Lecture 5: sensing the environment II

Question 1

What does “seeing” mean from the perspective of vision?
A) Detecting sound waves in the environment
B) Detecting wavelengths of the electromagnetic spectrum
C) Detecting electric fields from other organisms
D) Detecting radio waves through water

Answer 1

Correct Answer: B) Detecting wavelengths in the electromagnetic spectrum

Question 2

What is the visible light range for human vision?
A) 100–350 nm
B) 350–750 nm
C) 750–1,000 nm
D) 10⁻³–10¹ m

Answer 2

Correct Answer: B) 350–750 nm

Question 3

What does the narrow band of visible light suggest about humans?
A) We evolved in a terrestrial environment.
B) We evolved in aquatic environments.
C) We have the ability to detect microwaves.
D) We can perceive electric fields like sharks.

Answer 3

Correct Answer: B) We evolved in aquatic environments.

Question 4

Why can humans not see microwaves?
A) Microwaves are too fast to detect.
B) Microwaves experience significant attenuation in water.
C) Microwaves are too weak to interact with photoreceptor cells.
D) Microwaves fall outside the electromagnetic spectrum.

Answer 4

Correct Answer: B) Microwaves experience significant attenuation in water.

Question 5

What type of radiation do some aquatic organisms, like sharks, detect?
A) Visible light
B) Electric fields
C) Microwaves
D) Radio waves

Answer 5

Correct Answer: B) Electric fields

Question 6

What is the main function of stereocilia in hair cells?
A) To release neurotransmitters
B) To detect mechanical stimuli
C) To produce action potentials
D) To amplify sound waves

Answer 6

Correct Answer: B) To detect mechanical stimuli

Question 7

What happens to hair cells when stereocilia are displaced toward the kinocilium?
A) The cell hyperpolarizes.
B) The cell depolarizes.
C) The cell remains at resting potential.
D) Neurotransmitter release decreases.

Answer 7

Correct Answer: B) The cell depolarizes.

Question 8

What is the “dark current” in rod cells?
A) Continuous influx of K⁺ in the light
B) Continuous influx of Na⁺ in the dark
C) Continuous efflux of Na⁺ in the dark
D) Closing of cGMP-gated channels

Answer 8

Correct Answer: B) Continuous influx of Na⁺ in the dark

Question 9

What happens to rod cells in response to bright light?
A) They depolarize, increasing neurotransmitter release.
B) They hyperpolarize, reducing neurotransmitter release.
C) cGMP-gated Na⁺ channels open.
D) The resting membrane potential becomes less negative.

Answer 9

Correct Answer: B) They hyperpolarize, reducing neurotransmitter release.

Question 10

Which photoreceptor pigment is activated in rods by light?
A) Rhodopsin
B) Opsin
C) Photopsin
D) Melanopsin

Answer 10

Correct Answer: A) Rhodopsin

Question 11

Why does light hyperpolarize rod cells?
A) It opens K⁺ channels.
B) It reduces cGMP, closing Na⁺ channels.
C) It increases the activity of Na⁺/K⁺ ATPase pumps.
D) It activates calcium influx.

Answer 11

Correct Answer: B) It reduces cGMP, closing Na⁺ channels.

Question 12

Explain the process of phototransduction in rod cells, starting from light absorption. Explain each of the 6 steps.

Answer 12

1. Light is absorbed → Rhodopsin activated
   ✅ 2. Retinal changes from cis to trans → Rhodopsin fully activated
   ✅ 3. Rhodopsin activates transducin (G-protein)
   ✅ 4. Transducin activates phosphodiesterase (PDE)
   ✅ 5. PDE breaks down cGMP → Na⁺ channels close → Hyperpolarization
   ✅ 6. No Ca²⁺ entry → No neurotransmitter release (this means brain gets signal that we are percieving dim lighting - lack of neurotransmitter is perceived as light - dim light in this case)

Question 13

What is photoreception?
A) The ability to respond to sound waves
B) The ability to detect and respond to light
C) The process of producing photons
D) The process of forming visual pigments

Answer 13

Correct Answer: B) The ability to detect and respond to light

Question 14

Why did photoreception arise early in evolution?
A) Organisms needed to detect electric fields.
B) Sunlight was a weak selective force.
C) Sunlight was a strong selective force.
D) Light-sensitive proteins were absent in early organisms.

