Photosynthesis

For a plant to grow and survive, they need to carry out photosynthesis.
Photosynthesis takes places in the leaves, specifically the Chloroplasts
Within the chloroplast, there is a pigment called chlorophyll which absorbs light
Photosynthesis uses energy (light) to convert carbon dioxide and water into glucose and oxygen

Carbon Dioxide+ water→e+oxygen
6CO2+ 6H20→ C6H12O6+6O2
Photosyntheis requires light or energy in order for it to take place
This is an example of an endothermic reaction
This is because energy is transferred from the environment to chloroplasts by light

Carbon dioxide diffuses into the leaves through the stomata
Water is taken up through the soil by the roots and then transported to the leaves by the xylem

Plants use oxygen for respiration
Glucose is used for 5 main things:
1. Cellular respiration- It breaks the glucose apart to release energy
Photosynthesis traps the Sun’s light energy in glucose molecules. Cellsw around the plant break the glucose to release energy
2. Cellulose- Lots of glucose molecules can be combined to make cellulose, which is a complex carbohydrate that plants use to strengthen their cell wall
3. Starch- Glucose molecules can also combine to make starch, which is another complex carbohydrate. They have no particular function. It’s a better form of glucose for long term storage because
It is compact, meaning you can fit in more
It is also insoluble, meaning it won’t draw water into the cell
Most plant cells keep a good amount of starch to turn it into glucose later when photosynthesis is not happening as much (winter/night for example)
4. Amino Acids- They combine glucose molecules with nitrate ions, which they get from soil. They do this to make amino acids, in which they get protein
5. Oils and fats- Oils and fats can be stored as energy sources for the future

Plants growth rate is dependant on how fast they can photosynthesise.
The factors that affect rate of photosynthesis:
Light intensity
Temperature
Carbon dioxide concentration
Amount of chlorophyll



If plants have less chlorophyll, they won’t be able to carry as much photosynthesis as chlorophyll absorbs light.
Different plants have different amount of chlorophyll
The level in an individual plant varies due to
disease
Environmental stress
Lack of nutrients (water for example)
These things damage the chloroplasts, affecting chlorophyll

Limiting factors usually are: light intensity, carbon dioxide concentration and temperature
These always goes on the x-axis
As light intensity increases, so does the rate of photosynthesis. On a graph, when the line is flattened out, it is plateaud, meaning there is something else limiting photosynthesis such as carbon dioxide concentration or temperature

The more carbon dioxide a plant has, the higher the rate of photosynthesi. Just like light, after a while, it gets plateaud


However, regarding temperature, the rate of photosynthesis rises initially because enzymes work more quickly and molecules can move faster. However, the rate starts to fall because the enzymes are being denatured. By 45 degrees, they are denatured and the rate of reaction falls to 0.

In colder climate, farmers put their crops in greenhouses, which traps the sun’s heat, increasing the temperature
They can also provide artificial light, so photosynthesis can continue day and night
Some farmers pump carbon dioxide into the greenhouse or uses a paraffin heater, which releases both heat and carbon dioxide
Another advantage of greenhouses is that they are enclosed, pests, insects, etc cannot go through
Farmers could also use fertilisers to ensure that their plants are having all the essential minerals

A disadvantage of this is that this is very expensive