Cambridge A Levels A2 Biology Chapter 15 Control and Coordination
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Course
Cambridge A Levels A2 Biology
Institution
Chapter 15 Control and Coordination: 70 pages
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Chapter 15 Control and Coordination
15.1 Control and Coordination in Mammals
15.2 Control and Coordination in Plants
15.1 Control and Coordination in Mammals
Two Types of Information Transfer in Animals:
• Hormonal Communication
• Nervous Communication
Differences between nervous coordination and hormonal coordination
Nervous Coordination Hormonal Coordination
Differences
Messages are in the form of electrical impulses. Messages are in the form of chemical substances.
Speed of transmission is fast. Speed of transmission is slow.
Impulses travel along neurons. Hormones are transported in the blood plasma.
Immediate/rapid response Delayed response
Duration of the effect is rapid / short-lived. Duration of effect is long-lasting.
Eg: withdrawal of hand from hot object Eg: HGH (human growth hormone in the control of
growth
Responses are localized. (more precise) Responses can be wide-spread as target cells are
scattered throughout the body.
Response is at muscles/glands. Response is at target cells.
Similarities
Both involves cell signalling.
Both involves chemicals.
Both involves signal molecules binding to receptors.
,Hormonal Communication
Hormone
a chemical substance produced by an endocrine gland and carried by the blood.
• Hormones are ideal for controlling functions that do not need instant responses.
• Hormones such as insulin, glucagon, ADH and adrenaline are cell-signalling molecules
that are released into the blood.
• They are then carried long distances from the site of production to their various target
organs.
• Hormones are made in endocrine glands.
Gland
a group of cells that produces and releases one or more substances, a process known as
secretion.
Endocrine System
• Endocrine glands contain secretory cells that pass their products directly into the blood.
• As endocrine glands do not have ducts, they are often known as ductless glands.
• The endocrine system consists of all the ductless glands in the body.
• Examples of endocrine glands:
pituitary gland
the islets of Langerhans in the pancreas
the adrenal glands
the testes
the ovaries
Hormones only affect cells with receptors that the hormone can bind to (target cells).
▪ These are either found on the cell surface membrane, or inside cells.
▪ Receptors must be complementary to hormones for there to be an effect.
Hormones such as insulin, glucagon and ADH are peptides or small proteins.
1) They are water-soluble and so cannot cross the phospholipid bilayer of cell surface
membranes.
2) These hormones bind to receptors on the cell surface membranes of their target cells,
which activates second messengers to transfer the signal throughout the cytoplasm.
,Hormones such as testosterone, oestrogen and progesterone are steroid hormones.
▪ They are lipid-soluble and so can cross the phospholipid bilayer.
▪ These hormones bind to receptors in the cytoplasm or nucleus of their target cells.
, Nervous Communication
The mammalian nervous system consists of:
• Centre Nervous System (CNS)
The brain
Spinal cord
• Peripheral Nervous System (PNS)
Cranial nerves
Spinal nerves
Nerves are bundles of nerve cells.
Cranial nerves are attached to the brain and spinal nerves to the spinal cord.
Information is transferred in the form of nerve impulses, which travel along nerve cells at very
high speeds.
Nerve cells are also known as neurones, and they carry information directly to their target
cells.
Neurones coordinate
• the activities of sensory receptors (e.g. those in the eye)
• decision-making centres in the CNS
• effectors such as muscles and glands.
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