Year 8 Chemistry

We have just started studying Chemistry, after we finished Physics. The Particle Theory of Matter helps us understand why solids, liquids and gases behave the way we do.

Yesterday we did the classic experiment with ammonia and hydrogen chloride where ammonia diffuses much faster than HCl because its particles have half the mass of hydrogen chloride particles.

This experiment was much better.

We were investigating diffusion in liquids.

Because the particles in liquids are close together, like lots of people in a party, diffusion should be a lot slower. (imagine trying to get to the door in a room full of people)

Also, using substances with different particle masses we should be able to show much more clearly the different speeds of diffusion.

A petri dish is half filled with deionised water.

A spatula of lead nitrate crystals (careful, toxic) is added on one side, and a spatula of potassium iodide is added to the other side at exactly the same time.

After just over a minute later, this happened:

A yellow band appeared. This is crystals of lead iodide that are formed when the different particles mix. They react.

It is nearer the left where the lead nitrate crystals were added.

This means that potassium iodide particles must have diffused much faster across the dish.

This is because potassium iodide particles have half the mass of lead nitrate particles.

Even so it still took over a minute to travel just a few centimetres.

Year 9, electromagnetic induction

This Year 9 practical demonstrates one of the most important discoveries: the induction of an electrical current by a moving magnetic field.

electromagnetic induction and Michael Faraday

It was discovered by Michael Faraday in 1831.

When a magnetic field moves through a coil of wire, an electrical current is generated.

Similarly, when an electrical current flows through a coil, a magnetic field is generated. One begets the other!!

This extraordinary realisation that magnetic and electric fields were related changed the world forever.

It is the basis for transformers and electric motors used in everything from cars, to hairdryers, fans, fridges and air conditioners!

It is also what light is, and how it can travel through empty space!!!!!!  






In this photo, on the right a magnetic field pushed through a coil pushes an electrical current through the ammeter.
On the left, a 9V battery is pushing an electrical current through another coil, creating a magnetic field which is repelled by the round magnet below, causing the coil to spin really fast!!

Here is a picture of a light wave which works in exactly the same way!!

Year 9 Revision notes, Physics

You are allowed to use a calculator.

Pressure

Pressure is just a force acting over an area. 

Pressure = Force          Units of force - newtons, N      area  - square cm or square m

                  Area

So, units for pressure N/cm squared or N/m squared         1 N/m squared = 1 Pa, pascal

Small areas, high pressures         

Bullets, knives, nails etc.  

        

Large areas, small pressures.  Elephants have wide feet to reduce pressure

 Canadian Lynx, huge paws for running on snow.

Tractor tyres very wide for driving through mud

You will need to work out pressures exerted by regular solid objects by working out the area of contact.

Pressure in liquids

In an open system (open to the air) such as buckets, swimming pools, oceans etc. pressure is caused by the  weight of the liquid pushing against the sides of the container,and acting over a given area, for example 1 m squared. In other words it is caused by gravity.  

The deeper the liquid, the more weight acts, so more pressure.

Pressure in liquid = density x depth x g     where g is the force due to gravity on Earth, usually 10N/kg.

In just 10 m of water for example, pressure increases by 1,000 x 10 x 10 = 100,000 N/m squared

Pressure in a liquid only depends on depth, not on the shape or size of the container.

Pressure in a closed system, such as a bottle, balloon, piston etc. the pressure depends on the force applied to the liquid. Because liquid particles are already close together, they cannot be compressed (made smaller by squeezing).

Pressure then acts in all directions equally, and increases with increasing force.

As Pressure = Force/Area, by changing the area we can change the pressure.

This used in Hydraulic Machines to multiply a force.

Hydraulic machines can look complicated, but they can be simplified into a diagram as they all work in the same way.

 A small piston (small area) and a large piston (large area)

A force applied to the small piston causes pressure in the liquid, usually oil.

Because the pressure is the same everywhere, this pressure will act on the large piston causing a large force.

Pressure  =  Force 1      =  Force 2

                    Area 1            Area 2

Just put the known values into the formula and solve the maths.

In the above example, because the large piston has 4x the radius of the small piston, area is:

Pi x radius squared, so 16 times larger, so force will be 16 x bigger!

examples of hydraulic machines are: hydraulic press, hydraulic car jack, hydraulic brakes and the lifting arms of bulldozers and diggers.

