Category: Year10 Science

Year10 Science
Junior Science Curriculum

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How do we see? (Part2: Brain and vision)

Colour blindness and night blindness

Most forms of colour blindness, an inherited inability to distinguish between certain colours, result from the absence or a deficiency of one of the three cone photopigments. The most common type is red-green colour blindness, in which a photopigment sensitive to orange-red light or green light is missing. As a result, the person cannot distinguish between red and green. Prolonged vitamin A deficiency and the consequent below normal amount of rhodopsin may cause night blindness – an inability to see well at low light levels.

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The visual pathway

After considerable processing of visual signals in the retina at synapses among the various types of neurons, the axons of retinal ganglion cell provide output from the retina to the brain.

They exit the eyeball as the optic nerve (cranial nerve II).

(http://www.msstrength.com/ms-optic-nerve-attacks-and-symptoms/)

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Process of Visual Input in the Retina

Within the retina, certain features of visual input are enhanced while other features may be discarded. This is because there are only 1million ganglion cells but 126 million photoreceptors.

Once receptors in rods and cones receives message, the message is spread through the synaptic terminals of vision neurons. Everything that can be seen by one eye is that eye’s visual field. Because our eyes are located anteriorly in the head, the visual field of the two eyes overlap considerably. We have binocular vision due to the large region where the visual fields of the two eyes overlap. The visual field of each eye is divided into two regions. Moreover, visual information from the right half of each visual field is conveyed to the left side of the brain, where as visual information from the left half of each visual field is conveyed to the right side of the brain.

(ref: http://www.arn.org/docs/glicksman/120104%20fig3.jpg)

  1. Axons of all retinal ganglion cells in one eye exit the eyeball at the optic disc and form the optic nerve on that side.
  2. At the optic chiasm, axons from the temporal half of each retinal do not cross but continue directly to the thalamus on the same side.
  3. In contrast, axons from the nasal half of each retina cross and continue to the opposite thalamus.
  4. Axon branches of the retinal ganglion cells project to the mid brain, where they participate in circuits that govern constrictions of pupils in response to light and co-ordination of head and eye movements. Hypothalamus also establishes the patterns of sleep and other activities that occur on a daily schedule in response to intervals of light and darkness.
  5. The axons of thalamic neurons form the optic radiation as they project from the thalamus to the primary visual area of the cortex on the same side.

(ref: http://www.thebrainwiki.com/uploads/Forebrain/thalamus.jpg)


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Being a part of the cerebrum, They are located at the edges of the brain. Each temporal lobe deals with auditory processing and semantics of speech and vision. The temporal lobe hosts the hippocampus and is therefore involved in the formation of memories. Their function include Emotional Responses, Hearing, Memory and Speech.


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Sound

Sound is a form of energy. Being able to hear sound is one of our most important senses. Some of the sounds you hear are loud and some are soft. This is the intensity of the sound. Sounds can also be high or low. This is the pitch of the sound.

Sounds are made by something moving backwards and forwards. This is called vibrating. When you speak, vocal cords in your throat vibrate. When you play a guitar the strings vibrate to produce the sound.

Sound waves travel through the air. The air particles squash up and move apart! Sound can even travel through liquids and gases because the particles pass on the vibrations. Sounds travel fastest through solids, and slowest through gases.

  • Sound travels in all directions.
  • Sound travels in waves.

how the amplitude and frequency affects sound waves

  • Sound is made from vibrations.
  • Sound can be reflected, we call this an echo.
  • Sounds get louder as they closer and then fainter as they get further away.
  • Sounds travel to our ears.

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To learn about sounds in underwater visit http://www.divediscover.whoi.edu/expedition12/hottopics/sound.html

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Ionic bonding and Covalent bonding

Ionic bonding

Ionic bonding usually happens from reaction between metal and non-metal elements. You can see ionic bonding from a compound like NaCl (Sodium chloride). The forces of attraction between oppositely charged ions are called ionic bonds. As you can see in the diagram, Na+(Sodium ion) is a positive and Cl-(Chloride ion) is a negative ion. This is because sodium has lost one of its electron on it’s outer shell and chlorine has gained one electron from sodium element.

Sodium is an element but it becomes ion when it loses it’s electron from the outer shell. Chlorine is also an element – so it becomes negative ion as it gains a electron from the sodium.

An ionic bond (or electrovalent bond) is a type of chemical bond based on electrostatic forces between two oppositely-charged ions.

