5b) Selective Breeding

Organisms are selectively bred to develop the best features:
Best features:

• maximum yield of plants 
• good health and disease resistance 
• animals: fertility, not fatty, taste, docile (as pets) 
• plants: attractive, nice smell, shape, fresh 

How to selective breed:

1. Select organisms with desirable features (from existing stock) 
2. Breed them with one another 
3. Offspring: select the best of their offspring and breed them together
4. Repeat the process- consistent organisms 

5a) Food production

CROP PLANTS
You can artificially create the conditions for photosynthesis:

• enclosed 
• greenhouses and polythene tunnels increase the yield of certain crops
• artificial light ---> more photosynthesis 
• trapping heat 
• increase CO2 levels 
• increase temperature 

Greenhouses and Polythene tunnels: 

• increase CO2 levels- The more carbon dioxide present, the quicker the rate of photosynthesis and so increases the growth of crops at a faster speed 
• increase temperature- increasing the temperature raises the rate of metabolic reaction so the temperature needs to be at an optimum a very high temperature denatures the enzymes and low temperatures would reduce the metabolic rate. 
• increase of light intensity 

Fertilisers;

- replace missing elements 

- organic examples ---> nitrogen, manure and animal waste 

- most are chemically produced 

- too little has no effect 

- too much is expensive for people maintaining the crops

- Important elements are Nitrogen, Phosphorus and Potassium 

Reasons for pest control: 

cause crop damage and economic loses in high population

reduce photosynthesis and growth and damage appearance  

Pesticides:

Pros-

Kills pests

Quick results 

Increase and improve crop quality 

Prevent diseases found in fruit and vegetables 

Cons- 

Often poisonous to humans, must be used carefully 

harm other wildlife

expensive  

Biological Control:

Is alternative use of pesticides to reduce pests numbers. Introduces a predator which naturally feeds on them to reduce size.
Takes some time to fully eradicate.

Example: parasitic reduce pest numbers. They lay eggs inside whitefly egg (major pests of greenhouse gases) which prevents population increase. However can't cause crop damage.

MICRO-ORGANISMS

Yeast in the production of food:

1. Barley seeds are the main basis of beer. Seeds are germinated in large warehouses. The seeds produce an enzyme amylase during this.
2. Once the seeds have germinated they are killed and died, creating malt. The malt contains lots of amylase.
3. Malt is ground up and mixed with water in a mash tun (large container). During this time the amylase breaks down starches in the ground up seed mixture, converting it to sugars such as maltose and glucose.
4. Mash is boiled and filtered. Boiling results in denaturing of the amylase enzymes in the mixture. It must be filtered to remove residues of malt. 
5. Hops are added to the filtered solution and yeast is added. The yeast ferments sugars in the mixture creating carbon dioxide and alcohol as a result. 
6. The resulting mixture is high in alcohol and contains much carbon dioxide however it also contains yeast cells and hops. The beer is must be centrifuged, filtered and is sometimes pasteurised.
7. Beer is put into casks or barrels.  

The respiration rate of yeast:

The optimum temperature for yeast growth is 35-40C, if the temperature is too high enzymes become denatured. 

Glucose    --> Carbon Dioxide +   Alcohol 

C6H12O6 -->        2CO2        + 2C2H5OH     

Paper Two - Role of bacteria in the production of yoghurt:

• Yoghurt is made by the fermentation of milk by the bacteria called Lactic Acid Bacteria 
• This means that the bacteria respires anaerobically 
• Fermentation turns the liquid milk into a slightly sour semi solid food this is due to the lactic acid 
• Sugar in the yoghurt gives it energy and taste 
• Due to the build up of lactic acid the yoghurt has a low pH level- this prevents other micro-organisms from growing into the yoghurt 

(Lactose -->) Glucose --> Lactic Acid + Energy

                 C6H12O6 --> 2C3H6O3 (+ energy) 

Industrial Fermenter:

