UNIT 1

Question 1

What are the functions of light?

Answer 1

Source of energy and provides information to organisms about the physical world.

Question 2

Where does light come from?

Answer 2

It is made from the sun converting hydrogen into helium, creating energy as electromagnetic radiation that reaches the earth in about 8 minutes.

Question 3

What is electromagnetic radiation?

Answer 3

It is the energy produced by the sun as electromagnetic radiation that reaches the earth in about 8 minutes.

Question 4

How does electromagnetic radiation work?

Answer 4

Electromagnetic radiation moves in two waves (electrical/magnetic) that are at 90 degrees of each other, they can be distinguished by their wavelength (distance between two peaks).

Question 5

What consists of an electromagnetic wave?

Answer 5

A wave consists of energy particles called photons, they have no mass but a distinct amount of energy inversely related to its wavelength (blue light have photons with more energy, shorter wavelength have more energy).

Question 6

What is light?

Answer 6

Light is the portion of the electromagnetic spectrum that we can detect with our eyes, from about 400nm to 700nm, light outside this range is called infrared radiation/ ultraviolet light.

Question 7

What are the 3 possible fate for a photon when it hits an object?

Answer 7

It can be reflected off, transmitted through or absorbed.

Question 8

How can a photon be absorbed?

Answer 8

To be used, it has to be absorbed by a pigment molecule. Each pigment molecules can absorb different wavelengths, they are mostly chlorophyl a, retinal and indigo. The energy of a photon must be transferred to an electron of the pigment molecule, once that photon is absorbed by the electron, the electron becomes excited.

Question 9

Why can pigment molecules absorb photons?

Answer 9

They can absorb a photon because of their conjugated system (region where carbon atoms are covalently bonded with alternating single and double bonds), it allows them to delocalize electrons and make them more available to interact with a photon.

Question 10

What are the two necessities for a photon to be absorbed by a pigment molecule?

Answer 10

The electron of a pigment molecule can absorb only one photon, and the energy of the photon must match the energy difference between the ground and excited state.

Question 11

What determines the colour of a pigment?

Answer 11

The colour of a pigment is determined by the wavelength it can’t absorb. Chlorophyll is green because red and blue photons are captured but green photons are not absorbed and therefore are reflected.

Question 12

What is an action spectrum?

Answer 12

An action spectrum shows the effectiveness of different wavelengths to be absorbed.

Question 13

How can light be used as a source of energy?

Answer 13

Photosynthesis uses the energy from the sun to build sugar molecules from carbon dioxide and water, releasing oxygen as a by-product. Other organisms use light as energy but not as photosynthesis, Halobacterium contains bacteriorhodopsin which is a light-dependent proton pump that creates a proton gradient which generates ATP

Question 14

What is a photoreceptor?

Answer 14

It is the basic light-sensing system. The most common is rhodopsin which is the basis of vision in animals but also a photoreceptor for other organisms.

Question 15

What does rhodopsin consist of?

Answer 15

A rhodopsin molecule consists of a membrane protein called opsin that span the membrane multiple times to form a complex with a retinal molecule at the centre. When light is absorbed, the retinal molecule change its shape, which triggers alterations to the opsin protein which triggers other events like a change in ion concentration and electrical signals.

Question 16

What is an eyespot?

Answer 16

The eyespot is located in the chloroplast of cells, its photoreceptors allow the cell to sense light direction and intensity.

Question 17

How can photo-taxis be explained?

Answer 17

When some organisms use their flagella to move to or off the light source to stay in optimum light.

Question 18

How can photomorphogenesis be explained?

Answer 18

In plants, photomorphogenesis is the process of development that is activated when seeds are exposed to light.

Question 19

What is the necessary photoreceptor for photomorphogenesis?

Answer 19

Phytochrome is the necessary photoreceptor that when exposed to red light, becomes active and signals the nucleus which activates genes coding for proteins involved in photosynthesis and leaf development.

Question 20

What is the eye?

Answer 20

Is the organ that animals use to sense light, it requires a nervous system/brain to interpret the signals. It is though that they co-evolved because the brain is necessary to see.

Question 21

What is the simplest eye?

Answer 21

The simplest eyes are the ocellus which consists of about 100 photoreceptors cells lining in a cup, it is used to sense the light intensity and direction only, many animals have them, like insects, arthropods and molluscs.

Question 22

What are compound eyes?