Answer 14

Correct Answer: C) Sunlight was a strong selective force

Question 15

What allows photoreception to be possible in most organisms?
A) Clusters of photoreceptive organs
B) The presence of light-sensitive proteins called photopigments
C) High concentrations of neurotransmitters
D) The production of photons by photoreceptor cells

Answer 15

Correct Answer: B) The presence of light-sensitive proteins called photopigments

Question 16

What happens to photopigments when exposed to light?
A) They amplify photons.
B) They change conformation.
C) They produce ATP.
D) They are destroyed.

Answer 16

Correct Answer: B) They change conformation

Question 17

What is the primary function of photoreceptor cells?
A) To produce light
B) To convert photons into electrical signals
C) To increase cGMP levels
D) To cluster into sensory neurons

Answer 17

Correct Answer: B) To convert photons into electrical signals

Question 18

Where are photoreceptor cells commonly found?
A) In clusters within sensory organs such as the eyes
B) Spread evenly across the entire body
C) Only in aquatic organisms
D) Only in organisms exposed to UV radiation

Answer 18

Correct Answer: A) In clusters within sensory organs such as the eyes

Question 19

Which of the following statements about photoreceptor cells is true?
A) They are insensitive to light.
B) They directly produce neurotransmitters.
C) They are responsible for transducing photons into electrical signals.
D) They are only present in animals with complex eyes.

Answer 19

Correct Answer: C) They are responsible for transducing photons into electrical signals.

Question 20

Which of the following statements about ciliary photoreceptors is TRUE?
A) They are found primarily in invertebrates.
B) They rely on microvilli to detect light.
C) They are the main photoreceptors in vertebrates.
D) They are only found in aquatic organisms.

Answer 20

Correct Answer: C) They are the main photoreceptors in vertebrates.

Question 21

What are rhabdomeric photoreceptors primarily associated with?
A) Vertebrates
B) Invertebrates
C) Mammals only
D) Fish and amphibians

Answer 21

Correct Answer: B) Invertebrates

Question 22

Which structural feature is associated with rhabdomeric photoreceptors?
A) Microvilli
B) Cilia
C) Photopigments without membranes
D) Chloroplasts

Answer 22

Correct Answer: A) Microvilli

Question 23

Which of the following best describes ciliary photoreceptors?
A) They rely on microvilli for light detection.
B) They have a single cilium with a highly folded membrane.
C) They are only found in invertebrates.
D) They lack photopigments.

Answer 23

Correct Answer: B) They have a single cilium with a highly folded membrane.

Question 24

What is the primary function of the cilium in ciliary photoreceptors?
A) To generate action potentials.
B) To provide structural support.
C) To house photopigments for detecting light.
D) To process neurotransmitter release.

Answer 24

Correct Answer: C) To house photopigments for detecting light.

Question 25

Which of the following statements about mammalian photoreceptors is TRUE? A) Cones are specialized for dim light and black-and-white vision. B) Rods are used for detecting colors in bright light. C) Mammals have two types of ciliary photoreceptors: rods and cones. D) Both rods and cones function equally well in bright light.

Answer 25

Correct Answer: C) Mammals have two types of ciliary photoreceptors: rods and cones.

Question 26

Which of the following is FALSE about cones and rods? A) Cones are responsible for color vision and function best in bright light. B) Rods are specialized for dim light and black-and-white vision. C) Rods are less important than cones in nocturnal animals. D) Cones are less sensitive to light than rods.

Answer 26

Correct Answer: C) Rods are less important than cones in nocturnal animals.

Question 27

What distinguishes rods from cones? A) Rods function in bright light, while cones function in dim light. B) Cones are used for detecting color and bright light, while rods are used for dim light and black-and-white shades. C) Rods are present in invertebrates, while cones are exclusive to vertebrates. D) Cones rely on microvilli, while rods rely on a single cilium.

