3.1 - Food Security, Plant growth and Photosynthesis

• Food security is the ability of human populations to access food of sufficient quality and quantity
• The rapidly increasing human population around the world has resulted in rising demand for food worldwide, leading to concerns about food security
• Food security can be an issue for individuals, households, or entire countries
• Access is a key part of food security, including being able to afford it
• Some people suggest that current levels of food production will not meet the projected demands in the coming years
• Food production must be sustainable and not have a negative impact on the ecosystem and natural resources
• To maintain a sustainable food supply, increased plant productivity and manipulation of genetic diversity will be required
• Most human food comes from

  • Cereals
  • Potato
  • Roots
  • Legumes
• Breeders seek to develop crops with higher nutritional values, pest and disease resistance, and physical characteristics suited to rearing and harvesting
• All food production, plant or animal, depends on the process of photosynthesis
• Factors affecting food production

  • Light availability
  • Available nutrients
  • Water in the soil
  • Competition with other plants
• Increasing food production can only be achieved by improving efficiency through various practices
• Efficiency practices for increasing food production

  • Control of limiting factors
  • Planting high-yield strains
  • Removing competition from weeds and diseases
  • Developing pest-resistant crops
• Livestock production is less efficient than growing crops due to energy loss between trophic levels and high water intensity
• Livestock production is often possible in habitats unsuitable for growing crops
• People should be encouraged to eat more vegetables and cut down on meat to protect food security and sustainability
• Photosynthesis


  The process by which green plants trap light energy and use it to make carbohydrates
• Photosynthesis involves the absorption of light energy by pigments within chloroplasts
• Principal pigments in photosynthesis are chlorophyll a and b, which absorb light in the red and blue wavelengths
• Plants also contain carotenoids that extend the range of wavelengths absorbed and pass energy on to chlorophyll for photosynthesis
• Having multiple photosynthetic pigments increases the range of wavelengths of light that the plant can absorb, increasing photosynthesis
• When light is absorbed by pigments, electrons become excited and captured by the electron transport system, releasing energy
• First stage of photosynthesis

  When light is absorbed by the pigments, the electrons in the pigment molecule become excited and get captured by the electron transport system. This releases energy, with some of this energy being used to generate ATP by the enzyme ATP synthase. The rest of the energy is used for photolysis of water. Photolysis is the process by which water is split into oxygen, which is released into the atmosphere, and hydrogen. The hydrogen then becomes bonded to the coenzyme NADP to form NADPH and is transferred to the Calvin Cycle along with ATP
• Second stage of photosynthesis – Calvin Cycle


  The carbon fixation stage (Calvin Cycle) is a series of enzyme controlled reactions which does not require light. Carbon dioxide enters the cycle and becomes attached to RuBP (ribulose bisphophate) by the enzyme RuBisCO to produce 3-phosphoglycerate (3PG). The 3-phosphoglycerate that is produced is phosphorylated by ATP and combined with hydrogen from NADPH to form G3P (glyceraldehyde-3-phosphate). G3P is used to either regenerate RuBP or can be used to synthesise sugars, for example glucose. The Calvin Cycle is the temperature-dependent part of photosynthesis
• The glucose produced through photosynthesis can also be passed into other biosynthetic pathways to form DNA
• Uses of glucose made by photosynthesis

  • Energy source
  • Plant energy storage
  • Plant building material
  • Production of other types of food
• Glucose can be used as a substrate and broken down in plant cells by the process of respiration. The chemical energy released by respiration can be used by the plant for cellular activities such as protein synthesis or cell division
• Thousands of glucose molecules can be linked together to form the complex carbohydrate starch. Starch is stored inside plant cells as grains
• Thousands of glucose molecules can be linked together to form the complex carbohydrate cellulose. Cellulose is a very tough molecule that is used to build the cell wall of plant cells
• Glucose is an example of a carbohydrate - it contains the chemical elements carbon, hydrogen and oxygen. Plant cells can convert the sugar into another type of energy storage molecule - fat. Plant cells can also combine sugars with nitrates to make amino acids and use these to produce proteins