Photosynthesis

• What is the correct chemical formula for glucose?

  C₆H₁₂O₆
• Specialised animal and plant cells have adaptations to allow them to fulfil their specific roles.What is adaptation of a palisade mesophyll cell?

  Palisade mesophyll cells are adapted to carry out photosynthesis by having many chloroplasts, which is where photosynthesis occurs.

  Spongy mesophyll cells have spaces between them to allow gases to circulate and reach all cells in the leaf.
• The stomata open during daylight hours when carbon dioxide enters the leaf through diffusion. The stomata close at night as there is no need for CO2 so water loss would be greater than gain. This prevents dehydration of the leaves.
• Stomata are closed during hot dry weather because if they were open then too much water would evaporate from the leaf surface. If this happened it could cause the cell membranes to burst (plasmolysis) and the plant would die.
• Plants can also reduce water loss by producing waxy cuticles on the outside of the epidermis. These prevent water leaving the leaf by transpiration.
• Increasing temperature increases rate of reaction but only up to an optimum point beyond that enzymes denature and become useless. Temperature affects the speed of reactions by changing the kinetic energy of particles. Higher temperatures mean more collisions occur per second increasing the frequency of successful collisions with active sites on enzyme molecules. However, above the optimum temperature, bonds within the enzyme start to break down causing the shape of the protein to change and therefore its activity decreases.
• Translocation is the movement of sugars made in photosynthesis around the plant. It takes place via phloem tissue. Phloem tissue consists of sieve tubes that contain sugar solution called sap. Sap moves downwards under pressure from source to sink tissues.
• Plants can also reduce water loss by producing waxy cuticles on the outside of the epidermis that prevent water leaving the leaf.
• What is the function of guard cells?

  The function of guard cells is to regulate the opening and closing of stomata in plant leaves, controlling gas exchange and water loss.
• What is the function of phloem cells?

  Phloem cells transport the products of photosynthesis, including sugars and amino acids, around the plant.
• What are the products of photosynthesis

  Glucose and oxygen are the products of photosynthesis and the reactants in aerobic respiration.

  Glucose alone is the reactant of anaerobic respiration.
• Dim light

  1. Overall exchange of CO2 and O2 with air

  2. Rate of respiration = rate of photosynthesis

  3. O₂ used in photosynthesis

  4. CO₂ used in respiration
• No light = no photosynthesis so no carbon dioxide absorbed and no oxygen released
• Respiration still happens which is using oxygen and releasing carbon dioxide
• Bright light

  Rate of Photosynthesis is higher than the rate of Respiration
• Rate of Photosynthesis is higher than the rate of Respiration

  More CO₂ absorbed and more O₂ produced
• Respiration produces CO₂ but not enough for photosynthesis
• Bright light intensity

  Lots of CO₂ absorbed, more than needed for respiration so excess released to air
• Balanced formula for photosynthesis

  6CO2 + 6H2O → C6H12O6 + 6O2. 
• Plants make their own sugar by photosynthesis in the leaves then this travels to the rest of the plant through the phloem in translocation.