B8 - Photosynthesis

Question 1

What is photosynthesis

Answer 1

An endothermic chemical reaction that takes in light energy due to the chlorophyll in the chloroplasts

Question 2

Equations for photosynthesis

Answer 2

carbon dioxide + water —> glucose + oxygen
6CO₂ + 6H₂O —> C6H12O6 + 6O₂

Light also goes above arrow and chlorophyll goes below

Question 3

Factors that affect the rate of photosynthesis

Answer 3

• Conc. of CO2
• Light intensity
• Amount of chlorophyll
• Temperature

Question 4

Describe the relationship between light intensity and photosynthesis rate

Answer 4

• As light intensity increases, so does the rate of photosynthesis if it was a limiting factor
• This is due to there being more light energy
• However, this levels off and stays constant indicating that it is no longer a limiting factor

Question 5

Describe the relationship between CO2 conc. and photosynthesis rate

Answer 5

• As CO2 conc. increases, so does the rate of photosynthesis if it was a limiting factor
• However, this levels off and stays constant indicating that it is no longer a limiting factor

Question 6

Describe the relationship between temperature and photosynthesis rate

Answer 6

• As temp. increases, so does the rate of photosynthesis if it was a limiting factor
• This is due to there being more collisions with enzymes
• However, if the temperature increases too much, the enzymes will denature and photosynthesis rate decreases

Question 7

Describe the relationship between the amount of chlorophyll and photosynthesis rate

Answer 7

• As the amount of chlrophyll increases, the rate of photosynthesis also increases
• This is due to more light energy being absorbed

Question 8

Leaf adaptations for light absorbtion for photosynthesis

Answer 8

• Large SA to absorb more light
• Palisade mesophyll cells have lots of chlorophyll in chloroplasts
• Upper epidermis is transparent to allow light through

Question 9

Uses of glucose produced in photsynthesis

Answer 9

• Respiration to release energy
• Starch - energy store
• Lipids - energy store
• Cellulose - structure
• Amino acids - synthesise proteins for growth + repair

Question 10

What is needed for plants to make proteins

Answer 10

• Glucose to make amino acids
• Nitrate ions absorbed from soil or from insects (carnivorous plants)

Question 11

What ion is needed to make chlorophyll

Answer 11

Magneisum ions

Question 12

How to test if a leaf has photosynthesised

Answer 12

• Boil the leaf to kill it
• Place in boiling alcohol to remove chlorophyll making it white
• Place the leaf in hot water to soften it
• Add drops of iodine

If starch is present, iodine will go blue/black and it means photosynthesis has occured

Question 13

Relationship between light intenisty and distance from light source

Inverse square law

Answer 13

• As distance increases, light intensity decreases
• Light intensity is proportional to the inverse of the distance from the light squared

Question 14

Method for photosynthesis practical

Answer 14

• Place LED 10cm away from boiling tube
• Fill boiling tube with water and sodium hydrogen carbonate (release carbon dioxide)
• Add pondweed with cut end at the top and leave to acclimatise
• After 5 mins, start a stopwatch and count the number of bubbles produced in one minute
• Repeat to find a mean
• Repeat at different distances e.g. 20cm, 30cm

Question 15

Control variables for photsynthesis practical

Answer 15

• Temperature
• Type of light source
• Concentration of bicarbonate
• Piece of pondweed

Question 16

Leaf adaptations for carbon dioxide intake

Answer 16

• Guard cells open and close stomata
• Air spaces to allow diffusion inot leaf cells
• Leaves are thin for short diffusion distances

Question 17

Root hair cell adaptations for water intake

Answer 17

• Large SA for increased absorbtion
• Lots of mitochondria to provide energy for active transport

Question 18

Why can glucose not be stored as itself in the plant

Answer 18

• Glucose is soluble and would affect movement of water in snd out of plant by osmosis