Containers are used to grow bacteria and fungi in large amounts 

FISH FARMING 

Problem: fish are being driven to extinction 

Cause: overfishing, high demand and sushi 

Solutions: growing fish in enclosed areas, QUOTAS, license, make fish more expensive and tax

Open and Closed Farming:

+------------------------------------+---------------------------+
| Advantages                         | Disadvantages             |
+------------------------------------+---------------------------+
| control oxygen and temperature (C) | disease spreads rapidly   |
+------------------------------------+---------------------------+
| meet demands (C+O)                 | cost of food (C)          |
+------------------------------------+---------------------------+
| introduce new breeds and fast      | pollution from faeces     |
| growth                             |                           |
+------------------------------------+---------------------------+
| fish manure well (O+C)             | fish in tanks are carniv- |
|                                    | orous and hungry          |
+------------------------------------+---------------------------+
| surviving a predator attack (C)    | fined for: traces of      |
|                                    | antibiotics               |
+------------------------------------+---------------------------+
|                                    | fined for: reduction      |
|                                    | of non-harmful organisms  |
+------------------------------------+---------------------------+

4d) Human influences on the environment

Pollution of the air by sulfur dioxide and carbon monoxide:
Sulfur Dioxide-

1. Burning fossil fuels releases harmful gases like CO₂ and SO₂ 
2. The sulfur dioxide comes from sulfur impurities in the fossil fuels 
3. When this gas mixes with rain clouds it forms dilute sulfuric acid 
4. Then acid rain falls 
5. Internal combustion engines in cars and power stations are the main causes of acid rain

Carbon Monoxide- 

1. When fossil fuels are burnt without enough air supply they produce the gas carbon monoxide 
2. CO is a poisonous gas and when combined with red blood cells it prevents them from carrying oxygen 
3. Carbon monoxide's mostly released in car emissions. Most modern cars are fitted with catalytic converters that turn the carbon monoxide into carbon dioxide, decreasing the amount of CO that's released into the atmosphere. 

Greenhouse gases:
Some gases in the Earth's atmosphere prevent heat radiating into space from the Earth. This is called the greenhouse effect and the gases that are involved are called the greenhouse gases.
They include:

• water vapour 
• carbon dioxide 
• nitrous oxide 
• methane 
• CFC 

Human Activity and Greenhouse gases:

Carbon Dioxide:

- released into the atmosphere all the time as part of our everyday lives, in; car exhausts, industrial processes and as we burn fossil fuels 

- cutting down large forest areas (deforestation) can also effect the levels of carbon dioxide in the atmosphere 

Methane:

- produced from natural sources 

- also from cattle 

Nitrous Oxide: 

- released naturally by bacteria in soils and the ocean 

- a lot more is released from soils after fertiliser is used 

- also released from vehicle engines and industry 

CFCs:

- man-made chemicals that were once used in aerosol sprays and fridges 

- very powerful greenhouse gases 

- most countries no longer produce them as it damages the ozone layer (part of the upper atmosphere where ozone is found in higher concentrations) which then prevents UV radiation from reaching the Earth 

- some still remains from old fridges and are released through leaks 

Greenhouse gas results in an enhanced greenhouse effect and this may lead to global warming, which is a gradual increase of the Earth's overall temperature and consequences, examples are change in crop growth patterns or flooding due to polar ice caps melting.   

For Paper Two- Biological consequences of pollution of water by sewage:

• increases the number of micro organisms which then leads to the depletion of oxygen 
• causes eutrophication which is when the environment becomes enriched by nutrients 

Eutrophication:

When fertilisers leach into the water, it can cause eutrophication.

If too much fertiliser is applied into fields (like nitrates and phosphates) and it rains afterwards, nitrates can be easily washed through the soil into nearby rivers and lakes. 

