Biology

Question 1

How do you test for…

1) Starch
2) Reducing Sugars
3) Proteins
4) Lipids

in food?

Answer 1

Starch: Iodine will go from yellow to blue-black

Proteins: Biruet’s solution will go from blue to purple. To create a Biuret test, potassium hydroxide is mixed then 2 drops of copper sulfate are added.

Lipids:Add ethanol and shake - a white emulsion-fatty layer should form ifit is present as they dissolve in the ethanol.

Sugars: Benedict’s solution while heating which will turn anywhere from green to yellow to red, indicating how much sugar is present This is a semi-quantitative test. It mostly gives non-measurable values

Question 2

Explain how calorimetry can be used to measure the energy in food

Answer 2

Burn a known mass of the food under a boiling tube filled with a known volume of water.
Energy from the food will transfer to the water, causing a change in temperature
Calculate the change in temperature of the water, this gives an indication of how much energy was in the food

Question 3

Evaluate calorimetry tests for accuracy

Answer 3

Temperature increase should be made with same thermometer if comparing two foods to avoid any errors between different thermometers (random error).

The burning food should be held as close to the tube as possible, so that the flame heats the tube and not the surrounding air – this should be the same for each test.

The foods should be burnt completely, so that all energy is transferred from the food.

Question 4

Describe how DNA strands are held together

Answer 4

Parts of DNA have very slight electrical charges - a slightly negatively charged part of one base attracts a slightly positive charged part of another base. This forms a weak force of attraction called a hydrogen bond.

Question 5

Describe the overall structure of DNA

Answer 5

A double helix structure with nuecloetides.
Each nucleuotide contains a phosphate group and a sugar.
This forms a sugar phosphate backbone.
They also have bases which form complementary base pairs and joined together by weak hydrogen bonds.
The bases are adenine guanine thymine and cytosine with A being complimentary to T and C being complimentary to G.
The DNA forms a polymer because it is many nuceuotides joined together

Question 6

Describe how DNA is extracted from fruit

Answer 6

Wemash up some peas then put them into a beaker containg a solution of detergent and salt, then mix well.
The detergent will break down the cell membranes to release the DNA
The salt will cause the DNA to clump together
We then filter the mixture to get the froth and large, insoluble bits of cell out.
Then, we gently add some ice-cold ethanol to the filtered mixture.
The DNA will start to come out of the solution as it’s not soluble in cold ethanol. It will appear as a stringy white precipitate, that can be fished out with a glass rod.

Question 7

Describe the stages of mitosis

Answer 7

Mitosis

Interphase
Copies of the chromosomes are formed in the nucleus
Prophase
The nucleus starts to break up and spindle fibres appear.
Metaphase
The chromosomes are lined up on the spindle fibre across the middle of the cell
Anaphase
The chromosome copies are separated and moved to either side of the cell
Telophase
A membrane forms around each set of chromosomes to from a nuclei
Cytokeniesis
Cell surface membrane forms separating the two cells (In plants, a cell wall is also formed)

Question 8

Describe why mitosis is important for an organism

Answer 8

Mitosis is used for the growth and the repairing of cells.

Also, it is used in asexual reproduction to produce genetically identical offspring.

Question 9

Describe how mitosis produces genetically identical, diploid cells

Answer 9

Genetic material is replicated during the interphase, from 46 chromosomes to 92. Then, the cell divides once into two cells, both with 46 chromosomes.

Question 10

What produces gametes?

Answer 10

Meoisis

Question 11

Describe what happens in meiosis

Answer 11

The gamete-making cell is diploid

The chromosomes replicate.

The cells then divide, then divide again. Each of the final four daughter cells are haploid, and has a copy of one chromosome from each pair.

Question 12

Compare and contrast meoisis and mitosis.

Answer 12

Similarities:
Both a type of cell division
Both parent cells begin as diploid
Both produce daughter cells

Differences:
Mitosis only has 1 divison, where in meoisis there are 2 divisons
Daughter cells in mitosis are genetically identical diploid cells, whereas in meoisis they are genetically different haploid
Mitosis has 2 daughter cells where meoisis has 4 daughter cells

Question 13

State how the pathogen is spread and 1 way to prevent the spreading of this pathogen

cholera
tubercolosis
malaria
stomach ulcers
ebola
HIV

Answer 13

water - boil water to kill bacteria prior to drinking
airborne - ventilate buildings to reduce chance of breathing in bacteria in droplets of mucus coughed out by an infected person
mosquito vector - prevent mosquitos biting people by keeping them off skin
orally - cook food thoroughly to kill bacteria
body fluids - quarantine infected people
sexual fluids - use condoms

Question 14

How do lymphocytes respond to pathogens?

