Topic 6 Alevel Biology

• What is a stimulus in the context of survival and response?

  A stimulus is something that can be detected by an organism.
• What is the role of a receptor in an organism?

  A receptor is an organ or specialized cell that detects changes causing a stimulus.
• What is a response in the context of stimuli and receptors?

  A response is the action taken as a result of a detected stimulus.
• What is a taxis?

  A taxis is a response that involves movement in a specific direction.
• What is positive taxis?

  Positive taxis is movement towards the stimulus.
• What is negative taxis?

  Negative taxis is movement away from the stimulus.
• Give an example of positive chemotaxis.

  Mobile bacteria moving to an area with a higher concentration of glucose.
• What is kinesis?

  A kinesis is a response involving random movement in various directions.
• How does kinesis increase an organism's chances of survival?

  Kinesis increases the chance of entering different conditions more rapidly.
• What happens to a woodlouse placed in a dry area?

  It will speed up and change direction more frequently to find damp conditions.
• What are tropisms in plants?

  Tropisms are growth responses controlled by a directional stimulus.
• What is phototropism?

  Phototropism is the growth of plants towards light.
• How do shoots and roots respond to light in phototropism?

  Shoots are positively phototropic and grow towards light, while roots are negatively phototropic and grow away from light.
• What is indoleacetic acid (IAA)?

  IAA is an important auxin produced in the tips and shoots of flowering plants.
• How does IAA affect plant growth?

  The distribution of IAA controls tropisms and causes uneven growth if distributed unevenly.
• What happens when a shoot is illuminated from all sides?

  IAA is distributed evenly, causing elongation of cells across the zone of elongation.
• What occurs when a shoot is illuminated from one side?

  IAA moves towards the shaded part, causing elongation of the shaded side and bending towards the light.
• What is gravitropism in roots?

  Gravitropism is when IAA builds up on the lower side of the root, inhibiting growth and causing the root to bend downwards.
• What are reflexes?

  Reflexes are rapid automatic responses that protect an organism from harmful stimuli.
• What is the general path of a reflex arc?

  The general path is: Stimulus → Receptor → Sensory Neurone → Intermediate Neurone → Motor Neurone → Effector → Response.
• What does the sensory neurone do in a reflex arc?

  The sensory neurone carries the nerve impulse from the receptor to the spinal cord.
• Where is the intermediate neurone located?

  The intermediate neurone is located entirely in the spinal cord.
• What does the motor neurone do in a reflex arc?

  The motor neurone carries the nerve impulse from the spinal cord to the effector.
• What do receptors detect?

  Receptors detect changes in the internal and external environment.
• What are photoreceptors?

  Photoreceptors are light receptors in the eye.
• How does light enter the eye?

  Light enters the eye through the pupil, controlled by the iris.
• Where are photoreceptors located in the eye?

  Photoreceptors are located in the retina, specifically in the fovea.
• What happens to nerve impulses received by photoreceptors?

  Nerve impulses are carried via the optic nerve to the brain.
• What is the blind spot in the eye?

  The blind spot is where the optic nerve leaves the eye, with no photoreceptor cells present.
• What are the two types of photoreceptors in the retina?

  The two types are cones for color vision and rods for monochromatic vision.
• Where are cone cells most densely located?

  Cone cells are present at the greatest density in the fovea of the eye.
• What pigment do cone cells contain?

  Cone cells contain the pigment iodopsin.
• What is the light sensitivity of cone cells?

  Cone cells are not sensitive to light and require bright light to function.
• What are the three types of cone cells sensitive to?

  They are sensitive to the primary colors of light: red, green, or blue.
• What is the visual acuity provided by cone cells?

  Cone cells provide good visual acuity due to each having its own synapse.
• Where are rod cells mainly concentrated?

  Rod cells are mainly concentrated outside of the fovea.
• What pigment do rod cells contain?

  Rod cells contain the pigment rhodopsin.
• What is the light sensitivity of rod cells?

  Rod cells are very sensitive to light and function in low light conditions.
• What is the visual acuity provided by rod cells?

  Rod cells provide low visual acuity as multiple rods share the same synapse.
• What is the heart referred to as due to its ability to initiate its own contraction?

  The heart is referred to as myogenic.