B1.4

Question 1

Formula for photosynthesis

Answer 1

Water + carbon dioxide -> oxygen + glucose

Question 2

Define photosynthesis

Answer 2

Photosynthesis is the process in which green parts of the plants use carbon dioxide and water in the presence of sunlight and chlorophyll to produce glucose as food and in this process oxygen gas is released as a byproduct.

Question 3

What kind of reaction is photosynthesis?

Answer 3

Endothermic

Question 4

State reactants and products of photosynthesis

Answer 4

Reactants: carbon dioxide + water
Products: oxygen + glucose

Question 5

What does carbon dioxide do?

Answer 5

This diffuses through from the air into the plant through the stomata

Question 6

What does water do?

Answer 6

This enters the roots from the soil through the root hair cells

Question 7

Where does photosynthesis occur?

Answer 7

Chloroplasts (leaf)

Question 8

What are leafs green?

Answer 8

Because they contain the pigment chlorophyll

Question 9

What happens in photosynthesis

Answer 9

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 10

Name the 2 stages of photosynthesis

Answer 10

1. Light dependant
2. Light independent

Question 11

State what happens in the first stage if photosynthesis

Answer 11

The first stage is the light dependent stage of photosynthesis where energy transferred from light is used
to split water molecules into oxygen gas and hydrogen ions

Question 12

State what happens in the second stage of photosynthesis

Answer 12

The second stage isthe light independent stage of photosynthesis where carbon dioxide gas combines with the hydrogen ions produced in stage 1 of photosynthesis to make glucose

Question 13

State the uses of glucose

Answer 13

-Stored as starch - food store
-Used for respiration
-Stored in fruit as sucrose
-Used to build cellulose cell walls
- Combined with nitrogen to build protiens for grow and repair
-Biosynthesis into fats and oils for food and growth

Question 14

How can you test for starch when photosynthesis has taken place

Answer 14

1.Place leaf in boiling water for 1 minute to kill it
2.Place in boiling tube with ethanol
3.Place boiling tube in a water bath an boil until white (chlorophyll removed)
4.Wash leaf with water to remove ethanol and soften
5.Place on white tile and add 1-2 iodine drops
6.Watch for colour change in iodine.

Question 15

How do you destarch a plant

Answer 15

Keep it in the dark for a minimum of 24 hrs

Question 16

How do you prove chlorophyll is needed for photosynthesis

Answer 16

Take a variagated plant and destarch
Place the destarched plant in sunlight for several hours
Test oneof the leave with iodine for the presence of starch

Question 17

How do you prove light is needed for photosynthesis?

Answer 17

To prove light is needed for photosynthesis take a destarched plant and cover part of one of its leaves with black card or tin foil.
Light cannot reach the covered area of the leaf.
Place the plant in sunlight for several hours. Finally, remove the card from the leaf and test the leaf for the presence of starch

Question 18

How can you prove carbon dioxide is needed for photosynthesis

Answer 18

Take a destarched plant, and place it inside a polythene bag.
Before you seal the bag add a pot of soda lime .
This is a chemical that absorbs carbon dioxide and water vapour.
Place the plant in sunlight for several hours, before testing one of its leaves for the presence of starch.

Question 19

How can you prove oxygen is needed for photosynthesis

Answer 19

Place an upturned test tube above an aquatic plant such as the pondweed Elodea
. Put the apparatus in the light for maximum photosynthesis.
When you have collected a full tube of gas, place a glowing splint inside the tube.
It will relight because of the oxygen present.

Question 20

What 3 factors affect the rate of photosynthesis

Answer 20

• light intensity
• temperature
• carbon dioxide

Question 21

What is meant by limiting factor

Answer 21

A limiting factor is a condition, that when in shortage, slows down the rate of a reaction.

      - Light intensity, carbon dioxide concentration and temperature are limiting factors of photosynthesis.         They all affect the rate of the photosynthetic reaction, but in different ways

Question 22

How do we calculate rate of photosynthesis

Answer 22

Rate = 1/T
T = time

• measure how much glucose of oxygen a plant makes in a given time

Question 23

How does light intensity affect the rate of photosynthesis

Answer 23

The higher the light intensity, the faster the rate of photosynthesis. This continues until photosynthesis reaches its maximum rate.
In very low light levels or if there is no light, photosynthesis stops.

Question 24

How does carbon dioxide affect the rate of photosynthesis

Answer 24

The greater the carbon dioxide concentration, the faster the rate of reaction
However, the atmosphere only contains about 0.04% carbon dioxide.
This means that carbon dioxide is most commonly the limiting factor.
.

Question 25

How does temperature affect the rate of photosynthesis

Answer 25

Photosynthesis is a series of enzyme-controlled reactions. Therefore, the higher the temperature the faster the reactions occur. However, if the temperature is too high the enzymes will denature the reactions will stop.

Question 26

Why does the rate of photosynthesis drop if the temperature gets too high?

Answer 26

The enzymes will denature

Question 27

How to investigate the 3 factors’ effect on photosynthesis

Answer 27

Light intensity - place a light source at a different distances
Carbon dioxide - add different masses of potassium hydrogen carbonate powder to the water. Potassium hydrogen carbonate releases carbon dioxide to the atmosphere.
Temperature - place the apparatus in water baths at different temperatures

Question 28

What is inverse square law

Answer 28

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

Question 29

How do limiting factors interact?

Answer 29

When you investigate each of the limiting factors separately you see that, at some point, increasing the factor no longer makes a difference to the rate of photosynthesis. This is because one of the other factors is now in short supply - it becomes the limiting factor.