3.14 Chromosomes

3.14 recall that the nucleus of a cell contains chromosomes on which genes are located.

1. What are chromosomes, and what are they made of?
Chromosomes are Genetic information contained within the nucleus of a cell

Here you can see a pair of human chromosomes

Chromosomes are composed of a molecule known as DNA (Deoxyribonucleic acid), this DNA forms a shape known as the double helix [indicated in yellow in the above picture]

Sections of this DNA molecule are called Genes [see 3.15], one chromosome will have 1000’s of genes. Each gene carries the information for the construction of a Protein [see 3.16] the protein controls the characteristics associated with the gene (e.g. blood group)

DNA (Gene) -> Protein -> Characteristic

2. How many chromosomes?

Different organisms all have a different number of chromosomes
For example: a Cat has 38, a Chicken 78, a Chimp 42 and Humans have 46

3. Genes operate in pairs known as homologous pairs

This diagram illustrates some of the homologous pairs within an organism

Their Homologous nature and pairing is based upon the equal length of the chromosomes

If a gene is selected from one of the chromosomes in a homologous pair, its gene loci (position at which it is located in the chromosome) is the same in the pairing chromosome.

In a pair of chromosomes there are 2 versions of the same gene for one characteristic, one found in each chromosome but at the same gene loci. These versions are called Alleles.

3.1 Reproduction

3.1 understand the difference between sexual and asexual reproduction
An animal can be either Sexual or Asexual each type has it's own distinct characteristics as listed below


Sexual reproducing creatures

• They have a sex/gender, so can be identified as either male or female.
• They produce cells called 'Gametes', the sperm cell in males, and the egg cell in females
• To produce these Gametes, a type of cell division called Meiosis is used, which is A type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell.
• Fertilisation occurs, where opposite Gametes fuse together
• There is a broad variation in the individuals (i.e. humans are very different from each other)

Asexual reproducing creatures:

• There are no Sexes or Genders
• There are no Gametes
• Asexual reproduction involves Mitosis or Binary Fission (Note: Mitosis is used in Sexual reproducing creatures, but not for reproduction)
• No fertilisation because there are no Gametes
• There is little variation between individuals and this is due to mutations all others are "identical" also known as "clones"

4.9 Carbon Cycle

4.9 describe the stages in the carbon cycle, including respiration, photosynthesis, decomposition and combustion.

1. Photosynthesis
 When photosynthesis occurs, CO2 is used, therefore photosynthesis is responsible for reducing the atmospheric CO2

2. Feeding
 Passage of carbon through different trophic levels

3. Respiration
 Respiration produces CO2 and therefore adds more Carbon dioxide to the atmosphere

4. Decomposition
 All organisms eventually die, their organic molecules are broken down by the decomposer organisms (bacteria and fungi) this results in the release of Carbon Dioxide back into the atmosphere

5. Combustion
 Fossil fuels contain a large amount of carbon so when combusted release a large amount of CO2
 The main uses are industrial uses and also in motor vehicles
 Combustion can also happen natural through lighting and forest fires.

This diagram visually explains most of the concepts

4.14 The Enhanced Greenhouse effect.

4.14 understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to global warming and its consequences.

Pollution of Carbon dioxide, Methane and Water vapour (all greenhouse gases)
if the concentration of these increase in the atmosphere the Infra-red light will be re-emited backwaards towards the surface of earth, rather than escaping back into deep space. This will raise the average global temperature which is referred to as Global warming/

Consequences?
The Melting of Icecaps.... raised sea levels... changing ocean currents and winds
Ultimately ... Climate change.
this will result in the worlds Biome distribution changing... Deserts expanding etc.

4.13 Greenhouse gases

4.13 understand how human activities contribute to greenhouse gases.

The burning of fossil fuels results in more Carbon dioxide, and Nitrous oxide in the atmosphere which are greenhouse gases.

Farming cows causes a significant contribution of Methane from their digestion of crops (9% of the atmospheric gases)

Evapouration of water to form water vapour... Clouds are a significant contributor

Refrigeration/Solvents (CFC's) are associated with the absorption of UV light, and the breakdown of the Ozone layer

4.12 The Greenhouse Effect

4.12 recall that water vapour, carbon dioxide, nitrous oxide, methane and CFC's are greenhouse gases

This diagram explains the effect very well:

(a) is the UV light from the sun (short wavelength with high energy) 

(b) + (h) show that 50% is reflected back out into deep space (by things like clouds)

(c) represents absorption on the earth's surface, where the UV light is converted into Infra-red 
(d) shows the Infra-red (longer wavelength) being emitted back out
(e) some of this is lost out to space as heat
(f) shows the greenhouse gases (water vapour, CO₂, CH₄, etc.)

(g) The I.R. light hits the greenhouse gas and absorbs it, but then re-emits it but re-distributes it, with some of the I.R. heading back to earth

The Hypothesis of The Enhanced Greenhouse effect is that if we emit more Carbon dioxide and Methane they will absorb more of the escaping infra-red radiation and emit it back to earth, raising the temperature higher. and eventually causing Climate change.

CFC's (chlorofluorocarbon's)

 have an effect on the ozone layer (O₃)

CCl₃F à sunlight à CL₂F^- + CL^-
CL^- catalyses the breakdown of O₃ to O₂, O₃ is better at absorbing UV light than O₂ so we are basically removing the protection.

4.11 Gas Pollution

4.11 Understand the biological consequences of pollution of air by sulphur dioxide and by carbon monoxide.


Sulphur Dioxide. (SO₂)
Comes from the combustion of fossil fuels, and combustion of petrols in vehicles.
In the atmosphere Sulphur dioxide combines with water vapour in clouds and forms Sulphuric Acid! this is what is known as acid rain,

SO₂ + H2O = H₂SO₄

acid rain has many effects on plants and animals:

1. Trees and plants are often damaged by the sulphuric acid
2. Sulphuric acid in the soil causes Calcium and Magnesium Ions to become leached* out of the soil, so the plant can't grow.
3. Acid rain in lakes reduces the pH to make them acidic, this causes a release of Aluminium Ions, which causes a thickening of the mucus that lines the gills, and reduces the ability to take Oxygen from water (the fish suffocates)

Leach - Make (a soluble chemical or mineral) drain away from soil, ash, or similar material by the action of percolating liquid, esp. rainwater

• - the nutrient is quickly leached away

Carbon Monoxide (CO)

Fossil fuels i.e. Coal/gas are burned with insufficient (not enough) Oxygen

Carbon monoxide combines with Haemoglobin inside red blood cells and forms Carbaminohaemoglobin which blocks the haemoglobin  from carrying Oxygen, therefore reducing Oxygen circulation and too much can be fatal.