Answer 27

Correct Answer: B) Cones are used for detecting color and bright light, while rods are used for dim light and black-and-white shades.

Question 28

Which of the following is found in the outer segment of rods and cones? A) Nucleus B) Synaptic vesicles C) Discs with photopigments D) Mitochondria

Answer 28

Correct Answer: C) Discs with photopigments

Question 29

Which of the following is NOT a shared feature of rods and cones? A) Both are receptor cells. B) Both contain outer segments with discs that house photopigments. C) Both have synaptic terminals at the base. D) Rods are used for color vision, while cones are used for dim light.

Answer 29

Correct Answer: D) Rods are used for color vision, while cones are used for dim light.

Question 30

Where are the nucleus and organelles located in rods and cones? A) In the outer segment B) In the inner segment C) In the synaptic terminals D) In the photopigment discs

Answer 30

Correct Answer: B) In the inner segment

Question 31

Which of the following statements about rods and cones is FALSE? A) Rods and cones share similar structural features, including outer and inner segments. B) The outer segment contains discs that house photopigments. C) Synaptic terminals are located at the top of the cell. D) Rods are more extensively studied than cones.

Answer 31

correct Answer: C) Synaptic terminals are located at the top of the cell.

Question 32

Which of the following is a characteristic of rods? A) Faster response time than cones B) Detect specific color wavelengths C) High sensitivity in low light D) Found in high numbers in diurnal animals

Answer 32

Correct Answer: C) High sensitivity in low light

Question 33

Why do nocturnal animals have a high number of rods? A) Rods are more sensitive to color. B) Rods have higher sensitivity to dim light. C) Rods saturate in bright light. D) Rods require photopigments for high-speed responses.

Answer 33

Correct Answer: B) Rods have higher sensitivity to dim light.

Question 34

Which of the following is FALSE about frogs’ photoreceptors? A) Frogs only have rods but can still detect color. B) Frogs rely on cones for color detection. C) Frogs demonstrate diversity in the shape of rods and cones. D) Frogs use photopigment properties to detect color.

Answer 34

Correct Answer: B) Frogs rely on cones for color detection.

Question 35

What is a unique feature of rods compared to cones? A) Ability to detect multiple colors. B) Faster response times. C) Greater amounts of photopigment. D) Exclusively found in diurnal animals.

Answer 35

Correct Answer: C) Greater amounts of photopigment.

Question 36

What are the two components of a photopigment? A) Retinal and vitamin A B) Chromophore and G-protein coupled receptor C) Rhodopsin and opsin D) Chromophore and rhodopsin

Answer 36

Correct Answer: B) Chromophore and G-protein coupled receptor

Question 37

What is a chromophore? A) A protein responsible for initiating the phototransduction cascade B) A molecule that absorbs light and is a derivative of vitamin A C) A protein that stabilizes photoreceptor cells D) A molecule that reflects light to enhance vision

Answer 37

Correct Answer: B) A molecule that absorbs light and is a derivative of vitamin A

Question 38

Which of the following is TRUE about rhodopsin? A) It is a chromophore by itself. B) It consists of retinal and opsin. C) It is found only in cones. D) It does not vary in sensitivity to different wavelengths.

Answer 38

Correct Answer: B) It consists of retinal and opsin.

Question 39

Which of the following is FALSE about photopigments? A) Photopigments consist of a chromophore and a G-protein coupled receptor. B) Rhodopsin is a dominant photopigment found in animals. C) Retinal, a chromophore, is derived from vitamin A. D) Photopigments do not change shape in response to light.

Answer 39

Correct Answer: D) Photopigments do not change shape in response to light.

Question 40

What happens when light interacts with rhodopsin? A) Retinal is released into the extracellular environment. B) Retinal changes its shape, initiating a phototransduction cascade. C) Opsin becomes inactive and ceases signal transduction. D) G-proteins are inhibited, halting the visual signal.

