Coordination and Response IGCSE Biology Notes PDF

CAIE Biology IGCSE 14: Coordination and Response Notes (Content in bold is for Extended students only) This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0...

CAIE Biology IGCSE 14: Coordination and Response Notes (Content in bold is for Extended students only) This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0 https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Coordination and Response Both controlled movement and autonomic reflexes are carried out by the body’s nervous system. The nervous system coordinates and regulates body functions by sending electrical signals known as nerve impulses along a network of specialised nerve cells called neurones. This allows coordinated movement and a constant internal environment to be maintained (homeostasis). The nervous system consists of two main sections: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is made up of the brain and spinal cord, whereas the peripheral nervous system contains nerves outside of the brain and spinal cord, which carry impulses to and from the CNS. Types of neurone: Sensory - carries impulses from a receptor to the spinal cord and brain https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Relay (connector) - carries impulses between different parts of the central nervous system Motor (effector) - carries nervous impulses from the central nervous system to the effector, e.g. a muscle Reflexes: Some movement is involuntary; organisms have adapted to carry out automatic reflexes when in danger in order to quickly remove themselves from a hazard such as fire or sharp objects. This is known as the reflex action. As these reactions must occur almost instantly to protect the organism, the nervous impulse does not travel to the brain. Voluntary impulses are controlled by the brain. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Reflex arc: 1. A stimulus, such as heat from a flame, is detected by receptors. 2. The receptor sends an impulse down the sensory neurone to the spinal cord. 3. The relay neurone in the CNS passes the impulse to the motor neurone. 4. The impulse travels along the motor neurone to an effector (e.g. a muscle), which reacts to remove the organism from the danger. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Synapses: Synapse is a junction between two neurones. The synapse forms a gap called a synaptic cleft between the presynaptic neurone and the postsynaptic neurone. When an impulse arrives at the presynaptic neurone, vesicles in the neurone fuse with the membrane, releasing neurotransmitters into the synaptic cleft. The neurotransmitters diffuse across the synapse, binding to receptors on the postsynaptic neurone. This triggers a nervous impulse in the postsynaptic neurone, so the impulse can be transmitted to the other parts. Synapses ensure unidirectionality of nervous impulses, as the vesicles containing the neurotransmitter are only present in the presynaptic neurone, whilst the receptors are only present in the postsynaptic neurone, thus the impulse cannot travel backwards. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Sense organs Sense organs are groups of receptor cells which respond to a specific stimulus. The eye is a sense organ which responds to light. Other sense organs may respond to temperature, touch, sound and chemicals. Eye structure: Cornea - A clear layer which coats the iris. The cornea refracts light into the eye. Iris - The coloured section of the eye. This controls the amount of light that enters the eye by contracting and dilating the pupil. Pupil - Allows light into the eye Lens - Positioned behind the iris. The lens changes shape in order to focus the light on the retina. Retina - Contains light receptors or also called the photoreceptors called rod and cone cells which are sensitive to light of different colours. There are also many blood vessels which supply nutrients to these cells. Fovea - a section in the middle of the retina which contains a large amount of cone cells; this section provides the clearest image. Optic nerve - Each photoreceptor cell is attached to a neurone. These neurones group together to form the optic nerve, which carries the impulse to the brain. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Pupil reflex: The pupil of the eye can expand and contract to control the amount of light that enters the eye. This action is carried out by two sets of muscles, circular muscles and radial muscles, which work antagonistically. At low light intensities, the pupil dilates to allow more light to enter the eye by relaxing the circular muscles and contracting the radial muscles. At high light intensities, the pupil constricts to limit the amount of light entering the eye by relaxation of the radial muscles and contraction of the circular muscles. This is to prevent the eye being damaged by the bright light. Accommodation: The eye can focus on both near and far objects. This is achieved by changing the shape of the lens, which is controlled by ciliary muscles and suspensory ligaments. These work antagonistically. The shape of the lens, as well as its curvature, is altered to change the way light is refracted onto the retina, focusing the image. To focus on near objects, the ciliary muscles contract whilst the suspensory ligaments relax, making the lens fatter and curved. To focus on distant objects, the ciliary muscles relax whilst the suspensory ligaments contract, making the lens thinner and less curved. Rods and cones: Rods and cones are the two types of photoreceptor cells found in the eye: Type of photoreceptors Rods Cones Shape Rod-shaped Cone-shaped Function Used for monochromatic Used for colour vision in bright light. night vision as they are There are three types of cone cells, more sensitive to low each sensitive to a different colour levels of light (red, green and blue) Distribution Evenly distributed at the Concentrated at the fovea periphery of the retina; absent at the fovea https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Hormones The endocrine system produces and secretes hormones. Hormones are chemical substances that travel in the blood and are used for signalling in the body. They are produced in glands such as the pituitary and adrenal glands, before being excreted into the blood, where they travel to target organs and cause a change in the cells. Endocrine glands: A network of hormone-secreting glands make-up the endocrine system. This system helps to control growth, metabolism and homeostasis, among other functions. