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We are going to look at how the lungs are adapted for gas exchange. In humans, we have two lungs. Air passes into the lungs through a tube called the trachea. The trachea splits into two smaller tubes called...

A catalyst acts to lower the activation energy of the reaction. It speeds up the reaction without being used up. Binding of the catalyst alters the tertiary structure of the enzyme, causing the active site t...

Inactive forms of the pathogen are injected into the body This stimulates the white blood cells to produce antibodies On reinfection, the antibodies will be produced rapidly and be removed from the body befo...

Action potential reaches neurone.Voltage gated Ca²+ channels in the presynaptic membrane open.Calcium ions flow in, pushing acetylcholine filled vesicles to the presynaptic membrane.Vesicles fuse with the me...

Solutes (e.g sucrose) are transported in the phloem from source to sink. Sucrose is made at the leaves in the plant, this is actively transported into the phloem via companion cells. T his then lowers the wa...