Answer 40

Correct Answer: B) Retinal changes its shape, initiating a phototransduction cascade.

Question 41

What family of genes does the G-protein coupled receptor in photopigments belong to? A) Rhodopsin gene family B) Retinal gene family C) Opsin gene family D) Phototransduction gene family

Answer 41

Correct Answer: C) Opsin gene family

Question 42

What happens to 11-cis retinal when it absorbs a photon of light? A) It is converted to all-trans retinal. B) It is degraded into vitamin A. C) It remains unchanged. D) It is converted to an inactive form.

Answer 42

Correct Answer: A) It is converted to all-trans retinal.

Question 43

What is required for the conversion of all-trans retinal back to 11-cis retinal? A) GTP B) ATP C) ADP D) Photons of light

Answer 43

Correct Answer: B) ATP

Question 44

Why might it take time to adjust when moving from bright light into a dark room? A) The rods need time to regenerate photopigments as all-trans retinal is converted back to 11-cis retinal. B) Cones are overactive in low-light conditions. C) All-trans retinal degrades completely in low light. D) The photoreceptor cells stop functioning in the dark.

Answer 44

Correct Answer: A) The rods need time to regenerate photopigments as all-trans retinal is converted back to 11-cis retinal.

Question 45

Which of the following statements about retinal is FALSE? A) 11-cis retinal converts to all-trans retinal when exposed to light. B) ATP is required to convert all-trans retinal back to 11-cis retinal. C) Retinal undergoes a bleaching process after isomerization. D) The conversion of 11-cis retinal to all-trans retinal occurs in the absence of light.

Answer 45

Correct Answer: D) The conversion of 11-cis retinal to all-trans retinal occurs in the absence of light.

Question 46

What is the effect of light on photoreceptor cells? A) Light depolarizes the membrane. B) Light opens cation channels. C) Light hyperpolarizes the membrane. D) Light has no effect on photoreceptor cells.

Answer 46

Correct Answer: C) Light hyperpolarizes the membrane.

Question 47

How does light cause hyperpolarization in photoreceptor cells? A) By opening cGMP-gated Na⁺ channels B) By increasing cation influx C) By closing cGMP-gated Na⁺ channels D) By depolarizing cation channels

Answer 47

Correct Answer: C) By closing cGMP-gated Na⁺ channels

Question 48

Which of the following stimuli causes the greatest hyperpolarization? A) Dim light stimulus B) Medium light stimulus C) Bright light stimulus D) No light

Answer 48

Correct Answer: C) Bright light stimulus

Question 49

Which of the following statements about phototransduction is FALSE? A) Light hyperpolarizes photoreceptor cells. B) Phototransduction closes cation channels in response to light. C) Dim light produces a slight hyperpolarization. D) Hyperpolarization leads to the opening of cGMP-gated Na⁺ channels.

Answer 49

Correct Answer: D) Hyperpolarization leads to the opening of cGMP-gated Na⁺ channels.

Question 50

What is the role of phosphodiesterase (PDE) in phototransduction? A) It opens Na⁺ channels. B) It converts cGMP to GMP. C) It increases cGMP levels. D) It hyperpolarizes the photoreceptor directly.

Answer 50

Correct Answer: B) It converts cGMP to GMP.

Question 51

What does activated opsin do during phototransduction? A) It binds directly to cGMP. B) It activates transducin, a G protein. C) It increases the levels of cGMP. D) It opens cGMP-gated Na⁺ channels.

Answer 51

Correct Answer: B) It activates transducin, a G protein.

Question 52

Which of the following statements about phototransduction is TRUE? A) Light leads to the opening of cGMP-gated Na⁺ channels. B) The cell becomes depolarized in response to light. C) Less neurotransmitter is released when the cell is hyperpolarized. D) PDE converts GMP into cGMP, opening Na⁺ channels.

Answer 52

Correct Answer: C) Less neurotransmitter is released when the cell is hyperpolarized.