Pressure in gases

Unlike in liquids, gas particles are far apart and move around in all direction, colliding with each other and the sides of a container. The energy they have is Kinetic Energy, K.E.  It comes from the gas being heated.

These collisions cause the pressure.

In an inflated balloon, particles push out by colliding with the walls, the stretched rubber walls pull inwards. 

If the gas particles are pushed together using a force, there will be more collisions and a higher pressure!

We say that the pressure in a gas is inversely proportional to the volume.

in other words: if one gets bigger, the other gets smaller!

Atmospheric Pressure

The air around us is a gas. But as we get higher, the air molecules get further and further apart.

At the Earth's surface, the weight of air above pushes the molecules closer together.

At the top of Mount Everest, over 8km high, the air molecules are so far apart it is difficult to breathe.

If you add up all the weight of air in a 1 m square column, like here, it would come to about 100,000 N/m squared, sometimes called 1 atmosphere of pressure, 1 At.

How does temperature affect pressure?

Because gas pressure is caused by collisions, and the collisions depend on Kinetic Energy, changing the temperature will add or subtract energy.

Higher temperature, more energy, more collisions, more pressure!

So, an inflated balloon in a freezer, the gas loses energy, there are less collisions, pressure falls, and the balloon shrinks. Take it out, energy rises, collisions rise, pressure rises again.

Pressure is proportional to temperature.  If temperature rises, pressure rises.

Density

Density tells us how much MASS a given VOLUME of stuff has.

e.g. a block of iron would have more mass than the same size block of wood. Iron has higher DENSITY.

Density = Mass                            Mass, g or kg    Volume  cm cubed or m cubed
                 Volume

Density of regular objects.

It's easy to find the density of a regular object such as a cube, block, cylinder, sphere,cone etc.

Just remember the formulae to calculate volumes.

Mass can be found using a set of scales.

Write the formula for density, substitute the numbers, do the maths.

Density of liquids

We can measure the volume of a liquid using a measuring cylinder. just remember to take a proper reading as below.

Irregular Objects

To measure the volume of an irregular object, if it will fit into a measuring cylinder we can use the water displacement method.

Take reading before, and reading after adding the object. The difference is the volume of the object.

Mass using scales, write the density formula, plug in the numbers.

Densities of different materials are listed in secondary sources such as the internet. They can be used to work out volumes or masses of different objects such a steel beams, concrete blocks etc.  We can also use them to work out what an object could be made of, gold, for example.

Because particles in solids and liquids are close together, they have high densities.

Gases, on the other hand, where particles are very far apart, have very low densities.

Buoyancy and upthrust  - floating and sinking

An object in a liquid experiences an upward force called upthrust. It is caused by pressure increasing with liquid depth. There will then be more force acting on the object's bottom than its top.  This is an unbalanced force pushing upwards. See picture.

The higher the density of the liquid, the more weight acting so more pressure so more upthrust.

If this upthrust is greater than the downward force due to gravity (weight) the object will float.

If not, the object will sink.

So, if the density of the object is less than the density of the liquid, it floats!

Even though ships are made of iron, a very dense material, the inside of the ship is mostly very low density air.  Its overall density is not enough to make it sink!

Here is photo of a steel nut floating in liquid mercury, which has a very high density of about 14g/cm cubed.

Levers - simple machines

As well as changing speeds, changing shapes and changing directions, forces can make things turn.

This is called TORQUE, or TURNING FORCE or MOMENT OF FORCE.

This turning force increases the further the force acts from the turning point, called the pivot or fulcrum.

This is called a lever, it's a simple machine which can multiply a force.

Long levers can apply very large turning forces,

The force applied to the end of the lever is called the EFFORT.

The force applied to the other end is called the LOAD.

The size of the turning force:

Moment of Force = Force x Distance  (from the turning point or pivot.)

Equilibrium

If the moments of force of the EFFORT equals the LOAD, in other words nothing happens because they are balanced, we say the forces are IN EQUILIBRIUM.

A see-saw is a good example. Two people with different weights can sit at different distances from the centre of the see-saw making it balance.

Clockwise and Anti-clockwise Moments.

The force on the left tries to turn the lever left,

anti-clockwise, the right force tries to turn the lever right, clockwise.

Calculations:

Moment or Force = Force x Distance.

Anti-clockwise 4 x 80 = 320 Nm  (newton metres)

Clockwise         6 x 50 = 300 Nm

so, the total turning force must be 20 Nm anti-clockwise. The lever will turn to the left.

