B1.4 - Photosynthesis

Question 1

How does the plant get the carbon dioxide it needs for photosynthesis?

Answer 1

Carbon dioxide DIFFUSES from the air into the plant through the stomata

Question 2

How does the plant get the water it needs for photosynthesis

Answer 2

Water enters the roots from the soil through the root hair cells by osmosis

Question 3

What is the word equation for photosynthesis

Answer 3

Carbon dioxide + water —> glucose + oxygen

Question 4

What is the symbol equation for photosynthesis

Answer 4

6CO2 +6H2O —> C6H12O6 +6O2

Question 5

What are stomata?

Answer 5

They are tiny pores on the underside of the leaf.

They allow carbon dioxide to diffuse in and water vapour and oxygen to diffuse out

Question 6

Where does photosynthesis take place?

Answer 6

Inside the plants chloroplast.

This means it mainly occurs in the leaf but a small amount occurs in the green stem.

Question 7

Why are leaves and stems green?

Answer 7

They contain the pigment chlorophyll inside their chloroplasts

Question 8

How does photosynthesis work?

Answer 8

Light transfers energy from the Sun to chlorophyll where carbon dioxide and water react to make glucose. Glucose stores energy within its chemical bonds.

Question 9

What are the 2 main stages of photosynthesis

Answer 9

Light dependent and light independent

Question 10

What happens in the first stage? ( light dependent stage)

Answer 10

Energy transferred from the sun splits water molecules into oxygen gas and hydrogen ions.

Question 11

What happens in the second stage? (Light independent stage)

Answer 11

Carbon dioxide gas combines with the hydrogen ions to make glucose

Question 12

Is photosynthesis an endothermic or exothermic reaction?

Answer 12

Endothermic as energy must be transferred from the surroundings to keep it doing

Question 13

What does “photosynthesis” mean

Answer 13

Photo means using light
Synthesis means the creation of larger substances

Photosynthesis means using light to make a new substance

Question 14

How does the plant use the glucose produced?

Answer 14

The plant uses some of the glucose immediately in respiration

Other glucose molecules are converted into other sugar molecules

Glucose that isn’t needed straight away can be converted to

• starch ( a food store)
• Proteins
• fats and oils
• cellulose (to form cell walls)
• sucrose (stored in fruit)

Question 15

How can you test for starch?

Answer 15

• the plant converts glucose into starch if it isn’t used immediately

To test a plant for starch :

• take the leaf you are about to test and place it in a beaker of boiling water for a minute to kill it.
• place the lead into a boiling tube of ethanol to remove all the chlorophyll.
• wash the leaf with water to remove the ethanol
• spread the lead on a white tile
• add a few drops of iodine solution onto the leaf
• if starch is present the iodine will turn from yellow-brown to blue-black

Question 16

How can you destarch a plant?

Answer 16

Keeping the plant in the dark for a minimum of 24hrs

Question 17

How can you prove chlorophyll is needed for photosynthesis?

Answer 17

Variegated leaves only have chlorophyll in some areas of the leaf.

• to prove chlorophyll is needed you should place a destarched variegated plant in the sunlight for several hours.
• then test one of its leaves for the presence of starch.

Question 18

How can you prove light is needed for photosynthesis?

Answer 18

• take a destarched plant and cover part of one of its leaves with black card or tin foil so light cannot reach the covered area of the leaf.

Place the plant in sunlight for several hours

Remove the card and test the leaf for the presence of starch.

Question 19

How can you prove carbon dioxide is needed for photosynthesis

Answer 19

• take a destarched plant and place it inside a polythene bag.
• add a pot of soda lime (it absorbs carbon dioxide and water vapour) and seal the bag
• place the plant in sunlight for several hours before testing one of the leaves for the presence of starch.

Question 20

How can you prove oxygen is given off during photosynthesis?

Answer 20

Place an upturned test tube above an upturned plant.

Put the apparatus in the light for photosynthesis

When you have collected a full tube of gas place a glowing splint inside the test tube and it will light because of the oxygen present.

Question 21

What factors affect the rate of photosynthesis?

Answer 21

• light intensity
• carbon dioxide
• temperature

Question 22

How can you measure the rate of photosynthesis?

Answer 22

By measuring how much oxygen or glucose a plant makes in a given time.

Glucose is used to produce new cells so you can also measure the rate of photosynthesis by calculating the increase in biomass in a given time

Question 23

How can you CALCULATE the rate of photosynthesis ?

Answer 23

Rate = 1➗t

Rate = 1 ➗ time

Question 24

How does light intensity affect the rate of photosynthesis?

Answer 24

• the higher the light intensity, the faster the rate of photosynthesis
• this continues until photosynthesis reaches its maximum rate

Question 25

How does carbon dioxide affect the rate of photosynthesis?

Answer 25

• the greater the carbon dioxide concentration, the faster the rate of reaction
• the atmosphere only contains 0.04% of Carbon dioxide so it’s usually the limiting factor
• farmers can artificially increase the levels of CO2 to increase the rate of photosynthesis

Question 26

How does temperature affect the rate of photosynthesis?

Answer 26

Photosynthesis is a series of enzyme controlled reaction so the higher the temperature the faster the rate of reaction but if the temperature is too high the enzymes will denature and the reaction will stop.

Question 27

What is the inverse square law?

Answer 27

When you double the distance from a light source the light intensity falls by a factor of 4

Relative light intensity = 1 ➗(distance from light source)^2

Question 28

How can you alter light intensity to study its effect on photosynthesis

Answer 28

• place a light source different distances from the plant

Question 29

How can you alter carbon dioxide concentration to study its effect on photosynthesis

Answer 29

Add different masses of potassium hydrogen carbonate powder to the water

Potassium hydrogen carbonate releases carbon dioxide into the atmosphere

Question 30

How can you alter temperature to study its effect on photosynthesis

Answer 30

Place the apparatus in water baths at different temperatures

Question 31

How can you investigate the rate of photosynthesis

Answer 31

Using (e,g ) elodea (pondweed)

The volume of oxygen given of per minute is a measure of the rate of photosynthesis. You can measure this by counting the number of bubbles produced per minute