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Covalent bonding

Covalent bonds are forces that hold non-metal atoms together. The forces are formed when the atoms of a molecule share electrons.

As you may know, an atom is made of a tiny core called a nucleus, with tiny particles called electrons traveling about the nucleus. Sometimes when atoms come together, two electrons will start to travel about the nuclei of both atoms. The two atoms then share the pair of electrons.

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What is kinetic energy and potentional energy?

Kinetic energy

Kinetic Energy is energy that is in motion. Moving water and wind are good examples of kinetic energy. Electricity is also kinetic energy because even though you can’t see it happen, electricity involves electrons moving in conductors.

Energy makes change possible. We use it to do things for us. It moves cars along the road and boats over the water. It bakes a cake in the oven and keeps ice frozen in the freezer. It plays our favorite songs on the radio and lights our homes. Energy is needed for our bodies to grow and it allows our minds to think.

Scientists define energy as the ability to do work. Modern civilization is possible because we have learned how to change energy from one form to another and use it to do work for us and to live more comfortably.

Energy is found in different forms including light, heat, chemical, and motion.

Potential Energy

Energy is measured in the amount of “work” it does. Potential Energy is stored energy. Examples of potential energy are oil sitting in a barrel, or water in a lake in the mountains. This energy is referred to as potential energy, because if it were released, it would do a lot of work.

Energy can change from one form to another. A good example is a Roller Coaster. When it is on its way up, it is using kinetic energy since the energy is in motion. When it reaches the top it has potential (or stored) energy. When it goes down the hill it is using kinetic energy again.

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Science fair help: Burning peanut experiment

Measuring Energy

burn a peanut and boil water to meaure its calorie content

This is a particular method that measures energy in a peanut. A peanut burns producing an impressive amount of flame for a long time. The flame is used to boil away water and count the calories contained in the peanut.

Equation for calculating the calories in a peanut: To raise the temperature of 10 grams of water from 20 °C to 100 °C it takes:

Q = mcDT

Or, use the following equation to calculate the calories per gram of the peanut:

calories per gram = (heat gained by water)/(mass lost when peanut burned)

This is another way of doing the experiment.

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To learn more about this experiment visit

http://www.exo.net/~pauld/activities/food/burnapeanut.html

http://www.chymist.com/energy%20of%20a%20peanut.pdf

http://www.cerlabs.com/experiments/10875406238.pdf

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Bacteria

Functions of major parts

  • DNA: Contains genetic information for the bacteria. Controls all the chemical reactions within the cytoplasm.
  • Capsule: Protects bacteria from heat and chemicals
  • Flagellum: For movement.
  • Fimbriae/Pilli: For attachment (eg. on the surface of stomach)
  • Cell wall: Maintains the shape of the bacteria.
  • Ribosomes: For making protein.
  • Cytoplasm: This is where all the chemical reaction happens (including making proteins).
  • Plasma-membrane/ cell membrane: Controls what comes in and goes out.

Uses of Bacteria :

ref http://hubpages.com/hub/Uses-and-Classifications-of-Bacteria

  • A bacterium breaks down the organic fertilizer (decomposed vegetables and animal matter) into material that can be used by plants.
  • Some species of soil bacteria convert nitrogen into nitrites, compounds that are readily absorbed by plants.
  • Different commercial processes also need certain bacteria, like Anaerobic bacteria that ferment certain substances are used in the production of vinegar and some drugs, and in the aging process of cheeses.


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Hepatic portal vein

Usually the capillary beds of most tissues drain into veins are lead directly back to the heart. However hepatic portal vein is an exception. In this case, blood draining the intestine is leaded to a second set of capillary beds in the liver. Then the liver removes many of the materials that were absorbed by the intestine:

  • Glucose is removed and converted into glycogen.
  • Other monosaccharides are removed and converted into glucose.
  • Excess amino acids are removed and deaminated.
    • The amino group is converted into urea.
    • The residue can then enter the pathways of cellular respiration and be oxidized for energy.
  • Many nonnutritive molecules, such as ingested drugs, are removed by the liver and, often, detoxified.

The liver serves as a gatekeeper between the intestines and the general circulation. It screens blood reaching it in the hepatic portal system so that its composition when it leaves will be close to normal for the body.