In this example the system is balanced, in equilibrium.

This means all moments must also be balanced.

So: Anticlockwise moments  (3 x 10) + 2 (10 + x)   = 30 + 20 + 2x =  50 + 2x   Nm will be equal to :

Clockwise moment                4 x 24 = 96 Nm

solve the maths, and x will be 23 cm.  All examples like this are done in the same way.

Electrostatic Phenonomena

Electro (Greek for amber, elektron - charge)   and Static (not moving)

Rubbing certain objects such as rubber, plastics and amber with a cloth or fur or hair creates a CHARGE.

This charge can attract tings to it such as dust, small pieces of paper or even a stream of waster!

Charges can be POSITIVE or NEGATIVE  + or -

Different or unlike charges ATTRACT (pull) each other,  the same charges REPEL (push away).

Where do charges come from?

All materials are made of atoms. This is a model of an atom. They don't really look like this, it's impossible to draw an atom to scale. 

If the atom was the size of a football stadium, the nucleus (red and yellow balls) would be the size of a pea in the centre!!

Protons (red) have a positive charge.

Electrons (blue) have a negative charge

The yellow balls are neutrons, they have no charge.

Because, in an atom, there are the same number of protons and electrons, the total charge is zero.

Normally, electrons are very strongly bound to the atom.

But with some materials, like polythene and other plastics, the molecules they are made of are huge.

They are sometimes thousands of atoms long.

Here, the electrons are easier to pull off the atoms. And, because plastics are INSULATORS (they do not easily allow charges to flow through them) this now unbalanced charge will stay on the surface of the plastic.

With other materials the electrons may be pulled off the material doing the rubbing leaving the opposite charge on the plastic.

Why can't metals be charged?  Well, they can, but because metals are good CONDUCTORS, any charge will quickly spread out and leak away.  The metal dome on a van der graaf generator can be given a very large charge as long as it is insulated well.

van der graaf generator youtube

Risks or electric charges

Sometimes huge charges can build up in machines, or even clouds. This charge has to go somewhere, so if there is a big enough difference between charges in two objects a SPARK will jump between them, neutralising the charge.

This is what we see in a LIGHTNING STRIKE. Lightning can be very dangerous if it hits an object or person, generating extremely high temperatures that can burn or kill.

Buildings are protected with a strip of metal, usually copper, called a LIGHTNING CONDUCTOR which connects the building to the EARTH, called GROUNDING.

In a lightning storm, never shelter under a tree, as the tree can attract a lightning strike.
The safest place to be is in a car, not because of the rubber tyres, but because the metal car body act as a Faraday Cage, conducting the charge around you and into the ground.

Electrical Circuits

We have only just started this topic, but there will be a question on circuit symbols.

Year 8 Revision notes Term 1, 2016. Physics

You will be allowed to use a calculator in the Physics exam.

Speed.

formula: speed = distance/time 

units m/s (metres per second)  or km/h (kilometres per hour)

You will need to be able to calculate speeds, compare speeds, e.g. which is faster, 60m/s or 120 km/h?

60m/s = 60 x 60m/minute = 60x60x60 m/hour.  Divide by 1,000 (1,000 m in 1 km) = 216 km/h

If you can remember 3.6,  multiply m/s by 3.6 to get km/h

Measuring speed: Reaction time, 0.2 seconds, is the delay between viewing and action, e.g. pressing a button on a stopwatch.  Not very accurate.

For accurate readings we should use electronic timers and light gates.

Distance/time graphs

These show how distance changes as time goes on.

You will need to explain what is happening in a distance/time graph.

From graphs, we can learn 2 things:

a) The gradient or slope of the graph = rise over run, or y/x

                                                         
b) The AREA under the graph. y times x.

                                                           
rise/run = gradient.

For a distance/time graph, gradient is rise/run = y/x =  m/s = units for speed.

The area under a distance /time graph, y times x =  m x s  (ms) tells us nothing.

Straight lines mean constant speed.

A flat line, or zero gradient, distance is not changing = stopped, at rest or not moving.

Changing speed

When speed changes with time, an object gets faster, or slower. Changing speed is called ACCELERATION and can be positive, faster, or negative, slower.

In this graph, speed is increasing. 

The gradient or slope shows changing speed = acceleration.    Gradient = rise over run, = y/x 

                                                                              Units: speed/time = m/s divided by s = m/s/s or metres per second per second, or metres per second squared.

