Photosynthesis Flashcards

All 31 cards in this deck

What is the word equation for photosynthesis?

carbon dioxide + water $\rightarrow$ glucose + oxygen

What is the balanced symbol equation for photosynthesis?

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

What substance does $C_6H_{12}O_6$ stand for in the photosynthesis equation?

Glucose.

In terms of energy, what type of reaction is photosynthesis?

Endothermic — energy is transferred from the environment to the chloroplasts by light.

Which pigment absorbs the light used in photosynthesis, and in which structure is it found?

Chlorophyll, found in the chloroplasts.

True or false? Starch is a product of the photosynthesis reaction.

False. Glucose is the product; excess glucose is later converted into starch.

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

The rate increases, until light is no longer the limiting factor and the rate levels off.

What is the effect of increasing temperature on the rate of photosynthesis?

The rate increases up to an optimum, then falls because enzymes lose the shape of their active site (denature).

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

The rate increases, until carbon dioxide is no longer the limiting factor and the rate levels off.

What is the effect of a decrease in the amount of chlorophyll on the rate of photosynthesis?

The rate decreases, because less light can be absorbed.
e.g. the white parts of a variegated leaf photosynthesise less.

On a graph of rate of photosynthesis against light intensity, what does the part of the line that has levelled off tell you?

Light intensity is no longer the limiting factor — another factor, such as temperature or carbon dioxide concentration, is limiting the rate.

True or false? Above the optimum temperature the rate of photosynthesis keeps on rising.

False. The rate falls, because the enzymes lose the shape of their active site.

What is meant by a 'limiting factor' of photosynthesis?

A factor that, if increased, would increase the rate — it prevents the rate increasing further.

What is the inverse square law linking light intensity and distance from a lamp?

Light intensity $\propto \dfrac{1}{\text{distance}^2}$

According to the inverse square law, what happens to the light intensity reaching pondweed if the lamp is moved twice as far away?

It falls to one quarter, so the rate of photosynthesis falls if light is the limiting factor.

In a greenhouse, making the lamps brighter no longer increases the rate of photosynthesis. Which factors could be limiting the rate?

Temperature or carbon dioxide concentration (or amount of chlorophyll).

Why might a greenhouse grower choose not to raise the light, temperature and carbon dioxide to the maximum possible?

The cost of heating, lighting and adding carbon dioxide may be greater than the extra profit from the increased yield.

True or false? Increasing the light intensity will always increase the rate of photosynthesis.

False. It only increases the rate if light is the limiting factor.

What are the steps to investigate the effect of light intensity on the rate of photosynthesis using pondweed?
e.g. lamp at 10, 20 and 30 cm

1. Put pondweed in a boiling tube of sodium hydrogencarbonate solution, lamp 10 cm away.
2. Count the oxygen bubbles released in 1 minute; repeat and take a mean.
3. Repeat at 20 cm and 30 cm, keeping temperature and the pondweed the same.

In the pondweed light intensity investigation, which variables must be controlled?

Temperature, carbon dioxide supply (same sodium hydrogencarbonate solution), the same mass/length of pondweed and the same time period.

What are the steps to calculate a rate of photosynthesis from a bubble count?
e.g. 90 bubbles counted in 3 minutes

1. Divide bubbles by time: $90 \div 3 = 30$
2. State with the unit: 30 bubbles per minute
3. Convert if needed: $30 \times 60 = 1800$ bubbles per hour

Why is a heat shield, such as a glass tank of water, placed between the lamp and the pondweed?

It absorbs heat from the lamp so the temperature of the water stays constant.

How should an anomalous result be treated when working out the mean rate of photosynthesis from repeat readings?

Leave it out of the calculation — find the mean of the remaining repeat values.

Give one possible cause of an anomalous result in a pondweed photosynthesis investigation.

The scale was misread, air was trapped in the apparatus, the lamp was moved, or the temperature changed.

What makes a suitable scale and axis label when plotting rate of photosynthesis against temperature?

Equal intervals with the points filling at least half the grid, and the axis labelled with the quantity and unit, e.g. 'rate of photosynthesis in cm³/hour'.

Give the five uses of the glucose produced in photosynthesis.

Respiration; converted to insoluble starch for storage; used to make fats or oils for storage; used to make cellulose; used to make amino acids.

Why is glucose converted into starch for storage in plants?

Starch is insoluble, so it can be stored without affecting the water balance of the cell.

Which substance made from glucose strengthens plant cell walls?

Cellulose.

Which ions do plants absorb from the soil in order to make proteins?

Nitrate ions — used with glucose to make amino acids for protein synthesis.

True or false? Plants can make amino acids from glucose alone.

False. They also need nitrate ions absorbed from the soil.

What is glucose converted into for storage in plant seeds?

Fats or oils (lipids).