11. Photosynthesis.

Question 1

Define photosynthesis?

Answer 1

A chemical reaction where green plants make food, they use carbon dioxide form the air and water from the soil to make sugar <glucose> and oxygen.</glucose>

Question 2

What is the site of photosynthesis?

Answer 2

Chloroplasts in leaf cells

Question 3

Write the word equation for photosynthesis

Answer 3

Carbon dioxide + water—–> glucose +
Oxygen

Question 4

Name the raw materials of photosynthesis

Answer 4

Carbon dioxide and water

Question 5

Name the products of photosynthesis

Answer 5

Glucose and Oxygen

Question 6

What else does photosynthesis need for photosynthesis to happen

Answer 6

Light energy from the sun
AND
CHLOROPHYLL - sunlight is absorbed by a green pigment called chlorophyll and used to make glucose

Question 7

What molecule controls photosynthesis?

Answer 7

Enzymes like respiration, photosynthesis is also an enzyme dependant reaction.

Question 8

Where is chlorophyll found?

Answer 8

Chlorophyll is found in the organelle called the chloroplast found in cells at the top of the leaf.

Question 9

Briefly mention the steps to test a leaf for starch

Answer 9

1. Take a leaf and place in water
2. Boil the leaf for 5 minutes.
3. TURN OFF the Bunsen burner.
   4.Half fill a boiling tube with ethanol, and then add the boiled leaf.
4. Place this boiling tube into the beaker of water on the tripod.
5. Leave the leaf in ethanol for 5 minutes.
6. Remove the leaf from the ethanol and rinse it in water.
7. Spread out the leaf onto a white tile. Add 10 drops of iodine solution.

Question 10

What is the test for starch?

Answer 10

Iodine solution.
It turns from light brown to black blue in the presence of starch

Question 11

When we test a leaf for starch and we have a positive result for starch, what does this mean?

Answer 11

If iodine solution has proven the presence of starch, this shows that the plant has photosynthesised. Green plants make glucose during photosynthesis any glucose the plant does not use is stored as starch.

PHOTOSYNTHESIS HAS HAPPENED

Question 12

When testing a leaf for starch why do we boil a leaf?

Answer 12

This kills the leaf, stopping any chemical reactions.

Question 13

When testing a leaf for starch why turn of the Bunsen in stage 3?

Answer 13

The next stage uses an alcohol called ETHANOL, this is HIGHLY FLAMMABLE so we must turn Bunsen’s off for safety

Question 14

When testing a leaf for starch after boiling with water why do we then add it to BIOLING ETHANOL <stage 6>

Answer 14

The boiling ethanol dissolves the chlorophyll and removes the green colour from the leaf - it turns white so it is easy to see the change in colour.

Question 15

When testing a leaf for starch why do we rinse the leaf after it has been boiled in ethanol? <stage 7>

Answer 15

Washing with water removes the ethanol it also rehydrates/Softens the leaf, this makes it easier to lay flat and be ready for the iodine solution.

Question 16

How would you prove experimentally that light is needed for photosynthesis?

Answer 16

Cover a leaf with thick black card <to> and test for starch.
Remember to use a control leaf: one which has bee exposed to light</to>

Question 17

How would you prove experimentally that carbon dioxide needed for photosynthesis?

Answer 17

Place a plant in a bell jar with a chemical which absorbs carbon dioxide <sodium>, leave for two days and test the leaf for starch.</sodium>

Question 18

When proving that a plant needs carbon dioxide to photosynthesis, how would we set up the control and why?

Answer 18

The control is kept in exactly the same conditions as the experiment except the independent variable (sodium hydroxide) has been replaced with water. This means no carbon dioxide has been absorbed from the air.

The control is a comparison to show that the plant would make starch by photosynthesis if the sodium hydroxide were not absorbing the carbon dioxide.

This is the evidence that it is the independent variable which is responsible for the result.

Question 19

What is a variegated leaf?

Answer 19

Variegated leaves have green parts (where the cells contain chlorophyll) and white parts.

Question 20

How would you prove experimentally that chlorophyll is needed for photosynthesis?

Answer 20

Take a variegated leaf and test it for starch

Only the parts that were green become blue/black with iodine solution, showing the importance of chlorophyll in photosynthesis. The parts without chlorophyll do not photosynthesise, and so they do not make starch and the iodine does not change colour.

Question 21

How could you prove experimentally that oxygen is produced during photosynthesis

Answer 21

Perform the Elodea bubbler experiment

Use a pond weed called Elodea. A freshly cut stem of Elodea is placed upside down in a tube full of water. A small desk lamp is used as a light source. Gas bubbles will be released as the elodea photosynthesises and the gas will displace the water. We can test the gas collected and test it to prove it is oxygen.

Question 22

What is the test for oxygen? So we can test the gas collected during the elodea bubbler experiment.

Answer 22

We can prove the gas collected during photosynthesis is oxygen.

Keep the tube upside down, quickly let the water out and test with a glowing splint.

If oxygen is present it will relight a glowing splint

Question 23

What is a limiting factor in photosynthesis?

Answer 23

A limiting factor is a factor that can limit the rate of photosynthesis if it is in short supply.

Question 24

List thelimiting factors

Answer 24

Water, Carbon dioxide, Temperature and Light Intensity.

Question 25

Greenhouses can overcome the limiting factors of photosynthesis.
Write a description of how you would set up a greenhouse to ensure that the roses grow as well as possible by reducing the limiting factors as possible.

Answer 25

Set up
- Use a green house with as many clear glass panels as possible to increase light intensity/ natural sunlight <avoid>
- Also have artificial light so that photosynthesis can continue beyond daylight hours, or at a higher than normal light intensity.
- The use of paraffin lamps inside a greenhouse increases the rate of photosynthesis because the burning paraffin produces carbon dioxide as well as heat.
- If it is cold use a thermostat to control the temperature. Enzymes have an optimum temperature. If the plant is too cold the enzymes will only work very slowly, this means the rate of photosynthesis will be slow too
- If it is too warm open vents/windows so the plants do not become too hot - if the enzymes become to hot they will be denatures, no longer work and the plant with not photosynthesise and will die.
- Make sure plants are well watered, perhaps use an automated irrigation sysyem.</avoid>