1. Fertilisers enter the water, adding extra nutrients 
2. The extra nutrients cause algae to grow quickly and block out the sunlight 
3. Then plants in the water can not photosynthesise due to the lack of light and start to die 
4. With more food available, micro-organisms that feed on dead plants increase in number and deplete (use up) all the oxygen in the water 
5. Organisms that need oxygen, like fish, then start to die due to the lack of oxygen 

Deforestation Effects:

1. Leaching 
• when trees are removed nutrients get leached away, but don't get replaced so it leaves infertile soil 
2. Soil Erosion 
• when trees are removed, soil can be washed away by the rain (eroded), which can leave infertile ground 
3. Disturbing the water cycle
• Rainwater can run straight into the rivers which can lead to flooding 
• Makes the local climate drier when trees are cut down 
4. Disturbing the balance of carbon dioxide and oxygen
• When trees are cut down and burnt the stored carbon is released at once as Carbon Dioxide, this contributes to global warming.
• Fewer trees mean that less photosynthesis occurs releasing less oxygen. This causes the oxygen level in the atmosphere to drop 

Section 5

Use of biological resources

4c) Cycles within ecosystems

Paper Two- The Water Cycle:
The movement of water molecules between various locations. 



Precipitation: water from clouds to the ground
Condensation: Gas to liquid 
Transpiration: water leaves as a gas 
Evaporation: liquid to gas 
Percolation: process for a liquid slowly going through a filter e.g. soil 

The Carbon cycle:

Carbon is passed from the atmosphere as Carbon Dioxide to living organisms. It is then passed to one organism to the next in complex molecules and then finally returns to the atmosphere.



The only thing that removes CO₂ from the air is photosynthesis. Plants use it to make fats, carbohydrates and protein. Both plant and animal respiration puts CO₂ back into the atmosphere.
         Carbon from dead animals and plants can end up as fossil fuels, when this is burned (combustion) it releases carbon. Some dead animal and plants could be broken down by micro-organisms or be turned into useful products by humans.

Paper Two- The Nitrogen Cycle:

Atmosphere contains 78% nitrogen gas which is very unreactive so can't be therefore used directly by plants and animals 
Nitrogen is needed for making proteins for growth, so living organisms need to get it from somewhere 
Plants from soil--> nitrogen in the air is turned into nitrates before plants can use it 
Animals from plants--> get protein from eating plants 
Nitrogen fixation: turning nitrogen in the air to nitrogen compounds in the soil which plants can use. 
Two main ways:

• Lightning- nitrogen react with oxygen due to the energy from the lightning bolt. 
• Nitrogen fixing bacteria in roots and soil 

Different types of bacteria involved in the nitrogen cycle:

• Decomposers- break down of proteins, urea and ammonia 
• Nitrifying bacteria- ammonia into nitrates 
• Nitrogen fixing bacteria- N₂ into nitrogen compounds 
• Denitrifying bacteria- nitrates back into N₂ 

4b) Feeding relationships

Chains

• Start with a producer which make their own food from sun's energy 
• Primary consumers eat producers (herbivores) 
• Secondary consumers (carnivores) 
• Then tertiary consumers (carnivores) eat secondary consumers 
• Decomposers break down dead materials and waste 
• Stages are called TROPHIC LEVELS 
• Example: Grass ------> Rabbit ------> Fox 

Food chains are a sequence of feeding relationships between organisms showing who eats what and the movement of energy through trophic levels. 

Food webs is a network of interconnected food chains. It shows that one species affects another  

Pyramids of numbers: show the feeding relationships in the community- it takes many plants to feed herbivores and many herbivores to feed one carnivore. 

Pyramids of biomass: Shows mass of living material at each stage of the food chain is always less than the previous.

Pyramids of energy transfer: shows the transfer of energy through the food chain. 