What about the area under a speed/time graph?

Area = the area of the triangle formed by the graph.  1/2 height x base.

Units:  m/s x s = m,  metres.  The unit for distance.

Area under speed/time graph = distance traveled.

You should be able to do simple calculations for journeys, such as acceleration between 2 points, and distance travelled using speed/time graphs.

Formula for acceleration.        v is speed after, u is speed before     (u before v  in the alphabet)  and t is time.




  Using this formula is easy, just substitute what we know and do      the maths!

Sound

Anything that VIBRATES makes a sound. But, the sound needs something to travel in, a MEDIUM, which can be a solid, liquid or a gas.

Sound travels as a wave, but not quite like water waves. A vibrating object pushes and pulls particles in the medium around it. This squeezes and stretches the medium, which then makes the particles nearby do the same thing.
The sound then spreads out in all directions as a compression wave, or LONGITUDINAL WAVE.

A sound wave can be shown on an OSCILLOSCOPE as a wave, as above, but really it is showing high pressure (squeezed particles) as the top of the wave, and low pressure (stretched particles) as the bottom of the wave.

You need to remember these things about waves:

The number of waves passing a point in 1 second of time is called FREQUENCY. Units: hertz, Hz.

Wavelength and frequency tell us the pitch or note of the sound. Long wavelengths and low frequencies are low sounds, high frequencies and short wavelengths are high sounds.

Humans can hear frequencies of up to 20,000 Hz, but animals such as cats, dogs, bats and dolphins can hear much higher sounds.

Amplitude tells us the intensity of the sound, or how loud it is.  High amplitudes, loud, low amplitudes soft sounds.

The intensity of sound is measured in decibels, dB.  30 dB sound is 10 times louder than a 20 dB sound.  The safe level for sounds heard for long periods is about 80 to 90 dB.  Louder than that we should protect our ears with Ear Defenders of Ear Plugs.

Speed of Sound

In air, sound travels at about 330 m/s, faster if the air is hot and humid.

In water, about 1,500 m/s because particles in water are close together.

Much faster in solid objects like concrete or steel.

Musical Instruments

Different instruments can play the same notes, but they sound different. A piano sounds different to a violin.

This difference in sound is called TIMBRE.

Below are oscilloscope screens showing the same note played by a piano, guitar and violin in our music room.

 Piano

Violin

Guitar

Echolocation

When a sound wave hits an object, some of the sound is reflected back as an ECHO.

This idea is used by animals to 'see' things in the dark or in muddy water.

Bats and dolphins have developed this to a fine art.

Humans make use of echoes as fish-finders, SONAR in submarines and ships, and in Ultrasound machines in hospitals.

Light

Light isn't energy, but the transfer of energy from one place to the next.

Light is produced by LUMINOUS objects: Sun, stars, lamps, LCD screens, LED's, electrical sparks, and even BIOLUMINESCENCE in fireflies, some fish and even fungi.

Light travels in straight lines. We know this because when light is blocked, a shadow is cast. The name for a shadow is UMBRA, from umbrella. Half shadow, caused by light dispersion is a PENUMBRA.

Light travelling in straight lines explains how a pinhole camera works.

The thing the camera is pointed at is called the OBJECT. The picture on the screen at the back of the camera is called the IMAGE.

Because light travels in straight lines the image is upside-down, INVERTED

Seeing things

Light from luminous objects is EMITTED (given out)  and passes straight into our eyes, like the camera.

So how do we see non-luminous objects, like tables, cats and dogs?

When light hits an object some light is ABSORBED. But some light also bounces off. It is REFLECTED. This reflected light then enters our eyes.

If light passes straight through something, like air, clear water of clear glass it is TRANSMITTED.

Whether light is transmitted, reflected or absorbed depends on an object's material, what it is made of.

You must remember these terms.

Object:

Light is transmitted - object is transparent - water, air, glass

Light is transmitted but scattered in all directions - object is translucent - paper, ice, muddy water

Light is reflected or absorbed - object is opaque - wood, metal, concrete

Know how to label a diagram of the eye.

Speed of Light

The speed of light is about 300 million m/s, or 300,000 km/s.

Even at this speed, distances in space are huge. We measure these huge distances in terms of LIGHT YEARS l.y., the distance light travels in a year. About 9 trillion km.

Nearest star: 4.1 l.y.

