trees provide oxygen to the atmosphere; wetlands and forest provide clean water through filtration.
   

[Science Form 2] Diversity In Abundance

The variety of living organisms on Earth is known as biodiversity or biological diversity. Not only is it found in vertebrates, it also present in plants, invertebrates and microorganisms.

In addition, biodiversity exists at all levels of habitats and climates, such as forests, island, coral reefs, mountaintops and deserts.

Generally, there are three levels of biodiversity, and they are defined as below.

Genetic diversity

• The variation in genes within and between populations.

Species diversity

• The variation in the number and distribution of species within and between populations.

Ecosystem diversity

• The variation in habitats, communities and ecological processes within and between ecosystems.

Of the three levels, the common measure of biodiversity is species diversity.

Eg: The level of biodiversity in a forest is higher than that in a paddy field because a greater number of species can be found in a forest.

*******
Fact:
The number of known species on Earth is recorded at approximately 1.6 million, most of which are insects. However, the actual number of species on Earth may be up to 30 million.
*******

[Science Form 2] Experiment - Air Pressure

This is very interesting experiment. All you need is a hard-boiled egg, a bottle, and three matchsticks.

Here's what you do:

1. Make sure the mouth of the bottle is just small enough to keep the egg from falling inside.
2. Set the bottle on the table, and peel the egg.
3. Light the three matchsticks and drop them into the bottle.
4. Quickly place the egg over the mouth of the bottle.
   
   
   

This is what you would observe... the egg is sucked into the bottle.

1. Discuss with your partner how you would explain this phenomena and write it out.
Explanation: The lit matchsticks heat the air inside the bottle. When air is heated, it expands. As the heated air expands, some of it escapes out of the bottle. When the matches go out, the air inside the bottle cools and contracts, thus creating a lower air pressure inside the bottle than outside. The greater pressure outside the bottle forces the egg into the bottle.

2. Now, what would you do to get the egg out of the bottle?
Turn the bottle upside down and blow into it.

3. Explain your method.
The increased air pressure in the bottle will cause the egg to pop back out.

[Science Form 2] Different Stages For Water Treatment

1. Filtration
   
   • Here, the remaining substances and sediment pass through layers of sand filters and are removed.
     
     
2. Disinfection
   
   • In this tank, a small quantity of chlorine is added to the water to kill any remaining bacteria. A small amount of fluoride is also added to the water to help prevent tooth decay.
     
     
3. Coagulation
   
   • From the reservoir, water is pumped into this tank and mixed with slaked lime and alum. Alum makes the fine solid particles stick together and form larger solid lumps, and slaked lime reduces the acidity of the water.
     
     
4. Reservoirs
   
   • River water is pumped here and left for several days. During that time, sunlight kills most of the dangerous bacteria in the water. Mud, silt and other suspended substances will sink to the bottom and a metal screen removes large solid particles from the water.
     
     
5. Storage
   
   • Water that has been treated enters these tanks before being pumped into the supply ponds, which are usually found on hilltops or at higher levels. From the supply ponds, water flows through pipes to houses.
     
     
6. Sedimentation
   
   • The water then flows very slowly into these tanks, where the larger lumps sink to the bottom of the tank and are then removed.

[Science Form 2] Water

Water is perhaps the most important nutrient in our diets. In fact, a human adult needs to drink approximately two litres (8 glasses) of water every day to replenish the water that is lost from the body through the skin, respiratory tract, and urine.

However, 99.7% of the Earth's water supply is not usable by humans. This unusable water includes salt water, ice, and water vapour in the atmosphere.

Only fresh water, which is contained in rivers, lakes, and underground sources, can be used for human consumption. Furthermore, many freshwater sources are not suitable for human to drink.

Water containing dangerous microorganisms and large amounts of industrial waste or agriculture chemicals (eg pesticides) can be toxic and unfit for drinking. Hence, humans have a great need for a reliable source of clean fresh water for drinking.

In addition to the water needed for drinking, other uses of fresh water include household use (eg cooking and cleaning), industry, agriculture (eg irrigation), and recreation.

Hence, the quality of fresh water supply is important for virtually every aspect of our lives. Water that is supplied for domestic use must be treated to ensure it is clean.

The water supplied must meet the National Guidelines for the Quality of Drinking Water (1983), which is based on the World Health Organisation (WHO) Guidelines for the Quality of Drinking Water (1984).

[Science Form 2] Protecting Our Water Resources

Conservation is the sustainable use and management of natural resources, including wildlife, water, air, and earth deposits. Natural resources may be renewable or non-renewable.

The conservation of water involves ensuring that is not consumed faster than it can be replaced and ensuring that sufficient quantities are maintained for future generations to utilise.

Preservation, in contrast to conservation, attempts to maintain natural resources in their present condition. This is due to the concern that mankind is encroaching onto the environment through farming, industry, housing, tourism and other human developments, and that we are losing too much of what is 'natural'.

