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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Dendrites

Introduction Coordination among the different organs and organ systems in the body of animals is brought about by the nervous system. It is comprised of millions of neurons that are responsible for carrying messages in the form of nerve impulses from one part of the body to the other. These neurons have a cell body …

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Axons

Introduction The nervous system consists of neurons and neuroglial cells. Neurons are the excitable cells that can generate an action potential when stimulated by an environmental stimulus or other neurons. Neuroglial cells are responsible for providing support to the neurons. Neurons consist of a cell body that gives rise to cellular processes. These cellular processes …

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Gravitropism

Introduction There is a certain competition between plants for the two: Gravitropism and phototropism. Gravitropism, as the name suggests is defined to be the differential plant growth in response to gravity. To make it a bit simpler, let us divide the word into two. Gravity means in response to gravity whereas tropism refers growth of …

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Phototropism

Introduction Phototropism is to be defined as the tropic effect of the plant in response to the factor light. Let us break the word into two, ‘photo’ means light and’ tropism’ means turning to a direction in response to the stimulus. This process works in accordance with the other five different types of tropisms which …

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Actin

Introduction When it comes to muscle, understanding its structural organization is necessary to understand physiology. If there’s altered physiology, then it will be termed as Pathology. The sarcomere is highly organized, containing long cylindrical filaments called myofibrils that run parallel to the axis of the fiber. The dark bands on myofibrils are called A bands …

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Tropomyosin – A Muscle Protein

Introduction When it comes to the molecular mechanism of muscle contraction we are up with the explanation of Sliding Filament Theory. A sarcomere, which serves to be the basic unit of muscle contraction is made up of myofibrils which in turn are composed of actin and myosin filaments. The ratio of actin to myosin filament …

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Muscle and Contraction

Introduction Animals have a lot of differences from the plants in their mode of living, ways of obtaining food, adaptations to their habitat, etc. One of the major differences between animals and plants is that of movement or locomotion. Animals can move from one place to another while plants spend their life at the same …

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Myofibrils

Introduction Skeletal muscles are the most abundant tissues found in animals. They make up more than 40% of the total weight of an average human. These muscles are responsible for all kinds of movements exhibited by a human being. They are under voluntary control meaning that we can consciously control their contractions. Skeletal muscles are …

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Myosin

Introduction The contraction of skeletal muscles is responsible for all kinds of movements exhibited by animals. This contraction is possible due to the contractile proteins present inside the skeletal muscle cells. The contractile proteins, along with the regulatory proteins are organized in the form of myofibrils. Myofibrils are further divided into sarcomeres that serve as …

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Synaptic Transmission

Introduction Humans and other vertebrates have developed a highly efficient system of communication, the nervous system. It is a network of interconnected neurons that are capable of generating and transmitting nerve impulses. The communication process is based on the successful transmission of nerve impulses from one neuron to the other. Neurons are connected via specialized …

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