A Level Biology Revision Notes

Comprehensive A Level Biology revision notes providing information and assistance for all UK examination boards (AQA, OCR, Edexcel) as well as international curriculum (CIE).

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The circulatory system consists of the heart and the blood vessels through which the blood passes. These vessels form a complete circuit. (A closed circulatory system).

You know that the structure of living organisms comes in gradual levels. These levels begin with the systems, organs, tissues, cells and finally come the organelles. If we follow up this structural sequence of living organisms, we will find that the cells of any living organism are made up of organic and inorganic molecules and each of these molecules is made up of atoms as well.

The heart is a hollow muscular organ which lies in the middle of the chest cavity. It is enclosed in the pericardium that protects the heart and facilitates its pumping action. It is divided into four chambers.

By the early 1950’s there was strong evidence that DNA carries a cell’s genetic information of the cell and many people were trying to work out the structure of the DNA molecule and make a model of it.

Most living organisms are composed of several cells. But, are these cells irregular or disordered? Does each of them work separately from the other?

The enormous variety of proteins in living systems can be divided into two main groups: Structural proteins and Regulatory proteins.

Proteins represent the structural composition of all living organisms. All living organisms from the hugest animal to the extremely microscopic one are mainly made up of proteins. Proteins contribute to the biochemical processes preserving the life.

In cellular biology, osmosis refers to the collection of mechanisms that regulate the passage of solutes such as ions and small molecules through biological membranes, which are lipid bilayers that contain proteins embedded in them.

Carbohydrates are biological macromolecules made up of smaller molecules called monomers. Carbohydrates include sugars, starches and fibers. They are symbolized by the formula (CH2O)n. According to this formula, carbohydrates are made up of carbon (C), hydrogen (H) and oxygen (O) atoms in the ratio 1:2:1.

The progression of biology is thoroughly based upon the development of the technologies used in the science field related to the cell science (Cytology). This development has leaded to increase the ability of scientists to observe and analyze.