Plastids – Part – 2
2 Minutes
Photosynthesis in chloroplasts for students: learn about light reactions, dark reactions, and plant pigments. An English science lesson.
- Light and dark reactions inside the thylakoid and stroma
- Separating leaf pigments on filter paper using a solvent
- Internal and external factors that affect photosynthesis
What this lesson teaches
Photosynthesis is the process where plants use sunlight, carbon dioxide, and water to produce carbohydrates inside their chloroplasts. This food-making process takes place only in plant parts that contain the pigment chlorophyll, such as the buds, stems, and leaves.
The two steps in chloroplasts
The entire photosynthetic process happens in two separate stages located in different structures within the chloroplast. The first stage is the light-dependent reaction, which takes place in the thylakoid where pigments capture sunlight and convert it into chemical energy in the form of ATP and NADPH2. The second stage is the light-independent reaction, also called the dark reaction, which takes place in the stroma without needing sunlight. The ATP and NADPH2 travel from the thylakoid into the stroma, where they break down and use their stored energy along with carbon dioxide to produce carbohydrates.
Primary and accessory pigments
- Any pigment that aids the process of photosynthesis is called a photosynthetic pigment.
- Primary pigments convert light energy from the sun into chemical energy, while accessory pigments pass on that converted chemical energy.
- Leaves usually display the green color of the primary pigment because accessory pigments are present in much smaller amounts.
- Grinding a leaf, placing it on filter paper, and dipping it into a solvent causes the hidden pigment colors to separate.
- Some plants have leaves of other colors because accessory pigments are present in higher amounts than chlorophyll, yet photosynthesis still takes place.
Problems that affect photosynthesis
Both internal conditions inside the plant and external conditions in the environment can prevent photosynthesis from working properly. Inside the plant, problems arise if photosynthetic pigments are not produced properly or if carbohydrates accumulate too heavily on the chloroplast. From the outside, the process will not occur properly if carbon dioxide is unavailable, if sunlight fails to reach the plant, or if the surrounding temperature is not favorable.