what is photosynthesis?
an endothermic reaction by which plants synthesise glucose by absorbing light energy from the sun
where does photosynthesis take place?
in the leaves of a plant
what absorbs light energy?
chlorophyll
what is the word equation for photosynthesis?
carbon dioxide + water -> glucose + oxygen
what is the symbol equation for photosynthesis?
6CO2 + 6H2O -> C6H12O6 + 6O2
why is photosynthesis an endothermic reaction?
because energy is transferred from the environment to chloroplasts by light
what are the four main factors that affect the rate of photosynthesis?
- temperature
- light intensity
- carbon dioxide concentration
- the amount of chlorophyll
how does temperature affect the rate of photosynthesis?
- as the temperature increases, the enzymes involved in photosynthesis work faster so the rate increases
- if we keep increasing the temperature, the enzymes will denature and the rate of photosynthesis falls
how does light intensity affect the rate of photosynthesis?
increasing the light intensity increases the rate of photosynthesis until another factor becomes limiting
how does carbon dioxide concentration affect the rate of photosynthesis?
increasing the carbon dioxide concentration increases the rate of photosynthesis as CO2 is required to make glucose
how does the amount of chlorophyll affect the rate of photosynthesis?
decreasing the amount of chlorophyll decreases the rate of photosynthesis as chlorophyll is required to absorb light energy
what is a limiting factor?
an environmental factor which restricts the rate of photosynthesis
what are the uses of glucose produced in photosynthesis?
- used for respiration
- converted into insoluble starch for storage
- used to produce fat or oil for storage
- used to produce cellulose, which strengthens the cell wall
- used to produce amino acids for protein synthesis
where does respiration take place in a cell?
in the mitochondria
how are amino acids from glucose made?
plants need to absorb nitrate ions from the soil
how can you calculate the rate of photosynthesis? REQUIRED PRACTICAL 6
- take a boiling tube and place it 10cm away from an LED light source - an LED light is used as they do not release much heat
- fill the boiling tube with sodium hydrogen carbonate solution
- sodium hydrogen carbonate solution releases carbon dioxide, which is needed for photosynthesis
- put a piece of pondweed into the boiling tube with the cut end at the top
- leave this for 5 minutes to acclimatise to the conditions in the boiling tube
- start a stop watch and count the number of bubbles produced in one minute. Repeat two more times and calculate the mean number of bubbles produced in one minute
- Do the whole experiment again from the start at 20cm, then 30cm, then 40cm
what are the problems with practical 6?
- the number of bubbles can be too fast to count
- the bubbles are not always the same size. A large bubble would count the same as a small bubble
how can the problems with practical 6 be solved?
- place the pond weed under a funnel and catch the bubbles in a measuring cylinder
- then use the measuring cylinder to measure the volume of the oxygen gas produced
what is the inverse square law?
if we double the distance, the light falls by four times
why do mammals need the energy to keep warm?
- humans and other mammals need energy to keep warm
- we need energy for chemical reactions to build larger molecules
what is aerobic respiration?
an exothermic reaction in which glucose reacts with oxygen to release energy which can be used by cells
what is the word equation for aerobic respiration?
glucose + oxygen -> carbon dioxide + water
what is the symbol equation for aerobic respiration?
C6H12O6 + 6O2 -> 6CO2 + 6H2O
why does aerobic respiration release a great deal of energy?
because the glucose molecule has been fully oxidised