Question 53

Which of the following is FALSE about phototransduction? A) Light converts 11-cis retinal into all-trans retinal. B) Transducin activates phosphodiesterase (PDE). C) Hyperpolarization increases neurotransmitter release. D) Reduction in cGMP causes cGMP-gated Na⁺ channels to close.

Answer 53

Correct Answer: C) Hyperpolarization increases neurotransmitter release.

Question 54

Why do rod cells hyperpolarize when exposed to light? Explain the changes in ion channel activity, membrane potential, and neurotransmitter release.

Answer 54

In the presence of light, rhodopsin is activated, leading to the conversion of 11-cis retinal to all-trans retinal. Activated rhodopsin triggers a cascade where transducin (a G-protein) activates phosphodiesterase (PDE). PDE reduces cGMP levels by converting it to GMP. The reduction in cGMP causes cGMP-gated Na⁺ channels to close, stopping the influx of sodium ions (Na⁺). Potassium (K⁺) continues to leak out through potassium channels, making the inside of the cell more negative. This unbalanced potassium efflux causes the cell to hyperpolarize, lowering the membrane potential to around -70 mV. Hyperpolarization causes voltage-gated calcium (Ca²⁺) channels in the synaptic terminal to close. The decrease in calcium influx reduces the release of the neurotransmitters, signaling the presence of light to downstream neurons.

Question 55

Why do rod cells remain depolarized in the dark? Explain the role of ion channel activity, membrane potential, and neurotransmitter release.

Answer 55

In the dark, cGMP levels are high because no light is present to activate the phototransduction cascade. High cGMP levels keep cGMP-gated Na⁺ channels open, allowing sodium ions (Na⁺) to flow into the outer segment of the rod cell. This inward Na⁺ current, known as the dark current, is balanced by the continuous efflux of potassium (K⁺) through K⁺ leak channels in the inner segment. The membrane potential is maintained at a depolarized state of about -35 mV. Depolarization keeps voltage-gated calcium (Ca²⁺) channels in the synaptic terminal open. The influx of calcium ions allows the continuous release of neurotransmitters, which signals the absence of light to downstream neurons.

Question 56

Which type of eye is the simplest and found in barnacles? A) Flat-sheet eye B) Cup-shaped eye C) Vesicular eye D) Convex eye

Answer 56

Correct Answer: A) Flat-sheet eye

Question 57

Which type of eye allows for better shape distinction but lets in less light? A) Flat-sheet eye B) Cup-shaped eye C) Vesicular eye D) Compound eye

Answer 57

Correct Answer: B) Cup-shaped eye

Question 58

What is a distinguishing feature of the vesicular eye? A) It is dome-shaped with afferent neurons. B) It has a lens to focus light on the retina. C) It creates a mosaic image using ommatidia. D) It is the simplest form of an eye.

Answer 58

Correct Answer: B) It has a lens to focus light on the retina.

Question 59

What type of eye is found in insects? A) Flat-sheet eye B) Cup-shaped eye C) Vesicular eye D) Convex eye

Answer 59

Correct Answer: D) Convex eye

Question 60

What are the multicellular units that make up a compound eye called? A) Retinas B) Ommatidia C) Pigment layers D) Photoreceptors

Answer 60

Correct Answer: B) Ommatidia

Question 61

Which of the following is TRUE about ommatidia? A) Each ommatidium lacks its own lens and cornea. B) Ommatidia collectively create a mosaic image. C) Ommatidia are present in vesicular eyes. D) Each ommatidium processes color vision exclusively.

Answer 61

Correct Answer: B) Ommatidia collectively create a mosaic image.

Question 62

How does the number of ommatidia vary across species? A) All species have approximately the same number. B) The number ranges from 1 to 25,000 depending on the species. C) Larger animals always have fewer ommatidia. D) Dragonflies typically have fewer ommatidia than ants.

Answer 62

Correct Answer: B) The number ranges from 1 to 25,000 depending on the species.

Question 63

Which of the following species is most likely to have a convex eye? A) Barnacle B) Squid C) Dragonfly D) Cephalopod

Answer 63

Correct Answer: C) Dragonfly