Answer 14

Each pathogen has unique antigens on its surface
A lymphocyte with an anti-body that fits the antigen is activated
The lymphocyte divides many times to produce clones of identical lymphocytes
Some of the lymphocytes produce lots of antibodies which stick to the antigen and destroy them
Other lymphocytes stay in the blood as memory lymphocytes in case the same antigen returns

Question 15

Explain how immunisation works

Answer 15

A vaccination injects inactive/weak pathogens of a disease.
Lymphocytes with antibodies to tackle these are activated and memory lymphocytes are created
This means that if that pathogen infects the person after, there will be memory lymphocytes to tackle it quiclkly
This increases the person’s immunity to this disease as it reduces the severity of the symptoms and the time taken till the infection is dealt with

Question 16

Describe secondary immune response

Answer 16

After the second infection, the secondary response is a lot quicker.
It also produces a lot more antibodies
This is because of the already active memory lymphocytes

Question 17

Why are antibiotics useful for treating bacterial infections?

Answer 17

Antibiotics specifically target bacteria by inhibiting their ability to synthesize a cell wall. Human cells don’t have a cell wall - therefore remain unaffected.

Question 18

Explain how some bacteria become resistant to antibiotics

Answer 18

The population of bacteria have variation in their resistance to antibiotics.
The course of antibiotics kill most of the bacteria
Before the course is finished, the only remaining bacteria are the most resistant
If the course isn’t completed, the remaining (more resistant) bacteria will reproduce,
This will produce another generation of highly resistant bacteria which the antibiotic will be less effective against

Question 19

Identify main parts of the eye

Answer 19

There is a clear covering called the cornea covering the eye which refracts most of the light
Below this are the iris and the pupil
CIllary muscles alter the shape of the eye (constricting or dilating it)
A lens to fine tune the light refraction
At the back is the retina containing rods (detect light levels) and cones (detect colour. Don’t function well in dim light)
This is passed onto optic nerves which pass electrical impulses to the brain
Refracted light should meet at the retina

Question 20

How do receptor cells allow full colour vision in bright light?

Answer 20

The retina contains 2 photosensitive receptor cells - rods and cones. Cones are sensitive to colour changes, so allow us to see colour when light is sufficient.

Question 21

SB2h - What is a cataract?

Answer 21

Protein build up in the lens can cause it to become cloudy, clouding your vision.
This can be corrected by replacing the lens with a plastic one

Question 22

SB2h - What is myopia and hyperopia?

Causes
Treatment

Answer 22

Myopia is short sightedness (Can see close):

This is when light focuses too early (before the retina)
The eyeball is too long.
This can be fixed with a diverging lens.

Hyperopia is long sightedness (Can see far):

This is when light hasn’t focused by the time it reaches the retina.
The eyeball is too short.
This can be fixed with a converging lens

Question 23

SB4g - Describe the process of genetic engineering of bacteria to produce insulin.

Answer 23

DNA from a human cell is cut into pieces using enzymes from restriction enzymes. These make staggered cuts across DNA, leaving a few unpaired bases at each end called sticky ends.

Bacteria cells contain small circles of DNA called plasmids. The same restriction enzymes are used to cut plasmids open, leaving sticky ends with matching sets of unpaired bases.

The pieces of DNA containing the insulin gene are mixed with the plasmids. The bases in the sticky ends pair up, an enzyme called DNA ligase is then added, linking the DNA back into a continuous circle

The plasmids are inserted back into the bacteria. This can be grow in huge fermenters where they can make human insulin

Question 24

What are the problems with genetically engineering plants?

Answer 24

Genes may ‘hop’ onto wild plants, making them resistant

Reduce gene pool

Very expensive

Some people think its bad for your health to eat GMOs

Question 25

What are the risks of selective breeding?

Answer 25

Animals may loose an allele through this process.

