2.9 Photosynthesis

The graph shows how the rate of photosynthesis of a green plant varies with CO2 concentration at two different light intensities. The temperature is kept constant at 20 °C. What is the limiting factor at X?

• Chlorophyll

• Light intensity

• Temperature

• CO2 concentration

Answer explanation

Look to the right of the graph!

Tags

NGSS.HS-LS1-5

The apparatus shown was used to investigate the effect of varying carbon dioxide concentration on the rate of photosynthesis. Carbon dioxide concentrations were varied by adding different amounts of sodium hydrogen carbonate (NaHCO3) to water. What is the dependent variable in this investigation?

• Temperature

• Light intensity

• Amount of NaHCO3 added

• Volume of oxygen produced

Answer explanation

Dependent variable = one you are measuring in response to something you change

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NGSS.MS-LS1-6

What prevents plants from converting carbon dioxide into glucose in the dark?

• They do not have a source of energy.

• It is too cold.

• They do not require glucose during the night.

• Their enzymes are inhibited.

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NGSS.HS-LS1-5

If a plant is exposed to light, which colour of light would lead to the lowest rate of oxygen release by a green plant?

• Blue

• Red

• Green

• White

Answer explanation

Pigments like chlorophyll (the most common plant pigment) absorb different light colors. Chlorophyll specifically absorbs blue and red, and reflects green (because green is not absorbed).

Tags

NGSS.HS-LS1-5

What does the Rf value in thin-layer chromatography represent?

• The distance travelled by the pigment front in a fixed time period

• The distance from the origin to the solvent front at the end of the experiment

• The ratio of distances travelled by the pigment and solvent fronts

• The concentration of the pigment applied to the chromatography plate

Answer explanation

Plants produce carbon dioxide in respiration and use carbon dioxide in photosynthesis. The graph shows the volume of carbon dioxide exchanged in a plant at different light intensities. What is shown by the graph?

• There is no photosynthesis between W and X.

• There is no photosynthesis between Y and Z.

• There is more respiration than photosynthesis between Y and Z.

• There is more respiration than photosynthesis between W and X.

Tags

NGSS.HS-LS1-5

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The graph shows the effect of increasing light intensity on the rate of CO₂ uptake by a species of green plant maintained in conditions of constant temperature and CO₂ concentration. Which statement is consistent with the graph?

• Photosynthesis stops at high light intensity.

• Rates of photosynthesis increase with temperature.

• Cell respiration leads to net production of CO2 at low light intensity.

• There is a negative correlation between CO2 uptake and light intensity.

Answer explanation

At the lowest light intensity, there is a negative CO2 uptake. This means that there is CO2 being produced without being taken in.

Tags

NGSS.HS-LS1-5

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The graph shows the absorption spectra of chlorophyll a and chlorophyll b. What can be concluded from the graph?

• Both chlorophyll a and chlorophyll b absorb a large amount of green light

• Chlorophyll b absorbs red light more efficiently than blue light

• Other pigments must absorb light between blue and red in the spectrum

• Chlorophyll a and chlorophyll b have different absorption peaks

Answer explanation

Chlorophyll B's line is more dotted. Its peak is close to Chlorophyll A's line, but not exact.

Tags

NGSS.HS-LS1-5

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The graph shows the relationship between rate of photosynthesis and light intensity as influenced by both temperature and CO2 concentration. What conclusion can be drawn from the data in the graph?

• CO2 is always the limiting factor at low light intensities and temperatures.

• Light intensity is only the limiting factor at high light intensities.

• Temperature is only the limiting factor at high light intensities and CO2 concentrations.

• Both temperature and light intensity are limiting factors at 660 ppm CO2 and less than 200 W m–2 light intensity.

Answer explanation

Look at the axes! The limiting factor is temperature- where higher temperature allows for more photosynthesis (Y-axis to occur)

Tags

NGSS.HS-LS1-5

An experiment was set up so that each test tube contained water at a pH of 6.3 and a pH indicator. Test tubes 1 and 2 also contained a common pond autotroph. Carbon dioxide dissolves in water and forms carbonic acid. After three days the four test tubes were found to have these results. What conclusion can be drawn from test tube 1 and test tube 2?

• Test tube #1: photosynthesis has used CO2, test tube #2: respiration has produced CO2

• Test tube #1: photosynthesis has made the water more acidic, test tube #2: respiration has made the water less acidic

• Test tube #1: photosynthesis occurred but not respiration, test tube #2: respiration occurred but not photosynthesis

• No conclusion can be drawn, since pH in the controls has changed.

Answer explanation

Autotrophs are those that use light energy. Test tube #1 has been in the light, so photosynthesis can occur and carbon dioxide will be absorbed. Test tube #2 has been in the dark, so no photosynthesis can occur. This means only respiration is happening, which produces carbon dioxide. Carbon dioxide causes the pH to decrease.

Tags

NGSS.HS-LS1-5

NGSS.HS-LS2-5