B1.4 Photosynthesis

Question 1

What is photosynthesis?

Answer 1

The process by which a cell captures energy in sunlight and use it to make glucose

Question 2

How is carbon dioxide taken in?

Answer 2

Diffuses from the air through the stomata in the leaf

Question 3

How is water taken in?

Answer 3

Through the roots through osmosis

Question 4

What is the word equation for photosynthesis

Answer 4

Carbon dioxide + water -> glucose + oxygen

Question 5

Is photosynthesis exothermic or endothermic?

Answer 5

Endothermic

Question 6

Chemical equation for photosynthesis

Answer 6

6Co2 + 6H2O -> C6H12O6 + 6O2

Question 7

Where does photosynthesis occur?

Answer 7

In the plants chloroplast, generally in the green parts of a leaf because chlorophyll is the green pigment which transfers energy from the sun.

Question 8

What happens in the 2 stages of photosynthesis?

Answer 8

Stage 1(light dependent) - energy transferred by light splits water into hydrogen ions and oxygen gas

Stage 2(light independent) - carbon dioxide gas combines with the hydrogen ions to form glucose. Oxygen remains

Question 9

What happens to the glucose produced?

Answer 9

Used in respiration to make atp energy

Some glucose is stored as sugar in fruits and the stem, such as sucrose and fructose

Some glucose is used to synthesis larger molecules for growth(increase biomass) eg cellulose and protein

Most of it is converted to starch

Question 10

Why is some glucose converted to starch?

Answer 10

It is converted to starch to be a store of energy for use at night when the plant cannot photosynthesise.

Question 11

How can you test for starch?

Answer 11

Kill the leaf by putting it in boiling water and then boiling ethanol which removes all the chlorophyll. Then wash the ethanol off the leaf and put it on a white tile.

Next add iodine to the leaf. It will turn from yellow to blu/black if starch is present

Question 12

How do you destarch a plant?

Answer 12

Put it in a dark cupboard for 24 hours so that all the starch is used up

Question 13

How can you prove that chlorophyll is needed for photosynthesis?

Answer 13

Take a variegated lead which is stripy coloured. De starch it and then leave it in sunlight. Test for starch using iodine. Some areas should turn black while others stay yellow

Question 14

How do you prove that light is needed for photosynthesis?

Answer 14

Take a destarched leaf and put some card to cover up part of the leaf. Place the lead in sunlight and then remove the card after hours. Test for starch. The part that was covered up should be yellow

Question 15

How do you prove that carbon dioxide is needed for photosynthesis?

Answer 15

Put a destarched plant in a polyethylene bag and tie it tightly. Place a pot of soda lime somewhere inside to absorb carbon dioxide and water vapour. Place the plant in sunlight and then test for starch

Question 16

How do you prove that oxygen is given of during photosynthesis?

Answer 16

Place an aquatic plant in a beaker and put a test tube was over. Measure the bubbles given off or take the test tube and put a glowing splint in it to see if it lights

Question 17

What 3 limiting factors affect the rate of photosynthesis?

Answer 17

Light intensity, CO2 concentration, temperature.

Question 18

What is a limiting factor?

Answer 18

A limiting factor is a factor that stops photosynthesis from happening. Increasing other factors will have no effect unless you increase the limiting factor

Question 19

How do you measure rate if photosynthesis?

Answer 19

Mainly by measuring oxygen given off

Or measure the biomass since glucose is used to produce new cells

Use rate = 1/time

Question 20

How does light intensity affect rate of reaction?

Answer 20

The higher the light intensity, the faster the rate of photosynthesis until a certain point where a limiting factor stops it. This is because light transfers energy for photosynthesis (stage 1).

Question 21

How can you investigate the light intensity affect?

Answer 21

Place a light source at different distances from the plant and measure rate of photosynthesis by measuring oxygen using a gas syringe. Use the inverse square law to find the light intensity (y axis)

Question 22

What is the inverse square law?

Answer 22

Light intensity (lux) = 1/distance^2

Question 23

How does CO2 affect the rate of photosynthesis?

Answer 23

The greater the CO2 concentration the faster the rate of reaction until a point where there is a limiting factor. CO2 is usually the limiting factor.

Question 24

How do you control CO2 concentration in an experiment?

Answer 24

Dissolve potassium hydrogen carbonate to water which releases CO2

Question 25

How does temperature affect the rate of photosynthesis?

Answer 25

Since photosynthesis is Enzyme controlled, the higher the temperature, the faster the rate until the optimum point for the enzymes is reached. If the plant is too hot enzymes will denature and if it is too cold they will work too slowly

Question 26

How do you control temperature in an experiment?

Answer 26

Use a water bath