Photosynthesis Basics

Photosynthesis

• Photosynthesis is an endothermic reaction, transferring energy from sunlight to chloroplasts in green plants
• Chlorophyll, a green pigment, absorbs sunlight's energy, converting carbon dioxide and water into glucose
• Oxygen is released as a byproduct
• Plants are autotrophs capable of creating their own food
• They are producers, initiating food chains
• Glucose produced is used for energy in respiration, or stored as starch, lipids, cellulose (cell walls), or amino acids
• Raw materials for photosynthesis are carbon dioxide and water
• Light energy is not a substance, therefore not a raw material

Factors Affecting Photosynthesis Rate

• Plants have limited resources, restricting their photosynthetic rate
• Limiting factors include:
  • Temperature: Enzymes denature at high temperatures, reducing the reaction rate. At low temperatures, particles have low kinetic energy and collisions are infrequent
  • Light intensity: More light increases reaction rate until another factor becomes the limiting one
  • Carbon dioxide concentration: The reaction rate increases proportionally with carbon dioxide until another factor becomes the limiting one
• Chlorophyll and the number of chloroplasts also impact the rate, affected by diseases, nutrient deficiency, or genetic traits

Practical Investigating Photosynthesis

• Demonstrates oxygen production by plants submerged in water (e.g., pondweed)
• Oxygen is produced as bubbles
• Apparatus: beaker, pondweed, funnel, boiling tube, splint
• Method:
  • Submerge pondweed in a beaker of water
  • Invert a funnel over the pondweed
  • Place a boiling tube over the end of the funnel
  • Observe bubbles and test with a glowing splint (to identify oxygen)
• This can test rates of photosynthesis over time

Leaf Structure and Adaptations

• Leaves have specialized structures for optimal photosynthesis:
  • Wax cuticle: Protects against water loss
  • Upper epidermis: Thin, transparent for light penetration
  • Palisade mesophyll: Tightly packed chloroplasts for maximum light absorption
  • Spongy mesophyll: Has air spaces to maximize diffusion of gases (carbon dioxide and oxygen)
  • Lower epidermis: Contains stomata for gas exchange
  • Stomata: Open to allow carbon dioxide in, close to prevent water loss
  • Guard cells: Regulate stomata opening and closing
  • Vascular bundle: (xylem and phloem): Transports water, minerals, and sugars
• These structures are optimized for absorbing light, carrying out photosynthesis, and minimizing water loss

Plants and Mineral Ions

• Plants need various mineral ions for growth and health, beyond carbohydrates
• Two essential ions:
  • Magnesium: Needed to make chlorophyll
  • Nitrogen: Needed to make amino acids (proteins)
• Deficiencies in these ions result in visible symptoms (e.g., yellowing, stunted growth)

Balanced Diet

• A balanced diet contains the necessary proportions of food groups for good health:
  • Carbohydrates (energy)
  • Proteins (growth and repair)
  • Lipids (energy storage, insulation)
  • Fibre (intestinal health)
  • Vitamins and minerals (various functions)
  • Water (essential for bodily functions)
• Imbalances in these ratios leads to malnutrition, potentially causing various health issues such as starvation, coronary heart disease, constipation, and obesity

Role of Digestive Enzymes

• Digestive enzymes break down large, insoluble molecules into smaller, soluble molecules for absorption and assimilation
• Carbohydrases: Amylase (breaks down starch into maltose), Maltase (breaks maltose into glucose)
• Proteases: Pepsin (breaks proteins into polypeptide chains) and other proteases (break polypeptide chains into amino acids)
• Lipases: break down lipids into glycerol and fatty acids

Bile

• An alkaline substance produced by the liver
• Stored in the gall bladder
• It:
  • Neutralizes stomach acid
• Emulsifies fats (increases surface area for lipase action)

Small Intestine: Structure and Adaptations

• The small intestine is the primary site for nutrient absorption.
• Features increasing absorptive capacity include:
  • Large surface area: Folds, villi, microvilli
  • Thin walls: Short diffusion distance
  • Good blood supply (capillaries): Rapid transport of absorbed nutrients
  • Lacteals (lymph vessels): Carry absorbed fats (lipids)