B5: plant nutrition

1. Photosynthesis

• the process by which plants synthesize carbohydrates from raw materials using energy from light

6CO2+6H2O → C6H1206 + 6O2

• chlorophyll: green pigment found in chloroplasts within plant cells

  • Absorbs light energy → transfers light energy into chemical energy

• uses of carbohydrates

  • converted to starch molecules as an effective energy store

  • cellulose to build cell walls →

  • used in respiration→ provides energy

  • sucrose for transport

  • nectar to attract insects

  • converted to lipids for energy source in seeds

  • converted into amino acids when combined with other minerals

• minerals in plants

2. leaves

• structure of a leaf

  • wax cuticle: protective layer on top of the leaf → prevents evaporation

  • upper epidermis: thin and transparent → allows light to enter palisade mesophyll

  • spongy mesophyll: contains air spaces → increases surface area for diffusion

  • lower epidermis: guard cells and stomata

  • stomata: where gas exchange takes place → opens during the day, closes at night

    • mostly found under the leaf

  • vascular bundle: contains xylem and phloem → transports substances

  • xylem: transports water

  • phloem: transports sucrose and amino acid

• Adaptations of leaf structure:

  • large leaf surface area: increases rate of diffusion of CO2 and absorption of light

  • thin: allows CO2 to diffuse to palisade mesophyll cells quickly

  • chlorophyll: absorbs light energy for photosynthesis

  • network of veins: allows transport of nutrients

  • thin cuticle made of wax: protects the leaf without blocking sunlight

  • palisade cell at the top: maximizes absorption of light

  • vascular bundles: thick cell walls of tissue → help support the stem and leaf

3. Factors affecting photosynthesis

• Temperature: increases → rate of photosynthesis increases as photosynthesis is controlled by enzymes

  • temperature increases too much → enzymes could denature → photosynthesis rate goes down

• light intensity: more light → faster rate of photosynthesis

• carbon dioxide: more co2 → faster rate of photosynthesis

4. investigate the effect of light on the net gas exchange in an aquatic plant using a pH indicator such as hydrogencarbonate indicator

• Hydrogencarbonate indicator shows the carbon dioxide concentration in solution

• 

• Several leaves from the same plant are placed in stoppered boiling tubes containing some hydrogencarbonate indicator