Furthermore, this homeostatic mechanism works both ways. When, for example, the concentration of glucose in the blood drops between meals, the liver releases more to the blood by

  • converting its glycogen stores to glucose (glycogenolysis)
  • converting certain amino acids into glucose (gluconeogenesis)

ref: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/G/GITract.html

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Bile and Pancreatic juice

As the contents of the stomach become thoroughly liquefied, they pass into the duodenum(Small intestine). Duodenum is the first segment (about 10 inches long) of the small intestine.

Two ducts enter the duodenum:

  • one draining the gall bladder and hence the liver
  • the other draining the exocrine portion of the pancreas.

Bile

  • pH 7.6
  • bile acid: large globules of fat (liquid at body temperature) are emulsified into tiny droplets (about 1 µm in diameter) that can be more easily digested and absorbed.
  • Bile contains the products of the breakdown of hemoglobin removed by the liver from old red blood cells. The brownish/greenish color of the bile pigments imparts the characteristic brown color of the faeces.

Pancreatic juice

  • The pancreas consists of clusters if endocrine cells and exocrine cells whose secretions drain into the duodenum.
  • Contains:
  1. sodium bicarbonate (NaHCO3): This neutralizes the acidity of the fluid arriving from the stomach raising its pH to about 8.
  2. pancreatic amylase: This enzyme hydrolyzes starch into a mixture of maltose and glucose.
  3. pancreatic lipase: The enzyme hydrolyzes ingested fats into a mixture of fatty acids and monoglycerols. Its action is enhanced by the detergent effect of bile.
  4. trypsin
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RNA and DNA

Our body is made up of very complex proteins. In fact, it is not just us that is made up of very complex proteins. It is more accurate to say that all the living things are made up of very complex proteins. There are two kinds to proteins – functional protein and structural protein. What is the difference? Well, the functional protein helps with the chemical reactions in our cells – but the structural protein is like what you can see with your eyes and touch. You can touch your skin, finger nail, hair, skin… and organs inside your body!

Why am I talking about these things?

Because I am about to let you know that your cells contain all the information about these proteins. The information is used to make and control every single things which are inside and outside your cell. It is like an encyclopedia, written in the language that our body understands. Where can we find the information then? The famous DNA – inside the nucleus of a cell.

The DNA is a long double helix molecule. Helix is the shape of a twisted ladder.

May be you have seen this picture before. The DNA is made up of thousands and millions of a single unit called NUCLEOTIDE.

Nucleotides have another name – Nucleic acid. This is because we often have to see things from chemistry perspective to understand their property as a molecule.

DNA and RNA is all made up of nucleic acids. But only difference is that DNA is like a ‘REFERENCE COPY’ book in the library. As you know these REFERENCE COPY books cannot be taken out side the library. So, what do you do when you need an information from the book? You would photocopy the pages you need wouldn’t you? The RNA is like the photocopied pages which can take information from DNA in the nucleus to the cytoplasm to make proteins. This is because making protein needs big chemical reaction and this reaction can only take place in the cytoplasm.

This is how RNA and DNA looks like. As you can see RNA is single stranded and DNA is doubles stranded. The part you cannot see is the difference in length. DNA is way way longer than RNA because it contains whole information, unlikely, RNA is way way shorter than DNA because RNA only contains copy of a section in a DNA strand.

You will actually more things about RNAs and DNAs when you take senior Biology subject. Hope this helps for you to kick start! :)

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Friction

Our life is pull of forces. We cannot see them but we can see how they affect things. Forces can change the shape of something, its speed, or the direction that it is moving in.

This is an example of friction.

Forces are either pushes or pulls. These pictures show some changes caused by forces. Many forces need to touch an object before they can affect it. These are called contact forces.

Friction is the force between two touching objects. It can slow things down or make things stand still. The friction between our clothes and a chair stops us from sliding off it. Walking would be very difficult without the frictions between our feet and the floor – we would slip and slide everywhere.

Friction can also wear things away. The brake pads on a bicycle eventually wear away, and so do car tyres. Parts of your clothes get thinner as friction wears them away.

Friction produces heat and noise. If a car engine runs without any oil in it, the large friction between the moving parts inside the engine causes it to overheat and stop working. Rusty door hinges squeak and make a door difficult to open.

We can increase friction by using certain materials. Rubber produces a lot of riction which is useful to use. The tyres of a Formula One racing car stop the car from sliding off the road as it speeds round a sharp bend. The rubber mat in a bath stops us from slipping.

We can reduce friction by making surfaces smooth. Skiers wax the bottom of their skis to make them very smooth. This reduces friction and allows them to ski faster.