Answer 22

Compound eyes consists of thousands of ommatidia fitted together, from the signals of the ommatidia, the brain receives a mosaic image. They are common in arthropods.

Question 23

What are single-lens eyes?

Answer 23

Single-lens eye are in invertebrates and most vertebrates, light enters through the cornea and is concentrated by a lens and a layer of photoreceptors at the back record the image.

Question 24

What is the Darwin theory in regards to the eye evolution?

Answer 24

The human and animal eye (single-lens eye) evolved by mutation and natural selection over time from a primitive eye.

Question 25

Why is light used so much by organisms?

Answer 25

Light is used by organisms because it’s the most dominant electromagnetic radiation reaching earth. Shorter waves are absorbed by the ozone layer while longer waves are absorbed by water vapour and carbon dioxide in the atmosphere. The radiation of shorter wavelength than visible light has enough energy to destroy the bonds holding molecules together and would oxidize the molecule, while wavelengths longer don’t provide enough energy to excite the electrons.

Question 26

How can light directly affect biological molecules?

Answer 26

Light can also damage biological molecules and all organisms have defence mechanisms to prevent light damage or to repair it quickly.

Question 27

What is an example of the direct effects of light damage on biological molecules?

Answer 27

An example is the light damage in photosynthesis in photosystem II (light dependent). It absorbs about 10 000 photons per second, it needs the help of a repair system that repairs the damage done to specific proteins that constantly shuts down the PSII to maintain high rates of photosynthesis. Photosynthetic organisms also have carotenoids which are accessory pigments protecting it from damage by absorbing excess light and dissipating this energy as heat. They are necessary to protect photosystems.

Question 28

What is the range of ultraviolet radiation?

Answer 28

200nm-400nm

Question 29

Which types of UV rays reach the earth surface?

Answer 29

The ozone layer absorbs the most damaging form which is UV-C, but UV-A and UV-B do reach the earth surface.

Question 30

What can UV rays do?

Answer 30

It can ionize atoms in molecules, but DNA is particularly sensitive to it. When the two interacts, the formation in a dimer occurs in the DNA. It is explained by two based that becomes covalently bonded, it changes the shape of the DNA and prevent its replication. It can create mutations that could be harmful.

Question 31

What is the skin pigment that naked skin animals have to protect them from UV rays?

Answer 31

Melanin is a pigment that absorbs UV rays and is produced by organism with naked skin. It prevents UV rays to penetrate the skin and destroying folate which is the essential B vitamin.

Question 32

The level of melanin someone has depends on what?

Answer 32

The levels of melanin in humans depends on how much sunlight we receive, more sunlight = more melanin, it explains why some countries are deficient in vitamin D, those country don’t have much sunshine, and for people with high melanin levels, the UV rays needed to synthesize vitamin D are deficient, causing a vitamin D deficiency.

Question 33

What is the circadian rhythm?

Answer 33

Physiological and behavioural factors that have a 24hr rhythmicity (sleep-wake cycles, body temp., metabolic processes). They are not direct responses to the light environment, they are controlled by our biological clock which is set by the external light environment and can run a long time without any inputs from outside.

Question 34

Where is located the biological clock in most animals?

Answer 34

The biological clock in most animals is in the suprachiasmatic nucleus of the brain. It receives light from the eye and uses it to set the clock which then regulates bodily functions like the secretion of melatonin from the pineal gland.

Question 35

What does water do to light?

Answer 35

Water attenuates light to the point that almost no light goes beyond 150m, it absorbs longer wavelengths more than shorter wavelengths.

Question 36

What is the accessory photosynthetic pigment that is only found in aquatic plants?

Answer 36

Phytoerythrin is an accessory photosynthetic pigment only found in aquatic plants, it absorbs blue wavelengths and gives the plants a red colour (algae on ocean floor).

Question 37

What is light pollution?

Answer 37

The rapid proliferation of artificial light. It disrupts orientation in nocturnal animals that normally are used to the dark, while other animals benefits from it as it attract insects and therefore concentrating their prey.

Question 38

What is bioluminescence?

Answer 38

When an organism can produce light.

Question 39

How is bioluminescence created?

Answer 39

When ATP(chemical energy) excites an electron, when the electron goes back to its ground state, the energy is released as a photon of light. It is a highly efficient reaction because high heat production would be incompatible with life. They use it to attract, camouflage or communicate.