- Stomata are tiny pores mostly on the underside of leaves, responsible for CO₂ intake for photosynthesis.
- In darkness, stomata close to reduce water loss by transpiration; in light, they reopen to allow CO₂ entry.
- Transpiration occurs alongside photosynthesis, thus "transpiration is the price the plant pays for photosynthesis."
- The opening and closing of stomata depend on the movement of water in and out of guard cells, which have a thick inner and thin outer wall.
Definitions [5]
Define the following term:
Photolysis of water
Releasing electrons and dividing the water molecule (H2O) into its two components (Hydrogen and Oxygen). Photolysis is the term used to describe this reaction, which is characterised by the fracturing of molecules by light (photo = light, lysis = breaking).
Definition: Photosynthesis
Photosynthesis is the process by which living plant cells, containing chlorophyll, produce food substances (glucose and starch) from carbon dioxide and water by using light energy. Plants release oxygen as a byproduct during photosynthesis.
Define the following term:
Thylakoids
Thylakoids are indeed very small compartments that are present within chloroplasts. They are the locations where the light-dependent reactions of photosynthesis take place and contain chlorophyll. Nevertheless, the response could be simplified to enhance its clarity.
Define the following term:
Chloroplast
Chloroplasts are indeed miniature ovoid structures that are encased in a double membrane. Nevertheless, the response could offer a more succinct definition: Chloroplasts are the cellular organelles that are responsible for the process of photosynthesis in plant cells. They are the sites where photosynthesis occurs and contain thylakoids.
Define Photosynthesis.
In the presence of chlorophyll, photosynthesis is the process by which green plants and certain other organisms convert carbon dioxide and water into glucose (a form of sugar) using light energy, typically from the sun. As a byproduct, this process generates oxygen.
Chemica Equations [1]
Chemical Equation: Photosynthesis
The balanced chemical equation is: \[6\mathrm{CO}_{2}+12\mathrm{H}_{2}\mathrm{O}\frac{\text{light energy}}{\text{chlorophyll}}\mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6}+6\mathrm{H}_{2}\mathrm{O}+6\mathrm{O}_{2}\uparrow\]
Key Points
Key Points: Plastids
- Plastids are present only in plant cells and are of several types—chloroplasts, leucoplasts, and chromoplasts.
- They are double-membraned organelles with a proteinaceous matrix and contain DNA.
- Chloroplasts (green) contain chlorophyll in thylakoids and perform photosynthesis.
- Leucoplasts are colourless, store starch, and have no pigment.
- Chromoplasts are variously coloured, contain pigments like xanthophyll and carotene, and help in pollination by attracting pollinators.
Key Points: Chlorophyll
- Chlorophyll is the green pigment in plants, found in chloroplasts.
- It is located in the thylakoid walls inside the chloroplasts.
- Chloroplasts are mainly present in mesophyll cells of leaves.
- There are nine types of chlorophyll, but chlorophyll a and chlorophyll b are the most common.
- Chlorophyll absorbs blue and red light for photosynthesis and reflects green light.
Key Points: Stomatal Function and Movement
Key Points: Process of Photosynthesis
- Photosynthesis mainly occurs in mesophyll cells (palisade and spongy) of leaves, using chlorophyll to trap sunlight.
- Carbon dioxide enters the leaf via stomata by diffusion down a concentration gradient.
- Water is absorbed by roots, transported via the stem to mesophyll cells of the leaves.
- Using light energy, chlorophyll helps synthesize glucose (C₆H₁₂O₆) from CO₂ and H₂O, releasing O₂ as a by-product.
- The balanced chemical equation is: \[6\mathrm{CO}_{2}+12\mathrm{H}_{2}\mathrm{O}\frac{\text{light energy}}{\text{chlorophyll}}\mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6}+6\mathrm{H}_{2}\mathrm{O}+6\mathrm{O}_{2}\uparrow\]
Key Points: Products of Photosynthesis
- Glucose is used immediately, stored as starch, converted into sucrose, or used to make fats and proteins.
- Water produced may be reused in further photosynthesis.
- Oxygen mostly diffuses out, but some is used in photorespiration.
- Synthesized food is temporarily stored as starch in the leaf.
- At night, starch is converted back to sugar and translocated to other plant parts.
