Lesson 7 - Photosynthesis

The longer the wavelength of a photon of light, the _____.

• more energy the photon contains

• less energy the photon contains

• the more likely the photon will be absorbed by a pigment

• the less likely the photon will be absorbed by a pigment

Answer explanation

A photon’s wavelength correlates with its energy, with shorter wavelengths having more energy than longer wavelengths. The structure of a pigment molecule determines which wavelengths are absorbed. Different plant pigments vary in the wavelengths, and therefore colors, they absorb.

Tags

NGSS.HS-PS4-1

NGSS.HS-PS4-4

Leaves are green because the pigment chlorophyll a _____.

• absorbs green light

• absorbs blue and red light

• contains a high concentration of carotenoids

• degrades when exposed to light

Answer explanation

The structure of chlorophyll a allows it to absorb wavelengths of light in the blue and red regions. However, green and some yellow wavelengths cannot be absorbed and are reflected by chlorophyll a molecules instead. Because chlorophyll a is the most abundant plant pigment, we see plant leaves as the green color reflected from the leaves.

Accessory pigments within the chloroplast are responsible for _____.

• driving the splitting of water molecules

• absorbing photons of different wavelengths of light

• passing electrons across the thylakoid membrane

• creating organic molecules in the absence of light energy

Answer explanation

Pigments absorb specific wavelengths of light. Accessory pigments expand the range of light wavelengths a plant leaf can absorb. Typically present in leaves at much lower levels than chlorophyll a, the wavelengths (colors) reflected by these accessory pigments are rarely visible to the human eye.

Which of the following photosynthesis events is INCORRECTLY paired with its location?

• light-dependent reactions – stroma

• electron transport chain – thylakoid membrane

• Calvin cycle – stroma

• ATP synthase - thylakoid membrane

Answer explanation

The pigments that absorb light energy during the light-dependent reactions are nonpolar molecules that reside inside the hydrophobic interior of the thylakoid membranes. The transport of electrons through a series of thylakoid membrane proteins (ETC) pumps protons from the stroma into the thylakoid space. The position of the light-dependent reactions produces the proton gradient that drives synthesis of ATP as protons return to the stroma through ATP synthase.

Tags

NGSS.HS-LS1-5

What structural feature of a leaf allows plant cell chloroplasts to obtain CO₂ from the air?

• stomata

• vascular bundle

• chloroplast

• mesophyll

Answer explanation

Along the epidermal layer of a plant leaf are specialized cells that form pores to allow gas exchange. These pores, called stomata, are the only locations along the epidermis that allow gas exchange. After carbon dioxide diffuses into air spaces around the mesophyll cells inside a leaf, the CO₂ molecules diffuse directly across the plasma membrane, then across the outer and inner chloroplast membranes to enter the chloroplast stroma for use during the Calvin cycle.

The energy source for photosynthesis is _____.

• glucose

• ultraviolet light

• visible light

• oxygen

Answer explanation

Sunlight provides the energy for the light-dependent reactions of photosynthesis. Plant pigments absorb light wavelengths in the visible region of the electromagnetic spectrum. Therefore, visible light from the sun is the source of all energy that supports life in both photosynthetic organisms and the heterotrophs that feed on these autotrophs.

Tags

NGSS.HS-LS1-5

The function of photosynthesis is to produce _____.

• glucose

• carbon dioxide, water, and ATP

• ATP and oxygen

• glucose and oxygen

Answer explanation

Light energy reduces carbon dioxide by adding electrons and hydrogen to form glucose, a stable form of chemical energy. Although water is oxidized to oxygen gas during photosynthesis, the oxygen product is not produced for use directly by the plant cells. Oxygen gas is produced solely because the electrons in water are required to replenish photosystem II. Therefore, oxygen gas is a by-product of photosynthesis rather than an intentional, functional product of the pathway.

Tags

NGSS.HS-LS1-5

NGSS.HS-LS1-6

Which of the following are required for photosynthesis?

• glucose and water

• glucose and oxygen

• carbon dioxide, water, and energy

• glucose and carbon dioxide

Answer explanation

Although energy is not a reactant molecule, light energy reduces carbon dioxide by adding electrons and hydrogen to form glucose. During the light reactions, photosystem II delivers energized electrons into the electron transport pathway. Water is required to replenish photosystem II, delivering electrons to PS II as water molecules are oxidized to form oxygen gas.

Tags

NGSS.MS-LS1-6

How is the chlorophyll a molecule located inside the reaction center of a photosystem different from the pigments outside the reaction center?

• the reaction center chlorophyll a absorbs more light

• the non-reaction center pigments are not chlorophyll a molecules

• the reaction center chlorophyll a delivers excited electrons to the ETC

• the non-reaction center pigments are located outside the thylakoid membrane

Answer explanation

The non-reaction center pigments absorb light energy from the sun, energizing electrons and then passing the energy out of each pigment until it reaches the reaction center.  Unlike the non-reaction center pigments, the chlorophyll a in the reaction center delivers its energized electrons out of the photosystem into an electron transport chain.

Tags

NGSS.HS-LS1-5

The pigments responsible for light absorption are located in the _____.

• thylakoid membrane

• thylakoid lumen

• stroma

• epidermis

Answer explanation

Because photosynthetic pigments are nonpolar molecules, they reside inside a phosophilipid membrane rather than free-floating in a fluid lumen. Specifically, photosynthetic pigments reside inside the hydrophobic interior of the thylakoid membranes to direct production of ATP across this membrane, forming ATP directly in the chloroplast stroma for use during the Calvin cycle.

Tags

NGSS.HS-LS1-5