topic 9

• What is homeostasis?


  Maintaining a constant internal environment, and keeping conditions such as tempretature, water content, and glucose levels at a steady level to allow enzymes to function properly.
• What is the process of a coordinated response?


  Stimuli ---> Receptor ---> Response
• What is an example of a stimuli?


  - change in temperature

  - noise levels

  - increase in a certain chemical
• What is an example of a response?


  - muscle contractions

  - hormone release.
• What is the synapse/synaptic cleft?


  The small gap between two adjacent neurons, consisting of the presynaptic and postsynaptic membranes and the space between them, and this is where chemical messengers called neurotransmitters diffuse across.
• How is the nerve signal transferred?


  An impulse stimulates the release of a neurotransmitter from the relay neurone into the synapse, the neurotransmitter carrying the information from the relay neurone, diffuses down a concentration gradient across the synapse. These chemicals then set off a new electrical signal in the next neurone.
• What are three types of neurones?


  Sensory, motor and relay neurones
• What does a coordinated response require?

  - A stimulus (a change in the environment)

  - A receptor (receptor cells that detect stimuli)

  - An effector (produce a response)
• What is a tropism?


  - A growth response in a plant in which the direction of the stimulus determines the direction of growth in the plant

  1) phototropism (light)

  2) geotropism (gravity)
• What is a positive geotropism?


  Positive gravitropism occurs when roots grows downwards into the soil because they grow in the direction of gravity
• What is negative geotropism?


  Negative gravitropism occurs when shoots grow up toward sunlight in the opposite direction of gravity
• What is positive phototropism?


  Shoots grow towards light allowing them to maximise the amount of light they absorb for photosynthesis
• What is negative phototropism?


  Roots grow away from light ensuring that they grow deeper into the soil, anchoring the plant into the ground
• What is the strongest response, phototropism or geotropism?


  Phototropism - it is the strongest response of the shoots of a plant. They will grow towards the light so that their leaves can generate energy through photosynthesis.
• What is auxin?


  Auxin is a plant hormone that regulates phototropism and geotropism
• What do shoots do in response to light (phototropism)?


  - When a shoot tip is exposed to light, it accumulates more auxin on the side that is shaded than the side directing the light.

  - This makes the cells elongate faster on the shaded side, so the shoot bends towards the light.
• What do shoots do in response to gravity (geotropism)?


  - When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side.

  - This causes the lower side to grow faster, bending the shoot upwards.
• What do roots do in response to gravity (geotropism)?


  - A root growing sideways will accumulate more auxin on its lower side.

  - But in a root the extra auxin inhibits growth, meaning the cells on the top elongate faster, so the root bends downwards.
• What do roots do in response to light (phototropism)?


  - If a root starts being exposed to more light, more auxin accumulates on the more shaded side.

  - The auxin inhibits cell elongation on the shaded side, so the root bends downwards, back into the ground.
• What are the two response systems in the human body?

  - The nervous system

  - Hormones
• What are the differences between the hormonal and the nervous system?


  - The nervous system produces electrical impulses, which are fast, short term impulses.

  - Hormones produce chemicals which travel via blood, so they're slower acting, however longer lasting impulses.
• What does the central nervous system consist of?


  The brain and the spinal cord, Whig are linked to the sense organs via nerves.
• How do stimulation of receptors cause a response?


  Sense organs —> electrical impulses along nerves —> CNS —> rapid electrical impulses
• What is the reflex arc pathway?


  - The stimulus is detected by the receptor

  - An impulse is then transmitted down the sensory neurone towards the CNS

  - In the CNS there is a synapse and a relay neurone which take it through the CNS

  - The impulse then moves from the CNS to the effector through the motor neurone

  - The effector then causes a protective response against the stimulus, for example; muscles contract and pull your hand away from the stimulus (withdrawal reflex)
• What is the role of neurotransmitters?


  - They act as a chemical messenger carrying information from one neurone to another.

  - Neurotransmitters allow communication between the two cells on either side of the synaptic cleft, because nerve impulses can't travel across the synaptic cleft.
• What is the function of the eye as a receptor?


  Receptors in the eye are sensory cells that respond to light stimuli and transmit signals via the nerves to the brain.
• What is the function of the cornea?


  The cornea is the clear outer layer of the eye that helps to focus light onto the retina. It's a curved surface that helps to bend the light, making it easier for the lens to focus the light onto the retina.
• What is the function of the iris?


  The iris is the colored part of the eye that controls the amount of light that enters the eye, it does this by altering the size of the pupil.
• What is the function of the lens?


  The lens is a flexible structure located behind the iris that helps to focus light onto the retina. It changes shape to adjust the focus of the light, allowing us to see objects at different distances clearly.
• What is the function of the retina?


  The retina receives light that the lens has focused, and it converts the light into neural signals, and send these signals on to the brain for visual recognition.
• What is the function of the optic nerve?


  The optic nerve transmits electrical impulses from your eyes to your brain, your brain processes this sensory information so that you can see.
• How does the eye respond to changes in light intensity?


  Increased light = circular muscles contract, radial muscles relax, the pupil constricts to let less light in.

  
  

  Dim light = circular muscles relax, radial muscles contract, the pupil dilates to allow more light in, increasing vision.
• What is the reflex about allowing bright light into the eyes?


  Light receptors detect the bright light, and send a message along the sensory neurone, which tells the circular muscles in the iris to contract, therefore making the pupil smaller.
• How does the eye focus on near objects?


  NEAR = ciliary muscles contract, suspensory ligaments slacken, meaning the lens thickens and increases its curvature, this allows the eye to refract light rays from the near object more sharply and bring the object into focus on the retina.
• How does the eye focus on distant objects?


  DISTANCE = The suspensory ligaments contract, the ciliary muscles relax, the less becomes thinner and less curved, meaning it refracts light rays less strongly to focus on the retina.
• What is vasodilation (hot)?


  Blood vessels dilate - this means that more blood can pass close to the skin, and so more heat can be lost through conduction to the environment.

  
  

  Sweating - sweat glands open up, causing our skin to release more sweat through pores in the epidermis. When there is more sweat, more heat is given to the environment through evaporation.

  
  

  Skin hairs lie flat - the hair erector muscles relax, so hair traps less air and heat near the body so the skin is less insulated and heat can be lost more easily.
• What is vasoconstriction (cold)?


  Blood vessels constrict - this means that less blood can pass near to the skin so less heat is lost to the environment.

  
  

  Shivering - when shivering, energy is released as heat from the muscles as more respiration takes place to provide energy for the shivering.

  
  

  Skin hairs stand up - the hair erector muscles contract, causing more air to be trapped near the skin, leading to less heat loss as it provides insulation.

  
  

  Sweat less - by sweating less when you are cold, you lose less heat.
• What is the role of adrenaline?


  - Adrenaline is a hormone produced by the adrenal glands

  - It is produced in many situations such as; physical threat, excitement, noise, and bright lights

  - Triggers the 'fight or flight' response

  - Increased heart rate

  - Increased blood pressure

  - Pupil dilatation

  - Bronchioles widen
• What is the role of insulin?


  - Insulin is a hormone produced by the pancreas

  - Insulin is released to control the level of glucose in your blood

  - Regualtes metabolism

  - Allows the body to store extra sugar as fuel

  - Regulates blood sugar levels

  - Regulates glucose levels