Photosynthesis Flashcards

All 19 cards in this deck

State the word equation for photosynthesis.

carbon dioxide + water $\rightarrow$ glucose + oxygen
Light energy is needed.

State the balanced symbol equation for photosynthesis.

$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$

Which structure in a plant cell is the site of photosynthesis?

The chloroplast.
It contains chlorophyll, which absorbs the sunlight.

True or false? Photosynthesis is an exothermic reaction.

False. It is endothermic — light energy is taken in from the surroundings.

Why are photosynthetic organisms described as the main producers of food and biomass?

They use light energy to make glucose, which becomes the food and biomass that all other organisms depend on.

What is a limiting factor in photosynthesis?

A factor that is in short supply and so holds back the rate of photosynthesis.
e.g. light intensity, carbon dioxide concentration, temperature.

What is the effect of increasing carbon dioxide concentration on the rate of photosynthesis?

The rate increases, then levels off when carbon dioxide ceases to be the limiting factor.

True or false? Increasing the temperature always increases the rate of photosynthesis.

False. The rate rises to a maximum at the optimum temperature for the enzymes; above the optimum the enzymes are denatured and the rate falls.

On a graph of rate of photosynthesis against light intensity, what happens to the curve if the carbon dioxide concentration is increased?

It levels off at a higher rate, because carbon dioxide was the factor limiting the rate at high light intensity.

What is the effect of increasing light intensity on the rate of photosynthesis?

The rate increases, then levels off when light intensity ceases to be the limiting factor.

What is the inverse square law for light intensity from a lamp?

light intensity ∝ $\frac{1}{d^2}$, where d is the distance from the light source (doubling the distance gives a quarter of the light intensity).

Why do commercial growers use artificial lamps in glasshouses?

To raise the light intensity so light is no longer a limiting factor, increasing the rate of photosynthesis and the crop yield.

What are the steps to investigate the effect of light intensity on the rate of photosynthesis using pondweed?
e.g. lamp at 10 cm

1. Put pondweed in a tube of pond water with the lamp 10 cm away, a water bath between lamp and tube.
2. Count the oxygen bubbles given off in one minute = rate in bubbles per minute.
3. Repeat at other distances, working out light intensity as $1/d^2$.

Why is a water bath (tank of water) placed between the lamp and the pondweed?

To maintain a constant temperature — it acts as a heat shield, absorbing heat from the lamp.

Give three variables that must be controlled when investigating the effect of light intensity on the rate of photosynthesis.

Any three of: temperature; carbon dioxide concentration; volume of pond water; length/mass/type of pondweed; extraneous light (use the same light source).

Give one improvement that gives a more accurate measurement of the gas produced than counting bubbles by eye.

Collect the gas in a gas syringe or measuring cylinder to measure the volume of oxygen produced.
Or: film the bubbles with a video camera and count them in slow-motion playback.

If light intensity and carbon dioxide concentration are both high, which factor limits the rate of photosynthesis?

Temperature — the enzymes that control photosynthesis work slowly if it is too cool.

How is the rate of photosynthesis related to light intensity while light is the limiting factor?

It is directly proportional — doubling the light intensity doubles the rate, until carbon dioxide or temperature becomes the limiting factor.

Why is sodium hydrogencarbonate added to the water in the pondweed experiment?

It releases carbon dioxide into the water, so carbon dioxide is not a limiting factor.