Flashcards
Photosynthesis: How Plants Turn Light into Food
An oak tree grows from a small acorn into a giant weighing tons. Where does most of the dry mass of its wood come from?
minerals absorbed from the soil
water taken up by the roots
dead leaves rotting in the soil
carbon dioxide from the air
carbon dioxide from the air
Fill in the gaps.
In photosynthesis, six molecules of carbon dioxide and six molecules of water are turned into one molecule of
. . . . . and
. . . . . molecules of oxygen .
In photosynthesis, six molecules of carbon dioxide and six molecules of water are turned into one molecule of glucose and six molecules of oxygen .
Where do the oxygen atoms in the O2 released by photosynthesis come from?
from glucose broken down inside the chloroplast
from water molecules split in the light reactions
from air taken in through the leaf's pores
from carbon dioxide molecules split in the leaf
from water molecules split in the light reactions
Match each part of a plant with its role in photosynthesis.
thylakoid membrane
holds the pigments that capture light
Match each part of a plant with its role in photosynthesis.
stroma
fluid where carbon dioxide is built into sugar
Match each part of a plant with its role in photosynthesis.
stomata
tiny pores through which gases enter and leave the leaf
Match each part of a plant with its role in photosynthesis.
xylem
carries water up from the roots
True or false?
Chlorophyll absorbs red and blue light best and reflects much of the green light.
True or false?
A plant under pure green light photosynthesizes faster than under red light of the same brightness.
True or false?
Carotenoids absorb blue light, and their yellow and orange colors show in autumn when chlorophyll breaks down.
True or false?
Leaves look green because chlorophyll gives off green light when sunlight strikes it.
Put the steps of the light reactions in the order they happen to one electron.
Photosystem I absorbs light and boosts the electron to a high energy again.
The electron moves along the chain to photosystem I, losing energy on the way.
An excited electron leaves photosystem II and enters the electron transport chain.
Light energy absorbed by pigments is passed to photosystem II.
A carrier molecule takes the electron to the sugar-building reactions.
Put the steps of the light reactions in the order they happen to one electron.
1. Light energy absorbed by pigments is passed to photosystem II.
2. An excited electron leaves photosystem II and enters the electron transport chain.
3. The electron moves along the chain to photosystem I, losing energy on the way.
4. Photosystem I absorbs light and boosts the electron to a high energy again.
5. A carrier molecule takes the electron to the sugar-building reactions.
Inside a chloroplast, the enzyme ATP synthase makes ATP. What directly powers it?
energy released by breaking down glucose in the stroma
hydrogen ions flowing out of the thylakoid through it
light striking the enzyme and switching it on
electrons from chlorophyll attaching directly to ADP
hydrogen ions flowing out of the thylakoid through it
In the light reactions, electrons pass through photosystem II and then photosystem I. Which molecule accepts them at the end of this path?
oxygen
ADP
NADP+
carbon dioxide
A plant is moved from bright light into darkness. Why do its light-independent reactions stop soon afterward, even though they do not use light directly?
They need the oxygen released by the light reactions.
Carbon dioxide cannot enter the chloroplast without light.
They run out of the energy carriers made in the light reactions.
Their enzymes work only while warmed by sunlight.
They run out of the energy carriers made in the light reactions.
The light-independent reactions of photosynthesis form a cycle named after the American chemist who mapped them in the 1950s by tracing radioactive carbon-14. What is this cycle called?
Calvin cycle
True or false?
Pineapples and cacti open their stomata at night and store carbon dioxide until daytime.
True or false?
Corn and sugarcane first trap carbon dioxide in a four-carbon compound, which helps them in hot weather.
True or false?
Cacti keep their stomata wide open at midday to cool down by evaporation.
True or false?
On a hot day, closing the stomata saves water but also cuts the supply of carbon dioxide.
Tomatoes in a winter greenhouse are well watered and kept at an ideal temperature. Adding more lamps no longer makes them grow faster. What is most likely limiting their photosynthesis now?
the humidity of the air
the amount of oxygen in the air
the amount of carbon dioxide in the air
the amount of nitrogen gas in the air
the amount of carbon dioxide in the air
True or false?
Plant cells carry out cellular respiration both day and night.
True or false?
At night, a plant gives off carbon dioxide instead of taking it in.
True or false?
Plants respire only in their roots, because their leaves make their own sugar.
True or false?
Photosynthesis and cellular respiration both use an electron transport chain to make ATP.
Roughly half of all photosynthesis on Earth happens in the oceans. Which organisms do most of it?
kelp and other large seaweeds
mangrove forests along tropical coasts
phytoplankton drifting near the surface
seagrass meadows in shallow water
phytoplankton drifting near the surface
Chloroplasts have their own circular DNA and ribosomes, and they divide on their own inside the cell. What does this suggest about their origin?
They descend from bacteria swallowed by an ancient cell.
They broke off from the nucleus with some of its DNA.
They formed as the cell membrane folded around pigments.
They developed from mitochondria that began to use light.
They descend from bacteria swallowed by an ancient cell.
A potato plant makes sugar in its leaves, yet its tubers are packed with starch. Why does the plant store starch rather than glucose?
Starch can fuel cells without being broken down first.
Starch releases its energy faster when the tuber sprouts.
Starch does not dissolve, so it does not draw water into cells.
Glucose is poisonous to the plant's own cells in large amounts.
Starch does not dissolve, so it does not draw water into cells.