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A compilation of self written notes made for GCSE revision. This document was written using markdown. The uncompiled .md file can be viewed here:

To-Do 😰

• Physics
  • P1 - Matter
  • P2 -
• Biology
  • B1 - Cell Level Systems
  • B2 - Scaling up
  • B3 - Organism Level Systems
  • B4 - Community Level Systems
  • B5 - Genes, Inheritance and Selection
  • B6 - Global Challenges
  • B7 - Practical Skills
• Chemistry

Physics

P1 - Matter

The History of the Atomic Model

In 1897, JJ Thomson conducted several experiments which led him to the conclusion that atoms weren't just solid spheres like had been thought before. His model proposed an atom that consisted of negative particles(electrons) spread throughout a solid sphere. This was known as the plum pudding model.

Negative Particles Positive Body The plum pudding model. By: Alex Miao

In 1909, Ernest Rutherford with the help of Hans Geiger and Ernest Marsden, conducted the gold foil experiment. In which a beam of positively charged Alpha Particles was shot at a gold foil surrounded by a screen.

It was expected for the majority of the particles to pass straight through the foil, unaffected. However, during the experiment, a large number of particles diverged with some even deflecting of off the gold foil.

Radioactive source Screen Gold Foil Beam of Alpha Particles (α) The gold foil experiment. By: Alex Miao

This led to Rutherford proposing the nuclear model in 1911. This model presented the atom as having the majority of its mass concentrated in a tiny, positive nucleus. Surrounded by a cloud of negative electrons.

However, scientists soon realised that this model had its flaws. Due to the negative nature of electrons and the positive nature of the nucleus. An atom following Rutherford's model would collapse instantly due to electrostatic forces of attraction.

Finally, a few years later in 1913, Niels Bohr proposed a new model where electrons only existed in shells or fixed orbits based on its energy level.

The Atom

The nucleus contains protons and neutrons and is extremely small. With a radius of about $1\times 10^{-15}\textrm{m}$. Almost all the mass of atom (about $1\times10^{-23}\textrm{g}$), is concentrated in the nucleus.

The rest of an atom is mostly empty space. The negative electrons orbit around the nucleus and give it its overall size - a diameter of around $1\times10^{-10}\textrm{m}$. This means that the radius of the nucleus is around 10,000 times smaller than the radius of the atom.

Atom Model. By: Universe Today

Particle	Relative mass	Relative charge
Proton	1	+1
Neutron	1	0
Electron	0.0005	-1

Density

Biology

B1 - Cell Level Systems

Cells

An organism can be a eukaryote or a prokaryote.

Eukaryotes are made from complex eukaryotic cells. Prokaryotes are made from smaller and simpler prokaryotic cells.

Eukaryotic Cells

Types of eukaryotic cells include plant and animal cells. These consist of an array of complex structures.

CytoplasmNucleusCell membraneMitochondrionAnimal cell Cellulose cell wallPermanent vacuoleChloroplastPlant Cell Differences between simple animal and plant cells. By: Domdomegg

Animal Cell

1. Nucleus - Contains DNA in the form of chromosomes.

2. Cytoplasm - Dense liquid where most chemical reactions take place.

3. Mitochondria - Where cellular respiration take place and provides energy to the cell.

4. Cell Membrane - Holds the cell together and controls what can pass through the cell using a selective barrier. Also contain receptor molecules which are used for cell communication.

5. Ribosomes - The site of protein synthesis.

Plant Cell

Plant cells have everything that animal cells have, plus some additional structures:

1. Cellulose Cell Wall - A rigid cell wall that gives support for the cell.

2. Chloroplasts - Where photosynthesis occurs, contains green pigment called chlorophyll.

3. Permanent vacuole - Contains cell sap (a mixture of sugars, salt and water)

   Prokaryotic Cells

   One type of prokaryotic cell is a bacterial cell. Prokaryotic cells are typically uni-cellular, meaning the entire organisms consists of just a singular cell.

Cell membraneMurein cell wallNucleoidCytoplasmPlasmidFlagellumCell capsule Simple diagram of bacterium. By: domdomegg

A bacteria cell consists of:

1. Cytoplasm - Dense liquid where most chemical reactions take place

2. Cell Membrane and Wall - Provides structural support to the cell and controls what can pass through the cell using a selective barrier. Also contain receptor molecules which are used for cell communication.

3. Chromosomal DNA - A singular, circular strand of DNA that contains all the genes the bacteria needs.

4. Plasmids - Small rings of DNA that carry extra genes such as drug resistance that aren't always needed but may sometimes be used or exchanged between bacteria.

5. Flagella - Thread like structures that protrude out of the bacteria that allow it to propel itself.

   Microscopy

   Microscopes are used to examine objects that are too small to be seen by the naked eye. There are two main types of microscopes: light microscopes and electron microscopes.

   Light Microscopes

   Invented in the 1590s, light microscopes let us see things such as nuclei and chloroplasts.

   Parts of a light microscope

   The main parts of a light microscope include:

Chemistry

Made with the help of Cognito Edu, Wikimedia Commons, and all my teachers at school.

Let's hope I do well in my GCSEs 😬