Topic 6A+B: Survival and Response, and Receptors Flashcards
What type of behaviour is being shown if an organisms is moving directly towards or away from a stimulus? [1]
- Taxis
What type of behavioural response is being shown if an organism is moving slowly and turning a lot in a favourable condition?
- Kinesis
What is the name of a directional response that involves an organism either growing towards or away from a stimulus? [1]
- Tropism
Give one similarity and one difference between a taxis and a tropism. [2]
- Similarity - directional response (to a stimulus);
- Difference - taxis (whole) organism moves and tropism a growth (response).
IAA is a specific growth factor.
Name the process by which IAA moves from the growing regions of a plant shoot to other tissues. [1]
- Diffusion
When a young shoot is illuminated from one side, IAA stimulates growth on the shaded side. Explain why growth on the shaded sided helps to maintain the leaves in a favourable environment. [2]
- Causes plant to bend / grow towards light / positive phototropism;
- (Light) required for photosynthesis
How many neurones would you expect to find in a simple reflex arc? [1]
- 3 (sensory, relay and motor)
Suggest two advantages of simple reflexes. [2]
- Rapid;
- Protect against damage to body tissues;
- Do not have to be learnt;
- Help escape from predators;
- Enable homeostatic control
Describe how a Pacinian corpuscle produces a generator potential when stimulated. [3]
- (There are) stretch-mediated sodium ion channels (in the membrane);
- (Increased pressure) deforms lamella;
- Sodium ion channels open;
- Sodium ions diffuse in;
- Depolarisation (leading to generator potential)
“People with red-green colour blindness have green-sensitive cones but the green sensitive iodopsin does not function. They are unable to distinguish between red and green, and also between other colours.”
People with red-green colour blindness are unable to distinguish between r ed and green, and also between other colours. Explain why. [3]
- Green sensitive pigment/cones non-functional;
- Three different types of cone;
- Other/different colours seen due to stimulation of more than one cone.
Complete achromatopsia is a form of complete colour blindness. It is caused by having only rods and no functional cone cells.
People with complete achromatospia have difficulty in seeing detail. Explain why. [3]
- No (functional) cones
OR
Only rods; - Several rods connected to a single neurone;
- Single (set of) impulses to brain
The fovea of the eye of an eagle has a high density of cones. An eagle focuses the image of its prey into the fovea.
Explain how the fovea enables an eagle to see its prey in detail. [3]
- High (visual) acuity;
- (Each) cone is connected to a single neurone;
- (Cones send) separate impulses to brain
The retina of an owl has a high density of rod cells.
Explain how this enables an owl to hunt its prey at night. [3]
- High (visual) sensitivity;
- Several rods connected to a single neurone;
- Enough neurotransmitter to reach threshold
After student stared at a purple square and then looked at a white card. The card appeared green. Suggest why. [3]
- (When staring at purple) red sensitive and blue sensitive cones are stimulated;
- Red sensitive and blue sensitive cone cells become exhausted/stop working;
- Green sensitive cone cells still work
Nocturnal mammals are active at night. Describe how the number and distribution of rods and cones across the retina would differ in a nocturnal mammal from the number and distribution in a human. Explain your answer. [3]
- More rods and fewer cones present;
- Rods not mainly at periphery
- Rods have high sensitivity;
- Rhodopsin bleaches at low light intensities
Explain why it takes time for the rod cells to recover their sensitivity to light after moving into darkness. [2]
- Rhodopsin broken down by light;
- Time for resynthesis
When a person looks directly at an object, its image is focused on the fovea.
When the image is focused on the fovea, the person sees the object in colour.
Explain why. [3]
- Colour detected by cone cells;
- Fovea contains (mainly) cone cells;
- Three types of cone cells each sensitive to red, green or blue.
When a person looks directly at an object, its image is focused on the fovea.
Vision using the fovea has high visual acuity but low sensitivity to light compared with vision using other parts of the retina.
Explain why vision using the fovea has high visual acuity. [1]
- Each cone connected to separate neurone
When a person looks directly at an object, its image is focused on the fovea.
Vision using the fovea has high visual acuity but low sensitivity to light compared with vision using other parts of the retina.
Explain why vision using other parts of the retina has high sensitivity to light. [3]
- Many rods in other parts of retina;
- Rods allow high light sensitivity;
- Several rods are connected to a single neurone;
- This makes it more likely that enough neurotransmitter will be released to reach threshold
