4.1 Photosynthesis

Question 1

what is photosynthesis?

Answer 1

the process by which plants synthesise glucose using light energy from the sun. light energy is converted into chemical energy.

Question 2

where does photosynthesis take place?

Answer 2

within chloroplasts in leaf palisade cells. they contain chlorophyll, a pigment which absorbs light energy.

Question 3

state the equations for photosynthesis (work and symbol)

Answer 3

word: carbon dioxide + water -light-> glucose + oxygen
symbol: 6CO2 +6H20 -light-> C6H12O6 + 6O2

Question 4

is photosynthesis an endothermic or exothermic reaction, and why?

Answer 4

endothermic - energy is transferred from the environment to chloroplasts by light.

Question 5

how can you show that a plant gives of oxygen during photosynthesis?

Answer 5

using a water plant (e.g. Elodea), collect gas bubbles produced during photosynthesis. the gas will relight a glowing splint as it contains oxygen.

Question 6

give examples of leaf adaptatioins which maximise the rate of photosynthesis

Answer 6

• broad leaves - maximise surface area.
• thin leaves - short diffusion distance.
• chlorophyll present - trap light energy.
• veins - transport water to leaves via oxylem, remove photosynthesis produces via phloem.
• air spaces - allow CO2 to enter and O2 to leave.
• guard cells - control opening of stomata for gaseous exchange and prevent water loss.

Question 7

what are the four main factors that affect the rate of photosynthesis?

Answer 7

• temperature
• light intensity
• carbon dioxide concenrration
• amount of chlorophyll

Question 8

how does temperature affect the rate of photosynthesis?

Answer 8

increasing the temperature increases the rate of photosynthesis as the kinetic energy of particles is increased. the rate decreases past a certain temperature as enzymes become denatured.

Question 9

how does light intensity affect the rate of photosynthesis?

Answer 9

increasing the light intensity increases the rate of photosynthesis until another factor becomes limiting.

Question 10

how does carbon dioxide concentration affect the rate of photosynthesis?

Answer 10

increasing the carbon dioxide concentration increases the rate of photosynthesis (until another factor becomes limiting) as CO2 is required to make glucose.

Question 11

how does the amount of chlorophyll affect the rate of photosynthesis?

Answer 11

decreasing the amount of chlorophyll (e.g. dur to a lack of magnesium) decreases the rate of photosynthesis as chlorophyll is required to absorb light energy.

Question 12

what is a limiting factor?

Answer 12

an environmental factor which can restrict the rate of photosynthesis e.g. light intensity.

Question 13

explain how you can calculate the rate of photosynthesis by measuring oxygen production

Answer 13

• set up bubble potometer apparatus (pondweed in a sealed tube of water, attached to a capillary tube and a gas syringe).
• oxygen gas produced causes the bubble in the capillary tube to move. the distance moved by the bubble is used to calculate the volume of oxygen produced.

Question 14

how can farmers use their knowledge of limiting factors to increase their profits?

Answer 14

they can control temperature, light intensity and CO2 concentration to achieve the fastest possible rate of photosynthesis, leading to a greater yield.

Question 15

state the law which desscribes the relationship between the distance of a light source from a plant and light intensity

Answer 15

inverse square law - light intensity ⍺ 1/distance^2

Question 16

state 5 uses of the glucose produced during photosynthesis

Answer 16

• respiration
• starch for staorage
• cellulose for strength
• amino acids and protein synthesis (combined with nitrates)
• lipids for energy storage in seeds