This may be needed later on to help them survive/cope

All the animals become very similar and so any disease that affects one of them, affects all of them

Unethical as some animals live in conditions that aren’t comfortable (e.g chickens with a lot of meat can’t stand up)

Question 26

What are some uses of GMOs in agriculture and in medicine?

Answer 26

Agriculture:
Producing GMO plants which produce BT toxin, natural insecticide saves money. Often have higher yield

Medicine:
Treating genetic diseases
Producing insulin for diabetic patients

Question 27

Explain how temperature affects enzyme activity

Answer 27

At very low temperatures, the particles do not have enough energy to move, so the enzyme is inactive; the rate of reaction is very low

As the temperature increases, particles begin to move more as they gain kinetic energy; the rate of reaction will increase

Eventually, the enzyme reachs an optimum temperature where it is working at it’s fastest

However, if the temperature increases too far beyond that, the active site will begin to chagne shape and the rate of reaction will decrease

Eventually, if high enough temperatures are reached, the shape of the active site is changed to a point where the substrate is no longer able to bind to it. It becomes denatured.

Question 28

Explain the effect of pH on enzyme activity

Answer 28

An enzyme has an optimum pH where it works best.

The further away from this, it will get slower till it becomes denatured

Question 29

Describe the effect of substrate concentration on enzyme activity

Answer 29

At first, increasing substrate concentration will increase the rate of reaction because there are more substrate molecules so more collisions will occur.

However, after a point, increasing substrate concentration will have no affect because all active sites are busy.

Question 30

Describe the functions of different parts of the brain

Answer 30

Cerebellum - balance, coordinates our movements
Cerebral Cortex - cognitive function, language memory and conciousness
Medulla Oblongata - breathing rate, reflexes, heart rate

Question 31

What is a mutation?

Answer 31

A change in the base sequence that creates a new allele

Question 32

How can mutations occur?

Answer 32

They often occur during cell division, due to a mistake copying DNA

This is more likely to happen if there is damage to the DNA caused by radiation

Question 33

Describe possible effects of mutations on amino acid sequences

Answer 33

Due to a difference in the base sequence, the amino acid sequence may actually change. This may have an effect on the protein produced and therefore the phenotype.

Question 34

Describe how gene transcription is regulated

Answer 34

By limiting the amount of mRNA produced by a gene

Question 35

Explain the effects of mutations on protein activity

Answer 35

Mutations can often cause a different protein to be produced - or the same protein with increased/decreased functionality.

Question 36

Explain how mutations can influence RNA polymerase binding and so alter protein production.

Answer 36

Mutations to the non-coding part of the DNA can either increase or decrease the ability of RNA polymerase to bind to it. Therefore, it will increase/decrease the amount of mRNA produced, which in turn changes the amount of protein produced

Question 37

Describe the structure of a sensory neurone

Answer 37

A sensory neurone contains dendrites, which receive impulses from receptor cells. Then, it has a dendron which conducts the impulses towards the cell body.

It has a cell body, which contains the nucleus. Following that, the axon conducts the impulses away from the cell body to the axon terminals, where they pass the impulses to other neurones.

Question 38

Describe the routes that impulses take to and from the brain

Answer 38

Sense organs contain receptor cells, which convert stimuli into electrical impulses.

These electrical impulses travel through sensory neurones, to the CNS. The brain then processes this information and can send impulses to other parts of the body to cause a response.

Question 39

Explain the adaptations of sensory neurones

Answer 39

myelin sheath - fatty layer surrounding the axon, which electrically insulates the neurone to stop the signal losing energy

long axon - allow fast transmission over long distances

axon terminals - allow impulses to be transmitted to other neurones

Question 40

What causes colour-blindness?

Answer 40

Faulty cones that do not work properly, so they have difficulty in seeing some colors.

Question 41

Describe how to measure the optimum temperature / pH of an enzyme

Answer 41

Measure 2cm3 of amylase solution into a tube

Add 2cm3 of starch solution to the tube and place in the water bath

Start stop clock and stir mixture

Every 20 seconds, take a small amount of mixture and place a drop of it into a fresh drop of iodine solution.

Stop testing when the iodine solution stops changing color.

Repeat experiment, increasing temperature by 10 degrees each time. Or, if measuring pH add 1cm3 of a solution with a particular pH into the tube, then change pH used.

Question 42

State what is meant by optimum pH

Answer 42

The pH at which the reaciton works fastest