Organisms in the environment: Photosynthesis/ Limiting Factors

Question 1

equation for photosynthesis

Answer 1

light

carbon dioxide + water → glucose + oxygen

chlorophyll

Question 2

chemical equation for photosynthesis

Answer 2

CO₂ + H₂0 → C₆H₆O₆ +O2

Question 3

What part of a leaf absorbs the light enerfy?

Answer 3

chlorophyll in chloroplast

Question 4

What is the energy used for?

Answer 4

to convert carbon dioxide and water into glucose

Question 5

What happens to the oxygen produced/

Answer 5

• released into air
• it is a by-product

Question 6

What happens to the glucose produced?

Answer 6

• some is used straightaway for plant cells
• some is converted into insoluble starch for storage

Question 7

What substance is used to test leaves for starch?

Answer 7

iodine

Question 8

What is the colour change of the iodine if starch is present?

Answer 8

orangey-brown to bluey-black

Question 9

What are the limiting factors which affect the rate of photosynthesis?

Answer 9

• light
• temperature
• carbon dioxide

Question 10

How does light affect the rate of photosynthesis?

Answer 10

• as light intensifies, rate increases
• after a while, light will no longer be limiting factor
• temperature or carbon dioxide will be limiting factor

Question 11

How does carbon dioxide affect the rate of photosynthesis?

Answer 11

• as amount of carbon dioxide increases, rate increases
• after a while, it is no longer the limiting factor
• temperature or light must be limiting factor

Question 12

What substance could be used in an experiment to show the effect of CO₂ on rate of photosynthesis?

Answer 12

sodium hydrogencarbonate

Question 13

How does temperature affect the rate of photosynthesis?

Answer 13

• Low temp: slower rate:
• Higher temp (up to 45^oc): faster rate
• over 45^oc: enzymes needed for photosynthesis denature

Question 14

How do plants use glucose?

Answer 14

• convert into insoluble starch for storage
• convert to fats and oils to be stored in seeds
• respiration
• proteins: glucose combined with nitrate ions
• cellulose: cell walls

Question 15

How are greenhouses (polytunnels) used to make the most of photosynthesis?

Answer 15

• trap heat: temperature not limiting
• lots of windows to supply light (sometimes have artificial light)
• add CO₂ to air using paraffin heaters
• fertilisers (containing nitrate ions) increase healthy growth

Question 16

What are hydroponics?

Answer 16

• system which controls mineral ions in the water in order to speed up growth
• uses computer software

Question 17

Advantages of hydroponics

Answer 17

• fast turnover: high profit (yield)
• crops are clean - high quality
• less labour
• crops can be grown where land is poor
• less pests

Question 18

Disadvantages of Hydroponics

Answer 18

• expensive to install software
• affected by power cuts: system failure leads to rapid plant death
• plants need extra support because there is no soil