Milky Way galaxy: 100,000 l.y. across

Andromeda galaxy, our sister galaxy: 2.5 million l.y. away.

Reflection

Ray Diagrams. Know how to draw ray diagrams to explain why things happen.

Reflection in a plane (flat) mirror.

The object in a plane mirror is: Upright, the same size, the same distance from the mirror and VIRTUAL (not real).

Law of Reflection

i is the angle of incidence - angle of the incident or incoming light ray with the normal line.

r is the angle of reflection - angle of the reflected ray with the normal line. (red line)

i = r

Refraction

When light enters water from the air, it appears to bend. This bending of light is called refraction.

Ray diagrams explain what happens.

How much light is refracted depends on the medium the light leaves and on the medium

the light enters.

Why does refraction happen?

Light travels as waves, a bit like waves on a pond.

When a light wave enters a medium such as glass, it slows down (or at least appears to).

If one end of a wave enters the glass first, it will move slower than the other end and pull the wave around. When all the wave is in the glass it moves at the same, slower speed in a straight line again.

The same thing will happen in reverse when the wave leaves the glass. One end will speed up first.

The RATIO of the two speeds in, say, air and water, or air and glass, is called REFRACTIVE INDEX, R.I.

Given the speed of light in air is almost the same as in a vacuum, we can use RI to work out the speed of light in a given medium.

e.g. if light travels from air to water, and RI water is 3/2

RI = Speed of light in air                       3/2 = 300 million m/s                

        Speed of light in water                             speed of light in water

so, speed of light in water is 200 million m/s

note.

Light doesn't really slow down in water or glass. The light is being absorbed and emitted by particles in the medium. This takes a bit of time. Between particles the light travels at its normal speed, 300 million m/s.

More particles, or different particles, this happens more often or takes longer.

This explains why light speeds up again when it leaves the medium and enters air again.

Year 10 0610 Biology Revision Notes:

Life processes - Name and explain each of the 7 processes common to all living things using the mnemonic Mrs Gren

Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition.

Understand that in some organisms these processes are not obvious.

e.g. the dormant stage of plant seeds, corals and sponges, lichen etc.

Classification: Understand how all living things can be classified according to similarities.

Read this general article from the BBC:

BBC How did life begin?

CIE, only 5 Kingdoms:

- Prokaryotes: (Bacteria and Archaea)

and Eukaryotes:

- Animalia (Vertebrates and Invertebrates)

- Plantae

- Fungi

- Protokcista (Protists, protozoa etc.) A group of unrelated organisms which do not belong in the other 4 Kingdoms.

Using Keys:

Identify organisms using a key. Carefully follow instructions to identify unknown organisms, of different species or of closely related organisms.

Animals:

Invertebrates; The largest group of Animalia.

Divided into several Phyla (Phylum) according to their structure.

Arthropods - Jointed legs, hard external skeleton

e.g. Crustacea (Crabs, lobsters)

       Arachnida (Spiders, scorpions  8 legs)

       Insecta (Beetles, flies, wasps - 3 body parts, 6 legs, 2 pairs of wings)

       Myriapoda (Many legs - centipedes, millipedes, segmented body)

Molluscs - soft body, muscular foot, shell sometimes present

e.g. Cephalapods - octopus, squid

       Gastropods - slugs, snails, nudibrancha, clams

Echinoderms - spiny skin - Starfish, sea urchins

Porifera - Sponges

Cnidaria - Jellyfish and corals

 Annelida - Segmented worms - earthworm

 Flat worms - Flukes and tapeworms - parasites

 Nematodes - Roundworms, or unsegmented worms - most are parasites.

Vertebrates:

Fish, adapted to life in water, scales on their skin, breathe with gills. Ectothermic - 'cold blooded'

Amphibeans (2 stage life-cycle) moist skin, lay eggs in water, first stage have gills. Ectothermic.

e.g. frogs, toads, salamanders

Reptiles - evolved thicker skin, eggs with shells to move away from water. Ectothermic.

e.g. Lizards, snakes, crocodiles, turtles.

Birds - Some reptiles evolved into Birds, hard shelled eggs, feathers, endothermic -'warm blooded'

Mammals - Some reptiles evolved into mammals - produce milk, live young (apart from Monotremes), fur, endothermic. Some mammals returned to water, whales and dolphins.

Plants - evolved from plant-like protists. Green algae (seaweed)

Plants possess chloroplasts for photosynthesis.