Energy transfer:

1. Energy from sun
2. Plants photosynthesise
3. 90% of energy lost 
4. Some parts aren't eaten e.g. roots or bones and due to waste (faeces) 
5. Life processes e.g. respiration use some energy 
6. Move energy eventually lost to heat 
7. 10% total biomass 
• This is the energy that is transferred

4a) The organism in the environment

Important definitions
Habitat: where an organism lives
Population: all the organisms of a species in a habitat
Community: Different species in a habitat
Ecosystems: All organisms in an area and all of the non-living conditions

Quadrats
- Square frame enclosing a known area

1. Place a 1m ² quadrat on a random of investigation 
2. Count all organisms in quadrat 
3. Multiply number by total area of habitat 
• distributions of organisms 
1. Mark out a line in area 
2. collect data along line using quadrat 

Section 4

Ecology and the environment

3b) Inheritance

Nucleus of a cell contains chromosomes (23 pairs) where genes are located
Genes are bits that code for a specific protein and is a section of a molecule of DNA

A diploid human cell contains 46 chromosomes, organised into 23 pairs. One set comes from each parent (contained in haploid gametes)
A matching pain of chromosomes (one from each parent) forms a homologous pair, they code for the same characteristics/genes chromosomes are made up of 2 parts called sister chromatid which are visible during the replication.
Each of these is tightly coiled around protein (histones) in order to make it organised/compacted. When unwound the structure of DNA can be seen. It is made of two strands, which twist to form a double helix.

There are four different DNA bases:
C cytosine
G guanine
A adenine
T thymine

C + G go in a pair together whilst A + T are together

Nucleotide- unit that makes up DNA

Bases- chemicals in DNA that carry the genetic code 

Protein- the type of molecule that genes are coded for
Amino acids- small molecules that join to make proteins










Alleles are different versions of the same gene:

Dominant: An allele that always expresses itself whether it is partnered by a recessive allele or by another like itself.
Recessive: An alternative form of the gene that can be expressed only if a dominant allele of that gene is not present. An organism must have two copies of a recessive allele for that allele to be expressed.

Homozygous: Two alleles that are the same for that particular gene
Heterozygous: Two different alleles that are different for that particular gene

Phenotype: outward appearance of an organism which occur as a result of its genes e.g. blue eyes
Genotype: alleles that an organism has for a particular characterisitic, usually written as letters e.g. bb for blue eyes

For Paper Two- 
Co-dominance: neither allele is dominant or recessive so you show characteristics from both alleles,
For example blood group A and B are both dominant meaning that an offspring could possibly have blood group AB. 

A monohybrid cross is the study of the inheritance of one characteristic.

You need to be able to explain a monohybrid cross in terms of genotypes. This can be done by writing down:

• the phenotype and genotype of the parents
• the gametes which each can produce
• as a result the ways in which the gametes combine (offspring phenotype and genotype)

The best way to do this is to use the same layout each time; use a punnet square or cross diagram to show the possible genotypes of the offspring.

Family Pedigrees

Knowing how inheritance works helps to interpret a family pedigree which is a family tree of genetic disorders. 

To find out whether the allele is dominant you take a small branch from the family tree and if BOTH parents have the trait and ONE child doesn't it is dominant because if the trait were recessive all children would have the same trait. 

If the allele is recessive it means that NEITHER parents have the trait and ONE child does; this is possible because parents must be carrying the recessive allele and it has be passed on. 

Sex determination:

Out of the 23 pairs of chromosomes there are 2 chromosomes which determine whether you are a boy or a girl. 

All men have a X and Y chromosome. Y chromosome causes male characteristics.

All women have two X chromosomes. XX chromosome combination causes female characteristics. 

Parent phenotype          Male                                                  Female 

           genotype             XY                                                      XX

           gametes           X       Y                                                X      X 

Offspring  

		Female, XX
		X	X
Male, XY	X	XX	XX
		Female	Female
	Y	XY	XY
		Male	Male

There is an equal chance of having a boy or a girl

Mitosis:

Produces genetically identical cells

1) Interphase

Nuclear envelope to keep DNA in nucleus 

23 pairs of chromosomes from both parents 

Replication takes place here 

2) Prophase 

The DNA forms X-shaped chromosomes after the duplication/replication

3) Metaphase
Spindle fibres align the chromosomes into the centre after the nuclear envelope has been broken down
4) Anaphase
Splitting the chromatid into half from the centromere, so that the two arms of each chromosome go to opposite ends, also each individual part is a daughter chromosome.
5) Telophase
There are two separate nuclei within one cell and the nuclear envelope is reformed
6) Cytokinesis
The cytoplasm is then split into two genetically identical cells   

Why does mitosis take place?