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Example glands and functions: Gland Hormone Function Adrenal gland Adrenaline Secreted during the ‘fight or flight’ response, and when (located at the top stressed or excited. It leads to an increase in heart rate, of the kidneys) breathing rate and widened pupils. It also causes glycogen to be converted to glucose in cells, increasing the blood glucose concentration for use in respiration. Heart rate increases to provide more oxygen for this. Pancreas Insulin Decreases blood-glucose concentration. Glucagon Increases blood-glucose concentration. Testes Testosterone Maintains muscle and bone strength and plays a role in reproduction. Ovaries Oestrogen Regulates female reproductive system. Endocrine system vs nervous system: Nervous impulses travel along neurones whereas hormones travel in the blood. Nervous impulses are much quicker than hormones, as hormones must be transported in the blood whereas nervous impulses can travel along specialised nerve cells. Nervous impulses are instantaneous and short-lived, whereas a hormonal response can be long-lasting. The endocrine system uses chemicals (hormones) whereas the nervous system uses electrical signals. Homeostasis Homeostasis is the maintenance of a constant internal environment in organisms, despite external changes. This allows the environment to be at an optimum for cells to function. Internal conditions must be maintained between set limits and if these limits are exceeded, negative feedback mechanisms work to correct the change and restore the internal environment to the optimum. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Regulating blood-glucose concentration: The level of glucose in the blood must be maintained as part of homeostasis: If the level of glucose in the blood is too high, the water potential of the blood becomes very low, thus water moves out of cells into the blood by osmosis. This leads to cells shrinking and eventually dying. If the level is too low, water potential is high and thus water moves from the blood into the cells, causing them to burst. Maintaining a constant blood-glucose level therefore maintains a constant water potential so no unwanted osmosis occurs. In addition, it means that there is a reliable source of energy for cells. There are two hormones that are used to regulate blood-sugar levels: glucagon and insulin. Both of these are synthesised in cells in the pancreas and are released into the blood from here when the levels of blood-glucose are too high or too low: If a blood-glucose concentration is too high, this will be detected by the pancreas. The pancreas secretes Insulin into the blood. Insulin causes glucose to be converted to glycogen in the liver. It also causes more glucose molecules to diffuse into cells from the blood, lowering the amount of glucose in the blood. Glucagon is released when blood-glucose concentration is too low. Glucagon inhibits glucose being converted to glycogen in the liver and activates an enzyme that converts glycogen to glucose, making more glucose available to cells. It also decreases the respiratory rate in cells so that less glucose is used in respiration. People with diabetes cannot produce insulin. Type 1 diabetes is caused by an autoimmune response in which antibodies attack cells in the pancreas which usually make insulin. This means that no insulin can be produced. In type 2 diabetes, either not enough insulin is produced by the pancreas, or the cells do not respond correctly to the insulin. Type 1 diabetes is usually treated by patients injecting insulin themselves. There are several new treatments being developed, including the use of stem cells and artificial pancreases, although these treatments will be very expensive. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Regulating temperature: It is important to maintain a constant temperature of 37°C in humans as this is the optimum temperature for enzyme reactions. If the temperature was lower, the rate of reaction would decrease so reactions would take too long to occur. If it was too high, the enzymes may denature and prevent reactions from occurring. The temperature is regulated by the hypothalamus in the brain, which contains thermoreceptors. If the temperature moves away from the optimum, a response is triggered to return the temperature to the optimum. Reactions to a low internal temperature: Shivering - muscles contract to produce heat. Vasoconstriction - blood vessels constrict to reduce surface area and move away from the surface of the skin to reduce heat loss. Reactions to a high internal temperature: Sweating- sweat evaporates from the skin, reducing the surface temperature. Vasodilation - blood vessels dilate, causing more heat loss to the environment. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Tropic Responses Tropisms are growth movements in plants that occur in reaction to external stimuli. Plants can show a positive or negative response, and different parts of the plants can show different responses. Phototropism and gravitropism of a shoot is an example of the chemical control of plant growth. These responses are controlled by plant hormones called auxins which cause cell elongation. Auxins are made in shoot tips and move through the plant by diffusion and active transport (short distances), or via the phloem (longer distances). Gravitropism: Gravitropism (also known as geotropism) is a response to gravity. Shoots are negatively gravitropic, as they grow upwards against gravity, whereas roots are positively gravitropic. Phototropism: Phototropism is a response to light. Plant shoots are positively phototropic, as they move towards light in order to allow the plant to absorb more light to photosynthesise. Plant roots are negatively phototropic as they move away from light. Phototropic response: 1. Auxins are produced in the shoot tips, which are then transported down the shoot. 2. Light causes the auxin to move to the shady side of the shoot. 3. The auxin causes cell elongation on the shady side. 4. The cells grow faster on the shaded side, thus the shoot bends towards the light. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc