Photosynthesis and Diffusion: Biological Processes Explained

Photosynthesis

Photosynthesis is the fundamental process by which plants manufacture carbohydrates from raw materials using energy from light.

The Process of Photosynthesis

• Green plants take in CO2 through their leaves via diffusion.
• Water is absorbed through the plant's roots by osmosis and transported to the leaves through xylem vessels (moving upwards).
• Chloroplasts containing chlorophyll are responsible for trapping light energy. This energy is used to break up water molecules and then to bond hydrogen and CO2 to form glucose.
• Glucose is usually changed to sucrose for transport around the plant or to starch for storage.
• Oxygen is released as a waste product or used by the plant for respiration.

Factors Limiting Photosynthesis

Three factors can limit the speed of photosynthesis:

• Light intensity
• Concentration of CO2
• Temperature

Light Intensity

Photosynthesis increases when light gets brighter, but only up to a point. When a certain light intensity is reached, the rate of photosynthesis stays constant. A point is reached where all the chloroplasts cannot trap any more light.

CO2 Concentration

The higher the concentration of CO2, the faster the rate of photosynthesis. The air usually contains 0.04% CO2. The rate increases up to a point and then remains constant because another factor becomes limiting.

Temperature

The rate of photosynthesis decreases at high temperatures because enzymes in chloroplasts are denatured.

Limiting factor: Something present in the environment in such short supply that it restricts life processes.

Diffusion

Diffusion is the net movement of molecules from a region of high concentration to a region of lower concentration, down a concentration gradient.

It is a passive movement. Cells do not need to use energy to move the molecules.

Concentration Gradient: The difference between the concentration of molecules in two places is a “concentration gradient”.

Factors That Affect Diffusion

1. Distance: Molecules have to travel—the shorter the better.
2. Concentration Gradient: The bigger the better.
3. Surface Area: The larger the better. There are millions of alveoli in a lung, giving a huge surface area for the diffusion of O2.
4. Temperature: Molecules have more kinetic energy at higher temperatures, so more diffusion occurs in a given time.
5. Size of Molecule: The smaller the better. Small molecules diffuse faster than large molecules.