What is the word and balanced symbol equation for photosynthesis?
carbon dioxide + water → glucose + oxygen
6CO₂ + 6H₂O ⇌ C₆H₁₂O₆ + 6O₂
Where does photosynthesis occur?
In leaves, specifically the subcellular structures called chloroplasts which contain a pigment known as chlorophyll
What is an endothermic reaction?
A reaction where energy is transferred from the surroundings to help the reaction take place
How does carbon dioxide diffuse into the leaves?
Through the stomata
Give five uses of the glucose produced by photosynthesis
- used for (aerobic) respiration- to release energy
- stored as starch, which is insoluble (would not draw water in via osmosis) and makes it a better form of glucose for long time storage
- combines with nitrate ions absorbed from the soil to become amino acids, which make proteins
- stored as oil and fats- future energy source
- combined to make cellulose- a complex carbohydrate that strengthens the cell walls of plants
What four factors affect the rate of photosynthesis?
- Temperature
- Light intensity
- Carbon dioxide concentration
- Amount of chlorophyll
How does the amount chlorophyll affect the rate of photosynthesis?
If plants have less chlorophyll they would absorb less light from the sun and consequently would not be able to carry out as much photosynthesis
Describe the effect of increasing light intensity on the rate of photosynthesis
As light intensity increases so does the rate of photosynthesis up until a point where it plateaus, which means there must be another factor limiting the rate of photosynthesis such as temperature or the carbon dioxide concentration
Describe the effect of the carbon dioxide concentration on the rate of photosynthesis
As the level of carbon dioxide increases so does the rate of photosynthesis until a point where it plateaus, which means there is another limiting factor
Describe the effect of temperature on the rate of photosynthesis
Initially, as the temperature increases so does the rate of photosynthesis because the enzymes involved have more energy, move faster and can work more quickly. However, after a while the rate starts to drop again because the enzymes involved begin to denature. By around 45 degrees they are fully denatured so the rate of the reaction falls to zero
How do farmers artificially create the required conditions to maximise the rate of photosynthesis?
- In colder environments, greenhouses are used to trap the sun’s heat (increase the temperature)
- Can provide artificial light so that photosynthesis could continue all through the day and night
- Carbon dioxide could be pumped into the greenhouse or a paraffin heater could be used (releases both heat and carbon dioxide as it burns)
- A benefit of greenhouses is that they are enclosed so pests and pathogens can’t get to the plants as easily
- Fertilisers are used to promote growth by ensuring the plants have enough minerals
- Pesticides kill any unwanted bugs
- However this would all cost a lot of money so farmers would weigh up the extra cost vs the extra yield
What is the inverse square law?
Light intensity is indirectly proportional to the distance squared
light intensity ∝ 1/distance²
What is metabolism?
The total amount of chemical reactions taking place in an organism
What does metabolism include?
- conversion of glucose to starch, glycogen and cellulose
- the formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids
- the use of glucose and nitrate ions to form amino acids (protein synthesis)
- respiration
- breakdown of excess proteins to form urea for excretion
What is respiration?
an exothermic reaction that breaks down glucose and releases energy
What is the difference between aerobic and anaerobic respiration?
-In aerobic respiration glucose reacts with oxygen in the mitochondria to produce carbon dioxide, water and energy
-In anaerobic respiration (plants), glucose is converted into ethanol and carbon dioxide
-in yeast cells this is called fermentation (part of making bread and alcohol)
-In anaerobic respiration (animals) glucose is broken down in the absence of oxygen (in the cytoplasm) to produce lactic acid
What are the uses of glucose in plants?
- glucose can be combined with nitrate ions to make amino acids ( which can then be combined to form proteins)
- glucose can be converted into starch (which is insoluble)
- glucose can be converted in cellulose which strengthens plant walls
- glucose is used in respiration
- can be converted into lipids which are then stored
What is oxygen debt?
the extra oxygen needed after exercise to break down the lactic acid