• growth 
• repair of damaged cells 
• cloning 
• asexual reproduction to make identical cells 
• replacement of dead cells (dust) 

Meiosis:
Produces four haploid cells whose chromosomes are NOT identical

First Division-
Before the cell splits up it duplicates it DNA and one arm of each chromosome is the exact copy of the other arm.
Then the chromosomes line up in the middle during metaphase
The pairs are then pulled apart so the new cell only has one copy of each chromosome. Some of both parent goes into each new cell.
One from each pair passes to the daughter cells and has a mixture of mother and father chromosomes causing gene variation of its offspring.

Second Division-
Chromosomes then line up again in the centre of the cell and the arms are pulled apart and split into daughter cells.
Four haploid cells are produced at the end. The gametes are genetically different.

Comparisons of Mitosis and Meiosis:

	Mitosis	Meiosis
Where it happens	In most parts of the body	Ovaries, testes and anther (in plants)
Purpose	Growth and cell replacement	Production of gametes
No. of chromosomes in daughter cell	46 (23 pairs)	23
Number of divisions	One	Two
Haploid or Diploid	Diploid	Haploid
Identical daughter cells?	Yes	No
No. of daughter cells produced	Two	Four
Variation?	None	Yes

Variation:

Genetic Variation: due to genes which have been passed on. Examples include natural hair colour and gender 

Environmental Variation: Influences from outside- the environment Examples include tanned skin and scars 

Some variation comes from both the environment and genetically for example height, weight and freckles. If your malnourished it would effect your weight and also the height that you should've genetically inherited if you had eaten properly.

Discontinuous variation: can be categorised e.g. freckles and eye colour 

Continuous variation: has to be measured e.g. weight, height and hair length 

Mutations:

A mutation is a rare, random change in an organisms DNA that can be inherited. 

Mutations change the sequence of the DNA bases. It could stop the production of a protein, or might mean a different protein is produced entirely. This can lead to new characteristics due to the slight change in allele or gene and increase variation. 

Harmful:

Can affect offspring in their reproductive cells and they might develop an abnormality or die.

Diseases such as sickle cell and other genetic diseases 

Neutral:

Have no effect at all or occur in unimportant parts of the DNA.

Examples- hair colour and coat colour gene change

Benefits:

Can give an organism survival advantages. 

Paler or darker skin meaning that you can live in conditions where other people may not live comfortably. Being able to camouflage (wild animals) 

Paper Two- Increased risk of mutations:
Can be caused by exposing yourself to ionising radiation (gamma rays, x-rays or ultraviolet light) and chemicals called mutagens (chemicals in tobacco) 

Process of evolution and Natural Selection
Theory of evolution- Life began as simple organisms from which more complex organisms evolved (rather than just popping into existence). 

Natural Selection:

• Inheritable variation; slight mutations can give you a better chance at surviving in an environment 
• Overproduction of offspring; not all of the offspring will survive because they aren't well adapted, the more offspring you have the more variation
• Struggle to survive/ competition; variation of the animal best suited to the environment will survive and reproduce with an organism with similar qualities to have offspring that are very well suited.  

Antibiotic Resistance

Bacteria sometimes develop random mutations in their DNA, this leads to changes in the bacteria's characteristics. It means that the bacterium is less affected by a particular antibiotic.
The gene for resistance being passed on to lots of offspring- due to natural selection. This is how it spreads and becomes more common in a population of bacteria overtime.

The main steps in the development of resistance are:

1. Random changes or mutations occur in the genes of individual bacterial cells.
2. Some mutations protect the bacterial cell from the effects of the antibiotic.
3. Bacteria without the mutation die or cannot reproduce with the antibiotic present.
4. The resistant bacteria are able to reproduce with less competition from normal bacterial strains.

MRSA is very dangerous because it is resistant to most antibiotics. To slow down or stop the development of other strains of resistant bacteria, we should:

• always avoid the unnecessary use of antibiotics
• always complete the full course