Our water resources are part of a fragile system, which is potentially at risk. Generally, conservation and preservation of water quality takes place in two arenas: surface water quality - lakes, streams, rivers and ponds - and groundwater quality.

A combination of poor soils unsuitable for septic systems, a high water table, and an increasing amount of rural development may begin to threaten the quality of an area's water supply.

Specific regulations, such as those pertaining to soil erosion and sedimentation control practices, protection of wetland areas, increased water body set backs, the use of greenbelts or buffers, and density reductions are among the techniques that can assist in protecting water quality.

In the long run, it is cheaper to protect our water resources than it is to try to restore them.

[Science Form 2] Two Important Solutions

Acids and alkalis are two important kinds of solutions.

Acid comes from the latin word acidus, which means "sharp" or "sour". Some of the acids can be found in:

• Lemons/lemon juice, which contains citric acid,
• Oranges, which contain ascorbic acids,
• Ant and bee stings, which contain methanoic acid,
• Tea, which contains tannic acid,
• Soft drinks, which contain carbonic acid,
• Vinegar, which contains ethanoic acid, and
• Our body, which contains small compounds called amino acids.

There are different strengths of acids. The number of H⁺ ions formed in the solution determines the strength of an acid.

Examples of strong acids: hydrochloric acid, sulphuric acid and nitric acid.

Examples of weak acids: ethanoic acid, citric acid and carbonic acid.

Alkali comes from the Arabic word al-qaliy, which means "the ashes". Alkalis are present in many cleaning substances used in our homes today, especially in kitchen cleaners like oven spray, floor cleaners and creams for sinks.

Kitchen cleaners are alkaline because they contain ammonia or sodium hydroxide, which attack grease. Other common alkalis include sodium hydroxide, potassium hydroxide, calcium hydroxide and ammonia.

There are different strengths of alkalis. The number of OH^- ions in the solution determines the strength of an alkali.

Some examples of strong alkalis are calcium hydroxide, sodium hydroxide and potassium hydroxide, while the most recognisable and common weak alkali is ammonia.

[Science Form 2] Acids vs Alkalis

Acids

• Taste: Sour.
• Touch: Like water.
• Tested with litmus paper: Turn blue litmus red.
• pH value: From 0 to less than 7.
• Reaction with metals: Form hydrogen and a salt.
• Reaction with carbonates: Form a salt, water and carbon dioxide.
• Reaction with ammonium compounds: No reaction.

Alkalis

• Taste: Bitter.
• Touch: Soapy.
• Tested with litmus paper: Turn red litmus blue.
• pH value: From above 7 to 14.
• Reaction with metals: No reaction.
• Reaction with carbonates: No reaction.
• Reaction with ammonium compounds: Give off ammonia gas.

Note: Strong acids and alkalis are corrosive and dangerous.

[Science Form 2] Neutralisation

The process in which an acid reacts with an alkali to form a neutral solution containing a salt and water is called neutralisation.

As an acid is added to an alkali, the pH of the solution decrease. The end point of neutralisation is when pH value of the solution is 7. When this happens, it means that the alkali has been neutralised.

The balance of acids and alkalis is crucial for our good health and for our environment. If one dominates too much over the other, all sorts of things can go wrong and life on earth would be in peril.

Acid rain, fish deaths from acid rain, dirty swimming pools, Legionnaire bacteria outbreaks and indigestion are examples of acids and alkalis being out of balance.

The following are the examples of the application of neutralisation in our daily life:

1. Shampoos are usually slightly alkaline. They neutralise the acidic oil that the skin secretes to keep our hair healthy and strong.
   
   
2. Hair conditioner, which is slightly acidic, neutralises the residue of shampoo on the hair and makes the hair smooth and shiny.
   
   
3. Bee stings are acidic. They can be treated with bicarbonate powder, which is a weak alkali.
   
   
4. Toothpastes are alkaline. They neutralise the acid produced by bacteria that act on the food in our mouth.
   
   
5. Plants grow well in soil that is neutral. Farmers add slaked lime to reduce the acidity in the soil.

Facts:

• The plant hydrangeas only produces pink or white flowers in an alkaline soil, and blue flowers in an acidic soil.
  
  
• In order to digest food and kill the kinds of bacteria and viruses that come with the food, the inside of our stomach is acidic. As we drink more alkaline water; more hydrochloric acid is secreted to maintain the acidic pH value in our stomach.

[Science Form 2] Food Chain & Size Of Population

Will a change in the size of one population affect another population in the same food chain?

Yes, it will. This is because populations within a food chain are inter-independent upon one another.

For example, where there are too many giraffes, there will be insufficient trees and shrubs for all of the to eat.

Hence, more giraffes will tend to starve or die. On the other hand, where there are a fewer giraffes, it means trees and shrubs in the area have more opportunity to grow to maturity and to multiply.

Fewer giraffes also means less food is available for lions to feed on and more lions may starve to death.

Hence, where there are a fewer lions, the giraffe population may increase.

