This is all the content required for biology paper 2. Each topic/lesson subheading has a link to either a cognito or Free Science lessons video. This doc states if the topic is triple content. Also includes required practicals.
Biology paper 2 video notes
HOMEOSTASIS AND RESPONSE
Homeostasis:
- Homeostasis is the regulation of the internal conditions of a cell or organism to
maintain optimal conditions for function in response to internal and external changes.
- For example, any sort of exercise places demands on the body. For example
respiration will use glucose to generate energy. This can cause blood glucose
concentration to fall. The athlete’s body temp will rise. He will lose water through
sweating
- In an automatic control system, there are three features. Receptor cells detect
changes in the environment - stimulus. The receptor cells now pass information to a
coordination centre. It receives and processes the information from the receptor cells.
The coordination system now sends instructions to the effector. An effector is a
muscle or a gland. The job of an effector is to carry out the response (restore the
optimum level).
The nervous system:
- The nervous system consists of two parts: the central nervous system which is the
brain and spinal cord and then we have other nerves running to and from the CNS.
- Receptors - cells that detect stimuli (changes in the environment) and send electrical
impulses down neurons to the cns.
- Coordination centres - process the information received from the receptors, e.g.
CNS. This now sends electrical impulses down other neurons to effectors.
- Effectors - bring about responses to bring the conditions in the body back to optimum
levels e.g. muscles which contract or a gland which secretes hormones.
- When you touch a hot object, first the stimulus is detected by a receptor. In this case
the stimulus is heat and the receptor is in the skin. Electrical impulses now pass from
the receptor along a sensory neuron to the central nervous system. At the end of the
sensory neuron is a junction called a synapse. At the synapse a chemical is released
which now diffuses across to a relay neuron in the CNS where it triggers an electrical
impulse. This now passes across the relay neuron and reaches another synapse.
Once again a chemical is released which triggers an electrical impulse in a motor
neuron. The electrical impulse now passes down the motor neuron to an effector. In
this case the effector is a muscle. The muscle now contracts and pulls the hand away
from the heat. Pulling the hand away is the response.
- Receptor cells convert a stimulus into an electrical impulse. This electrical impulse
travels along cells called sensory neurons to the central nervous system. Here, the
information is processed and the appropriate response is coordinated resulting in an
electrical impulse being sent along a relay neuron then a motor neuron to effector.
The effectors carry out the response.
- Automatic responses which take place before you have time to think are called
reflexes. They are important as they prevent the individual from getting hurt. This is
because the information travels down a pathway called a reflex arc, allowing vital
responses to take place quickly. This pathway is different from the usual response to
stimuli because the impulse does not pass through the conscious areas of your brain.
- Synapses are the gaps between two neurons. When the impulse reaches the end of
the first neuron, a chemical is released into the synapse. This chemical diffuses
, across the synapse. When the chemical reaches the second neuron, it triggers the
impulse to begin again in the next neuron.
- Your reaction time is how long it takes you to respond to a stimulus.
The brain (triple):
- It’s difficult to treat brain damage or
diseases. The brain is protected by the
skull so drugs given to treat diseases
cannot always reach the brain
because of the membranes that
surround it. Secondly, the structures of
the brain are extremely complex and
it’s difficult to work out exactly which
parts of the brain carry out specific
functions. Lastly, the brain is extremely
delicate and easy to damage.
- To investigate the brain, many scientists look at patients who have suffered brain
damage. By looking to see where the damage has taken place, they can try to link
that part of the brain to its function. We can also electrically stimulate different parts
of the brain and look at the effects on the person’s behaviour. We can use MRI
scanning to look at which part of the brain is the most active during different
activities.
The eye (triple):
- Retina: layer of light sensitive cells found at the back of the eye. When light hits this,
the cells are stimulated. Impulses are sent to the brain, which interprets the
information to create an image
- Optic nerve: a nerve that leaves the eye and leads to the brain. It carries the
impulses from the retina to the brain to create an image.
- Sclera: white outer layer which supports the structures inside the eye. It is strong to
prevent some damage to the eye.
- Cornea: the transparent front of the eye. It allows light through and the curved
surface bends and focuses light onto the retina.
- Iris: muscles that surround the pupil. They contract or relax to alter the size of the
pupil. In bright light, the circular muscles contract and radial muscles relax to make
the pupil smaller - avoiding damage to the retina. In dim light, the circular muscles
relax and the radial muscles contract to make the pupil larger - so more light can
enter to create a better image.
-
, How the eye focuses (triple):
- The ability to change the shape of the lens to focus on near or distant objects is
called accommodation:
- Light from near objects needs to be focused a large amount. The ciliary muscle
contracts and this causes the suspensory ligaments to loosen. Now the lens is
thicker and refracts the light rays more strongly. The light rays are now focused to a
point on the retina.
- Light from distant objects needs to be focused only a relatively small amount. In this
case, the ciliary muscle relaxes and the suspensory ligaments are pulled tight. The
lens is now pulled thin. Because the lens is thin, the light rays are only slightly
refracted. The light rays are now focused on the retina.
- Long-sightedness is called hyperopia. These people cannot focus on nearby objects.
In this case, the light is focused at a point behind the retina. The lens is too flat so it
cannot refract light enough. Long sight can be treated by using glasses with convex
lenses, these partially focus the light on the retina before it enters the eye.
- Short sight is myopia. People with short sight can’t focus on distant objects. The light
is focused at a point in front of the retina. It can also be caused when the lens is too
thick. Short sight can be treated using glasses with concave lenses to partially
unfocus the light before it enters the eye.
- Contact lenses - work in the same way as glasses but allow activities such as sport
to be carried out, hard or soft contact lenses last for different lengths of time.
- Laser eye surgery - lasers can be used to either reduce the thickness of the cornea
(so it refracts light less) to treat myopia or change its curvature (so it refracts light
more strongly) to treat hyperopia.
- Replacement lens- Hyperopia can be treated by replacing the lens with an artificial
one made of clear plastic (or adding the plastic on top of the natural lens). The risks
include damage to retina or cataracts developing.
Thermoregulation (triple):
- The thermoregulatory centre which monitors and controls body temperature is found
in the brain. Has receptors that monitor the temperature of the blood. Has receptors
in the skin that send impulses to the thermoregulatory centre.
- Human body temperature is 37.5 degrees celsius. When the body temperature gets
too high (for example if a person is exercising), sweat glands release sweat onto the
surface of the skin. The sweat now evaporates, increasing energy transfer away from
the body, cooling it down.
- Under the surface of the skin, we have a fine network of blood capillaries which are
supplied with blood by blood vessels deeper in the skin. If we get too hot, the blood
vessels dilate causing the skin to turn red. This is called vasodilation. Because the
blood vessels have dilated which means more blood flows closer to the surface of the
skin. This results in increased energy transfer from the body.
- If the body is too cold, the blood vessels supplying the capillaries constrict. This is
called vasoconstriction. Less blood now flows closer to the surface and less heat is
lost from the body. We also respond when our body temperature drops too low by
shivering. When we shiver, or muscles contract. To generate energy for this
contraction the muscle cells increase their rate of respiration. This releases heat
which warms the body. Hair stands on end to create an insulating layer, trapping
warm air.
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