Moved on to land as Mosses 400 mya (no roots, small leaves, reproduce using spores, live in wet places.)

Ferns evolved vascular tissues (wood) for support. Better adapted to land, Reproduce by spores (male and female gametes (sex cells) that swim in water.

300 mya Conifers appeared - suited to colder, drier climate. First seeds, produced in cones. Gymnosperms - naked seed.

165 mya first flowering plants appeared - Angiosperms (covered seeds) Seeds protected in an ovary which forms a fruit.  Today 80% of all plants are flowering plants.

2 main groups: 

Monocotyledon (seed has 1 cotyledon as food store) parallel veins in leaves, long thin leaf. e.g. rice, grasses, orchids

Dicotyledon - (seed has 2 cotyledons) branched veins in leaves e.g. most flowering trees, bean plants.

Cells

All cells have:  a cell membrane, nuclear material, cytoplasm. (apart from mammalian blood cells which have lost the nucleus.

Understand all cells are fundamentally similar apart from:

Prokaryotes have no nucleus

Fungi have cell walls made of chitin.

Plants have a visible vacuole, a cellulose cell wall and may contain chloroplasts.

Most cells are HETEROTROPHIC (feed on organic molecules)

Plants cells are AUTOTROPHIC (can make their own food by photosynthesis)

You need to know the functions of the different parts of the cell.

Magnification:

Cells are small and only visible under a microscope. 

Magnification = Apparent size/Real size.

At 400x magnification, if a drawing of a cell is 10mm, the real size must 1/400th the size.

10mm divided by 400 = 0.025mm   1000 micrometres = 1mm.

0.025mm = 25 micrometres.

Blood cells are even smaller, 15 micrometres - can squeeze through narrow capillaries, no nucleus to save space.

Bacteria - about 2 micrometres

Virus - 0.1 micrometre

Plant Cells

Cellulose cell wall, large vacuole filled with cell sap (aqueous solution), nucleus, maybe chloroplasts.

Root hair cells - adapted to take in water and minerals from soil.

Xylem - long thin tubes that carry water from roots to leaves.

Guard cells - pair of cells in a stoma (stomata) holes in leaves allowing gas to enter and leave.

Organisation of cells:

Organelle (inside cell) ------Cell-----Tissue--------Organ---------Organ system---------Organism

Movement In and Out of Cells

Diffusion -

no energy needed- random movement of particles in a liquid or gas (kinetic energy, collisions) until particles evenly distributed EQUILIBRIUM

Osmosis

- diffusion of water across a semi or partially permeable membrane (cell membrane) from a high water potential to low water potential or dilute solution to a more concentrated solution. No energy needed.

Solution: Solute (solid) dissolved in Solvent (e.g. water - aqueous solution)

Active Transport - 

allows movement of particles against a concentration gradient e.g. mineral ions into root hair cells.  - Needs ENERGY. Uses carrier proteins.

Phagocytosis

-Some cells engulf molecules by flowing around them e.g. white blood cells, amoeba.

Organic molecules

Found in all living things.

Organic molecules contain chains, branches and rings of carbon atoms.

They also contain hydrogen, and usually contain oxygen.

4 main groups:

Carbohydrates - sugars and starches

Proteins

Lipids - fats and oils

Nucleic acids - found in genetic material

Carbohydrates

monosaccharides - single or simple sugars, soluble in water, e.g. glucose and fructose

disaccharides - double sugars e.g. sucrose, maltose, lactose

polysaccharides - long chains and branches of monosaccharides e.g. starch, glycogen, cellulose

Proteins

Long chains or branches of amino acid sub-units (20 different amino acids) can make almost limitless different proteins. The order of amino acids is controlled by GENES in the nucleus.

Lipids

3 chains of FATTY ACIDS joined together by a molecule of GLYCEROL

Found in plants and animal cells.

Food Tests

You must learn the 4 main tests for the different groups, the names of the reagents and the colours for positive and negative tests.

                           

Enzymes

Enzymes are special proteins that control all biochemical reactions in METABOLISM.

They are Biological Catalysts, which mean they speed up reactions but themselves remain unchanged.

Without enzymes, biochemical reactions would be too slow.

Lock and Key mechanism - enzymes are SPECIFIC, they only work in a single reaction.

The enzyme shape controls the reaction.

SUBSTRATE molecules (small molecules) are built into large ones, PRODUCTS.

Large molecules can be broken down again into small ones.

Enzymes are affected by:

Temperature - too cold, not enough energy, too hot, enzyme is killed, DENATURED.

Best temperature is OPTIMUM TEMPERATURE.  Animals 37 degrees C. Plants 25 degrees C.

pH - acid or alkaline. Varies according to where the enzyme acts. pH 6 in mouth, pH 2 in stomach etc.

Catalase - breaks down hydrogen peroxide

Lipase - breaks down lipids

Amylase - breaks down starch

Protease - breaks down protein

Lactase - breaks down lactose in milk

Enzymes in the mouth - salivary glands - amylase

Stomach - produces lipase and protease

Pancreas - produces many enzymes including amylase and lipase

Small intestine - more enzymes such as lactase, sucrase etc.

Year 8 Physics. Investigating the Refractive Index of a Glass Block.

Practical exercise.

Our Method:

We placed a glass block onto a plane piece of paper, and shone a laser light ray through it at 3 different angles.

On each ray we marked two crosses, removed the block after drawing around it, and drew the rays.

Next we measured the angles of the incident rays, i and the refracted rays, r.

Just like here in the photo:

What we found:

If we took the sine of each angle.  sin i divided by sin r, we got 1.43.

This is the Refractive Index (RI) of the block!!!!

IGCSE Biology Year10 0610 Biochemical tests

Testing for Organic Molecules or Biochemicals

This part of the syllabus is really fun. There are many different tests that help us differentiate between the main groups of organic molecules; Lipids (fats and oils), Carbohydrates (sugars, starches etc.) Proteins and Nucleic acids (found in genetic material such as DNA).

Test for Protein

This is the test for protein which we did today.

First, we mixed a testing solution called Biuret Reagent. 

You can buy it, but it's much more fun to mix our own. 

Biuret Reagent.

Ask the teacher to premix 0.5 molar solution of potassium hydroxide, KOH. That's 28g solid KOH diluted in water to 1 litre (1 dm cubed).   

Before the test, add about 0.1g copper sulfate to a few drops of water (about 1/4 of a spatula) in a test-tube.

Add the copper sulfate solution to about 2 ml KOH in a large test-tube. It turns a nice bright blue colour.  That's it!!!  Biuret Reagent.

You can't store this solution for more than a few days, so just make enough for the lesson.

The test:

We need to make sure the test works, so we test it on a 2ml solution of peptone (the smelly solid we use to make agar plates to grow bacteria) or biuret solution, which contains the same bonds found in proteins that make the test work. This is a POSITIVE TEST.

Simply gently pour the Biuret Reagent you made into the test solution. Swirl gently, and you should see a beautiful violet colour just like here in our picture.

Choose a colour pencil closest to the test result and copy it into your notebook. Simple, and it helps you to remember.

Carbohydrate Tests

The tests for carbohydrates are: The Starch Test and Testing for Reducing Sugars.

Starch Test.

This is the easiest test to do. Simply take a small sample of starch in a test-tube as a POSITIVE TEST.

-Add about 2 ml distilled water and shake. Starch doesn't dissolve in water, but will give a milky white suspension.

-Add a few drops of 1% Iodine solution, a red/orange colour.

In a positive test it will turn a dark blue, almost black colour as in the photo.

The dark colour is made as Iodine atoms become trapped inside the starch molecules, forming a complex.

Test for Reducing Sugars

Reducing sugars are monosaccharides (single sugars) such as glucose and fructose.

Caution: Lactose, a disaccharide found in milk, also gives a positive test!! As does sucrose treated with acid!

This is a very dramatic test.

Method:  We dissolved a sample of glucose in distilled water in a test-tube, A, as a positive test, and dissolved a similar amount of sucrose, B, as a negative test.

We added  a similar volume of Benedict's Reagent to each test-tube.                                                       https://en.wikipedia.org/wiki/Benedict%27s_reagent 

Here's a photo:

Both samples are a bright blue due to the presence of copper (ii) ions.

Next, both test-tubes are heated gently in a Bunsen-burner flame for about 2 minutes. Always point the test-tube away from people and never look down into it.

Test-tube B, the negative test, didn't change colour, it stayed blue.

Test-tube A, the positive test with glucose solution, changed to a bright brick-red colour.

The red colour comes from the copper (ii) ions being reduced to copper(i) ions by glucose.

A really cool test!