[Science Form 2] Food Chain & Energy

In a food chain, energy is passed from one link to the other. When a herbivore eats, only a fraction of the energy that it gets from its food becomes new body mass; the rest of the energy is lost as waste or used to carry out its life processes, such as movements, digestion and reproduction.

When a herbivore is eaten by a carnivore, it passes only a small amount of its total energy to the carnivore. Of the energy transferred from the herbivore to the carnivore, some energy will be "wasted" or "used up" by the carnivore. The carnivore then has to eat many other herbivores to get enough energy to grow.

Because of the large amount of energy that is lost in each link, the amount of energy that is transferred through the links get less.

The further along the food chain you go, the less food there is, and hence, less energy remains available. In other words, a large mass of living things at the base is required to support a smaller number of consumers at the top of the link. Hence, many herbivores are needed to support a few carnivore.

[Science Form 2] Food Chain

A food chain demonstrates the feeding relationship between living organisms in an ecosystem.

It consist of a sequence of organisms starting with a producer (i.e. plants), followed by a primary consumer, the secondary consumer and ending with the tertiary consumer.

A simple food chain could start with the grass (producer), which is consumed by rabbits (primary consumer), who get consumed by foxes (secondary consumer).

Grass -> Rabbit -> Foxes

Sometimes, you may find that a food chain can appear more complex than the one above.

Take a look at the below illustration.

GRASS -> Grasshopper -> Rat -> Snake -> Hawk -> Mushroom -nutrient-> GRASS

After the hawk dies, fungi (like mushrooms and other decomposers break down the carcass and turn the remains of the hawk into nutrients, which are released into the soil.

The nutrients (with other factors like sunshine and water) will cause the grass to grow.

It's an interesting circle of life!

[Science Form 2] Types of Eye Defects

The eye can detect colours because of the cone cells in the retina at the back of the eye. These cells, if functioning properly, can detect the three primary colour:- red, blue and green, and combinations of them.

For someone who has colour-blindness, these cells do not work properly, resulting in their inability to see certain things in their actual colour.

A person who has hypermetropia/hyperopia/long-sightdness has blurred vision when looking at objects close to them, but clearer vision when looking at objects in the distance.

This is because images of the objects they are looking at are formed behind the retina. By placing a convex lense in front of the eye with this defect, this condition can be corrected.

On the other hand, a person who has clear vision when looking at objects close to them, but blurred vision when looking at objects in the distance has a vision defect called myopia.

This happens because light from the objects form their respective images before it reaches the retina. By placing a concave lense in front of the eye with this defect, the images move back to the retina. Thus, a clear vision can be obtained.

Another condition in which one has blurred vision when looking at objects both near and far is called presbyopia. It is a perfectly natural condition that will eventually affect us all, and can be corrected by wearing bifocal glasses.

Positioning a cylindrical lense in front of an eye that has astigmatism will refract light in one direction more than in the other.

Thus, a person who has distorted vision as a result of this condition will then be able to see clearly.

Schematic diagram of the human eye

[Science Form 2] Damaging Footprints: The Effect Of Human Activity

We should conserve all species and maintain the biodiversity of living organisms because the loss of biodiversity affect the stability and functions the various habitat. Habitat loss is the major reason why biodiversity is threatened.

Certain human activities are known to have destroyed the natural habitats of living organisms. Many species have become extinct due to these human activities; many more are threatened and some are already on the brink of extinction.

Below are the examples of activities that contribute to habitat loss and threaten biodiversity:

1. Activity: Illegal logging
   Effects: Destroys forests and cause the living organisms in them to lose their natural habitat; destructs the ecosystem.
   
   
2. Activity: Poaching/hunting of wild animals
   Effects: Destroys the cycle of life and causes imbalance in the food chain, thus affecting the survival of other animals.
   
   
3. Activity: Deforestation for agricultural and housing development
   Effects: Causes soil erosion and landslides; destructs fertile topsoil, thus creating arid and barren landscapes.
   
   
4. Activity: Over Fishing
   Effects: Disrupts the food chain in the ocean, thus affecting the survival of other marine animals; jeopardises future food supply for human survival.
   
   
5. Activity: Mining
   Effects: Causes soil erosion and landslides; destructs fertile topsoil, thus creating arid and barren landscapes.

[Science Form 2] Living Organism & Man

• A camel provide transportation, food and milk to Man. Their skin is also used to make clothing and tents for shelter against desert winds.
  
  
• Trees take in carbon dioxide from the atmosphere and release oxygen durin photosynthesis. They also prevent soil erosion and reduce the surrounding temperature on a hot day.
  
  
• Bees are important agents of pollination; hence, they contribute to the continuance of species. Bees also make honey, which is consumed by Man as food and medicines.
  
  
• The fish provides Man with food for survival. It is rich source of protein too.
  
  
• Mushrooms and fungi are a source of medicines, and they are also food for Man. Mushrooms are agents for the break down and decay of wood and leaves into humus and compost, which are vital for plant growth.