PHOTOSYNTHESIS

Question 1

Why do plants photosynthesise?

Answer 1

To make their own food.

Question 2

Where does photosynthesis happen?

Answer 2

In the chlorophyll inside the chloroplasts.

Question 3

What type of reaction is photosynthesis?

Answer 3

Endothermic.

Because it needs an input of energy from the environment.

Question 4

What is the equation for photosynthesis?

Answer 4

Carbon dioxide + water —-> glucose + oxygen

6CO2 + 6H2O —-> C6H12O6 + 6O2

Question 5

What is oxygen in photosynthesis?

Answer 5

A by-product.

Question 6

How are leaves perfectly adapted for photosynthesis?

Answer 6

Leaves are broad, which gives them a large surface area.

Thin so the diffusion distance for the gases is short.

Contain chloroplasts and chlorophyll to absorb light.

Remove products of photosynthesis in the phloem tube. Bring plenty of water in the xylem tubes.

Air spaces to allow carbon dioxide to get to the cells and oxygen to leave by diffusion.

Guard cells that open and close the stomata to regulate gas exchange.

Question 7

How is light a limiting factor of photosynthesis?

Answer 7

If there is plenty of light, lots of photosynthesis will happen. If there is little or no light, photosynthesis will stop.

Question 8

How is temperature a limiting factor of photosynthesis?

Answer 8

As the temperature rises, the rate of photosynthesis also increases as the reaction speed up. However, photosynthesis is controlled by enzymes. Most enzymes become denatured at around 40-50 degrees celsius. Therefore, if the temperature gets too high, the enzymes controlling photosynthesis are denatured and the rate of photosynthesis will fall.

Question 9

How is the carbon dioxide concentration a limiting factor of photosynthesis?

Answer 9

Increasing the carbon dioxide rate increases the rate of photosynthesis. The carbon dioxide concentration around a plant tends to rise at night because in the dark a plant repaired but does not photosynthesise. As light intensity and temperature increase in the morning, most of the carbon dioxide around the plant gets used up.

Question 10

Explain the light intensity and inverse square law.

Answer 10

As the distance of the light from the plant increases, the light intensity decreases. This is an inverse relationship, as one goes up the other goes down. 
Light intensity (inverse sign) 1/distance*2. 
For example, if you double the distance between the light and your plant, light intensity falls by a quarter.

Question 11

What do plants build glucose into?

Answer 11

Complex carbohydrates such as cellulose.

Question 12

What do plants use cellulose for?

Answer 12

To strengthen their cell walls.

Question 13

What do plants convert some of their glucose into?

Answer 13

Into starch to be stored.

Question 14

Why don’t plants keep the glucose as it is?

Answer 14

Glucose is soluble in water. If it was stored in the plant cells, it would affect they way water moves into and out of the cells by osmosis. Lots of glucose stored in plants could affect The water balance of the whole plant.

Question 15

Why do plants convert glucose into starch?

Answer 15

Starch is insoluble in water. It is the main energy store.

It provides an energy store for when it is dark or when light levels are low.

Question 16

How do you test for starch?

Answer 16

The iodine solution test.
Keep a plant in the dark for 24 hours. - the green chlorophyll would mask any colour change if this step doesn’t occur. Or the waxy cuticles would keep the iodine out.
You must boil the leaves in ethanol to destroy the waxy cuticle and remove the colour. The leaves are then rinsed in hot water to soften them.
Then add iodine. If starch is present it will turn blue-black.

The leaf that has been in the light will turn blue black. The iodine solution on the leaf kept in the dark remains orange-red.

Question 17

What may the okays use glucose for?

Answer 17

To make amino acids which can be built up into proteins to be used in the plant for example as enzymes.
The plant may also make lipids to build up fats and oils. They are sometimes used in cell walls to make them stronger.

Question 18

What does the greenhouse allow you to do?

Answer 18

Control any limiting factors. Eg amount of light, carbon dioxide and temperature.

Question 19

What system is know as hydroponics?

Answer 19

Growing plants in martinet filled water instead of soil.

Question 20

What is the palisade layer?

Answer 20

The location of photosynthesis.

Has chloroplasts.

Question 21

What is the lower epidermis layer?

Answer 21

Where the stomata are.

Question 22

What does the upper epidermis do?

Answer 22

Provides protection.

Question 23

What is an endothermic reaction?

Answer 23

A reaction that requires a transfer of energy from the environment.

Question 24

What is glucose?

Answer 24

A simple sugar.

Question 25

What is a limiting factor?

Answer 25

Limits the rate of the reaction, for example photosynthesis.

Question 26

What is photosynthesis?

Answer 26

The process by which plants make food using carbon dioxide, water and light.